Effect of β-Si3N4 seed particles on the property of sintered reaction-bonded silicon nitride

The effect of seeding on the microstructural development and mechanical properties of sintered reaction-bonded silicon nitride was investigated by the use of beta-Si3N4 particles. Seeding of an appropriate amount of the beta-Si3N4 particles gave rise to the promotion of density and the resulting increase in fracture strength and hardness. The fracture toughness was also increased due to the development of elongated grains. On the other hand, addition of a large amount of seed particles showed lower strength and fracture toughness owing to the coalescence of large elongated grains. By seeding of 2 wt% beta-Si3N4 particles on Si powders of 7 micron, high fracture strength of 1100 MPa and fracture toughness of 7.2 MPa.m1/2 were obtained in sintered reaction-bonded silicon nitride ceramics. 16 refs.