Abstract: As a typical brittle material, YAG crystals are highly prone to microcracks during optical processing, which seriously affects the surface quality of the components. Fracture toughness (KIC ) reflects the ability of a material to resist crack extension, and accurate measurement of KIC at the microscopic scale is of great significance for ultra-precision processing of YAG crystals. Nanoindentation experiments were carried out on the three typical crystal faces (100), (110), and (111) of YAG crystals in this work. Firstly, the indentation hardness (H) and elastic modulus (E) of samples with different crystal faces were measured using a Berkovich diamond indenter, and the radial crack length c generated by the Cube-corner diamond indenter was measured by scanning electron microscopy. Then, based on the experimentally measured H, E and c, the KIC of (100), (110) and (111) crystal faces were calculated to be 1.473 MPa⋅m1/2 , 2.194 MPa⋅m1/2 and 1.700 MPa⋅m1/2 , respectively. Furthermore, the essential reasons for the different KIC of the three crystal faces were explored through surface energy analysis.

Key words: fracture toughness, yttrium aluminum garnet crystal, nanoindentation, Berkovich indenter, Cube-corner indenter, surface energy