Interactions between prismatic dislocation loop and coherent twin boundary under nanoindentation investigated by molecular dynamics

Despite the intense interest in coherent twin boundary (CTB) of nanotwinned materials, many details of interactions between the complex dislocation (prismatic dislocation loop (PDL)) and CTB in a single crystal remain mysteries. In this study, molecular dynamics (MD) simulation of the nanoindentation on single crystal copper with CTBs has been presented. At the initial stage of nanoindentation, indenter moves downward and PDLs form. Thompson's tetrahedron notation has been adopted to scrutinize the process of PDL's formation without cross-slip and release from the indented place. Dislocations at PDLs' side edge are stair-rod partial dislocations, including two Lomer-Cottrell locks and two Hirth Locks. Then the interactions between PDL and CTB drive the migration of CTB. As a result, a parallelogram step which is bounded by Frank partial dislocations has been left, implying the formation of twinning dislocations. When the indenter moves further, the interactions repeat and twinning dislocations multiply. Our simulation results shed light on the interactions between PDL and CTB and would provide a new insight into understanding the role CTB plays during mechanical deformation.