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Shimizu, Kazuyuki*; Yamaguchi, Masatake; Akamaru, Satoshi*; Nishimura, Katsuhiko*; Abe, Rion*; Sasaki, Taisuke*; Wang, Y.*; Toda, Hiroyuki*
Scripta Materialia, 265, p.116730_1 - 116730_7, 2025/08
Shimizu, Kazuyuki*; Toda, Hiroyuki*; Hirayama, Kyosuke*; Fujihara, Hiro*; Tsuru, Tomohito; Yamaguchi, Masatake; Sasaki, Taisuke*; Uesugi, Masayuki*; Takeuchi, Akihisa*
International Journal of Hydrogen Energy, 109, p.1421 - 1436, 2025/03
Times Cited Count:1 Percentile:0.00(Chemistry, Physical)Our preceding investigation revealed that multiple hydrogen traps at coherent interfaces of MgZn precipitates initiated spontaneous interface decohesion, causing hydrogen-induced quasicleavage cracking in Al-Zn-Mg alloys. Herein, we performed a quantitative and systematic investigation to discern the mechanisms by which hydrogen trapped at coherent/semi-coherent interfaces of precipitates could influence macroscopic hydrogen embrittlement by modulating the coherent interface of MgZn
through aging. To explore this hydrogen embrittlement phenomenon based on hydrogen trapping at the precipitate interface, we determined the hydrogen trapping energy of the semi-coherent MgZn
interface via first-principles calculations (0.56 eV/atom). Hydrogen partitioning of all hydrogen trapping sites, including vacancies, grain boundaries, and coherent and semi-coherent MgZn
interfaces, revealed that in overaged alloys, over 90% of the hydrogen was sequestered at semi-coherent interfaces. Owing to the inherent characteristics of the MgZn
interface, the hydrogen sequestered at the semi-coherent interface decreased the interfacial cohesive energy, causing semispontaneous decohesion of the interface and quasicleavage fracture in the Al-Zn-Mg alloys. These results implied that intergranular fracture was not directly induced by hydrogen trapped at grain boundaries but rather by the decohesion of precipitate interfaces along grain boundaries.
Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito
Scripta Materialia, 255, p.116366_1 - 116366_5, 2025/01
Times Cited Count:0 Percentile:0.00(Nanoscience & Nanotechnology)Reduction of grain boundary cohesive energy by hydrogen has been considered as one of the candidate causes of grain boundary fracture in steels and aluminum alloys. Recently, the effects of grain boundary segregation elements have been investigated by first-principles calculations, but there are few studies that quantitatively estimate the grain boundary cohesive energy. In this study, we describe a quantitative evaluation method using first-principles calculation results and show some examples of experimental calculations.
Okada, Kazuho*; Shibata, Akinobu*; Kimura, Yuji*; Yamaguchi, Masatake; Ebihara, Kenichi; Tsuji, Nobuhiro*
Acta Materialia, 280, p.120288_1 - 120288_14, 2024/11
Times Cited Count:1 Percentile:0.00(Materials Science, Multidisciplinary)Ahmed, A.*; Uttarasak, K.*; Tsuchiya, Taiki*; Lee, S.*; Nishimura, Katsuhiko*; Nunomura, Norio*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; Toda, Hiroyuki*; Yamaguchi, Masatake; et al.
Journal of Alloys and Compounds, 988, p.174234_1 - 174234_9, 2024/06
Times Cited Count:10 Percentile:96.34(Chemistry, Physical)This study aims to clarify the growth process of the-phase in Al-Mg-Si alloys from the point of view of morphology evolution. For this research, the
-phase orientation relationship, shape, growth process, misfit value, and interfacial condition between the
-phase and Al matrix were investigated using high-resolution transmission electron microscopy (HR-TEM), focus ion beam (FIB), and optical microscope (OM). Results include the identification of {111}
facets at the edges of the
-phase, as well as the proposal of two new three-dimensional shapes for the
-phase. We purposed the morphology evolution during the growth process of Mg
Si crystal and calculated the misfit to understand the unstable (111)
facet has a higher misfit value as compared to the (001)
and (011)
facets. Our observations provide how they influence the behavior of Mg
Si crystals.
