An entropy-based design and preparation methodology for carbides intended for the hard phases in composite coating

Abstract

In the presented study, a (Ti_1/2Nb_1/6Ta_1/6W_1/6)C (HEC) carbide intended for the hard phases with single-phase FCC solid-solution structure was designed and synthesized. The HEC crystal model was initially constructed for structural optimization and lattice energy calculation. Subsequently, based on the theories of the single-phase formation ability of high-entropy compounds, including mixing entropy ΔS_mix, mixing enthalpy ΔH_mix, lattice distortion δ and valence electron concentration (VEC), the HEC with the nominal composition of (Ti_1/2Nb_1/6Ta_1/6W_1/6)C was optimized and followed by the synthesis processing of carbothermal reduction. With the increase of the sintering time, the reaction became more complete but the synthesized HEC powders tended to coarsen. The microstructures showed that the (Ti_1/2Nb_1/6Ta_1/6W_1/6)C HEC formed a single FCC phase with severe lattice distortion, which proved the validity of composition design of HEC. Moreover, the HEC exhibited superior microhardness of 21.91 GPa and Young's modulus of 144.88 GPa compared to traditional single principal element carbides of TiC and WC, along with excellent high-temperature stability as well. The (Ti_1/2Nb_1/6Ta_1/6W_1/6)C HEC composite coating was prepared by laser cladding. The average hardness value of the HEC coating is 688.2 HV_0.5, which is 50.85% higher than that of the TiC coating (456.2 HV_0.5). HEC exhibits good corrosion resistance. Its self-corrosion potential is 0.02176 V, and the self-corrosion current density is 1×10^-6 A/cm². This study not only developed a high entropy carbide reinforcement with high thermal stability and good mechanical properties applicable to wear resistant composite coatings, but also provides a comprehensive design strategy of high entropy materials based on the multiple high-entropy design criteria.