Research On Insulation Coating Technology Of Iron-based Soft Magnetic Powder

Soft Magnetic Composite materials（SMCs）is a basic functional material used for electromagnetic conversion.It is fabricated by coating the soft magnetic particles with insulating materials and subsequent powder metallurgy technique.Because of its excellent properties such as high saturation magnetization,high resistivity,and low eddy current loss,it has a promising future in medium and high frequency electromagnetic devices.As a composite material,the properties of coating layer and the coating methods have a great influence on the comprehensive performance.As a kind of semiconductor material,soft ferrite has ferrimagnetism and high resistivity（10²～10⁸Ω?m）,which is a kind of excellent insulting materical.Spark plasma sintering（SPS）is an advanced powder metallurgy technology.It is widely used in the sintering of ceramics,alloys,composite materials and other powders.Therefore,the SMCs which was coated with soft ferrite and fabricated by SPS has been extensively studied.However,it is found through research that the interface diffusion and interface reaction between the soft magnetic substrate and the insulating coating during spark plasma sintering lead to the decrease of the resistivity of the insulting layer.In order to explore the factors that affect the resistivity of the cladding layer,and further improve the performance of soft magnetic composite materials in medium and high frequency applications,the main research contents of this paper are as follows:（1）The powder vibration device was independently designed,and creatively combined it with the vacuum evaporation equipment.By allowing the powder particles to vibrate continuously during evaporation,the purpose of completely and uniformly depositing the Mg coating layer on the surface of the particles is achieved.The effect of vacuum evaporation time on the properties of coating layer is explored.By controlling the evaporation time,different coating layers are obtained.As the evaporation time increases,the Mg coating layer gradually becomes complete.When the evaporation time reaches 90 minutes,the most uniform and dense coating layer was obtained.When the time exceeds 90 minutes,flocculent agglomeration began to appear on the surface of the soft magnetic powders;（2）The influence of the Mg O/Zn_0.5Ni_0.5Fe₂O₄ double coating structure on the resistivity and magnetic properties of the soft magnetic composite powder is explored.The Mg O diffusion barrier coating layer was prepared by surface oxidation treatment,and the Zn_0.5Ni_0.5Fe₂O₄ insulating layer was added outside the Mg O diffusion barrier coating layer by manual grinding.the Mg O/Zn_0.5Ni_0.5Fe₂O₄ double-layer coating structure was obtained through the above methods.The resistivity of the obtained soft magnetic composite powder is up to 2.39?10⁹μΩ?cm,and the saturation magnetization is above 170 emu/g.Compared with the Fe-6.5wt%Si/Zn_0.5Ni_0.5Fe₂O₄ soft magnetic powder,the added Mg O coating layer has almost no effect on the electromagnetic properties;（3）SMCs were prepared by spark plasma sintering technology,and the influence of the Mg O diffusion barrier coating layer on the resistivity and electromagnetic properties of the sintered SMCs was explored.The resistivity of SMCs without Mg O diffusion barrier coating layer is 1.8?10³μΩ?cm,and the saturation magnetization is 172.9 emu/g.After adding the Mg O diffusion barrier coating layer,the resistivity is up to 1.22?10⁵μΩ?cm.It’s 67.8 times higher than the sample without Mg O diffusion barrier coating layer.The saturation magnetization still remain at 170.0 emu/g.