| Sendust alloy has been used as raw materials to fabricate magnetic heads and cores because of its excellent soft magnetic properties and low prices. However, weak deformability has limited its wider application. In this dissertation, Co doped nanocrystalline Sendust alloy with high working temperature as well as high frequency properties could be prepared while technical parameters and components were changed.(Fe1-xCox)85Si9.6Al5.4 (wt%) (x = 0, 0.05, 0.10, 0.15, 0.20) alloy ribbons have been prepared using melt spinning, high energy ball milling has been employed to achieve flakes with large aspect ratio, making sure of its excellent high frequency properties, the ball milled powders were then heat treated under the protection of Nitrogen to get excellent soft magnetic properties. The microstructure, soft magnetic properties and Curie temperature (Tc) of samples with different technical parameters and components were studied systematically using SEM, XRD, VSM and MTG respectively. The annuluses were made from Co-doped Sendust alloy powder mixed with proper epoxide resin and high frequency properties were measured using Impedance Analyzer.X-ray Diffraction has been used to analyze phase composition and structural parameters. As shown that, disordered bcc α-Fe phase and ordered superlattice D03 phase have been found in Co free Sendust melt spun ribbons and Co addition made the disordered phase changed from α-Fe to a-Fe(Co). Ball milling is beneficial for the refinement of grains, meanwhile, it also made phase transformation from ordered DO3 phase to disordered phase happened. The diffraction peaks of DO3 phase disappeared completely while samples were milled for only 20 h. According to the results of SEM, largest aspect ratio could be achieved while the sample was milled for 70 h. The transformation from disordered to ordered phase happened during heat treatment. Accompanied with the increase of heat-treated temperature, the diffraction peaks of D03 phase became more and more obvious and long-range order got higher.Internal strain increased greatly at the stage of ball milling and it deteriorated soft magnetic properties a lot, the coercivity increased from 8.675 Gs to 29.099 Gs when (Fe0.85Co0.15)85Si9.66Al5.4 alloy ribbons were ball milled for 70 h. Heat treatment was beneficial for minimizing the coercivity. Saturation magnetization (Ms) was found to increase duringheat treatment due to the followed two reasons: The transformation from disordered to ordered phase and the increase of long-range order. Ms of 129.8 Am2/kg could be achieved in (Fe0.85Co0.15)85Si9.6Al5.4 powder when it was heat treated at 773 K for 30 min after ball milling for 70 h. No obvious effects on properties of alloy powder have been found since higher annealing temperature and longer holding time were employed. Curie temperature (Tc) has been greatly improved when Co was added to the sample. Tc of 1000 K could be achieved when x=0.20 while that of Co free sample is only 740 K. Grain size as well as phase composition were distinct in different directions of the melt spun ribbons, introducing the discrimination of soft magnetic properties. Better performance could be achieved along the direction of melt spun ribbons.The impacts of ball milling technics as well as Co content on high frequency properties of Co doped Sendust alloy have been discussed systematically. Relative stable values of μ' and μ" of (Fe1-xCox)85Si9.6A15.4 alloy powder could be achieved near cutoff frequency, indicating a potential application at the range of GHz. Coaxial annuluses of Φ19×Φ10×3 mm have been prepared using the mixed magnetic powder and epoxide resin. The cutoff frequency of magnetic ring made from sample annealed at 773 K is 1.154 GHz. The highest cutoff frequency could be achieved when the samples was milled for 70 h, at which highest aspect . ratio could be achieved.
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