DISORDERING BEHAVIOR OF ALLOYS BASED ON FE3AL

Iron aluminides containing about 28 at.% Al have the D0(3) ordered str ucture in equilibrium below about 550-degrees-C and the B2 ordered str ucture above that, with the disordered state existing at temperatures above about 900-degrees-C. The transition from the D0(3) state to the B2 state has been examined for several alloys containing various alloy ing additions using X-ray diffraction, differential scanning calorimet ry and in situ transmission electron microscopy. Some of the alloying additions investigated lead to changes in both the kinetics of orderin g and disordering as well as modifying the temperature range of stabil ity of the D0(3) state. While the alloys examined lose most of the D0( 3) order at the critical transition temperature, there is clear eviden ce of remnant long range order for temperatures up to 100-200-degrees- C above this critical temperature, at least for some of the more compl ex alloys. The retention of this order may be caused by solute remaini ng on specific lattice sites after disordering of the majority Fe and Al atoms.