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藤原 比呂*; 戸田 裕之*; 海老原 健一; 小林 正和*; 眞山 剛*; 平山 恭介*; 清水 一行*; 竹内 晃久*; 上椙 真之*
International Journal of Plasticity, 174, p.103897_1 - 103897_22, 2024/03
被引用回数：9 パーセンタイル：93.27(Engineering, Mechanical)高強度化したアルミ合金において水素脆化は、理解し解決すべき問題である。アルミ合金において、水素が析出物界面に蓄積し脆化の原因となっていると考えられている。しかし、き裂付近の水素分布と応力場の局所的な相互作用について、空間的な複雑さを考慮した定量的な知見は明らかでない。本研究では、結晶塑性有限要素法と水素拡散解析を組み合わせたマルチモーダル3次元画像ベースシミュレーションを用い、実際のき裂近傍の応力分布と、それが水素分布に及ぼす影響およびき裂発生確率に及ぼす影響を捉えることを試みた。その結果、粒界き裂は、その先端近傍の水素蓄積により、MgZn
析出物の半整合界面の凝集エネルギーが低下した領域で擬へき開き裂に遷移することが分かった。この結果は、本シミュレーション手法がナノスケールの剥離とマクロスケールの脆性破壊の橋渡しに成功したことを示すものと考える。
Zhang, X.*; Gong, W.; 他8名*
International Journal of Plasticity, 173, p.103896_1 - 103896_24, 2024/02
被引用回数：22 パーセンタイル：99.08(Engineering, Mechanical)The distribution and partitioning of solute atoms in age-hardenable aluminum (Al) alloys markedly impact strength, ductility and failure of alloy materials, thus rendering the understanding of dislocation-obstacle (solute-rich features) interactions crucial in the development of a new class of heat-treatable Al alloys. Here, we investigate the slip mechanisms, strain localization and strain hardening of a high Mg-content lightweight AlMgZn-based crossover alloy aged to different conditions with the focus on the dislocation-obstacle interactions. It is found that due to different elemental partitioning between matrix and solute-rich features the interaction of dislocations with obstacles can be drastically different for samples with varying precipitates. The dislocations in the under-aged and near peak-aged samples show predominantly planar slip, which produces strain localization. Whereas in the over-aged sample, gliding dislocations initially bend between adjacent precipitates lying in the slip planes, and subsequently surmount them by local cross slip processes, giving rise to homogeneous slip. It is discovered that strain localization in the form of coarse slip bands induces strain hardening in the under-aged material. To understand the enhanced strain hardening observed in the under-aged sample, four key influencing factors are proposed. In addition, the predicted yield strengths for the solution-treated and artificially aged materials match well with those experimentally measured values.
萩原 幸司*; 眞山 剛*; 山崎 倫昭*; Harjo, S.; 徳永 透子*; 山本 和輝*; 杉田 三佳*; 青山 海琳*; Gong, W.; 西本 宗矢*
International Journal of Plasticity, 173, p.103865_1 - 103865_21, 2024/02
被引用回数：24 パーセンタイル：98.62(Engineering, Mechanical)The unique control mechanisms of the plastic deformation of two-phase extruded alloy composed of Mg and long-period stacking ordered (LPSO) phase were clarified by comparison with those of other Mg solid-solution alloys, focusing on the question of why do the Mg/LPSO two-phase alloys exhibit both large elongation and high strength? The stress-strain curves for each grain in the alloys could be imaginary estimated using neutron diffraction analysis during the tensile test. The results demonstrate that the deformation behaviors of the worked and recrystallized grains are significantly different in all the Mg-extruded alloys owing to the strong plastic anisotropy in Mg with hexagonal close-packed (hcp) structure. Therefore, the deformation behavior is controlled by a composite-like deformation mechanism, even in single-phase Mg solid-solution alloys.
X-ray synchrotron diffractionLi, H.*; Liu, Y.*; Zhao, W.*; Liu, B.*; 冨永 亜希; 菖蒲 敬久; Wei, D.*
International Journal of Plasticity, 165, p.103612_1 - 103612_20, 2023/06
被引用回数：27 パーセンタイル：94.81(Engineering, Mechanical)コバルトフリーのマルエージング鋼の強度特性を明らかにするために、高エネルギー放射光X線回折法を利用したその場引張試験を行った。マルテンサイト相とオーステナイト相からの回折プロファイルが得られ、それらの強度及び幅が負荷に伴い変化している様子が観察された。回折プロファイルを解析した結果、時効(as-aged)材では、低応力レベルにてマルテンサイトの含有量が緩やかに減少し、高応力レベルでは急激に減少した。一方、熱処理(as-solution)材では、応力の増加とともにオーステナイト相がマルテンサイト相に著しく転移変態している結果が得られた。これらのことがそれぞれの強度特性に起因していることを明らかにした。
Wei, D.*; Gong, W.; 都留 智仁; Lobzenko, I.; Li, X.*; Harjo, S.; 川崎 卓郎; Do, H.-S.*; Bae, J. W.*; Wagner, C.*; et al.
