Combining muon spin relaxation and DFT simulations of hydrogen trapping in AlMn

清水 一行*; 西村 克彦*; 松田 健二*; 赤丸 悟士*; 布村 紀男*; 並木 孝洋*; 土屋 大樹*; Lee, S.*; 髭本 亘; 都留 智仁; et al.

Scripta Materialia, 245, p.116051_1 - 116051_6, 2024/05

https://doi.org/10.1016/j.scriptamat.2024.116051

質量ppmレベルの水素は金属材料の水素脆化を引き起こすが、水素の捕獲部位を実験的に解明することは極めて困難である。我々は、正ミュオンが水素の軽い同位体として作用することを利用して、物質中の水素の捕獲状態を研究した。ゼロ磁場ミュオンスピン緩和実験と密度汎関数理論(DFT)計算をAlMnに対して行った。AlMnにおける水素のDFT計算の結果、4つの水素トラップサイトが見つかり、その水素トラップエネルギーはeV/atom単位で0.168(サイト1), 0.312(サイト2), 0.364(サイト3), 0.495(サイト4)であった。推定された双極子磁場幅の温度変化()は、94, 193, 236Kでステップ状の変化を示した。サイト密度を考慮すると、観測されたの変化温度は、サイト1, 3, 4にミュオンがトラップされたものと解釈される。

Effects of dislocation arrangement and character on the work hardening of lath martensitic steels

段野下 宙志*; 長谷川 寛*; 樋口 翔*; 松田 広志*; Gong, W.; 川崎 卓郎; Harjo, S.; 梅澤 修*

Scripta Materialia, 236, p.115648_1 - 115648_5, 2023/11

https://doi.org/10.1016/j.scriptamat.2023.115648

Work-hardening behavior of a lath martensitic Fe-18Ni alloy during tensile deformation is discussed based on the Taylor's equation. The dislocation characteristics are monitored using in situ neutron diffraction. In the specimens of as-quenched (AQ) and tempered at 573 K (T573), the dislocations are extremely dense and randomly arranged. The dislocations in AQ and T573 form dislocation cells as deformation progresses. Consequently, a composite condition comprising cell walls and cell interiors is formed, and the coefficient in the Taylor's equation increases. Cells are already present in the specimen tempered at 773 K (T773), which has a low dislocation density and a large fraction of edge-type dislocations. As deformation continues, the dislocation density of T773 increases, its cell size decreases, and its composite condition become stronger. Simultaneously, the edge-type dislocation fraction decreases, keeping unchanged. Thus, both the dislocation arrangement and character affected , thereby affecting the work-hardening behavior.

Compressive deformation behavior of AZ31 alloy at 21K; An neutron diffraction study

Gong, W.; 川崎 卓郎; Zheng, R.*; 眞山 剛*; Sun, B.*; 相澤 一也; Harjo, S.; 辻 伸泰*

Scripta Materialia, 225, p.115161_1 - 115161_5, 2023/03

https://doi.org/10.1016/j.scriptamat.2022.115161

Deformation behavior during uniaxial compression at 21 K and 298 K in a commercial AZ31 magnesium alloy was studied by neutron diffraction. Decreasing the deformation temperature resulted in a slight increase in yield stress (115 MPa 139 MPa), but a remarkable enhancement in both the fracture stress (365 MPa 551 MPa) and fracture strain (12.8% 16.5%). The low temperature sensitivity of the {102} extension twinning which governed the macroscopic yielding led to the slight increase in yield stress. At 21K, basal slip was suppressed, while the extension twinning was promoted resulted in higher twin volume fraction. In the late stage of deformation, the {101}-{102} double twinning was suppressed, which is considered to be the reason to delay the fracture at 21 K.

Regulation of strength and ductility of single-phase twinning-induced plasticity high-entropy alloys

Wei, D.*; Gong, W.; 川崎 卓郎; Harjo, S.; 加藤 秀実*

Scripta Materialia, 216, p.114738_1 - 114738_6, 2022/07

https://doi.org/10.1016/j.scriptamat.2022.114738

Near-equiatomic single-phase twining-induced plasticity (TWIP) high-entropy alloys (HEAs) exhibit a good combination of strength and ductility, but their modest yield strength requires further improvement. Here, we propose a strategy for markedly enhancing their strength while retaining satisfactory ductility, taking advantage of the temperature dependence of the stacking fault energy. The room-temperature strength of a representative TWIP HEA was improved by the cryogenic pre-deformation-induced dislocations, martensite, nanotwins, and stacking faults. The tensile properties were further tuned by subsequent annealing to obtain partially recovered or recrystallized microstructures. The influence of regulated microstructures on the yield strength was clarified by neutron diffraction line profile analysis. This study presents possibilities for fabricating advanced HEAs by tuning the substructures.

