Kinetic control of deformation-induced martensitic transformation as a toughening mechanism in advanced metastable austenitic alloys

Achieving an optimal strength-ductility balance is a central challenge in the design of advanced metallic materials. The development of novel metastable alloys that exhibit a deformation-induced martensitic transformation (DIMT) effect presents a promising avenue for addressing this issue. While these alloys exhibit relatively high ductility under standard conditions, a further enhancement is essential to circumvent the strength-ductility trade-off and enable their use in structural engineering applications. This review focuses on the pivotal role of precisely controlling the kinetics of the DIMT as a novel toughening mechanism in order to boost ductility in metastable alloys and particularly high-entropy alloys (HEAs). Initially, the importance of metastability engineering on the strength-ductility synergy is discussed, and then the critical factors affecting the DIMT kinetics are explored. The review also examines important kinetic models relevant to advanced steels and HEAs. Additionally, the key strategies are analyzed for controlling the thermodynamics and kinetics of DIMT: (I) manipulating the chemical composition, (II) grain refinement in highly metastable alloys, (III) a microstructural engineering approach, including implementing partitioning by heat treatment, introducing dislocation substructures, and constructing hierarchical microstructures. Finally, the existing research gaps are examined, and directions are explained for future exploration, including the development of novel chemical compositions, controlled thermomechanical processing routes, and applying machine learning models to predict different features of DIMT.