Composition design of eutectic high-entropy alloys: a review

Eutectic high-entropy alloys (EHEAs) offer a good balance between strength and ductility alongside excellent castability and chemical homogeneity. However, identifying optimal eutectic compositions in HEAs has been a persistent challenge primarily due to the lacuna of higher-order phase diagrams. Since their discovery in 2014, following sporadic reports, the compositional design of EHEAs has relied on a trial-and-error empirical approach through experimental adjustments, which is time-consuming, costly, and often ineffective. Recently, the CALPHAD (CALculation of PHAse Diagrams) methodology has emerged as an effective alternative to empirical approaches despite its notable limitations. Combinatorial approaches have also been explored to design EHEA compositions, albeit with significant reliance on existing databases. However, despite a decade of efforts, there remains no universal design strategy for EHEA compositions to date, highlighting the need to address this research gap. To this end, the present article provides a critical review of the hitherto reported efforts in the composition design and development of EHEAs, categorizing them broadly into empirical, CALPHAD, and combinatorial approaches for the first time. This analysis aims to underscore the persistent challenges in designing EHEA compositions and provide insights to guide future research toward more effective strategies.