Dislocation interactions at reduced strain rates in atomistic simulations of nanocrystalline Al

During the propagation of a lattice dislocation in a nanocrystalline structure, the grain boundary (GB) has to interact with the impinging Burgers vector. Such interaction mechanisms are usually classified as dislocation-GB accommodation and often ascribed to atomic shuffling or stress assisted free volume migration. Here we present a dislocation-GB interaction mechanism where misfit regions available in a nanosized GB can assist the propagation of a lattice dislocation. The mechanism occurs at strain rates 2 orders of magnitude lower than those usually applied in molecular dynamics. An impinging dislocation with a Burgers vector unfavourable to pass the ledge structures of the GB, double cross-slips and interacts with a dislocation loop nucleated from a misfit region of the GB. This results in the cooperative propagation of two perfect dislocations that facilitate the slip of the initial lattice dislocation on a plane with low resolved shear stress. Additionally, the interaction of this dislocation with a dislocation nucleated from another GB and gliding on a parallel slip plane, results in the emission of a vacancy in the grain interior (Figure 1). Both mechanisms are only observed at a reduced strain rate of 106/s and do not occur at higher strain rates of 108/s where high Schmid factor slip systems are preferred. The observed dislocation events are preceded and/or accompanied by several time-dependent GB accommodation processes, brought to the foreground by the reduced strain rate of the simulation, such as GB dislocation upwards motion, local GB migration and GB diffusion.