TRANSIENT B32-LIKE ORDER DURING THE EARLY STAGES OF ORDERING IN UNDERCOOLED FE3AL

Chemical disorder-->D03 order transformations were studied in Fe3Al. The materials were prepared as nearly random solid solutions by piston-anvil quenching and then annealed at 200 and 300-degrees-C to develop order. The evolution of order was measured by X-ray diffractometry, transmission electron microscopy and Mossbauer spectrometry. X-ray diffractometry showed a transient appearance of B32-like order during the early stage of ordering at 300-degrees-C when the ordered domains were small (about 30-50 angstrom). This was consistent with results from Mossbauer spectrometry. Although it is possible that small isolated regions of B32 order may be forming, it is also possible that the B32 order may be located at antiphase domain boundaries. Even if the B32-like order is related to antiphase domain boundaries, we show that Fe3Al has a kinetic tendency to form B32 order at 300-degrees-C. With longer annealing times, this B32 order disappears, and equilibrium D0(3) order is obtained.