Phase transformations during mechanical alloying and subsequent heating of FeAlB powders

Elemental powder mixtures of (Fe50Al50)100-xBx (x = 5, 10, 20 and 30 vol%) were subjected to mechanical alloying. The thermal behaviour of the milled powders was examined by differential scanning calorimetry. Structural and phase transformations occurring in the powders throughout mechanical alloying and during subsequent heating in the calorimeter were investigated by X-ray diffraction. It was found that for all the powder mixtures, a nanocrystalline Fe(Al) solid solution was formed during milling. For the powders containing 20 and 30% of B, an amorphous phase was also present in the ball milled product and for the latter one it was the prevalent phase. Thus, the content of B in the powder mixture affects phase transformations which take place during mechanical alloying of FeAlB powders. It was also found that the increase of B content in the mixtures causes more intense decrease of the Fe(Al) grain size during milling. Microscopy examinations revealed that the produced powders have composite structure with B particles embedded in the nanocrystalline Fe(Al) solid solution matrix or in the two phase amorphous and nanocrystalline matrix, depending on B content. Upon heating of the ball milled products containing 5 and 10% of B, the Fe(Al) solid solution transformed into the ordered FeAl intermetallic phase. During heating of the ball milled products containing 20 and 30% of B, the amorphous phase crystallised and a phase isomorphic with the AlFe2B2 one was formed.