Effects of vacancy concentration on the edge dislocation motion in copper by atomic simulations

Abstract

Nonequilibirum vacancy concentration widely appears in crystals under many extreme loading conditions, but receives relatively few attentions. In this work, we systematically explore the influence of a serial of different vacancy concentrations on the edge dislocation motion in copper using molecular dynamics (MD) simulations. Our result shows that the vacancy would hinder the dislocation motion, but the mechanism depends on the detailed dislocation motion regions. In thermally activated region, its influence is mainly reflected by modifying the dynamic and static threshold stresses required for edge dislocation initiation and continuous motion. In the linear region, the hindering mechanism is gradually transformed from phonon damping to vacancy pinning with the increasing vacancy concentration. In contrasts, the dislocation structure is almost unchanged under different vacancy concentrations in the non-linear region. Under high applied stress, high vacancy concentration will cause the dislocation velocity to jump back and forth between transonic and subsonic velocities more frequently. It has been attributed to the reactions between the dislocation and vacancies. The latter may result in dislocation local constriction and climbing. Moreover, a mobility equation suitable for describing edge dislocations at different non-equilibrium vacancy concentrations is proposed, which fits the MD results well. Finally, the roles of the nonequilibirum vacancy concentration on the edge dislocation motion is interpreted using the degrading elastic property and stacking fault energy.