Zirconium carbide and hafnium carbide are ultra-high temperature ceramics (UHTCs) that have high hardness and melting points exceeding 3500K which lend to their use in nuclear and aeronautical applications. For these applications, precise knowledge of the phase stability of the material as a function of composition, temperature, and pressure is required.
Zirconium and hafnium are often mutually contaminated as a result of their mining process. The effect of this contamination is explored by considering the published CALPHAD assessments of this system and DFT calculations. These are considered in a thermodynamic assessment of the carbon-hafnium-zirconium system, taking into account recent experimental and theoretical data.