Effects of Phase Composition on Microstructure and Mechanical Properties of Lu2O3-doped Porous Silicon Nitride Ceramics

Porous silicon nitride ceramics (Si3N4) were fabricated by pressureless sintering using different particle size of silicon nitride powder. Lu2O3 was used as sintering additive. According to phase relationships in the ternary system Si3N4-SiO2-Lu2O3, porous Si3N4 ceramics with different phase composition were designed through the change of the content of SiO2 which was formed by the oxidation at 800°C in air. Porous Si3N4 with different phase compositions was obtained after sintering at 1800°C in N2 atmosphere. A small content of SiO2 favored the formation of secondary phase Lu4Si2O7N2, while large content of SiO2 favored the formation of secondary phase Lu2Si2O7 and Si2N2O. Porous Si3N4 ceramics with secondary phase Lu4Si2O7N2 had a flexural strength of 207 MPa, while that with secondary phase Si2N2O and Lu2Si2O7 had lower flexural strength.