Researcher Database

Naoyuki HASHIMOTO
Faculty of Engineering Materials Science and Engineering Energy Materials
Professor

Researcher Profile and Settings

Affiliation

  • Faculty of Engineering Materials Science and Engineering Energy Materials

Job Title

  • Professor

J-Global ID

Research Interests

  • Fusion Engineering   Microstructural Analysis   Irradiation Gamage   Structure Materials   Material Physics   

Research Areas

  • Energy / Nuclear fusion

Academic & Professional Experience

  • 2016/04 - Today Hokkaido University Faculty of Engineering, Materials Science and Engineering Professor
  • 2006/08 - 2016/03 Hokkaido University Faculty of Engineering, Materials Science and Engineering Associate Professor
  • 2001/08 - 2006/07 University of Tennessee Materials Science and Engineering Research Assistant Professor
  • 1997/01 - 2001/07 Oak Ridge National Laboratory, USA Metals and Ceramics Division Postdoctoral Research Associate
  • 1996/04 - 1996/12 Hokkaidou University Faculty of Engineering Lecturer

Education

  • 1991/04 - 1996/03  Hokkaido University  Graduate School of Engineering  Metallurgy
  • 1987/04 - 1991/03  Hokkaido University  Faculty of Engineering  Metallurgy

Association Memberships

  • The Minerals, Metals & Materials Society   Materials Research Society   THE IRON AND STEEL INSTITUTE OF JAPAN   THE JAPANESE SOCIETY OF MICROSCOPY   ATOMIC ENERGY SOCIETY OF JAPAN   THE JAPAN INSTITUTE OF METALS   

Research Activities

Published Papers

  • Highly Correlated Size and Composition of Pt/Au Alloy Nanoparticles via Magnetron Sputtering onto Liquid
    L. Deng, M.T. Nguyen, J Shi, Y.R. Chau, T. Tokunaga, M. Kudo, S. Matsumura, N. Hashimoto, T. Yonezawa
    Langmuir 36 3004 - 3015 2020/03 [Refereed][Not invited]
  • Behavior of hydrogen at Fe/W interface: a first-principle calculation study
    Jingming Shi, Naoyuki Hashimoto, Shigehito Isobe
    Journal of Nuclear Science and Technology 1 - 8 2020/03 [Refereed][Not invited]
  • Doping of Interstitials (H, He, C, N) in CrCoFeNi High Entropy Alloy: A DFT Study
    Jingming Shi, N. Hashimoto
    Materials transactions 61 (4) 616 - 621 2020/03 [Refereed][Not invited]
  • Irradiation Effects on Al0.3CoCrFeNi and CoCrMnFeNi High- Entropy Alloys
    W-Y Chen, M.A. Kirk, N. Hashimoto, J-W Yeh, X. Liu, Y Chen
    Journal of Nuclear Materials 2020/03 [Refereed][Not invited]
  • Cu-Containing High Entropy Alloys for Nuclear Fusion Application
    Yu Lei, N. Hashimoto, S. Isobe
    Materials Transactions 61 (7) 1247 - 1251 2020/03 [Refereed][Not invited]
  • Radiation Effects in Ferritic Steels and Advanced Ferritic-Martensitic Steels
    Naoyuki Hashimoto, Ryuta Kasada, Baldev Raj, M. Vijayalakshmi
    Comprehensive Nuclear Materials 4 (2012) 97 - 121 2020/02 [Refereed][Not invited]
  • Effects of the experimentally revealed one-dimensional migration behavior of self-interstitial atom clusters on the decreasing behavior of their number density in electron-irradiated α-iron
    Y. Abe, Y. Satoh, N. Hashimoto, S. Ohnuki
    Philosophical Magazine 100 (1) 110 - 125 2020/01 [Refereed][Not invited]
  • Hydrogen ab/desorption properties of light metal hydroxide systems
    F. Tanaka, Y. Nakagawa, S. Isobe, N. Hashimoto
    International Journal of Hydrogen Energy in press 2020/01 [Refereed][Not invited]
  • Recent activities in the field of nuclear materials and nuclear fuels
    N. Hashimoto, K. Kurosaki
    Journal of Nuclear Science and Technology 56 (2) 147 - 149 2019/12 [Refereed][Not invited]
  • C.H. Lee, Y. Nakagawa, S. Isobe, N. Hashimoto, S. Sugino, H. Miyaoka, T. Ichikawa
    Journal of Alloys and Compounds 801 645 - 650 2019 [Refereed][Not invited]
  • Effect of Heat Load on Microstructural Development in Irradiated Low Alloy Steels
    S. Goto, N. Hashimoto
    Nuclear Materials and Energy (in press) 2018/08 [Refereed][Not invited]
  • Development of F82H composite Materials with A High Thermal Conductivity
    Z. Chen, Y. Sawa, N. Hashimoto
    Nuclear Materials and Energy 16 133 - 136 2018/07 [Refereed][Not invited]
  • Study on Synergistic Effects of H and He in alpha-Fe
    J. Shi, N. Hashimoto
    Nuclear Materials and Energy 16 212 - 216 2018/07 [Refereed][Not invited]
  • Microstructure Development during Aging in Electron-irradiated 316L Model Alloy
    Shintaro INOUE, Naoyuki HASHIMOTO
    Nuclear Materials and Energy 16 46 - 51 2018/07 [Refereed][Not invited]
  • S. Chen, Y. Wang, N. Hashimoto, S. Ohnuki
    Nuclear Materials and Energy 15 203 - 207 2352-1791 2018/05/01 [Refereed][Not invited]
     
    Oxide dispersion strengthened (ODS) alloys, which contain a high number density of nano-scale oxide particles, are supposed to prevent the long-range diffusion of defects therefore enhance irradiation resistance. The large amount of interfaces between oxide particles and matrix are expected to trap helium atoms as well as vacancies and interstitial atoms. In this study, Fe, F82H-IEA steel and F82H-ODS steel were irradiated with He+ ions at room temperature. Post-irradiation annealing was carried out over a temperature range 200–600 °C with the increment of 100 °C. The change of indentation hardness and the evolution of cavities during post-irradiation annealing were investigated using nanoindentation and transmission electron microscopy (TEM). After post-irradiation annealing at 300 °C, Fe with 2000 appm He showed additional hardening, while at temperature above 500 °C, it showed a large stage of hardness recovery. On the contrary, no temperature dependence of hardness was observed in F82H-IEA steel or F82H-ODS steel during the post-irradiation annealing process. Therefore, the large stage of hardness recovery is expected to be above 600 °C for the latter materials. The reason for the additional hardening in Fe at 300 °C was speculated to be re-structure of the irradiation induced defects. TEM observations revealed the homogeneous distribution of cavities in all as-irradiated materials, and the increase in cavity size and the decrease in cavity number density after post-irradiation annealing at 650 °C. The mechanism of the formation of radiation damage and its development with post-irradiation annealing were discussed.
  • Yuta Suzuki, Naoyuki Hashimoto
    Nuclear Materials and Energy 15 208 - 213 2352-1791 2018/05/01 [Refereed][Not invited]
     
    Duplex stainless steel has been used as a structural material for light water reactors. It is well known that the thermal aging during operation causes spinodal decomposition to Cr-rich (α’) phase and Fe-rich (α) phase in the ferrite phase, resulting in brittlement. In order to understand the mechanism of this phenomena and the effect of irradiation, a duplex model alloy (Fe-25Cr-10Ni-2.5Mo-1Mn) prepared by arc melting and thermally aged in the appropriate condition was subjected to accelerated irradiation by a multi-beam ultra-high voltage electron microscope and partially an ion accelerator in this study. Spinodal decomposition of Fe and Cr was confirmed in the model alloy aged at 450 °C. In addition, the electron beam irradiation to aged model alloy resulted in the decrease in the amplitude of spinodal decomposition. From this experiment, it was suggested that spinodal decomposition could be suppressed by accelerated irradiation.
  • Yuki Nakagawa, Chung-Hyun Lee, Kouki Matsui, Kohei Kousaka, Shigehito Isobe, Naoyuki Hashimoto, Shotaro Yamaguchi, Hiroki Miyaoka, Takayuki Ichikawa, Yoshitsugu Kojima
    Journal of Alloys and Compounds 734 55 - 59 0925-8388 2018/02/15 [Refereed][Not invited]
     
    Hydrogen desorption properties of α-AlH3 doped with Nb species (Nb, Nb2O5 and NbF5) were investigated. Doping Nb species improved the desorption properties of AlH3. In particular, 1 mol% NbF5-doped AlH3 showed the lowest onset desorption temperature at 60 °C. Compared with Nb- or Nb2O5-doped AlH3, the fine distribution of dopant was successfully achieved in NbF5-doped AlH3. The apparent activation energy for hydrogen desorption of AlH3 was slightly decreased with the dopant of NbF5. The improvement of desorption properties might be due to the finely dispersed Nb and/or AlF3, which are formed by the reaction between NbF5 and AlH3 (surface Al2O3).
  • Tengfei Zhang, Yongming Wang, Tao Song, Hikaru Miyaoka, Keita Shinzato, Hiroki Miyaoka, Takayuki Ichikawa, Siqi Shi, Xiaogang Zhang, Shigehito Isobe, Naoyuki Hashimoto, Yoshitsugu Kojima
    Joule 2542-4351 2018 [Refereed][Not invited]
     
    Lithium borohydride ammoniates can be readily generated by LiBH4 absorbing ammonia at room temperature. Li(NH3)nBH4 (0 < n ≤ 2) performed high ionic conductivity near room temperature, e.g., 2.21 × 10−3 S cm−1 for mono-ammoniate at 40°C. A drastic increase in ionic conductivity occurs around 38°C due to the structural change resulting from ammonia desorption. Moreover, the jump of the ionic conductivity is reversible because ammonia absorption/desorption acts as a switch for the structural change. The experimental results show that the stable electrochemical window for the sample is ∼4 V. The crystal structure of Li(NH3)nBH4 (0 < n ≤ 1) can be easily changed while the equilibrium dynamically changes with temperature. First-principles calculation results also indicate that Li(NH3)BH4 exerts an expected compatibility in contact with lithium iron phosphate cathode material. Finally, by introducing a gas instead of substituting an element, a dynamic change of crystal structure is achieved, accompanied with the improvement of lithium ionic conductivity. The progress of lithium-ion battery technology has been inseparable from the innovation of electrolyte materials. Compared with the traditional organic liquid electrolytes, stable solid-state electrolytes are safe, easy to assemble, and inexpensive. However, the large-scale application of solid-state electrolytes is currently limited owing to its low ionic conductivity at room temperature. Generally, lithium ionic conductivity of a solid electrolyte is easily influenced by its crystal structure and defect density, rather than others, and the gas absorption/desorption reaction is an easy way to induce the structural change in solids. Here, we first propose a new concept of utilizing the gas absorption/desorption reaction to improve the ionic conductivity of solids, and demonstrate the ionic conductivity jump of lithium borohydride ammoniates switched by ammonia desorption and absorption at around room temperature. Lithium ionic conductivity up to 10−3 S cm−1 can be achieved from solid-state lithium borohydride ammoniates near room temperature. The gradual change of crystal structure from Li(NH3)BH4 to Li(NH3)xBH4 (0 < x < 1) with the increase of temperature indicates a dynamic equilibrium formed in a closed system. The electrochemical properties of lithium borohydride ammoniates have been investigated. The amount of ammonia as a switch is a key factor controlling the lithium ionic conductivity.
  • Kodai Toyota, Naoyuki Hashimoto
    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals 82 (5) 147 - 152 0021-4876 2018 [Refereed][Not invited]
     
    FeCrAl ferritic steel is one of candidate structure materials for nextgeneration nuclear and fusion reactor due to its good corrosion resistance by alumina layer formed on surface. While, the effect of aluminum on microstructural evolution under neutron irradiation seems not to be clear. In this study, insitu electron irradiation experiment was carried out for Fe12Cr5Al and Fe12Cr in order to investigate the difference of damage evolution between with and without aluminum. Electron irradiation to Fe12Cr5Al resulted in less number density and larger size of dislocation loops compared with that in Fe12Cr. This suggested that aluminum in matrix would have a strong interaction with vacancy, leading to more interstitial flow into dislocation loops.
  • N. Hashimoto, S. Goto, S. Inoue, E. Suzuki
    JOURNAL OF NUCLEAR MATERIALS 495 1 - 5 0022-3115 2017/11 [Refereed][Not invited]
     
    An austenitic model alloy (316L) and a low alloy steel (A533B) were exposed to constant or fluctuating temperature after electron irradiation to a cumulative damage level of 1 displacement per atom. 316L model alloy was exposed to LWR operating temperature during electron irradiation, and were exposed to a higher temperature at a high heating and cooling rates. The annealing experiment after irradiation to 316L resulted in the change in irradiation-induced microstructure; both the size and the number density of Frank loop and black dots were decreased, while the volume fraction of void was increased. In the case of A533B, the aging experiment after electron irradiation resulted in the shrinkage or the disappearance of black dots and the growth of dislocation loops. It is suggested that during annealing and/or aging at a high temperature the excess vacancies could be provided and flew into each defect feature, resulting in that interstitial type feature could be diminished, while vacancy type increased in volume fraction if exists. (C) 2017 Elsevier B.V. All rights reserved.
  • Shigehito Isobe, Hao Yao, Yongming Wang, Hiroshi Kawasaki, Naoyuki Hashimoto, Somei Ohnuki
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 42 (31) 20398 - 20398 0360-3199 2017/08 [Refereed][Not invited]
  • Tengfei Zhang, Shigehito Isobe, Ankur Jain, Yongming Wang, Shotaro Yamaguchi, Hiroki Miyaoka, Takayuki Ichikawa, Yoshitsugu Kojima, Naoyuki Hashimoto
    JOURNAL OF ALLOYS AND COMPOUNDS 711 400 - 405 0925-8388 2017/07 [Refereed][Not invited]
     
    Lithium metatitanate (Li2TiO3) doped magnesium hydride (MgH2) has been investigated in this paper. Desorption properties of the sample with catalyst are compared to the pure MgH2. Particularly, MgH2 doped with 5 mol % Li2TiO3 started to desorb hydrogen at 170 degrees C with a peak temperature at 211 degrees C, which is 100 degrees C and 80 degrees C lower than that of the as-milled MgH2. The reversibility and cyclability of sample with catalyst have also been investigated. Compared with the raw material, the desorption activation energy was reduced from 113 kJ/mol to 84 kJ/mol. Furthermore, the catalytic mechanism was discussed according to the experimental results. (C) 2017 Elsevier B.V. All rights reserved.
  • Shigehito Isobe, Akifumi Ono, Hao Yao, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    Applied Physics Letters 96 (22) 0003-6951 2017/06/26 [Refereed][Not invited]
     
    In situ observation on dehydrogenation of MgH2 was performed by using transmission electron microscope (TEM). The dehydrogenation of MgH 2 with 1 mol % Nb2 O5 and formation of nanosized Mg particles were observed at 150 °C. Nb2 O5 was not confirmed in diffraction patterns and TEM images probably due to wide dispersion. On MgH2 with 10 mol % Nb2 O5, the high resolution TEM could recognize the dehydrogenation at the interface between MgH2 and Nb2 O5, proceeding with increasing temperature. This suggests that hydrogen atoms could diffuse from MgH 2 phase to the interface between Mg and Nb2 O5, resulting in formation of hydrogen molecules at the interface. © 2010 American Institute of Physics.
  • Shigehito Isobe, Akifumi Ono, Hao Yao, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    APPLIED PHYSICS LETTERS 110 (26) 0003-6951 2017/06 [Refereed][Not invited]
  • Hao Yao, Hiroshi Kawasaki, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 58 (6) 971 - 971 1345-9678 2017 [Refereed][Not invited]
  • Unique Hydrogen Desorption Properties of LiAlH4/h-BN composites
    Y. Nakagawa, S. Isobe, T. Ohki, N. Hashimoto
    Inorganics 5 71  2017 [Refereed][Not invited]
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Chaomei Liu, Naoyuki Hashimoto, Keisuke Takahashi
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 18 (39) 27623 - 27629 1463-9076 2016/10 [Refereed][Not invited]
     
    High efficiency catalysts are needed to improve the kinetics of complex hydrides for practical applications. In this study, lithium metatitanate (Li2TiO3) is introduced in lithium alanate (LiAlH4), and the catalytic effect for notable complex/metal hydrides, such as LiAlH4, is investigated. Experiment results indicate that Li2TiO3 improves the kinetics of LiAlH4. In particular, Li2TiO3 dramatically improves the onset temperature of LiAlH4, which decreases to 75 degrees C and is within the temperature range for use in proton exchange membrane fuel cells. Transmission electron microscopy (TEM) observations help understand the catalytic effect of Li2TiO3 in the nanoscale. First principles calculations also show the improvement of H- and Li+ mobility by doping Li2TiO3, where calculations indicate that the physical origin of the catalytic effect is due to two factors: charge transfer and minor surface relaxation. Thus, experimental and theoretical evidence reveals the catalytic mechanism of Li2TiO3 in LiAlH4.
  • Tengfei Zhang, Yuki Nakagawa, Takenobu Wakasugi, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    ACS APPLIED MATERIALS & INTERFACES 8 (23) 14548 - 14551 1944-8244 2016/06 [Refereed][Not invited]
     
    A window type of the environmental cell system for a high-voltage electron microscope was developed and applied to in situ observation of a palladium (Pd) thin film. For in situ hydrogenation of Pd thin films, the distances of the lattice fringes were 0.20 and 0.23 nm, which correspond to the lattice d spacings of beta-phase (200) and (111) planes. Expansion of the Pd lattice happened as a result of phase transformation from the alpha phase to the beta phase. In particular, the lattice fringes were clearly distinguished, and the dislocation behavior during Pd hydrogenation was easily recognized according to the corresponding inverse fast fourier transform images. Furthermore, significant growth in the number of dislocations was observed at the grain boundary during increasing hydrogen pressure in the cell.
  • Yuki Nakagawa, Tengfei Zhang, Masaumi Kitamura, Shigehito Isobe, Satoshi Hino, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF CHEMICAL AND ENGINEERING DATA 61 (5) 1924 - 1929 0021-9568 2016/05 [Refereed][Not invited]
     
    The effects of metal-based additives in a wide range of elements doping into ammonia borane (AB) were systematically investigated. Pure transition metals in period 4 and total of 17 metal chlorides were selected as additives and ball-milled with AB. Metal chloride additives were effective to decrease H-2 desorption temperature and the amounts of by product gas emissions of AB, whereas pure transition metals did not show any ability because they did not work as Lewis acids. The strong correlation between H-2 desorption temperature and the Pauling electronegativity of metal (chi(p)) was observed. Mn+ of MCln would work as Lewis acid to initiate the AB dehydrocoupling reaction. The amount of NH3 emission was correlated with the ionic radius of M, suggesting MCln center dot mNH(3) complexes be formed in this system. AB-CuCl2 and AB-AgCl mixtures showed the similar H-2 desorption processes. The Cl-containing intermediate phase would destabilize AB during reaction.
  • Y. Satoh, Y. Abe, H. Abe, Y. Matsukawa, S. Kano, S. Ohnuki, N. Hashimoto
    PHILOSOPHICAL MAGAZINE 96 (21) 2219 - 2242 1478-6435 2016 [Refereed][Not invited]
     
    We performed in situ observation of one-dimensional (1D) migration of self-interstitial atom (SIA) clusters in iron under electron irradiation at 110-300 K using high-voltage electron microscopy. Most 1D migration was stepwise positional changes of SIA clusters at irregular time intervals at all temperatures. The frequency of 1D migration did not depend on the irradiation temperature. It was directly proportional to the damage rate, suggesting that 1D migration was induced by electron irradiation. In contrast, the 1D migration distance depended on the temperature: distribution of the distance ranged over 100 nm above 250 K, decreased steeply between 250 and 150 K and was less than 20 nm below 150 K. The distance was independent of the damage rate at all temperatures. Next, we examined fluctuation in the interaction energy between an SIA cluster and vacancies of random distribution at concentrations 10(-4)-10(-2), using molecular statics simulations. The fluctuation was found to trap SIA clusters of 4 nm diameter at vacancy concentrations higher than 10(-3). We proposed that 1D migration was interrupted by impurity atoms at temperatures higher than 250 K, and by vacancies accumulated at high concentration under electron irradiation at low temperatures where vacancies are not thermally mobile.
  • Shigehito Isobe, Katsuhiro Kudoh, Satoshi Hino, Kenji Hara, Naoyuki Hashimoto, Somei Ohnuki
    APPLIED PHYSICS LETTERS 107 (8) 081602  0003-6951 2015/08 [Refereed][Not invited]
     
    In this letter, catalytic efficiency of Nb, NbO, Nb2O3, NbO2, and Nb2O5 for dissociation and recombination of hydrogen were experimentally investigated. On the surface of Nb and Nb oxides in a gas mixture of H-2 and D-2, H-2 and D-2 molecules can be dissociated to H and D atoms; then, H-2, D-2, and HD molecules can be produced according to the law of probability. With increase of frequency of the dissociation and recombination, HD ratio increases. The ratio of H-2 and HD gas was analyzed by quadrupole mass spectrometry. As a result, NbO showed the highest catalytic activity towards hydrogen dissociation and recombination. (C) 2015 AIP Publishing LLC.
  • Hiroshi Oka, Yutaka Sato, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 462 470 - 474 0022-3115 2015/07 [Refereed][Not invited]
     
    Depth dependence of hardness in ion-irradiated 316 stainless steel was evaluated by the sectioning of damaged region and subsequent nano-indentation. The range of plastically deformed region by the nano-indentation was supplementarily investigated by transmission electron microscopy. When the indentation depth was the critical indentation depth, h(c) which was derived from the Nix-Gao plot, the dislocation structure was observed from the specimen surface to right below the bottom of the ion-irradiated region. To verify the depth dependence of hardness, the "multi-layer model" was introduced in this study. The multi-layer model is based on the following assumptions; (1) the ion-irradiated region can be divided into sub-layers having their own local hardness, H-L; (2) the hardness can be the product off and H-L in each sub-layer where f is the volume fraction of a deformation zone; and (3) the deformation zone can be a hemisphere. Eventually, through the sectioning and following nano-indentation, H-L, in each sub-layer was experimentally evaluated. Further the correlation between the displacement damage and the irradiation hardening Delta H in this study agreed with that of neutron irradiation experiments. (C) 2015 Elsevier B.V. All rights reserved.
  • Eni Sugiarti, Kemas A. Zaini, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Shigenari Hayashi
    OXIDATION OF METALS 83 (5-6) 453 - 464 0030-770X 2015/06 [Refereed][Not invited]
     
    Metastable Al2O3 scale formation on NiCoCrAl coated layers was investigated during initial-stage reaction for up to 100 h exposure at 800 A degrees C in air. NiCoCrAl was diffusion-coated onto low carbon steel by electroplating a NiCo layer followed by pack-cementation deposition of Cr and Al. The microstructural characterization of as-coated and oxidized samples was carried out at the micro- and nano-scales. The XRD and diffraction pattern in TEM analysis revealed the presence of metastable Al2O3, spinel NiAl2O4 and cubic (Cr,Al)(2)O-3 in the oxide. The phase identification using XRD and electron diffraction analysis associated with the coating composition was plotted on an isothermal oxidation map.
  • Seiji Sakuraya, Keisuke Takahashi, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF PHYSICS-CONDENSED MATTER 27 (17) 0953-8984 2015/05 [Refereed][Not invited]
     
    The diffusion mechanism of point defects within alpha-Fe with a single vacancy is investigated using the density functional theory. Calculation reveals that H has a slight effect towards Fe diffusion to a vacancy. He has a strong binding with a vacancy; therefore, Fe diffusion is unlikely to happen. The diffusion of C and N from a vacancy has a high barrier. However, Fe diffusion to a vacancy decreases if the C and N diffuse from a vacancy. Thus, the effect of interstitial atoms within alpha-Fe with a single vacancy towards diffusion and a possible diffusion pathway is discussed.
  • Seiji Sakuraya, Keisuke Takahashi, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF PHYSICS-CONDENSED MATTER 27 (17) 0953-8984 2015/05 [Refereed][Not invited]
     
    The diffusion mechanism of point defects within alpha-Fe with a single vacancy is investigated using the density functional theory. Calculation reveals that H has a slight effect towards Fe diffusion to a vacancy. He has a strong binding with a vacancy; therefore, Fe diffusion is unlikely to happen. The diffusion of C and N from a vacancy has a high barrier. However, Fe diffusion to a vacancy decreases if the C and N diffuse from a vacancy. Thus, the effect of interstitial atoms within alpha-Fe with a single vacancy towards diffusion and a possible diffusion pathway is discussed.
  • Eni Sugiarti, Fredina Destyorini, Kemas A. Zaini, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Shigenari Hayashi
    SURFACE & COATINGS TECHNOLOGY 265 68 - 77 0257-8972 2015/03 [Refereed][Not invited]
     
    Coatings formed from NiCoCrAl were deposited by a combination of electroplating and pack cementation on a carbon steel substrate. The effect of Co concentration and temperature on the oxidation and hardness properties of the carbon steel was studied. The microstructure and morphology of the coatings were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microhardness of the coated samples was evaluated by a Vickers microhardness tester. FeNi(5%)CoCrAl coated sample exhibited better oxidation and hardness properties than that of FeNi(1%)CoCrAl coated sample. The microstructure and phase constitution of these coatings developed at 800 degrees C were similar. Samples coated at 800 degrees C and 1000 degrees C consisted of three and two layers, respectively. The formation of an intermetallic layer in all the coatings was confirmed. The gamma-(Ni,Fe), beta-(Ni,Al) and zeta exagonal structures were identified in the coated layers of all samples, while orthorhombic Al3Ni was only identified in the samples coated at 800 degrees C An analysis of the correlations between the structure, hardness properties, oxidation behaviors, and phase formation is also discussed. (C) 2015 Elsevier B.V. All rights reserved.
  • Tengfei Zhang, Shigehito Isobe, Motoaki Matsuo, Shin-ichi Orimo, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    ACS CATALYSIS 5 (3) 1552 - 1555 2155-5435 2015/03 [Refereed][Not invited]
     
