Phase assemblage and properties of a nonoxide composite fabricated by a two-step gas-pressure sintering

In this work, a composite composed of $\beta$-Sialon (Z=4) and ZrN has been fabricated by a two-step gas-pressure sintering method, and the effects of ZrN content and applied pressure on the phase behavior, densification and mechanical properties have been investigated. The phase behaviors were mainly dependent on the ZrN content and the applied pressure. The composites composed of $\beta$-Sialon (Z=4), ZrN, 15R-Sialon (0.4 MPa) and 12H-Sialon (0.7 MPa) as major phases, with different intermediate phases depending on the ZrN content. It is revealed that with the two-step sintering technique, a higher applied gas pressure has a positive effect on mass loss, and significantly improved the mechanical properties. The addition of ZrN particles greatly helped the densification behavior, reduced the mass loss, and increased fracture toughness of the composites, but decreased hardness due to formation of intermediate phases and grain coarsening. The addition of ZrN increased the fracture toughness due to the toughening mechanisms of crack branching, crack deflection and crack bridging.