Yamaguchi, Masatake; Tsuru, Tomohito; Ebihara, Kenichi; Itakura, Mitsuhiro; Matsuda, Kenji*; Shimizu, Kazuyuki*; Toda, Hiroyuki*
Materials Transactions, 61(10), p.1907 - 1911, 2020/10
no abstracts in English
Harjo, S.; Aizawa, Kazuya; Gong, W.*; Kawasaki, Takuro
Materials Transactions, 61(5), p.828 - 832, 2020/04
Konno, Azusa; Ono, Naoko*; Ukai, Shigeharu*; Kondo, Sosuke*; Hashitomi, Okinobu*; Kimura, Akihiko*
Materials Transactions, 60(11), p.2260 - 2266, 2019/11
A stability of cuboidal ' phase under heavy irradiation was studied for newly developed Ni-based Oxide Dispersion Strengthened (ODS) superalloy as a candidate for the core structural materials in VHTR or GFR. The ion irradiation was applied at 873K, 1073K, 1273K and the dose was 100 dpa. The ' phase remained the cuboidal shape at 873K but got out of the shape at 1073K after irradiation. Those growths can be explained by the Nelson-Hudson-Mazey (NHM) model. For the result of 1273K irradiation, however, huge ' phase appeared in the whole irradiated area at the post irradiation-observation. This behavior is interpreted in terms of disordering of the ordered ' phase due to cascade collision, and thus increasing Gibbs free energy of the disordered phase induces a change of the element distribution inside the irradiated area. The ordered ' phase was reproduced from the disordered state at the cooling after ion irradiation.
Saito, Kei*; Hirade, Tetsuya; Takai, Kenichi*
Metallurgical and Materials Transactions A, 50(11), p.5091 - 5102, 2019/11
An attempt was made to separate and identify hydrogen peaks desorbed from lattice defects formed by plastic-strain in the presence of hydrogen in tempered martensitic steel showing quasi-cleavage fracture using thermal desorption spectroscopy from a low temperature (L-TDS) and positron annihilation spectroscopy (PAS). The L-TDS results made it possible to separate two peaks, namely, that of the original desorption and also that of new desorption. The PAS results revealed that the new desorption obtained by L-TDS corresponded to vacancy-type defects. Hydrogen enhanced vacancy-type defect concentration, approximately 10 order in terms of atomic ratio, formed within 1.5 mm from the fracture surface, These results indicate that the accumulation of excess vacancy-type defects enhanced by hydrogen in the local region can lead to nanovoid nucleation and coalescence in plastic deformation, resulting in quasi-cleavage fracture of tempered martensitic steel.
Matsuda, Kenji*; Yasumoto, Toru*; Bendo, A.*; Tsuchiya, Taiki*; Lee, S.*; Nishimura, Katsuhiko*; Nunomura, Norio*; Marioara, C. D.*; Lervik, A.*; Holmestad, R.*; et al.
Materials Transactions, 60(8), p.1688 - 1696, 2019/08
no abstracts in English
Wakui, Takashi; Ishii, Hideaki*; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Wakai, Eiichi; Takada, Hiroshi; Futakawa, Masatoshi
Materials Transactions, 60(6), p.1026 - 1033, 2019/06
The mercury target has large size as 22.214.171.124 m. In view of reducing the amount of wastes, we studied the structure so that the fore part could be separated. The flange is required to have high seal performance less than 110 Pa m/s. Invar with low thermal expansion is a candidate. Due to its low stiffness, however, the flange may deform when it is fastened by bolts. Practically invar is reinforced with stainless steel where all interface between them has to be bonded completely with the HIP bonding. In this study, we made specimens at four temperatures and conducted tensile tests. The specimen bonded at 973 K had little diffusion layer, and so fractured at the interface. The tensile strength reduced with increasing the temperature, and the reduced amount was about 10% at 1473 K. The analyzed residual stresses near the interface increased by 50% at maximum. Then, we concluded that the optimum temperature was 1173 K.
Kitamura, Akane; Ishikawa, Norito; Kondo, Keietsu; Fujimura, Yuki; Yamamoto, Shunya*; Yamaki, Tetsuya*
Transactions of the Materials Research Society of Japan, 44(3), p.85 - 88, 2019/06
Swift heavy ions can create nanosized hillocks on the surfaces of various ceramics. When these materials are irradiated with swift heavy ions at normal incidence, each ion impact results in the formation of a single hillock on the surfaces. In contrast, irradiation at grazing incidence forms chains of multiple hillocks on the surface, for example, for strontium titanate (SrTiO). So far, chains of multiple hillocks have been investigated using atomic force microscopy (AFM). It should be noted that AFM measurements involve systematic errors of several nanometers due to the finite size of the probe tip. Consequently, it is possible that the image of one hillock may merge with that of a neighboring hillock even if the two hillocks are well separated. In contrast to AFM, field-emission scanning electron microscopy (FE-SEM) is a useful technique for obtaining higher-resolution images. In this study, we observed multiple nanohillocks on the surfaces of SrTiO using FE-SEM. Crystals of SrTiO(100) and 0.05 wt% Nb-doped SrTiO(100) were irradiated with 350 MeV Xe ions, respectively, at grazing incidence, where the angle between the sample surface and the beam was less than 2. On the SrTiO surface, a chain of periodic nanohillocks is created along the ion path. In contrast, black lines accompanied by hillocks are observed on the Nb-doped SrTiO surface.
