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Journal Articles

Quantitative estimation method of the effect of segregated solute on hydrogen-enhanced decohesion at a grain boundary

Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito

Scripta Materialia, 255, p.116366_1 - 116366_5, 2025/01

 Times Cited Count:0

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.

Journal Articles

Effect of carbon segregation at prior austenite grain boundary on hydrogen-related crack propagation behavior in 3Mn-0.2C martensitic steels

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:0 Percentile:0.00(Materials Science, Multidisciplinary)

Journal Articles

Morphology evolution of $$beta$$-phase in Al-Mg-Si alloys during aging treatment

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:3 Percentile:87.51(Chemistry, Physical)

This study aims to clarify the growth process of the$$beta$$-phase in Al-Mg-Si alloys from the point of view of morphology evolution. For this research, the $$beta$$-phase orientation relationship, shape, growth process, misfit value, and interfacial condition between the $$beta$$-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} $$beta$$ facets at the edges of the $$beta$$-phase, as well as the proposal of two new three-dimensional shapes for the $$beta$$-phase. We purposed the morphology evolution during the growth process of Mg$$_2$$Si crystal and calculated the misfit to understand the unstable (111)$$beta$$ facet has a higher misfit value as compared to the (001)$$beta$$ and (011)$$beta$$ facets. Our observations provide how they influence the behavior of Mg$$_2$$Si crystals.

Journal Articles

Crystal defects and first-principles calculations; Grain boundary embrittlement, slip deformation, etc.

Yamaguchi, Masatake

Nihon Genshiryoku Gakkai-Shi ATOMO$$Sigma$$, 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.

Journal Articles

The Contribution of Cr and Ni to hydrogen absorption energy in Fe-Cr-Ni austenitic systems; A First-principles study

Moriyama, Junichiro*; Takakuwa, Osamu*; Yamaguchi, Masatake; Ogawa, Yuhei*; Tsuzaki, Kaneaki*

Computational Materials Science, 232, p.112650_1 - 112650_11, 2024/01

 Times Cited Count:2 Percentile:37.82(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.

Journal Articles

First-principles calculations of hydrogen trapping energy on incoherent interfaces of aluminum alloys

Yamaguchi, Masatake; Ebihara, Kenichi; Tsuru, Tomohito; Itakura, Mitsuhiro

Materials Transactions, 64(11), p.2553 - 2559, 2023/11

 Times Cited Count:4 Percentile:42.11(Materials Science, Multidisciplinary)

We attempted to calculate the hydrogen trapping energies on the incoherent interfaces of MgZn$$_2$$ precipitates and Mg$$_2$$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$$_2$$Si in the aluminum matrix.

Journal Articles

Specificity and embrittling mechanism of liquid metal embrittlement; First-principles calculations

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.

Journal Articles

Hydrogen embrittlement and its prevention in 7XXX aluminum alloys with high Zn concentrations

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:1 Percentile:22.95(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.

Journal Articles

Non-stoichiometric $$fcc$$-base GdO$$_{x}$$ precipitations in a Mg-Zn-Gd alloy

Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*

Materials Transactions, 64(8), p.2022 - 2025, 2023/08

 Times Cited Count:1 Percentile:0.00(Materials Science, Multidisciplinary)

We have found that, during $$in-situ$$ scanning transmission electron microscopy observations, heating of a Mg$$_{97}$$Zn$$_{1}$$Gd$$_{2}$$ (at.%) alloy at 623K leads to dynamic precipitations of face-centered-cubic ($$fcc$$)-based Gd nanoparticles. With the aid of density-functional theory (DFT) calculations, the observed lattice constant of 5.32${AA}$, which is larger than that expected for pure $$fcc$$-Gd of 5.06${AA}$, 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 $$fcc$$-Gd-based oxide phase with a wide non-stoichiometry range by occupying either tetrahedral or octahedral interstitial positions, being represented as GdO$$_{x}$$.

Journal Articles

Identification of hydrogen trapping in aluminum alloys $$via$$ muon spin relaxation method and first-principles calculations

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:1 Percentile:22.95(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 $$Delta$$ 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 $$Delta$$ 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.

