Microstructure and mechanical properties of NbC-matrix hardmetals with secondary carbide addition and different metal binders

NbC has a relatively high hardness (19.6 GPa) and melting temperature (3600 °C) and is usually applied as a grain growth inhibitor in WC-Co hardmetals. The current study reports on the influence of the sintering technology and overall chemical composition on the microstructure and mechanical properties of NbC-based hardmetals, using Co as a binder. The partial replacement of NbC by 5 wt.% WC, Mo2C, VC or TiC allows one to significantly improve the hardness and toughness of the NbC-Co materials. The influence of different binders, i.e., Co, 316L stainless steel and Fe3Al on the microstructure and mechanical properties of NbC-based hardmetals was also investigated. The powder mixtures were sintered in the solid state by PECS and liquid state by conventional vacuum sintering. Detailed microstructural analysis was conducted by EPMA elemental mapping and WDS point analysis. Mechanical properties, including Vickers hardness and indentation toughness were assessed.