Microstructural characterization of gas-pressure-sintered α-silicon nitride containing β-phase seeds

The starting α-Si3N4 powders with or without the addition of β-phase seeds using Y2O3 and Al2O3 as sintering aids were gas-pressure-sintered with the conditions, 0.9 MPa nitrogen gas at 1850 °C for 1 h. The microscopic evidence indicates that β-Si3N4 seeds incorporated in the starting α-Si3N4 powders play an important role in microstructural development and mechanical properties for silicon nitride. The growth of β-Si3N4 grains is initiated from the seeds, resulting in a core/shell microstructure was observed in the abnormal grain growth. As a result, the fracture toughness of silicon nitride was improved from 5.5 to 7.6 MPa m1/2 by adding β-phase seeds.