Effect of nano-Al2O3 and Y2O3 on the properties and microstructure of Si3N4

Nano-Al2O3 and Y2O3 had a significant effect on the microstructural evolution and mechanical properties of Si3N4. With the addition of nano-Al2O3, large elongated grains were developed and the grain boundary phase decreased. Besides, the proportion of intergranular fracture increased for nano-Al2O3-doped Si3N4. The highest fracture toughness of nano-Al2O3-doped Si3N4 was 9.5 MPa m1/2 (7.2 MPa m1/2 for submicro- Al2O3-doped Si3N4). The increase in mechanical properties might be ascribed to the formation of large elongated grains, the reduction of secondary phases and the “pullout” of elongated grains.