Agarwal Garvit, Dongare Avinash M
Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA.
Sci Rep. 2019 Mar 5;9(1):3550. doi: 10.1038/s41598-019-39958-w.
Large scale molecular dynamics (MD) simulations are carried out to investigate the twinning behavior as well as the atomic scale micromechanisms of growth of tension and compression twins in polycrystalline Mg microstructures at high strain rates. A new defect characterization algorithm (extended-common neighbor analysis (E-CNA)) is developed that allows for an efficient identification of various types of twins in HCP microstructures. Unlike other local orientation analysis methods, the E-CNA method allows for atomic scale characterization of the structure of different types of twin boundaries in HCP microstructures. The MD simulations suggest that the local orientation of individual grains with the loading axis plays a critical role in determining the ability of grains to nucleate either compression twins or tension twins. The twinning behavior is observed through nucleation of a pair of planar faults and lateral growth of the twins occurs through nucleation of steps along the planar faults. The kinetics of migration of steps that determine the rate of growth of twins are investigated at the atomic scales. The twin tip velocity computed at high strain rates compares well with the experimentally reported values in the literature.
进行大规模分子动力学（MD）模拟，以研究多晶镁微结构在高应变速率下的孪生行为以及拉伸和压缩孪晶生长的原子尺度微观机制。开发了一种新的缺陷表征算法（扩展公共邻域分析（E-CNA）），该算法能够高效识别六方密堆积（HCP）微结构中的各种孪晶类型。与其他局部取向分析方法不同，E-CNA方法能够对HCP微结构中不同类型孪晶界的结构进行原子尺度表征。MD模拟表明，单个晶粒相对于加载轴的局部取向在决定晶粒形成压缩孪晶或拉伸孪晶的能力方面起着关键作用。通过一对平面位错的形核观察孪生行为，孪晶的横向生长通过沿平面位错的台阶形核发生。在原子尺度上研究了决定孪晶生长速率的台阶迁移动力学。在高应变速率下计算得到的孪晶尖端速度与文献中实验报道的值吻合良好。
