WC–Si3N4 composites prepared by two-step spark plasma sintering

Abstract

The WC−xwt.% Si3N4 (x=1–15) composites were prepared by two-step spark plasma sintering. The densification behavior, phase constitution, microstructure and mechanical properties of the WC–Si3N4 composite were investigated. Addition of a small amount of Si3N4 to WC can significantly facilitate sintering due to liquid sintering. After two-step sintering, the α→β-Si3N4 transformation rate and the fracture toughness increase with the Si3N4 content, and then decrease as the Si3N4 content exceeds 10wt.%. As the Si3N4 content reaches 10wt.%, the α→β-Si3N4 transition rate reaches ~100%, and the fracture toughness of the specimen reaches 10.94MPa·m1/2. The existence of Si in the starting powder helps eliminate the formation of decarburized-phase W2C. During liquid-sintering, abnormal WC-grain growth tends to happen through two-dimensional nucleation. When the Si3N4 content increases to 3wt.% and above, abnormal WC-grain growth is suppressed due to the pinning effect by Si3N4 particles. As the Si3N4 content increases from 3 to 15wt.%, the average WC-grain size increases until the Si3N4 content reaches 12wt.%, and then decrease. With the Si3N4 content increases, the hardness of the specimens monotonically decreases.