Formation of nanocrystalline Fe–Co powders produced by mechanical alloying

The structural and magnetic properties of Fe–Co alloy powders produced by mechanical alloying of elemental powders were investigated. In this research, two kinds of milling methods (cyclic and conventional operation) were adopted to optimize the milling process. Consequently, the alloy powder with average grain size 10–15 nm was obtained. The cyclic operation had an advantage over conventional milling in that a smaller-grained structure could be obtained with less milling time. Maximum Ms was obtained at the composition of 30 at.% Co. Due to the high amount of internal strain introduced during milling, relatively high coercivities were obtained. The coercivity was decreased fairly through the relief of the internal strain by heat treatment. Over 95% of the theoretical density was attained after the spark plasma sintering at 900°C for 5 min with applying pressure of 60 MPa. The sintered specimen remains nanostructured with a grain size of about 30 nm.