Thermodynamic modelling of vacancies in zirconium carbide

Zirconium carbide is of interest in nuclear and aerospace industries due to its stability and strength at extremely high temperatures. Its properties are strongly affected by significant carbon vacancies that give a wide range of stability. In conventional CALPHAD thermodynamic modelling, these vacancies are assumed to be randomly distributed and properties relating to the vacancies are not directly considered. However recent experimental and first-principles insights suggest the presence of vacancy-ordering and different regimes within the phase diagram that are dominated by either structural or thermal vacancies.

Using first-principles calculations, the character of the vacancies is elucidated and mapped. Calculations of defect-related properties are used to inform development of Gibbs energy models that may be used where the thermodynamic properties are highly dependent on point defects and their ordering. Incorporating such information directly into the thermodynamic database provides a physically consistent description which should allow further predictive ability.