Phase equilibria and thermodynamics of Mn-C, Mn-Si, Si-C binary systems and Mn-Si-C ternary system by critical evaluation, combined with experiment and thermodynamic modeling

Critical evaluation and thermodynamic optimization of Mn-C, Mn-Si, Si-C binary systems and Mn-Si-C ternary system were carried out over the whole composition range from room temperature to above the liquidus temperature. In order to provide critical experimental input for the thermodynamic modeling, some key experiments were carried out in the present study. The liquid solution was modeled using the Modified Quasichemical Model (MQM) in the pair approximation in order to take into account the Short-Range Ordering (SRO) exhibited in the solution. In particular, the SRO observed in the Mn-C binary liquid was reasonably accounted for by the present thermodynamic model, while the conventional random mixing model was not able to properly describe the SRO. All solid solutions were modeled using the Compound Energy Formalism (CEF). Model parameters were optimized to best reproduce the important thermodynamic properties and phase equilibrium data in three binary systems. By taking a reasonable interpolation method for Gibbs free energy of the liquid solution in the ternary Mn-Si-C system, it was shown that the present model successfully reproduced thermodynamic and phase equilibrium data in the ternary system without any adjustable ternary parameter. The present database can be used as a part of larger thermodynamic database for the ferromanganese alloy.