Liquid phase assisted synthesis of (Ti,V,Nb,Ta,W)C-Ni high entropy carbide cermets by conventional pressureless sintering

Abstract

Two-phase fully dense high entropy carbide (HEC) cermets were successfully prepared following the conventional cemented carbide/cermet processing route. Cold isostatically pressed equimolar TiC, VC, NbC, TaC and WC powder mixtures with 12 vol% Ni binder were pressureless sintered in the solid state and liquid phase sintering regimes respectively. A homogeneous rock-salt (space group Fm3¯m) HEC phase embedded in a nickel alloy binder was attained by liquid phase sintering at 1420°C. Thermodynamic simulations were conducted to predict the equilibrium phases and carbide/binder phase contents. The phase evolution was investigated at seven different sintering temperatures in the 900–1420°C window. Thermogravimetry and differential scanning calorimetry analysis were performed to follow up the sintering process. Electron probe microanalysis was used to map the elemental distribution as well as to quantify the constituent phase contents. Nanoindentation were performed to correlate the difference in mechanical properties of the core-rim structured HEC grains with the chemical composition. The liquid phase sintered (Ti,V,Nb,Ta,W)C - 12 vol% Ni had a Vickers hardness of 14.3 GPa and Palmqvist indentation fracture toughness of 9.2 MPa. m1/2.