Spark plasma sinterability and dry sliding-wear resistance of WC densified with Co, Co+Ni, and Co+Ni+Cr. (November 2020) - Boukantar, Aniss-Rabah
Abstract: The spark plasma sinterability and the dry sliding-wear resistance of ultrafine-grained WC densified with ~16.7 vol% of Co, Co+Ni, and Co+Ni+Cr, compositions equivalent to that of the typical WC-10wt.%Co, were investigated and compared critically. Firstly, it was found that the partial substitutions of Co by Ni or by Ni+Cr are detrimental for the pressureless ultrafast sinterability, but much more in the latter than the former case, attributable to the higher eutectic temperatures during liquid-phase sintering. However, it was also observed that, thanks to the auxiliary stress supplementing the sintering stresses, the ultrafast sinterability with pressure is affected by these partial substitutions either not at all (Co by Ni) or very little (Co by Ni+Cr), making it possible in all cases to obtain fully-dense WC cermets with almost no grain growth at the same spark plasma sintering temperature. And secondly, it was found that these cemented carbides are very resistant to dry sliding wear, but that WC-(Co+Ni+Cr) is markedly more so, attributable essentially to its greater hardness. This is due to wear occurring essentially by two-body abrasion dominated by plastic deformation (ploughing), plus some oxidative wear with formation of tribo-oxidation layers that, although not entirely coherent, are nonetheless beneficial for the wear resistance. Highlights: A critical comparison has been made between the spark-plasma sinterability and dry sliding-wear resistance of WC densified with Co, Co+Ni, and Co+Ni+Cr. Partial substitutions of Co by Ni and by Ni+Cr reduce the pressureless ultrafast sinterability of WC. The metal binder (Co, Co+Ni, or Co+Ni+Cr) does not condition, however, the ultrafast sinterability under the typical pressures applied in conventional SPS. WC-(Co+Ni+Cr) is markedly harder than both WC-Co and WC-(Co+Ni), while still preserving a high fracture toughness. WC-(Co+Ni+Cr) has excellent intrinsic dry sliding-wear resistance that comparatively exceeds those of WC-Co and WC-(Co+Ni). Wear of these cemented carbides under dry sliding contact in air occurs principally by two-body abrasion dominated by plastic deformation, with some oxidative wear.