    This paper presents a relationship between ionic mobility and reaction kinetics for the Li-N-H system after doping LiTi2O4. The structural characteristic of this fast ionic conductor was introduced to the complex-hydride system. On one hand, the properties of the dehydrogenation process were improved significantly. On the other hand, the relationship between lithium ionic conductivity and the catalytic effect on the dehydrogenation was investigated according to the alternating current (AC) impedance results. The lithium ionic conductivity of samples with catalyst was higher than the samples without catalyst. Especially, the conductivity of LiNH2 and LiH mixtures with LiTi2O4 was almost 1.5 times higher than that of LiNH2 and LiH. The mobility of the Li+ ions between LiH and LiNH2 solid phases was enhanced by adding LiTi2O4.
  • An In-Situ, Environmental Cell-Holder of Conventional Transmission Electron Microscope and Its Applications
    Y. Wang, T. Wakasugi, H. Nagakura, S. Isobe, N. Hashimoto, S. Ohnuki
    MICROSCOPY Oxford 64 I119  2015 [Refereed][Not invited]
  • Development of High Pressure Gas Environmental Cell and its Application to Hydrogen Reaction
    H. Nagakura, T. Wakasugi, K. Ohkubo, T. Tanioka, T. Endo, S. Isobe, Y. Wang, N. Hashimoto, S. Ohnuki
    MICROSCOPY Oxford 64 I119  2015 [Refereed][Not invited]
  • Multi-layer Method combined with Nano-indentation, FIB and XTEM for Nano-hardness Measurement
    R. Kurishiba, T. Endo, N. Miyazaki, Y. Wang, H. Oka, Y. Sato, A. Sawa, N. Hashimoto, S. Ohnuki
    MICROSCOPY Oxford 64 I119  2015 [Refereed][Not invited]
  • Effect of Pack Cementation Temperature on Oxidation Behavior of NiCoCrAl Coated Layer
    E. Sugiarti, K. A. Zaini, Y Wang, N. Hashimoto, S. Ohnuki, S. Hayashi
    0.4028/www.scientific.net/AMR.1112.353 2015 [Refereed][Not invited]
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    RSC ADVANCES 5 (24) 18375 - 18378 2046-2069 2015 [Refereed][Not invited]
     
    We have decreased the end temperature of the Li-N-H system, a hydrogen storage material developed in 2002, to below 260 degrees C, and obtained a lowest peak temperature of 223 degrees C.
  • S. Chen, Y. Wang, K. Tadaki, N. Hashimoto, S. Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 455 (1-3) 301 - 305 0022-3115 2014/12 [Refereed][Not invited]
     
    Helium implantation was performed to investigate irradiation hardening in ferritic/martensitic steels. Depth dependence of nano-hardness was obtained using a Berkovich nano-indenter, and then nano-hardness was extracted from Nix-Gao model. The correlation between irradiation hardening and the concentration 500-2000 appm of helium was plotted. Nano-hardness increases as a function of helium concentration. F82H-ODS with a higher nano-hardness provides a lower irradiation hardening than F82H-IEA. Cross-sectional transmission electron microscopy (XTEM) revealed that cavities with a uniform distribution were formed after helium implantation at 2000 appm helium concentration, showing a mean size of 1.1 nm with an average number density of 4.9 x 10(23) m(-3) in F82H-IEA and 1.3 nm with 7.4 x 10(23) m(-3) in F82H-ODS. Orowan model was applied to evaluate the hardening from dispersed cavities. The significant difference of hardening between calculation and nano-indentation result of F82H-ODS indicates that oxide particles may shield the hardening effect from cavities because of the complex multi-interaction. (C) 2014 Elsevier B.V. All rights reserved.
  • Yongming Wang, Takenobu Wakasugi, Shigehito Isobe, Naoyuki Hashimoto, Somei Ohnuki
    MICROSCOPY 63 (6) 437 - 447 2050-5698 2014/12 [Refereed][Not invited]
     
    Transmission electron microscope (TEM) observation of light metal hydrides is complicated by the instability of these materials under electron irradiation. In this study, the electron kinetic energy dependences of the interactions of incident electrons with lithium, sodium and magnesium hydrides, as well as the constituting element effect on the interactions, were theoretically discussed, and electron irradiation damage to these hydrides was examined using in situ TEM. The results indicate that high incident electron kinetic energy helps alleviate the irradiation damage resulting from inelastic or elastic scattering of the incident electrons in the TEM. Therefore, observations and characterizations of these materials would benefit from increased, instead decreased, TEM operating voltage.
  • Yongming Wang, Takenobu Wakasugi, Shigehito Isobe, Naoyuki Hashimoto, Somei Ohnuki
    MICROSCOPY 63 (6) 437 - 447 2050-5698 2014/12 [Refereed][Not invited]
     
    Transmission electron microscope (TEM) observation of light metal hydrides is complicated by the instability of these materials under electron irradiation. In this study, the electron kinetic energy dependences of the interactions of incident electrons with lithium, sodium and magnesium hydrides, as well as the constituting element effect on the interactions, were theoretically discussed, and electron irradiation damage to these hydrides was examined using in situ TEM. The results indicate that high incident electron kinetic energy helps alleviate the irradiation damage resulting from inelastic or elastic scattering of the incident electrons in the TEM. Therefore, observations and characterizations of these materials would benefit from increased, instead decreased, TEM operating voltage.
  • Yongming Wang, Takenobu Wakasugi, Shigehito Isobe, Naoyuki Hashimoto, Somei Ohnuki
    MICROSCOPY 63 (6) 437 - 447 2050-5698 2014/12 [Refereed][Not invited]
     
    Transmission electron microscope (TEM) observation of light metal hydrides is complicated by the instability of these materials under electron irradiation. In this study, the electron kinetic energy dependences of the interactions of incident electrons with lithium, sodium and magnesium hydrides, as well as the constituting element effect on the interactions, were theoretically discussed, and electron irradiation damage to these hydrides was examined using in situ TEM. The results indicate that high incident electron kinetic energy helps alleviate the irradiation damage resulting from inelastic or elastic scattering of the incident electrons in the TEM. Therefore, observations and characterizations of these materials would benefit from increased, instead decreased, TEM operating voltage.
  • H. Oka, N. Hashimoto, T. Muroga, A. Kimura, M. A. Sokolov, T. Yamamoto, S. Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 455 (1-3) 454 - 459 0022-3115 2014/12 [Refereed][Not invited]
     
    F82H-IEA and its EB-weld joint were irradiated at 573 and 773 K up to 9.6 dpa and the irradiation effect on its mechanical properties and microstructure were investigated. A hardness profile across the weld joint before irradiation showed the hardness in transformed region (TR) was high and especially that in the-edge of TR was the highest (high hardness region: HHR) compared to base metal (BM). These hardness distribution was correspond to grain size distribution. After irradiation, hardening in HHR was small compared to other region in the sample. In tensile test, the amount of hardening in yield strength and ultimate tensile strength of F82H EB-weld joint was almost similar to that of F82H-IEA but the fracture position of EB-weld joint was at the boundary of TR and BM. Therefore, the TR/BM boundary is the structural weak point in F82H EB-weld joint after irradiation. As the plastic instability was observed, the dislocation channeling deformation can be expected though the dislocation channel was not observed in this study. (C) 2014 Elsevier B.V. All rights reserved.
  • H. Homma, N. Hashimoto, S. Ohnuki
    Prehospital and Disaster Medicine 1645 1945-1938 2014/11/07 [Refereed][Not invited]
     
    One of the critical issues for development of the nuclear fusion demonstration reactor (DEMO) is the high heat flux on heat-resistant equipments, especially the blanket and divertor. Materials of such equipments require relatively high thermal conductivities. In this study, we developed iron-based composite materials with carbon nanotube (CNT) and copper, which have high thermal diffusivities, by means of Hot Pressing (HP) and Spark Plasma Sintering (SPS). The thermal diffusivity in the iron/CNT composites was not high enough compared with that of pure iron, while iron/copper composite showed a relatively high thermal diffusivity in the joining conditions. One of the reasons not to be improved thermal diffusivity could be non-mono-dispersion of CNT by the formation of carbides in the matrix.
  • Seiji Sakuraya, Keisuke Takahashi, Shuai Wang, Naoyuki Hashimoto, Somei Ohnuki
    SOLID STATE COMMUNICATIONS 195 70 - 73 0038-1098 2014/10 [Refereed][Not invited]
     
    The effects of impurities of H, He, C, and N in alpha-Fe are investigated in terms of electronic structures using the density functional theory. Calculations reveal that H and He are stable at the T-site while C and N are stable at the O-site within alpha-Fe. The local strain field by H, He, C, and N in alpha-Fe causes structural elongation. Furthermore, the decrease of magnetic moment of Fe upon the introduction of C and N is Found where the charge transfer is responsible. H, He, C, and N affect the electronic structure of alpha-Fe and change the fundamental physical properties of alpha-Fe. (C) 2014 Elsevier Ltd. All rights reserved.
  • Seiji Sakuraya, Keisuke Takahashi, Shuai Wang, Naoyuki Hashimoto, Somei Ohnuki
    SOLID STATE COMMUNICATIONS 195 70 - 73 0038-1098 2014/10 [Refereed][Not invited]
     
    The effects of impurities of H, He, C, and N in alpha-Fe are investigated in terms of electronic structures using the density functional theory. Calculations reveal that H and He are stable at the T-site while C and N are stable at the O-site within alpha-Fe. The local strain field by H, He, C, and N in alpha-Fe causes structural elongation. Furthermore, the decrease of magnetic moment of Fe upon the introduction of C and N is Found where the charge transfer is responsible. H, He, C, and N affect the electronic structure of alpha-Fe and change the fundamental physical properties of alpha-Fe. (C) 2014 Elsevier Ltd. All rights reserved.
  • Shigehito Isobe, Ayaka Umeda, Takenobu Wakasugi, Tao Ma, Ryo Yamagami, Satoshi Hino, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 55 (8) 1175 - 1178 1345-9678 2014/08 [Refereed][Not invited]
     
    We propose the microstructural change model of magnesium hydride catalyzed by Nb2O5 during hydrogenation. The ball-milled composites, MgH2 and 1 mol% Nb2O5, were dehydrogenated and then rehydrogenated for varied time at room temperature under 0.1 MPa H-2 atmosphere. The crystallite size of Mg and MgH2 was evaluated by powder X-ray diffraction (XRD) measurement and confirmed by transmission electron microscopy (TEM) observation. The crystallite size of generated MgH2 was smaller than that of Mg and did not change significantly with increasing time of hydrogenation. It is suggested that the number density of MgH2 crystallites increases during the hydrogenation process.
  • Shigehito Isobe, Yudai Ikarashi, Hao Yao, Satoshi Hino, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 55 (8) 1138 - 1140 1345-9678 2014/08 [Refereed][Not invited]
     
    Recently, LiAlH4 has attracted attention as one of the most promising hydrogen storage materials, because LiAlH4 is able to release large amount of hydrogen (7.9 mass%H-2) below 250 degrees C. However, the kinetics of the dehydrogenation reaction of LiAlH4 is too slow for applications to fuel cell vehicles. To improve the dehydrogenation kinetics, the dopant effect of TiCl3 has been investigated in this research. Here, LiAlH4 doped with various ratios (0, 0.1, 0.2, 0.5, 1.0, and 2.0 mol%) of TiCl3 were prepared by ball milling for 30 min under a 1.0 MPa H-2 atmosphere. The decomposition of LiAlH4 proceeds via a two-step reaction and the dehydrogenation kinetics of each step were compared to determine the optimum amount of TiCl3 that would assist the process. With increasing of TiCl3 amount, the dehydrogenation temperature for both of the reactions decreased. Activation energies decreased with increasing TiCl3 amount, however the amount of desorbed hydrogen decreased. Considering the kinetics and hydrogen capacity in the both steps, the results suggest that the optimum amount of doped TiCl3 for the dehydrogenation of LiAlH4 is around 0.2 mol%.
  • Shuai Wang, May L. Martin, Petros Sofronis, Somei Ohnuki, Naoyuki Hashimoto, Ian M. Robertson
    ACTA MATERIALIA 69 275 - 282 1359-6454 2014/05 [Refereed][Not invited]
     
    The hydrogen embrittlement of a commercial-grade pure iron was examined by using repeated stress-relaxation tests under simultaneous cathodic hydrogen charging. The hydrogen-charged iron, containing an estimated 25.8 appm H, fractured after repeated transients, with a total strain of The fracture mode was intergranular. Thermal activation measurements show a decrease in activation volume and free energy, which is consistent with hydrogen enhancing the dislocation velocity. The microstructure beneath the intergranular facets displays a dislocation cell structure more complex than expected for intergranular fracture and this strainto-failure. It is proposed that hydrogen accelerates the evolution of the dislocation microstructure through the hydrogen-enhanced plasticity mechanism and this work-hardening of the matrix along with the attendant hydrogen concentration at the grain boundaries are crucial steps in causing the observed hydrogen-induced intergranular failure. (c) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • Hiroshi Oka, Masashi Watanabe, Somei Ohnuki, Naoyuki Hashimoto, Shinichiro Yamashita, Satoshi Ohtsuka
    JOURNAL OF NUCLEAR MATERIALS 447 (1-3) 248 - 253 0022-3115 2014/04 [Refereed][Not invited]
     
    An oxide dispersion strengthened (ODS) austenitic stainless steel was developed by mechanical alloying (MA) of advanced SUS316 stainless steel. A nano-characterization was performed to understand details of the effect of minor alloying elements in the distribution of dispersoids. It is shown that Y2O3 particles dissolve into the austenitic matrix after the MA for 6 h. Annealing at 1073 K or higher temperatures result in a distribution of fine oxide particles in the recrystallized grains in the ODS austenitic stainless steel. Additions of Hafnium or Zirconium led to the distribution of finer oxide particles than in samples without these elements, resulting in an increase in the hardness of the samples. The most effective concentration of Hf and Zr to increase the hardness was 0.6 and 0.2-0.3 wt%, respectively. (C) 2014 Elsevier B.V. All rights reserved.
  • N. Hashimoto, S. Oie, H. Homma, S. Ohnuki
    MATERIALS TRANSACTIONS 55 (3) 458 - 460 1345-9678 2014/03 [Refereed][Not invited]
     
    In-situ observations of microstructure evolution of the electron-irradiated multi-wall carbon nanotubes (MWCNT) were carried out by using a high voltage electron microscope (HVEM). Electron irradiation at relatively low temperatures exhibited changes in the structure of the MWCNT, such as in the distance and ruggedness of walls. The MWCNT appeared to be stable during electron irradiation at relatively high temperatures probably due to a higher probability of recombination between knock-on atoms and vacancies in walls, meaning that composites developed with CNT could be stable and maintain high thermal conductivity during irradiation at high temperatures.
  • Somei Ohnuki, Naoyuki Hashimoto, Erwan Oliviero, Jonathan Hinks, Hattar Khalid
    MATERIALS TRANSACTIONS 55 (3) 395 - 395 1345-9678 2014/03 [Refereed][Not invited]
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    CHEMCATCHEM 6 (3) 724 - 727 1867-3880 2014/03 [Refereed][Not invited]
     
    In this study, LiTi2O4 was synthesized as a possible catalyst in the Li-N-H system. The properties of hydrogen desorption in the Li-N-H system with a homogeneous catalyst have been investigated. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that the single phase of LiTi2O4 was successfully synthesized and it was stable in the sample after high energy ball-milling and heat treatment. LiTi2O4 exhibited a catalytic effect in the Li-N-H system according to the thermogravimetry differential thermal analysis results. During dehydrogenation, a storage capacity of 5.7wt% was obtained under moderate temperature. A sharp peak of thermal gas desorption mass spectrometry curve occurred at 227 degrees C. Furthermore, the catalytic mechanism of LiTi2O4 in the Li-N-H system was discussed in accordance with the experimental results.
  • Siwei Chen, Kohei Tadaki, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 55 (3) 443 - 446 1345-9678 2014/03 [Refereed][Not invited]
     
    In-situ observations of ferritic/martensitic steels by electron irradiation with a 1.25 MeV high voltage microscope at 573 K were carried out to study damage evolution in the steels. The development of interstitial type loops and cavities in both of the two steels, F82H-IEA and F82H-ODS, showed smaller and more numerous defects in the ODS steel. The cavities were formed preferentially at the interface between oxide particles and matrix. The results suggest that ODS particles may function to suppress the nucleation and growth of loops and cavities arising from irradiation. The effect of pre-implanted helium was also studied. The pre-implanted helium led to a homogenous distribution of black dots and cavities in the steels, and these may act as sinks for point defects arising from irradiation, causing a suppression of the subsequent growth of loops and cavities. The hardening corresponding to the microstructural evolution was estimated by assuming parameters extracted from the ion irradiation.
  • N. Hashimoto, S. Sakuraya, J. Tanimoto, S. Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 445 (1-3) 224 - 226 0022-3115 2014/02 [Refereed][Not invited]
     
    Effects of impurities, such as carbon, nitrogen, helium and hydrogen, on microstructural evolution in pure iron were investigated by means of a multi-beam electron microscope. Growth rate of dislocation loops were measured to calculate vacancy migration energies. In all irradiation temperature conditions, both the size and the number density of dislocation loops were increased as a function of dose. Irradiation with more impurities showed an increase in the temperature dependence of the dislocation loop growth rate compared to irradiation with little impurities. The in situ experiment indicated that the net migration energy of vacancies could be increased due to trapping by impurities, and the effect of C and N on the migration energy of vacancy would be larger than that of W, V, Ta. Furthermore, H and He would increase vacancy migration energy greater than C and N, as well as W, V. Ta. The density functional theory (DFT), applied to the atomic models of BCC iron, indicated an increase in vacancy migration energy by the trapping of impurity atoms, that is a good agreement with this in situ experiment. (C) 2013 Elsevier B.V. All rights reserved.
  • N. Hashimoto, S. Sakuraya, J. Tanimoto, S. Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 445 (1-3) 224 - 226 0022-3115 2014/02 [Refereed][Not invited]
     
    Effects of impurities, such as carbon, nitrogen, helium and hydrogen, on microstructural evolution in pure iron were investigated by means of a multi-beam electron microscope. Growth rate of dislocation loops were measured to calculate vacancy migration energies. In all irradiation temperature conditions, both the size and the number density of dislocation loops were increased as a function of dose. Irradiation with more impurities showed an increase in the temperature dependence of the dislocation loop growth rate compared to irradiation with little impurities. The in situ experiment indicated that the net migration energy of vacancies could be increased due to trapping by impurities, and the effect of C and N on the migration energy of vacancy would be larger than that of W, V, Ta. Furthermore, H and He would increase vacancy migration energy greater than C and N, as well as W, V. Ta. The density functional theory (DFT), applied to the atomic models of BCC iron, indicated an increase in vacancy migration energy by the trapping of impurity atoms, that is a good agreement with this in situ experiment. (C) 2013 Elsevier B.V. All rights reserved.
  • H. Homma, N. Hashimoto, S. Ohnuki
    Materials Research Society Symposium Proceedings 1645 0272-9172 2014 [Refereed][Not invited]
     
    One of the critical issues for development of the nuclear fusion demonstration reactor (DEMO) is the high heat flux on heat-resistant equipments, especially the blanket and divertor. Materials of such equipments require relatively high thermal conductivities. In this study, we developed iron-based composite materials with carbon nanotube (CNT) and copper, which have high thermal diffusivities, by means of Hot Pressing (HP) and Spark Plasma Sintering (SPS). The thermal diffusivity in the iron/CNT composites was not high enough compared with that of pure iron, while iron/copper composite showed a relatively high thermal diffusivity in the joining conditions. One of the reasons not to be improved thermal diffusivity could be non-mono-dispersion of CNT by the formation of carbides in the matrix. Copyright © Materials Research Society 2014.
  • Siwei Chen, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    PHILOSOPHICAL MAGAZINE LETTERS 94 (7) 433 - 438 0950-0839 2014 [Refereed][Not invited]
     
    The onset of plasticity during nanoindentation is a new method to investigate the irradiation damage of structural materials in fission and fusion reactors. In this paper, nanoindentation experiment was carried out to helium implanted F82H-IEA and nano-sized oxide dispersion strengthened F82H-ODS steels for studying the elastic-plastic transition at a constant loading rate. The onset of plasticity shifted after helium implantation. By a statistical thermal activation model, activation volume was extracted to discuss the strength of barrier for dislocation motion. The results reveal an increase in the pinning force and number density of effective obstacles for dislocation motion in He-implanted F82H-IEA, and a decrease in the local pinning force without changing the density of effective obstacles in He-implanted F82H-ODS.
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Hiroshi Oka, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF MATERIALS CHEMISTRY A 2 (12) 4361 - 4365 2050-7488 2014 [Refereed][Not invited]
     
    In this study, LiTi2O4 was synthesized as a possible catalyst for complex metal hydrides. LiTi2O4 was stable in the sample after high-energy ball milling and heat treatment. LiTi2O4 exhibited a catalytic effect among the samples of MgH2, LiAlH4 and LiNH2. The desorption kinetics and the purity of the desorbed hydrogen gas have been improved by doping LiTi2O4. Furthermore, the catalytic mechanism of LiTi2O4 was discussed in accordance with the experimental results.
  • S. Eni, K. Zaini, Y. Wang, N. Hashimoto, S. Hayashi, S. Ohnuki
    Advanced Materials Research 896 586 - 590 1022-6680 2014 [Refereed][Not invited]
     
    The corrosion of carbon steel is major infrastructure degradation problem in most industries, including chemical materials, mineral, and petrochemical industries. Coating on carbon steel is one of the techniques to improve corrosion resistance in extreme environments. In present work, NiCoCrAl was diffusion-coated onto low carbon steel by electrodeposition for NiCo and pack cementation for Cr and Al. The cross section of coated specimen was observed and analyzed using SEM and TEM. Two types of coating processes were conducted to promote the formation of bond-coat layer on carbon steel substrate with different temperature coating process. SEM and EDS results show that the coating comprises three layers on the substrate: intermetallics zone of Ni(Al) and Al(Cr) and interdiffusion zone of Ni(Co). By XTEM observation, it was found that γ(Ni,Fe) and ζ hexagonal structure were identified in all specimens. Orthorhombic structure with the Al3Ni was identified in specimen developed at temperature of 800°C. Further, the top surface of a 1000°C specimen has two phases of β-NiAl and ζ hexagonal structure. In order to understand the performance of two types coating system with different temperature process, oxidation test at temperature of 800°C for 100 hours has been carried out and the result shows that coating system which was developed at 800°C has better oxidation resistance than the system developed at 1000°C. © (2014) Trans Tech Publications, Switzerland.
  • Yuki Nakagawa, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Liang Zeng, Shusheng Liu, Takayuki Ichikawa, Yoshitsugu Kojima
    JOURNAL OF ALLOYS AND COMPOUNDS 580 S163 - S166 0925-8388 2013/12 [Refereed][Not invited]
     
    Dehydrogenation processes of alpha- and gamma-AlH3 were investigated by in situ transmission electron microscopy observations. The relationship between Al2O3 thickness and dehydrogenation kinetics was also clarified. The initial shape of alpha-AlH3 particle was cubic and that of gamma-AlH3 particle was rod-shaped. The process of gamma-AlH3 was quite similar with alpha-AlH3. The precipitation and growth of Al was observed in both processes. The dehydrogenation kinetics did not depend on Al2O3 thickness. It was found that milling effect on the dehydrogenation kinetics was larger than doping effect. The dehydrogenation process was discussed in terms of both microscopic and kinetic studies. (C) 2013 Elsevier B.V. All rights reserved.
  • Takenobu Wakasugi, Shigehito Isobe, Ayaka Umeda, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF ALLOYS AND COMPOUNDS 580 S127 - S130 0925-8388 2013/12 [Refereed][Not invited]
     
    A close type of an environmental cell was developed for a high voltage electron microscope. Using this cell allowed an in situ observation of hydrogenation in Pd particles under H-2 gas of 0.05 MPa at RT. Two types of window films, Tri-Acetyl-Cellulose (TAC) and Silicon Nitride (SiN), were used for testing the contamination on the sample, as well as the strength for pressure. We confirmed the hydrogenation in diffraction patterns and images, and additionally the image resolution of 0.19 urn was obtained by using a SiN film with a thickness of 17 nm. (C) 2013 Elsevier B.V. All rights reserved.
  • Shigehito Isobe, Sumito Yamada, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Hiroki Miyaoka, Takayuki Ichikawa, Yoshitsugu Kojima
    Journal of Applied Physics 114 (9) 093509-093509-7  0021-8979 2013/09/07 [Refereed][Not invited]
     
    Li-C-H system, which can store about 5.0 mass% of rechargeable H 2, has been reported as a promising hydrogen storage system by Ichikawa [Appl. Phys. Lett. 86, 241914 (2005) Mater. Trans. 46, 1757 (2005)]. This system was investigated from the thermodynamic and structural viewpoints. However, hydrogen absorption/desorption mechanism and the state of hydrogen atoms absorbed in the composite have not been clarified yet. In order to find new or better hydrogen storage system, graphite powder and nano-structural graphite ball-milled under H2 and Ar atmosphere were prepared and milled with Li and Mg under Ar atmosphere in this study. Microstructural analysis for those samples by transmission electron microscope revealed that LiC6 and/or LiC12 were formed in Li-C-H system. On the other hand, MgC2 was found in Mg-C-H system ball-milled under H 2 atmosphere, but not in the system ball-milled under Ar atmosphere. These results indicated that nano-structure in composites of nano-structural graphite is different from that of alkali (-earth) metal. For these reasons, metal-C-H system can be recognized to be a new family of hydrogen storage materials. © 2013 AIP Publishing LLC.
  • 山上亮, 礒部繁人, 王永明, 橋本直幸, 大貫惣明
    日本金属学会講演概要(CD-ROM) 153rd ROMBUNNO.6  1342-5730 2013/09/03 [Not refereed][Not invited]
  • Shuai Wang, Naoyuki Hashimoto, Somei Ohnuki
    SCIENTIFIC REPORTS 3 2045-2322 2013/09 [Refereed][Not invited]
     
    Employing the empirical embedded-atom method potentials, the evolution of edge and screw dislocation core structure is calculated at different hydrogen concentrations. With hydrogen, the core energy and Peierls potential are reduced for all dislocations. A broaden-core and a quasi-split core structure are observed for edge and screw dislocation respectively. The screw dislocation and hydrogen interaction in body-centred cubic iron is found to be not mainly due to the change of elastic modulus, but the variation of dislocation core structure.
  • Shuai Wang, Naoyuki Hashimoto, Yongming Wang, Somei Ohnuki
    ACTA MATERIALIA 61 (13) 4734 - 4742 1359-6454 2013/08 [Refereed][Not invited]
     
    In order to monitor the influence of hydrogen on the coupled evolution of dislocation velocity and mobile dislocation density, we applied repeated transients to pure iron under simultaneous hydrogen cathodic charging conditions. The effective activation volume and the thermal stress were determined at different hydrogen concentrations. The effective activation volume decreases immediately with cathodic charging. At high hydrogen concentrations, the activation volume decreases and the thermal stress increases rapidly. The density of mobile dislocations in the hydrogen-charged iron has a lower rate of exhaustion than the hydrogen-free one. The thermal activation energy decreases and the average dislocation velocity increases as a function of hydrogen concentration. Transmission electron microscopy reveals hydrogen-induced tangled dislocations, which indicates a weakening of the repulsive stress field between dislocations. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • Shaoning Jiang, Farong Wan, Yi Long, Jianchao He, Pingping Liu, Somei Ohnuki, Naoyaki Hashimoto
    ACTA METALLURGICA SINICA-ENGLISH LETTERS 26 (3) 303 - 306 1006-7191 2013/06 [Refereed][Not invited]
     
