Mechanical properties of high-entropy carbides prepared by high-pressure sintering: Role of carbon stoichiometry

The scarcity of carbon in high-entropy carbides is widely recognized to significantly affect their fabrication and performance. However, achieving both high hardness and plasticity in these carbides remains a formidable challenge. This study investigates the impact of carbon vacancies on the phase structure and mechanical properties of high-entropy carbides, particularly (Hf0.25Zr0.25Nb0.25Ta0.25)Cx (x = 1, 0.8, 0.6, or 0.5), utilizing density functional theory calculations and experimental analysis. Theoretical computations indicate a rock-salt structure for the carbides, with reduced cell parameters as carbon vacancies increase. Notably, carbides with lower carbon content exhibit softer characteristics, as evidenced by Pugh's ratio. Experimental fabrication and testing reveal a decrease in Vickers hardness with decreasing carbon content, attributed to changes in bonding types. Certain compositions, particularly (Hf0.25Zr0.25Nb0.25Ta0.25)C0.6 and (Hf0.25Zr0.25Nb0.25Ta0.25)C0.5, display plastic behavior alongside high hardness, offering promising avenues for future research and design of high-entropy ceramics.