Nucleation and propagation of dislocations in nanocrystalline fcc metals

Detailed analysis of the nucleation and propagation of dislocations from grain boundaries in nanocrystalline Al using molecular dynamics reveals that: (1) the leading and trailing partial dislocations are nucleated at different regions within a grain boundary or even different grain boundaries; (2) propagation is hindered by a pinning–depinning mechanism influenced by the relative orientation between the Burgers vector and the ledge geometry of the grain boundary and (3) depinning is thermally activated and therefore not purely mechanically driven. These new aspects of nucleation and propagation are important for incorporation into mesoscopic models describing nanocrystalline plasticity.