    To study the effect of tungsten, vanadium and tantalum on the microstructures in CLAM (China Low Activation Martensitic) steel after irradiation respectively, the microstructures of Fe-M (M= V,W, To) model alloys were investigated after implanted deuterium ions using an ion accelerator at 773 K. After implanted deuterium ion, TEM (Transmission Electron Microscope) observation and EDX (Energy Dispersive X-ray Spectrom) analysis have been carried out. The result showed that tiny voids were observed in all model alloys after implanted the same dose of deuterium ions. The swelling rate in FeTa alloy was the smallest among the three alloys. Unlike FeW and FeV alloys, there was the segregation in FeTa alloy under a fluence of 5x10(17) D+/cm(2) at 773 K. A theoretical analysis showed that the void growth in FeTa alloy slowed down due to tantalum segregation near voids. It indicates that tantalum plays an important role in the improved irradiation resistance of CLAM steel.
  • Tao Ma, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF PHYSICAL CHEMISTRY C 117 (20) 10302 - 10307 1932-7447 2013/05 [Refereed][Not invited]
     
    The state of Nb-contained catalysts in MgH2 nanocomposites was investigated during the full cycle. X-ray diffraction (XRD) results showed that Nb2O5 and Nb reacted with MgH2 during ball-milling, forming NbH2 and NbH, respectively. In the following dehydrogenation, the (di)hydride decomposed, and Nb was produced. Then NbH was generated in both samples after rehydrogenation. Similar composition in both samples suggests that the catalytic effect follows the same mechanism, the Nb-gateway model, in which Nb facilitates the hydrogen transportation from MgH2 to the outside. By contrast, NbO remained during the full cycle. Scanning and transmission electron microscopy (SEM and TEM) observations revealed that the Nb2O5-doped sample tended to be refined in size, compared to the Nb-doped and NbO-doped ones. Nb crystals in the Nb2O5-doped sample were observed to be highly dispersed in the sample, with 10-20 nm in size. Given all that, tiny Nb crystals distributed in the composites worked as the gateway facilitating hydrogen transportation and improving dehydrogenation properties.
  • Hao Yao, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 38 (9) 3689 - 3694 0360-3199 2013/03 [Refereed][Not invited]
     
    The thermal decomposition process of lithium alanate (LiAlH4) was investigated by TEM, TG-DTA and XRD. It was shown that LiAlH4 decomposes through a two-step reaction: a liquid-to-solid phase transition in the first step of the decomposition and a solid-to-solid reaction in the second step of the decomposition, both steps accompanied by hydrogen release. The particle size of the aluminum (Al), which formed in the first decomposition step, was much larger than that in the second decomposition step. In addition, Al particles formed in the liquid phase of LiAlH4 in the first decomposition step, while, they form in solid phase of Li3AlH6 in the second decomposition step, resulting in the kinetics of the first decomposition step being faster than that of the second decomposition step. The investigation clearly demonstrated the reaction model of the decomposition of LiAlH4 in the nano-scale, showing different diffusion processes of Al in each of the decomposition steps. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
  • Shuai Wang, Keisuke Takahashi, Naoyuki Hashimoto, Shigehito Isobe, Somei Ohnuki
    SCRIPTA MATERIALIA 68 (5) 249 - 252 1359-6462 2013/03 [Refereed][Not invited]
     
    The effect of hydrogen in body-centered cubic iron is explored by using the density function theory. Hydrogen atoms increase the concentration of free electrons in the simulation cell and undergo bonding interaction with Fe atoms. Elastic interaction between hydrogen and screw dislocations was found, caused by the anisotropic strain components of the hydrogen atoms in the tetrahedral sites. The dependence of the hydrogen-screw dislocation interaction on hydrogen concentration is confirmed by repeated stress relaxation tests. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • Shuai Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 562 101 - 108 0921-5093 2013/02 [Refereed][Not invited]
     
    To evaluate the hydrogen effect on coupled evolution of dislocation velocity and mobile dislocation density in Fe-based alloys, thermal activation parameters and dislocation structures were obtained using repeated stress relaxation tests on pure iron, Fe-8Cr alloy and F82H steel. For all samples, hydrogen charging increases stress relaxation rate, but decreases the thermal activation volume, internal stress ratio, and exhausting rate of mobile dislocation density. In pure iron, typical hydrogen enhanced softening was only found in high H concentrations, and tangled dislocation structures were observed by Transmission Electron Microscopy (TEM). In Fe-8Cr alloy and F82H steel, hydrogen enhanced softening was observed at all H concentrations, leading to tangled and polygonized dislocation structures along precipitates. The thermal activation energy is reduced in hydrogen charged pure iron, while in Fe-8Cr and F82H steel the activation energies are almost stable because of the pinning effect of precipitates. (C) 2012 Elsevier B.V. All rights reserved.
  • Shuai Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 562 101 - 108 0921-5093 2013/02 [Refereed][Not invited]
     
    To evaluate the hydrogen effect on coupled evolution of dislocation velocity and mobile dislocation density in Fe-based alloys, thermal activation parameters and dislocation structures were obtained using repeated stress relaxation tests on pure iron, Fe-8Cr alloy and F82H steel. For all samples, hydrogen charging increases stress relaxation rate, but decreases the thermal activation volume, internal stress ratio, and exhausting rate of mobile dislocation density. In pure iron, typical hydrogen enhanced softening was only found in high H concentrations, and tangled dislocation structures were observed by Transmission Electron Microscopy (TEM). In Fe-8Cr alloy and F82H steel, hydrogen enhanced softening was observed at all H concentrations, leading to tangled and polygonized dislocation structures along precipitates. The thermal activation energy is reduced in hydrogen charged pure iron, while in Fe-8Cr and F82H steel the activation energies are almost stable because of the pinning effect of precipitates. (C) 2012 Elsevier B.V. All rights reserved.
  • Shuai Wang, Somei Ohnuki, Naoyuki Hashimoto, Keisuke Chiba
    Materials Science and Engineering A 560 332 - 338 0921-5093 2013/01/10 [Refereed][Not invited]
     
    To study the interaction of hydrogen and surface structure of iron, two types of tensile test are carried out under hydrogen gas environment and cathodic hydrogen charging condition. According to the tensile tests, hydrogen induces reduction of flow stress (softening) for the specimens without deformed surface, but increase of flow stress (hardening) for the one with deformed surface. The results of jump tests signify that hydrogen enhances the dislocation mobility by reducing the thermal activation volume for overcoming barriers, and because of this, in the samples with smooth surface, homogeneously distributed hydrogen leads to the softening effect. On the other hand, the deformed layer just under the surface has larger solubility of H due to trap sites provided by dislocation cell structures. As a result of hydrogen shielding effect, the strong interaction between dislocations in surface layer and multiplication of new defects causes the hardening effect. © 2012 Elsevier B.V.
  • Shuai Wang, Somei Ohnuki, Naoyuki Hashimoto, Keisuke Chiba
    Materials Science and Engineering A 560 332 - 338 0921-5093 2013/01/10 [Refereed][Not invited]
     
    To study the interaction of hydrogen and surface structure of iron, two types of tensile test are carried out under hydrogen gas environment and cathodic hydrogen charging condition. According to the tensile tests, hydrogen induces reduction of flow stress (softening) for the specimens without deformed surface, but increase of flow stress (hardening) for the one with deformed surface. The results of jump tests signify that hydrogen enhances the dislocation mobility by reducing the thermal activation volume for overcoming barriers, and because of this, in the samples with smooth surface, homogeneously distributed hydrogen leads to the softening effect. On the other hand, the deformed layer just under the surface has larger solubility of H due to trap sites provided by dislocation cell structures. As a result of hydrogen shielding effect, the strong interaction between dislocations in surface layer and multiplication of new defects causes the hardening effect. © 2012 Elsevier B.V.
  • C. Liu, N. Hashimoto, S. Ohnuki, M. Ando, K. Shiba
    MATERIALS TRANSACTIONS 54 (1) 96 - 101 1345-9678 2013 [Refereed][Not invited]
     
    An Fe-8Cr model alloy was irradiated in the TIARA facility with 10.5 MeV Fe3+ ions and/or 1.05 MeV He+ ions at 100-300 degrees C to 0.1-10 dpa. Irradiated specimens were characterized using transmission electron microscopy and a nano-indentation technique. Visible defect clusters were not detectable by TEM for doses below similar to 0.1 dpa, while spatially heterogeneous dislocation loop rafts were visible for a dose of 10 dpa in single ion irradiation. The loop rafts formation was impeded in dual ion irradiation with the implantation of helium atoms at 10 dpa. Ion irradiation led to increases in hardening with increasing doses. Further, log-log plots of irradiation hardening at 100, 250 and 300 degrees C, which fit the dose dependence of the irradiation hardening using Delta H proportional to (dpa)(n), indicate that the decreases of n values with lower temperatures are due to a tendency towards saturation in the irradiation hardening.
  • H. Hayashi, N. Hashimoto, S. Ohnuki
    Journal of Nuclear Materials 442 (1-3) S830 - S833 0022-3115 2013 [Refereed][Not invited]
     
    To investigate the stability of precipitates in ZIRLO under irradiation, specimens were irradiated by Ni+ ions and electrons at 573 K. Precipitates were analyzed by transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). Non-irradiated ZIRLO included two types of precipitates: BCC Zr-Nb and HCP Zr-Nb-Fe. After ion irradiation, the Zr-Nb-type precipitate remained BCC, while the Zr-Nb-Fe-type became amorphous without Fe depletion. This was likely due to the higher dose rate of ion irradiation compared to that of neutron irradiation, resulting in a reduced defect for the amorphous transition to occur. No precipitate change was observed after electron irradiation to 5 dpa. Results suggest that the stability of the precipitate depends on the type of damage, i.e. electrons vs. ions with presence or absence of cascades. © 2013 Elsevier B.V. All rights reserved.
  • Naoyuki Hashimoto, Hiroshi Oka, Takeo Muroga, Takuya Nagasaka, Akihiko Kimura, Shigeharu Ukai, Takuya Yamamoto, Michail A. Sokolov
    MATERIALS TRANSACTIONS 54 (4) 442 - 445 1345-9678 2013 [Refereed][Not invited]
     
    Under the TITAN project, in order to determine the contributions of different microstructural features to strength and to deformation mode, microstructure of deformed flat tensile specimens of irradiated reduced activation F82H IEA and its joint were investigated by transmission electron microscopy (TEM), following tensile test and fracture surface examination by scanning electron microscopy (SEM). After irradiation, changes in yield strength, deformation mode, and strain-hardening capacity were seen, with the magnitude of the changes dependent on irradiation temperature. Irradiation to F82H IEA at 573 K led to a significant loss of strain-hardening capacity with a large change in yield strength. There was a tendency for a reduction in strain rate to cause a decrease in yield strength and elongation. While, irradiation at 773 K had little effect on strength, but a reduction in strain rate caused a decrease in ductility. SEM revealed fracture surfaces showing a martensitic mixed quasi-cleavage and ductile-dimple fracture in all samples. TEM have exhibited defect free bands (dislocation channels) in the necked region irradiated at 573 K. This suggests that dislocation channeling would be the dominant deformation mechanism in this steel irradiated at 573 K, resulting in the loss of strain-hardening capacity. While, the necked region of the irradiated F82H IEA joint, where showed less hardening than F82H IEA, has showed deformation bands only. From these results, it is suggested that the pre-irradiation microstructure, especially the dislocation density, could affect the post-irradiation deformation mode.
  • N. Hashimoto, J. Tanimoto, T. Kubota, H. Kinoshita, S. Ohnuki
    Journal of Nuclear Materials 442 (1-3) S796 - S799 0022-3115 2013 [Refereed][Not invited]
     
    Effects of helium and hydrogen gas on microstructural evolution in pure iron, Fe-8Cr, and F82H IEA were investigated by means of a multi-beam electron microscope. Growth rate and saturated number density of dislocation loops were measured to calculate migration energies of point defects. In all irradiation temperature conditions, both the size and the number density of dislocation loops were increased as a function of dose. Irradiation with helium and hydrogen showed an increase in the temperature dependence of the dislocation loop growth rate compared to irradiation without helium and hydrogen. On the other hand, little difference was observed in the saturated loop number density at each irradiation temperature. The migration energy of interstitials was determined to be 0.3 eV for both types of irradiation. The migration energy of vacancies was determined to be 0.9 eV for electron irradiation. This in situ experiment indicated that the net migration energy of vacancies could be increased due to trapping by helium and hydrogen. Irradiation experiments indicated that net migration energy of vacancy in F82H IEA irradiated with helium or hydrogen tended to be higher compared to that in pure iron and Fe-8Cr, which could relate not only to helium and hydrogen, but also to carbon and nitrogen concentration in matrix. © 2013 Elsevier B.V. All rights reserved.
  • Shigehito Isobe, Miki Dohkoshi, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Satoshi Hino, Takayuki Ichikawa, Yoshitsugu Kojima
    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals The Japan Institute of Metals and Materials 77 (12) 571 - 574 0021-4876 2013 [Refereed][Not invited]
     
    In order to clarify the reaction mechanism of the hydrogenation process in the Li2NH system, we have observed the partially hydrogenated samples by transmission electron microscopy (TEM). From the TEM images of partially hydrogenated samples, it was shown that the LiNH2 phase was located between Li2NH phase, which was almost at the center of the particle, and LiH partioles with the size of 100 nm. This result indicated that LiH was generated and grew up at the outside of the complex particle of Li2NH and LiNH2 with Li moving from the center to the surface of the particle © 2013 The Japan Institute of Metals and Materials.
  • N. Hashimoto, J. Tanimoto, T. Kubota, H. Kinoshita, S. Ohnuki
    Journal of Nuclear Materials 442 (1-3) S796 - S799 0022-3115 2013 [Refereed][Not invited]
     
    Effects of helium and hydrogen gas on microstructural evolution in pure iron, Fe-8Cr, and F82H IEA were investigated by means of a multi-beam electron microscope. Growth rate and saturated number density of dislocation loops were measured to calculate migration energies of point defects. In all irradiation temperature conditions, both the size and the number density of dislocation loops were increased as a function of dose. Irradiation with helium and hydrogen showed an increase in the temperature dependence of the dislocation loop growth rate compared to irradiation without helium and hydrogen. On the other hand, little difference was observed in the saturated loop number density at each irradiation temperature. The migration energy of interstitials was determined to be 0.3 eV for both types of irradiation. The migration energy of vacancies was determined to be 0.9 eV for electron irradiation. This in situ experiment indicated that the net migration energy of vacancies could be increased due to trapping by helium and hydrogen. Irradiation experiments indicated that net migration energy of vacancy in F82H IEA irradiated with helium or hydrogen tended to be higher compared to that in pure iron and Fe-8Cr, which could relate not only to helium and hydrogen, but also to carbon and nitrogen concentration in matrix. © 2013 Elsevier B.V. All rights reserved.
  • Tengfei Zhang, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    RSC ADVANCES 3 (18) 6311 - 6314 2046-2069 2013 [Refereed][Not invited]
     
    The reaction mechanism of the (de) hydrogenation of a LiNH2 + LiH mixture with a nanoscale catalyst has been investigated. In this research, the position of each solid phase was examined by transmission electron microscopy (TEM). The observation showed that LiH particles, around 100 nm in size, formed around LiNH2 in the hydrogenation process. According to in situ TEM observation of the dehydrogenation process, the LiH particles became smaller as they reacted with LiNH2. Fine particles of Li2NH with crystallites of size 30-40 nm formed on the surface of the LiNH2. It indicated that H+ from the LiNH2 moved to the interface and combined with H- from the LiH in the dehydrogenation process, consequently H-2 was released. At the same time, Li+ ions diffused from the LiH to the LiNH2 through the interface and Li2NH formed. On the other hand, it was confirmed that the catalyst was located at the interface between the LiH and LiNH2. It was found that the catalyst had the effect of improving the migration of Li+ from LiH to LiNH2.
  • Hiroshi Oka, Masashi Watanabe, Naoyuki Hashimoto, Somei Ohnuki, Shinichiro Yamashita, Satoshi Ohtsuka
    Journal of Nuclear Materials 442 (1-3) 164 - 168 0022-3115 2013 [Refereed][Not invited]
     
    In this study, identification of the crystal structure and analysis of the orientation relationship of oxide particles in an oxide dispersion strengthened austenitic stainless steel was carried out. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy showed that most of the oxide particles had a faceted shape and consisted of a complex oxide, the anion-deficient fluorite structure Y2Hf2O7. Selected area diffraction patterns and HRTEM indicated that the faceted oxide particle has a cube-on-cube orientation relationship with the surrounding matrix. In addition, strain fields were observed around the oxide particle with given reflection conditions, indicating that it surrounds the oxide particle. The observed strain fields would affect glide dislocation pinning and the migration of irradiation-induced point defects. © 2013 Elsevier B.V. All rights reserved.
  • Zhu YanYong, Wan FaRong, Gao Jin, Han WenTuo, Huang YiNa, Jiang ShaoNing, Qiao JianSheng, Zhao Fei, Yang ShanWu, Somei Ohnuki, Naoyuki Hashimoto
    SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY 55 (11) 2057 - 2061 1674-7348 2012/11 [Refereed][Not invited]
     
    China Low Activation Martensitic (CLAM) steel is being studied to develop the structural materials for a fusion reactor, which has been designed based on the well-known 9Cr1.5WVTa steel. The effect of tempering temperature on hardness and microstructure of CLAM steel was studied. The strength of CLAM steel increased by adding silicon, and the ductility remained constant. Conversely, while CLAM steel maintained good ductility with the addition of yttrium, its tensile strengths were greatly degraded. Behaviors under electron irradiation of CLAM steel were examined using the high voltage electron microscope. Electron irradiation at 450A degrees C formed many voids in CLAM steel with basic composition, whereas CLAM with silicon steel did not change the microstructure significantly.
  • Tao Ma, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    CATALYSTS 2 (3) 344 - 351 2073-4344 2012/09 [Refereed][Not invited]
     
    We report a study on the desorption properties, crystallography and chemical state of MgH2 and 1 mol% Nb2O5 ball-milled composites. Desorption temperatures of the composites decreased with increase of ball-milling time. Size of MgH2 crystallites decreased during ball-milling. Reduction of Nb2O5 after ball-milling was confirmed by tracing the chemical state of Nb and was further supported by TEM observation. The reduced phases may act as more effective catalysts improving the desorption properties.
  • Tao Ma, Shigehito Isobe, Keisuke Takahashi, Yongming Wang, Shuai Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF PHYSICAL CHEMISTRY C 116 (32) 17089 - 17093 1932-7447 2012/08 [Refereed][Not invited]
     
    Mg-Nb2O5 evaporated composites, which were prepared by evaporating Mg thermally on single crystals of Nb2O5, were investigated in this work. We attempted to hydrogenate the sample under 5 bar H-2 atmosphere at 250 degrees C for 2 h. The electron microscope was used to observe the microstructure of the as-prepared and hydrogenated samples. It was found that the phase transition occurred along the particular orientation where Mg(002) is parallel to MgH2(101) or MgO(200). Density functional theory calculations were carried out on MgH2 and MgO slabs, showing that MgH2(101) and MgO(200) have the lowest surface-formation energy. On the basis of the observation and calculation, the phase-transition process of Mg during hydrogenation and oxidation was discussed. Finally, a structural model including Mg-Mg distance adjustment and layer shift was proposed to demonstrate the phase-transition process.
  • Hao Yao, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF ELECTRON MICROSCOPY 60 (6) 375 - 378 0022-0744 2011/12 [Refereed][Not invited]
     
    A plastic bag method was developed to observe air-sensitive samples on microstructure and phase distribution without exposure to air during the holder transfer process into the transmission electron microscope (TEM). As an example, a type of lithium aluminum hydride (Li(3)AlH(6)) was observed in the TEM to demonstrate the effectiveness of this method. Results show that the plastic bag method is a simple and practical TEM transfer method utilized to reduce air contact for a series of air-sensitive materials.
  • B. V. Cockeram, R. W. Smith, N. Hashimoto, L. L. Snead
    JOURNAL OF NUCLEAR MATERIALS 418 (1-3) 121 - 136 0022-3115 2011/11 [Refereed][Not invited]
     
    TEM examinations and swelling measurements were performed on commercially available wrought Low Carbon Arc Cast (LCAC), La-oxide Oxide Dispersion Strengthened (ODS), and TZM molybdenum alloys following irradiation in the High Flux Isotope Reactor (HEIR) at 300 degrees C, 600 degrees C, and 900 degrees C to neutron fluences between 1.05 and 24.7 x 10(25) n/m(2) (E > 0.1 MeV), or 0.6-13.1 dpa. The defect structure, hardening, and swelling were shown to be strongly dependent on irradiation temperature and starting microstructure. Irradiation at 300 degrees C results in the formation of a high number density of fine loops and voids (similar to 1 nm) that produce significant hardening and low swelling that is comparable for all alloys. Irradiation at 600 degrees C-784 degrees C produces a high number density of larger voids (5-6 nm) that results in significant hardening with the highest swelling. A low number density of the largest void sizes (8-30 nm) are formed for the 900 degrees C irradiation that result in low hardening and less swelling than observed for the 600 degrees C irradiation. The fine grain size of ODS Mo results in a higher concentration of denuded zones along grain boundaries and improved ductile-laminate toughening that results in improved resistance to irradiation embrittlement for the 600 degrees C irradiations. Irradiation-induced formation of precipitates rich in transmutation products is observed at the highest dose, and it is likely that these features exert an influence on subsequent void growth. (C) 2011 Elsevier B.V. All rights reserved.
  • Takakuni Nishi, N. Hashimoto, S. Ohnuki, T. Yamamoto, G. R. Odette
    JOURNAL OF NUCLEAR MATERIALS 417 (1-3) 936 - 939 0022-3115 2011/10 [Refereed][Not invited]
     
    Electron irradiations using a high voltage electron microscope were conducted on several reactor pressure vessel model alloys in order to investigate the effects of alloying elements on the formation and development of defect clusters. In addition, the effects of alloying elements on yield stress change after irradiation were considered, comparing the mean size and number density of dislocation loops with the irradiation-induced hardening. High Cu alloys formed Cu and Mn-Ni-Si rich clusters, and these are important in determining the yield stress increase. High Ni alloys formed a high density of small dislocation loops and probably Mn-Ni-Si rich cluster, which have the effect of increasing the yield stress. High P enhanced radiation-induced segregation on grain boundary, helping prevent dislocation movement. (C) 2011 Elsevier B.V. All rights reserved.
  • H. Seto, N. Hashimoto, H. Kinoshita, S. Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 417 (1-3) 1018 - 1021 0022-3115 2011/10 [Refereed][Not invited]
     
    An Fe-8Cr model alloy was irradiated under two modes: simple electron irradiation and dual-beam-irradiation by electrons and helium ions, and in situ observed in the high voltage electron microscope (JEOL JEM-ARM-1300 operated at 1250 kV) at temperatures ranging from 300 to 500 degrees C. At all temperatures, the size and number density of dislocation loops increased as a function of dose on both specimens. It appears that the dual-irradiated specimens showed greater temperature dependence on the growth rate of dislocation loop than that of electron-irradiated. However, there was little difference in temperature dependence of the saturated loop number density. The migration energy of interstitials was determined to be 0.23 eV for both types of irradiation. The migration energy of vacancies was determined to be 0.95 eV for electron irradiation. From this in situ experiment, it is indicated that the net migration energy of vacancies could be increased due to trapping by helium. (C) 2011 Elsevier B.V. All rights reserved.
  • C. Z. Yu, H. Oka, N. Hashimoto, S. Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 417 (1-3) 286 - 288 0022-3115 2011/10 [Refereed][Not invited]
     
    Development of irradiation damage structure in ODS ferritic steels was studied by means of in-situ observation of HVEM up to 10 dpa at 773 K. In this study, standard ODS steel, Fe-16Cr-4A1-2W-0.35Y(2)O(3) and other of steels including Zr or Hf were examined. During electron-irradiation, preferential nucleation of dislocation loops was observed on oxide particles. In Hf- or Zr-added steels dislocation loops showed a low growth rate and a low number density compared with the standard steel. These results are explained by the sink effect at the interface between the matrix and oxide particles. (C) 2011 Elsevier B.V. All rights reserved.
  • H. Oka, M. Watanabe, H. Kinoshita, T. Shibayama, N. Hashimoto, S. Ohnuki, S. Yamashita, S. Ohtsuka
    JOURNAL OF NUCLEAR MATERIALS 417 (1-3) 279 - 282 0022-3115 2011/10 [Refereed][Not invited]
     
    The oxide dispersion strengthening method was applied to an austenitic stainless steel based on SUS316 by mechanical alloying with additions of minor alloying elements. This ODS austenitic stainless steel was electron-irradiated to investigate the damage structure. Microstructural observation revealed that ODS austenitic stainless steel has a fine distribution of complex oxides. The in situ observation during electron irradiation showed that both dislocation loops and small cavities nucleated at the interface between oxide particles and matrix. In the case of helium implantation, defect clusters also nucleated at the interface. These results suggest that the oxide interface is an effective sink for irradiation-induced point defects and helium atoms. (C) 2010 Elsevier B.V. All rights reserved.
  • C. Liu, C. Yu, N. Hashimoto, S. Ohnuki, M. Ando, K. Shiba, S. Jitsukawa
    JOURNAL OF NUCLEAR MATERIALS 417 (1-3) 270 - 273 0022-3115 2011/10 [Refereed][Not invited]
     
    The radiation-hardening of oxide dispersion strengthened (ODS) alloys was examined using ion irradiation and nano-indentation. In this work, three ODS steels were irradiated in the TIARA facility at JAEA with 10.5 MeV Fe(3+) ions up to a dose of 20 dpa at 250 and 380 degrees C. Micro-hardness measurements were carried out on the ion-irradiated specimens with ultra-low load indention. Micro-structures were investigated by transmission electron microscopy (TEM) to examine the contribution of various types of defects to the radiation-hardening. All three steels showed increases in the hardness after the ion irradiation, and F82H-ODS showed the lowest radiation-hardening, which suggests that F82H-ODS has the better radiation resistance. Small amounts of particle dissolution was also confirmed in all of the steels after the irradiation. (C) 2011 Elsevier B.V. All rights reserved.
  • N. Hashimoto, H. Tanigawa, H. Kinoshita, S. Ohnuki
    JOURNAL OF NUCLEAR MATERIALS 417 (1-3) 1009 - 1012 0022-3115 2011/10 [Refereed][Not invited]
     