Sekio, Yoshihiro; Sakaguchi, Norihito*
Materials Transactions, 60(5), p.678 - 687, 2019/05
The quantitative evaluation of vacancy migration energies in high nickel model alloy was conducted by analyzing the void denuded zone (VDZ) width formed near grain boundaries under neutron and electron irradiation. The microstructures of Fe-15Cr-xNi (x=15, 20, 25, 30 mass%) alloys that were neutron irradiated at 749 K and electron irradiated at 576 K-824 K were examined. The VDZ widths increased with increasing Ni content in both irradiation experiments, which implies an increase of the vacancy mobility. The vacancy migration energies were estimated from the temperature dependence of the VDZ widths, and the energies were 1.09, 0.97, 0.90, and 0.77 eV for the alloys containing 15, 20, 25, and 30 mass% Ni, respectively. From the obtained energies, the effective vacancy diffusivity and excess vacancy concentration were estimated using the analytical equation of the VDZ width, which quantitatively confirmed the increase of the vacancy mobility with increasing Ni content.
Yoneda, Yasuhiro; Harada, Makoto; Takano, Masahide
Transactions of the Materials Research Society of Japan, 44(2), p.61 - 64, 2019/04
We performed three-dimensional observation of simulated fuel debris using Synchrotron Computed Tomography (CT). CT was used to make the inside of fuel debris clear. The CT observation provides that a clear contrast in the zirconia rich part and concrete rich part. Zirconia heavier than concrete moved to the lower part when crystals precipitate and aggregates near the bottom surface. As a result, phase separation occurs. The phase separation is caused by the difference in the composition ratio of zirconia, and can also be observed difference in crystal growth mode by composition ratio.
Igawa, Naoki; Kodama, Katsuaki; Taguchi, Tomitsugu*; Yoshida, Yukihiko*; Matsukawa, Takeshi*; Hoshikawa, Akinori*; Ishigaki, Toru*
Transactions of the Materials Research Society of Japan, 43(6), p.329 - 332, 2018/12
For the understanding of the crystal structural effect on the electrical properties, the local disorder in BaSnInO which is one of the excellent proton conductors for solid oxide fuel cells was estimated by using the Atomic Pair Distribution Function (PDF) analysis method with the neutron diffraction. The local structure is almost the same as the average structure which was estimated by the Rietveld analysis using the cubic crystal structure (space group, ) in the atomic distance range of 6. The PDF profile was fitted better using the tetragonal crystal structure with the space group of 4/ than those with in the range 6. Those results indicate the presence of the local disorder in the lattice. In this work, the relationship between the average and local structures of BaSnInO will be discussed.
Kato, Masaji*; Nara, Yoshitaka*; Okazaki, Yuki*; Kono, Masanori*; Sato, Toshinori; Sato, Tsutomu*; Takahashi, Manabu*
Materials Transactions, 59(9), p.1427 - 1432, 2018/09
To ensure the safe geological disposal of radioactive waste, it is important to determine the permeability (hydraulic conductivity) of clays. The transient pulse method is suitable for low-permeability materials because it requires a relatively short time to determine their permeability. Upstream pore pressure typically increases in the measurement conducted via the transient pulse method. However, this procedure cannot be used to determine the permeability of clays due to the increase in pore pressure. Therefore, the transient pulse method has never been applied to determine clay permeability. In this study, we applied the transient pulse method to a clay sample to determine its permeability while decreasing the downstream pore pressure.
Murasawa, Kodai*; Takamura, Masato*; Kumagai, Masayoshi*; Ikeda, Yoshimasa*; Suzuki, Hiroshi; Otake, Yoshie*; Hama, Takayuki*; Suzuki, Shinsuke*
Materials Transactions, 59(7), p.1135 - 1141, 2018/07
Suzuki, Yoshitaka; Kitagawa, Tomoya*; Namekawa, Yoji*; Matsukura, Minoru*; Nishikata, Kaori; Mimura, Hitoshi*; Tsuchiya, Kunihiko
Transactions of the Materials Research Society of Japan, 43(2), p.75 - 80, 2018/04
no abstracts in English
Yoneda, Yasuhiro; Kunisada, Ryoichi*; Chikada, Tsukasa*; Ueno, Shintaro*; Ohara, Koji*; Wada, Satoshi*
Transactions of the Materials Research Society of Japan, 43(2), p.93 - 96, 2018/04
KNbO nanocrystals were grown by solvothermal technique assisted by a microwave treatment. We performed high-energy X-ray diffraction to extract average and local structural parameters. The particle size can be evaluated by the Scherrer's equation. The unit cell size was reduced as the particle size increased. The local structure was found to be a rhombohedral structure, which was similar to that of the bulk KNbO.
