Ab-initio investigation for the microscopic thermodynamics and kinetics of martensitic transformation

Martensitic transformation (MT) path in Fe-based alloys remains uncertain in spite of decades of research. Lots of relevant works, which mostly focused on the simplest Bain path, have been completed by the state-of-the-art first-principles methods based on density functional theory. In this work, the element effects on microscopic thermodynamics and kinetics of the MT are investigated in terms of two different paths, including the well-known shear dominated Bogers-Burgers path and a recently proposed shuffle dominated path. Adding common elements, e.g. Ni, Mn, Cr, Si and C, into steel could induce different kinetics of the MT, as reflected by the energy barrier, which further determines the physically realistic MT path for different alloys. Furthermore, the addition of 3d transition metals may adjust the transformation equilibrium between the tetragonal α martensite and the hexagonal ε martensite, as reflected by their inverse effect on the energy barrier for the α MT and the stacking fault energy relating to the ε formation. An expected correlation between the thermodynamic driving force and the kinetic energy barrier for the MT is confirmed in binary Fe–Ni and Fe–Cr systems with changing the concentration of the alloying elements. These two paths for the MT are elaborately compared and discussed to reveal the nature of atomic movement in the MT, dominated by shear or shuffle.