Study On Soft Magnetic Properties Of Fe-Cu-Si-B Nanocrystalline Alloys With High Saturation Magnetic Induction

Since the nanocrystalline alloys have been developed,researchers take particular care of this kind of soft magnetic materials.Nanocrystalline alloys with excellent soft magnetic properties and relative high saturation magnetic flux density are studied until now.However,recently,new soft magnetic nanocrystalline alloys with high saturation magnetic flux density and low core loss have been required.This paper studies high Fe content Fe-Cu-Si-B alloy system which is characterized with high saturation magnetic flux density（B_S>1.80 T）,low coercivity（H_C～20 A/m）and low core loss.Fe-Cu-Si-Cu alloys is insensitive to annealing environment due to this kind of alloys are exclusive of readily oxidizable elements like P,Zr et al.In addition,Fe-Cu-Si-Cu alloy system presents broad market prospect and promising application foreground because of the absence of expensive early transition metal（EMT）elements including Nb,Mo,V etc.The effects of substituting Al for B and that of substituting Co for Fe on Fe_80.5Si₄B₁₄Cu_1.5 nanocrystalline alloy for improving magnetic softness and amorphous forming ability,as well as exploring the action of Cu clusters during nanocrystallizing program are studied.The single-roller melt-spinning method was performed to fabricate as-quenched ribbons on all alloy ingots.Then as-quenched samples were annealed at various temperature based on DSC curves to obtain nanocrystalline alloys.The superfluous addition of Al into Fe_80.5Cu_1.5Si₄B_14-xAl_x alloys deteriorate the amorphous forming ability.The alloys with Al content exceeding 2 at.%exhibit a significant different nanocrystallization characteristic that the primary crystallization process is transience instead of long for no Al and little Al substituted alloys.It is reasonable that the addition of excessive Al of above 2 at.%on Fe-Cu-Si-B alloy results in coarse Cu clusters in as-quenched state or Cu clustering after the primary crystallization.Therefore there are not enough high number density of Cu clusters and/or primary crystals acting as nucleation sites for precipitation of Fe（Si）nanocrystallites in as-cast samples to ensure the microstructure consists of nanocrystalline grains embedded in an amorphous matrix.It can be obviously observed that the grain sizes and coercivities of alloys with appropriate Al content exhibit more outstanding than those of no Al alloy.The Fe_80.5Cu_1.5Si4B13Al1 alloy annealed at 370℃exhibits the excellent soft magnetic properties including both high saturation magnetic flux density of 1.84 T and low coercivity of 10.2 A/m.In Fe_80.5-xCo_xSi₄B₁₄Cu_1.5（x=0,1,2,4,10 at.%）alloy system,except the alloys with Co content of 4 and 10 at.%,other alloys exhibit excellent soft magnetic characteristic.The too much Co addition into Fe_80.5-xCo_xSi₄B₁₄Cu_1.5 alloy system inhibits Cu clustering which leads to the absence of dense number density of crystal nuclei forα-Fe phase in as-quenched ribbons.Furthermore,this phenomenon results in enlarging the crystallite size,worsening coercivity and hardening magnetic properties.After annealing alloys with a series of compositions at different temperature,the relationship between coercivity and grain size is compared from various dimensions.The data suggest that the grain size and coercivity has the same variation tendency with annealing temperature and Co content which is corresponding to G.Herzer’s effect anisotropy theory.