Thermodynamic analysis of metal segregation in dual phase high entropy ceramics

Abstract

Equilibrium Gibbs' free energy calculations were used to determine metal segregation trends between boride and carbide solid solutions containing two metals that are relevant to dual phase high entropy ceramics. The model predicted that Ti had the strongest tendency to segregate to the boride phase followed by Zr, Nb, Mo, V, Hf, and Ta, which matches experimental results of measured compositions. The ratio of a metal in the carbide phase to the content of the same metal in the corresponding metal boride had a linear trend with the change in standard Gibbs' free energy of reaction for a metal carbide reacting with B4C to produce its corresponding metal boride and carbon. The proposed model was used to predict the changes in standard Gibbs' free energy for CrC→CrB2 to be −260 kJ and WC→WB2 to be 148 kJ, which indicates that Cr has the strongest segregation to the boride and W has the strongest segregation to the carbide. The proposed model can be used to estimate the segregation of metals in dual phase high entropy boride-carbide ceramics of any boride/carbide ratio or metal content.