Effects of the thermodynamic parameters of the hcp phase on the stacking fault energy calculations in the Fe-Mn and Fe-Mn-C systems

The thermodynamic parameters of the ε (hcp) phase with respect to the γ (fcc) phase in the Fe-Mn system have been re-visited by utilizing the least squares refinement method applied to experimental values of enthalpy and T0 temperatures. The new best converged equilibrium description produces ΔGfcc→hcp without affecting the stable phase diagram of the entire Fe-Mn system. Based on the proposed parameters, the stacking fault energy (SFE), related to the stability of the fcc phase with respect to the hcp phase, was then evaluated in the Fe-Mn and Fe-Mn-C systems as a function of Mn and C contents as well as temperature. The SFE was found to be more sensitive to temperature for paramagnetic alloys while it is more sensitive to the Mn content for antiferromagnetic alloys. Through this study, it is proven that a phase diagram, T0 temperature, composition and temperature dependence of the SFE can be all predicted by a single set of thermodynamic parameters. A consistent reproducibility of the present model was confirmed for 0-29 wt% of Mn by experimental data used for optimization.