Preparation And Properties Research Of FeSiBPCu Nanocrystalline Soft Magnetic Alloys

Nanocrystalline soft-magnetic alloys are mostly fabricated from partially crystallizing the amorphous precursors,has gradually become one of the hotspots of scientific research due to its excellent properties such as high saturation magnetic flux density,high effective permeability,low coercivity and low high frequency loss.Since FINEMET alloys were first prepared,NANOPERM,HITPERM and NANOMET alloys have been developed one after another over the past three decades.Among them,NANOMET alloy has been studied most in recent years.However,the limitation of its amorphous forming ability,narrow crystallization window and strict nanocrystallization process added a lot of difficulty to further improve comprehensive soft magnetic properties.Therefore,it is important to explore a soft magnetic material with good amorphous forming ability,excellent comprehensive soft magnetic properties,wide crystallizing window and simple preparation process.The research contents of this paper include two systems:(1)FeSiBPCCu system and(2)FeCoSiBPCu alloy system with high copper content;Two annealing methods:(1)general heat treatment and(2)longitudinal magnetic field heat treatment.Firstly,on the basis of Fe83.3Si4B8P4Cu0.7 system alloy,the effects of substitution of C for P on amorphous forming ability,crystallization behavior,thermomechanical properties,microstructures and soft magnetic properties of FeSiBPCCu alloy were studied.FeSiBPCCu nanocrystalline alloys were prepared by annealed for short time at a relatively high temperature.The results have shown that the addition of C effectively inhibits surface crystallization,the increase of critical thickness of quenched ribbon and the decrease of melting entropy improves the amorphous forming ability of FeSiBPCCu amorphous alloy.The increase of crystallization volume fraction lead to the increase of Bs,while Hc decreases first and then increases.The Fe83.3Si4B8P2C2Cu0.7 nanocrystalline alloy was successfully synthesized with high AFA with 35μm in critical thickness and good SMPs combined with Bs of 1.84 T,low Hc of 4.8 A/m and high effective permeability of 13,540,the grain size is 22±0.5nm;excessive C content leaded larger coercivity but improved the frequency and DC superposition performance.The combination of high Bs and high resistance to DC bias promises potential material in DC superposition application.Secondly,based on the above work,Lower Si and C-content Fes3.3Si2Bi3-xPxC1Cu0.7(x=0-6)alloys were developed with the aim of understanding the role of P in amorphous forming ability(AFA),structural and soft magnetic properties.Solidification processes analysis revealed that proper P addition decreases the liquidus temperature and leads to the approach of eutectic point hence favors the amorphous formation,while excessive P addition causes the opposites therefore deteriorates the AFA.Microstructure measurement indicated P addition promotes the homogeneous precipitation of a-Fe phase during the annealing process,resulting in a uniform nanostructure.Saturation magnetic flux density(Bs)increases linearly with increasing P addition while coercivity(Hc)takes an inverse variation.The Fe83.3Si2B9P4C1Cu0.7 nanocrystalline alloy was successfully developed with relatively higher AFA with 3 6±1μm in critical thickness and good SMPs combined with high Bs of 1.78 T,low Hc of 4.6 A/m and high effective permeability of 15100.Finally,the effect of P/Cu ratio on the amorphous forming ability and the effect of magnetic field heat treatment process on the properties and structure of the alloy were studied in the FeSiBPCu system with high copper content.We have proved that FeSiBPCu alloy with high Cu content has a wide crystallization annealing temperature zone and time window due to the interaction of P and Cu thus has wide range of industrial application value.The results have shown that for high Cu system,the presence of appropriate P is critical for amorphous formation,and the optimum P/Cu ratio is between 2.5 and 4.5.Longitudinal magnetic field crystallization heat treatment combined with furnace cooling process can make the alloy have excellent soft magnetic properties due to the change of domain structure inside the alloy.Saturation magnetic flux density(Bs)increases linearly with increasing P addition while coercivity(Hc)takes an inverse variation.The of Fe66.3Co15S14B8P5Cu1.7 nanocrystalline alloy could reach 1.79T and the Hc is as low as 4.8A/m,the loss of Fe66.3Co15Si4B8P5Cu1.7 nanocrystalline alloy at intermediate frequency(1 kHz)and high frequency(20 kHz)can be reduced by 35%and 54%than that of amorphous alloysr espectively.In summary,the aim of this study is to synthesize Fe(Co)SiP(C)Cu nanocrystalline soft magnetic alloys combined with high amorphous forming ability,excellent controllable soft magnetic properties,simple preparation process and low price It is expected to expand the industrial application of high saturation magnetic flux density nanocrystalline alloy.