Research Progress on the Preparation and Characterization of Ultra Refractory TaxHf1-xC Solid Solution Ceramics

TaxHf1-xC (0 < x < 1) solid solution ceramics, a series of solid solutions of tantalum carbide (TaC) and hafnium carbide (HfC) over the whole range of composition, have been considered as promising candidates for many important applications which can tolerate temperature above 3000 K due to their high melting points (> 4000 K), high hardness (similar to 30 GPa), low coefficient of thermal expansion, excellent oxidation resistance, and excellent ablation resistance. Over the past decades, some extreme conditions required for aerospace industry have greatly promoted the development of TaxHf1-xC materials, and dozens of literatures were published in this area. In this paper, the research progress of TaxHf1-xC solid solution ceramics was introduced in terms of powder synthesis techniques, densification methods and mechanism, mechanical properties at room temperature, thermophysical properties, oxidation and ablation resistance. Advantages and disadvantages of three common techniques (solid solution between metal carbides, carbonization reaction of metals, and carbothermal reduction of metal oxides) for synthesizing TaxHf1-xC powder as well as the difficulties in densification of TaxHf1-xC solid solution ceramics were analyzed. Influence of sintering process on microstructure and mechanical properties at room temperature of TaxHf1-xC solid solution ceramics was discussed briefly. The hardness, elastic modulus, K-IC, melting point, thermal conductivity, coefficient of thermal expansion, oxidation and ablation behavior of TaxHf1-xC solid solution ceramics with different Ta/Hf ratios were summarized. It revealed that TaxHf1-xC solid solution ceramics will obtain a good performance on both mechanical properties and oxidation resistance when Ta/Hf was approximate 1. Furthermore, the remaining challenges and future outlook of TaxHf1-xC solid solution ceramics were also addressed.

Automated summary

TaxHf1-xC solid solution ceramics, with characteristics of high melting points, high hardness, low coefficient of thermal expansion, excellent oxidation resistance, and ablation resistance, show excellent mechanical and oxidation properties when Ta/Hf ratio is approximate 1.