Crystallography of High Entropy Metal Carbides—A New Class of Ultrahigh Temperature and Irradiation Resistant Ceramics

We will describe the unique crystallography and microstructure of high-entropy Mo-Nb-Ta-V-W carbides prepared using a novel solvothermal synthesis process. The compounds were produced by mixing metal chlorides and carbon powder in the presence of molten lithium. Solvothermal synthesis occurs at a high temperature (upwards of 2000°C), which allows the carbides to undergo reaction-driven alloying and form single-phase solid solutions of nanopowders without the need for further thermal treatment. We have produced binary, ternary, quaternary, quinary, and senary metal carbides through systematic manipulation of elemental composition, particularly counteracting the tendency of WC and MoC to form. Solid solutions have been confirmed by a combination of X-ray diffraction and energy dispersive spectroscopy. Subsequently, spark plasma sintering (SPS) was used to obtain dense specimens. Carbon was added to the carbide powders to facilitate densification of the targeted compositions at a low sintering temperature (1600°C), compared to typical temperatures required for carbides. Low temperature sintering avoids heat-driven grain growth and allows for a finer grain size distribution.