Fabrication and characterization of NbC-CoCrFeNiMn high-entropy alloy cermets

NbC based cermets with CoCrFeNiMn high-entropy alloys (HEAs) binders were fabricated by powder metallurgy. The effects of sintering temperatures on the microstructure and mechanical properties of NbC-HEAs cermets were systematically examined. The results show that the relative densities of NbC-HEAs sintered at different temperatures were about 90%. The XRD shows that a brittle M₂₃C₆ (M = Cr, Co, Fe, Ni) phase was detected in the cermets. The average particle size of NbC increased with increasing the sintering temperature. The coarsening of NbC particles caused the decrease of hardness and transverse bending strength (TRS) of the cermets. The highest TRS (497 MPa) was obtained for the cermet sintered at 1400 °C. The calculated activation energy was 696.6 kJ/mol, which was much higher than those in single element binders. Large cracks were observed for the cermets sintered at high temperatures, which suggested grain coarsening could reduce the toughness of cermets.