金属Mg二阶锥面<c+a>刃位错运动特性的分子动力学模拟

Motion Characteristics of <c+a> Edge Dislocation on the Second-Order Pyramidal Plane in Magnesium Simulated by Molecular Dynamics

采用分子动力学方法模拟金属Mg的二阶锥面<c+a>刃位错在温度为300 K下的运动过程,研究不同大小及方向的外加剪切应力作用下的位错运动特性和结构演化规律。结果表明,实际驱动位错运动的有效剪切应力低于外加剪切应力;位错运动速率随外加剪切应力的增大而线性增大,在同等剪切应力下,对应于c轴拉伸变形时的位错运动速率高于c轴压缩,相应的拖曳系数显著高于同等温度下基面和柱面刃位错。位错运动特性的拉-压非对称性本质上与外加剪切应力对扩展位错宽度的影响有关。

Magnesium has a hcp lattice structure,in which insufficient independent slip systems are available to accommodate applied plastic deformation at room temperature.The ductility of Mg is intimately related to the fundamental behaviors of pyramidal<c+a>dislocations,which are the major contributor to c-axis strain.In this study,the motion of<c+a>edge dislocation on the second-order pyramidal plane in Mg under external shear stress of different magnitudes and directions are simulated by molecular dynamics at 300 K,and the motion and structural evolution of dislocations are studied.The results show that the effective shear stress causing dislocation motion is lower than the external applied one and the dislocation velocity increases linearly with increasing applied shear stress.Under the same level of external shear stress,the dislocation velocity in shearing leading to c-axis tension deformation is higher than that for shearing leading to c-axis compression,and in both cases the corresponding viscous drag coefficients are significantly higher than those for basal and prismatic edge dislocations at the same temperature.The tension-compression asymmetry of dislocation motion is essentially related to the effect of applied shear stress on the extended dislocation width.