Effect Of Y2O3 and Yb2O3 on the microstructure and mechanical properties of silicon nitride

The effect Of Y2O3 and Yb2O3 on the microstructure and mechanical propertie s of silicon nitride was investigated. The effect of heat-treatment on the crystallization of grain boundary phases and on the high-temperature streng th was also studied. Sinterability and alpha to beta phase transformation o f silicon nitride with Y2O3 were more pronounced than that with Yb2O3, for the same additive content. A wider grain size distribution and a larger ave rage grain size were observed in the specimens with Y2O3. The specimens wit h Yb2O3 showed higher flexure strength, hardness and fracture toughness owi ng to a more frequent pullout of grains. Strength retention of silicon nitr ide at elevated temperatures was attributed to the crystallization and refr actoriness of the grain boundary phases. (C) 2001 Elsevier Science Ltd and Techna S.r.l. All rights reserved.