Critical stress prediction upon accurate dislocation core description
Critical stress prediction upon accurate dislocation core description
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DOI：
10.1016/j.actamat.2022.117989
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发表时间：
2022-07
期刊：
影响因子：
9.4
通讯作者：
A. Mohammed;O. Celebi;H. Sehitoglu
中科院分区：
文献类型：
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作者：
A. Mohammed;O. Celebi;H. Sehitoglu
现有的摩擦（临界）应力的测定方法是非常不令人满意的，因为与确定位错的“核心宽度”和性质的核心前进。本研究以< 011>面心立方（FCC）材料中的a/2扩展位错（限定层错的部分位错）为研究对象，严格推导了具有连续应变能和原子错配能的芯宽度。应变能的计算使用完全各向异性的Eshelby-Stroh形式主义容纳的a/6< 112>肖克利偏组成的纯刃/纯螺旋a/2< 011>位错的固有混合字符。错配能量是从临界故障能量的滑移面输入到一个新的错配模型捕获的滑移面的晶格结构，并涉及离散的Wigner-Seitz细胞面积在每个晶格网站，推进超过80岁的错配能量模型，已经错过了这两个概念的作用。在文献中，首次严格地从α/2< 011>扩展位错的总能量的优化轨迹导出了位错核的运动性质。结果表明，每个a/6< 112>分块的核是间歇性的（“之字形”运动），而不是一起运动，这使得层错宽度在扩展位错前进期间波动。临界应力涉及到一个依赖于几何学的施密德因素的组合，为每个Shockley偏，也首次透露。所提出的模型被用来预测临界应力的多个FCC材料，包括高熵合金（HEA），显示出良好的协议与实验。这项工作为快速可靠地评估不同晶格结构（例如六方晶格）的多种成分开辟了未来的途径，超越了先前的临界应力指数模型，该模型可能产生高达两个数量级的误差。
Existing approaches for friction (critical) stress determination are highly unsatisfactory because of empiricism associated with determination of dislocation “core-width” and nature of core-advance. This study, focusing on the a/2< 011> extended-dislocation (partials bounding a stacking-fault) in Face-Centered-Cubic (FCC) materials, rigorously derives the core-width with continuum strain-energy and atomistic misfit-energy considerations. The strain-energy is calculated using the fully-anisotropic Eshelby-Stroh formalism accommodating the inherent mixed characters of the a/6< 112> Shockley-partials constituting pure-edge/pure-screw a/2< 011> dislocations. The misfit-energy is determined from critical fault-energies of the slip-plane input to a novel misfit-model capturing the lattice structure of the slip-plane and involving the discrete Wigner-Seitz cell area at each lattice site, advancing over an 80-year old misfit-energy model that has missed the role of both concepts. For the first time in literature, the nature of motion of the a/2< 011> extended-dislocation's core is rigorously derived from an optimized trajectory of its total-energy. It is shown that each a/6< 112> partial's core moves intermittently (“zig-zag” motion), and not together, allowing the stacking-fault width to fluctuate during advance of the extended-dislocation. The critical stress is shown to involve a trajectory-dependent combination of Schmid factors for each Shockley-partial, also revealed for the first time. The proposed model is used to predict critical stress for multiple FCC materials, including a high-entropy alloy (HEA), displaying excellent agreement with experiments. The work opens future avenues for rapid reliable assessment of a multitude of compositions across varying lattice structures (eg hexagonal lattices), advancing over prior exponential models for critical stress which can produce errors as high as two orders of magnitude.