Fabrication and characterization of Si3N4 reinforced Al2O3-based ceramic tool materials

Abstract Al 2 O 3 –Si 3 N 4 composites ceramic tool materials with Y 2 O 3 as sintering additive were fabricated by the hot pressing process at 1450 °C for 30 min under 32 MPa in vacuum. Different mass fractions of Si 3 N 4 as reinforcements were employed. The mechanical properties, microstructure, strengthening and toughening mechanisms of the composites were investigated. The content of Si 3 N 4 had significant effect on the mechanical properties and microstructure of the composites. Al 2 O 3 -25 wt% Si 3 N 4 -1 wt% Y 2 O 3 had the optimum comprehensive mechanical properties with flexural strength, fracture toughness, Vickers hardness and relative density of 768.7±63.9 MPa, 6.8±0.4 MPa m 1/2 , 19.6±0.4 GPa and 99.6±0.2% respectively. A core–shell structure with Si 3 N 4 as core and Al 2 O 3 as shell was firstly formed in the composite. The core–shell structure was generated through a rapid dissolution–transport–precipitation process. Elongated β-Si 3 N 4 grains with a diameter of 0.3–0.5 µm and aspect ratio of 5 were in-situ synthesized. The improved mechanical properties were attributed to the strengthening and toughening mechanisms including the mixed fracture mode of intergranular and transgranular fracture, the crack deflection, the high grain boundary strength, the pinning and bridging effects of the core–shell structure and the elongated grains.