Strain rate effect on plastic deformation of nanocrystalline copper investigated by molecular dynamics

The strain rate effect on the plastic deformation of nanocrystalline copper with mean grain sizes in the range of 3.8-27.3 nm has been investigated by using molecular dynamics simulation. The simulated results indicate that the critical mean grain size corresponding to the transition of plastic deformation mechanism is little influenced by the strain rate in the strain-rate range of 1×107-1×1010 s−1. The simulated grain-size dependence of the strain rate sensitivity for strain rate below 1×108 s−1 is in agreement with the experimental results of nanocrystalline copper reported in literatures. The strain rate sensitivity values for the simulated samples with mean grain sizes of 3.8 and 5.5 nm are 0.073 and 0.065 respectively. These results reveal that the stress-driven grain-boundary plastic deformation mechanisms such as grain-boundary sliding and migration are not as sensitive to strain rate as that expected for the thermally assisted mechanisms. Furthermore it is found that if the stacking faults act as obstacles to the motion of partial dislocations the strain rate sensitivity will increase.