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

α/β-Si₃N₄ composites with various α/β phase ratios were prepared by hot pressing at 1600°–1650°C with MgSiN₂ 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 Si₃N₄-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-Si₃N₄ ceramics (16 GPa). The microstructures and mechanical properties can be tailored by choosing the additive and controlling the heating schedule.