Mechanical and tribological properties of spark plasma sintered WC-Co-Ni-Al₂O₃ cermets with Co substitution by Al₂O₃

Herein, the mechanical and tribological behaviour of spark plasma sintered WC-(8-x)Co-Ni-xAl₂O₃ cermets at 1250 °C was studied. Five compositions were prepared by altering the Co content from 8 to 0 wt% and replacing it with alumina. The microstructural and mechanical properties were thoroughly analysed using SEM, XRD, density measurements, Vickers hardness testing (at various loads up to 100 kgf), and tribological evaluation under dry sliding conditions. The results revealed that all compositions achieved high densification levels, a slight decrease in elastic modulus was observed as the alumina content increased, while microhardness exhibited a significant improvement. The Vickers hardness of the composites increased from 1623 HV for the free-Al₂O₃ cermet (WC-Co-Ni) to 2310 HV for the WC-Ni-Al₂O₃ cermet. The cermets were evaluated using a ball-on-disc apparatus under dry sliding conditions with two different balls (Al₂O₃ and WC-6Co). Against the WC ball, the addition of Al₂O₃ improved the wear resistance of the WC cermet, while maintaining a relatively low friction coefficient. In contrast, when tested against the alumina ball, the friction coefficient increased with increasing Al₂O₃ content from ∼0.22 to ∼0.32. However, the best overall balance between hardness (1980 HV), fracture toughness (∼8 MPa m^1/2), and wear resistance was achieved with the WC-4Co-4 Al₂O₃-2Ni composition.