    Electron-beam-welded reduced-activation ferritic/martensitic steel F82H, which is one of prime candidate materials for experimental fusion reactors, have been irradiated by electron and helium ion beams using a High Voltage Electron Microscope (HVEM) as the experimental evaluation of the modeling and simulations. Growth rate and saturated number density of dislocation loops have been measured to calculate the migration energies of point defects. Electron irradiation experiment indicated that net migration energy of vacancy in the welded metal of F82H tended to be lower compared to that in base metal, which could be relating to difference of carbon concentration in matrix. In the case of dual beam (electron and helium) irradiation, net migration energies of vacancy were slightly higher than that in electron beam irradiation. This result indicates that vacancy would be trapped by implanted helium due to their strong interaction and appeared to have higher migration energy. (C) 2010 Elsevier B.V. All rights reserved.
  • Tao Ma, Shigehito Isobe, Eri Morita, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki, Toru Kimura, Takayuki Ichikawa, Yoshitsugu Kojima
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (19) 12319 - 12323 0360-3199 2011/09 [Refereed][Not invited]
     
    We reported on the hydrogen desorption properties, microstructure, kinetics, and chemical bonding state of catalyst surface for composites of MgH(2) and 1 mol% Nb(2)O(5) ball-milled for 0.02 h, 0.2 h, 2 h, 20 h under 1 MPa H(2) atmosphere, as well as hand-mixed (HM) one. Hydrogen desorption properties were significantly improved by ball-milling with Nb(2)O(5). Then, we estimated by Kissinger Method the activation energy (E(a)) of hydrogen desorption reaction that decreased with the increase of ball-milling time. Especially, E(a) of the sample ball-milled for 0.2 h was drastically decreased, compared with that of the sample ball-milled for 0.02 h. TEM observations revealed that the distribution of Nb(2)O(5) in MgH(2) was gradually improved during ball-milling. On the other hand, we confirmed by XPS that in the sample ball-milled for 0.2 h, Nb(2)O(5-x) phase(s) existed at least on the surface. It can be suggested that these deoxidized Nb(2)O(5-x) phases eventually decrease E(a) as substantial catalyst rather than Nb(2)O(5) itself. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
  • T. Yoshiie, T. Ito, H. Iwase, Y. Kaneko, M. Kawai, I. Kishida, S. Kunieda, K. Sato, S. Shimakawa, F. Shimizu, S. Hashimoto, N. Hashimoto, T. Fukahori, Y. Watanabe, Q. Xu, S. Ishino
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 269 (14) 1740 - 1743 0168-583X 2011/07 [Refereed][Not invited]
     
    Changes in mechanical property of Ni under irradiation by 3 GeV protons were estimated by multi-scale modeling. The code consisted of four parts. The first part was based on the Particle and Heavy-Ion Transport code System (PHITS) code for nuclear reactions, and modeled the interactions between high energy protons and nuclei in the target. The second part covered atomic collisions by particles without nuclear reactions. Because the energy of the particles was high, subcascade analysis was employed. The direct formation of clusters and the number of mobile defects were estimated using molecular dynamics (MD) and kinetic Monte-Carlo (kMC) methods in each subcascade. The third part considered damage structural evolutions estimated by reaction kinetic analysis. The fourth part involved the estimation of mechanical property change using three-dimensional discrete dislocation dynamics (DDD). Using the above four part code, stress-strain curves for high energy proton irradiated Ni were obtained. (C) 2010 Elsevier B.V. All rights reserved.
  • T. Muroga, D. K. Sze, K. Okuno, T. Terai, A. Kimura, R. J. Kurtz, A. Sagara, R. Nygren, Y. Ueda, R. P. Doerner, J. P. Sharpe, T. Kunugi, N. B. Morley, Y. Hatano, M. A. Sokolov, T. Yamamoto, A. Hasegawa, Y. Katoh, N. Ohno, K. Tokunaga, S. Konishi, S. Fukuda, P. Calderoni, T. Yokomine, K. Messadek, Y. Oya, N. Hashimoto, T. Hinoki, H. Hashizume, T. Norimatsu, T. Shikama, R. E. Stoller, K. A. Tanaka, M. S. Tillack
    FUSION SCIENCE AND TECHNOLOGY 60 (1) 321 - 328 1536-1055 2011/07 [Refereed][Not invited]
     
    Japan-US cooperation program TITAN (Tritium, Irradiation and Thermofluid for America and Nippon) started in April 2007 as 6-year project. This is the summary report at the midterm of the project. Historical overview of the Japan-US cooperation programs and direction of the TITAN project in its second half are presented in addition to the technical highlights.
  • Eni Sugiarti, Youngmin Wang, Naoyuki Hashimoto, Somei Ohnuki, Toshio Narita
    MATERIALS TRANSACTIONS 52 (3) 319 - 323 1345-9678 2011/03 [Refereed][Not invited]
     
    An electron microscopy phase characterization was carried out for a Re-based diffusion barrier layer, which was deposited on the Nb substrate used as an ultra high temperature material. The coating process produced three layers; an outer Cr(Re) layer, an intermediate Cr-Nb-Re layer, and an inner Nb(Re) layer. The Cr-Nb-Re layer is considered to act as a diffusion barrier layer between the substrate and the outer Cr(Re) reservoir layer. The Cr(Re) and Nb(Re) layers are in single phase with a similar bcc structures, but they are different in structure from the intermediate layer, which is composed of a dual phase of Re63Cr25Nb17 with a cubic structure and Nb42Re33Cr25 with a hexagonal structure determined by transmission electron microscopy (TEM) in this study. [doi:10.2320/matertrans.MB201022]
  • Huang YiNa, Wan FaRong, Xiao Xin, Somei Ohnuki, Naoyuki Hashimoto
    SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY 54 (1) 111 - 114 1674-7348 2011/01 [Refereed][Not invited]
     
    As Reduced Activation Ferritic/Martensitic (RAFM) steel is considered the primary candidate for use as a structural material in fusion power reactors, many countries are developing different kinds of RAFM. China is developing new CLAM (China Low Activation Martensitic) steel. The study investigates microstructural changes in CLAM steel implanted with deuterium ions induced by 1250 keV electron irradiation from R. T. to 873 K, and observes both the growth and shrinkage of the defect clusters produced by deuterium ion implantation under the electron irradiation.
  • S. Eni, Y. Wang, N. Hashimoto, S. Ohnuki, T. Narita
    HIGH-TEMPERATURE OXIDATION AND CORROSION 2010 696 318 - + 0255-5476 2011 [Refereed][Not invited]
     
    Cross-sectional structures of a Re-based diffusion barrier coating on Nb as ultra high temperature material were investigated in order to verify the crystalline structure and composition of the coated layer. Three types coating specimens were prepared by electroplating Re from an aqueous solution on an Nb substrate, followed by Cr-pack cementation in vacuum. The coating process produced three distinct layers; an outer Cr(Re) layer, an intermediate Re-Cr-Nb layer, and an inner Nb(Re) layer. A crystal structure of Cr(Re) and Nb(Re) layers possess similar single crystal bcc structure. The Re-Cr-Nb layer expected to act as a diffusion barrier between the substrate and the outer reservoir layer was comprised of cubic chi phase and hexagonal Laves C14 phase. Moreover, several crystal defects such as dislocations and stacking faults as well as voids and cracks are observed in the coating specimen.
  • Huang YiNa, Wan FaRong, Xiao Xin, Somei Ohnuki, Naoyuki Hashimoto
    SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY 54 (1) 111 - 114 1674-7348 2011/01 [Refereed][Not invited]
     
    As Reduced Activation Ferritic/Martensitic (RAFM) steel is considered the primary candidate for use as a structural material in fusion power reactors, many countries are developing different kinds of RAFM. China is developing new CLAM (China Low Activation Martensitic) steel. The study investigates microstructural changes in CLAM steel implanted with deuterium ions induced by 1250 keV electron irradiation from R. T. to 873 K, and observes both the growth and shrinkage of the defect clusters produced by deuterium ion implantation under the electron irradiation.
  • Yina Huang, Farong Wan, Xin Xiao, Shi Shi, Yi Long, Somei Ohnuki, Naoyuki Hashimoto
    FUSION ENGINEERING AND DESIGN 85 (10-12) 2203 - 2206 0920-3796 2010/12 [Refereed][Not invited]
     
    There are many works on the interaction between helium and irradiation defects, but not so many on hydrogen. Especially, the isotopic atoms of hydrogen, deuterium or tritium would exist in the environment of fusion reaction. However, few works were reported about the isotope effect of hydrogen on irradiation damage. This work used ion accelerator to implant ions of hydrogen or deuterium into the samples of pure iron at R.T., followed by annealing at high temperature to make the defects develop into large dislocation loops. The electron irradiation by high voltage electron microscope was carried out to check the nature of loops. The isotopic effect on the bias of dislocation loops was discussed. (C) 2010 Elsevier B.V. All rights reserved.
  • Shigehito Isobe, Hao Yao, Yongming Wang, Hiroshi Kawasaki, Naoyuki Hashimoto, Somei Ohnuki
    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 35 (14) 7563 - 7567 0360-3199 2010/07 [Not refereed][Not invited]
     
    In-situ transmission electron microscopy (TEM) has been performed to observe decomposition process of sodium alanate (NaAlH4) in this work. NaAlH4 was ground in a glove box under inert gas, and then it was transferred into microscope without exposed to air by Plastic Bag Method. The results of in-situ electron beam diffraction showed that NaAlH4 decomposed to Na3AlH6 + Al, and NaH + Al during heated up to 150 and 200 degrees C, respectively. Moreover, we obtained the result of high-resolution (HR) TEM images about the decomposition of NaAlH4 by high voltage electron microscopy (HVEM) of 1250 key. It showed that the porous structures appeared with increase of temperature. This should be from structural defects and/or cavities due to volume change of the phases. It was also shown that Na3AlH6 and Al particles with the grain size of several 10 nm were irregularly distributed near the pores. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
  • Hao Yao, Hiroshi Kawasaki, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 51 (5) 1016 - 1019 1345-9678 2010/05 [Refereed][Not invited]
     
    Sodium alanate (NaAlH4) was ground in a dove box in inert gas and transferred to a microscope without exposing the samples to air, using a plastic bag method. The results of in-situ electron beam diffraction showed that NaAlH4 decomposed to Na3AlH6 and Al, and then to NaH and Al when heated to 150 degrees C and then 200 degrees C. The decomposition of NaAlH4 was observed by ex-situ transmission electron microscopy (TEM) at 1250 keV. Porous structures appeared when the samples were heated and dehydrogenated. These are likely due to structural defects or are cavities due to volume changes between phases. The Na3AlH6 and Al particles were found to distribute around the pores. [doi:10.2320/matertrans.MBW200902]
  • Hao Yao, Hiroshi Kawasaki, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    MATERIALS TRANSACTIONS 51 (5) 1016 - 1019 1345-9678 2010/05 [Not refereed][Not invited]
     
    Sodium alanate (NaAlH4) was ground in a dove box in inert gas and transferred to a microscope without exposing the samples to air, using a plastic bag method. The results of in-situ electron beam diffraction showed that NaAlH4 decomposed to Na3AlH6 and Al, and then to NaH and Al when heated to 150 degrees C and then 200 degrees C. The decomposition of NaAlH4 was observed by ex-situ transmission electron microscopy (TEM) at 1250 keV. Porous structures appeared when the samples were heated and dehydrogenated. These are likely due to structural defects or are cavities due to volume changes between phases. The Na3AlH6 and Al particles were found to distribute around the pores. [doi:10.2320/matertrans.MBW200902]
  • Shigehito Isobe, Akifumi Ono, Hao Yao, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    APPLIED PHYSICS LETTERS 96 (22) 223109  0003-6951 2010/05 [Refereed][Not invited]
     
    In situ observation on dehydrogenation of MgH2 was performed by using transmission electron microscope (TEM). The dehydrogenation of MgH2 with 1 mol % Nb2O5 and formation of nanosized Mg particles were observed at 150 degrees C. Nb2O5 was not confirmed in diffraction patterns and TEM images probably due to wide dispersion. On MgH2 with 10 mol % Nb2O5, the high resolution TEM could recognize the dehydrogenation at the interface between MgH2 and Nb2O5, proceeding with increasing temperature. This suggests that hydrogen atoms could diffuse from MgH2 phase to the interface between Mg and Nb2O5, resulting in formation of hydrogen molecules at the interface. (C) 2010 American Institute of Physics. [doi:10.1063/1.3442910]
  • Akifumi Ono, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF THE JAPAN INSTITUTE OF METALS 74 (3) 205 - 208 0021-4876 2010/03 [Refereed][Not invited]
     
    In situ observation of the catalytic action of MgH2-1 mol%Nb2O5 and MgH2-10 mol%Nb2O5 was carried out by using transmission electron microscopy (TEM). In case of MgH2-1 mol%Nb2O5, TEM analysis indicated that MgH2 started to decompose at 150 degrees C and nano size particle of Mg formed. However, Nb2O5 was not observed in the diffraction pattern and images. In case of MgH2-10 mol%Nb2O5, high resolution images, FFT and IFFT, revealed that the decomposition of MgH2 started with the contact region in Nb2O5 and Mg formed. The result suggested that the reaction of dehydration could proceed due to hydrogen diffusion to the Mg-Nb2O5 interface.
  • Akifumi Ono, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    JOURNAL OF THE JAPAN INSTITUTE OF METALS 74 (3) 205 - 208 0021-4876 2010/03 [Refereed][Not invited]
     
    In situ observation of the catalytic action of MgH2-1 mol%Nb2O5 and MgH2-10 mol%Nb2O5 was carried out by using transmission electron microscopy (TEM). In case of MgH2-1 mol%Nb2O5, TEM analysis indicated that MgH2 started to decompose at 150 degrees C and nano size particle of Mg formed. However, Nb2O5 was not observed in the diffraction pattern and images. In case of MgH2-10 mol%Nb2O5, high resolution images, FFT and IFFT, revealed that the decomposition of MgH2 started with the contact region in Nb2O5 and Mg formed. The result suggested that the reaction of dehydration could proceed due to hydrogen diffusion to the Mg-Nb2O5 interface.
  • Akifumi Ono, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals 日本金属学会 74 (3) 205 - 208 0021-4876 2010/03 [Not refereed][Not invited]
     
    In-situ observation of the catalytic action of MgH2-1 mol%Nb2O5 and MgH2-10 mol%Nb2O 5 was carried out by using transmission electron microscopy (TEM). In case of MgH2-1 mol%Nb2O5, TEM analysis indicated that MgH2 started to decompose at 150°C and nano-size particle of Mg formed. However, Nb2O5 was not observed in the diffraction pattern and images. In case of MgH2-10 mol%Nb 2O5, high resolution images, FFT and IFFT, revealed that the decomposition of MgH2 started with the contact region in Nb 2O5 and Mg formed. The result suggested that the reaction of dehydration could proceed due to hydrogen diffusion to the Mg-Nb 2O5 interface. © 2010 The Japan Institute of Metals.
  • Eri Morita, Akifumi Ono, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki
    PRICM 7, PTS 1-3 654-656 2867 - 2870 0255-5476 2010 [Refereed][Not invited]
     
    We carried out in-situ observation on the catalytic effect of Nb(2)O(5) in MgH(2) by using a high voltage transmission electron microscope (HVEM). We synthesized two kinds of samples, which were prepared by ball milling and by hand mixing. In milled sample, Nb(2)O(5) was not confirmed from high resolution images, however, NbO was identified. As the temperature increased, the decomposition of MgH(2) proceeded, while Mg formed and grew. It suggested that NbO had the catalytic effect to promote the dehydrogenation of MgH(2). In mixed sample, which was prepared to clearly observe the boundary between the catalyst and Mg phase, it was revealed that the dehydrogenation started from the boundary of MgH(2) and Nb(2)O(5). This result suggested that the dehydrogenation could proceed with hydrogen diffusion from MgH(2) through Mg phase to the boundary.
  • In-situ TEM Observation with Environmental Cell for Hydrogen Storage Materials
    礒部 繁人, 王 永明, 奥寺 公也, 平澤 寛子, 橋本 直幸, 大貫 惣明
    まてりあ : 日本金属学会会報 48 (12) 2009/12/01 [Refereed][Not invited]
  • ISOBE Shigehito, WANG Yongming, OKUDERA Koya, HIRASAWA Hiroko, HASHIMOTO Naoyuki, OHNUKI Somei
    まてりあ : 日本金属学会会報 48 (12) 1340-2625 2009/12/01 [Not refereed][Not invited]
  • Hiroyasu Tanigawa, Ronald L. Klueh, Naoyuki Hashimoto, Mikhail A. Sokolov
    JOURNAL OF NUCLEAR MATERIALS 386-88 231 - 235 0022-3115 2009/04 [Refereed][Not invited]
     
    It has been reported that reduced-activation ferritic/martensitic steels (RAFMs), such as F82H, ORNL9Cr-2WVTa, and JLF-1 showed a variety of changes in ductile-brittle transition temperature and yield stress after irradiation at 300 degrees C up to 5 dpa, and those differences could not be interpreted solely by the difference of dislocation microstructure induced by irradiation. In this paper, various microstructural analyses on low-temperature irradiated RAFMs were summarized with the emphasis on F82H, and a possible mechanism for the irradiation hardening was suggested. The possible contribution of dislocation channeling structure and back stress were indicated. (C) 2009 Elsevier B.V. All rights reserved.
  • Hiroyasu Tanigawa, Ronald L. Klueh, Naoyuki Hashimoto, Mikhail A. Sokolov
    JOURNAL OF NUCLEAR MATERIALS 386-88 231 - 235 0022-3115 2009/04 [Refereed][Not invited]
     
    It has been reported that reduced-activation ferritic/martensitic steels (RAFMs), such as F82H, ORNL9Cr-2WVTa, and JLF-1 showed a variety of changes in ductile-brittle transition temperature and yield stress after irradiation at 300 degrees C up to 5 dpa, and those differences could not be interpreted solely by the difference of dislocation microstructure induced by irradiation. In this paper, various microstructural analyses on low-temperature irradiated RAFMs were summarized with the emphasis on F82H, and a possible mechanism for the irradiation hardening was suggested. The possible contribution of dislocation channeling structure and back stress were indicated. (C) 2009 Elsevier B.V. All rights reserved.
  • Super ODS Steels R&D for Fuel Cladding of Next Generation Nuclear Systems 2) Effect of Minor Alloying Elements
    S. Ohnuki, N. Hashimoto, S. Ukai, A. Kimura, M. Inoue, T. KaitoT. Fujisawa, T. Okuda, F. Abe
    Proc. of Int. Conf. on Advanced Power Plant, Tokyo, Japan, May 10-14, 2009, Paper 9306 2009 [Not refereed][Not invited]
  • Meimei Li, M. Eldrup, T. S. Byun, N. Hashimo, L. L. Snead, S. J. Zinkle
    JOURNAL OF NUCLEAR MATERIALS 376 (1) 11 - 28 0022-3115 2008/05 [Refereed][Not invited]
     
    Polycrystalline molybdenum was irradiated in the hydraulic tube facility at the High Flux Isotope Reactor to doses ranging from 7.2 x 10(-5) to 0.28 dpa at similar to 80 degrees C. As-irradiated microstructure was characterized by room-temperature electrical resistivity measurements, transmission electron microscopy (TEM) and positron annihilation spectroscopy (PAS). Tensile tests were carried out between -50 and 100 degrees C over the strain rate range 1 x 10(-5) to 1 x 10(-2) s(-1). Fractography was performed by scanning electron microscopy (SEM), and the deformation microstructure was examined by TEM after tensile testing. Irradiation-induced defects became visible by TEM at similar to 0.001 dpa. Both their density and mean size increased with increasing dose. Submicroscopic three-dimensional cavities were detected by PAS even at similar to 0.0001 dpa. The cavity density increased with increasing dose, while their mean size and size distribution was relatively insensitive to neutron dose. It is suggested that the formation of visible dislocation loops was predominantly a nucleation and growth process, while in-cascade vacancy clustering may be significant in Mo. Neutron irradiation reduced the temperature and strain rate dependence of the yield stress, leading to radiation softening in Mo at lower doses. Irradiation had practically no influence on the magnitude and the temperature and strain rate dependence of the plastic instability stress. (C) 2008 Published by Elsevier B.V.
  • OKUBO N, WAKAI E, YAMASHITA S, ANDO M, OTSUKA S, JITSUKAWA S, HASHIMOTO N, OHNUKI S
    日本原子力研究開発機構JAEA-Review 29  2008/03 [Not refereed][Not invited]
  • R. L. Klueh, M. A. Sokolov, N. Hashimoto
    JOURNAL OF NUCLEAR MATERIALS 374 (1-2) 220 - 228 0022-3115 2008/02 [Refereed][Not invited]
     
    Tensile and Charpy specimens of four normalized-and-tempered martensitic steels were irradiated to 23-33 dpa at 376-405 degrees C in the Experimental Breeder Reactor (EBR-II). The steels were the ORNL reduced-activation steel 9Cr-2WVTa and that containing 2% Ni (9Cr-2WVTa-2Ni), modified 9Cr-lMo (9Cr-2WVTa), and Sandvik HT9 (12Cr-1MoVW). Two tempering conditions were used for 9Cr-2WVTa and 9Cr-2WVTa 2Ni: 1 h at 700 degrees C and 1 h at 750 degrees C. The 9Cr-1MoVNb and 12Cr-1MoVW were tempered 1 h at 760 degrees C. These heat treatments produced tempered-martensite microstructures for all steels except 9Cr-2WVTa-2Ni tempered at 750 degrees C, where a duplex structure of tempered and untempered martensite formed. Based on changes in tensile and Charpy impact properties, the results demonstrated the superiority in strength and ductility of the 9Cr-2WVTa reduced-activation steel over the commercial steels. Comparison of the mechanical properties after irradiation of 9Cr-2WVTa-2Ni and 9Cr-2WVTa steels indicated a favorable effect of nickel that could lead to development of a heat treatment for improved irradiation resistance. Published by Elsevier B.V.
  • T. S. Byun, N. Hashimoto
    EFFECTS OF RADIATION ON MATERIALS: 23RD INTERNATIONAL SYMPOSIUM 1492 (8) 121 - 133 1040-1695 2008 [Refereed][Not invited]
     
    Localized deformation mechanisms and strain-hardening behaviors in irradiated 316 and 316LN stainless steels were investigated, and a theoretical model was proposed to explain the linear strain-hardening behavior during the localized deformation. After low temperature irradiation to significant doses, the deformation microstructure changed from dislocation tangles to channels or mechanical twins. It was also observed that irradiation hardening straightened gliding dislocations and increased the tendency for forming pileups. Regardless of these microstructural changes, the strain-hardening behavior was relatively insensitive to the irradiation. This dose-independent strain-hardening rate resulted in dose independence of the true stress parameters, such as the plastic instability stress and true fracture stress. In the proposed model, the long-range back stress was formulated as a function of the number of pileup dislocations per slip band and the number of slip bands in a grain. The calculation results confirmed the experimental observation that strain-hardening rate was insensitive to the change in deformation mechanism because the long-range back stress hardening became as high as the hardening by tangled dislocations.
  • TANIGAWA Hiroyasu, HIROSE Takanori, WAKAI Eiichi, JITSUKAWA Shiro, SOKOLOV Mikhail A, KLUEH Ronald L, HASHIMOTO Naoyuki
    Trans Am Nucl Soc 98 1132 - 1133 0003-018X 2008 [Not refereed][Not invited]
  • Meimei Li, T. S. Byun, N. Hashimoto, L. L. Snead, S. J. Zinkle
    JOURNAL OF NUCLEAR MATERIALS 371 (1-3) 53 - 60 0022-3115 2007/09 [Refereed][Not invited]
     
    Molybdenum was neutron-irradiated near 80 degrees C at doses of 7.2 x 10(-5), 7.2 x 10(-4), 7.2 x 10(-3), 0.072 and 0.28 dpa. irradiated Mo was tensile tested over a temperature range of -50 to 100 degrees C at a strain rate of I X, 10-3 S-1. It was found that the yield stress of irradiated Mo decreased at lower temperatures and increased at higher temperatures, resulting in reduced temperature dependence of yielding at lower doses (< 0.001 dpa); the yield stress was increased, and the temperature dependence of yielding was nearly unchanged upon further irradiation at higher doses (> 0.001 dpa). The temperature dependence of the yield stress for unirradiated and irradiated Mo is consistent with the theoretical expression of the Fleischer model for interactions of dislocations with tetragonal strain fields. (c) 2007 Published by Elsevier B.V.
  • T. Yamamoto, G. R. Odette, P. Miao, D. T. Hoelzer, J. Bentley, N. Hashimoto, H. Tanigawa, R. J. Kurtz
    JOURNAL OF NUCLEAR MATERIALS 367 399 - 410 0022-3115 2007/08 [Refereed][Not invited]
     
    A novel in situ Ni-59(n,alpha) reaction He-implanter technique is described, that can be used to characterize the effect of the He/dpa ratio on microstructural evolution and changes in the flow properties of various materials at fusion relevant conditions. :Irradiations in the high flux isotope reactor resulted in alpha-implantation from 1 to 5 mu m thick NiAl coatings on TEM discs producing a uniform He concentration of 5-50 appin He/dpa to a depth of 5-8 mu m. Initial post-irradiation TEM observacions of MA957 irradiated to 9 dpa and 380 appin He at 500 degrees C provide strong evidence for the existence of a high density of small <= 1 nm size bubbles trapped on nano-scale YTiO clusters. In contrast, similar irradiations of Eurofer 97, described in a companion paper, produce a lower number density of larger cavities, which may be a mixture of bubbles and voids.,(c) 2007 Elsevier B.V. All rights reserved.
  • Meimei Li, N. Hashimoto, T. S. Byun, L. L. Snead, S. J. Zinkle
    JOURNAL OF NUCLEAR MATERIALS 367 817 - 822 0022-3115 2007/08 [Refereed][Not invited]
     
