Experimental determination and thermodynamic calculation of phase equilibria in the Fe-Mn-Al system

The phase equilibria among the face-centered cubic (fcc), body-centered cubic (bcc), and beta Mn phases at 800, 900, 1000, 1100, and 1200 degrees C were examined by electron probe microanalysis (EPMA), and the A2/B2 and B2/D0(3) ordering temperatures were also determined using the diffusion couple method and differential scanning calorimetry (DSC). The critical temperatures for the A2/B2 and B2/D0(3) ordering were found to increase with increasing Mn content. Thermodynamic assessment of the Fe-Mn-Al system was also undertaken with use of experimental data for the phase equilibria and order-disorder transition temperatures using the CALPHAD (Calculation of Phase Diagrams) method. The Gibbs energies of the liquid, alpha Mn, beta Mn, fcc, and epsilon phases were described by the subregular solution model and that of the bcc phase was represented by the two-sublattice model. The thermodynamic parameters for describing the phase equilibria and the ordering of the bcc phase were optimized with good agreement between the calculated and experimental results.