X-Ray Diffraction, Microstructure, and Mössbauer Studies of Fe₇₂Al₂₈ Alloy Elaborated by Mechanical Milling

Nanocrystalline Fe₇₂Al₂₈ alloy samples were prepared by mechanical alloying process using planetary high-energy ball mill. The alloy formation and different physical properties were investigated as a function of milling time, t, (in the 0-24 h range) by means of X-ray diffraction technique, scanning electron microscopy (SEM), energy dispersive X-ray, and Mössbauer spectroscopy. The complete formation of bcc-FeAl solid solution was observed after 4 h of milling. The lattice parameter quickly increased to a maximum value of 0.291 nm within the first hours of 12 h of milling, then decreased to a value of 0.2885 nm after 24 h. The grain size decreased from 55 to 10 nm, while the strain increased from 0.18 to 0.88%. Grain morphologies at different formation stages were observed by SEM. The Mössbauer spectrum showed the presence of a singlet and sextet after 4 h of milling. The singlet indicated the presence of paramagnetic phase characteristic of A₂ disordered structure and the sextet with a mean hyperfine field, 〈H _hf〉, of 21 T was indicative of ordered DO₃ structure. After 8 h of milling, the paramagnetic phase disappeared allowing the appearance of a sextet. For the higher milling time, i.e., 24 h, the Mössbauer spectrum was analyzed with two components. The first with 〈H _hf〉 equal to 29.9 T and the second with a 〈H _hf〉 value of 10.25 T.