A molecular dynamics investigation into plastic deformation mechanism of nanocrystalline copper for different nanoscratching rates

Abstract

The plastic deformation mechanisms of nanoscratching process are investigated through the study of a rigid diamond tip sliding against nanocrystalline Cu using molecular dynamics (MD) simulation. Special attentions are paid to the scratching rate effects, as well as the crystal structural effects from single crystalline, polycrystalline and nanotwinned (NT) polycrystalline. With the increase of scratching rate, scratching force and workpiece temperature increase continuously due to severe plastic deformation and large chip volume, resulting in dislocation slip, GB slip, and twinning/detwinning. Scratching rate also governs the distributions of potential energy and kinetic energy of all the atoms, revealing the rate-dependent plastic deformation. Specifically, the plastic deformation for different scratching rates depends on the competition of scratching force, workpiece temperature and tool–workpiece contacting time that affect dislocation evolution. In addition, the results show that the plastic deformation due to scratching of single crystalline Cu is dominated by the dislocation–dislocation interactions. And the scratching induced plastic deformation of polycrystalline Cu is determined by the dislocation-grain boundary (GB) interactions. As for NT polycrystalline Cu under scratching, it is the dislocation–GB–twin boundary (TB) interactions accompanied with the twinning/detwinning process. While the presented MD simulations and the associated conclusions are based on nanocrystalline Cu, it is believed that the current deformation mechanism could also be applied to other face-centered-cubic nanocrystalline metals.