Gas-pressure sintering of β-silicon nitride containing Y2O3 and Nd2O3

Y2O3-Nd2O3-doped β-Si3N4 was sintered at 1700°C to 1900°C for 4 h in 10 MPa N2, and the effect of the amount of the additives and sintering temperatures on strength, fracture toughness and the microstructure was investigated. A dense material (>98% of the theoretical) was obtained by firing at 1900°C with addition of 1 to 10 mol% of oxides. Rod-like β-Si3N4 grains developed by firing at 1900°C increased the fracture toughness up to 7.8 MPa √m because of the pull-out and the crack-deflection mechanism. The material made from β-Si3N4 powder had a high Weibull modulus than that from α-Si3N4 powder.