Solid-state reactions in the Al-Fe system induced by ball milling of elemental powders

Abstract

Elemental aluminium and iron powders have been mechanically alloyed in the atomic Al∶Fe ratios of 1∶1 and 1∶3. The structural evolution of the samples was followed by X-ray diffraction and differential calorimetry. Extended milling caused the formation of an almost completely disordered b c c solid solution instead of the equilibrium B2 and DO₃ compounds. Upon heating to 700 °C the formation of the B2 phase was observed in the equiatomic samples and no significant variation of the long-range state of order in the iron-rich samples. Upon heating of samples pre-milled for short or intermediate times, at about 400 °C, the nucleation and growth of Al₅Fe₂ was observed which, upon further heating to 700 °C, transformed to the B2 phase or to the b c c solid solution, depending on the sample composition. These results suggest that the solid-state reactions proceed through diffusion of iron atoms in the aluminium layers, and that for an iron concentration in these layers below about 50 at%, the Al(Fe) solid solution could be in a metastable phase.