Mechanical Properties and Nanoindentation Size Effects of YAG Crystals with Different Crystal Faces

In this study, the anisotropic mechanical properties of YAG crystal (100), (110), and (111) crystal faces are investigated by nanoindentation experiments. The load-displacement curves, hardness (H) and elastic modulus (E) are obtained for each crystal face at different maximum loads. The loading curves of the three crystal faces showed displacement mutations, which are caused by microcracks during indentation of the indenter. The H and E of three crystal faces dropped as the indentation depth increased, obviously indicating indentation size effect (ISE). The H and E magnitude sequence of the three crystal faces is: (110) > (111) > (100). The surface energy is calculated by the Cambridge Serial Total Energy Package (CASTEP) program to explain the experimental phenomenon that the hardness and elastic modulus of the three crystal faces are different. Using the Nix-Gao model to fit the Hardness-indentation depth data, the hardness H0 of the (100), (110), and (111) crystal faces without strain gradient effect are obtained as 12.978, 15.61, and 15.432 GPa, respectively, which can be used as a reference value for the hardness of YAG crystals. The characteristic lengths h* of (100), (110), and (111) crystal faces are 730.545, 362.049, and 375.196 nm, respectively.