Fabrication and characterization of Sialon-Si3N4 graded nano-composite ceramic tool materials

Sialon-Si3N4 graded nano-composite ceramic tool materials with five-layered symmetrical distribution were fabricated by using hot pressing technique. Mechanical property tests have been conducted to determine the optimal structural parameters and sintering parameters. The residual stresses in the surface layer of the graded ceramic tool materials were calculated by the indentation method. The experiment results showed that Sialon-Si3N4 graded ceramic tool materials with a thickness ratio of 0.3, which were sintered under a pressure of 35 MPa at a sintering temperature of 1700-1750 °C for 60 min, had optimum mechanical properties. And the graded structure can induce residual compressive stresses in the material surface layer. The characterization revealed a typical duplex distribution with small β-Si3N4 grains embedded in the matrix of large β-Si3N4 grains. This duplex microstructure can contribute to the improvement of flexural strength and fracture toughness. Additionally, a mix of intergranular and transgranular fracture, crack deflection and crack bridging in the material surface layer contributed to the strengthening and toughening mechanisms for Sialon-Si3N4 graded ceramic tool materials.