Atomistic simulation studies on deformation mechanism of nanocrystalline cobalt

An approach is developed to investigate the deformation behavior of hexagonal close-packed (hcp) nanocrystalline (nc) cobalt by computer simulations. The microstructures are modeled by a grain growth theory, and the mechanical deformation behavior is investigated using molecular dynamics simulation in nc-cobalt samples with an average grain size of 10 nm. The deformation mechanisms are found to involve both full and partial dislocation activities. Despite the small stacking fault energy of nc-cobalt, surprisingly the deformation twinning is not prevalent in the model cobalt sample. The simulation suggests that unlike the easy twinning events in coarse-grained hcp metals, deformation of nanocrystalline cobalt is primarily controlled by partial dislocation slips and stacking faults. The continuous accumulation of deformation faults eventually leads to hcp to face-centred cubic allotropic phase transformation during tension and compression of nc-cobalt.