Mechanical and tribological characteristics of tungsten cermet composites sintered with Co-based and zirconia mixed binders

Abstract

The influence of cobalt based and zirconia mixed binder additives on the mechanical properties and tribological characteristics of WC based spark plasma sintered cermet composites was investigated. Varied weight proportions of zirconia stabilized with yttria along with constant weights of 9Co/WC–4.5CO–2Cr–5Ni metallic binder were blended with WC, consolidated and sintered using spark plasma sintering process. The composites produced were characterized using SEM and XRD analyses, density measurements, mechanical properties and wear test evaluations. The results show that the use of the mixed binder additives did not significantly affect the densification process as relative densities above 92% (7.5% less than that achieved using only the Co based metallic binders) were achieved using SPS processing. However, the grain size was observed to increase with increase in zirconia content in the mixed bond composites, and the hardness values decreased with increase in zirconia content. The toughness and fracture toughness showed significant improvement with the addition of zirconia. Also the coefficient of friction for the mixed binder sintered composites were on the average lower than that of the cermet composites without zirconia. Pseudoplastic properties characterized by the presence of delaminations were the primary wear mechanism observed for the zirconia containing cermets; while pits and wear groove formations were observed in the cermets without zirconia.