The effect of milling speed on the structural properties of mechanically alloyed Fe-45%Ni powders

FeNi-based alloy powders are interesting in their applications as soft magnetic materials with low coercivity and high permeability. Their magnetic properties are closely related to their microstructure and particle size. In this study, nanocrystalline Fe-45%Ni alloy powders were prepared using a planetary ball mill. The effects of ball milling speed (the vial rotation speed (ω) and the disc rotation speed (Ω)) on the microstructure and particle size of Fe-45%Ni alloy powders have been studied. The face-centered-cubic (FCC) γ-(Fe, Ni) solid solution phase was identified by X-ray diffraction (XRD). The lattice parameter, lattice strain, grain size and quantitative amount of γ-(Fe, Ni) phase have been estimated from Rietveld's powder structure refinement analysis of XRD data. The powder morphology and particle size were examined using scanning electron microscopy (SEM). The results showed that the FCC γ-(Fe, Ni) phase could be observed completely at the vial rotation speed of 350 rpm and the milling time of 24 h. We also found that the higher milling speed leads to higher milling energy, larger lattice parameter, larger particle size and lower grain size of the investigated system.