Microstructure and Mechanical Performance of Silicon Nitride Ceramics with Seeds Addition

With Y2O3:Al2O3 of different weight ratios as sintering additives and 3wt% beta-Si3N4 seeds addition, silicon nitride ceramics were prepared by gas pressure sintering. The phase composition, density, microstructure, room temperature as well as elevated temperature mechanical properties were investigated. The experimental results indicated that the alpha ->beta phase transformation of silicon nitride would be finished at 1800 degrees C for 2 h, and the densities of all specimens were over 97% of theoretical density. Compared with the specimen without seeds addition, the room temperature bending strength, the elevated temperature flexural strength at 1200 degrees C and the fracture toughness of the specimen with 6wt%Y2O3-4.5wt%Al2O3 and 3wt% beta-Si3N4 seeds addition can be improved by 20%, 16% and 8%, respectively.