Mössbauer probe spectroscopy studies of initial stage of Al-Fe mechanical alloying

Phase evolution during early stages of mechanical alloying of Cu–13 wt.% Al powder mixtures in a high-energy ball mill

“…The closest analogue of the NSP found by the DD method is the Cu 1Àx Al x solid solution observed by the XRD analysis and confirmed by 27 Al NMR. However, the elemental compositions of these phases differ substantially from each other.…”

“…Such phases have been previously observed in mechanically alloyed Al-Fe [27] and Al-Cr [28] mixtures. Structurally, these phases can exist as 2D inter-crystallite layers, rather than 3D grains, thus behaving as X-ray amorphous during the XRD phase analysis.…”

“…A low speed was not enough to narrow the lines due to their large width; therefore, only stationary spectra were recorded. In order to obtain the correct line shape of 27 Al NMR spectra, the spin echo pulse sequence p/2-s-p-s was applied (Hahn echo). The duration of the p/2 pulse in the sequence was 0.5 ls.…”

“…Thus, for Cu-15 at.% Al mixture the increase of milling time from 2 to 70 h was accompanied by transformation of metallic aluminum to a supersaturated solid solution of aluminum in copper, which was revealed by analysis of the 27 Al Nuclear Magnetic Resonance (NMR) spectra (line $1000 ppm) [8]. The X-ray diffraction (XRD) phase analysis and thermal analysis of Cu-Al mixtures mechanically milled for 1-8 h allowed to suggest the following transformation sequence: Cu + Al ?…”

“…The static spin echo 27 Al NMR spectra of the mechanically alloyed Cu-13 wt.% Al powders contain at least 5 lines (Figs. 4 and 5).…”