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Sintering and High-Temperature Strength of (Ti,Hf,Ta)C Medium-Entropy Ceramics Consolidated by Biphasic Carbide Powders

F.L. Qin, F.L. Qin, X.G. Wang, X.F. Wang, Q.Q. Yang, R.Z. Li, W. Gao, C. Zhang, D.Y. Jiang

Journal of Ceramic Science and Technology, Vol. 14, No. 1 (2023), pp. 39-48

DOI: 10.4416/JCST2023-00002

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Abstract

This study reports for the first time on the preparation of medium-entropy (Ti,Hf,Ta)C-based powders with biphasic composition of Hf(Ti,Ta)C and Ti,Ta(Hf)C based on carbothermal reduction of TiO2, Ta2O5 and HfO2 with graphite. The synthesized (Ti,Hf,Ta)C-based powders had a fine particle size of 200 – 300 nm and low oxygen content of 0.42 wt%. After sintering at 2 100 °C for 1 h, single-phase (Ti,Hf,Ta)C ceramics were obtained. The effect of the Hf element content on the densification and grain growth of (Ti,Hf,Ta)C medium-entropy ceramics was investigated and compared with monocarbide ceramics (TiC, HfC, TaC). The final sintered medium-entropy (Ti,Hf,Ta)C ceramics prepared by means of hot pressing at 2 100 °C had fine grains (0.92 ± 0.4 μm) and a relative density of 93.3 %. The Hf element significantly inhibited the densification and grain growth of (Ti,Hf,Ta)C ceramics due to its lattice distortion and the sluggish diffusion effects. The equimolar ratio (Ti,Hf,Ta)C corresponding to (Ti1/3Hf1/3Ta1/3)C had ultra-high strength at 1 600 °C (639 ± 38 MPa) and 1 800 °C (697 ± 26 MPa). The ultra-high strength of (Ti,Hf,Ta)C medium-entropy ceramics is the result of the collaborative optimization of the superfine microstructure (grain size of 0.92 ± 0.4 μm) and strong grain boundary strength.

Keywords

Medium-entropy ceramics (Ti,Hf,Ta)C, sluggish diffusion effect, high-temperature flexural strength.

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