EXPERIMENTAL AND THEORETICAL-STUDIES ON PHASE SEPARATIONS IN THE FE-AL-CO ORDERING ALLOY SYSTEM

Phase separations in iron-rich Fe-Al-Co ternary alloys were investigated by means of transmission electron microscopy, differential thermal analysis and magnetization measurement. Two kinds of phase separations have been found at 923 K; A2+B2 and B2+B2*. The former occurs in a tongue-shaped composition region ranging from Fe-12 at % Al-15 at % Co to Fe-35 at % Al 45 at % Co and the latter appears in the small region bordering on the Fe Al binary side of the A2 + B2 field. These two-phase fields have theoretically been evaluated on the basis of the so-called Bragg-Williams-Gorsky model taking account of not only chemical but also magnetic interactions. The magnetic ordering accounts for the expansion of the A2 + B2 coexistent region. In the measurement of magnetic properties, large increases in coercive force, H(c), and residual magnetic flux density, B(r), were observed in the two-phase microstructures.