High Hardness α-Si3N4 Ceramics Reinforced by Rod-like β-Si3N4 Seed Particles

Dense α-Si 3 N 4 ceramics were fabricated by the tape casting technique using La 2 O 3 as a sintering additive to effectively suppress the α-β transformation. Addition of a small amount of elongated β-Si 3 N 4 seed particles significantly improved the toughness of sintered bodies from about 2 to 6 MPa.m 1/2 . It was found that both strength and toughness showed a linear dependence on the β-Si 3 N 4 content, while hardness remained almost constant up to a β-content of 43%. Consequently, it was possible to fabricate the α/β-Si 3 N 4 composites that showed much higher hardness (about 19 GPa) than ordinary Si 3 N 4 and SiAlON ceramics, as well as comparable strength (about 800 MPa) and toughness (about 6 MPa.m 1/2 ).