Method for Synthesizing a High-Entropy Carbide in an Ionic Melt

The refractory metal carbides TiC, ZrC, HfC, NbC, and TaC have excellent physical, chemical, and mechanical properties as materials for ultra-high temperature ceramics. The most refractory of them are TaC and HfC, the melting temperatures of which approach 4000°C. The high hardness, strength, and wear resistance of refractory carbides is also noteworthy. Therefore, natural interest in high-entropy carbides (HECs) based on them is grounded: they are becoming an important class of new ceramic materials, since they potentially have more advanced applied properties. However, the production of such materials by classical metallurgical methods is a difficult problem. In modern investigations, HEC samples are most often synthesized using expensive special equipment (plasma spark sintering methods, high-energy planetary mills, etc.) and relatively long preparation of precursors for sample fabrication. Here, we describe a new approach to synthesizing a multicomponent (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C carbide using an electrochemical process at a temperature not exceeding 1173 K. This technique is based on the phenomenon of currentless metal transfer in molten salts. After sequential metal transfer, the sample is washed from an electrolyte and then sintered in a vacuum furnace. According to X-ray diffraction analysis, the resulting HEC is a single-phase fcc solid solution. The X-ray diffraction pattern of the synthesized sample is in good agreement with the X-ray diffraction pattern calculated by the Debye formula for a supercell of 64 000 atoms. A compacted HEC sample is prepared by pressing a pellet 10 mm in diameter in a mold with the addition of cobalt as a matrix metal. After vacuum sintering, the sample is polished for examination in a scanning electron microscope. Elemental mapping of the sample surface is performed; it demonstrates a satisfactory distribution of the metals that make up the HEC. The measured microhardness of the sample turned out to be lower than the values reported by other authors, which can be due to some residual porosity of the sample.