Plastic deformation in nanotwinned copper mediated by source mechanisms based on Frank dislocations

Frank partial dislocations are common defects at twin boundaries that can be found at annealing twins or formed by dislocation-twin boundary interactions. These sessile twin boundary dislocations favor dislocation emission from twin boundaries as reported in literature, to explain reduced pop-in stresses during nano-indentation in Cu near a twin boundary. This study presents molecular dynamics simulation results for Cu samples, containing a twin boundary with an initial Frank partial dislocation dipole. The postulated nucleation of a 60° lattice dislocation from dissociated Frank partial dislocations at twin boundary is confirmed and its energetics is discussed. Two cooperative transmission & reflection mechanisms triggered by the interaction of 60° lattice dislocations and twin boundaries are identified. For a single 60° lattice dislocation captured within a twin lamella a new stable dislocation source mechanism is uncovered, emitting screw dislocations to both sides of the lamella. The source relies on the cooperative transmission & reflection mechanisms, occurring on both twin boundaries forming the lamella. This new stable source mechanism could contribute to explain extended plastic deformation in nanotwinned materials.