Mitigation of damage during surface finishing of sapphire using laser-assisted machining

Abstract

Machining of hard, crystalline ceramics is time-consuming, expensive and vital in many industries, but getting good results is challenging because of the surface damage it can cause. For sapphire machining damage can be especially detrimental because it can create significant stresses in the surface and sub-surface regions. Worst case, the stresses are relieved by crack propagation, fracture, and chipping at the surface. Conventional machining with a single point diamond-turning machine was compared to the same method with a laser simultaneously focused through a diamond stylus. The laser makes ductile machining more favorable and provides in situ annealing of damage. Micro-Raman spectroscopy was used to quantify residual stresses and optical microscopy was used to identify cracking. A reduction in the residual stresses was achieved when using the laser. This is seen most dramatically at higher laser powers, where fracture, cracking and chipping can be alleviated.