Insights into hot deformation of medium entropy alloys: Softening mechanisms, microstructural evolution, and constitutive modelling—a comprehensive review

The recent discovery of multicomponent principal alloys and the enhanced comprehension of their physical metallurgy have significantly advanced the understanding of microstructure engineering and material selection for high-tech applications. The exceptional combination of characteristics found in MEAs can be attributed to their distinctive phase constitution, which is aided by their multi-principal constituents. These properties are seldom encountered in ordinary alloys. Nevertheless, the use of these materials in their as-cast state is challenging due to issues such as the presence of heterogeneity in their chemical makeup, shrinkage porosity, unrefined dendritic structure, and the presence of a quasi-stable eutectic at grain boundaries. Consequently, the utilization of hot deformation methods for the purpose of achieving uniform and refined microstructures in as-cast MEAs has garnered significant interest as a viable approach to address these limitations. This review provides a comprehensive summary of the hot deformation characteristics of MEAs. Factors such as the alloy composition, the phase constituent, deformation parameters and recrystallization mechanisms were observed to influence the microstructural development and phase transition, flow curve characteristics, and mechanical characteristics of MEAs. Additionally, the use of processing map analysis for the determination of optimal processing zones for the hot deformation of MEAs was appraised. The discussion also encompassed the constitutive model description, molecular dynamics modeling, and machine learning algorithm for the prediction of the governing deformation mechanism and the deformation flow stress. Finally, future research directions are suggested.