Experimental studies on critical compositions for fabricating single-phase high entropy carbides based on the calculated phase diagram of (VNbTaMoW)0.5Cx (0 < x < 0.6)

Abstract

In this paper, the phase diagram of (VNbTaMoW)0.5Cx (0 < x < 0.6) was first calculated. We establish the complete phase diagram in two spatial dimensions from analysis the statistics of order phase parameters. To obtain high-entropy carbides and validate the calculated results, a series of (VNbTaMoW)C were sintered at different temperature. The single-phase carbide of (VNbTaMoW)C were synthesized at 1800 °C, which is higher than the theoretically calculated temperature in phase diagram. The reason is that the estimated temperature was calculated by mixing entropy for experimentally reported ideal solid solution models that simplified the temperature dependent parameters. Phase composition of (VNbTaMoW)C sintered at/below 1800 °C agrees well with the calculation results in phase diagram. Furthermore, we have systematically investigated the single-phase formation ability of four-metal and three-metal composition based on five elements (V, Nb, Ta, Mo, W). A total of 5 types of four-metal compositions and 10 types of three-metal compositions can be generated. However, for each composition, only 4 kinds four-metal and 6 kinds three-metal compositions can form single phase carbides. Those as-prepared single-phase carbides exhibit enhanced mechanical properties compared to the calculated values according to the rule of mixtures from constituent monocarbides.