Thermodynamic modeling of the Al-C-Mn system supported by ab initio calculations

A CALPHAD-type thermodynamic assessment of the Al-C-Mn system was carried out in the present work. Special attention was paid to the ternary kappa-phase with the aid of ab initio calculations. The enthalpies of formation at 0 K of all end-members of the kappa phase were derived from the ab initio calculations and utilized in the present optimization. The kappa phase was modeled as an ordered form of the fcc structure for the substitutional sub-lattices, employing the following formula within the framework of compound energy formalism: (Al,Mn)(0.25)(Al,Mn)(0.25)(Al,Mn)(0.25)(Al,Mn)(0.25)(C,Va)(0.25). With the present optimized model parameters, the wide homogeneity range of the kappa phase was reproduced satisfactorily. Comparison between the predicted and measured phase equilibria as well as the ab initio calculation results validates the present optimized model parameters.