Effects Of Cr And Surface Crystallization On Fe-based Amorphous/Nanocrystalline Soft Magnetic Alloys

Fe-based amorphous and nanocrystalline alloys stand out from soft magnetic materials due to their unique microstructure and excellent comprehensive magnetic properties.However,the Fe-based amorphous and nanocrystalline alloy systems currently developed still have some shortcomings.The saturation magnetic induction and permeability of Fe-based amorphous alloy（such as commonly used Metglas 2605alloy）are low,and the amorphous state is a metastable state.Thus,large grains may precipitate at high temperature,which deteriorates the soft magnetic properties.The Fe-based nanocrystalline alloy with high saturation magnetic induction（such as Nanomet alloy）often has high Fe content and weak amorphous forming ability.The surface crystallization will occur in the as-spun state,and the requirements of annealing treatment process are harsh.In addition,Fe-based amorphous and nanocrystalline alloys are required to have certain corrosion resistance in practical applications,and corrosion of the alloys may aggravate the failure.Therefore,it is necessary to develop Fe-based amorphous and nanocrystalline alloys with good magnetic properties,corrosion resistance and loose heat treatment condition.Therefore,the effects of Cr addition on the structure and properties of Fe-based amorphous alloys and nanocrystalline alloys were investigated in this paper,respectively.Moreover,the effect of surface crystallization on the properties of high Fe nanocrystalline alloys and the evolution of microstructure and magnetic structure during heat treatment were also studied.The main research contents and results of this paper are as follows:（1）The effects of Cr element addition on the thermal stability,structure,magnetic properties and corrosion resistance of Fe_80-xSi₈B₁₁Cu₁Cr_xamorphous alloy were systematically investigated.The results show that the Cr element can improve the thermal stability of Fe Si BCu amorphous alloy.Although the B_sof the amorphous alloy decreases slightly,the soft magnetic properties of the alloy are improved,the coercive force is significantly reduced,and the permeability is significantly improved.The internal magnetic domain becomes wider and uniform with the addition of Cr element.In addition,the corrosion resistance of the alloy ribbon containing Cr element is enhanced,and the oxide film on the surface is not easy to fall off after corrosion,which can provide better protection for the alloy matrix.（2）The effects of Cr element addition on the thermal stability,structure,magnetic properties and corrosion resistance of(Fe_83.3Si₄B₈P₄Cu_0.7)_99-xCr_xnanocrystalline alloy were systematically studied.The results show that the proper amount of Cr element is helpful to improve the amorphous forming ability and thermal stability of Fe Si BPCu alloy,and extends the annealing temperature range.Adding Cr element in the range that does not significantly reduce B_sresults in the formation of a large number of uniform fineα-Fe nanocrystalline grains because of that Cr atoms are dispersed in the amorphous matrix during crystallization annealing,which hinders the further growth of grains.Therefore,Cr element can effectively improve the soft magnetic properties of Fe Si BPCu nanocrystalline alloys.When Cr content is 1 at.%,the nanocrystalline alloy has a high B_sof 1.66 T,a low H_cof 2.7A/m,and a high μ_e of 14172 at 1 k Hz.The addition of Cr element also significantly improves the corrosion resistance of the alloy ribbon.（3）The surface crystallization phenomenon of Fe_81.5+xSi₃B_10-xP_3.5C_0.2Cu_0.8Nb₁nanocrystalline alloy was investigated.The results show that the increase of Fe content is accompanied by the phenomenon of surface crystallization,which increases the B_sof nanocrystalline alloy and enlarges the annealing temperature window.Surface crystallization will cause out-of-plane anisotropy of the as-spun alloy ribbon,which deteriorates the soft magnetic properties.After crystallization annealing,the nanocrystals are distributed uniformly on the surface and inside of the alloy,and the magnetic domain structure becomes wider.The Fe_83.5Si₃B₈P_3.5C_0.2Cu_0.8Nb₁alloy exhibits excellent comprehensive soft magnetic properties,including high B_sof 1.68 T,low H_cof 6.43 A/m,and highμ_eof 18600 at 1k Hz.This study helps to broaden the scope of compositional design of nanocrystalline alloys with high Fe content.