STRONG DECREASE OF THE ACTIVATION-ENERGY AS A FUNCTION OF AL CONTENT IN FEALX ALLOYS (X LESS-THAN-OR-EQUAL-TO 30 AT PERCENT) DEDUCED FROM KINETIC MEASUREMENTS OF ORDERING

The kinetics of short and long-range order in the FeAlx alloys have been systematically studied. The results were obtained in the A2 solid solution (x = 0.10 and 0.17), in the DO3 ordered phase (x = 0.23, 0.27, 0.30) and in the A2 + DO3 two-phase region (x = 0.19), using 4K or in situ resistometry. The kinetic curves are well described by a classical model with a lognormal distribution of the relaxation times whose center varies with the temperature according to an Arrhenius law. An important point of this work is the strong decrease of the activation energy with the aluminium content and with the appearance of the DO3 ordered phase, as well as quite short relaxation times. These results show an abnormally high atomic mobility that can be attributed to a decrease of the migration energy through a lattice dynamics effect, as recently proposed in models which explain the enhanced diffusion observed in some b.c.c. transition metals and alloys. © 1990.