Nanoindentation and nanoscratch tests of YAG single crystals: An investigation into mechanical properties, surface formation characteristic, and theoretical model of edge-breaking size

Nanoindentation and nanoscratch tests of YAG single crystals were systematically performed. The mechanical properties including elastic recovery rate, elastic modulus, nano hardness and fracture toughness of YAG single crystals were obtained by the nanoindentation tests. The surface morphologies of the scratched grooves were analysed using scanning electron microscopy. The formation characteristics of YAG single crystals induced by varied-depth nanoscratch indicated that there was distinct brittle-to-ductile transition phenomenon during the scratching process. Surface radial cracks occurred prior to the edge-breaking phenomenon, and transverse cracks extending to the surface of the work material dominated the brittle removal of YAG single crystals. A theoretical model of the edge-breaking size during the nanoscratch process was developed by considering the stress intensity factor, elastic recovery rate, and residual force. This model indicated that the edge-breaking size increased as the normal force, average elastic recovery rate and elastic modulus increased, but decreased as the nanoindenter tip radius, fracture toughness and nano hardness increased. When the average elastic recovery rate was within 17.5%-20% (the maximum elastic recovery rate was within 35%-40%), the values predicted by the theoretical model agreed well with the experimental values, and the average en or was less than 5%. The model could provide theoretical guidance for analysing the surface generation characteristics of brittle solid materials during the abrasive processing at brittle removal regime.