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Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*
Materials Transactions, 65(8), p.899 - 906, 2024/08
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)It is indispensable to suppress hydrogen embrittlement (HE) to develop the strength of the Al-Zn-Mg alloy. Because intergranular fracture (IGF) is mainly observed when HE occurs in the alloy, we need to understand the IGF initiation to suppress HE. In the present study, we investigated the stress, strain, and H concentration, which influence the IGF initiation, in actual fractured regions by simulation of a crystal plasticity finite element method and H diffusion analysis in a 3D image-based model, which was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. Combining the simulation and in-situ observation of the tensile test sample by X-ray CT, we examined the stress, strain, and H concentration, and discussed the IG crack initiation condition. As a result, it is revealed that stress normal to grain boundary induced by crystal plasticity dominates IG crack initiation while the accumulation of H due to stress has little impact on it.
Fujihara, Hiro*; Toda, Hiroyuki*; Ebihara, Kenichi; Kobayashi, Masakazu*; Mayama, Tsuyoshi*; Hirayama, Kyosuke*; Shimizu, Kazuyuki*; Takeuchi, Akihisa*; Uesugi, Masayuki*
International Journal of Plasticity, 174, p.103897_1 - 103897_22, 2024/03
Times Cited Count：9 Percentile：93.27(Engineering, Mechanical)Hydrogen(H) embrittlement in high-strength aluminum(Al) alloys is a crucial problem. H accumulation at the interface of precipitates in Al alloy is considered to cause embrittlement. However, there is no quantitative knowledge regarding the interaction between H distribution and stress field near cracks. In this study, using a multi-modal three-dimensional image-based simulation combining the crystal plasticity finite element method and H diffusion analysis, we tried to capture the stress distribution near the crack, its influence on the H distribution, and the probability of crack initiation in the experimental condition. As a result, it was found that grain boundary cracks transition to quasi-cleavage cracks in the region where the cohesive energy of the semi-coherent interface of MgZn
precipitates decreases due to H accumulation near the tip. We believe the present simulation method successfully bridges nanoscale delamination and macroscale brittle fracture.
Taniguchi, Koji*; Huang, P.-J.*; Sagayama, Hajime*; Kiyanagi, Ryoji; Oishi, Kazuki*; Kito, Shunsuke*; Nakamura, Yuiga*; Miyasaka, Hitoshi*
Physical Review Materials (Internet), 8(2), p.024409_1 - 024409_10, 2024/02
Times Cited Count：3 Percentile：51.02(Materials Science, Multidisciplinary)Tang, J.*; Wang, Y.*; Fujihara, Hiro*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; Ebihara, Kenichi; Takeuchi, Akihisa*; Uesugi, Masayuki*; Toda, Hiroyuki*
Scripta Materialia, 239, p.115804_1 - 115804_5, 2024/01
Times Cited Count：11 Percentile：80.41(Nanoscience & Nanotechnology)Stress corrosion cracking (SCC) behaviors induced by the combination of external and internal hydrogen (H) in an Al-Zn-Mg-Cu alloy were systematically investigated via in situ 3D characterization techniques. SCC of the Al-Zn-Mg-Cu alloy could initiate and propagate in the potential crack region where the H concentration exceeded a critical value, in which the nanoscopic H-induced decohesion of 
-MgZn precipitates resulted in macroscopic cracking. External H that penetrated the alloy from the environment played a crucial role during the SCC of the Al-Zn-Mg-Cu alloy by generating gradient-distributed H-affected zones near the crack tips, which made Al alloys in water environment more sensitive to SCC. Additionally, the pre-existing internal H was driven toward the crack tips during plastic deformation. It was involved in the SCC and made contributions to both the cracks initiation and propagation.
Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*
Keikinzoku, 73(11), p.530 - 536, 2023/11
In Al-Zn-Mg alloys, suppression of hydrogen embrittlement is necessary to improve their strength. In this study, the distribution of stress, strain, and hydrogen concentration in the actual fracture region was investigated using the crystal plasticity finite element method and hydrogen diffusion analysis based on a model derived from three-dimensional polycrystalline microstructural data obtained by X-ray CT. In addition, the distributions of stress, strain, and hydrogen concentration were compared with the actual crack initiation behavior by combining in-situ observation of tensile tests using X-ray CT and simulation. The results show that stress loading perpendicular to the grain boundary due to crystal plasticity dominates grain boundary crack initiation. It was also found that internal hydrogen accumulation due to crystal plasticity has little effect on crack initiation.
Ishii, Yui*; Yamamoto, Arisa*; Sato, Naoki*; Nambu, Yusuke*; Kawamura, Seiko; Murai, Naoki; Ohara, Koji*; Kawaguchi, Shogo*; Mori, Takao*; Mori, Shigeo*
Physical Review B, 106(13), p.134111_1 - 134111_7, 2022/10
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Uehara, Akihiro*; Akiyama, Daisuke*; Ikeda, Atsushi; Numako, Chiya*; Terada, Yasuko*; Nitta, Kiyofumi*; Ina, Toshiaki*; Takeda-Homma, Shino*; Kirishima, Akira*; Sato, Nobuaki*
Journal of Nuclear Materials, 559, p.153422_1 - 153422_11, 2022/02
Times Cited Count：4 Percentile：51.78(Materials Science, Multidisciplinary)MnGa thin films underneath a protection layerKono, Takashi*; Kakoki, Masaaki*; Yoshikawa, Tomoki*; Wang, X.*; Sumida, Kazuki; Muro, Takayuki*; Goto, Kazuki*; Sakuraba, Yuya*; Umetsu, Rie*; Kimura, Akio*
Physical Review B, 104(19), p.195112_1 - 195112_8, 2021/11
Times Cited Count：5 Percentile：23.69(Materials Science, Multidisciplinary)Angle-resolved photoelectron spectroscopy utilizing soft X-ray synchrotron radiation was applied to Heusler-type CoMnGa thin films that have a 1-nm Al capping layer. The bulk Fermi surfaces and band structures varied along the out-of-plane momentum, stemming from the three-dimensional crystal structure, in the absence of any in situ surface treatment. In addition, there were characteristic intersecting bands (Weyl cones), with crossing points near the Fermi level, which were consistent with computed results. The Weyl cones are of bulk origin and are responsible for the high anomalous Nernst and the anomalous Hall coefficients. A close comparison of the experimental band structures in CoMnGe and CoMnGa indicated that the rigid band picture is valid in both alloys and that fine carrier tuning is possible by replacing Ga with Ge to improve the anomalous conductivity.
Matsumura, Daiju; Kato, Kazuo*
Hoshako, 34(1), p.3 - 11, 2021/01
no abstracts in English
Al
(
= La, Ce, 
= Cu, Au)Tsutsui, Satoshi*; Kaneko, Koji; Pospisil, J.; Haga, Yoshinori
Physica B; Condensed Matter, 536, p.24 - 27, 2018/05
Times Cited Count：3 Percentile：13.43(Physics, Condensed Matter)
synchrotron X-ray diffraction during heatingMorooka, Satoshi; Kanata, Hiroyuki*; Oba, Yojiro*; Sato, Masugu*
Heisei-28-Nendo SPring-8 Sangyo Shinbunya Shien Kadai, Ippan Kadai (Sangyo Bunya) Jisshi Hokokusho, p.95 - 98, 2017/00
no abstracts in English
Ni synchrotron radiation-based M
ssbauer spectroscopy of nickel-based nanoparticles with hexagonal structureMasuda, Ryo*; Kobayashi, Yasuhiro*; Kitao, Shinji*; Kurokuzu, Masayuki*; Saito, Makina*; Yoda, Yoshitaka*; Mitsui, Takaya; Hosoi, Kohei*; Kobayashi, Hirokazu*; Kitagawa, Hiroshi*; et al.
