Molecular Dynamics Simulation of (c+a) Edge Dislocation Core Structure in HCP Crystal

The core structures of (c+a) edge dislocation in a HCP crystal have been investigated by computer simulation. An elastic perfect edge dislocation with Burgers vector (c+a) was introduced into the crystal, which was relaxed by molecular dynamic method. In this calculation, a Lennard-Jones type pair potential is used. Two types of core are stable at 0K; one is a perfect dislocation and the other is two 1/2(c+a) partial dislocations. While the core spreaded into two 1/2(c+a) partial dislocations was still stable at higher temperatures, the core of perfect dislocation extended parallel to basal plane. Changes of these core structures by application of shear stress have been also investigated. The two 1/2(c+a) partial dislocations glided separately on the slip plane. In contrast, the extended core emitted a 1/2(c+a) partial dislocations and expand stacking fault with increasing stress, but the rest part of dislocation did not move. These results suggest that the (c+a) edge dislocation glides on the plane as two 1/2(c+a) partial dislocations and becomes to be sessile due to change of core structure. This change of core structure from glissile to sessile causes the anormalous temperature dependence of yield stress observed in HCP metals.