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 nanoscale to atomic-scale during ultrasonic vibration-assisted (UVA) nanoscratching of monocrystalline AlN with a single-point diamond tip. Simulation results suggest UVA-scratching exhibits lower tangential force, normal force, and friction coefficient under the same scratching depth as ordinary scratching. UVA-scratching demonstrates stronger material removal than ordinary scratching due primarily to the vibration-induced rise of the local temperature to facilitate atomic bond breakage and 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 UVA-scratching mode than with the ordinary scratching mode. UVA-scratching produces a smoother scratched surface. For instance, the root mean square of the surface after UVA-scratching is only about one-third of that after ordinary scratching at the same scratching depth. Furthermore, utilizing ultrasonic vibration can reduce scratching-induced material pile-up and the subsurface damage primarily consisting of dislocations and stacking faults. This is because vibration can reduce the stress distribution range and restrain stress concentration. This work can provide useful knowledge for high-quality and efficient ultra-precision surface machining for hard-brittle materials.