Corroboration of a multiscale approach with all atom calculations in analysis of dislocation nucleation from surface steps

Abstract

We present a comparative study of the influence of atomic-scale surface steps on dislocation nucleation at crystal surfaces based on an all atom method and a hierarchal multiscale approach. The multiscale approach is based on the variational boundary integral formulation of the Peiersl–Nabarro dislocation model in which interatomic layer potentials derived from atomic calculations of generalized stacking fault energy surfaces are incorporated. We have studied nucleation of screw dislocations in two bcc material systems, molybdenum and tantalum, subjected to simple shear stress. Compared to dislocation nucleation from perfectly flat surfaces, the presence of atomic scale surface steps rapidly reduces the critical stress for dislocation nucleation by almost an order of magnitude as the step height increases. In addition, they may influence the slip planes on which dislocation nucleation occurs. The results of the all atom method and the multiscale approach are in good agreement, even for steps with height of only a single atomic layer. Such corroboration supports the further use of the multiscale approach to study dislocation nucleation phenomena in more realistic geometries of technological importance, which are beyond the reach of all current atom simulations.