Anisotropy origins of coefficient of friction and scratch hardness in nano scratching monocrystalline copper

The monocrystalline Cu material mechanical properties at the micro and nano scale show complex anisotropy and size effects. However, the anisotropy of scratch hardness and coefficient of friction (COF) in micro-nano scratching monocrystalline Cu has not been well explained. In this paper, we conducted the nano-scratching experiments and corresponding molecular dynamics (MD) simulation under ramp normal force mode along two representative crystal orientations thereby investigating the anisotropy origins of scratch hardness and COF. The research results indicate that, for monocrystalline Cu materials, the scratch hardness and COF are closely related to the atomic slip resistance F_slip caused by the activated <1 1 0> {1 1 1} slip systems.