HCP金属における(<I>c</I>+<I>a</I>)転位芯構造の分子動力学シミュレーション

Abstract

The core structures of (c+a) dislocations in HCP metals have been investigated by molecular dynamics simulation using a Lennard-Jones type pair potential. The edge dislocation has two types of stable core structures at 0 K; one is a perfect dislocation (Type-A) and the other is two 1⁄2(c+a) partial dislocations (Type-B). While the Type-B core is stable at 30 K and 293 K, the Type-A core extends parallel to the basal plane at 30 K. The Type-A core at 0 K transforms to the Type-B core by increasing temperature from 0 K to 293 K. In contrast, the extended Type-A core at 30 K is still stable at 293 K. These results suggest that the (c+a) edge dislocation glides on the {11\bar22} plane as two 1⁄2(c+a) partial dislocations and becomes sessile due to changes of the core structure. The screw dislocation exhibits a stable core spread over two {10\bar11} type planes at 0 K. The core transforms to unsymmetrical structure at 293 K, which is spread over {11\bar22} and {10\bar11}, and to a core spread parallel to {11\bar22} at 1000 K. The dependence of the yield stress on the shear direction can be explained from these core structures of screw dislocation.