Lattice rigidity in high-entropy carbide ceramics with carbon vacancies

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 (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-1-(x) (HEC1-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 HEC1-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 HEC1-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.