Ab initio phase diagrams of binary alloys in the low solute concentration limit.

Abstract

Phase diagrams are crucial to the design of new materials, to understand their phase stability and metastability under different thermodynamic conditions, such as composition, temperature, and pressure. Here, we use an ab initio approach to study the phase diagram of a binary alloy within the low concentration limit of a solute. Using the ab initio molecular dynamics calculations based on density functional theory, we estimate the solute partitioning ratios in solid-liquid phase equilibria. The chemical potential difference between the solvent and solute atoms in both solid and liquid phases is calculated using thermodynamic integration. As an illustration of the techniques, we have applied this method to reproduce the phase diagram of the Al-Mg alloy at zero pressure. We also compute the ab initio solid-liquid coexistence curve of pure Al by applying the phase-coexistence method with the free energy correction technique. The calculated results are in close agreement with the experiment, demonstrating the reliability of the models.