Effect of densification technology on the microstructure and mechanical properties of high-entropy (Ti, Zr, Hf, Nb, Ta)C ceramic-based cermets

High-entropy ceramic-based cermets represent a new and promising direction in improving the mechanical properties of conventional hardmetals through the formation of complex microstructures during synthesis. This has been systematically studied in two Co-free, high-entropy (Ti,Zr,Hf,Nb,Ta)C ceramic-based cermets using 10 wt% Ni and 10 wt% FeCrAl metallic binders during hot-press and spark plasma sintering. Fully densified microstructures were achieved in the temperature range of 1400–1500 °C, which is below the melting points of the pure Ni and FeCrAl alloy, owing to the liquid-phase assisted sintering. The optimal densification routes resulted in Vickers hardness (HV₃₀) of 16.77 ± 0.72 and 18.32 ± 0.99 GPa, and fracture toughness (K_{Ic_SENB}) of 5.31 ± 0.41 and 4.83 ± 0.50 MPa m^0.5, respectively for the Ni and FeCrAl bonded cermets. The improved damage tolerance of these cermets compared to the base (Ti,Zr,Hf,Nb,Ta)C high-entropy carbide is related to the reduced grain size and microstructural toughening mechanisms (e.g. crack deflection and bridging).