Study on the brittle-plastic transition of YAG crystals based on nano-scratch experiments

Abstract YAG crystals are typically hard and brittle materials that are prone to be damaged during optical processing. In order to improve processing quality, it is necessary to avoid brittle damage as much as possible so that the material is removed in the plastic domain, so it is particularly important to study the critical conditions for the brittle-plastic transition of YAG crystals. The brittle-plastic transition of the (100) and (111) crystal faces of YAG crystals was investigated by variable load and constant load nano-scratch experiments. By analyzing the scratch morphology and friction-scratch distance curves, the critical load of brittle plastic transition for each crystal surface is obtained. The results show that the critical loads of (100) and (111) crystal faces for brittle-plastic transformation under variable load nano-scratch experiments are 113.575 mN and 84.05 mN, respectively, and the different critical loads of the two crystal faces are due to the discrepancy of surface energy. According to Griffith’s fracture theory, because the surface energy of (100) crystal face is higher, the energy required for brittle fracture of the crystal surface is higher, so the critical load of brittle-plastic transition is larger. Finally, the correctness of the critical load was verified by constant load nano-scratch experiments.