Preparation of Single-phase High Entropy Carbides by a Modified Citric Acid Complexing Method

We developed a new method to synthesize single-phase transition metal carbide powders by combining citric acid complexing method and ball-milling dispersion. High-entropy carbides (Zr0.25Ti0.25Ta0.25Nb0.25)C (4TmC), (Zr0.2Ti0.2Ta0.2Nb0.2Hf0.2)C (5TmC-H) and (Zr0.2Ti0.2Ta0.2Nb0.2Mo0.2)C (5TmC-M) were successfully fabricated by this method using low-cost raw materials. The element and phase composition and microstructures of the obtained carbide powders were investigated. The relationships of synthesis process and temperature with chemical composition were also discussed. (Zr0.25Ti0.25Ta0.25Nb0.25)C can be obtained by a one-step process at 1550 °C, while (Zr0.2Ti0.2Ta0.2Nb0.2Hf0.2)C and (Zr0.2Ti0.2Ta0.2Nb0.2Mo0.2)C are fabricated by a two-step process of carbothermal reduction followed by solid solution at the temperatures not lower than 1850 °C and 1650 °C. The higher synthesis temperatures of the five-component carbides are attributed to the obvious sluggish diffusion effect induced by the larger lattice distortions. The particle sizes of (Zr0.25Ti0.25Ta0.25Nb0.25)C, (Zr0.2Ti0.2Ta0.2Nb0.2Hf0.2)C and (Zr0.2Ti0.2Ta0.2Nb0.2Mo0.2)C powders are 118.2±26.1 nm (at 1550 °C), 284.8±73.7 nm (at 1850 °C) and 65.5±13.9 nm (at 1750 °C), respectively.