Study of nanocrystalline and amorphous powders prepared by mechanical alloying

The process of mechanical alloying consists of intimate mixing and mechanical working of elemental powders in a high-energy ball mill. It has been well established that this process is able to produce nanocrystalline and amorphous material. In this study, the structural effects of mechanical alloying of pure Fe, Fe₅₀W₅₀ and Fe₅₀Mo₅₀ powders were investigated by X-ray diffraction and Mössbauer spectroscopy. For all cases, nanocrystalline and/or amorphous fractions were found after milling. The resulting particle size was determined by X-ray diffraction. Pure Fe does not amorphize even after prolonged milling times. For the nanocrystalline powder, significant changes in the linewidth and the hyperfine field are found. Powder mixtures of Fe₅₀Mo₅₀ and Fe₅₀W₅₀ are completely amorphous after milling times of 10 h, as seen by Mössbauer spectroscopy, but nanocrystalline fractions of the non-iron part are still found in X-ray diffraction. Also in the amorphous state, further changes in the hyperfine parameters are found with increasing milling time.