Entropy-driven phase stability and slow diffusion kinetics in an Al0.5CoCrCuFeNi high entropy alloy

Previous work on the stability of the solid solution phases in the high entropy alloys is inconclusive. We used a series of thermo-mechanical treatments to study the stability of the solid solution phases in a high-entropy Al0.5CoCrCuFeNi alloy. The solid solution phases were found to be stable, against the intermetallic compounds, at high temperatures >850 °C and at low temperatures <300 °C. At intermediate temperatures, however, the intermetallic σ-phase co-existed with the solid solution phases. The experimental observations were verified by the thermodynamic calculation results. The mechanisms for the phase stability, both at equilibrium and after quenching-equivalent annealing treatments, were discussed, and the roles of high entropy and slow diffusion kinetics were highlighted.

► Phases in the as-cast HEAs are not the equilibrium phases at the room temperature.
► The sluggish diffusion kinetics in HEAs slows down the phase transformation.
► The high entropy favors the stability of solid solutions at elevated temperatures.