Phase transformations during mechanical alloying of Fe–50% Al and subsequent heating of the milling product

Iron–aluminum alloy of Fe–50% Al composition was prepared by mechanical alloying (MA) of the elemental powders. Thermal behaviour of the milled powders was examined by differential scanning calorimetry (DSC). The phase transformations and structural changes occurring in the studied material during mechanical alloying and during subsequent heating in a calorimeter were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy. The final product of the MA process was the nanocrystalline Fe(Al) solid solution with a mean crystallite size of 15 nm. It was found that the Fe(Al) solid solution was formed not by the gradual solution of Al into bcc Fe but by the rapid formation of small zones of Fe(Al) with the ultimate composition, coexisting with the remaining Al and Fe phases. With the increase of milling time all Al atoms became dissolved in the bcc Fe. The disordered Fe(Al) solid solution transformed into the ordered FeAl intermetallic compound upon heating of the milling product in the calorimeter. After the heating the material remained nanocrystalline. The Mössbauer study of the heated samples showed two types of Fe atomic configurations: the dominating one related to the ordered FeAl phase and the other one related to iron atoms located in less ordered regions.