A CALPHAD assessment of the Al–Mn–C system supported by ab initio calculations

Abstract

The Al–Mn–C ternary system has been thermodynamically evaluated using the CALPHAD method. Published data on phase equilibria have been critically examined and used to optimize the model parameters. The phase model for the κ AlMn3C phase (E21) has been changed to (Al,Mn)1(Al,Mn)3(C,Va)1 for improved reproduction of stability ranges and phase equilibria at 1100 °C and 1200 °C. The solid solution phase parameters of γ-Mn, ε-AlMn, ε-Mn4C have been adjusted to reproduce experimental ternary phase equilibria. Density functional theory-based ab initio calculations of enthalpies of formation at 0 K were performed to guide the modeling of the κ phase and elucidate general energetic trends. Reasonable liquidus temperatures were achieved by adjustments to the stability of the liquid phase. The Mn5C2 phase model was extended to Mn5(C,Al)2 which allows aluminium on the carbon sublattice. The CALPHAD calculations were performed with the optimized set of parameters and compared with the available experimental data and changes to previous work were elucidated.