Dislocation motion, constriction and cross-slip in fcc metals

A Finnis/Sinclair-type interatomic potential for copper is used to examine the properties of dissociated screw dislocations in the face-centred cubic lattice.The critical stress for dislocation motion is found to be a sensitive function of the partial dislocation separation, with a lower limit at least 85% smaller than the Peierls stress.The constriction of Heidenreich-Shockley partials is modelled using an applied stress which interacts only with the edge Burgers vectors; recombination is not observed, but there is a critical separation below which the potential energy of the dislocation rises very rapidly.The classical model of cross-slip, in which the dislocation cannot leave its slip plane unless it is fully constricted, is found to be incorrect.Instead, crossslip is possible at all partial separations, provided the driving stress is large enough.Finally, a new mechanism for cross-slip nucleation is described.