Computational study of core structure and Peierls stress of dissociated dislocations in nickel

We study the core structure and determine the Peierls stress (PS) of dissociated ½ ⟨110⟩ dislocations in FCC nickel by atomistic molecular dynamics simulations, using an EAM potential. Different pictures for the behaviour of edge and screw dislocations of this type emerge from the results of the simulations. On the one hand, the edge dislocation is observed to dissociate along a path that corresponds to the crystallographic Burgers vector of partials. The separation distance between partials is found to be a multiple of the lattice constant. Under the action of an external stress, the partials move in phase and behave globally as a rigid complex. Correspondingly, the PS for a single partial is close to the effective PS for the extended dislocation. On the other hand, in the screw dislocation, the separation distance is smaller and close to a half-integer of the lattice constant. The strong core overlap produces a significant reduction of the lateral Burgers vector in the dissociation process. Under a stress, the partials move out of phase and the separation distance undergoes some modulations. In this case, the effective PS is found to be smaller than the PS for partials.