| Focusing on the external environment of?energy saving and emission reduction?and?reduce the cost and increase the efficiency?of the world and further meeting the requirements of the future frequency conversion control technology,it is very necessary to develop the nanocrystalline soft magnetic composite iron core that both bears the high energy density input and satisfies the low iron loss.Due to the excellent soft magnetic properties such as high saturation magnetic induction,permeability,low coercive force,excellent mechanical properties and low cost,the iron-based nanocrystalline soft magnetic composites have a wide application in the field of functional and structural materials,such as the core materials in transformer,motor,transformer,reactor etc,and play an important role in the development of electronic power technology.However,due to the limitation of nanocrystal forming ability,the obtained soft magnetic alloy exhibits unstable performance,large loss and small size,which seriously restricts its application.Therefore,it is of great significance to develop a new high-magnetic,low-iron loss iron-based nanocrystalline soft magnetic material and explore the preparation process of large-sized bulk nanocrystalline soft magnetic materials.In order to meet the requirements of future motor inverter control technology,it is necessary to develop a nanocrystalline soft magnetic composite core that can possess both high magnetic sensitivity and low iron loss.In this paper,a new preparation method of FeSiBCr nanocrystalline soft magnetic composite core was proposed.First,the influences of the process parameters(sintering temperature,sintering pressure,heating rate and holding time)on the organization,microstructure,mechanical properties and electromagnetic properties of FeSiBCr nanocrystalline soft magnetic cores were studied,which provided a theoretical basis for producing the FeSiBCr nanocrystalline soft magnetic composite core.Next,using FeSiBCr iron-based soft magnetic amorphous powder as raw material,the FeSiBCr/Si O 2core-shell heterostructure amorphous composite powder was synthesized by the reverse micro-emulsion method and chemical liquid deposition method respectively.Then,FeSiBCr/Si O2 nanocrystals were obtained by one step forming.The influence of coating synthesis process on the microstructure and main electromagnetic properties of FeSiBCr nanocrystalline soft magnetic composite core was systematically studied.An electric hot pressing sintering technology was developed for preparing FeSiBCr nanocrystalline soft magnetic core from FeSiBCr amorphous powders.The findings indicated that increasing of sintering temperature that can significantly increase the density,microhardness,compressive strength and saturation magnetization of the soft magnetic core,so the coercive force and resistivity of the sintered compact were lowered.However,if the sintering temperature was too high,the cubic structure of Fe23B6 hard magnetic phase was prec ipitated in the iron core,and the grain size of the?-Fe(Si)phase of the bcc structure was too large,so the mechanical properties and magnetic properties of the alloy were deteriorated.The optimum sintering temperature should be slightly higher than the initial crystallization peak temperature Tp1 and lower than the secondary crystallization temperature Tx2.An increase of sintering pressure can significantly increase the density,compressive strength and microhardness of the sintered block,and improve the magnetic properties of the sintered block,but the increase of the sintering pressure will promote the crystal formation of the amorphous phase in the sintered block.An increase of the heating rate can inhibit the crystallization of the amorphous phase,and the amorphous powder can be more easily formed into an amorphous phase or a uniform nanocrystalline phase during sintering,and the mechanical properties and magnetic properties of the sintered compact can be improved.A prolongation of the holding time can promote the increase of the iron core density and the crystallization of the amorphous phase,and increase the grain size of the crystallized phase.But the excessive holding time will cause the mechanical properties and magnetic properties of the sintered block to deteriorate seriously.The optimum sintering pressure,holding time and heating rate for preparing FeSiBCr alloy should be around 60Mpa,10minute and 50?/min.The reverse microemulsion method With subsequent electric hot pressing sintering technology,the FeSiBCr/Si O2 nanocrystalline soft magnetic composite core was prepared.By adjusting the dropping amount of the silicon source TEOS to control the thickness and uniformity of the Si O2insulating layer,the influence of the Si O2 layer on the electromagnetic properties of the composite core was studied.It was found that when the amount of TEOS is increased from 6m L to 15m L,the continuity of the insulating layer first became better and then worse,and the thickness of the shell and the density of the core first increased and then decreased,while the values of Ms,?r and P first decreased and then increased.When the amount of TEOS is 12 m L,the uniform continuity of the insulating shell was shown to be the best,and the integrated electromagnetic properties of the prepared nanocrystalline composite core were optimal.However,no matter how much the TEOS was added,the magnetic particles were not completely covered with the insulating layer.The insulating layer was always interrupted,and the continuity was poor.Through chemical liquid phase and the electric hot pressing sintering technology,FeSiBCr/Si O2 nanocrystalline soft magnetic composite was prepared.By adjusting the single process parameter such as the amount of TEOS,the coating temperature,the water content or the ammonia content,the rates of hydrolysis and polycondensation of TEOS were controlled to affect the uniformity,continuity and thickness of the Si O2 insulating layer.The results showed that the thickness of the Si O2 insulating coating increased first and the decreased,and uniform continuity first became better and then worse when the amount of TEOS added from the silicon source,water content or ammonia content increased.When the coating temperature increased,the thickness of the coating layer continued to increase,and the uniform continuity gradually became better.As the thickness of the Si O 2 insulating layer increased and the continuity and uniformity became better,the Ms value and initial?rof the composite core were slightly decreased,and Hc and Mr were slightly increased,but the?of the prepared sample was gradually increased.The frequency stability became better,and the iron loss obtained at high frequencies decreased obviously.The results demonstrated that when the amount of TEOS was 10m L,the water content was6.4m L,the ammonia content was 1.8m L,and the coating temperature was 50?,the coating layer was uniformly continuous and compact,the shell thickness was suitable,and the comprehensive performance of the sample was the best.At this time,the thickness of the Si O2 insulating shell layer was about 160nm,Ms was 155.7 emu/g,Hcwas 15.6 Oe,?was 1.83×10-4?·m,and P1/10 was only 0.21 W/kg.In this paper,by introducing the SiO2 insulating layer among the FeSiBCr amorphous alloy particles,so the eddy current was confined in the tiny area of the magnetic particles,and the effective radius of the eddy current movement was reduced,and the eddy current loss can be greatly reduced.Meanwhile,the electric hot pressing sintering technology was used for one-step producing the bulk FeSiBCr/Si O2nanocrystalline soft magnetic composite core,which provided a new way to prepare large-sized nanocrystalline iron cores and expand the application range of iron-based nanocrystals. |
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