    Molybdenum was neutron-irradiated near 80 degrees C to doses of 7.2 x 10(-5), 7.2 x 10(-4), 7.2 x 10(-3), 0.072 and 0.28 dpa. Post;irradiation examination included electrical resistivity and tensile properties measured at room temperature. Microstructure of irradiated specimens was examined by TEM and the defect cluster density and cluster mean size were characterized. Measurements of electrical resistivity and cluster density showed sublinear defect accumulation behavior. The mean size of visible defect clusters increased with increasing dose. Yield stress decreased at 7.2 x 10(-5) and 7.2 x 10(-4) dpa, then increased significantly with increasing dose up to 0.072 dpa and saturated. It appeared that there was a transition in hardening from weak obstacles to strong obstacles. It is suggested that the formation of sessile defect clusters in neutron-irradiated Mo is mainly associated with diffusive nucleation and growth rather than in-cascade clustering. Published by Elsevier B.V.
  • R. L. Klueh, N. Hashimoto, P. J. Maziasz
    JOURNAL OF NUCLEAR MATERIALS 367 48 - 53 0022-3115 2007/08 [Refereed][Not invited]
     
    For increased fusion power plant efficiency, steels for operation at 650 degrees C and higher are sought. Based on the science of precipitate strengthening, a thermo-mechanical treatment (TMT) was developed that increased the strength from room temperature to 700 degrees C of commercial nitrogen-containing steels and new steels designed for the TMT. At 700 degrees C increases in yield stress of 80 and 200% were observed for a commercial steel and a new steel, respectively, compared to commercial normalized-and-tempered steels. Creep-rupture strength was similarly improved. Depending on the TMT, precipitates were up to eight-times smaller at a number density four orders of magnitude greater than those in a conventionally heat treated steel of similar composition. (C) 2007 Elsevier B.V. All rights reserved.
  • N. Hashimoto, T. S. Byun
    JOURNAL OF NUCLEAR MATERIALS 367 960 - 965 0022-3115 2007/08 [Refereed][Not invited]
     
    The deformed microstructure in 316 stainless steel (316SS) after neutron irradiation in the range of 65-100 degrees C to 0.78 dpa was investigated by transmission electron microscopy (TEM). Deformation-induced martensite transformation and dislocation channeling were observed at irradiation dose higher than 0.1 dpa. Estimation of the resolved shear stress (RSS) associated with each dislocation channel indicated a tendency for the RSS and channel width to be greatest when the angle between tensile axis and slip plane normal is around 45 degrees. Furthermore, channel width increased with increasing RSS, indicating that the most extensive localized channel deformation tends to occur at a high RSS level. Deformation-induced martensite phase was found at various strain levels even at room temperature and tends to be exhibited mainly at intersections of channels. This suggests that a very high stress could lead to the gamma -> alpha martensite formation by the spreading of a Shockley partial dislocation over successive < 111 >(fcc) planes. (C) 2007 Published by Elsevier B.V.
  • Tanigawa, H., Sakasegawa, H., Hashimoto, N., Klueh, R.L., Ando, M., Sokolov, M.A.
    Journal of Nuclear Materials 367-370 A (SPEC. ISS.) 42 - 47 2007 [Refereed][Not invited]
  • Koya Okudera, Koichi Hamada, Takanori Suda, Naoyuki Hashimoto, Somei Ohnuki
    ADVANCED MATERIALS AND PROCESSING 26-28 877 - + 1022-6680 2007 [Refereed][Not invited]
     
    "Environmental cell" microscopy was applied for surveying gas reaction of hydrides in magnesium base alloys, which are candidates for hydrogen storage materials in advanced hydrogen energy systems. In order to clarify the mechanism of hydrogenation process, in-situ experiment has been carried out by using a 200 kV transmission electron microscope (TEM) equipped with a newly developed environmental cell, which is capable to 0.1 MPa in the temperature range between R. T. and 200 degrees C. When hydrogen gas reacted with magnesium powders, straightening of surface steps (60 similar to 70 nm in height) was observed, indicating that volume expansion occurred. In addition, the formation of MgH2 was indicated in selected-area-diffraction patterns (SADP). The precise study on this in-situ experiment, as well as its improvement, will be continued, with using transparent films.
  • Hiroshi Kawasaki, Somei Ohnuki, Takanori Suda, Naoyuki Hashimoto, Yoshitsugu Kojima
    PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3 561-565 1621 - + 0255-5476 2007 [Refereed][Not invited]
     
    NaAIH(4) has a theoretical hydrogen capacity of 5.6 wt. % with two-step reaction, and the control of the reaction temperature and reversibility is a critical issue for onboard application. To clarify nano-structural details of decomposition of NaAIH(4), the in-situ annealing experiment was carried out in a high resolution microscope. It was confirmed that NaAIH(4) decomposed at between 200 and 300 degrees C, resulted in formation of many gas bubbles at interface between the particle and oxide film. A reactive intermediate, Na(3)AIH(6), may decompose in this temperature range. Sodium alanate particle was originally agglomeration of small nano-sized crystal with the size of 10 - 20 nm, and the crystal grain grew to 110 nm in diameter after completing decomposition at around 400 degrees C. This is the first step for examination of the micro structural response of catalysts on hydrogen storage materials.
  • N. Hashimoto, T. S. Byun
    PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3 561-565 1769 - + 0255-5476 2007 [Refereed][Not invited]
     
    The effects of neutron-irradiation near 80 degrees C on the deformation behavior of hexagonal close packed (hcp) materials, zirconium and zircalloy-4, were investigated by transmission electron microscopy (TEM). Particular emphasis is placed on the deformation microstructure responsible for the changes in mechanical behavior. Neutron irradiation at low temperature up to 1 dpa induced a high number density of defect clusters, which resulted in irradiation-induced hardening. Dislocation channel deformation is observed for doses greater than 0.1 dpa, and is coincident with prompt plastic instability at yield. TEM analysis suggests that the loss of work hardening capacity in irradiated zirconium and zircaloy-4 at higher doses is mainly due to dislocation channels that are formed under a high local resolved shear stress, leading to the observed localized deformation.
  • Hiroshi Kawasaki, Somei Ohnuki, Takanori Suda, Naoyuki Hashimoto, Yoshitsugu Kojima
    PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3 561-565 1621 - + 0255-5476 2007 [Refereed][Not invited]
     
    NaAIH(4) has a theoretical hydrogen capacity of 5.6 wt. % with two-step reaction, and the control of the reaction temperature and reversibility is a critical issue for onboard application. To clarify nano-structural details of decomposition of NaAIH(4), the in-situ annealing experiment was carried out in a high resolution microscope. It was confirmed that NaAIH(4) decomposed at between 200 and 300 degrees C, resulted in formation of many gas bubbles at interface between the particle and oxide film. A reactive intermediate, Na(3)AIH(6), may decompose in this temperature range. Sodium alanate particle was originally agglomeration of small nano-sized crystal with the size of 10 - 20 nm, and the crystal grain grew to 110 nm in diameter after completing decomposition at around 400 degrees C. This is the first step for examination of the micro structural response of catalysts on hydrogen storage materials.
  • R. L. Klueh, N. Hashimoto, M. A. Sokolov, P. J. Maziasz, K. Shiba, S. Jitsukawa
    JOURNAL OF NUCLEAR MATERIALS 357 (1-3) 169 - 182 0022-3115 2006/10 [Refereed][Not invited]
     
    In part I of this helium-effects study on ferritic/martensitic steels, results were presented on tensile and Charpy impact properties of 9Cr-1MoVNb (modified 9Cr-1Mo) and 12Cr-1MoVW (Sandvik HT9) steels and these steels containing 2% Ni after irradiation in the High Flux Isotope Reactor (HFIR) to 10-12 dpa at 300 and 400 degrees C and in the Fast Flux Test Facility (FFTF) to 15 dpa at 393 degrees C. The results indicated that helium caused an increment of hardening above irradiation hardening produced in the absence of helium. In addition to helium-effects studies on ferritic/martensitic steels using nickel doping, studies have also been conducted over the years using boron doping, ion implantation, and spallation neutron sources. In these previous investigations, observations of hardening and embrittlement were made that were attributed to helium. In this paper, the new results and those from previous helium-effects studies are reviewed and analyzed. (c) 2006 Elsevier B.V. All rights reserved.
  • R. L. Klueh, N. Hashimoto, M. A. Sokolov, K. Shiba, S. Jitsukawa
    JOURNAL OF NUCLEAR MATERIALS 357 (1-3) 156 - 168 0022-3115 2006/10 [Refereed][Not invited]
     
    Tensile and Charpy specimens of 9Cr-1MoVNb (modified 9Cr-1Mo) and 12Cr-1MoVW (Sandvik HT9) steels and these steels doped with 2% Ni were irradiated at 300 and 400 degrees C in the High Flux Isotope Reactor (HFIR) up to 12 dpa and at 393 degrees C in the Fast Flux Test Facility (FFTF) to approximate to 15 dpa. In HFIR, a mixed-spectrum reactor, (n, alpha) reactions of thermal neutrons with Ni-58 produce helium in the steels. Little helium is produced during irradiation in FFTF. After HFIR irradiation, the yield stress of all steels increased, with the largest increases occurring for nickel-doped steels. The ductile-brittle transition temperature (DBTT) increased up to two times and 1.7 times more in steels with 2% Ni than in those without the nickel addition after HFIR irradiation at 300 and 400 degrees C, respectively. Much smaller differences occurred between these steels after irradiation in FFTF. The DBTT increases for steels with 2% Ni after HFIR irradiation were 2-4 times greater than after FFTF irradiation. Results indicated there was hardening due to helium in addition to hardening by displacement damage and irradiation-induced precipitation. (c) 2006 Elsevier B.V. All rights reserved.
  • Thak Sang Byun, Naoyuki Hashimoto
    JOURNAL OF NUCLEAR MATERIALS 354 (1-3) 123 - 130 0022-3115 2006/08 [Refereed][Not invited]
     
    Low-temperature irradiation can significantly harden metallic materials and often results in microscopic strain localization such as dislocation channeling during deformation. In true stress-true strain analyses, however, the strain localization does not significantly affect macroscopic strain-hardening behavior. It was attempted to explain the strain-hardening behavior during strain localization in terms of long-range back stresses. In theoretical modeling the long-range back stress was formulated as a function of the number of residual pileup dislocations at a grain boundary and the number of localized bands formed in a grain. The strain-hardening rates in channel deformation were calculated for ten face-centered cubic (fcc) and body-centered cubic (bee) metals. A few residual dislocations in each channel could account for the strain-hardening rates as high as those for uniform deformation. It was also shown that the strain-hardening behavior predicted by the long-range back stress model resembled the empirical strain-hardening behaviors, which result from both localized and non-localized deformations. The predicted plastic instability stress was comparable to the tensile test data. (c) 2006 Elsevier B.V. All rights reserved.
  • TS Byun, N Hashimoto, K Farrell
    JOURNAL OF NUCLEAR MATERIALS 351 (1-3) 303 - 315 0022-3115 2006/06 [Refereed][Not invited]
     
    Microscopic and macroscopic deformation modes in type 316 stainless steels after low-temperature irradiation have been mapped into the true stress-dose coordinate system. This paper defines and explains the deformation modes in 316 and 316LN stainless steels and suggests the procedures to produce a deformation mode map. A variety of microstructural features such as dislocation tangles and pileups, dislocation channels, stacking faults, and twins have been observed in the deformation of irradiated stainless steels. Attempts were also made to depict macroscopic phenomena such as uniform deformation, necking, and final fracture in the map. Stress criteria for twinning, channeling, plastic instability, and final failure were proposed and used to establish boundaries between the different deformation modes. Two alternative strain localization mechanisms, twinning and channeling, shared the high-dose region. The region of stable plastic deformation became narrower as dose increased, while the elastic deformation region was enlarged with dose and the unstable deformation region was kept unchanged over the whole dose range. (c) 2006 Elsevier B.V. All rights reserved.
  • Y. Katoh, N. Hashimoto, S. Kondo, L. L. Snead, A. Kohyama
    JOURNAL OF NUCLEAR MATERIALS 351 (1-3) 228 - 240 0022-3115 2006/06 [Refereed][Not invited]
     
    Microstructural development in chemically vapor-deposited (CVD) high-purity beta-SiC during neutron and self-ion irradiation at elevated temperatures was studied. The CVD SiC samples were examined by transmission electron microscopy following neutron irradiation to 4.5-7.7 x 10(25) n/m(2) (E > 0. 1 MeV) at 300 and 800 degrees C and 5.1 MeV Si2+ ion irradiation up to similar to 200 dpa at 600-1400 degrees C. The evolution of various irradiation-produced defects including black spot defects, dislocation loops, network dislocations, and cavities was characterized as a function of irradiation temperature and fluence. It was demonstrated that the black spot defects and small dislocation loops continue to dominate at relatively low temperatures (<similar to 800 degrees C), whereas they grow into Frank faulted loops and finally develop into dislocation networks at a higher temperature (1400 degrees C). Substantial cavity formation on grain boundaries and stacking faults was confirmed after ion irradiation at 1400 degrees C. These observations were discussed in relation with the known irradiation phenomena in SiC, such as low temperature swelling and cavity swelling. (c) 2006 Elsevier B.V. All rights reserved.
  • N Hashimoto, TS Byun, K Farrell
    JOURNAL OF NUCLEAR MATERIALS 351 (1-3) 295 - 302 0022-3115 2006/06 [Refereed][Not invited]
     
    Plastically deformed microstructures in neutron-irradiated face centered cubic (fcc) materials, copper.. nickel, and 316 stainless steel (316SS), were investigated by transmission electron microscopy (TEM). Neutron irradiation in the range of 65-100 degrees C up to 1 displacement per atom (dpa) induced a high number density of black spots. stacking fault tetrahedra (SFT) and Frank loops, which resulted in irradiation-induced hardening. Deformation of irradiated fcc materials induced various micro structures, such as dislocation channels, stacking faults, and twins. In the 316SS irradiated to 0.1-0.8 dpa, the deformation microstructure consisted of a mixture of dislocation bands, tangles, twins, dislocation channels, and also martensite phase. Deformation-induced martensite transformation tends to occur with dislocation channeling, suggesting that localized deformation could lead to transformation of austenite to martensite at a high stress level. At higher irradiation doses (0.1-1 dpa), dislocation channeling became the dominant deformation mode in fec materials, and is coincident with prompt plastic instability at yield. The channel width seems to be wider when the angle between tensile direction and dislocation slip direction is close to 45 degrees. Furthermore, the correlation between channel width and resolved shear stress appears to be material dependent, with copper having the greatest slope and 316SS the smallest. (c) 2006 Elsevier B.V. All rights reserved.
  • TS Byun, N Hashimoto, K Farrell, EH Lee
    JOURNAL OF NUCLEAR MATERIALS 349 (3) 251 - 264 0022-3115 2006/03 [Refereed][Not invited]
     
    Characteristics of localized dislocation glide were investigated for 316 and 316LN stainless steels and pure vanadium after ion or neutron irradiation near room temperature and deformation by a uniaxial tensile load or by a multiaxial bending load. In the irradiated 316 stainless steels, both the uniaxial tensile loading and the multiaxial bend loading produced straight localized bands in the form of channels and twins. In vanadium specimens, on the other hand, curved channels were observed after tensile deformation, and these became a common feature after multiaxial bend deformation. No twin was observed in vanadium. A river pattern of channels was observed in the bent samples after irradiation to a high dose of 0.69 dpa. A highly curved channel can be formed by successive cross slip of screw dislocations. Also, the channel width was not constant along the channels; channel widening occurred when weak defect clusters were removed by the gliding screw dislocations changing their paths by cross slip. It is believed that the dissociation of dislocations into partials and high angles between easy glide planes suppresses the formation of curved channels, while a multiaxial stress state, or a higher stress constraint, increases the tendency for channel bending and widening, (c) 2005 Elsevier B.V. All rights reserved.
  • Strain Localization in Irradiated Materials
    T.S. Byun, N. Hashimoto
    Nuclear Engineering and Technology 38 (7) 619 - 638 2006 [Refereed][Not invited]
  • R. L. Klueh, N. Hashimoto, P. J. Maziasz
    21ST IEEE/NPSS SYMPOSIUM ON FUSION ENGINEERING - SOFE 05 287 - 290 2006 [Refereed][Not invited]
     
    Martensitic steels are considered for structural applications for fusion power plants, but they are limited by strength to operating temperatures below 550-600 degrees C. For increased plant efficiency, steels for > 650 degrees C service are sought. Based on the science of precipitate strengthening, a thermo-mechanical treatment (TMT) was developed that respectively increased strength at 700 degrees C of commercial nitrogen-containing steels and new steels designed for the TMT to 80 and 200% greater than for commercial steels with a conventional heat treatment. Precipitates in the steels after the TMT were up to eight-times smaller at a number density four orders of magnitude greater.
  • N Hashimoto, JD Hunn, N Parikh, S Gilliam, S Gidcumb, B Patnaik, LL Snead
    JOURNAL OF NUCLEAR MATERIALS 347 (3) 307 - 313 0022-3115 2005/12 [Refereed][Not invited]
     
    The helium retention characteristics and helium bubble distribution in tungsten were studied using He-3(d,p)(4) He nuclear reaction analysis (NRA) and transmission electron microscopy (TEM) on two forms of tungsten: single crystal and polycrystalline, implanted to 1 X 10(19) He-3/m(2) at 850 degrees C and annealed at 2000 degrees C. The NRA results revealed that as-implanted single crystal and polycrystalline tungsten exhibited similar helium retention characteristics. Stepwise annealing reduced the helium retention in both single crystal and polycrystalline tungsten when the number of implantation steps and annealing time were increased. The TEM results indicated that microstructure played a large role in helium trapping; the existence of grain boundaries led to significant cavity formation and greater cavity growth. Single crystal tungsten had less trapping sites for helium, allowing long range He diffusion during annealing. The decrease of He retention in polycrystalline tungsten during stepwise annealing was probably due to significant recrystallization, resulting in decrease of grain boundary density. (c) 2005 Elsevier B.V. All rights reserved.
  • RL Klueh, N Hashimoto, PJ Maziasz
    SCRIPTA MATERIALIA 53 (3) 275 - 280 1359-6462 2005/08 [Refereed][Not invited]
     
    Nano-sized precipitates were produced in nitrogen-containing commercial martensitic steels by a new thermomechanical treatment (TMT). A steel with the TMT should have a maximum operating temperature > 50 degrees C over the steel given a conventional heat treatment. A > 100 degrees C increase should be possible for a steel developed for the TMT. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.
  • N Hashimoto, JD Hunn, N Parikh, S Gilliam, S Gidcumb, B Patnaik, LL Snead
    FUSION SCIENCE AND TECHNOLOGY 47 (4) 881 - 885 1536-1055 2005/05 [Refereed][Not invited]
     
    To understand the helium retention characteristics and helium bubble distribution in tungsten, He-3(d,p)He-4 nuclear reaction analysis (NRA) and transmission electron microscopy (TEM) have been performed for two forms of tungsten: single crystal and polycrystalline, implanted up to 1x10(19) He-3/m(2) at 850 degrees C and annealed at 2000 degrees C. The NRA results indicated that as-implanted single crystal and polycrystalline tungsten exhibited similar helium retention characteristics. In addition, a flash anneal at 2000 degrees C had no effect on the retention of helium. However, when 10(19) He/m(2) was implanted into single crystal tungsten in 1000 cycles of 10(16) He/m(2) each followed by a 2000 degrees C flash anneal, the observed helium yield dropped by 95% compared to 70% for polycrystalline tungsten. The microstructure of single crystal tungsten implanted with 1x10(19) He/m(2) and annealed at 2000 degrees C in a single step showed numerous tiny cavities at a depth of similar to 1.6 mu m, while no visible cavities were observed in the 1000 step annealed single crystal. However, in the case of polycrystalline tungsten, a single step annealing led to significant cavity growth at grain boundaries. The reduced He retention suggests a preference for inertial fusion energy armor of single crystal over polycrystalline tungsten.
  • N Hashimoto, TS Byun, K Farrell, SJ Zinkle
    JOURNAL OF NUCLEAR MATERIALS 336 (2-3) 225 - 232 0022-3115 2005/02 [Refereed][Not invited]
     
    The deformation microstructure of irradiated pure vanadium has been investigated by transmission electron microscopy. Dislocation pileup on grain boundaries were observed in the deformed specimens irradiated to 0.012 dpa, indicating that the source of channeling could not be grain boundary only. TEM analysis suggested a relationship between tensile direction and channeling-occurred grain: there is a tendency that directions of the applied stress with greater resolved shear stress lie on the trace containing [0 11] and [112] directions. Channel width is wider in case the angle between tensile direction and dislocation slip direction is close to 45degrees. There is a dose dependence on the correlation between channel width and resolved shear stress, the slope of this correlation decreased with increasing dose. It is suggested that the loss of work hardening capacity in irradiated pure vanadium could be mainly due to dislocation channeling locally formed with high resolved shear stress. (C) 2004 Elsevier B.V. All rights reserved.
  • N Hashimoto, TS Byun, K Farrell, SJ Zinkle
    JOURNAL OF NUCLEAR MATERIALS 336 (2-3) 225 - 232 0022-3115 2005/02 [Refereed][Not invited]
     
    The deformation microstructure of irradiated pure vanadium has been investigated by transmission electron microscopy. Dislocation pileup on grain boundaries were observed in the deformed specimens irradiated to 0.012 dpa, indicating that the source of channeling could not be grain boundary only. TEM analysis suggested a relationship between tensile direction and channeling-occurred grain: there is a tendency that directions of the applied stress with greater resolved shear stress lie on the trace containing [0 11] and [112] directions. Channel width is wider in case the angle between tensile direction and dislocation slip direction is close to 45degrees. There is a dose dependence on the correlation between channel width and resolved shear stress, the slope of this correlation decreased with increasing dose. It is suggested that the loss of work hardening capacity in irradiated pure vanadium could be mainly due to dislocation channeling locally formed with high resolved shear stress. (C) 2004 Elsevier B.V. All rights reserved.
  • K Farrell, TS Byun, N Hashimoto
    JOURNAL OF NUCLEAR MATERIALS 335 (3) 471 - 486 0022-3115 2004/12 [Refereed][Not invited]
     
    The deformation microstructures of neutron-irradiated nuclear structural alloys, A533B steel, 316 stainless steel, and Zircaloy-4, have been investigated by tensile testing and transmission electron microscopy to map the extent of strain localization processes in plastic deformation. Miniature specimens with a thickness of 0.25mm were irradiated to five levels of neutron dose in the range 0.0001-0.9 displacements per atom (dpa) at 65-100degreesC and deformed at room temperature at a nominal strain rate of 10(-3) s(-1). Four modes of deformation were identified, namely three-dimensional dislocation cell formation, planar dislocation activity, fine scale twinning, and dislocation channel deformation (DCD) in which the radiation damage structure has been swept away. The modes varied with material, dose, and strain level. These observations are used to construct the first strain-neutron fluence-deformation mode maps for the test materials. Overall, irradiation encourages planar deformation which is seen as a precursor to DCD and which contributes to changes in the tensile curve, particularly reduced work hardening and diminished uniform ductility. The fluence dependence of the increase in yield stress, DeltaYS = alpha(phit)(n) had an exponent of 0.4-0.5 for fluences up to about 3 x 10(22) n m(-2) (similar to0.05 dpa) and 0.08-0.15 for higher fluences, consistent with estimated saturation in radiation damage microstructure but also concurrent with the acceleration of gross strain localization associated with DCD. (C) 2004 Elsevier B.V. All rights reserved.
  • TS Byun, N Hashimoto, K Farrell
    ACTA MATERIALIA 52 (13) 3889 - 3899 1359-6454 2004/08 [Refereed][Not invited]
     
    The temperature dependencies of true strain-hardening and plastic-in stability properties are investigated for austenitic stainless steels; including annealed 304, 316 316LN, and 20% cold-worked 316LN, at test temperatures from -150 to 450 degreesC. In both annealed and cold-worked conditions, strength decreases with increasing temperature, while ductility peaks below room temperature and is least at about 400 degreesC. At room temperature or below, the strain-hardening behavior exhibits two stages consisting of a rapid decrease for small strains and an increase-decrease cycle before plastic instability occurs. At higher temperatures the strain-hardening rate decreases monotonically with strain. The characteristics of these strain-hardening behaviors are explained by changes in deformation microstructure. Transmission electron microscopy (TEM) of the deformed 316LN steel shows that twins, stacking faults, and/or martensite laths, along with dislocations, are formed at subzero temperatures, and dislocation-dominant microstructures at elevated temperatures. It is also shown that the average strain-hardening rate during necking to failure is almost equal to the true stress at the onset of necking. This stress is called the plastic instability stress (PIS). Cold-worked specimens fail by prompt necking at yield when the yield stress exceeds the PIS of annealed material, indicating that the PIS is independent of prior cold work. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
  • TS Byun, K Farrell, N Hashimoto
    JOURNAL OF NUCLEAR MATERIALS 329 998 - 1002 0022-3115 2004/08 [Refereed][Not invited]
     
    Plastic instability in uniaxial tensile deformation has been investigated for the body centered cubic (bcc) and hexagonal close packed (hcp) pure metals, V, Nb, Mo, and Zr, after low temperature (60-100 degreesC) neutron irradiation up to 0.7 dpa. Relatively ductile metals, V, Nb, and Zr, experienced uniform deformation prior to necking at low doses and prompt plastic instability at yield at high doses. Mo failed in a brittle mode within the elastic limit at doses above 0.0001 dpa. V showed a quasi-brittle failure at the highest dose of 0.69 dpa. In the ductile metals, plastic instability at yield occurred when the yield stress exceeded the plastic instability stress (PIS), which was nearly independent of dose. The PIS values for V, Nb, Mo, and Zr were about 390, 370, 510, and 170 MPa, respectively. The coincidence of plastic instability at yield and dislocation channeling cannot be generalized for all metallic materials. (C) 2004 Elsevier B.V. All rights reserved.
  • N Hashimoto, TS Byun, K Farrell, SJ Zinkle
    JOURNAL OF NUCLEAR MATERIALS 329 947 - 952 0022-3115 2004/08 [Refereed][Not invited]
     
    The effects of neutron-irradiation near 80 degreesC on the deformation behavior of pure polycrystalline metals vanadium (body centered cubic, BCC), copper (face centered cubic, FCC) and zirconium (hexagonal close packed, HCP) have been investigated. Dislocation channel deformation is observed in all metals, and is coincident with prompt plastic instability at yield. Dislocation pileup was observed at grain boundaries in the deformed vanadium irradiated to 0.012 dpa, indicating that channel formation could lead to dislocation pileup and the resulting stress localization could be a source of grain boundary cracking. TEM analysis suggests that the loss of work hardening capacity in irradiated V, Cu, and Zr at higher doses is mainly due to dislocation channeling in local regions that experience a high resolved shear stress. (C) 2004 Elsevier B.V. All rights reserved.
  • Tanigawa, H., Hashimoto, N., Sakasegawa, H., Klueh, R.L., Sokolov, M.A., Shiba, K., Jitsukawa, S., Kohyama, A.
    Journal of Nuclear Materials 329-333 (1-3 PART A) 283 - 288 2004 [Refereed][Not invited]
  • RL Klueh, N Hashimoto, M Sokolov
    Effects of Radiation on Materials: 21st International Symposium 1447 376 - 390 1040-1695 2004 [Refereed][Not invited]
     
