Molecular dynamics simulations of nanoscratching of 3C SiC

We have carried out molecular dynamics simulations of nanoindentation followed by scratching at constant depth on the Si-terminated (0 0 1) surface of 3C SiC. The dependence of the friction coefficient, scratch hardness, and wear on scratching depth, velocity, direction, and indenter size and shape are investigated. In general, both the scratch hardness and friction coefficient increase with indentation depth but decrease with increasing scratching speed. We also find that the scratch hardness and friction coefficient are anisotropic, i.e. they are larger when scratching in the [1 1 0] direction than in the [1 0 0] direction. The friction coefficient also depends on the rake angle of the tool and is larger for a pyramidal indenter, due to the presence of a large negative rake angle in this case. While the primary mode of wear observed for scratching is ploughing in good agreement with experimental studies, there is significantly more pile-up and chip formation in the [1 1 0] direction. We have also used the shortest path ring distribution, pair-correlation function, bond-angle distribution and bond number analysis to investigate the nature of the plastic deformation due to nanoscratching. We find that scratching leads to a partial amorphization of the material along the scratching trajectory. The size of the amorphization region increases with scratching velocity, thus explaining the decrease in scratch hardness and friction coefficient for higher scratching velocities.