Mechanical alloying of FeCo nanocrystalline magnetic powders

Mechanical alloying of the Fe₅₀Co₅₀ equiatomic-magnetic alloy from elemental powders has been studied. Two milling speeds of 200 rpm and 300 rpm were used to process these powders. The as-milled powders were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The mixing of Fe and Co was completed in 200 min at a milling speed of 300 rpm; however, an increase in saturation magnetization was observed up to 10-h milling, indicating an increase in compositional homogeneity as a function of milling time. These findings were also reflected in the XRD results. During the milling of Fe and Co at 300 rpm, an increase of powder size was observed after 100-min milling. Further milling at 300 rpm led to a reduction in powder size; the decrease of powder size was more effective when milling was conducted at 200 rpm. This was attributed to a difference in the milling mechanisms dominating at these two speeds. The TEM observation showed that a banded microstructure was observed in the as-milled powders. The banded structure consists of grains, many of which show texture effects. After further milling, the banded structure became finer, then randomly arranged, and finally disappeared.