Properties of NbC–Co cermets obtained by spark plasma sintering

Sub-micrometer sized NbC–Co powder mixtures with 8, 12, 18 or 24.5 wt.% Co were consolidated by spark plasma sintering (SPS) for 2 min at 1200–1280 °C and 30–60 MPa. The optimum densification conditions were determined by analysing the dimensional change of the NbC–12 wt.% Co powder compact. SPS for 2 min at 1280 °C under a pressure of 60 MPa allowed full densification of the NbC–Co cermets with limited NbC grain growth. The microstructure is characterized as a highly interconnected NbC grain network with an inhomogeneously distributed Co binder. The Vickers hardness increased from 11.70 to 15.40 GPa whereas the fracture toughness decreased from 9.0 to 5.5 MPa m1 / 2 with decreasing Co content from 24.5 to 8 wt.%.