MECHANICAL-PROPERTIES AND OXIDATION RESIS TANCE OF SILICON-NITRIDE PRODUCED FROM LOW PURITY BETA-POWDER

Low-cost and low-purity beta-Si3N4 powder was sintered at 1900 degrees C for 8h in 1 MPa nitrogen gas with 2 mol% Y2O3-2 mol%A1(2)O(3) addit ives, Fully densified bodies were obtained by the gas-pressured-sinter ing. This material had a strength of 689 MPa and a fracture toughness of 6.4 MPa . m(1/2), Furthermore, the high temperature strength, oxida tion resistance, fatigue parameter were measured, The degradation of s trength at elevated temperature was less than 5 % up to 900 degrees C, No fatal defect was created in 100h-oxidation in 900 degrees C-air, T he fatigue parameter was on a level with general material produced fro m alpha-rich powder. These properties are adequate for structural mate rial application.