Metallic glass instability induced by the continuous dislocation absorption at an amorphous/crystalline interface
Metallic glass instability induced by the continuous dislocation absorption at an amorphous/crystalline interface
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DOI：
10.1016/j.actamat.2020.02.038
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发表时间：
2020-05-01
期刊：
影响因子：
9.4
通讯作者：
Xiong, Liming
中科院分区：
文献类型：
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作者：
Thanh Phan;Rigelesaiyin, Ji;Xiong, Liming
非晶/晶态金属复合材料（A/C-MC）将金属玻璃与晶态金属集成在一个系统中。在变形条件下，A/C-MC中的非晶-晶界面（ACI）吸收位错，并可能从根本上改变材料的强度以牺牲塑性为代价的困境。然而，这种材料的发展仍然处于试错阶段，由于缺乏明确的理解，当位错介导的塑性流入玻璃相时，非晶组分如何变得不稳定。为了满足这一需求，在这里，我们专注于获得物理见解的位错ACI反应在A/C-MCs通过原子模拟。（i）通过在低至10（4）K/s的冷却速率下对熔化的金属玻璃进行退火，数字模拟出与实验结果接近的界面结构;（ii）将位错吸收事件与塑性剪切下A/C-MC中剪切转变区（STZ）的激活相关联;（iii）确定了玻璃相中连续位错吸收引起的不稳定性的机制;（iv）校准了一组本构关系、动力学规则和模型参数，其可以在连续体水平上用于基于有效温度概念的STZ理论;和（v）表征了不稳定带之前的局部应力状态，并将宏观水平的玻璃不稳定性判据建立在坚实的原子基础上。我们的主要发现是：（a）当原子模拟中的冷却速率降低到实验可比水平时，ACI处存在纳米级结构转变;（b）参与STZ的原子数量随着在位错-ACI反应的早期阶段到达ACI的位错数量呈指数增加，但与后期阶段吸收的位错数量成线性比例;（B）参与STZ的原子数量呈指数增加;（c）金属玻璃中位错吸收引起的不稳定性通过三阶段过程发生，即，二十面体（ICO）团簇之间STZ的激活，新形成STZ的合并，然后ICO的崩溃：（d）连续本构关系和动力学规则中的模型参数对冷却速率敏感;和（e）玻璃相不稳定带之前的局部应力状态与Mohr-库仑准则，而不考虑宏观水平上的外加应力。所获得的知识可以提供一个连接的A/C-MC的原子变形物理与其整体的机械性能，这是目前难以实现在实验室实验的途径。(C)2020 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
An amorphous/crystalline metallic composite (A/C-MC) integrates metallic glass with crystalline metals in one system. The amorphous-crystalline interface (ACI) in A/C-MCs under deformation absorbs dislocations and may fundamentally change the dilemma that the strength comes at the expense of the ductility of a material. However, the development of such materials is still at a trial and error stage due to the lack of a clear-cut understanding on how the amorphous component become instable when a dislocation-mediated plasticity flows into the glassy phases. To meet this need, here we focus on gaining the physical insights into the dislocation-ACI reaction in A/C-MCs through atomistic simulations. We have (i) digitally resembled an interface structure close to that in experiments by annealing melted metallic glasses at cooling rates as low as similar to 10(4 )K/s; (ii) correlated the dislocation absorption events with the activation of shear transformation zones (STZs) in A/C-MCs under a plastic shear; (iii) identified the mechanisms responsible for a continuous dislocation absorption-induced instability in glassy phases; (iv) calibrated a set of constitutive relations, kinetic rules, and model parameters that can be used in an effective temperature concept-based STZ theories at the continuum level; and (v) characterized the local stress states ahead of the instability band and lay the macroscopic-level glass instability criterion on a firm atomistic basis. Our major findings are: (a) there exists a nanoscale structure transition at the ACI when the cooling rate in the atomistic simulations is reduced to an experimentally-comparable level; (b) the number of atoms participating in the STZs exponentially increases with the number of dislocations arriving at the ACI at an early stage of the dislocation-ACI reaction, but is linearly proportional to the number of absorbed dislocations at a later stage; (c) the dislocation absorption-induced instability in metallic glasses occurs through a three-stage process, i.e., the activation of STZs in the region between icosahedral (ICO) clusters, the coalescence of newly formed STZs, and then the break-down of ICOs; (d) the model parameters in the continuum-level constitutive relations and kinetic rules are found to be sensitive to cooling rates; and (e) the local stress states ahead of the instability band in glassy phases map surprisingly well with the Mohr-Coulomb criterion regardless of the applied stress at the macroscopic level. The gained knowledge may provide a pathway of connecting the atomistic deformation physics of an A/C-MC with its overall mechanical performance, which is currently difficult to achieve in laboratory experiments. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.