Preparation And Magnetic Properties Of High Performance FeSiBMCu Nanocrystalline Alloys

Fe-based nanocrystalline alloys are a kind of soft magnetic materials with nanocrystalline structure obtained by annealing the amorphous alloys.Fe-based nanocrystalline soft-magnetic materials have attracted worldwide attention due to their excellent magnetic properties,including relatively low coercivity(Hc),high saturation magnetic induction density(Bs),permeability(?e)and low saturation magnetostriction(?s),which can effectively reduce the core loss and noise,and have been widely used in power electronics flied,such as switching power supply,high-precision current transformer,common mode choke coil,high-frequency transformers and so on.Finemet is one of the nanocrystalline alloy with excellent soft magnetic properties and have been widely used,while because of the low Fe content and high content of Nb with high price,this alloy shows low Bs and high cost.In order to reduce the cost and improve the Bs,the FeSiBNbCu nanocrystalline alloys with high Bs and excellent soft magnetic properties were successfully developed via composition adjustment;the surface crystallization of Fe-rich FeSiBNbCu was eliminated by the substitution of Nb with Mo;the effect of surface crystallization degree on the soft magnetic properties was studied by using the Fe-rich FeSiBNbCu as the research object.The main research contents and results are as follows:(1)The Fe78-xSi13B8NbxCu1(x=0,1,2 and 3)nanocrystalline alloys with excellent soft magnetic properties,high thermal stability and high Bs were successfully developed.The effect of Nb content on the soft magnetic properties,thermal stability and microstructure evolution were also systematically studied.It is found that proper Nb addition can refine the grain size to 10 nm,and the Fe76Si13B8Nb2Cu1 show an excellent soft magnetic properties including high Bs of 1.39 T,low Hc of 1.5 A/m and high ?e of 21,500 at 1 kHz.The Fe76Si13B8Nb2Cu1 nanocrystalline alloy also show a large annealing temperature range of over 100?and annealing time range of 60 min,which means this alloy have an excellent thermal stability and soft magnetic properties.(2)The Fe82Cu1Si4B11.5Nb1.5-xMox(x=0,0.75 and 1.5 at.%)nanocrystalline alloys system with high Bs of 1.74 T were successfully developed and the effect of Mo on the amorphous forming ability,soft magnetic properties and microstructure were also investigated.It is found that the addition of Mo can enhance the amorphous forming ability,while the less Mo addition have no obvious effect.All the alloys exhibited excellent soft-magnetic properties with low Hc of 8.9?10.8 A/m,high ?e of 11,500?11,900 at 1 kHz and high Bs of 1.67?1.72 T after annealing.In addition,the Mo-doped alloys have an excellent high frequency characteristics,which make these alloys are suitable for high frequency electronic equipment.(3)The effect of surface crystallization degree on soft magnetic properties,thermal stability and microstructure evolution were studied by using the Fe82Cu1Si4B11.5Nb1.5 nanocrystalline alloy with different microstructure under various wheel speeds.It is found that the samples with surface crystallization show a wider annealing temperature range than the sample with completely amorphous structure,and proper surface crystallization can decrease the core loss,but excessive surface crystallization will increase the core loss.At last,the crystallization mechanism of nanocrystalline alloys with surface crystallization layers was discussed from the aspects of diffusion and competitive processes.