Fabrication Of In Situ Elongated Beta-Sialon Grains Bonded To Tungsten Carbide Via Two-Step Spark Plasma Sintering

In order to reduce the difficulty of preparing binder-less cemented carbide and further broaden its application prospects, tungsten carbide toughened by in situ elongated beta-Sialon grains was developed via sintering ballmilled WC and alpha-Si3N4 powders using Al2O3-ZrO2 as a sintering aid and transformation additive. The twostep spark plasma sintering of the mixture at 1650 degrees C with dwelling at 1500 degrees C for 10 min was conducted under 30 MPa uniaxial pressure, and the densification behaviors, phase transformations, mechanical properties, and microstructures of the produced composites were investigated. The addition of Al2O3-ZrO2 reduced the initial temperature of the densification process by approximately 100 degrees C and its final temperature by 200 degrees C (compared with the densification temperatures of pure WC and Si3N4 materials) and fully transformed alpha-Si3N4 to Sialon (Si-Al-O-N) phases. Microstructural characterization data showed that the WC matrix contained homogeneously distributed equiaxed and elongated beta-Si5AlON7 grains. The WC composites containing in situ elongated beta-Sialon grains exhibited an optimal hardness of 18.93 +/- 0.03 GPa and enhanced fracture toughness of 10.43 +/- 0.27 MPa m(1/2). The toughening mechanism of the beta-Sialon phase involved the pull-out of elongated grains and crack bridging.