    An Fe-9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa) steel has a smaller prior-austenite grain size than this same composition without tantalum (9Cr-2W) when the steels are given a similar heat treatment. Except for prior-austenite grain size, the microstructures of the steels are similar before irradiation, and they develop similar changes in microstructure during irradiation. Nevertheless, the 9Cr-2WVTa shows less effect of irradiation on the Charpy behavior. To determine the effect of grain size on the Charpy properties of the 9Cr-2VrV and 9Cr-2WVTa, specimens of the two steels were given various normalization heat treatments to produce different prior austenite grain sizes, and the tensile and impact properties were determined. For the smaller prior-austenite grain sizes, the 9Cr-2VrV steel had impact properties similar to or better than those of the 9Cr-2WVTa steel. Differences in the microstructures of the steels were used to explain the observations and what they mean for developing steels with improved properties.
  • T Muroga, H Watanabe, K Fukumoto, M Satou, A Kimura, SJ Zinkle, N Hashimoto, DT Hoelzer, AL Qualls
    FUSION SCIENCE AND TECHNOLOGY 44 (2) 450 - 454 1536-1055 2003/09 [Refereed][Not invited]
     
    The Varying Temperature Irradiation Experiment in the High Flux Isotope Reactor (HFIR) was carried out in the framework of the Japan-USA fusion cooperation program (JUPITER). The objective of the experiment is to investigate the performance of fusion structural materials subject to temperature variation during operation. The experiment will also contribute to re-examining the available fission reactor irradiation data including temperature transient. The irradiation for the experiment was performed from July 1998 to May 1999. Some results of the Post-Irradiation Examination are now available. This paper summarizes the highlights of the experimental results and insights obtained through the experiment about the temperature variation effects on materials performance under irradiation.
  • N Hashimoto, RL Klueh, M Ando, H Tanigawa, T Sawai, K Shiba
    FUSION SCIENCE AND TECHNOLOGY 44 (2) 490 - 494 1536-1055 2003/09 [Refereed][Not invited]
     
    In order to determine the contributions of different microstructural features to strength and to deformation mode, microstructure of deformed flat tensile specimens of irradiated reduced activation F82H (IEA heat) base metal (BM) and its tungsten inert-gas (TIG) weldments (weld metal and weld joint) were investigated by transmission electron microscopy (TEM), following fracture surface examination by scanning electron microscopy (SEM). After irradiation, the fracture surfaces of F82H BM and TIG weldment showed a martensitic mixed quasi-cleavage and ductile-dimple fracture. The microstructure of the deformed region of irradiated F82H BM contained dislocation channels. This suggests that dislocation channeling could be the dominant deformation mechanism in this steel, resulting in the loss of strain-hardening capacity. While, the necked region of the irradiated F82H TIG, where showed less hardening than F82H BM, showed deformation bands only. From these results, it is suggested that the pre-irradiation microstructure, especially the dislocation density, could affect the post-irradiation deformation mode.
  • M Shoyama, N Hashimoto
    SENSORS AND ACTUATORS B-CHEMICAL 93 (1-3) 585 - 589 0925-4005 2003/08 [Refereed][Not invited]
     
    Effects of poly ethylene glycol (PEG) addition on the microstructure and CO sensing characteristics of SnO2 thin films prepared by sol-gel method were investigated. Microstructure of SnO2 thin film was drastically developed by the addition of PEG, indicating that the addition of PEG was effective to prevent the agglomeration of SnO2 particles. CO sensitivity of SnO2 thin films increased as PEG content increased, and drastically improved to 565 at operating temperature of 773 K. This result shows about 12 times larger than that of PEG-free SnO2 thin film (48). It is considered that the enhancement of the sensitivity was caused by high surface area of nano-sized SnO2 Particles. (C) 2003 Elsevier Science B.V. All rights reserved.
  • H Tanigawa, M Ando, T Sawai, K Shiba
    FUSION SCIENCE AND TECHNOLOGY 44 (1) 219 - 223 1536-1055 2003/07 [Refereed][Not invited]
     
    Previous work reported that a TIG weld joint of F82H exhibited low irradiation hardening in a tensile test, compared to the base metal. Microhardness tests and microstructure observation on the neutron-irradiated TIG weld joint of F82H revealed that the over-tempered zone in the heat-affected zone (HAZ) exhibited this good performance. The region in the HAZ where the prior austenite grain size became very fine during welding also exhibited lower irradiation hardening. Hypotheses for these low-hardening mechanisms were proposed based on the phase diagram and grain size.
  • N Hashimoto, JD Hunn, TS Byun, LK Mansur
    JOURNAL OF NUCLEAR MATERIALS 318 300 - 306 0022-3115 2003/05 [Refereed][Not invited]
     
    As an assessment for a possible accelerator beam line window material for the US Spallation Neutron Source (SNS) target, performance, radiation-induced hardening and microstructural evolution in Inconel 718 were investigated in both solution annealed (SA) and precipitation hardened (PH) conditions. Irradiations were carried out using 3.5 MeV Fe+, 370 keV He+ and 180 keV H+ either singly or simultaneously at 200degreesC to simulate the damage and He/H production in the SNS target vessel wall. This resulted in systematic hardening in SA Inconel and gradual net softening in the PH material. TEM microstructural analysis showed the hardening was associated with the formation of small loop and faulted loop structures. Helium-irradiated specimens included more loops and cavities than Fe. ion-irradiated specimens. Softening of the PH material was due to dissolution of the gamma'/gamma" precipitates. High doses of helium were implanted in order to study the effect of high retention of gaseous transmutation products. Simultaneous with the hardening and/or softening due to the displacement damage cascade, helium filled cavities produced additional hardening at high concentrations. (C) 2003 Elsevier Science B.V. All rights reserved.
  • E Wakai, N Hashimoto, JP Robertson, T Sawai, A Hishinuma
    JOURNAL OF NUCLEAR MATERIALS 307 352 - 356 0022-3115 2002/12 [Refereed][Not invited]
     
    The effects of cold working and impurities on swelling behavior in austenitic stainless steels irradiated at 400 'C to 17.3 dpa under spectrally tailored conditions in the Oak Ridge research reactor and high flux isotope reactor were investigated. The specimens were 20% cold-worked JPCA, 316R, K (low carbon (0.02%)) and C (low carbon (0.02%) and doped with 0.08%, niobium). The helium generation rate was about 15 appm He/dpa. Cavities, dislocation loops and carbides were formed by irradiation in these steels. The swelling in the JPCA-CW and 316-CW was 0.003% and 0.004%, respectively and in the C-CW and K-CW was 0.02% and 0.01%, respectively. Swelling in K and C steels was strongly reduced by 20% cold-work, and the swelling in JPCA-CW and 316R-CW steels was comparable to JPCA-SA and 316R-SA steels. The synergistic treatments of addition of some impurities and cold working are very effective for the suppression of swelling at 400 degreesC in austenitic stainless steels. (C) 2002 Elsevier Science B.V. All rights reserved.
  • E Wakai, Y Miwa, N Hashimoto, JP Robertson, RL Klueh, K Shiba, K Abiko, S Furuno, S Jitsukawa
    JOURNAL OF NUCLEAR MATERIALS 307 203 - 211 0022-3115 2002/12 [Refereed][Not invited]
     
    The synergistic effect of displacement damage and hydrogen or helium atoms on microstructures in F82H steel irradiated at 250-400 degreesC to 2.8-51 dpa in HFIR has been examined Using isotopes Of Fe-54 or B-10. Hydrogen atoms increased slightly the formation of dislocation loops and changed the Burgers vector for some parts of dislocation loops, and they also affected on the formation of cavity at 250 degreesC to 2.8 dpa. Helium atoms also influenced them at around 300 degreesC, and the effect of helium atoms was enhanced at 400 degreesC. Furthermore, the relations between microstructures and radiation-hardening or ductile to brittle transition temperature (DBTT) shift in F82H steel were discussed. The cause of the shift increase of DBTT is thought to be due to the hardening of dislocation loops and the formation of alpha'-precipitates on dislocation loops. (C) 2002 Elsevier Science B.V. All rights reserved.
  • SJ Zinkle, N Hashimoto, DT Hoelzer, AL Qualls, T Muroga, BN Singh
    JOURNAL OF NUCLEAR MATERIALS 307 192 - 196 0022-3115 2002/12 [Refereed][Not invited]
     
    Specimens of pure copper, a high purity austenitic stainless steel, and V-4Cr-4Ti were exposed to eight cycles of either constant temperature or periodic temperature variations during neutron irradiation in the High Flux Isotopes Reactor to a cumulative damage level of 4-5 displacements per atom, Specimens exposed to periodic temperature variations experienced a low temperature (360 degreesC) during the initial 10% of accrued dose in each of the eight cycles, and a higher temperature (520 degreesC) during the remaining 90%,, of accrued dose in each cycle, The microstructures Of the irradiated stainless steel and V-4Cr-4Ti were qualitatively similar to companion specimens that were continuously maintained at 520 degreesC during, the entire irradiation. The microstructural observations on pure copper irradiated at a constant temperature of 340 degreesC in this experiment are also summarized. The main radiation-induced microstructural features consisted of dislocation loops, stacking fault tetrahedra and voids in the stainless steel, Ti-rich precipitates in the V alloy, and voids (along with a low density of stacking fault tetrahedra) in copper. (C) 2002 Elsevier Science B.V. All rights reserved.
  • RL Klueh, PJ Maziasz, IS Kim, L Heatherly, DT Hoelzer, N Hashimoto, EA Kenik, K Miyahara
    JOURNAL OF NUCLEAR MATERIALS 307 773 - 777 0022-3115 2002/12 [Refereed][Not invited]
     
    The tensile and creep properties of two oxide dispersion-strengthened (ODS) steels with nominal compositions of Fe-12Cr-0.25Y(2)O(3) (designated 12Y1) and Fe-12Cr-2.5W-0.4Ti-0.25Y(2)O(3), (12YWT) were investigated. Optical microscopy, transmission electron microscopy, and atom probe field ion microscopy studies indicated that the 12YWT contained a high density of extremely fine Y-Ti-O clusters, compared to the much larger oxide particles in the 12Y1. The fine dispersion of particles gave the 12YWT better tensile and creep properties compared to commercial ODS alloys and ferritic/martensitic steels that would be replaced by the new ODS steel. (C) 2002 Elsevier Science B.V. All rights reserved.
  • N Hashimoto, RL Klueh, K Shiba
    JOURNAL OF NUCLEAR MATERIALS 307 222 - 228 0022-3115 2002/12 [Refereed][Not invited]
     
    In the absence of a 14 MeV neutron source, the effect of helium on structural materials for fusion must be simulated using fission reactors. Helium effects in ferritic/martensitic steels have been studied by adding nickel and boron and irradiating in a mixed-spectrum reactor. Although the nickel- and boron-doping techniques have limitations and difficulties to estimate helium effects on the ferritic/martensitic steels, past irradiation experiments using these techniques have demonstrated similar effects on the swelling and Charpy impact properties that are indicative of a helium effect. Although both techniques have disadvantages, it should be possible to plan experiments using the nickel- and boron-doping techniques to develop an understanding of the effects of helium on mechanical properties. (C) 2002 Elsevier Science B.V. All rights reserved.
  • N Hashimoto, RL Klueh
    JOURNAL OF NUCLEAR MATERIALS 305 (2-3) 153 - 158 0022-3115 2002/10 [Refereed][Not invited]
     
    The microstructures of reduced-activation ferritic/martensitic steels, 9Cr-1MoVNb, 9Cr-1MoVNb-2Ni, 9Cr-2WVTa and 9Cr-2WVTa doped with 2% Ni, irradiated at 400 degreesC up to 12 dpa in the high flux isotope reactor, were investigated by transmission electron microscopy. The cavity number density of Ni-doped steels was higher than that of Ni-undoped steels due to the higher concentration of helium. There was no difference of cavity number density between the steels tempered at 700 and 750 degreesC, but the mean size of the cavities in the steels tempered at 750 degreesC was larger than that tempered at 700 degreesC. There was a tendency for the number density of loops in Ni-doped steels to be higher than in Ni-undoped steels. In addition; the mean size of loops in the steels tempered at 750 degreesC was larger than for those tempered at 700 degreesC, while there was not much difference of number density between them. In the steels doped with Ni, irradiation-produced precipitates, identified as M6C(eta)-type carbide and MA phase, were found in the 9Cr-2VWTa-2Ni steel and 9Cr-1MoVNb-2Ni, respectively. Irradiation of Ni-doped steels showed the effect of helium on cavity nucleation, however, the effect of helium on dislocation structure and precipitation was not made clear. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Microstructural Analysis of Ion-Irradiation-Induced Hardening in Inconel 718
    N. Hashimoto, J.D Hunn, T.S. Byun, L.K. Mansur
    J. Nucl. Mater. 318 300 - 306 2002 [Refereed][Not invited]
  • T Kobayashi, N Natanani, T Hirakawa, M Suzuki, T Miyake, M Chiwa, T Yuhara, N Hashimoto, K Inoue, K Yamamura, N Agus, Sinogaya, JR, K Nakane, A Kume, T Arakaki, H Sakugawa
    ENVIRONMENTAL POLLUTION 118 (3) 383 - 391 0269-7491 2002 [Refereed][Not invited]
     
    The hydroxyi radical (.OH) is generated in polluted dew on the needle surfaces of Japanese red pine (Pinus densiflora Sieb. et Zucc.). This free radical, which is a potent oxidant, is assumed to be a cause of ecophysiological disorders of declining trees on the urban-facing side of Mt. Gokurakuji, western Japan. Mists of .OH-generating N(III) (HNO2 and NO2-) and HOOH + Fe + oxalate solutions (50 and 100 muM, pH 5.1-5.4) simulating the dew water were applied to the foliage of pine seedlings grown in open-top chambers in the early morning. Needles treated with 100 muM N(III) tended to have a greater maximum CO2 assimilation rate (A(max)), a greater stomatal conductance (g(s)) and a greater needle nitrogen content (N-needle), suggesting that N(III) mist acts as a fertilizer rather than as a phytotoxin. On the other hand, needles treated with 100 muM HOOH + Fe + oxalate solution showed the smallest A(max), g(s), and N-needle, suggesting that the combination of HOOH + Fe + oxalate caused a decrease in needle productivity. The effects of HOOH + Fe + oxalate mist on pine needles were very similar to the symptoms of declining trees at Mt. Gokurakuji. (C), 2002 Elsevier Science Ltd. All rights reserved.
  • Y Miwa, E Wakai, K Shiba, N Hashimoto, JP Robertson, AF Rowcliffe, A Hishinuma
    JOURNAL OF NUCLEAR MATERIALS 283 (Pt.A) 334 - 338 0022-3115 2000/12 [Refereed][Not invited]
     
    Reduced-activation ferritic/martensitic steel, F82H (8Cr-2W-0.2V-0.04Ta-0.1C), and variants doped with isotopically tailored boron were irradiated at 673 K up to 51 dpa in the high flux isotope reactor (HFIR). The concentrations of B-10 in these alloys were 4, 62, and 325 appm during HFIR irradiation which resulted in the production of 4, 62 and 325 appm He, respectively After irradiation, transmission electron microscopy (TEM) was carried out. The number density of cavities increased and the average diameter of cavities decreased with increasing amounts of B-10. The number density decreased and the average diameter increased with increasing displacement damage. Swelling increased as a function of displacement damage and He concentration. (C) 2000 Elsevier Science B.V. All rights reserved.
  • E Wakai, N Hashimoto, Y Miwa, JP Robertson, RL Klueh, K Shiba, S Jistukawa
    JOURNAL OF NUCLEAR MATERIALS 283 (Pt.B) 799 - 805 0022-3115 2000/12 [Refereed][Not invited]
     
    The effects of helium production and heat treatment on the swelling of F82H steel irradiated in the HFIR to 51 dpa have been investigated using B-10, Ni-58 and Ni-60-doped specimens. The swelling of tempered F82H-std and F82H doped with B-10 irradiated at 400 degreesC ranged from 0.52% to 1.2%, while the swelling of the non-tempered F82H doped with Ni-58 or Ni-60 was less than 0.02%. At 300 degreesC the swelling in all steels was insignificant. In the F82H + Ni, a high number of density carbides formed in the matrix at these temperatures. The production of helium atoms enhanced the swelling of the F82H steel. However, the non-tempered treatment for the F82H + Ni suppressed remarkably the swelling. The cause of low swelling in the F82H + Ni may be due to the occurrence of the high density of carbides acting as sinks or the decrease of mobility of vacancies interacting with carbon atoms in matrix. (C) 2000 Elsevier Science B.V. All rights reserved.
  • E Wakai, N Hashimoto, JP Robertson, S Jistukawa, T Sawai, A Hishinuma
    JOURNAL OF NUCLEAR MATERIALS 283 (Pt.A) 435 - 439 0022-3115 2000/12 [Refereed][Not invited]
     
    The synergistic effect of displacement damage and helium generation under neutron irradiation on tensile behavior and microstructures of austenitic stainless steels was investigated. The steels were irradiated at 400 degreesC in the spectrally-tailored (ST) Oak Ridge research reactor/high flux isotope reactor (ORR/HFIR) capsule to 17 dpa with a helium production of about 200 appm and in the HFIR target capsule to 21 and 34 dpa with 1590 and 2500 appm He, respectively. The increase of yield strength in the target irradiation was larger than that in the ST irradiation because of the high-number density of Frank loops, bubbles, voids, and carbides. Based on the theory of dispersed barrier hardening, the strengths evaluated from these clusters coincide with the measured increase of yield strengths. This analysis suggests that the main factors of radiation hardening in the ST and the target irradiation at 400 degreesC are Frank-type loops and cavities, respectively (C) 2000 Elsevier Science B.V. All rights reserved.
  • RL Klueh, N Hashimoto, RF Buck, MA Sokolov
    JOURNAL OF NUCLEAR MATERIALS 283 (Pt.A) 697 - 701 0022-3115 2000/12 [Refereed][Not invited]
     
    The A-21 steel is an Fe-Cr-Co-Ni-Mo-Ti-C steel that is strengthened by a fine distribution of titanium carbide (TIC) precipitates formed by thermomechanical treatment. Transmission electron microscopy of the A-21 reveals a high number density of small TiC particles uniformly distributed in the matrix. Below approximate to 600 degreesC, the strength of A-21 is less than the average value for conventional Cr-Mo or reduced-activation ferritic/martensitic steels. However, the strength is greater above 600 degreesC. The Charpy impact properties of A-21 are comparable to those of the conventional and reduced-activation steels. Due to the fine TiC particles in the matrix, the creep-rupture properties of A-21 are superior to those of conventional Cr-Mo or reduced-activation Cr-W steels. Although the composition of the A-21 is not applicable for fusion because of the cobalt, the innovative production process may offer a route to an improved steel for fusion. (C) 2000 Elsevier Science B.V. All rights reserved.
  • N Hashimoto, SJ Zinkle, AF Rowcliffe, JP Robertson, S Jitsukawa
    JOURNAL OF NUCLEAR MATERIALS 283 (Pt.A) 528 - 534 0022-3115 2000/12 [Refereed][Not invited]
     
    Plastically deformed microstructures in neutron-irradiated austenitic stainless steel were investigated by transmission electron microscopy (TEM). Neutron irradiation at 60 degreesC and 330 degreesC to about 7 dpa induced a high number density of faulted loops and black dots, which resulted in irradiation-induced hardening. In the specimen irradiated at 60 degreesC and tensile tested at 25 degreesC at a strain rate of 4x10(-4) s(-1), the deformation microstructure consisted of twins, elongated faulted loops, and lath and twin martensite phase. In the specimens irradiated and tested at 330 degreesC at a strain rate of 4x10(-4) and 4x10(-6) s(-1), in addition to these features, dislocation channeling was also observed. The TEM examination suggests that lath and twin martensite can form during tensile testing at both of these temperatures. Examination of the specimens irradiated and tensile tested at 330 degreesC indicated that twinning was the predominant deformation mode at slower strain rate and dislocation channeling was favored at higher temperature. From the micrographs taken from the {111} plane streak in a diffraction pattern, it is suggested that faulted loops could be the principal twin initiation site during deformation. (C) 2000 Elsevier Science B.V. All rights reserved.
  • IS Kim, JD Hunn, N Hashimoto, DL Larson, PJ Maziasz, K Miyahara, EH Lee
    JOURNAL OF NUCLEAR MATERIALS 280 (3) 264 - 274 0022-3115 2000/09 [Refereed][Not invited]
     
    In an attempt to explore the potential of oxide dispersion strengthened (ODS) ferritic steels for fission and fusion structural materials applications, a set of ODS steels with varying oxide particle dispersion were irradiated at 650 degrees C, using 3.2 MeV Fe+ and 330 keV He+ ions simultaneously. The void formation mechanisms in these ODS steels were studied by juxtaposing the response of a 9Cr-2WVTa ferritic/martensitic steel and solution annealed AISI 316LN austenitic stainless steel under the same irradiation conditions. The results showed that void formation was suppressed progressively by introducing and retaining a higher dislocation density and finer precipitate particles. Theoretical analyses suggest that the delayed onset of void formation in ODS steels stems from the enhanced point defect recombination in the high density dislocation microstructure, lower dislocation bias due to oxide particle pinning, and a very fine dispersion of helium bubbles caused by trapping helium atoms at the particle-matrix interfaces. (C) 2000 Elsevier Science B.V. All rights reserved.
  • EH Lee, TS Byun, JD Hunn, N Hashimoto, K Farrell
    JOURNAL OF NUCLEAR MATERIALS 281 (1) 65 - 70 0022-3115 2000/09 [Refereed][Not invited]
     
    There is considerable interest in understanding how dislocations interact with defect clusters produced by radiation to evaluate and remedy the radiation induced degradation of mechanical properties. In this paper, it is demonstrated that deformation mechanisms for irradiated materials can be studied with small TEM disks by employing a disk-bend method. Results showed that dominant deformation modes in ion-irradiated austenitic steel were planar glide and microtwinning. It was concluded that the disk-bend method will be a powerful tool in studying deformation microstructures of irradiated materials. (C) 2000 Elsevier Science B.V. All rights reserved.
  • N Hashimoto, E Wakai, JP Robertson, T Sawai, A Hishinuma
    JOURNAL OF NUCLEAR MATERIALS 280 (2) 186 - 195 0022-3115 2000/08 [Refereed][Not invited]
     
    Microstructural evolution in solution-annealed Japanese-PCA (JPCA-SPI) and four other austenitic stainless steels, irradiated at 400 degrees C to 17.3 dpa in the ORR and the high flux isotope reactor (HFIR) spectrally tailored experiment, were investigated by transmission electron microscopy (TEM). The mean He/dpa ratio throughout the irradiation fell between 12 and 16 appm He/dpa, which is close to the He/dpa values expected for fusion. In all the specimens, a bimodal size distribution of cavities was observed and the number densities were about 1.0 x 10(22) m(-3). There was no significant difference between the number densities in the different alloys, although the root mean cubes of the cavity radius are quite different for each alloy. Precipitates of the MC type were also observed in the matrix and on grain boundaries in all alloys except a high-purity (HP) ternary alloy. The JPCA-SA (including 0.06% carbon and 0.027% phosphorus) and standard type 316 steel (including 0.06% carbon and 0.028% phosphorus) showed quite low-swelling values of about 0.016 and 0.015%, respectively, while a HP ternary austenitic alloy showed the highest swelling value of 2.9%. This suggests that the existence of impurities affects the cavity growth in austenitic stainless steels even at 400 degrees C. (C) 2000 Elsevier Science B.V. All rights reserved.
  • EH Lee, JD Hunn, N Hashimoto, LK Mansur
    JOURNAL OF NUCLEAR MATERIALS 278 (2-3) 266 - 272 0022-3115 2000/04 [Refereed][Not invited]
     
    For an assessment of the future US spallation neutron source (SNS) target performance, radiation induced hardening and microstructural evolution were investigated as a function of ion dose for EC316LN stainless steel. Irradiation was carried out using 3.5 MeV Fe+, 360 keV He+, and 180 keV H+ simultaneous ion-beams at 200 degrees C to simulate the damage, He and H production in the SNS target vessel wall, At low dose (< dpa), the predominant defects were black dots whose number density saturated rapidly within a few dpa. This was followed by the evolution of interstitial loops whose number density saturated below 15 dpa. Although He-bubbles were not visible, severely scalloped loops suggested that the implanted He/H atoms existed in the form of small clusters. Comparison with reported neutron irradiation data showed that hardening and ductility loss occurred mostly in the black dot regime (<1 dpa), but that good ductility (>20% elongation) was maintained up to a dose level of similar or equal to 10 dpa. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Deformation Mechanisms in Martensitic Steels Irradiated in HFIR
    N. Hashimoto, S.J. Zinkle, R.L Klueh, A.F. Rowcliffe, K. Shiba
    Mat. Res. Soc. Symp. Proc. 650 R1.10.  2000 [Refereed][Not invited]
  • Microstructural Evolution of Ni-doped Ferritic/martensitic Steels Irradiated in HFIR
    N. Hashimoto, R.L. Klueh, J.P. Robertson
    Mat. Res. Soc. Symp. Proc. 650 R3.6.  2000 [Refereed][Not invited]
  • N Hashimoto, E Wakai, JP Robertson
    JOURNAL OF NUCLEAR MATERIALS 273 (1) 95 - 101 0022-3115 1999/06 [Refereed][Not invited]
     
    An austenitic stainless steel 316LN irradiated to damage levels of about 3 dpa at irradiation temperatures of about 90 degrees C and 250 degrees C has been examined by transmission electron microscopy. The irradiation at 90 degrees C and 250 degrees C induced a dislocation loop density of 3.5 x 10(22) and 5.2 x 10(22) m(-3) and a black dot density of 2.2 x 10(23) and 1.1 x 10(23) m-3 respectively, in the steel. A low density (<1 x 10(19) m(-3)) of radiation-enhanced precipitates was observed in the matrix. No cavities were observed. These features are correlated with the changes in tensile properties. It is concluded that the dislocation loops and the black dots cause irradiation hardening and a decrease in the uniform elongation in the 316LN steel irradiated at low temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.
  • H Kanda, N Hashimoto, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 271 311 - 315 0022-3115 1999/05 [Refereed][Not invited]
     
