Various reactions between edge or screw dislocations and interstitial Frank loops were studied by means of molecular dynamics simulations. The calculations were performed at 600K using an embedded atom method potential describing a face-centered cubic material with a low stacking-fault energy. An interaction matrix was determined that provided the corresponding interaction strength. In order to investigate the role of pile-ups, simulations with one or two dislocations in the cell were performed. It was found that screw and edge dislocations behaved very differently. Edge dislocations sheared Frank loops in 2 out of 3 cases, while screw dislocations systematically unfaulted Frank loops via mechanisms that involved cross-slip. After unfaulting, they were strongly pinned by the formation of extended helical turns. The simulations revealed a novel unpinning effect that led to clear band-broadening. This process involved the junction of 2 screw dislocations around a helical turn (arm-exchange) and the transfer of a dislocation from its initial glide plane to an upper glide plane (elevator effect).

Atomic-Scale Plasticity in the Presence of Frank Loops. T.Nogaret, C.Robertson, D.Rodney: Philosophical Magazine, 2007, 87[6], 945-66