Deformation characteristics and surface generation modelling of crack-free grinding of GGG single crystals

Gallium gadolinium garnet (GGG) single crystals are the primary host material for making the high-power solid-state lasers. GGG single crystals are difficult-to-machine materials due to their high hardness and brittleness. Ultra-precision grinding experiments of GGG crystals was carried out, which generated the ground surface and subsurface free of brittle fracture and cracks. The TEM examination demonstrated that the plastic formation of GGG crystals induced by ultra-precision grinding was dominated by the slippage of (114) crystal planes, as well as nanocrystallization and amorphization. Morphology and roughness of the ground surfaces were measured by AFM. A theoretical model was developed for predicting the surface morphologies and surface roughness by considering the random distributions of the radius, location and protrusion height of abrasive grits. The simulated results were found to be in good agreement with the experiment. This model is thus useful for understanding the effect of material deformation and removal on the surface finish in ultra-precision grinding of hard and brittle crystals, and can provide meaningful guidance for optimizing the process parameters of grinding of hard and brittle crystals.