In metastable high-entropy alloys (HEAs), the decrease of phase stability enables the development of dual-phase microstructure (interface hardening) and occurrence of strain-induced martensitic transformation (transformation-induced hardening), which overcomes the strength–ductility trade-off. The stacking-fault energy (SFE) is closely related to the phase stability and plays a key role in controlling the underlying deformation mechanism and hence the mechanical performance of HEAs. Here, we review some approaches of SFE calculation, including theoretical and experimental methods as well as the factors affecting SFE. Several compositional systems related to metastable HEAs are also briefly reviewed. Furthermore, we show the unique microstructure and the structure–property relationship of the metastable HEAs. Furthermore, some potential research topics in the future are also proposed.
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