Development and Application of Composites Based on Sialon.

Effects of microstructures and additions of secondary phases in sialon ceramics on strength, fracture toughness and fatigue properties were investigated to obtain the composites based on sialon ceramics with high reliability for both rapid fracture and delayed failure. The addition of SiC particles increased the creep resistance at elevated temperature because of decreasing the amount and the thickness of intergranular glassy phase. In-situ-toughened sialon with elongated grains have high fracture toughness and high strength. On the other hand, oxide content in the intergranular phase and grain size affected slow crack growth attributable to the stress corrosion by humidity in air, and fatigue under cyclic loading was remarkably accelerated in the material with coarse grains. SiC whisker in insitu-toughened sialon improved fatigue properties at room temperature and the creep resistance without decreasing its strength and fracture toughness.