Atomic-scale understanding of graphene oxide lubrication-assisted grinding of GaN crystals

To understand the material removal and damage evolution mechanisms of GaN crystals involved in graphene oxide (GO) lubrication-assisted grinding, molecular dynamics (MD) simulations of single-grit grinding were performed under different GO concentrations. The findings demonstrated that the GO nanosheets presented a favorable dispersion behavior in the low-concentration coolant; however, at excessively high concentrations, they exhibited severe agglomeration, which hindered the effective interaction between GO nanosheets and the workpiece. With the increase in GO concentration, the material removal rate, elastic recovery amount, normal grinding stress, surface roughness, and subsurface damage depth initially decreased and subsequently increased. Grinding assisted by GO lubrication at an appropriate GO concentration effectively minimized the grinding force, friction coefficient, grinding temperature, grinding stress, elastic recovery, and dislocation density compared to dry grinding and pure water-lubricated grinding, thereby enhancing both surface and subsurface quality. In addition, appropriately reducing the grinding depth and increasing the grinding speed effectively minimized the subsurface damage depth. However, an excessively high grinding speed would lead to an increase in both grinding temperature and surface roughness. These findings not only enhance our understanding of the atomic-scale removal mechanisms of GaN substrates facilitated by GO nanosheets in abrasive machining process, but also present a novel strategy for the efficient and ultra-precision machining of other brittle solids.