Journal Articles

DFT calculation of high-angle kink boundary in 18R-LPSO alloy

Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*

Materials Transactions, 64(4), p.813 - 816, 2023/04

 Times Cited Count:3 Percentile:56.29(Materials Science, Multidisciplinary)

Journal Articles

Atomistic weak interaction criterion for the specificity of liquid metal embrittlement

Yamaguchi, Masatake; Tsuru, Tomohito; Itakura, Mitsuhiro; Abe, Eiji*

Scientific Reports (Internet), 12(1), p.10886_1 - 10886_7, 2022/07

 Times Cited Count:2 Percentile:17.95(Multidisciplinary Sciences)

no abstracts in English

Journal Articles

Effect of uniaxial tensile strain on binding energy of hydrogen atoms to vacancy-carbon-hydrogen complexes in $$alpha$$-iron

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:4 Percentile:63.92(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Dislocation core structure and motion in pure titanium and titanium alloys; A First-principles study

Tsuru, Tomohito; Itakura, Mitsuhiro; Yamaguchi, Masatake; Watanabe, Chihiro*; Miura, Hiromi*

Computational Materials Science, 203, p.111081_1 - 111081_9, 2022/02

 Times Cited Count:12 Percentile:56.09(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 $$alpha$$-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 $$alpha$$-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 $$alpha$$-Ti alloys.

Journal Articles

Hydrogen-trapping energy in screw and edge dislocations in aluminum; First-principles calculations

Yamaguchi, Masatake; Itakura, Mitsuhiro; Tsuru, Tomohito; Ebihara, Kenichi

Materials Transactions, 62(5), p.582 - 589, 2021/05

 Times Cited Count:16 Percentile:69.73(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Density functional theory study of solute cluster growth processes in Mg-Y-Zn LPSO alloys

Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*

Acta Materialia, 203, p.116491_1 - 116491_9, 2021/01

 Times Cited Count:25 Percentile:87.04(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.

Journal Articles

Spontaneous debonding behaviour of reinforcement fine particles in aluminium; Toward high-strength metallic materials development

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.

Journal Articles

Hydrogen trapping in Mg$$_2$$Si and Al$$_7$$FeCu$$_2$$ intermetallic compounds in aluminum alloy; First-principles calculations

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:17 Percentile:64.27(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

The Possible transition mechanism for the meta-stable phase in the 7xxx aluminium

Bendo, A.*; Matsuda, Kenji*; Nishimura, Katsuhiko*; Nunomura, Norio*; Tsuchiya, Taiki*; Lee, S.*; Marioara, C. D.*; Tsuru, Tomohito; Yamaguchi, Masatake; Shimizu, Kazuyuki*; et al.

Materials Science and Technology, 36(15), p.1621 - 1627, 2020/09

 Times Cited Count:11 Percentile:52.71(Materials Science, Multidisciplinary)

Metastable phases in aluminum alloys are the primary nano-scale precipitates which have the biggest contribution to the increase in the tangible mechanical properties. The continuous increase in hardness in the 7xxx aluminum alloys is associated with the phase transformation from clusters or GP-zones to the metastable $$eta'$$ phase. The transformation which is structural and compositional should occur following the path of the lowest activation energy. This work is an attempt to gain insight into how the structural transformation may occur based on the shortest route of diffusion for the eventual structure to result in that of $$eta'$$ phase. However, for the compositional transformation to occur, the proposed mechanism may not stand, since it is a prerequisite for the atoms to be at very precise positions in the aluminum lattice, at the very beginning of structural transformation, which may completely differ from that of the GP-zones atomic arrangements.

Journal Articles

Non-basal dislocation nucleation site of solid solution magnesium alloy

Somekawa, Hidetoshi*; Basha, D. A.*; Singh, A.*; Tsuru, Tomohito; Yamaguchi, Masatake

Materials Transactions, 61(6), p.1172 - 1175, 2020/06

 Times Cited Count:15 Percentile:64.27(Materials Science, Multidisciplinary)

The effect of grain boundary segregation on plastic deformation was investigated using the MgY solid solution binary alloy. Deformed microstructural observations revealed many traces of prismatic $$<a>$$ dislocations as well as basal dislocations. These dislocations were nucleated at grain boundaries with segregation of yttrium element. By comparison of material factors of binary alloy, the alloying elements having low critical resolved shear stress (CRSS) of non-basal plane and large grain boundary (twin boundary) segregation energy led to activation of non-basal dislocations in the vicinity of grain boundaries. The MgCa alloy had similar material factors and showed the same deformed microstructures as those of the alloys containing rare-earth element, which indicate that calcium element is an alternative alloying element.

293 (Records 1-20 displayed on this page)