Preparation, Structure And Magnetic Studies Of Fe-Co Alloy Magnetic Powder And Soft Magnetic Composite

Fe-Co alloys have attracted widespread interest,because Co combined with Fe can increase the magnetic properties and operating temperature of Fe.Fe-Co alloys have high saturation magnetization,high Curie temperature,high magnetic permeability and low coercive force,and have wide application prospects in many fields,such as automotive industry,aviation generators,computer read/write heads and so on.In this paper,Fe-Co alloys magnetic powders were prepared using powder metallurgy.The effects of temperature and compositions on the morphology,microstructure,and static magnetic properties were studied.FeCo/Si O₂ soft magnetic composites were also prepared by doping SiO₂,and the effect of additives on the frequency characteristics of soft magnetic composites were studied.The researches purpose is make Fe-Co alloy to be used in higher frequency bands by doping SiO₂ to increase the electrical resistivity of Fe-Co alloy and reduce eddy current losses.The main contents have the following aspects:1.To provide the basis for the temperature of reduction/diffusion,using carbonyl iron powder?Fe?and cobalt powder?Co?as raw materials,Fe_1-xCo_x?x=0.25,0.35,0.40,0.50?alloys were prepared by powder metallurgy methods.It is demonstrated that the lattice constant of the sample is close to the theoretical value of the alloy at the 800?of sintering temperature.The grain size increases as the temperature increases.The static magnetic properties at 800?are better than that of other sintering temperatures.When the Co content is 35 at%,the Fe-Co alloy has the largest lattice constant,uniform grain size distribution,and the best magnetic properties with the saturation magnetization of 242 emu/g.2.The iron oxide?Fe₂O₃?and cobalt trioxide?Co₃O₄?as raw materials,Fe_1-x-x Co_x?x=0.25,0.35,0.40,0.50?alloys powders were prepared by hydrogen reduction/diffusion combined with powder metallurgy.It is easy to make the particles agglomerate at high temperature.According to the basis of the powder metallurgy methods by using carbonyl iron powder?Fe?and cobalt powder?Co?as raw materials,the reduction/diffusion reaction temperature was chosed lower than800?.When the reduction/diffusion temperature is 750?,the lattice constant of the sample is close to the theoretical value of the alloy,and the grain size increases with the increase of the reduction/diffusion temperature.The magnetic properties of sample at 750???_s=209 emu/g,H_c=65 Oe?are superior to that of the other temperatures.However,powder particle have the phenomenon of sintering.When the Co content is 35 at%,the lattice constant of the sample is close to the theoretical value and the magnetic properties are the best??_s=215 emu/g?.3.Although the Fe-Co with Co content of 35 at%has the best magnetic properties,overall consideration,we chose Fe_0.5Co_0.5.5 with a higher Curie temperature as the original powder.In order to disperse Fe_0.5Co_0.5.5 powder particles,the surfactants are added to mill.It was found that the sintered particles were successfully dispersed.The FeCo/SiO₂ soft magnetic composites were studied,it was found that magnetic permeability increases as the increased density.The magnetic permeability decreases,and the resonant frequency increases as the SiO₂ content increases or the sintering temperature decreases.When sintering temperature is 800?,the resonance frequency?f_r?and real permeability??'?of FeCo/SiO₂ soft magnetic composites with 10 wt%SiO₂ content reaches 9.2 kHz and 145,respectively.However,due to nonuniform the particle size distribution and irregular particles shape,the frequency characteristic rule of Fe Co/SiO₂ soft magnetic composites is not good.4.Using the carbonyl iron powder which has spherical particles,uniform size distribution and good dispersion as the original powder to prepare the Fe/SiO₂ soft magnetic composites.It can be seen that as the SiO₂ content increases,the initial permeability decreases,and the resonant frequency increases.As the sintering temperature increases,the magnetic permeability increases and the frequency decreases.When sintering temperature is 800?,the resonance frequency?f_r?and real permeability??'?of Fe/SiO₂ soft magnetic composites with 7 wt%SiO₂ content reaches18.1kHz and 153,respectively.The effect of sintering temperature and SiO₂ content on resonant frequency of Fe/SiO₂ soft magnetic composites is obvious.So the dispersivity and morphology of the original powder have a great influence on the preparation and magnetic properties of the soft magnetic composite materials.