Atomistic study of material removal behavior during ultrasonic vibration-assisted nanoscratching of single-crystal AlN

Molecular dynamics simulations were used to investigate surface material removal and subsurface damage at the nanoscale to the atomic scale during ultrasonic vibration-assisted (UVA) nanoscratching of single-crystal AlN with a single-point diamond tip. The simulation results suggest that UVA-scratching results in a lower tangential force, normal force, and friction coefficient than ordinary scratching at the same scratch depth. UVA-scratching results in a greater material removal rate than ordinary scratching because of the vibration-induced rise in the local temperature, which facilitates atomic bond breakage and the lateral extension of stacking faults in the superficial layer. Uniform monolayer removal consisting of the outermost Al atoms and the connected N atoms is easier to achieve in the scratching path with the UVA-scratching mode than with the ordinary scratching mode. UVA-scratching produces a smoother scratched surface. For example, the root mean square of the surface after UVA-scratching is only approximately one-third of that after ordinary scratching at the same scratch depth. Furthermore, ultrasonic vibration can reduce scratching-induced material pile-up and subsurface damage, which primarily consists of dislocations and stacking faults. This is because vibration can reduce the stress distribution range and restrain the stress concentration. This work can provide useful knowledge for high-quality and efficient ultraprecision surface machining for hard-brittle materials.