حسین رعنایی

In this research work, microstructural evolution, nanocrystalline formation and magnetic behaviorof nanostructured Co57Fe13Nb8Ta4B18 alloy prepared by mechanical alloying are investigated. The structural and magnetic properties are characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The results of SEM, demonstrate the evolution and grain refinement of particles powder with increasing milling time. The pattern of XRD indicate (Fe-Co) solid solution with bcc lattice formed after 12h of milling time. With increasing milling time, niobium and tantalum solubility in cobalt and iron lattice increase, leading to decrease of crystalline sizes. After 160h milling, only one peak is observed in the peak position of Fe-Co. The crystallite size and strain reach to value about 7.8nm and %1.12 respectively for 120h milling time. The saturation magnetization suddenly decreases up to 24h due to dissolution of non-ferromagnetic atomin microstructure and finally it increases at the end of milling process to a value about 115.5 emu/g. The coercivity inhances from the initial stage of milling time up to 70h and then it decreases to the end of milling time. Heat treatment on the milled sample for 160h at 243? leads to the reduction of the crystallite size from value about 10.4nm to 7.7 nm and the reduction of coercivity from 123.4Oe to 111.6Oe. Both saturation magnetization and coercivity increases after annealing at 427? accompanied with grain growth.