Meso-scale analysis for peculiar mechanisms of pyramidal slip in hcp metals

在77K-293K范围内，通过[112^-0]拉伸实验，在镁和镁锂单晶中激活了二级锥体滑移。各晶体的屈服应力随温度的升高而增大，即反常的温度依赖关系。在293K-473K范围内，锥体滑移也被激活，不存在棱柱滑移。尽管施密德因子相同，[112^-0]和[11^-00]拉伸和压缩的棱柱滑移的屈服应力是不同的。在分子动力学模拟中，(C A)螺型位错的核心在两个{101^-1}面上扩展。螺芯通过双交叉滑移在{112^-2}和{101^-1}之间移动。(C A)刃位错具有两种核心结构。这两种类型核心都不是以负份额和[112^-0]压缩方式移动。部分位错核以[0001]拉伸和压缩方式移动，加载方向不同，应力变化不大。这些结果表明，(c，a)刃位错的运动不仅受剪切应力的影响，而且还受滑移面上的法向应力的影响。从模拟结果可以总结出二次锥体滑移的变形过程。

{112^^-2}<<11>^^^-23> second order pyramidal slip was activated in Mg and Mg-Li single crystals by [112^^-0] tensile test in the range of 77K -293K. Yields stress of each crystal increase with increasing temperature, namely anomalous temperature dependence. The pyramidal slip were also activated in the range of 293K -473k and there is no prismatic slip. Activities of pyramidal slip was related to ductility of polycrystalline magnesium.{101^^-1}<<11>^^^-23> first order pyramidal slip was activated in [0001] tensile and compression. Yield stress of prismatic slip in [112^^-0] and [11^^-00] tension and compression were different in spite of same Schmid's factor.In molecular dynamics simulation using Lennard-Jones (L-J) potential, the core of (c+a) screw dislocation extended on two {101^^-1} plane. The screw core was moved between {112^^-2} and {101^^-1} by double cross slip.(c+a) edge dislocation have two type of core structures. Both type of core are not move in negative share and [112^^-0] compression. Partial dislocation cores move by [0001] tensile and compression, and the stress is little different by loading direction. These results shows that motion of (c+a) edge dislocation is affected not only shear stress but also normal stress on slip plane.From simulation results can summarize the deformation process by secondary pyramidal slip.