Preparation And Properties Of FeSiBCuNb Nanocrystalline Magnetic Powder Cores

Magnetic powder cores(MPCs),a kind of soft magnetic composite material,are made of magnetic powder after insulation coating.It has the advantages of high resistivity,high width and constant magnetic permeability.Therefore,it is widely used in electronic systems,such as transformers and DC converters,switching power supplies,chokes,etc.With the growth of miniaturization and high frequency of electronic products,as an important electronic component,the performance requirements of magnetic powder core are also improved,including good frequency stability,high saturation magnetization and permeability,low loss and excellent DC-bias performance.Among many magnetic powder cores,Fe based amorphous/nanocrystalline magnetic powder core is favored by researchers because of its good high frequency performance,but its development is limited by its poor thermal stability and relatively low permeability.Preparation of nanocrystalline magnetic powder cores with excellent comprehensive performance to meet the application of higher frequency range has become a hot spot in the application research of magnetic powder cores.Therefore,based on the composition of Finemet alloy,Fe_73.5Si_13.5B₉Cu₁Nb₃alloy with excellent soft magnetic properties was obtained by microalloying,and nanocrystalline magnetic powder cores were prepared with this alloy composition.The experiment is mainly divided into three parts.Firstly,Fe_73.5Si_13.5B₉Cu₁Nb₃amorphous powders were prepared by mechanical alloying method and strip crushing method respectively,and then nanocrystalline magnetic powder cores were prepared by the same process.Secondly,in order to reduce the dilution effect of non-magnetic coating material on magnetic properties of magnetic powder cores,Fe_73.5Si_13.5B₉Cu₁Nb₃amorphous powders prepared by strip crushing method were taken as an example Ni Cu Zn ferrite/FeSiBCuNb nanocrystalline magnetic powder cores were prepared by coating Ni Cu Zn ferrite insulating layer on its surface by chemical coprecipitation method.Finally,FeSiAl/FeSiBCuNb nanocrystalline composite magnetic powder cores were prepared by mixing FeSiAl powders after oxidation treatment and Fe_73.5Si_13.5B₉Cu₁Nb₃amorphous powders prepared by strip crushing method in different mass ratios.The effects of milling process,insulation coating,forming pressure,annealing process and powder compounding on the effective permeability,loss,quality factor and DC bias performance of magnetic powder cores were discussed.The main results are as follows:(1)Both the mechanical alloying method and the strips crushing method can successfully prepare Fe_73.5Si_13.5B₉Cu₁Nb₃amorphous powders.For the FeSiBCuNb nanocrystalline magnetic powder cores prepared under two different milling conditions,there are great differences in their properties.Among them,the effective magnetic permeability of the magnetic powder core made of mechanically alloyed powders is 22,the loss is 245.7 W/kg(Bm=0.1 T,f=100 k Hz),the quality factor is 45,and the DC bias performance is 80%at 100 Oe.Compared with the magnetic powder cores made of mechanically alloyed powders,the magnetic powder cores made of crushed ribbons powders show better comprehensive properties,including:higher effective magnetic permeability of43,lower loss is 98.2 W/kg(Bm=0.1 T,f=100 k Hz),the quality factor is 58 at the maximum,and the DC bias performance is 49%at 100 Oe.(2)For Ni Cu Zn ferrite/FeSiBCuNb nanocrystalline magnetic powder cores,with the molding pressure increases from 1000 MPa to 1800 MPa,the effective permeability first raises and then reduces,the loss first reduces and then raises,the quality factor first raises and then reduces,and the DC bias performance decreases.When the molding pressure is1600 MPa,the comprehensive performance of the magnetic powder core is the best:the effective permeability is 60,the loss is 85.1 W/kg when f=100 k Hz and Bm=0.1 T,the quality factor is 35,and the DC bias performance is 44%.With the annealing temperature increasing from 500?to 700?,the effective permeability first increases and then decreases,and the maximum value reaches 81 at 550?;the loss first reduces and then raises.When heat treatment temperature is 550?,the loss of the magnetic powder core is the smallest,which is 78.2 W/kg(Bm=0.1 T,f=100 k Hz).When the temperature reaches700?,the effective permeability can be as high as 87%under the DC bias field of 100 Oe,which shows good DC interference resistance.(3)For the FeSiAl/FeSiBCuNb nanocrystalline composite magnetic powder cores,because the FeSiAl powders are filled between the amorphous powders,the density is significantly increased and the eddy current loss is significantly reduced.With the increase of FeSiAl powders content from 0 wt.%to 40 wt.%,the density of magnetic powder core increases from 5.085 g/cm³to 5.415 g/cm³.The effective permeability of composite magnetic powder cores first raises and then decreases,the loss first decreases and then increases,the quality factor first increases and then reduces,and the DC-bias performance floats tiny.When the mass fraction of FeSiAl powders is 20 wt.%,the composite core has good comprehensive properties:the effective permeability is 98,which is 20%higher than that of the core without FeSiAl powders;the loss of the core is 65.1 W/kg(Bm=0.1 T,f=100k Hz);the quality factor is 45,and the DC bias performance is 53%.(4)For the FeSiAl-20%/FeSiBCuNb nanocrystalline magnetic powder cores,with the holding time increases from 0.5 h to 2 h,the effective permeability of the magnetic powder core first increases and then decreases,and the loss and quality factor first increase and then decrease with the increase of the holding time.When the holding time is 1.5 h,the overall performance of the magnetic powder core is the best:the effective permeability is as high as116,but its frequency stability is reduced;the magnetic loss is 55.6 W/kg(Bm=0.1 T,f=100k Hz),the quality factor is 63.The change of the holding time has little effect on the DC bias performance of the composite magnetic powder core.When the applied DC field is 100 Oe,the DC bias performance of all magnetic powder core samples is maintained above 50%.