Mechanical Properties and Oxidation Resistance of Silicon Nitride Produced from Low Purity β-Powder

Abstract

Low-cost and low-purity β-Si₃N₄ powder was sintered at 1900°C for 8h in 1 MPa nitrogen gas with 2mol% Y₂O₃-2mol%Al₂O₃ additives. Fully densified bodies were obtained by the gas-pressured-sintering. This material had a strength of 689 MPa and a fracture toughness of 6.4 MPa·m^1/2. Furthermore, the high temperature strength, oxidation resistance, fatigue parameter were measured. The degradation of strength at elevated temperature was less than 5% up to 900°C. No fatal defect was created in 100h-oxidation in 900°C-air. The fatigue parameter was on a level with general material produced from α-rich powder. These properties are adequate for structural material application.