Preparation and mechanical properties of self-reinforced in situ Si₃N₄ composite with La₂O₃ and Y₂O₃ additives

Self-reinforced in situ Si₃N₄ composite material was prepared with high amount of La₂O₃ and Y₂O₃ additives by two-step hot pressing, and the optimum amount of additives was determined. The volume fraction of boundary glass phase was calculated based on the equilibrium of equivalent number in chemical reaction. For material with 15 mol% additives, flexural strength and fracture toughness at room temperature were 960 MPa and 12.3 MPa m ^1/2 , respectively. At temperature of 1350°C, flexural strength was maintained to 720 MPa and fracture toughness was significantly increased to 23.9 MPa m ^1/2 because of the high refractory of oxynitride glass containing compositions of La and Y. Self-reinforced mechanism was mainly responsible for crack deflection along the elongated β-Si₃N₄ grains.