Harjo, S.; Kawasaki, Takuro; Tomota, Yo*; Gong, W.*; Aizawa, Kazuya; Tichy, G.*; Shi, Z.*; Ungar, T.*
Metallurgical and Materials Transactions A, 48(9), p.4080 - 4092, 2017/09
Kojima, Hiroshi*; Kaneno, Yasuyuki*; Ochi, Masaaki*; Semboshi, Satoshi*; Hori, Fuminobu*; Saito, Yuichi*; Ishikawa, Norito; Okamoto, Yoshihiro; Iwase, Akihiro*
Materials Transactions, 58(5), p.739 - 748, 2017/05
Bulk samples of NiNb and NiTa intermetallic compounds were irradiated with 16 MeV Au, 4.5 MeV Ni, 4.5 MeV Al, 200 MeV Xe and 1.0 MeV He ions, and the change in near-surface lattice structure was investigated by means of the grazing incidence X-ray diffraction (GIXD)and EXAFS. The NiNb and NiTa lattice structures transform from the ordered structures (orthorhombic and monoclinic structures for NiNb and NiTa, respectively) to the amorphous state by the Au, Ni, Al and Xe ion irradiations. Irrespective of such heavy ion species or energies, the lattice structure transformation to the amorphous state almost correlate with the density of energy deposited through elastic collisions.
Yoneda, Yasuhiro; Tsuji, Takuya; Matsumura, Daiju; Okamoto, Yoshihiro; Takaki, Seiya; Takano, Masahide
Transactions of the Materials Research Society of Japan, 42(2), p.23 - 26, 2017/04
ZnN is a possible candidate for the diluent material for nitride fuels containing transuranium elements. Pellets of inert matrix material ZrN, and surrogate nitride fuel material DyZrN, are fabricated for the purpose of investigating the crystal structure. Lattice parameters of DyZrN followed the Vegard's low, in spite of the large lattice mismatch ( 7%) between DyN and ZrN. Local structure analysis was performed by X-ray absorption fine structure (XAFS) and atomic pair-distribution function (PDF) methods. The Zr-N nearest neighbor bond distance changed as changing the Dy composition. The complex local structure of DyN and ZrN is related to the preferable effects of ZrN.
Mayumi, Ren*; Semboshi, Satoshi*; Okamoto, Yoshihiro; Saito, Yuichi*; Yoshiie, Toshimasa*; Iwase, Akihiro*
Transactions of the Materials Research Society of Japan, 42(1), p.9 - 14, 2017/02
AlCu binary alloys were irradiated with 16 MeV Au, 4.5 MeV Ni or 4.5 MeV Al ions at room temperature. Changes in surface hardness and the local atomic structure around Cu atoms were examined by using the Vickers hardness measurement and the EXAFS measurements, respectively. Some specimens were aged at 453 K and Vickers hardness was measured. The computer simulation was also performed by using the rate equation method. The hardness of irradiated specimens increased much faster than that of the aged specimens and it became larger than the maximum value of the hardness for the aged specimens. The comparison of the experimental EXAFS result with that of FEFF simulation suggests that the ion irradiation produced small Cu precipitates in the specimens. The computer simulation visualized the growth process of Cu precipitates during the irradiation, and the result qualitatively corresponds to the experimental result.
Ebihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake
Materials Transactions, 58(1), p.26 - 32, 2017/01
In order to evaluate grain boundary (GB) phosphorous (P) segregation in nuclear reactor pressure vessel steels under irradiation, the rate-theory model based on first-principles calculations is developed. In this study, we evaluated the diffusion coefficient of the mixed interstitial dumbbell of a P atom and an iron(Fe) atom using a kinetic Monte Carlo (kMC) simulation based on first-principles calculations. The evaluated diffusion coefficient was almost the same with the diffusion coefficient of P atoms which migrate via octahedral interstitial sites, and was much faster than that for P transport by vacancies. Furthermore, from the simulation of the irradiation induced GB P segregation using the model which was modified to include P atoms of octahedral interstitial sites, it was found that the boundary condition at GB is not valid for P atoms of octahedral interstitial sites
Ungr, T.*; Harjo, S.; Kawasaki, Takuro; Tomota, Yo*; Ribrik, G.*; Shi, Z.*
Metallurgical and Materials Transactions A, 48(1), p.159 - 167, 2017/01