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 °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 Fe–Ga phase diagrams proposed by W. Köster 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 °C, an incomplete, if any, transition
from a metastable (A2 or D03) to the equilibrium (L12) state is seen after annealing for 300 h. Alloys with
25.5–28.1%Ga annealed at 450–500 °C for 300 h exhibit only the equilibrium L12 phase. Annealing at 575 °C
for 300 h leads to an incomplete transition, too, indicating that the highest transition rate occurs at 100–150 °C
undercooling. |
