Effects of Thin Film Coating on Ultra-Precision Machining of Single-Crystalline Sapphire

Sapphire has been widely used in a variety of applications thanks to its superior thermal, electrical, optical, and mechanical properties. Since sapphire is a brittle material, it is of critical importance to have a complete understanding of mechanisms leading to plastic deformation and crack formation for the machining of this material. In experiments, the machining of sapphire is commonly assisted by thin film coatings with materials such as mineral oil, wax, glue and other adhesives and it has been known that these coatings play significant roles in influencing the critical depth of cut (CDC) and the formation and propagation of cracks. In this study, we introduce a model using the molecular dynamics (MD) method to investigate the effects of different coating films on the machining mechanisms of sapphire. Ultra-precision cutting simulations are performed on coated sapphire models with thin films of different adhesion, and the results are compared with uncoated models. The adhesion of coating films is controlled by adjusting the interaction parameters between the thin film and the sapphire substrate. Effects of thin film coating are further analyzed by investigating the deformation and fracture mechanisms at atomistic levels.