Interface-dependent nanoscale friction of copper bicrystals: tilt versus twist

Abstract

Interfaces with different structural units have a strong impact on their microscopic deformation behavior and correlated macroscopic mechanical response. In current study, we elucidate the underlying nanoscale friction mechanisms of Cu bicrystals by means of molecular dynamics simulations. Four grain boundaries, i.e., pure tilt and twist with two misorientation angles of 7.63° and 67.38°, are considered to address the grain boundary structure dependence of the friction. While the small- and high-angle tilt grain boundaries are respectively composed of parallel edge dislocation dipoles and edge dislocations of like sign, the small- and high-angle twist ones respectively incorporate two sets of intersecting screw dislocations and a planar defect. Simulation results demonstrate that the grain boundary resistance to dislocation motion and absorption, as well as the grain boundary evolution, are significantly varied with grain boundary structural units. It is found that splitting, annihilation and generation of grain boundary dislocations are the three competing decomposition mechanisms of the well-defined grain boundaries. The anisotropic dislocation-grain boundary interactions in turn results in a strong grain boundary structure dependence of the frictional response for scratching in the vicinity of grain boundaries. These findings will not only advance our understanding of the interface-dependent nanoscale friction behavior of metals, but also provide rational design guidelines for the synthesis of advanced functional nanostructured materials with unique internal interface textures.