Carbon Content Optimization and Performance Characterization of High Entropy Carbonitride Ceramics

This study systematically investigates the effects of excess carbon content (0, 5, 10, 15 at%) on the phase composition, microstructure, and mechanical properties of (Hf, Ti, V,W, Zr)(C,N) high entropy carbonitride ceramics fabricated through combined carbothermal reduction nitridation and SPS under identical processing conditions. Microstructural characterization reveals that four high entropy carbonitride powders contain high entropy phases along with WC, residual carbon, and oxide solid solution phases. After sintering at 2000°C, the ceramics primarily consist of high entropy matrix phases and oxide solid solutions phases, while the HECN‐15C sample additionally retains residual carbon. The ceramics exhibit relative densities of 99.2% ± 0.7%, 98.27% ± 0.6%, 97.09% ± 0.2%, and 93.71% ± 0.3%. Mechanical testing demonstrates hardness values ranging from 22.13% ± 1.02% to 25.29 ± 1.79 GPa and fracture toughness between 3.66 ± 0.38 and 4.28 ± 0.24 MPa m 1/2 across the series. Optimal performance is achieved at 10 at% excess carbon content, which exhibits highest hardness (25.29 ± 1.79 GPa) and toughness (4.28 ± 0.24 MPa m 1/2 ). However, further increasing carbon to 15 at% degrades mechanical properties (22.13 ± 1.02 GPa hardness), (3.66 ± 0.38 MPa m 1/2 toughness). Precise control of carbon content in raw materials is very important, this work plays an important guiding role for the further development of high entropy carbonitride ceramic.