Effects of α/β ratio in starting powder on microstructure and mechanical properties of silicon nitride ceramics

The effects of α/β ratio in the starting powder on microstructure development and mechanical properties of sintered silicon nitride ceramics were investigated. With increasing β-phase content, the microstructure became finer, the finest-grained microstructure was developed from the powder with pure β-phase, whereas a duplex microstructure was developed from high α-phase content powder. The results show that the microstructure of silicon nitride ceramics can be tailored by changing the α/β ratio in the starting powder. The mechanical properties have an optimum region where the α/β ratio equals 1. Both flexural strength and fracture toughness can be improved by controlling size, number, aspect ratio and size distribution of the rod-like β-Si3N4 grains