Effect of β-Si3N4 seed crystal on the microstructure and mechanical properties of sintered reaction-bonded silicon nitride

beta-Si3N4 Seed crystal has been synthesized from alpha-Si3N4 powder. Reaction-bonded Si3N4/SiC composite has been fabricated with beta-Si3N4 seed crystals. The nitridation behavior and the changes in mechanical properties resulting from the addition of seed crystals were studied before and after gas pressure sintering. Addition of seeds showed a considerable improvement in the nitridation, resulting in increase in fracture strength of the composite. Highly nitrided reaction-bonded Si3N4 (RBSN) as a result of the addition of seed crystals gave rise to high strength of composite after postsintering. Fracture toughness of the seeded Si3N4 was also improved up to 35% compared to the baseline Si3N4 Micrographs showed that the seeded Si3N4 developed a bimodal microstructure which resulted in an improvement in fracture toughness.