Artificial neural network molecular mechanics of iron grain boundaries

椎原 良典*; 金澤 良亮*; 松中 大介*; Lobzenko, I.; 都留 智仁; 香山 正憲*; 森 英喜*

Scripta Materialia, 207, p.114268_1 - 114268_4, 2022/01

https://doi.org/10.1016/j.scriptamat.2021.114268

本研究では、最新の人工ニューラルネットワーク(ANN)ポテンシャルに基づく分子力学を使用した鉄中の46種類の対称傾角粒界の粒界(GB)エネルギーを評価した。粒界エネルギー計算の精度の検証のため、密度汎関数理論(DFT)に基づく第一原理計算、および古典的な経験ポテンシャルである、埋め込み原子法(EAM)、および修正EAM(MEAM)との比較を行った。その結果、EAMとMEAMはDFTの結果(平均約27%)とは大きく異なっていた一方、ANNポテンシャルによる結果はDFTの結果(平均5%)と非常によく一致していることを確認した。GBの一軸引張計算では、EAMとMEAMにおける延性挙動のアーティファクトが改善され、ANNポテンシャルではDFTで観察されたGBの脆性破壊傾向を再現した。これらの結果は、需要の高い鉄におけるANNポテンシャルの有効性を示している。

Role of retained austenite in low alloy steel at low temperature monitored by neutron diffraction

山下 享介; 諸岡 聡; Harjo, S.; 川崎 卓郎; 古賀 紀光*; 梅澤 修*

Scripta Materialia, 177, p.6 - 10, 2020/03

https://doi.org/10.1016/j.scriptamat.2019.10.002

neutron diffraction measurements during tensile tests at low temperatures of a low alloy steel containing retained austenite have been performed. Evolutions of phase fractions and phase stresses were analyzed and discussed with the progress of deformation. The role of austenite in the steel during deformation at low temperatures was observed not to directly in the contribution to the strengths but in the improvement of the elongation by transformation of austenite to martensite -and in the increasing of the work-hardening rate by an increase in the phase fraction of martensite and the work hardening of martensite.

Neutron computed tomography of phase separation structures in solidified Cu-Co alloys and investigation of relationship between the structures and melt convection during solidification

庄司 衛太*; 磯谷 祥世*; 鈴木 陸人*; 久保 正樹*; 塚田 隆夫*; 甲斐 哲也; 篠原 武尚; 松本 吉弘*; 福山 博之*

Scripta Materialia, 175, p.29 - 32, 2020/01

https://doi.org/10.1016/j.scriptamat.2019.08.041

The effect of melt convection on the phase separation structures in undercooled Cu- Co alloys was investigated using the electromagnetic levitation technique, where the melt convection was controlled by applying a static magnetic field. The three-dimensional phase separation structures of the solidified Cu-Co alloys were first observed using neutron computed tomography. A large number of small spherical Co-rich phases were dispersed in the Cu-rich phase matrix when the static magnetic field was relatively small. In contrast, several coalesced Co-rich phases, which were elongated along the direction of the static magnetic field, appeared in the higher strength of static magnetic field.

neutron diffraction study of phase stress evolution in a ferrous medium-entropy alloy under low-temperature tensile loading

Bae, J. W.*; Kim, J. G.*; Park, J. M.*; Woo, W.*; Harjo, S.; Kim, H. S.*

Scripta Materialia, 165, p.60 - 63, 2019/05

https://doi.org/10.1016/j.scriptamat.2019.02.027

Phase stress evolution of face-centered cubic (FCC) and deformation-induced body-centered cubic (BCC) phases was measured in recently developed ferrous medium-entropy alloy. This was done during tensile deformation at -137C using neutron diffraction measurement for the quantitative interpretation of the role of martensitic transformation on the improved low-temperature tensile properties. The strain-hardening rate curve exhibits two-stage hardening behavior, and the phase stress and stress contribution from the BCC phase increases significantly while that from FCC phase decreases during plastic deformation. This is a direct demonstration that BCC phase contributes significantly to the increase in strength and strain hardening.

Reverse austenite transformation behavior in a tempered martensite low-alloy steel studied using neutron diffraction

友田 陽*; Gong, W.*; Harjo, S.; 篠崎 智也*

Scripta Materialia, 133, p.79 - 82, 2017/05

AA2017-0349.pdf:2.43MB

https://doi.org/10.1016/j.scriptamat.2017.02.017

The microstructure evolution during reverse transformation of a Cr-Ni-Mo steel consisting of tempered lath martensite and Cr carbide was examined using neutron diffraction at high temperatures. The microstructural change from a reversed coarse-grained structure to a fine-grained polygonal structure by further annealing was monitored through a decrease in the diffraction intensity caused by primary extinction and the full width at half maximum. This result is different from that for a bainite steel, showing good coincidence with the observations using electron back scatter diffraction.

Orientation relationship between -phase and high-pressure -phase of pure group IV transition metals

足立 望*; 戸高 義一*; 鈴木 裕士; 梅本 実*

Scripta Materialia, 98, p.1 - 4, 2015/03

https://doi.org/10.1016/j.scriptamat.2014.10.029

中性子回折法により第IV族遷移純金属の高圧相の変形集合組織を評価した。0001方位は高圧ねじり過程により導入されたせん断ひずみの増加によりせん断方向に徐々に揃う様子が確認された。変形集合組織は、相の主すべり系が{11-20}0001であることを示唆している。逆変態相に対する機械的に安定した相の方位関係を観察した結果、SilcockおよびRabinkinにより提案された方位関係と似ていることを確認した。