X-ray Diffraction, Microstructure and M(o)ssbauer Studies of Nanostructured Fe72AI28 Powder

摘要

Nanocrystalline Fe72Al28 alloy samples were prepared by the 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 the X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) and Mossbauer spectroscopy. The complete formation of bcc-FeAl solid solution is observed after 4 h of milling. The lattice parameter, a (nm), quickly increases within the first hours of milling and reaches a maximum value of 0.291 nm at 12 h of milling time; then a (nm) decreases to a value of 0.2885 nm for 24 h. The grain size decreases from 55 to 10 nm, while the strain increases from 0.18% to 0.88%. Grain morphologies at different formation stages were observed by SEM. The Mossbauer spectra show different behaviors with the increase of milling time. Indeed, after 4 h, the Mossbauer spectrum shows the presence of a singlet and sextet. The singlet indicates the presence of paramagnetic phase characteristic of A2 disordered structure and the sextet with a mean hyperfine field, , of 21 T is indicative of ordered DO3 structure. After 8 h of milling, the paramagnetic phase disappears leading to the appearance of a sextet, with a mean hyperfine field, Hhf, equal to 24.18 T which is characteristic of DO3' structure. For the higher milling time i.e. 24 h, the Mossbauer spectrum was analyzed with two components. The first one with equal to 29.9 T is still indicative of ordered DO3, however, the second with a value of 10.25 T is characteristic of the fine domain B2 ordered structure.