The Fe-Ga phase diagram: Revisited

The microstructures and phase compositions of Fe-Ga alloys with Ga contents from 15 to 45 at.% are investigated in detail applying prolonged annealing treatments at temperatures below 600 degrees C. X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating-sample magnetometry (VSM), and Electron backscatter diffraction (EBSD) coupled with scanning electron microscopy (SEM) methods were used in this investigation. The results are compared with predictions of four existing FeeGa phase diagrams proposed by W. Koster et al. (1977), J. Bras et al. (1977), O. Kubaschewski (1982), and H. Okamoto (1993). Several important inconsistencies are found and required corrections of the positions of three equilibrium boundaries. Below 400 degrees C, an incomplete, if any, transition from a metastable (A2 or D0(3)) to the equilibrium (L1(2)) state is seen after annealing for 300 h. Alloys with 25.5-28.1%Ga annealed at 450 -500 degrees C for 300 h exhibit only the equilibrium L12 phase. Annealing at 575 degrees C for 300 h leads to an incomplete transition, too, indicating that the highest transition rate occurs at 100-150 degrees C undercooling. (C) 2020 Elsevier B.V. All rights reserved.