International Journal of Plasticity, 159, p.103443_1 - 103443_18, 2022/12
被引用回数：107 パーセンタイル：99.79(Engineering, Mechanical)Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions.
neutron diffractionWei, D.*; Gong, W.; 都留 智仁; 川崎 卓郎; Harjo, S.; Cai, B.*; Liaw, P. K.*; 加藤 秀実*
International Journal of Plasticity, 158, p.103417_1 - 103417_17, 2022/11
被引用回数：54 パーセンタイル：98.44(Engineering, Mechanical)In this study, we investigated the yielding and hardening behaviors of the Cantor alloy and FCC-phase Co-rich HEAs with different SFEs by in situ neutron diffraction combined with the first-principles method and electron-microscopy characterizations. The Co-rich HEAs exhibited a higher intrinsic yield strength than the Cantor alloy, mainly because of the larger shear modulus or modulus misfit, and grain refinement being more effective in improving the yield strength of low-SFE HEAs. Furthermore, higher flow stresses and better ductility of the Co-rich HEAs are attributed to the greater dislocation density and a larger number of stacking faults, which enhanced the strain-hardening rate during tensile deformation. The low SFE promoted mechanical twinning, and martensitic transformation contributed to higher strain-hardening rates.
Zhang, X. X.*; Knoop, D.*; Andr
, H.*; Harjo, S.; 川崎 卓郎; Lutz, A.*; Lahres, M.*
International Journal of Plasticity, 140, p.102972_1 - 102972_20, 2021/05
被引用回数：47 パーセンタイル：95.10(Engineering, Mechanical)To better understand and predict the mechanical properties of additive manufacturing (AM) Al-Si-Mg alloys, developing a physically-based constitutive model is crucial. Among different models, the dislocation-density-based Kocks-Mecking (K-M) constitutive model has been widely used. In-situ neutron diffraction, a powerful method to measure the phase stress and dislocation density in bulk polycrystalline materials under loading, is employed to investigate the AM AlSi3.5Mg1.5 and AlSi3.5Mg2.5 (wt.%) alloys. Based on the present measured and previous experimental data, a multiscale constitutive model is developed for different AM Al-Si-Mg alloys.
Nb with the L1 structure岡本 範彦*; 竹本 昌平*; Chen, Z. M. T.*; 山口 正剛; 乾 晴行*
International Journal of Plasticity, 97, p.145 - 158, 2017/10
被引用回数：14 パーセンタイル：52.40(Engineering, Mechanical)The deformation behaviour of IrNb with stoichiometric and off-stoichiometric compositions has been investigated as functions of crystal orientation and deformation temperature. The critical resolved shear stress (CRSS) for (111)[
01] slip in stoichiometric IrNb exhibits a marginal temperature dependence at all temperatures with neither strong negative temperature dependence at low temperatures nor positive (anomalous) temperature dependence at high temperatures. The CRSS for (111)[01] slip exhibits orientation dependence, neither. The [01] dislocation dissociates into the anti-phase boundary (APB)-type scheme and is observed to be smoothly curved on the (111) slip plane at all temperatures, indicating the planar core structure. This is exactly what is known for the perfect dislocation in many pure FCC metals and is the reason for the observed FCC metal-like deformation behaviour of IrNb. The absence of yield stress anomaly in IrNb is discussed in terms of anisotropy in planar fault energies and elastic constants calculated by first principles calculations and experimentally determined in the present study.
青柳 吉輝*; 都留 智仁; 下川 智嗣*
International Journal of Plasticity, 55, p.43 - 57, 2014/04
被引用回数：48 パーセンタイル：87.58(Engineering, Mechanical)結晶粒径が1
m未満の超微細粒材料は驚くべき強度特性を持つことが知られており、材料科学の分野においてこのような特性を扱うことができる計算科学的手法が求められている。粒径がサブミクロンオーダーになる場合、粒のサイズに応じて転位源から転位ループは張出しにくくなる。そこで我々は粒界と転位源の影響を両方考慮した結晶塑性モデルを新たに構築し、超微細粒材料の機械特性に転位源が与える影響について検討を行った。
青柳 吉輝*; 小林 遼太郎*; 加治 芳行; 志澤 一之*
International Journal of Plasticity, 47, p.13 - 28, 2013/08
被引用回数：28 パーセンタイル：71.44(Engineering, Mechanical)本研究では、セル構造及びサブグレインに関する転位パターニングを表現する反応-拡散方程式を導出する。変形場における転位パターンの生成を表現するために、すべり速度,応力,セル構造形成における転位の相互作用の効果に関する情報を反応-拡散方程式の反応速度係数に導入する。さらに、転位パターニングに基づくマルチスケール結晶塑性モデルを提案する。そこで、本モデルを用いてFCC多結晶体の強ひずみ圧縮変形させる場合の擬3次元有限要素法-差分法シミュレーションを実施する。セル構造,サブグレイン,高密度転位壁の形成、並びに結晶粒のサブディビジョン化といった結晶微細化の初期プロセスを再現する。また、転位組織が超微細粒の形成に及ぼす影響について検討する。
