On the Phase Configurational Entropy of Dual-Phase γ/γ′ Multi-principal Element Alloys: A Case Study on the Al–Cu–Fe–Ni–Ti System

Configurational entropy is an important indicator of the formability of single solid solutions in multi-principal element alloys, typically estimated by using nominal compositions. However, nearly half of reported alloys consist of multiple phases rather than a single solid solution, leading to the redistribution of components among the constituent phases. In the present work, we evaluated the configurational entropy of constituent phases and the phase fraction-weighted configurational entropy in dual-phase γ/γ′ multi-principal element alloys within the Al–Cu–Fe–Ni–Ti quinary system. Two alloys, with the highest configurational entropy in either γ or γ′ phase, respectively, were selected by employing the high-throughput CALPHAD method and fabricated. It was found that the configurational entropies of constituent γ and γ′ phases, as well as the phase fraction-weighted value being lower than that of the nominal composition. The thermodynamic constraint of phase equilibria determines the elemental partitioning of the components in the constituent phases for multi-phase high-entropy alloys.