Yamaguchi, Masatake
Nihon Genshiryoku Gakkai-Shi ATOMO, 66(6), p.291 - 294, 2024/06
First-principles calculations of lattice defects in metals became available around year 2000 and were gradually performed for planar defects such as surface and grain boundaries, point defects such as atomic vacancies, and line defects such as dislocation cores, in the order of ease of calculation. The author introduces some examples of first-principles calculations of microscopic properties, which seem to strongly influence macroscopic material properties.
Moriyama, Junichiro*; Takakuwa, Osamu*; Yamaguchi, Masatake; Ogawa, Yuhei*; Tsuzaki, Kaneaki*
Computational Materials Science, 232, p.112650_1 - 112650_11, 2024/01
Times Cited Count:4 Percentile:44.20(Materials Science, Multidisciplinary)The present study focuses on a novel hydrogen-improved strength-ductility balance in some practical Fe-Cr-Ni-based austenitic alloys, which directly depends on the solute hydrogen content. The hydrogen absorption energy of the Fe-Cr-Ni model alloys with the face-centered cubic structure was examined using first-principles calculations to verify the contribution of Cr and Ni substitutions from Fe to the hydrogen solubility in the alloys. The Cr substitution substantially reduced the hydrogen absorption energy compared to the Ni substitution, whereby the increased Cr/Ni ratio exerts higher hydrogen solubility. The propensity in the calculations coincided with the experimental results obtained previously in the practical alloys with various Cr / Ni ratios.
Yamaguchi, Masatake; Ebihara, Kenichi; Tsuru, Tomohito; Itakura, Mitsuhiro
Materials Transactions, 64(11), p.2553 - 2559, 2023/11
Times Cited Count:9 Percentile:74.17(Materials Science, Multidisciplinary)We attempted to calculate the hydrogen trapping energies on the incoherent interfaces of MgZn precipitates and Mg
Si crystallites in aluminum alloys from first-principles calculations. Since the unit cell containing the incoherent interface does not satisfy the periodic boundary condition, resulting in a discontinuity of crystal blocks, the hydrogen trapping energy was calculated in a region far from the discontinuity (vacuum) region. We found considerable trapping energies for hydrogen atoms at the incoherent interfaces consisting of assumed atomistic arrangement. We also conducted preliminary calculations of the reduction in the cohesive energy by hydrogen trapping on the incoherent interfaces of Mg
Si in the aluminum matrix.
Yamaguchi, Masatake
Materia, 62(10), p.646 - 651, 2023/10
The tendency of solid metal in contact with a liquid metal to undergo brittle fracture is called liquid metal embrittlement. The degree of embrittlement varies depending on the liquid-solid metal combination, called the element selectivity (specificity) of liquid metal embrittlement. We have added further explanations to a published paper that discusses the energetics of embrittlement-prone combinations and possible embrittling mechanisms based on energetic considerations from first-principles calculations.
Shimizu, Kazuyuki*; Toda, Hiroyuki*; Fujihara, Hiro*; Yamaguchi, Masatake; Uesugi, Masayuki*; Takeuchi, Akihisa*; Nishijima, Masahiko*; Kamada, Yasuhiro*
Corrosion, 79(8), p.818 - 830, 2023/08
Times Cited Count:4 Percentile:38.78(Materials Science, Multidisciplinary)7xxx aluminum alloys are representative high-strength aluminum alloys; however, mechanical property degradation due to hydrogen hinders further strengthening. We propose the dispersion of Mn-based second-phase particles as a novel technique for preventing 7xxx aluminum alloy hydrogen embrittlement. In this study, the deformation and fracture behaviors of high hydrogen 7xxx alloys containing 0.0% Mn and 0.6% Mn are observed in situ using synchrotron radiation X-ray tomography. The obtained macroscopic hydrogen embrittlement is quantitatively analyzed based on hydrogen partitioning in alloys. Adding 0.6% Mn, generating second-phase particles with high hydrogen trapping abilities, significantly suppresses hydrogen-induced quasicleavage fracture.
Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
Materials Transactions, 64(8), p.2022 - 2025, 2023/08
Times Cited Count:1 Percentile:13.75(Materials Science, Multidisciplinary)We have found that, during scanning transmission electron microscopy observations, heating of a Mg
Zn
Gd
(at.%) alloy at 623K leads to dynamic precipitations of face-centered-cubic (
)-based Gd nanoparticles. With the aid of density-functional theory (DFT) calculations, the observed lattice constant of 5.32
, which is larger than that expected for pure
-Gd of 5.06
, is likely to be due to oxygen atoms inserted at tetrahedral interstitial sites with essentially a fractional occupation. Systematic DFT calculations show possible occurrences of
-Gd-based oxide phase with a wide non-stoichiometry range by occupying either tetrahedral or octahedral interstitial positions, being represented as GdO
.
Tsuru, Tomohito; Nishimura, Katsuhiko*; Matsuda, Kenji*; Nunomura, Norio*; Namiki, Takahiro*; Lee, S.*; Higemoto, Wataru; Matsuzaki, Teiichiro*; Yamaguchi, Masatake; Ebihara, Kenichi; et al.
Metallurgical and Materials Transactions A, 54(6), p.2374 - 2383, 2023/06
Times Cited Count:2 Percentile:26.77(Materials Science, Multidisciplinary)Although hydrogen embrittlement susceptibility of high-strength Al alloys is recognized as a critical issue in the practical use of Al alloys, identifying the hydrogen trapping or distribution has been challenging. In the present study, an effective approach based on experiment and simulation is proposed to explore the potential trap sites in Al alloys. Zero-field muon spin relaxation experiments were carried out for Al-0.5%Mg, Al-0.2%Cu, Al-0.15%Ti, Al-0.011%Ti, Al-0.28%V, and Al-0.015%V (at.%) in the temperature range from 5 to 300 K. The temperature variations of the dipole field widths have revealed three peaks for Al-0.5%Mg, four peaks for Al-0.2%Cu, three peaks for Al-0.011%Ti and Al-0.015%V. Atomic configurations of the muon trapping sites corresponding to the observed peaks are well assigned using the first-principles calculations for the trap energies of hydrogen around a solute and solute-vacancy pair. The extracted linear relationship between the muon
peak temperature and the trap energy enables us to explore the potential alloying elements and their complex that have strong binding energies with hydrogen in Al alloys.
Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*
Materials Transactions, 64(4), p.813 - 816, 2023/04
Times Cited Count:3 Percentile:38.78(Materials Science, Multidisciplinary)Yamaguchi, Masatake; Tsuru, Tomohito; Itakura, Mitsuhiro; Abe, Eiji*
Scientific Reports (Internet), 12(1), p.10886_1 - 10886_7, 2022/07
Times Cited Count:4 Percentile:21.07(Multidisciplinary Sciences)no abstracts in English
Hirayama, Shintaro*; Sato, Koichi*; Kato, Daiji*; Iwakiri, Hirotomo*; Yamaguchi, Masatake; Watanabe, Yoshiyuki*; Nozawa, Takashi*
Nuclear Materials and Energy (Internet), 31, p.101179_1 - 101179_9, 2022/06
Times Cited Count:6 Percentile:70.05(Nuclear Science & Technology)no abstracts in English
Tsuru, Tomohito; Itakura, Mitsuhiro; Yamaguchi, Masatake; Watanabe, Chihiro*; Miura, Hiromi*
Computational Materials Science, 203, p.111081_1 - 111081_9, 2022/02
Times Cited Count:17 Percentile:66.08(Materials Science, Multidisciplinary)The deformation mode of some titanium (Ti) alloys differs from that of pure Ti due to the presence of alloying elements in -phase. Herein, we investigated all possible slip modes in pure Ti and the effects of Al and V solutes as typical additive elements on the dislocation motion in
-Ti alloys using density functional theory (DFT) calculations. The stacking fault (SF) energies in possible slip planes indicated that both Al and V solutes reduce the SF energy in the basal plane and, in contrast, the Al solute increases the SF energy particularly in the prismatic plane. DFT calculations were subsequently performed to simulate dislocation core structures. The energy landscape of the transition between all possible dislocation core structures and the barriers for dislocation glide in various slip planes clarified the nature of dislocation motion in pure Ti. (i) the energy of prismatic core is higher than most stable pyramidal core, and thereby dislocations need to overcome the energy barrier of the cross-slip (22.8 meV/b) when they move in the prismatic plane, (ii) the energy difference between the prismatic and basal cores is larger (127 meV/b), that indicates the basal slip does not activate, (iii) however, the Peierls barrier for motion in the basal plane is not as high (16 meV/b). Direct calculations for the dislocation core around solutes revealed that both Al and V solutes facilitate dislocation motion in the basal plane by reducing the energy difference between the prismatic and basal cores. The effect of solutes characterizes the difference in the deformation mode of pure Ti and
-Ti alloys.
