The structural and compositional changes during mechanical milling of Fe–Cr powder (10 wt% Cr) were followed by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction (XRD), Mössbauer spectroscopy and magnetization measurement. All these techniques give complementary information about the alloying process during milling. Different particles are cold welded and elongated to form composite granules in the initial stage of milling (5–10 h). The crystalline order is also destroyed heavily and nanosize crystallites are formed during early milling. Chromium diffusion in the iron lattice starts somewhat late (after 20 h of milling) when composite granules flatten, reducing the distance between iron and chromium layers. Though compositional homogeneity is achieved up to nanometre scale in 65 h of milling, atomic diffusion of the species still continues up to 100 h of milling.

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Interesting differences were noticed in the alloying process during ball milling of Fe-10 wt.% Cr and Fe-20 wt.% Cr alloys by 57 Fe Mössbauer spectroscopic studies. In both cases, there is almost no diffusion of Fe in Cr or vice versa up to 20 h of milling time. As the powders are milled for another 20 h substantive changes occur in the Mössbauer spectra showing atomic level mixing. But the two compositions behave differently with respect to alloying. Fe-20 wt.% Cr sample does not differ much in the hyperfine field distribution as it is milled from 40 to 100 h. On the other hand, the hyperfine field distribution keeps on changing with milling time for Fe-10 wt.% Cr sample even up to 100 h of milling. The average crystallite size is found to be 7.5 nm for Fe-10 wt.% Cr and 6.5 nm in Fe-20 wt.% Cr after milling.

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