The use of niobium carbide as grain growth inhibitor in WC-10Co cemented carbides

Abstract

A key parameter in the processing of tungsten carbide materials is the control of the grain growth during the sintering stage. To limit the grain coarsening, grain growth inhibitors are added during the mixing of the powders. Those are transition metal carbides (vanadium, chromium, niobium, molybdenum) that are added in small amounts. Niobium carbide is an efficient GGI and can bring enhanced fracture toughness and reasonable hardness. The influence of niobium carbide (alone or with a combination of other inhibitors) on the grain growth was studied. To ensure a good homogeneity, a two-step ball milling was carried out: the first with cobalt and inhibitors, the second with WC and the doped-cobalt powder. The powders were sintered by vacuum sintering before the characterization of mechanical properties such as hardness and toughness. Niobium carbide is found to be an effective inhibitor since the mechanical properties are superior compared to the other inhibitors. Hardness and fracture toughness are 1858 ± 31 HV₃₀ and 9.8 ± 0.2 MPa√m for NbC alone and 1930 ± 22 HV₃₀ and 9.4 ± 0.3 MPa√m for the mixture NbC+Cr₃C₂ respectively.