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

Abstract

Densification, microstructure and tribomechanical properties of spark plasma sintering (SPS) processed β-SiAlON (20–40 wt%) bonded WC matrix composites have been reported. All the specimens achieved almost their theoretical density values after SPS at 1750 °C for 25 min under 40 MPa. Incorporation of β-SiAlON in WC significantly altered the densification trend of the composites resembling that of pure β-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 β-SiAlON phase. The interface region between WC and β-SiAlON was found to be free of any reaction product. Energy dispersive X-ray spectrum confirmed presence of characteristics elements in both WC and β-SiAlON phases in the composite. The maximum Vickers hardness (~18 GPa) and fracture toughness (~6.8 MPa-m0.5) under 10 kgf were obtained for the 30 wt% β-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% β-SiAlON/WC composite and higher true hardness (~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 ~46–55 times higher specific wear rate of the β-Si3N4 ball when rubbed against the composites compared to that (~8 × 10−6 mm3/N-m) obtained against pure WC. Formation of compacted flaky tribo-layer within the wear track of the composites was evidenced.