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 degrees 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 beta-Si3N4 grains. (C) 1999 Elsevier Science Ltd. All rights reserved.