Scientific Reports (Internet), 6, p.20861_1 - 20861_8, 2016/02
Times Cited Count：10 Percentile：40.59(Multidisciplinary Sciences)
Co
O filmHu, W.*; Hayashi, Koichi*; Fukumura, Tomoteru*; Akagi, Kazuto*; Tsukada, Masaru*; Happo, Naohisa*; Hosokawa, Shinya*; Owada, Kenji; Takahashi, Masamitsu; Suzuki, Motohiro*; et al.
Applied Physics Letters, 106(22), p.222403_1 - 222403_5, 2015/06
Times Cited Count：41 Percentile：80.40(Physics, Applied)ssbauer spectroscopyMibu, Ko*; Mitsui, Takaya; Tanaka, Masaaki*; Masuda, Ryo*; Kitao, Shinji*; Kobayashi, Yasuhiro*; Yoda, Yoshitaka*; Seto, Makoto*
Journal of Applied Physics, 117(17), p.17E126_1 - 17E126_4, 2015/05
Times Cited Count：2 Percentile：8.37(Physics, Applied)Kishimoto, Shunji*; Mitsui, Takaya; Haruki, Rie*; Yoda, Yoshitaka*; Taniguchi, Takashi*; Shimazaki, Shoichi*; Ikeno, Masahiro*; Saito, Masatoshi*; Tanaka, Manobu*
Journal of Instrumentation (Internet), 10(5), p.C05030_1 - C05030_6, 2015/05
Times Cited Count：6 Percentile：25.87(Instruments & Instrumentation)
Fe polarization dependent synchrotron Mssbauer spectroscopy using a diamond phase plate and an iron borate nuclear Bragg monochromatorMitsui, Takaya; Imai, Yasuhiko*; Masuda, Ryo*; Seto, Makoto*; Mibu, Ko*
Journal of Synchrotron Radiation, 22(2), p.427 - 435, 2015/03
Times Cited Count：11 Percentile：50.01(Instruments & Instrumentation)Motokawa, Ryuhei; Endo, Hitoshi*; Yokoyama, Shingo*; Ogawa, Hiroki*; Kobayashi, Toru; Suzuki, Shinichi; Yaita, Tsuyoshi
Langmuir, 30(50), p.15127 - 15134, 2014/12
Times Cited Count：27 Percentile：60.68(Chemistry, Multidisciplinary)Murakami, Motohiko*; Goncharov, A. F.*; Hirao, Naohisa*; Masuda, Ryo*; Mitsui, Takaya; Thomas, S. M.*; Bina, C. R.*
Nature Communications (Internet), 5, p.5428_1 - 5428_6, 2014/11
Times Cited Count：20 Percentile：49.86(Multidisciplinary Sciences)Fe by multichannel scaling with a 64 pixel silicon avalanche photodiode linear-array detectorKishimoto, Shunji*; Mitsui, Takaya; Haruki, Rie*; Yoda, Yoshitaka*; Taniguchi, Takashi*; Shimazaki, Shoichi*; Ikeno, Masahiro*; Saito, Masatoshi*; Tanaka, Manobu*
Review of Scientific Instruments, 85(11), p.113102_1 - 113102_5, 2014/11
Times Cited Count：9 Percentile：37.59(Instruments & Instrumentation)
-bearing Mg-perovskite and its crystal chemistry at high pressureMashimo, Izumi*; Otani, Eiji*; Hirao, Naohisa*; Mitsui, Takaya; Masuda, Ryo*; Seto, Makoto*; Sakai, Takeshi*; Takahashi, Suguru*; Nakano, Satoshi*
American Mineralogist, 99(8-9), p.1555 - 1561, 2014/08
Times Cited Count：7 Percentile：22.19(Geochemistry & Geophysics)