Phase equilibria and stability of ordered b.c.c. phases in the Fe-rich portion of the Fe-Ga system

Phase equilibria among the A2, B2, DO3, L1(2) and D0(19) phases in the Fe-rich portion of the Fe-Ga binary system were determined by transmission and scanning electron microscopies (TEM and SEM) and energy dispersion spectroscopy (EDS), mainly using a conventional diffusion couple (DC) technique. The phase stability of the B2 and D0(3) ordered phases in the metastable b.c.c. phase region was also investigated using concentration gradient method (CGM). It was found that the phase equilibria below 25 at.%Ga almost coincide with the assessed phase diagram, whereas the Fe3Ga (L1(2)) single-phase region exists up to about 30 at%Ga and to about 690 degreesC. The phase boundaries between the A2 and D03 phases including the metastable equilibrium exhibit a complicated behavior in analogy with the Fe-Al system. The A2-->B2-->D0(3) order-disorder and the paramagnetic-->ferromagnetic transition temperatures were also investigated by differential scanning calorimetry (DSC). (C) 2002 Elsevier Science B.V. All rights reserved.