Subsurface damage in sapphire ultra-precision grinding

This work is to investigate the subsurface damage distribution law and suppression methods in sapphire ultra-precision grinding. The grinding strategies of rough grinding, semi-finish grinding and ultra-precision grinding are used to suppress the subsurface damage, the effects of grinding wheel grit size and number of grinding passes on the subsurface damage are investigated. First, cross-section polishing, FIB, and ion beam polishing were employed to reveal the scale and distribution of subsurface damage. Second, chemical etching was performed on the subsurface, the subsurface cracks with different grinding strategies were exposed, and the crack distribution density was obtained by image processing. Then, the subsurface deformation behavior and microcrack formation mechanism were investigated by TEM. The damage scales of different grinding strategies were evaluated using photothermal absorption. Ultimate, ultra-precision grinding can control the subsurface damage scale to 3.9 μm, the mechanisms of subsurface damage generation and removal were revealed. Meanwhile, a subsurface damage model more suitable for the combined grinding strategy was proposed.