The significant influence of carbon content on mechanical and thermal properties of (VNbTaMoW)0.5Cx high entropy carbides

Abstract

The high-entropy formation possibility of (VNbTaMoW)0.5Cx was first analyzed by phase diagram and then a series of single-phase (VNbTaMoW)0.5Cx was fabricated by SPS. We investigated the mechanical properties and thermal conductivity of (VNbTaMoW)0.5Cx as C stoichiometry is varied. As C stoichiometry is increased from 0.345 to 0.35, multi-phase evolves into a single rock-salt phase. The high entropy phase formation depends on C atoms and vacancies, which increase the total number of microscopic states, and then increases the overall configuration entropy and lattice distortion energy. A highly carbon-deficient condition (C=0.345) leads to FCC structure disintegration and drives metal rich Mo2C phase evolution. As the carbon stoichiometry increases from 0.35 to 0.5, the nanohardness and flexure strength of (VNbTaMoW)0.5Cx first increase and reach the peak values of 48 GPa and 410 MPa ((VNbTaMoW)0.5C0.4), then decrease. The point defects concentration in (VNbTaMoW)0.5Cx drastically change with carbon stoichiometry, which affects the structure, mechanical properties and thermal conductivity of high-entropy (VNbTaMoW)0.5Cx. The thermal conductivity of (VNbTaMoW)Cx first decreases and then gradually increases with an increase in carbon content. Low carbon content (VNbTaMoW)C with primarily metallic bonding is electronically thermal conductivity. As the carbon content increase, the high-entropy (VNbTaMoW)C is covalent bonding and phonon contribution to thermal conductivity plays a great role.