Yamaguchi, Masatake; Itakura, Mitsuhiro; Tsuru, Tomohito; Ebihara, Kenichi
Materials Transactions, 62(5), p.582 - 589, 2021/05
Times Cited Count:19 Percentile:74.68(Materials Science, Multidisciplinary)no abstracts in English
Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*
Acta Materialia, 203, p.116491_1 - 116491_9, 2021/01
Times Cited Count:27 Percentile:84.90(Materials Science, Multidisciplinary)Solute cluster in LPSO alloys plays a key role in their idiosyncratic plastic behavior such as kink formation and kink strengthening. Identifying the atomistic details of the cluster structure is a prerequisite for any atomistic modeling of LPSO alloys aiming for their improved strength and ductility, but there have been uncertainty about interstitial atom in the cluster. While density functional theory calculations have shown that inclusion of interstitial atom is energetically favorable, it has been unclear how the extra atom is provided, how much of the cluster have interstitial atoms, and what kind of element they are. In the present work we use density functional theory calculations to investigate the growth process of the solute cluster, specifically that of Mg-Y-Zn LPSO alloy, to determine the precise atomistic structure of solute cluster. We show that a pair of an interstitial atom and a vacancy is spontaneously created when a certain number of solute atoms are absorbed into the cluster, and all the full-grown cluster should include interstitial atom. We also show that interstitial atom is either Mg or Y atom, while Zn interstitial atom is extremely rare. These knowledge greatly simplifies atomistic modeling of solute clusters in Mg-Y-Zn alloy. Owing to the vacancies emitted from the cluster, vacancy density should be over-saturated in regions where solute clusters are growing, and the increased vacancy density accelerates cluster growth.
Toda, Hiroyuki*; Tsuru, Tomohito; Yamaguchi, Masatake; Matsuda, Kenji*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*
Kagaku, 75(10), p.48 - 53, 2020/10
Highly-concentrated precipitations play therefore dominant role in mechanical properties and hydrogen embrittlement of aluminum alloys. It has been considered that the coherent interface between matrix and precipitation does not contribute to the crack initiation and embrittlement due to its coherency. Here, we discovered the origin of unprecedented quasi-cleavage fracture mode. Hydrogen partitioning at various defect sites is investigated comprehensively combined with experiment, theory and first-principles calculations. We demonstrate that despite low excess free volume, the aluminum-precipitation interface is more preferable trap site than void and grain boundary. The cohesivity of the interface deteriorates significantly with increasing occupancy while hydrogen atoms are trapped stably up to extremely high occupancy equivalent to spontaneous cleavage.
Yamaguchi, Masatake; Tsuru, Tomohito; Ebihara, Kenichi; Itakura, Mitsuhiro; Matsuda, Kenji*; Shimizu, Kazuyuki*; Toda, Hiroyuki*
Materials Transactions, 61(10), p.1907 - 1911, 2020/10
Times Cited Count:20 Percentile:70.06(Materials Science, Multidisciplinary)no abstracts in English