Dislocation constriction and cross-slip: An ab initio study

A model based on the Peierls framework of dislocations is developed. The theory allows the study of dislocations spreading at more than one slip planes. As an example, we study dislocation cross-slip and constriction processes in two contrasting fcc metals, Al and Ag. The energetic parameters entering the model are determined from ab initio calculations. We find that the screw dislocation in Al can cross-slip spontaneously in contrast with the screw dislocation in Ag, which splits into partials and cannot cross-slip without first being constricted. The response of the dislocations to an external stress is examined in detail. We determine the dislocation constriction energy and the critical stress for cross-slip, and from the latter, we estimate the cross-slip energy barrier for the straight screw dislocations.