In the present paper, a high energy milling process has been used to alloy Fe and B in the proportion 2:1. X-ray diffraction and Mössbauer spectroscopy were used to follow the solid state reaction among the alloy components and phase formation during thermal treatments of the final milled alloy, at distinct temperatures and environments. X-ray, DSC and Mössbauer data of the 310 h milled alloy show the presence of three phases: small fractions of α-Fe (n-Fe) and Fe 2 B (n-Fe 2 B) nanocrystalline phases and a large amount of amorphous Fe 2 B (a-Fe 2 B) phase (73%). Heat treatment of the milled alloy was done in a high vacuum furnace, followed by in situ Mössbauer measurements, or by annealing the sample sealed in a quartz tube. It is shown that segregation and crystallization effects thermally induced in the samples have been enhanced by the presence of oxygen in the residual atmosphere, being less effective in the case where the sample was continuously pumped during the annealing. These effects may have occurred due to boron oxidation. Also, the presence of a tet-Fe 3 B phase in the annealed samples has been observed. The high temperature Mössbauer spectra for the sample annealed at 823 K indicate that the n-Fe 2 B, n-Fe 3 B and n-Fe phases exhibit superparamagnetic behaviour, with estimated blocking temperatures of 723 and 823 K, respectively. The amorphous a-Fe 2 B phase has a T C value estimated at about 823 K that fits into the system reported for amorphous Fe/B ribbons.

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