Predicting the stacking fault energy of austenitic Fe-Mn and Fe-Mn-C alloys by Thermodynamic Modeling with Modified Interfacial Energy Term

Abstract

Stacking fault energy (SFE) plays a crucial role in determining the deformation mechanisms and phase transformations in Fe–Mn alloys. It has been known for a long time that Fe-Mn steels are plastically deformed through strain-induced martensitic formation, mechanical twinning, and finally through pure dislocation glide, depending on SFE value. The method of thermodynamic modeling to estimate SFE of Fe-Mn alloys have advantages over other methods to estimate SFE such as transmission electron microscopy, X-ray diffraction, Ab initio (first-principles) calculations. This study aims to improve the estimation SFE in Fe–Mn and Fe-Mn-C alloys by thermodynamic modeling. A modified model is proposed to estimate interfacial energy between gamma (FCC) and epsilon (HCP) phases. Unlike previous studies that assume a constant interfacial energy, in this study it is modeled as a parabolic function of chemical and magnetic Gibbs free energy. Using experimental SFE data from literature, interfacial energy was estimated and its temperature as well as composition dependence was establish. The modified thermodynamic model was validated against experimental results and observed to be in good agreement. It was also used to analyse the effects of composition, temperature, and grain size on SFE of Fe-Mn and Fe-Mn-C alloys. Additionally, the model was used to determine SFE at the martensitic start temperature (Ms) to assess driving force of austenite-to-ε-martensite transformation.