Effects of Al concentration variations on solid-solution formation of AlCoCuNiPt HEA: Insights from first-principles calculations

Abstract

Numerous guidelines have been proposed to help researchers predict single solid-solution formation in high-entropy alloys (HEAs). However, the fundamental mechanisms behind this process are still not fully understood. Small changes in the composition or concentration of the constituents can dramatically impact solid-solution formation, further complicating our understanding of this phenomenon. Therefore, this study investigates the impact of changes in Al-concentration on the tendency of AlCoCuNiPt to form a single solid solution phase using density functional theory (DFT). The findings reveal that increasing Al concentration reduces the tendency of single solid-solution formation of AlCoCuNiPt, likely due to the strong interaction of Al with Pt and Ni, driven by their significant electronegativity differences. Higher Al concentrations also cause uneven charge distribution, increasing the system's enthalpy, which can lead to formation of intermetallic phases. Comparative analysis with PdCoCuNiPt highlights the importance of combining elements with similar electronegativity values. Unlike AlCoCuNiPt, PdCoCuNiPt remains stable across different Pd concentrations, with consistent charge transfer among its elements. These results suggest that even charge distribution is crucial for single solid-solution HEA.