Fabrication of Hard and Strong α/β‐Si3N4 Composites With MgSiN2 as Addivitives

α/β-Si 3 N 4 composites with various α/β phase ratios were prepared by hot pressing at 1600°-1650°C with MgSiN 2 as sintering additives. An excellent combination of mechanical properties (Vickers indentation hardness of 23.1 GPa, fracture strength of about 1000MPa, and toughness of 6.3 MPa·m 1/2 ) could be obtained. Compared with conventional Si 3 N 4 -based ceramics, this new material has obvious advantages. It is as hard as typical in-situ-reinforced α-Sialon, but much stronger than the latter (700 MPa). It has comparable fracture strength and toughness, but is much harder than β-Si 3 N 4 ceramics (16 GPa). The microstructures and mechanical properties can be tailored by choosing the additive and controlling the heating schedule.