Effect of nano-Al 2O 3 and Y 2O 3 on the properties and microstructure of Si 3N 4

Abstract

Nano-Al 2O 3 and Y 2O 3 had a significant effect on the microstructural evolution and mechanical properties of Si 3N 4. With the addition of nano-Al 2O 3, large elongated grains were developed and the grain boundary phase decreased. Besides, the proportion of intergranular fracture increased for nano-Al 2O 3-doped Si 3N 4. The highest fracture toughness of nano-Al 2O 3-doped Si 3N 4 was 9.5 MPa m 1/2 (7.2 MPa m 1/2 for submicro- Al 2O 3-doped Si 3N 4). 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.