The role of slow screw dislocations in controlling fast strain avalanche dynamics in body-centered cubic metals
The role of slow screw dislocations in controlling fast strain avalanche dynamics in body-centered cubic metals
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DOI：
10.1016/j.ijplas.2019.08.008
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发表时间：
2020-01-01
影响因子：
9.8
通讯作者：
Ghoniem, Nasr
中科院分区：
文献类型：
--
作者：
Cui, Yinan;Po, Giacomo;Ghoniem, Nasr
由于扭结对形核和迁移的热激活过程，体心立方(BCC)晶体的塑性由缓慢的螺位错运动控制。通过三维离散位错动力学模拟，揭示了这种缓慢的螺旋位错行为如何导致体心立方钨(W)柱中极快的应变爆发，这是体心立方金属的典型特征。结果表明，在低应变率下，应变爆发以无螺位错运动为主，而在高应变率下，螺位错对应变爆发的影响较大。结果表明，螺位错引起的总应变爆发量和部分应变爆发量均服从指数为0.65的幂函数统计，呈现出速率依赖性。相应塑性应变率的标准差也服从相似的幂定律统计。螺位错的作用归因于位错源操作性质在不同应变率下的变化。根据模拟方法的独特性，以很高的空间分辨率再现了滑移区和塑性应变的分布，并讨论了相应的塑性变形空间分布。
Plasticity in body centered cubic (BCC) crystals is shown to be controlled by slow screw dislocation motion, owing to the thermally-activated process of kink pair nucleation and migration. Through three dimensional discrete dislocation dynamics simulations, this work unravels the mystery of how such slow screw dislocation behavior contributes to extremely rapid strain bursts in submicron BCC tungsten (W) pillars, which is typical of BCC metals. It is found that strain bursts are dominated by the motion of non-screw dislocations at low strain rate, but are more influenced by screw dislocations at high strain rate. The total, and partial strain burst magnitude due to screw dislocations alone, are found to exhibit rate dependence following a power law statistics with exponent of 0.65. Similar power law statistics are also obeyed for the standard deviation of the corresponding plastic strain rate. The role of screw dislocations is attributed to the changing nature of dislocation source operation at different strain rates. The corresponding spatial distribution of plastic deformation is also discussed based on the uniqueness of the simulation method in reproducing the distribution of slipped area and plastic strain with very high spatial resolution.