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

• WC − x wt.% Si3N4 (x = 1–15) composites were prepared by two-step spark plasma sintering
• Addition of a small amount of Si3N4 to WC can significantly facilitate sintering.
• The α → β–Si3N4 transformation process is susceptible to the weight ratio of WC and Si3N4.
• WC–10 wt.% Si3N4 shows the best comprehensive mechanical performance.

The WC − x wt.% 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 10 wt.%. As the Si3N4 content reaches 10 wt.%, the α → β-Si3N4 transition rate reaches ~ 100%, and the fracture toughness of the specimen reaches 10.94 MPa·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 3 wt.% and above, abnormal WC-grain growth is suppressed due to the pinning effect by Si3N4 particles. As the Si3N4 content increases from 3 to 15 wt.%, the average WC-grain size increases until the Si3N4 content reaches 12 wt.%, and then decrease. With the Si3N4 content increases, the hardness of the specimens monotonically decreases.