| The Fe-6.5wt.%Si alloys, as a kind of excellent soft magnetic materials, exhibit high permeability, low core loss and near zero magnetostriction, which is the key to realize low energy consumption, low fever, micro miniaturization, low noise, high stability and green environmental protection for electric-magnetic conversion equipment. However, with increasing the Si content, the Fe-6.5wt.%Si alloys are very brittle and their ductility is almost zero at room temperature, which limits the production and application.In order to avoid difficulties caused by the brittleness of Fe-6.5wt.%Si alloys, this paper takes preparation Fe-6.5wt.%Si soft core with high induction, low core loss and removing rolling as the starting point. The Si O2 insulating coating was coated firstly on the surface of Fe-6.5wt.%Si particles through micro-oxidation coating, simple ball milling, and in situ chemical deposition process, respectively. And then the interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores thus obtained were sintered by spark plasma sintering(SPS). The methods of control of microstructures, and effects of electric-magnetic properties of the interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores were investigated in this paper. The specific research contents and research results are as follows:(1) The amorphous/nanocrystalline Fe-Si soft magnetic alloy was prepared with Fe-Si-Cu-B-Nb amorphous powders as as raw material through Spark Plasma Sintering(SPS) technology. The microstructural feature and evolution from amorphous to nanocrystalline, and the static magnetism change rule were investigated. The results demonstrates that the whole crystallization process followed sequence of amorphous ' α-Fe(Si) + amorphous(530℃) 'α-Fe(Si) + Fe23B6(680℃) as sintering temperature was increased from 480℃ to 730℃. Moreover, the saturation magnetizations(Ms) of the samples obtained increased first and then decreased, while the values of coercive force(Hc) changed in the opposite direction. The Fe-Si soft magnetic alloy with amorphous and nanocrystalline mixed system sintered at 630℃ showed excellent soft magnetic properties with saturation magnetization at 137.5 emu/g, coercivity at 5 Oe and remanence(Mr) at 1.0 emu/g. The sintering temperature for compeling crystallization is 730℃. The static magnetism was worse through the Fe23B6 when sintered over 680℃.(2) The amorphous Fe-Si alloy ribbons were firstly prepared by melt spinning, then the Si O2 coating was coated on the Fe-Si alloy powders through micro-oxidation coating, after that the interparticle insulative Fe-Si/Si O2 soft cores thus obtained were sintered by SPS. The effects of micro-oxidation coating time and sintering temperature on densities, microstructures, and static magnetic properties were investigated. The results showed that the grain size and the relative density of of the interparticle insulative Fe-Si/Si O2 soft cores increased with increasing micro-oxidation coating time. Moreover, the the saturation magnetizations(Ms) of the samples obtained decreased first and then increased, while the values of coercive force(Hc) changed in the opposite direction. The soft magnetic properties changed better first and thenworse when sintered from 600℃ to 1000℃. The simple, which was micro-oxidation coated for 5h and the sintered at 800℃, showed the best soft magnetic properties with saturation magnetization at 128.8 emu/g, coercivity at 28.3 Oe and remanence(Mr) at 3.5 emu/g.(3) The Fe-6.5wt.%Si/Si O2 core-shell powders and interparticle insulative soft cores was prepared with sphere Fe-6.5wt.%Si particles as raw material through simple ball milling, and spark plasma sintering(SPS) technology, respectively. The effects of raw material ratios, simple ball milling parameters, and sintering temperature on microstructures, and static magnetic properties were investigated. The relative densities of the composite compacts increase with the sintering temperature, while the values of Hc and electrical resistivity(ρ) change in the opposite direction. The Ms fluctuates around an identical value(153 emu/g) with increasing the sintering temperature from 800 °C to 1250 °C. In addition, with raw material ratios of Fe-6.5wt.%Si particles increasesd, the relative densities, Ms, relative permeability(μr) increased, but the values of electrical resistivity decreased and the effect of decreased core loss get poor due to the homogeneity of Si O2 insulating coating decreased. Compared with stainless steel ball mill, after changed to agate ball mill, the values of Ms and Hc remained unchanged. The value of ρ increased two orders of magnitude(7.9?10-3Ω·m), and the core loss showed a lower value. When the mass ratio of Fe-6.5wt.%Si particles is 0.8 and sintered at 1050℃, the Fe-6.5wt.%Si/Si O2 soft cores showed the best soft magnetic properties with saturation magnetization at 128.8 emu/g, and coercivity at 28.3 Oe. When compared with the Fe-6.5wt.%Si soft cores without Si O2 insulating coating(9.7?10-7Ω·m, W5/10=116.7 W/kg), the interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores showed the higher ρ and lower core loss(7.9?10-3Ω·m, 7.2W/kg).(4) Core-shell structured Fe-6.5wt.%Si/Si O2 particles and interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores with tunable insulating layer thickness were prepared by in-situ chemical deposition combined with the following spark plasma sintering process. The thicknesses of Si O2 insulation layer could be tailored by altering the added silica source concentration(the volume of silica source for each gram of Fe-6.5wt.%Si particles) to regulate hydrolyzation rate during in-situ chemical deposition process. The effect of the thicknesses of Si O2 insulation layer on electric-magnetic properties of the interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores were investigated. Most of conductive Fe-6.5wt.%Si alloy particles were coated with Si O2 insulating layer in interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores. The presence of Si O2 insulating layer could increase electrical resistivity and reduce effective radius of eddy current for Fe-6.5wt.%Si alloy. The good soft magnetic properties, including high saturation magnetization, low coercivity and good frequency stability, were also obtained for the interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores. The results indicated that the thickness of Si O2 layer and electrical resistivity of Fe-6.5wt.%Si/Si O2 soft cores increased with increasing TEOS concentration from 0.1 to 0.5 ml/g, while saturation magnetization, relative permeability and core loss appeared the reverse tendencies. When introducing TEOS concentration of 0.3 ml/g, the interparticle insulative Fe-6.5wt.%Si/Si O2 soft cores showed the best soft magnetic properties with saturation magnetization at 128.8 emu/g, and coercivity at 28.3 Oe. the values of W5/10 k for intergranular insulated Fe-6.5wt.%Si/Si O2 composite compacts is only 12.7W/kg, which also lower than those of Fe-6.5wt.%Si alloy cores of JFE Steel Corporation(17.9W/kg), drop 1/3 on average.The work in this paper provided a promising route to effectively decrease core loss through introducing Si O2 insulating layer between Fe-6.5wt.%Si alloy particles. The presence of Si O2 insulating layer could increase electrical resistivity and reduce effective radius of eddy current for Fe-6.5wt.%Si soft cores. It is demonstrated that the Fe-6.5wt.%Si/Si O2 composite compacts have excellent soft magnetic properties with low core loss and thus the method developed could be used to produce miniature magnetic components for applications in the medium and high frequency fields. |
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