Anisotropy of surface fracture of sapphire plates with basal orientation upon friction

The influence of the anisotropy of the crystal structure of sapphire plates on the process of their mechanical wear has been revealed by using cyclic circular motion of silicon carbide spherical indenter over their surface. It is shown that in this friction geometry, crack formation areas are formed on the basal plane. Their centers are located 120 degrees apart from each other along the perimeter of the annular friction trace. Analysis of the crack distribution enables to determine the orientations of the velocity vector relative to the rhombohedral planes responsible for maximum and minimum wear of the sapphire plate of basal orientation.