Characteristics of ZrO2-Dispersed Si3N4 without Additives Fabricated by Hot Isostatic Pressing

Dense, ZrO2‐dispersed Si3N4 composites without additives were fabricated at 180 MPa and ∼1850° to 1900°C for l h by hot isostatic pressing using a glass‐encapsulation method; the densities reached >96% of theoretical. The dispersion of 20 wt% of 2.5YZrO2 (2.5 mol% Y2O3) in Si3N4 was advantageous to increase the room‐temperature fracture toughness (∼7.5 MPa˙m1/2) without degradation of hardness (∼15 GPa) because of the high retention of tetragonal ZrO2. The dependence of fracture toughness of Si3N4–2.5YZrO2 on ZrO2 content can be related to the formation of zirconium oxynitride because of the reaction between ZrO2 and Si3N4 matrix in hot isostatic pressing.