Mechanical alloying (MA) of Fe1-xCrx powder mixtures was performed over a wide range of concentration. Both x-ray diffraction and TEM analyses show that, after 30 hours of milling, the powder particles consist of nanocrystalline grains less than 10 nm in size. The kinetics of mixing is studied by Mössbauer spectrometry. This is the first time that the FeCr mixing state has been studied as a function of the milling conditions and the initial powder composition. This mixing state is defined by a parameter (d) calculated from the hyperfine field values. The alloying process is weakly composition dependent (for x40 at.% Cr), but is linked to the energy input to the powder. Especially an energy threshold must be transferred to the powder to reach a complete alloying. By studying the hyperfine field distributions of the Mössbauer spectra (for Cr<40 at.%), it seems that the Fe1-xCrx nanograin cores are quite homogeneous in composition and have hyperfine parameters close to those of the bulk alloys.

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Mechanical alloying of iron and chromium powder mixtures was performed from 0 to 190 h milling times. X-ray diffraction, Mössbauer spectrometry and differential scanning calorimetry were used to determine the structural and magnetic properties of the intergranular zone, which was associated with a very disordered grain boundary structure, paramagnetic at 300 K. This structure is assumed to be due to the presence of oxygen and nitrogen atoms, forming a mixture of amorphous FeCr + O + N alloy. Between 21 and 85 h, the hyperfine parameters of the magnetic contribution, and therefore the properties of the Fe 60 Cr 40 nanograin cores, are constant, but the paramagnetic fraction associated with the intergranular zone increases. At 85 h, the paramagnetic contribution represents 100% of the Mössbauer spectrum.Moreover, after very long milling times, we have evidenced a de-mixing reaction which results in preferential oxidation and nitrogenation within the very disordered structure.

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