R. Umino, X. J. Liu, Y. Sutou, C. P. Wang, I. Ohnuma, R. Kainuma, K. Ishida, Tohoku University, Sendai, Japan
The phase equilibria of the Fe-Mn-Al ternary system are of great importance in the development of austenitic stainless without Ni and Cr, cryogenic alloys and magnetic materials. In the present paper, the phase equilibria among the fcc, bcc and ß-Mn phases at 800, 900 and 1000˚C were determined by means of a metallograph and an electron probe microanalyzer (EPMA). Furthermore, the A2/B2/D03 ordering temperatures were determined by the diffusion couple method and differential scanning calorimetry (DSC). The results show that critical temperatures for the A2/B2 ordering decrease, but that those for the B2/D03 ordering increase with increasing Mn contents. Thermodynamic assessment of the Fe-Mn-Al system was also carried out based on the experimental data of the phase equilibria and ordering of the bcc phase using the CALPHAD (Calculation of Phase Diagrams) method, in which the Gibbs energies of the liquid, fcc phases are described by the subregular solution model and that of the bcc phase is represented by the two-sublattice model in order to fit the experimental data of the A2/B2 ordering. The thermodynamic parameters for describing the phase equilibria and the ordering of the bcc phase were optimized, and good agreement between the calculated results and experimental data was obtained.
Summary: The phase diagrams of the Fe-Mn-Al ternary system were experimentally determined by the DSC and EPMA techniques. Based on those results, thermodynamic assessment was carried out, and a good agreement between the experimental and calculated data was obtained.
