Processing and properties of high entropy carbides

High entropy carbides (HECs) are novel materials developed in recent years that have attracted a lot of research interests. Unlike traditional carbides (containing one or two metals), HECs with multiple metals could form a very large number of different compositions that could have interesting and promising properties. The high entropy effect stabilises multi-component carbide phases and forms compositions that might otherwise not be stable. After several years of investigation of HECs, several methods of synthesising HECs have been developed. The microstructures and properties of HECs have been studied and compared with traditional carbides. Many interesting discoveries in HECs have been made. This paper reviews the theories, technologies, findings and insights gained from previous studies on HECs. The basic theory of HECs, the prediction of synthesisability of HEC phases from theoretical calculations, and some rules observed from experimental results are summarised. The preparation methods of HECs (powders, coatings, films and ceramics) and their microstructures are reviewed. Their properties, including thermal and electrical, mechanical and tribological, and oxidation, irradiation, and corrosion resistance of HECs are reviewed and discussed. Compared with traditional carbides, there is a great potential to develop new HECs due to their designable and complex compositions, and this review can guide future studies.