Ordering and disordering processes in MA and MM intermetallic iron aluminide powders

The formation of the FeAl intermetallic compound has been investigated by annealing a mechanically milled powder and a mechanically cryoalloyed powder. First, the morphological transformations that result from both milling processes were analysed, giving special emphasis to the cryoalloyed powder; the evolution of continuous cold welding and fracturing during milling was assessed by means of scanning electron microscopy (SEM). The lattice parameter changes of both powders were then evaluated as a function of milling time using profile fitting and Rietveld analysis of the XRD data. The powder thermal stability was also examined by differential scanning calorimetry (DSC) and the detected transformations were discussed according to the structural changes observed in X-ray temperature-dependent measurements. Furthermore, Mossbauer data has been used to compare the different atom rearrangements, from that of an ideal B2 structure and a typical bcc-Fe type to a disordered A2-solid solution and their temperature-induced ordering processes.