Molecular dynamics simulation of screw dislocations interacting with interstitial frank loops in a model FCC crystal

Molecular dynamics simulations of screw dislocations interacting with interstitial Frank loops are performed using specific boundary conditions in a model face-centered-cubic nickel crystal, in a configuration favorable to the formation of a helical turn on the dislocation. Both the interaction mechanism and the pinning stress caused by the defects are studied. In particular, we show (1) that the interactions involve athermal cross-slip events, (2) that the shape of the loop has a strong influence: loops with edges along <110> directions are unfaulted while loops with <121> edges are just sheared and (3) that the Frank loops are strong obstacles with unpinning reactions involving Orowan processes. The consequences of these observations on clear band formation are discussed. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.