    The phenomenon of grain boundary migration due to boundary diffusion via vacancies is a well-known process for recrystallization and grain growth during annealing. This phenomenon is known as diffusion-induced grain boundary migration (DIGM) and has been recognized in various binary systems. On the other hand, grain boundary migration often occurs under irradiation. Furthermore, such radiation-induced grain boundary migration (RIGM) gives rise to solute segregation. In order to investigate the RIGM mechanism and the interaction between solutes and point defects during the migration, stainless steel and Ni-Si model alloys were electron-irradiated using a HVEM. RIGM was often observed in stainless steels during irradiation. The migration rate of boundary varied, and three stages of the migration were recognized. At lower temperatures, incubation periods up to the occurrence of the boundary migration were observed prior to first stage. These behaviors were recognized particularly for lower solute containing alloys. From the relation between the migration rates at stage I and inverse temperatures, activation energies for the boundary migration were estimated. In comparison to the activation energy without irradiation, these values were very low. This suggests that the RIGM is caused by the flow of mixed-dumbbells toward the grain boundary. The interaction between solute and point defects and the effective defect concentration generating segregation will be discussed. (C) 1999 Elsevier Science B.V. Allrights reserved.
  • H Kanda, H Takahashi, N Hashimoto, N Sakaguchi
    INTERGRANULAR AND INTERPHASE BOUNDARIES IN MATERIALS, IIB98 294-2 (2) 157 - 160 0255-5476 1999 [Refereed][Not invited]
     
    In order to investigate the mechanisms of radiation-induced grain boundary migration, a 316 model steel and Ni-(2-10)at%Si model alloys were electron-irradiated, Boundary migration was often observed in stainless steels and the model alloys during irradiation. An initial incubation and three migration stages were observed. The incubation period depended on irradiation temperature and solute concentration. From the temperature dependence of boundary migration velocity during the first stage and the incubation response, activation energies were estimated. The activation energies obtained for each alloy were lower than that for boundary migration under thermal annealing. It is suggested from these results that the grain boundary migration under irradiation is caused by enhanced boundary diffusion and preferential rearrangement of under sized interstitial solute atoms diffusing via a mixed dumbbell mechanism towards the grain boundary.
  • N Hashimoto, E Wakai, JP Robertson
    JOURNAL OF ELECTRON MICROSCOPY 48 (5) 575 - 580 0022-0744 1999 [Refereed][Not invited]
     
    An austenitic stainless steel 316LN irradiated to damage levels of about 3 dpa at irradiation temperatures of about 90 degrees C and 250 degrees C has been examined by transmission electron microscopy. The irradiation at 90 degrees C and 250 degrees C induced a dislocation loop density of 3.5 x 10(22) m(-3) and 5.2 x 10(22) m(-3), and a black dot density of 2.2 x 10(23) m(-3) and 1.1 x 10(23) m(-3), respectively, in the steel. A low density (<1 x 10(19) m(-3)) of radiation-enhanced precipitates was observed in the matrix at both irradiation temperatures. No cavities were observed at both irradiation temperatures. These features are correlated with the changes in tensile properties. It is concluded that the dislocation loops and the black dots cause irradiation hardening and a decrease in the uniform elongation in the 316LN steel irradiated at low temperatures.
  • N Hashimoto, Y Eda, H Takahashi
    JOURNAL OF NUCLEAR MATERIALS 239 (1-3) 180 - 184 0022-3115 1996/12 [Refereed][Not invited]
     
    Fe-Cr-Ni, Ni-Al and Ni-Si alloys were electron-irradiated using a high voltage electron microscope (1 MeV), and in situ observations of the structural evolution and micro-chemical analysis were carried out. During the irradiation, the grain boundaries in the irradiated region migrated, while no grain boundary migration occurred in the unirradiated area. The occurrence of boundary migration depended on the orientation relationship of the boundary interfaces. Grain boundary migration took place in Fe-Cr-Ni and Ni-Si alloys with large crystal orientation difference between the two grains across a grain boundary. In Ni-Al, however, the grain boundary migration did not occur. The solute segregation was caused at grain boundary under irradiation and this segregation behavior was closely related to solute size, namely the concentrations of undersized Ni and oversized Cr elements in Fe-Cr-Ni alloy increased and reduced at grain boundary, respectively. The same dependence of segregation on the solute size was derived in Ni-Si and Ni-Al alloys, in which Si and Al solutes are undersized and oversized elements, respectively. Therefore, Si solute enriched and Al solute depleted at grain boundary From the present segregation behavior, it is suggested that the flow of point defects into the boundary is the cause of grain boundary migration.
  • S Watanabe, N Sakaguchi, N Hashimoto, M Nakamura, H Takahashi, C Namba, NQ Lam
    JOURNAL OF NUCLEAR MATERIALS 232 (2-3) 113 - 118 0022-3115 1996/09 [Refereed][Not invited]
     
    A computer simulation and an electron irradiation in a high voltage electron microscope (1000 kV) were used to study radiation-induced solute segregation and point defect flow in typical austenitic Fe-Cr-Ni alloys. The calculation was conducted by solving the coupled rate equations for solute and defect concentrations considering the Kirkendall effect at a moving grain boundary sink. The experimental solute redistribution profiles were explained qualitatively. Redistribution of nickel and chromium solutes near the grain boundaries and simultaneously grain boundary migration occurred during irradiation. The amount of nickel enrichment at a grain boundary was especially remarkable, comparing to the amount of chromium depletion. It is suggested that grain boundary migration may contribute to the flow of under-sized nickel solute toward the boundary. The influence of the probe size on EDS analysis of compositional profiles was investigated, with some experimental data.
  • H Takahashi, N Hashimoto, H Kanda
    INTERFACE SCIENCE 4 (3-4) 221 - 228 0927-7056 1996 [Refereed][Not invited]
     
    Fe-Cr-Ni, Ni-Al and Ni-Si alloys, and 316L stainless steels as reference were electron-irradiated using a high voltage electron microscope (1MV), and in-situ observations of structural evolution and micro-chemical analysis were carried out. From the compositional analysis it was found that nickel was enriched and chromium depleted near grain boundary in Fe-Cr-Ni alloys including 316L stainless steels, and that simultaneously grain boundary migration was caused during irradiation, even if no grain boundary migration occurred in the un-irradiated area at the same irradiation temperature. The occurrence of boundary migration strongly depended upon orientation relationship between boundary interfaces. It is suggested that grain boundary migration under irradiation remarkably occurs in the alloys in which solute enrichment is taken place at the grain boundary as a result of the flow of radiation-introduced point defects into grain boundary and that their magnitude depend upon net flow of point defect, especially that of under-sized interstitial atoms.
  • H Takahashi, N Sakaguchi, N Hashimoto, S Watanabe
    INTERGRANULAR AND INTERPHASE BOUNDARIES IN MATERIALS, PT 2 207- 561 - 564 0255-5476 1996 [Refereed][Not invited]
     
    Fe-Cr-Ni,Ni-Si and Ni-Al alloys were electron-irradiated using a high voltage electronmicroscopy (1000kV),and in situ observation on structural evolution and microchemical analysis were carried out. When the Fe-Cr-Ni alloy was irradiated, there occurred the nucleation of dislocation loops followed by voids and at the same time grain boundary migration occurred. The compositional analysis after irradiation of an area including the migrated grain boundary indicated nickel enrichment and chromium depletion. Furthermore the grain boundary tended to migrate toward a coarser facing boundary plane. The same grain boundary migration and compositional change at the boundary was recognized in Ni-Si alloy. These results suggested that boundary migration and solutes redistribution are closely related to irradiation-introduced point defects flow, especially interstitial atoms and the direction of the boundary migration depends on the relationship between the two grains.
  • S WATANABE, N SAKAGUCHI, N HASHIMOTO, H TAKAHASHI
    JOURNAL OF NUCLEAR MATERIALS 224 (2) 158 - 168 0022-3115 1995/08 [Refereed][Not invited]
     
    An irradiation-induced phenomenon was studied on account of solute segregation and concurrent grain boundary migration in a model Fe-Cr-Ni alloy during electron irradiation with a high voltage electron microscope (1000 kV) and also by computer simulation. The calculation was conducted by solving the coupled rate equations for solute and defect concentrations, which involve the Kirkendall effects at a grain boundary sink, so that the solute redistribution profiles experimentally obtained were quantitatively explained. We also extensively studied the effects of the probe size in the EDS analysis on composition profiles, the Gibbsian segregation in the vicinity of a grain boundary and the discriminant of segregation under irradiation, as well as other important factors that influence the phenomenon.
  • H TAKAHASHI, N HASHIMOTO, S WATANABE
    ULTRAMICROSCOPY 56 (1-3) 193 - 199 0304-3991 1994/11 [Refereed][Not invited]
     
    An Fe-Cr-Ni alloy was electron-irradiated using a high voltage electron microscope (1 MV), and in situ observations on the structural evolution and microchemical analysis were carried out. The compositional analysis showed that under irradiation an area near a grain boundary was nickel-enriched and chromium-depleted, and that, simultaneously, grain boundary migration occurred. Moreover, the distance of the grain boundary migration increased almost linearly with the degree of segregation, and the migration occurred predominantly in the direction perpendicular to close-packed crystal planes. Underpinned with computer calculations, it is suggested that when the radiation-induced point defects flow into the grain boundary, boundary migration and solute redistribution occur. Furthermore, the magnitude of the effects depends on the net point defect flow, especially that of interstitial atoms.
  • Theoretical and Experimental Studies of Irradiation-Induced Grain Boundary Migration and Segregation
    H. Takahashi, N. Hashimoto, S. Watanabe, N.Q. Lam
    The 1994 Gordon Res. Conf. on Particle Solid Interactions 1994 [Refereed][Not invited]
  • H TAKAHASHI, N HASHIMOTO
    MATERIALS TRANSACTIONS JIM 34 (11) 1027 - 1030 0916-1821 1993/11 [Refereed][Not invited]
     
    A Fe-Cr-Ni model alloy was electron-irradiated using a high voltage electron microscopy (1000 kV), and in-situ observations on structural evolution and microchemical analyses were carried out. When the Fe-Cr-Ni alloy was irradiated, the nucleations of dislocation loops followed by voids were observed and at the same time when a grain boundary migration occurred. The compositional analysis after irradiation of an area including a grain boundary indicated nickel enrichment and chromium depletion near the grain boundary. It is suggested that when the radiation-induced point defects flow into the grain boundary, boundary migration and solutes redistribution are induced and the magnitudes depend on net point defects flow, especially that of interstitial atoms.
  • Damage Rate Dependence of Electron-irradiation Behaviors in Fe-Cr-Ni Model Alloy
    H. Takahashi, N. Hashimoto
    Bulletin of Faculty of Engineering in Hokkaido University 162 81 - 89 1992 [Refereed][Not invited]

Books etc

  • 乾, 晴行 編著 (Joint work第6章 種々の応用 6-3 核融合炉構造材料)
    内田老鶴圃 2020/05 (ISBN: 9784753651375) x, 279p
  • Radiation Effects in Ferritic Steels and Advanced Ferritic-Martensitic Steels
    Naoyuki HashimotoRyuta, KasadaBaldev RajM. Vijayalakshmi (Joint workRadiation Effects in Ferritic Steels and Advanced Ferritic-Martensitic Steels)
    Reference Module in Materials Science and Materials Engineering 2020/03
  • 水素貯蔵材料の開発と応用
    橋本直幸 (Contributorマグネシウムを用いた水素除去システム)
    シーエムシー出版 2016/04

Conference Activities & Talks

  • Effect of solute atoms on dislocation loop formation in FeCrAl alloys  [Not invited]
    Naoyuki HASHIMOTO, Yixian TANG, Kodai TOYOTA
    日本原子力学会2020年秋の年会  2020/09
  • Irradiation damage in high entropy alloys ~ Defect analysis by in-situ observation  [Not invited]
    Naoyuki HASHIMOTO, Wei-ying CHEN
    日本金属学会・2020年春期(第166回)講演大会  2020/03
  • He and H effect on cavity formation and growth mechanism in irradiated ferritic steels  [Not invited]
    Naoyuki HASHIMOTO
    日本金属学会日本鉄鋼協会両支部合同冬季講演大会  2020/01
  • 高濃度固溶体合金における照射損傷挙動の直接観察  [Not invited]
    橋本直幸, W-Y Chen, J-W Yeh
    日本顕微鏡学会北海道支部学術講演会  2019/12
  • In-situ observation of irradiation damage in FeCrNiMn-based High Entropy Alloys  [Not invited]
    N. Hashimoto, W-Y Chen, J-W Yeh
    SNU-HU Joint Symposium The 8th Symposium on Materials Science and Engineering  2019/11
  • In-situ observation of radiation damage in FeCrNiMn high entropy alloys  [Not invited]
    N. Hashimoto, Weiyin Chen, Jienwei Yeh
    The 19th International Conference of Fusion Reactor Materials  2019/10
  • Direct observation of H and He effect on cavity formation in alpha-iron under irradiation  [Not invited]
    N. Hashimoto, D. Hamaguchi, H. Tanigawa
    The 19th International Conference of Fusion Reactor Materials  2019/10
  • 改良ステンレス鋼燃料被覆管のBWR装荷に向けた研究開発(4)〜(8)中性子照射材の微細組織評価挙動評価  [Not invited]
    橋本直幸, 唐一翔, 坂本寛, 山下真一郎
    日本原子力学会・2019年秋の年会  2019/09
  • Study on H in Fe/W interface by DFT calculation  [Not invited]
    N. Hashimoto, J. Shi
    NuMat 2018 (The Nuclear Materials Conference)  2018/10
  • Comparison of microstructural development between Fe-12Cr and Fe-12Cr-5Al under Irradiation  [Not invited]
    N. Hashimoto, K. Toyota, Y. Tang, K. Sakamoto, S. Yamashita
    NuMat 2018 (The Nuclear Materials Conference)  2018/10
  • Microstructural evolution in electron-irradiated CoCrFeNi High Entropy Alloys  [Not invited]
    N. Hashimoto, Y. Ono, Y. Lei
    The 14th Japan-China Symposium on Materials for Advanced Energy Systems and Fission & Fusion Engineering, Sendai 2018.9.25-9.27  2018/09
  • In-situ observation of SiC oxidation under environmentally-controlled electron irradiation  [Not invited]
    Naoyuki HASHIMOTO
    5th Workshop On TEM With In Situ Irradiation (WOTWISI-5)  2018/04
  • Current status and prospects of irradiation study on fusion reactor materials  [Invited]
    Naoyuki HASHIMOTO
    AESJ  2018/03
  • Irradiation damage in CoCrMnFeNi High Entropy Alloy  [Not invited]
    Naoyuki HASHIMOTO, Yuta ONO
    JIM  2018/03
  • CoCrMnFeNi系高エントロピー合金の照射損傷  [Not invited]
    橋本直幸
    平成29年度材料照射研究会  2018/01
  • Effect of Grain Boundaries on Microstructure Evolution in F82H Under Irradiation  [Not invited]
    Naoyuki HASHIMOTO
    The 18th International Conference of Fusion Reactor Materials  2017/11
  • Effect of Heat Load on Microstructural Development in Irradiated Steels  [Invited]
    Naoyuki HASHIMOTO
    TMS 2017 146th Annual Meeting & Exhibition  2017/02
  • In-situ observation of SiC oxidation under environmentally-controlled electron irradiation  [Not invited]
    Naoyuki HASHIMOTO
    The 41st Inter. Conf. on Adv. Ceramics (ICACC 2017)  2017/01
  • 環境セルを用いたSiCの照射下酸化挙動の直接観察  [Not invited]
    橋本直幸
    日本顕微鏡学会北海道支部学術講演会  2016/12
  • Effect of hydrogen on microstructure evolution and tensile property in irradiated iron  [Not invited]
    Naoyuki HASHIMOTO
    HU-SNU Joint Symposium The 5th Symposium on Materials Science and Engineering  2016/11
  • 被照射鉄鋼材料の熱時効による損傷組織変化  [Not invited]
    橋本直幸
    平成28年度材料照射研究会  2016/10
  • Development of iron-based composite materials with high thermal conductivity  [Not invited]
    Naoyuki HASHIMOTO
    The 7th International Symposium of Advanced Energy Science~ Frontiers of Zero Emission Energy  2016/09
  • Development of iron-based composite materials with high thermal conductivity  [Not invited]
    Naoyuki HASHIMOTO
    The 9th Pacific Rim International Conference on Advanced Materials and Processing (PRICM9)  2016/08
  • 原子炉用鋼における照射損傷組織の熱時効による回復  [Not invited]
    橋本直幸
    日本顕微鏡学会第72回学術講演会  2016/06
  • 安全性を追求した革新的炉心材料利用技術の研究開発 (3) 炉心用SiC材料の雰囲気制御電子線照射試験  [Not invited]
    橋本直幸
    日本原子力学会・2016年春の年会  2016/03
  • Effect of Heat Load on Microstructural Development in Irradiated Steels  [Invited]
    Naoyuki HASHIMOTO
    The Fourth Workshop On TEM With In Situ Irradiation, (WOTWISI-4)  2016/03
  • 被照射低合金鋼の熱処理による組織変化  [Not invited]
    橋本直幸
    日本金属学会日本鉄鋼協会両支部合同冬季講演大会  2015/12
  • フェライト鋼における照射損傷組織の熱処理による回復  [Invited]
    橋本直幸
    日本顕微鏡学会北海道支部学術講演会  2015/12
  • Effect of hydrogen on microstructure evolution and tensile property in irradiated iron  [Not invited]
    Naoyuki HASHIMOTO
    HU-SNU Joint Symposium The 4th Symposium on Materials Science and Engineering  2015/11
  • Development of iron-based composite with high thermal conductivity for DEMO  [Not invited]
    Naoyuki HASHIMOTO
    The 4th Japan-Korea Joint Workshop on Nuclear Materials – Nuclear Fusion Materials  2015/10
  • Effect of hydrogen on microstructure evolution and tensile property in irradiated iron  [Not invited]
    Naoyuki HASHIMOTO
    The 17th International Conference of Fusion Reactor Materials  2015/10
  • フェライト/マルテンサイト鋼の照射下微細組織変化に及ぼす粒界の影響  [Not invited]
    橋本直幸
    日本原子力学会・2015年秋の大会  2015/09
  • Heavy Irradiation Effect on Fe-based Composite Materials with a High Thermal Conductivity  [Not invited]
    Naoyuki HASHIMOTO
    第6回京大エネルギー理工学研究所国際シンポジウム  2015/09
  • Effect of impurity atoms on microstructural change in irradiated Fe-based materials  [Not invited]
    Naoyuki HASHIMOTO
    第6回京大エネルギー理工学研究所国際シンポジウム  2015/09
  • 安全な『水素吸蔵材料による無電力型爆発防止システム』の開発研究Ⅱ(1)全体研究  [Not invited]
    橋本直幸
    日本原子力学会・2015年春の大会  2015/03
  • Interaction between Vacancy-Hydrogen Complexes and Dislocation Motion in Alpha-Iron  [Not invited]
    Naoyuki HASHIMOTO
    Materials Research Society (MRS) 2014 Fall Meeting  2014/12
  • Development and application of environmental cell for In-situ observation of irradiated materials  [Not invited]
    Naoyuki HASHIMOTO
    HU-SNU Joint Symposium The 3rd Symposium on Materials Science and Engineering  2014/11
  • Development of Fe-based composite materials for diverter by sintering with carbon nanofiber  [Not invited]
    Naoyuki HASHIMOTO
    The Nuclear Materials Conference 2014  2014/10
  • Effects of Hydrogen and Helium on Swelling in Electron-irradiated Pure Iron  [Not invited]
    Naoyuki HASHIMOTO
    MH2014  2014/07
  • 安全な『水素吸蔵材料による無電力型爆発防止システム』の開発研究(1)全体研究  [Not invited]
    橋本直幸
    日本原子力学会・2014年春の大会  2014/03

MISC

  • 窪洋志, 橋本直幸, 礒部繁人, 大貫惣明, 王師  日本鉄鋼協会日本金属学会両支部合同冬季講演大会概要集  2015-  35  2015/12/17  [Not refereed][Not invited]
  • 礒部繁人, 松井亨樹, 中川祐貴, 橋本直幸, 大貫惣明  日本鉄鋼協会日本金属学会両支部合同冬季講演大会概要集  2015-  37  2015/12/17  [Not refereed][Not invited]
  • 須貝理佐, 礒部繁人, 橋本直幸, 大貫惣明  日本鉄鋼協会日本金属学会両支部合同冬季講演大会概要集  2015-  36  2015/12/17  [Not refereed][Not invited]
  • 広田裕也, 中川祐貴, 中川祐貴, 礒部繁人, 橋本直幸, 大貫惣明  日本鉄鋼協会日本金属学会両支部合同冬季講演大会概要集  2015-  36  2015/12/17  [Not refereed][Not invited]
  • 窪洋志, 橋本直幸, 礒部繁人, 大貫惣明, 王師  日本金属学会講演概要(CD-ROM)  157th-  ROMBUNNO.315  2015/09/02  [Not refereed][Not invited]
  • 尾森健吾, 礒部繁人, 礒部繁人, 須貝理佐, 日野聡, 王永明, 橋本直幸, 大貫惣明  日本金属学会講演概要(CD-ROM)  157th-  ROMBUNNO.S3.44  2015/09/02  [Not refereed][Not invited]
  • 鈴木恵理子, 橋本直幸, 礒部繁人, 大貫惣明  日本金属学会講演概要(CD-ROM)  157th-  ROMBUNNO.243  2015/09/02  [Not refereed][Not invited]
  • 佐藤裕樹, 阿部陽介, 阿部弘亨, 松川義孝, 叶野翔, 大貫惣明, 橋本直幸  日本金属学会講演概要(CD-ROM)  156th-  ROMBUNNO.299  2015/03/04  [Not refereed][Not invited]
  • Research and Development of Innovative Technologies for Nuclear Reactor Core Material with Enhanced Safety
    Yoshiyuki Kawaharada, Fumihisa Kano, Yumiko Tsuchiya, Kazuo Kakiuchi, Kazunari Okonogi, Shinichi Higuchi, Tatsuya Hinoki, Naoyuki Hashimoto, Somei Ohnuki  WRFPM 2014 2014 Water Reactor Fuel Performance Meeting/ Top Fuel / LWR Fuel Performance Meeting Sendai, Japan  2014/09  [Refereed][Not invited]
  • KIMURA Akihiko, HASHIMOTO Naoyuki, NOH Sanghoon, YABUUCHI Kiyohiro, OHNUKI Somei  Journal of plasma and fusion research  89-  (11)  731  -736  2013/11/25  [Not refereed][Not invited]
     
    ブランケット製作における枢要な課題である構造材料の接合・被覆技術開発および接合部の健全性に及ぼす中性子照射影響を調べ,材料システム統合化を行った.開発が困難とされていたODS鋼の接合法として,固相拡散接合(SSDB)および摩擦撹拌接合(FSW)法が適していることや電子ビーム(EB)溶接したF82H鋼ジョイントの照射後引張特性が母材と同等であることが判明した.また,十分な強度をもつW/ODS鋼ジョイント製作の可能性を示した.
  • 阿部弘亨, 石嵜貴大, 叶野翔, LI Feng, 谷川博康, 濱口大, 橋本直幸, 永瀬丈嗣, 保田英洋  日本原子力学会秋の大会予稿集(CD-ROM)  2013-  ROMBUNNO.B49  2013/08/20  [Not refereed][Not invited]
  • 谷川博康, 安堂正己, 酒瀬川英雄, 渡辺淑之, 叶野翔, 橋本直幸, 阿部弘亨  日本原子力学会秋の大会予稿集(CD-ROM)  2013-  ROMBUNNO.B48  2013/08/20  [Not refereed][Not invited]
  • Hiroshi Oka, Yosuke Yamazaki, Hiroshi Kinoshita, Naoyuki Hashimoto, Somei Ohnuki, Shinichiro Yamashita, Satoshi Ohtsuka  Materials Research Society Symposium Proceedings  1298-  21  -25  2011  [Refereed][Not invited]
     
    Oxide dispersion strengthened austenitic stainless steel (ODS316), which is based on advanced SUS316 steel, has been developed by mechanically alloying and hot extrusion. Hafnium and titanium were added to make a fine distribution of oxide particles. The stability of oxide particles dispersed in ODS316 under irradiation was evaluated after 250 keV Fe+ irradiation up to high doses at 500°C. TEM observation and EDS analysis indicated that fine complex oxide particles with Y, Hf and Ti were mainly dispersed in the matrix. There are no significant changes in the distribution and the size of oxide particles after irradiation. It was also revealed that the constitution ratio of Ti in complex oxide appeared to be decreased after irradiation. This diffuse-out of Ti during irradiation could be explained by the difference in oxide formation energy among alloying elements. © 2011 Materials Research Society.
  • 低放射化フェライト・マルテンサイト鋼接合部の損傷組織に及 ぼすガス原子の効果
    橋本直幸, 長坂琢也, 笠田竜太, 檜木達也, 木村晃彦, 大貫惣明, 鵜飼重治, M. Sokolov, T. Yamamoto  第8回核融合エネルギー連合講演会 新たなエネルギー革命を起こす科学技術“核融合”  2010/06/10  [Refereed][Not invited]
  • 先進核融合炉ブランケット用ODS 鋼の接合・被覆技術開発
    盧相熏, 藪内聖皓, 大野直子, 岩田憲幸, 笠田竜太, 長坂琢也, 檜木達也, 木村晃彦, 橋本直幸, 大貫惣明, 鵜飼重治, M. Sokolov, T. Yamamoto  第8回核融合エネルギー連合講演会 新たなエネルギー革命を起こす科学技術“核融合”  2010/06/10  [Refereed][Not invited]
  • Akifumi Ono, Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki  JOURNAL OF THE JAPAN INSTITUTE OF METALS  74-  (3)  205  -208  2010/03  [Refereed][Not invited]
     
