Densification, microstructure and tribomechanical properties of SPS processed β-SiAlON bonded WC composites

Densification, microstructure and tribomechanical properties of spark plasma sintering (SPS) processed beta-SiAlON (20-40 wt%) bonded WC matrix composites have been reported. All the specimens achieved almost their theoretical density values after SPS at 1750 degrees C for 25 min under 40 MPa. Incorporation of beta-SiAlON in WC significantly altered the densification trend of the composites resembling that of pure beta-SiAlON. Microstructural investigations using scanning and transmission electron microscopy revealed formation of principally equiaxed, micron sized WC grains surrounded by the sub-micron to micron sized beta-SiAlON phase. The interface region between WC and beta-SiAlON was found to be free of any reaction product. Energy dispersive X-ray spectrum confirmed presence of characteristics elements in both WC and beta-SiAlON phases in the composite. The maximum Vickers hardness (similar to 18 GPa) and fracture toughness (similar to 6.8 MPa-m(0.5)) under 10 kgf were obtained for the 30 wt% beta-SiAlON/WC composite. These were almost 6% and 50% higher, respectively, than those obtained for pure WC. Indentation size effect (ISE) analyses of some selected specimens indicated moderate sensitivity towards ISE (Meyer's exponent = 1.802) of the 30 wt% beta-SiAlON/WC composite and higher true hardness (similar to 15.4 GPa) than those obtained for both the constituent phases. The load dependence of fracture toughness of some selected specimens has also been reported. Unlubricated wear studies under 30 N up to 250 m using ball-on-disc configuration indicated similar to 46-55 times higher specific wear rate of the beta-Si3N4 ball when rubbed against the composites compared to that (similar to 8 x 10(-6) mm(3)/N-m) obtained against pure WC. Formation of compacted flaky tribo-layer within the wear track of the composites was evidenced.