Prediction of phase stabilities of solid solutions for high entropy alloys

Abstract

Accurately predicting the phase stabilities of high entropy alloys (HEAs) is of significance for alloy design and development. The predicted results of the existing established thermodynamic approaches have a large deviation from the actual results. To avoid this problem, a new simplifying prediction scheme is proposed and reported in this study, which was built on the experimental results of 130 HEAs combining ten elements, including Al, Co, Cr, Cu, Fe, Mn, Mo, Ni, Ti and V. Firstly, the bond enthalpies between atom pairs in condensed solid solutions (BCC or FCC) were reasonably estimated by applying the Ab-initio method. Secondly, from a thermodynamic standpoint of the correlation between the bond enthalpies and the interaction parameters, a new quantified technique of the interaction parameters between elements was established. Then, the mixing enthalpies of the solid solutions with specific crystal structures, as well as the Gibbs free energies of the intermetallic compounds, have been extracted. Thus, by contrasting the Gibbs free energies of the alloy system before and after precipitation, an overall basic approach to predicting the phase stability has been developed. This method has taken into account the change of the Gibbs free energy of the solid solution after the separation of intermetallic compounds, the calculated results have evolved into more accurate and reliable ones and can point out which kind of complex phase (Sigma phase or Laves phase) would precipitate in the HEAs, offering a fundamentally new approach with high credibility for predicting the phase stability of the HEAs.