    In situ observation of the catalytic action of MgH2-1 mol%Nb2O5 and MgH2-10 mol%Nb2O5 was carried out by using transmission electron microscopy (TEM). In case of MgH2-1 mol%Nb2O5, TEM analysis indicated that MgH2 started to decompose at 150 degrees C and nano size particle of Mg formed. However, Nb2O5 was not observed in the diffraction pattern and images. In case of MgH2-10 mol%Nb2O5, high resolution images, FFT and IFFT, revealed that the decomposition of MgH2 started with the contact region in Nb2O5 and Mg formed. The result suggested that the reaction of dehydration could proceed due to hydrogen diffusion to the Mg-Nb2O5 interface.
  • In-site TEM observation for reaction of LiH and NaH with NH3 by means of environmental cell
    H. Hirasawa, S. Isobe, Y. Wang, H. Yamamoto, H. Miyaoka, N. Hashimoto, S. Ohnuki, T. Ichikawa, Y. Kojima  Mater. Res. Soc. Symp. Proc.  1216-  W03-34  2010  [Refereed][Not invited]
  • R&D on Materials Engineering for DEMO Blanket: Objective
    H Tanigawa, E Wakai, S Jitsukawa, Komazaki, Y Kohno, R Kasada, K Morishita, A Kimura, Hashimoto, S Ohnuki, H Abe Nogami  implementation in 2007 and 2008, progress, schedule (whole period and breakdown for 2007 and 2008), 2nd Workshop on DEMO in the Broader Approach Activities, Japan Atomic Energy Agency, Tokyo, Japan, 2008.1.28-30  2008  [Refereed][Not invited]
  • Role of Annealing for Improving Hydrogen Storage Properties of Ti-Cr-V Alloy
    Yasuhiro Munekata, Kota Washio, Takanori Suda, Naoyuki Hashimoto, Somei Ohnuki, Hironobu Arashima, Hideaki Ito  Mater. Res. Soc. Symp. Proc.  971E-  Z07  -Z12  2007  [Refereed][Not invited]
  • Development of Environmental Cell and its Application to Hydrogen Storage Materials
    Koya Okudera, Koichi Hamada, Takanori Suda, Naoyuki Hashimoto, Somei Ohnuki, Yasuaki Kawai, Yoshitsugu Kojima  Mater. Res. Soc. Symp. Proc.  981E-  Z07  -Z12  2007  [Refereed][Not invited]
  • Effect of Minor Alloying Element on Dispersing Nano-particles in ODS Steel
    Y. Uchida, S. Ohnuki, N. Hashimoto, T. Suda, T. Nagai, T. Shibayama, K. Hamada, N. Akasaka, S. Yamashita, S. Ohstuka, T. Yoshitake  Mater. Res. Soc. Symp. Proc.  981E-  JJ07  -JJ09  2007  [Refereed][Not invited]
  • Microstructural Analysis on Helium Retention of Ion-irradiated and Annealed Tungsten Foils
    N. Hashimoto, J.D. Hunn, N. Parikh, S. Gilliam, S. Gidcumb, B. Patnaik, L.L. Snead  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (37)  91  -98  2005  [Refereed][Not invited]
  • RL Klueh, N Hashimoto, M Sokolov  Effects of Radiation on Materials: 21st International Symposium  1447-  376  -390  2004  [Refereed][Not invited]
     
    An Fe-9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa) steel has a smaller prior-austenite grain size than this same composition without tantalum (9Cr-2W) when the steels are given a similar heat treatment. Except for prior-austenite grain size, the microstructures of the steels are similar before irradiation, and they develop similar changes in microstructure during irradiation. Nevertheless, the 9Cr-2WVTa shows less effect of irradiation on the Charpy behavior. To determine the effect of grain size on the Charpy properties of the 9Cr-2VrV and 9Cr-2WVTa, specimens of the two steels were given various normalization heat treatments to produce different prior austenite grain sizes, and the tensile and impact properties were determined. For the smaller prior-austenite grain sizes, the 9Cr-2VrV steel had impact properties similar to or better than those of the 9Cr-2WVTa steel. Differences in the microstructures of the steels were used to explain the observations and what they mean for developing steels with improved properties.
  • Helium Retention of Ion-irradiated and Annealed Tungsten Foils
    N. Hashimoto, J.D. Hunn, N. Parikh, S. Gilliam, B. Patnaik, L.L. Snead  Proc. for 04 Symposium on Advanced Research of Energy Technology  2004  [Refereed][Not invited]
  • Analysis of Ta-rich MX Precipitates in RAFs
    H. Tanigawa, H. Sakasegawa, N. Hashimoto, S.J. Zinkle, R.L. Kuleh, A. Kohyama  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (35)  30  -32  2004  [Refereed][Not invited]
  • On The Effect of Fatigue Precracking on The Microstructure Around Precrack in 1TCT Fracture Toughness Specimen of F82H-IEA
    H. Tanigawa, N. Hashimoto, M. Ando, M.A. Sokolov, R.L. Klueh, Fusion Reactor Materials Semiannual Report for Period, Ending December, DOE/ER  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (35)  58  -66  2004  [Refereed][Not invited]
  • TEM Observation Around Crack in Fatigue-precracked 1TCT Fracture Toughness Specimen of F82H-IEA
    N. Hashimoto, H. Tanigawa, M. Ando, M.A. Sokolov  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (35)  67  -70  2004  [Refereed][Not invited]
  • Comparison of Microstructure between Neutron-irradiated Reduced-activation Ferritic/martensitic Steels, F82H-IEA, JLF-1, and ORNL9Cr
    N. Hashimoto, H. Tanigawa, M. Ando, T. Sawai, K. Shiba, R.L. Klueh  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (35)  41  -44  2004  [Refereed][Not invited]
  • SJ Zinkle, N Hashimoto, Y Matsukawa, RE Stoller, YN Osetsky  RADIATION EFFECTS AND ION-BEAM PROCESSING OF MATERIALS  792-  3  -12  2004  [Refereed][Not invited]
     
    Recent molecular dynamics and transmission electron microscopy results on irradiated metallic materials are reviewed, with an emphasis on defect production in the displacement cascade and the fluence- and temperature-dependent accumulation of defect clusters. Materials analyzed include Fe, V, Cu, austenitic stainless steel, V4%Cr4%Ti, and ferritic/martensitic steel. Intrinsic differences between the defect accumulation behavior of body centered cubic (BCC) and face centered cubic (FCC) metals are highlighted. Results on the temperature-dependent vacancy cluster density of Cu are discussed in terms of thermal stability of stacking fault tetrahedra (SFTs). Finally, recent results on deformation behavior of irradiated, quenched, and deformed metals are discussed, with particular emphasis on flow localization mechanisms (e.g., dislocation channeling), and experimental and molecular dynamics studies of the detailed dislocation-defect cluster interactions.
  • 酒瀬川英雄, 谷川博康, HASHIMOTO N, GROSSBECK M L, 荻原寛之, 実川資朗, 幸野豊, 香山晃  日本金属学会講演概要  133rd-  297  2003/10/11  [Not refereed][Not invited]
  • Deformation Microstructure of A Reduced-activation Ferritic/martensitic Steel Irradiated in HFIR
    N. Hashimoto, M. Ando, H. Tanigawa, T. Sawai, K. Shiba, R.L. Klueh  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (33)  73  -78  2003  [Refereed][Not invited]
  • Microstructural Evolution of Reduced-Activation 9Cr-Steels in HFIR-CTR-62/63 Experiment
    N. Hashimoto, R. L. Klueh  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (31)  91  -97  2002  [Refereed][Not invited]
  • Tensile and Creep Properties of An Oxide Dispersion-strengthened Ferritic Steel
    R.L. Klueh, P.J. Maziasz, D.T. Hoelzer, N. Hashimoto, I.S. Kim, K. Miyahara  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (31)  104  -105  2002  [Refereed][Not invited]
  • Mapping Flow Localization Process in Deformation of Irradiated Reactor Structural Alloys
    K. Farrell, T.S. Byun, N. Hashimoto  ORNL/TM-2002  66-  2002  [Refereed][Not invited]
  • Effect of Heat Treatment and Tantalum on Microstructure and Mechanical Properties of Fe-9Cr-2W-0.25V Steel
    R.L. Klueh, N. Hashimoto, M.A. Sokolov  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (32)  28  -39  2002  [Refereed][Not invited]
  • Fracture Surface of A Reduced-activation Martensitic Steel Irradiated in HFIR
    N. Hashimoto, H. Tanigawa, K. Shiba, R.L. Klueh  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (32)  24  -27  2002  [Refereed][Not invited]
  • K Farrell, TS Byun, JW Jones, LT Gibson, RG Sitterson, N Hashimoto, JL Bailey, MJ Gardner  SMALL SPECIMEN TEST TECHNIQUES: FOURTH VOLUME  1418-  283  -293  2002  [Refereed][Not invited]
     
    Irradiation-hardened metals undergo changes in plastic deformation modes that degrade mechanical properties. Variation of deformation mode as a function of fluence and level of strain can be tracked with deformation mode maps. Mapping requires many tensile tests and TEM specimens. To streamline the process, a special tensile test cradle and refined TEM specimen preparation techniques have been developed. The 0.25 mm-thick sheet tensile specimen with dogbone shape is sufficient to ensure bulk mechanical behavior and eliminates grinding operations for the TEM pieces. Extraneous strains that might arise in such a small specimen from pin loading or friction gripping are avoided by loading the specimen under its shoulders in a small, sliding cradle which also prevents accidental damage during remote handling in and out of the tensile machine. After straining, three TEM pieces each 1.5 mm square are cut from the gauge section in one pass in a special jig using a slow speed rotary saw fitted with ganged blades. To accommodate these square specimens during electrochemical thinning, the specimen holder is custom altered. Finally, for TEM examination, the thinned specimen is supported by an auxiliary platform constructed from molybdenum foil rings.
  • Effect of Periodic Temperature Variations on the Microstructure of Neutron-Irradiated Metals
    S.J. Zinkle, N. Hashimoto, D.T. Hoelzer, A.L. Qualls, T. Muroga  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (29)  162  -167  2001  [Refereed][Not invited]
  • A Potential Ferritic/martensitic Steel for Fusion Applications
    R.L. Klueh, N. Hashimoto, R.F. Buck, M.A. Sokolov  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (27)  140  -148  2000  [Refereed][Not invited]
  • Microstructure and Mechanical Properties of Oxide Dispersion-strengthened Steels
    R.L. Klueh, P.J. Maziasz, D.J. Larson, N. Hashimoto, L. Heatherly, M.K. Miller, I-S. Kim, K. Miyahara  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (28)  123  -130  2000  [Refereed][Not invited]
  • Microstructural Evolution of 9Cr-2WVTa Steels in HFIR-CTR62/63 Experiment
    N. Hashimoto, R.L. Klueh  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (28)  147  -154  2000  [Refereed][Not invited]
  • Swelling of F82H Irradiated at 678 K to 7 dpa in HFIR
    Y. Miwa, E. Wakai, K. Shiba, N. Hashimoto, J.P. Robertson, A.F. Rowcliffe  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (25)  175  -182  1999  [Refereed][Not invited]
  • Microstructural Evolution of Cold-worked Austenitic Stainless Steels Irradiated to 17 dpa in Spectrally Tailored Experiments of the ORR and the HFIR at 400°C
    E. Wakai, N. Hashimoto, J.P. Robertson, T. Sawai, A. Hishinuma  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (25)  197  -201  1999  [Refereed][Not invited]
  • Swelling of the HFIR-irradiated F82H, F82H+10B, and F82H+58Ni Steels
    E. Wakai, N. Hashimoto, K. Shiba, Y. Miwa, J.P. Robertson, R.L. Klueh  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (25)  161  -169  1999  [Refereed][Not invited]
  • Hydrogen Production Effect on Microstructure of HFIR-irradiated Low Activation F82H Steel Using 54Fe Isotope
    E. Wakai, N. Hashimoto, K. Shiba, Y. Miwa, J.P. Robertson, R.L. Klueh  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (25)  151  -160  1999  [Refereed][Not invited]
  • Microstructure of Isotopically-tailored F82H and HT9 Irradiated at 400°C in HFIR
    N. Hashimoto, J.P. Robertson, A.F. Rowcliffe, Y. Miwa, K. Shiba  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (26)  170  -174  1999  [Refereed][Not invited]
  • Microstructure of Isotopically Tailored Martensitic Steel HT9 Irradiated at 400°C to 7 dpa in HFIR
    N. Hashimoto, J.P. Robertson, K. Shiba  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (26)  96  -101  1999  [Refereed][Not invited]
  • Damage structure and precipitation behavior of HFIR-irradiated in F82H and F82H+10B steels
    E. Wakai, N. Hashimoto, K. Shiba, J.P. Robertson, R.L. Klueh  Fusion Reactor Materials, DOE/ER  313-23-  170  -178  1998  [Refereed][Not invited]
  • Microstructural Evolution of HFIR-irradiated Low Activation F82H and F82H-10B Steels
    E. Wakai, N. Hashimoto, K. Shiba, T. Sawai, J.P. Robertson, R.L. Klueh, A.F. Rowcliffe, A. Hishinuma  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (23)  190  -197  1998  [Refereed][Not invited]
  • Damage Structure of Austenitic Stainless Steel 316LN Irradiated at Low Temperature in HFIR
    N. Hashimoto, E. Wakai, J.P. Robertson, M.L. Grossbeck, A.F. Rowcliffe  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (23)  234  -242  1998  [Refereed][Not invited]
  • Microstructural Analysis of Ferritic/martensitic Steels Irradiated at Low temperature in HFIR
    N. Hashimoto, E. Wakai, J.P. Robertson, A.F. Rowcliffe  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (24)  163  -170  1998  [Refereed][Not invited]
  • H Kinoshita, N Hashimoto, S Ohnuki, H Takahashi  SCIENCE REPORTS OF THE RESEARCH INSTITUTES TOHOKU UNIVERSITY SERIES A-PHYSICS CHEMISTRY AND METALLURGY  45-  (1)  19  -22  1997/03  [Refereed][Not invited]
     
    A SUS316 and a JPCA were irradiated at 643, 793 and 873 K to 30 dpa in FFTF (Fast Flux Test Facility)/MOTA (Material Open Test Assembly) during its cycle 11 operation to investigate the effect of high helium generation rate on cavity formation under neutron irradiation. In FFTF/MOTA, (n, alpha) reaction of boron isotope can produce a large amount of helium atoms in SUS316 and JPCA. In all of temperature conditions, cavities were observed in both alloys with different contens of B-10. In view of number density, size distribution and mean size of cavity in the alloys, the effect of helium generation rate on the nuclation and the growth of cavity is discussed.
  • Microstructural development of austenitic stainless steels irradiated at 400C to 17 dpa in HFIR
    E. Wakai, N. Hashimoto, T. Sawai, J.P. Robertson, A. Hishinuma  Fusion Reactor Materials, DOE/ER  313-22-  159  -168  1997  [Refereed][Not invited]
  • Microstructural Evolution of Austenitic Stainless Steels Irradiated to 17 dpa in Spectrally Tailored experiment of the ORR and the HFIR at 400oC
    E. Wakai, N.?Hashimoto, T.?Sawai, J.P. Robertson, L.T.?Gibson, I. Ioka, A. Hishinuma  Fusion Reactor Materials Semiannual Report  DOE/ER-0313-  (22)  159  -163  1997  [Refereed][Not invited]
  • Effect of Crystal Orientation on Grain Boundary Migration and Radiation-Induced Segregation
    N. Hashimoto, S. Watanabe, H. Takahashi  Interface Science and Materials Interconnection Proc. of JIMIS-8  383  -386  1996  [Refereed][Not invited]
  • Radiation-Induced Grain Boundary Migration in Alloys
    N. Hashimoto, H. Takahashi  Proc. for 96 Symposium on Advanced Research of Energy Technology  377  -384  1996  [Refereed][Not invited]
  • Effect of Orientation on Grain Boundary Migration and Radiation-induced Segregation under Irradiation
    N. Hashimoto, H. Takahashi  Bulletin of Faculty of Engineering in Hokkaido University  172-  33  -38  1995  [Refereed][Not invited]

Industrial Property Rights

Awards & Honors

  • 2020/09 Materials Science and Technology Division, Atomic Energy Society of Japan Achievement Award
     Study on Impurity Effect on Point Defect Mobility in Atomic Energy Structure Materials 
    受賞者: Naoyuki HASHIMOTO
  • 2019/10 The 19th International Conference on Fusion Reactor Materials Excellent Poster Award
     Effect of H and He on Incoherent Fe/W Interface: A DFT Study 
    受賞者: Jingming SHI;Naoyuki HASHIMOTO
  • 2019/01 JIM Hokkaido Branch Excellent Research Award
     軽金属水酸化物系の水素放出・吸蔵特性評価及び水素放出速度の向上 
    受賞者: F. TANAKA;S. ISOBE;N. HASHIMOTO
  • 2018/11 The 16th International Symposium of Metal-Hydrogen systems Excellent Poster Award
     Catalytic effect on Hydrogen ab/desorption properties of light metal hydroxide system 
    受賞者: F. Tanaka;S. Isobe;Y. Nakagawa;N. Hashimoto
  • 2018/07 JIM Hokkaido Branch Excellent Poster Award
     高エントロピー合金における空孔の移動度 
    受賞者: Yuta ONO;Naoyuki HASHIMOTO
  • 2018/01 材料照射研究会 最優秀ポスター発表賞
     低合金鋼の照射損傷組織に及ぼす熱負荷の影響 
    受賞者: 後藤俊太;橋本直幸
  • 2017/07 日本金属学会北海道支部 奨励賞
     低合金鋼の照射損傷組織に及ぼす熱負荷の影響 
    受賞者: 後藤俊太;橋本直幸
  • 2016/12 日本金属学会北海道支部 奨励賞
     DEMO炉用鉄系複合材料の試作とその機械的性質 
    受賞者: 佐和雄樹;橋本直幸
  • 2016/11 The 5th HU-SNU Joint Symposium on Materials Science and Engineering EXCELLENT POSTER AWARD
     Effect of Surface Coatings on Hydrogen Environment Embrittlement in Fe-8Cr Model Alloy 
    受賞者: Pisanu Punyapor;橋本直幸
  • 2016/10 水素化物に関わる次世代学術・応用展開若手研究会 最優秀ポスター賞
     グラフェン上金属ナノ粒子の水素化特性 
    受賞者: 尾森健吾;礒部繁人;橋本直幸
  • 2016/09 水素若手研究会 優秀ポスター賞
     NbF5添加による AlH3の水素放出速度の改善 
    受賞者: 李忠賢;礒部繁人;橋本直幸
  • 2016/01 Hokkaido University Hokkaido University President Award
     
    受賞者: Naoyuki HASHIMOTO
  • 2015/03 Hokkaido University Hokkaido University President Award
     
    受賞者: Naoyuki HASHIMOTO
  • 2015/02 The 3rd International Doctoral Student Symp. on Materials Science Best Poster Award
     Effect of Hydrogen Environment on Mechanical Properties of Fe-xCr Alloys 
    受賞者: Pisanu Punyaporn;橋本直幸
  • 2014/12 日本顕微鏡学会北海道支部 日本顕微鏡学会北海道支部会支部長賞
     
    受賞者: 澤厚貴;橋本直幸;大貫惣明
  • 2014/11 The 2nd HU-SNU Joint Symposium Excellent Poster Award
     Effect of Lithium Ion Conduction on Hydrogen Desorption of LiNH2-LiH Solid Composite 
    受賞者: 張騰飛;礒部繁人;橋本直幸
  • 2014/09 The 12th Japan-China Symposium on Materials for Advanced Energy Systems and Fission & Fusion Engineering Young Researcher’s Award
     Helium effect on activation volume by nanoindentation 
    受賞者: S. Chen;N. Hashimoto;S. Ohnuki
  • 2014/08 水素若手研究会2014 優秀ポスター賞
     グラフェン上の鉄ナノ粒子の水素吸蔵 ~DFT 計算と放出実験~ 
    受賞者: 中川祐貴;礒部繁人;橋本直幸;大貫惣明
  • 2014/07 日本金属学会・日本鉄鋼協会両支部合同サマーセッション 優秀ポスター賞
     メタルアラネートと複合化処理したアンモニアボランの水素放出プロセスの検討 
    受賞者: 中川祐貴;礒部繁人;橋本直幸;大貫惣明
  • 2013/07 日本金属学会・日本鉄鋼協会両支部合同サマーセッション 優秀ポスター賞
     Mg/Pd薄膜水素貯蔵材料の作製と評価 
    受賞者: 千葉翔太朗;礒部繁人;橋本直幸;大貫惣明
  • 2013/01 日本金属学会北海道支部 奨励賞
     
    受賞者: 佐藤豊;岡弘;橋本直幸;大貫惣明
  • 2012/10 Inter. Symp. on Metal-Hydrogen Systems MH2012 CHALLENGING SPIRITS POSTER AWARD
     In-situ observation in hydrogen stotrage reaction by environmental cell for high voltage electron microscope 
    受賞者: 若杉剛伸;礒部繁人;橋本直幸;大貫惣明
  • 2012/01 日本鉄鋼協会北海道支部 若手表彰
     
    受賞者: 佐久間秀祐;橋本直幸;大貫惣明;谷川博康
  • 2011/08 Asian-Core University Program on Advanced Energy Science, International Symposium on Advanced Energy Systems and Materials Poster Award
     TEM investigation of de/hydrogenation reaction in Li-N-H materials 
    受賞者: T. Zhang;S. Isobe;Y. Wang;Naoyuki HASHIMOTO;S. Ohnuki
  • 2011/07 日本金属学会北海道支部会 優秀ポスター賞
     
    受賞者: 谷本順矢;橋本直幸;大貫惣明;木下博嗣
  • 2011/03 Asian-Core University Program on Advanced Energy Science, International Symposium on Advanced Energy Systems and Materials Poster Award
     In-situ TEM observation of hydrogenation reaction in Mg catalyzed with Nb2O5 
    受賞者: A. Umeda;T. Wakasugi;S. Isobe;Y. Wang;Naoyuki HASHIMOTO;S. Ohnuki
  • 2011/03 Asian-Core University Program on Advanced Energy Science, International Symposium on Advanced Energy Systems and Materials Poster Presentation Award
     Study on Decomposition Process of Sodium Alanate by Means of Transmission Electron Microscope 
    受賞者: Hao Yao;S. Isobe;Y. Wang;Naoyuki HASHIMOTO;S. Ohnuki
  • 2011/01 日本金属学会・鉄鋼協会北海道支部合同講演大会 研究奨励賞
     High Resolution Electron Microscopy Observation of Intermetallic Compound formed in the Coated Layer on Nb Substrate 
    受賞者: S. Eni;Y. Wang;Naoyuki HASHIMOTO;S. Ohnuki;T.Narita
  • 2011/01 日本金属学会・鉄鋼協会北海道支部合同講演大会 奨励賞
     水素化マグネシウムの反応速度と触媒表面の化学結合状態の関係 
    受賞者: 森田襟;馬濤;礒部繁人;王永明;橋本直幸;大貫惣明;木村通;市川貴之;小島由継
  • 2010/12 日本顕微鏡学会北海道支部 若手研究奨励賞
     
    受賞者: 佐久間秀祐;橋本直幸;大貫惣明;谷川博康
  • 2010/10 10th Japan China Symposium Materials for Advanced Energy Systems and Fission & Fusion Engineering EXCELLENT POSTER AWARD
     Effect of H and He on microstructural evolution in Ferritic/martensitic steels during iraradiation 
    受賞者: S. Wang;Naoyuki HASHIMOTO;S. Ohnuki
  • 2010/07 日本金属学会・鉄鋼協会北海道支部合同講演大会 優秀ポスター賞
     水素貯蔵材料AB-MH(M=Li,Na)複合物質の微細構造 
    受賞者: 李忠賢;礒部繁人;王永明;橋本直幸;大貫惣明;Yu Zhang;市川貴之;小島由継
  • 2010/03 Japan Institute of Metals Metallography Award
     Dislocation Channeling Deformation in Neutron-irradiated 316SS 
    受賞者: Naoyuki HASHIMOTO
  • 2010/03 Japan Institute of Metals Excellent Paper Award
     
    受賞者: A. Ono;S. Isobe;Y. Wang;N. Hashimoto;S. Ohnuki
  • 1996/07 Japan Institute of Metals Excellent Poster Award
     
    受賞者: Naoyuki HASHIMOTO
  • 1995/12 Japan Institute of Metals Excellent Poster Award
     
    受賞者: Naoyuki HASHIMOTO

Research Grants & Projects

  • Research on New FCC Structure Materials by Stacking Fault Energy Control
    JSPS:科学研究助成基金助成金 基盤研究C
    Date (from‐to) : 2020/04 -2023/03
  • 低放射化高濃度固溶体合金の探索と創製
    JSPS:Grant-in-Aid for Scientific Research on Innovative Areas
    Date (from‐to) : 2019/04 -2021/03 
    Author : Naoyuki HASHIMOTO
  • 核分裂生成物の個体核燃料に対するぬれ性と放出挙動
    日本学術振興会:科学研究助成基金助成金 基盤研究B
    Date (from‐to) : 2018/04 -2021/03 
    Author : 黒崎 健
  • 無電力型高機能水素捕集装置の開発及び高性能化
    北海道ガス:大学研究支援
    Date (from‐to) : 2015/04 -2016/03 
    Author : 橋本直幸
  • 安全性を追求した革新的炉心材料利用技術に関する研究開発
    科学技術振興機構:原子力システム研究開発
    Date (from‐to) : 2012/10 -2016/03 
    Author : 吉田紀之
  • 安全な『水素吸蔵材料による無電力型 爆発防止システム』の開発研究
    科学技術振興機構:原子力基礎基盤戦略研究イニシアティブ
    Date (from‐to) : 2012/10 -2015/03 
    Author : 橋本直幸
  • 日本学術振興会:科学研究助成基金助成金 挑戦的萌芽研究
    Date (from‐to) : 2012/04 -2015/03 
    Author : 橋本直幸
  • 定置水素貯蔵高圧タンク材料の水素脆性に及ぼす表面層の寄与
    北海道ガス:大学研究支援
    Date (from‐to) : 2010/04 -2011/03 
    Author : 橋本直幸

Educational Activities

Teaching Experience

  • Advanced Energy Materials
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : Energy Reactor Materials (Fission, Fusion), Radiation Damage, Hydrogen Storage Materials, Metal-Hydrogen System, Hydrogen embrittlement
  • Advanced Energy Materials
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 工学院
    キーワード : Energy Reactor Materials (Fission, Fusion), Radiation Damage, Hydrogen Storage Materials, Metal-Hydrogen System, Hydrogen embrittlement
  • Advanced Energy Materials
    開講年度 : 2018
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : エネルギー炉用材料(原子炉材料,核融合炉材料)、照射損傷、水素吸蔵材料、金属‐水素系熱力学、水素脆性
  • Advanced Energy Materials
    開講年度 : 2018
    課程区分 : 博士後期課程
    開講学部 : 工学院
    キーワード : Energy Reactor Materials (Fission, Fusion), Radiation Damage, Hydrogen Storage Materials, Metal-Hydrogen System, Hydrogen embrittlement
  • Introduction to Material Physics
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 結晶構造 結晶欠陥 固体拡散 材料の強度 転位
  • Engineering Materials - Metals and Alloys
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 鉄鋼材料、非鉄材料、構造材料、機能材料、材料設計
  • Introduction to Materials Engineering
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 金属材料、電子、原子、結晶構造、機能性、構造材、表面、反応プロセス
  • Engineering of Materials Design
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 金属材料、電子、原子、結晶構造、機能性、構造材、表面、反応プロセス


Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.