Precipitation in the equiatomic high-entropy alloy CrMnFeCoNi

CrMnFeCoNi is widely considered to be an exemplar high-entropy alloy, which is stable as a single solid-solution phase at all temperatures below its melting point. Here, for the first time, the formation of two distinct types of Cr-rich precipitate in coarse-grained CrMnFeCoNi is reported following prolonged exposures at 700 °C. The precipitates were identified as M₂₃C₆ and the σ phase, and their formation in unworked material during heat treatments without an applied stress indicated that they are equilibrium phases. Therefore, CrMnFeCoNi can no longer be regarded as thermodynamically stable as a single phase at all temperatures below its solidus.