Predicting the BCC-FCC phase diagram of medium entropy alloys with first-principles calculations and statistical mechanics

Abstract

We predicted the BCC-FCC phase diagram of medium entropy alloys  with density functional theory calculations, cluster expansion methods, and generalized quasi-chemical approximation. Alloys are versatile with more constituents, which lead to various applications. The multicomponent nature, in the meantime, generates a larger configurational  entropy, thus lower free energy and higher stability. However, the complexity of alloys dramatically increases as the number of constituents  increases, resulting in a huge configuration space that is hard to explore either experimentally or computationally. In this work, we applied a statistical mechanics method "generalized quasi-chemical approximation," which calculates the free energy from statistical average of configurations.  The energy of the considered configurations was obtained via the  cluster expansion methods based on first-principles data. The predicted energy and resulting phase diagram were shown to provide reasonable accuracy compared to Monte Carlo and CALPHAD, but with much lower computational costs. Our results demonstrate that this methodology can be effective in investigating properties of binary, ternary, and quaternary alloys.