Deformation anisotropy of nano-scratching on C-plane of sapphire: A molecular dynamics study and experiment

Sapphire is a typical anisotropic material due to its unique crystal structure. The study on the influence of anisotropy on the deformation mechanism has significance in guiding the processing of sapphire. In this study, the scratching were carried out on C-plane sapphire along [(1) over bar 010], [(2) over bar 110], [(1) over bar 100] and [(1) over bar2 (1) over bar0] directions by molecular dynamics simulation. Moreover, scratching experiments were conducted on C-plane sapphire along [(1) over bar 010] and [(1) over bar2 (1) over bar0] directions to compare with the simulation results. The results show that the activation of the prismatic slip affects the morphology and stress distribution on scratching surface in simulation and present evidences that the prismatic slip system provides nucleation conditions for cracks in experiment. The lateral flow of removed materials of the scratches along [(1) over bar 010] and [(1) over bar 100] directions which are parallel to the A-plane is more significant than that along [(2) over bar 110] and [(1) over bar2 (1) over bar0] directions. This study also shows that the scratches along [(1) over bar 010] and [(1) over bar 100] directions which are parallel to the A-plane result in a smaller thickness of subsurface damage layer. Besides, the transmission electron microscopy images of the cross-section have been compared with the simulation images, which validate the subsurface defects and reveal the difference of the symmetry of subsurface damage along different scratching directions.