Abstract
Processes of phase separations into A2 and DO3 at 773 K in Fe-Al-V ternary ordertng alloys were investigated by means of transmission electron microscopy. Sequences of phase separation from the A2, B2 or DO3 single phase state into the A2+DO3 equilibrium state were classified into three types. (1) In the alloys near the phase boundary A2/A2+DO3, the phase separation of A2 into A2+DO3 occurs directly without through any intermediate state. (2) In the alloys whose compositions are located in the centre area of the A2+DO3 field, phase decomposition from B2 into B2+DO3 arises, followed by the phase separation into A2+DO3. (3) In the alloys near the boundary between DO3/A2+DO3, continuous ordering from the B2 to DO3 phase occurs at first, and then A2 phase is formed on the antiphase boundaries of the DO3 phase. Finally, small particles of A2 precipitate in the ordered domains of the DO3 matrix. These sequences of phase separations could be explained from the hierarchy of free energies among the A2, B2 and DO3 phases.
