Characterization of Nanostructured Fe65Co35 Powders

Nanostructured alloys have received an extra quantity of interest in the various fields of materials engineering because of their prominent physical and chemical properties [1]. The magnetic materials have revolutionized our lives. These materials are used in electronic, computer and telecommunication industries. Different types of magnetic materials have been used including pure iron and its alloys [2]. There are several methods to prepare the nanocrystalline materials. Among these methods, mechanical alloying (MA) is a powerful and relatively simple technique which allows the preparation of nanostructured magnetic alloys [3]. The MA causes a gradual refinement of internal structure of the powders to nanometer scales due to the sever plastic deformations [4]. In the nanostructured alloys, the grain size is smaller than the exchange length, due to the random distribution of nanoscale grains [5,6] and consequently some magnetic properties can be improved. However, the presence of stresses and defects introduced by MA can deteriorate the magnetic properties [2, 6, 7]. Nevertheless, the MA process is a powerful means for producing the metastable nonequilibrium phases and amorphous alloys [3, 8, 9]. This process causes deformation, fragmentation and rewelding of the powders until they mix intimately to from true solid solutions [3, 10]. Pure iron is a good ferromagnetic material. The resistivity of iron is very low, i.e. it experiences high eddy current losses. Alloyed iron provides higher magnetic permeability and lower total core losses and results in devices having higher efficiencies than devices using pure iron cores [7]. Cobalt in iron is unique in increasing simultaneously the saturation magnetization and Curie temperature [6]. As the Fe–Co soft magnetic alloy has low coercive field, low hysteresis and eddy-current loss, high electric permeability and high saturation magnetization, it has been extensively investigated in the previous works on many aspects such as electronic structures, mechanical properties and structural transformations [11–12].

Iron–cobalt alloy have the highest saturation magnetization of all known magnetic alloys [13]. However, the results of previous works show that the maximum saturation magnetization occurs at a concentration of 35 at % Co [6, 14, 15]. The peculiarity of the Fe–Cr system is the existence of a wide miscibility gap in the phase diagram where both Fe and Cr are insoluble at room temperature [6]. In the FeCr alloy system prepared by MA, the formation of a bcc phase has been seen [9]. The addition of Cr to Fe affects the transition temperatures from a-bcc solid solution to c-fcc one, increases the resistivity and improves the dynamic properties slightly, decreases the saturation magnetization by dilution of the magnetic atoms, also improves the corrosion resistance. It has been reported that the addition of Cr to FeCo films is essential to improve magneto crystalline anisotropy in order to be used as magnetic recording material [17]. The present work deals with the preparation of nanocrystalline Fe65Co35and (Fe65Co35)90Cr10 powders by ball milling. The aim of this work is to study the structural and magnetic changes which take place during MA (Fe65Co35)90Cr10 powder mixtures. The Cr effect is investigated by the comparison of the results with those obtained on binary (Fe65Co35) prepared with the same conditions.

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