Spark plasma sintered high hardness α/β Si3N4 composites with MgSiN2 as additives

α/β Si3N4 composites were prepared by spark plasma sintering at 1340–1500 °C for 3–12 min with MgSiN2 as additives. The hardest α/β Si3N4 composite has a Vickers indentation hardness of 21.4 GPa, which is as hard as α-Sialon ceramics and harder than ordinary β-Si3N4 ceramics. The fracture toughness increased from 5.7 to 7.7 MPa m1/2 with the β-Si3N4 content increasing from 21 to 76 wt.%, and the Vickers indentation hardness of the latter was 19.0 GPa.