Quantifying the dynamics of dislocation kinks in iron and tungsten through atomistic simulations
Quantifying the dynamics of dislocation kinks in iron and tungsten through atomistic simulations
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DOI：
10.1016/j.ijplas.2020.102675
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发表时间：
2020-05
影响因子：
9.8
通讯作者：
Rigelesaiyin Ji;T. Phan;Hao Chen;L. Xiong
中科院分区：
文献类型：
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作者：
Rigelesaiyin Ji;T. Phan;Hao Chen;L. Xiong
当铁（Fe）和钨(W)等高孔径势垒材料发生变形时，位错扭结很容易被激活。在一定条件下，随后的扭结动力学可以决定位错迁移率和材料的整体性能。本文以1 / 2 <111>螺旋位错线上的热致扭结扩散为例，通过原子模拟量化了b.c.c铁和钨的扭结动力学。结果表明：在Fe和W中，包括扩散系数（Dkink）和耗散参数（γkink）在内的扭结动力学对位错线方向上的模拟胞尺寸（asL）非常敏感：l越大，Dkink越高，γkink越小。通过对数十至数百纳米位错的扭结扩散的一系列计算分析，得出了描述三阶段相关扭结动力学的标度定律。人们发现，如果想从原子模拟中得到一个收敛的金，最小值至少需要几百纳米。这超出了使用适度计算资源的原子级模型的范围。为了解释el依赖的扭结动力学，我们使用两种不同的原子应力公式计算扭结诱导的局部应力场，即广泛使用的Virial和最近开发的机械应力公式。结果表明：(1)el依赖的扭结动力学是由扭结与其周期像之间的长时间弹性相互作用引起的；（ii）维里应力公式低估了这种相互作用。这项工作奠定了在原子基础上对扭结控制的位错动力学的连续描述。它还将支持多尺度方法的发展，以解决在形变下b.c.c金属或其他高佩尔势垒材料中μm长的位错线的运动与沿线本身的原子级扭结扩散之间的耦合动力学。
When high-Peierls-barrier materials such as iron (Fe) and tungsten (W) are deformed, dislocation kinks can be easily activated. The subsequent kink dynamics may dictate the dislocation mobility and the material's overall performance under certain conditions. In this work, taking the thermal-induced kink diffusion along ½<111> screw dislocation lines as an example, the kink dynamics in b.c.c. iron and tungsten are quantified through atomistic simulations. Results show that in both Fe and W, the kink dynamics, including its diffusion coefficient (Dkink) and dissipation parameter (γkink), are sensitive to the dimension (noted asL) of a simulation cell size along the dislocation line direction: the largerL, the higherDkink, and the smallerγkink. A scaling law for describing the three-stageL-dependent kink dynamics is extracted from a series of computational analysis of the kink diffusion along dislocations withLranging from tens to hundreds of nanometers. It is found that, if a convergedDkinkis desired from atomistic simulations, the minimumLneeds to be at least hundreds of nanometers. This is beyond the reach of an atomic-level model using a modest computational resource. To explain theL-dependent kink dynamics, we calculate the kink-induced local stress fields using two different atomistic stress formula, i.e., a widely-used Virial and a recently developed mechanical stress formula. Results suggest: (i) theL-dependent kink dynamics is caused by the long-range elastic interaction between the kink and its periodic images; and (ii) the Virial stress formula underestimates such interactions. This work lays the continuum description of kink-controlled dislocation dynamics on an atomistic foundation. It will also support the development of multiscale methods for addressing the coupled dynamics between the motion of a μm-long dislocation line and the atomic-level kink diffusion along the line itself in b.c.c. metals or other high-Peierls-barrier materials under deformation.