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 κ-phase with the aid of ab initio calculations. The enthalpies of formation at 0 K of all end-members of the κ phase were derived from the ab initio calculations and utilized in the present optimization. The κ 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 κ 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.