Lattice rigidity in high‐entropy carbide ceramics with carbon vacancies

Abstract Due to the presence of core effects of high‐entropy materials, it is believed that the impact of carbon vacancy in high‐entropy carbides may differ from that of transition metal monocarbides. In this work, nonstoichiometric high‐entropy carbides (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C 1− x (HEC 1− x ) with variable carbon vacancy concentration were fabricated by spark plasma sintering using powder mixtures of high‐entropy carbide and metallic powders. Compared with the corresponding monocarbides, the decline rates of lattice constant and elastic modulus were obviously slower as carbon vacancy concentration increased, indicating a more rigid crystalline lattice in the high‐entropy carbide. The valence electron number for HEC 1− x ceramics with the highest hardness is 7.6, which is inconsistent with the theoretically predicted value of 8.4 for the traditional transition metal carbides. When the carbon vacancy concentration in HEC 1− x ceramics is above 20%, the promoting effect of carbon vacancy on grain growth will outweigh the inhibiting effect of sluggish diffusion on grain growth, causing grains to grow quickly.