Thermodynamic description of the Al−Fe−Nb system

The Al−Fe−Nb system was critically assessed by means of the CALPHAD technique. The solution phases (liquid, face-centered cubic and body-centered cubic) were modeled with the Redlich-Kister equation. The thermodynamic models of compounds Al13Fe4, Al2Fe and Al5Fe2 in the Al-Fe system and Al3Nb and AlNb3 in the Al-Nb system kept consistent with ones in the corresponding binary systems. The Fe2Nb and μ in the Fe-Nb system, Al8Fe5 in the Al-Fe system, and AlNb2 in the Al-Nb system were treated as the formulae (Al,Fe,Nb)2(Fe,Nb), (Al,Fe,Nb)1Nb4(Fe,Nb)2(Al,Fe,Nb)6, (Al,Fe,Nb)8(Al,Fe,Nb)5 and (Al,Nb)0.533(Al,Fe,Nb)0.333Nb0.134, respectively. B2 phase was treated as the ordered phase of bcc phase with the thermodynamic models (Al,Fe,Nb)0.5(Al,Fe,Nb)0.5(Va)3 and (Al,Fe,Nb)0.25(Al,Fe,Nb)0.25(Al,Fe,Nb)0.25(Al,Fe,Nb)0.25(Va)3. On the basis of optimized thermodynamic parameters of Al-Fe, Al-Nb and Fe-Nb systems in literature, the Al-Fe-Nb system was optimized in the present work. One set of self-consistent thermodynamic parameters of the Al-Fe-Nb system was obtained corresponding to B2 ordered phase with two kinds of thermodynamic model. Five experimental isothermal sections at 1073, 1273, 1423, 1573 and 1723 K, and the liquidus surface projection were well reproduced in the present work.