Atomistic simulation of cross-slip processes in model fcc structures

Abstract

Three-dimensional cross-slipped core structures of (a/2)[110] screw dislocations in model fcc structures are simulated using lattice statics within the embedded-atom method (EAM) formalism. Two parametric EAM potentials fitted to the elastic and structural properties of fcc Ni were used for the simulations. The two- and three-dimensional Green's function techniques newly developed by Rao et al, are used to relax the boundary forces in the simulations. Core structures and energetics of the constrictions occurring in the cross-slip process are studied. The core structure of the constrictions are diffuse, as opposed to a point constriction as envisaged by Stroh. The two constrictions formed by cross-slip onto a cross {111} plane have significantly different energy profiles, at variance with classical continuum theory of Stroh. This suggests that self-stress forces and atomistics dominate the energetics of the cross-slip process; the far-field elastic-energy contribution to cross-slip appears to be minimal. However, the Shockley partial separation distances near the constrictions as well as the variation in cross-slip energy with stacking-fault energy are in reasonable agreement with continuum predictions. Cross-slip energies estimated for Cu and Ni from these calculations show reasonable agreement with experimental data. The cross-slip energy shows a significantly weaker dependence on the Escaig stress compared with elasticity calculations. The activation volume for the cross-slip process is estimated to be of the order of 20b ³ at an applied Escaig stress of 10⁻³μ in Cu, an order of magnitude lower than experimental estimates and continuum predictions.