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

The phase equilibria among the face-centered cubic (fee), body-centered cubic (bcc), and βMn phases at 800, 900, 1000, 1100, and 1200°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/D0₃ 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, αMn, βMn, fcc, and ε 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.