Deformation-induced martensitic transformations: A strategy for overcoming the strength-ductility trade-off in high-entropy alloys

High-entropy alloys (HEAs) have become an important topic in modern materials science due to their exceptional properties. Despite their attractive properties, achieving a superior strength-ductility synergy has been, and remains, a major challenge. In practice, overcoming the strength-ductility trade-off in HEAs is an overriding priority which may open the opportunity for the development of high-performance alloys. It is well-established that high-strength steels benefitted from metastability engineering by manipulating the deformation mechanisms to facilitate a deformation-induced martensitic transformation which provides acceptable ductility. Accordingly, and following this same approach, a metastable HEA was developed which exhibited a desirable combination of strength and ductility. This review is designed specifically to give a comprehensive description of the deformation mechanisms in these materials and to provide an overall perspective on the importance of material characteristics and processing variables. The discussion is centred for different HEAs on the significance of the transformation-induced plasticity in breaking the strength-ductility trade-off and thereafter to examine some challenges and research gaps which require future attention. The understanding of the HEAs achieved to date demonstrates that there is a large potential for the future enhancement and optimization of these alloys in developing high-performance materials for a wide range of applications.