Defects, Dislocations and disorder during deformation, milling and quenching of an FeAl alloy

The behaviour of FeAl during disordering on milling and re-ordering on annealing has been extensively studied and characterised. The mechanisms by which changes occur are not, however, well established. The role of defects created during milling on bringing about disorder is not clear; neither is the importance of their movement and annihilation during re-ordering. The structures of FeAl samples given a variety of thermal and mechanical pre-treatments have been examined here, as well as their behaviour on annealing. Three material preparations have been examined to distinguish the separate roles of vacancies and dislocations, with their associated APE faults, on disordering and re-ordering. Samples quenched from high temperature have large numbers of thermal vacancies: they show low temperature recovery as local atomic movement and re-ordering takes place, but full recovery by long range point defect movement is only possible at high temperatures. Heavily deformed samples recover at very low temperatures by easy dislocation glide and APE annihilation, with higher temperature recovery occurring by dislocation cross slip, reactions and decompositions. Deformation-induced disordering, and reordering on annealing, can largely be described through the large density of APBs, with each fault representing a thin plane of disorder. Lightly milled powder samples behave similarly to the deformed samples, with simultaneous dislocation recovery and reordering occurring on annealing, but after large amounts of milling dislocation movement is difficult and recovery is delayed to higher temperatures where diffusional mechanisms can assist.