Effect of grain boundary additions of Al, Ta, Ni, Zr, and Ag on the plastic deformation and mechanical properties of nanocrystalline copper investigated by molecular dynamics simulations

Abstract The effect of grain boundary (GB) additions of Al, Ta, Ni, Zr, and Ag on the plastic deformation and mechanical properties of nanocrystalline copper is investigated using molecular dynamics simulations. The simulation results indicate that adding Al, Ta, Zr, Ag, and Ni to the GBs can increase the flow stress of nanocrystalline copper by 79.0%, 15.5%, 6.7%, 4.9%, and 4.5%, respectively. Moreover, the flow stress increases with increasing concentrations of Al and Ta, while for Zr and Ag the flow stress increases first and then decreases with increasing their concentrations. The strengthening effect is related to the grain size refinement induced by the GB doping and plastic deformation. At 10% strain, the average grain size of the Cu-8 at.% Al sample is reduced by 15.8% relative to the unstrained pure nanocrystalline copper, representing the largest grain refinement among those doping elements. The grain size refinement cannot be entirely attributed to the atomic size mismatch between the addition and the matrix atoms. The GBs are significantly broadened by the additions of Al, Ta, and Zr. The additions of Al, Ta, Zr, and Ag decrease the dislocation density induced by both the initial thermal relaxation and plastic deformation, which suggests that these GB additions inhibit the dislocation-based deformation mechanism. The additions of Al and Ta still have significant strengthening effect on nanocrystalline copper at high temperature, which increase the flow stress by 49.2% and 12.2% at a concentration of 8 at.%, respectively. These findings indicate that both the types of addition elements and their concentrations are critical factors to be taken into account when utilizing the GB doping approach to strengthen nanocrystalline copper.