Preparation And Electromagnetic Properties Of FeCoNiCuAl High Entropy Alloy Powders

The equimolar ratio FeCoNiCuAl,FeCoNiCu_xAl_{（x=0.2-0.7）}and FeCo_0.6NiCu_0.5Al_x=0.2-0.5high-entropy alloy powders are prepared by mechanical alloying.The equimolar ratio FeCoNiCuAl alloy powders are milled in different milling time（10h,30h,50h,70h and 90h）and then all samples are annealed at 773 K.The FeCoNiCu_xAl alloy powders are milled 90h and FeCoNiCu_0.5Al powders annealed at different temperature（673 K,773 K and 873 K）.The FeCo_0.6NiCu_0.5Al_x=0.2-0.5 alloy powders are milled 70h and then all samples are annealed at773 K.The microstructure,morphology,particle size,magnetic and electromagnetic performance of powders were studied by X-ray diffraction（XRD）,scanning electron microscope（SEM）,laser scattering particle size distribution analyzer,vibrating sample magnetometer（VSM）and vector networ K analyzer.The equimolar ratio FeCoNiCuAl:The results indicate that fla Ky particles,which formed in the process of ball milling,show a soft magnetic character,as well as,the ranges of coercivity（H_c）are 67.6-105.1 O_e and the values of saturation magnetization（M_s）range from69.1 emu/g to 94.2 emu/g.As the increasing of the milling time,the real part of complex permittivity（ε′）increase firstly and then decrease,however,the imaginary part of complex permittivity（ε″）close to zero for all the samples.Meanwhile,the real part of complex permeability（μ′）are 1.26-1.56 and the imaginary part of complex permeability（μ″）are0.28-0.36 with change of milling time.The reflection loss（RL）of powders can reach-10 dB or less and 30h-milling sample shows the maximum RL is-19.17 dB at 7.84 GHz with the thic Kness of 2 mm.After annealing,there appear two new phases,CoFe₂O₄ and AlFe_3,that improve the values of M_s.The crystal structure of FeCoNiCu_x=0.2-0.7Al powders are simple FCC and BCC phases.The microscopic morphology of powders are fla Ky.The FeCoNiCu_xAl alloys with different Cu contents are soft magnetic materials,which possess high saturation magnetization（75.05-82.51emu/g）and low coercivity（93.68-103.38O_e）.The reflection loss（RL）of FeCoNiCu_xAl alloy powders all can reach-10 dB or less and and the maximum RL value is-28.04 dB at Cu_x=0.5.The value of reflection loss is closely related to the complex permittivity and permittivity.Improving surface polarization with large aspect ratio of fla Ky powders and high conductivity can enhance permittivity.Meanwhile,high saturation magnetization of soft magnetic materials can reinforce permeability.These can promote the FeCoNiCu_xAl alloy powders absorbing microwaves.Different temperatures annealing treatment can change phases,morphology,conductivity and saturation magnetization,which ma Ke the values of RL improving differently,and the maximum RL value is-40.05 dB at 673 K annealing.The FeCo_0.6NiCu_0.5Al_x=0.2-0.5 alloy powders show simple FCC and BCC phases,large aspect ratio fla Ky powder particles and soft magnetic properties（high saturation magnetization:87.2-93.4emu/g;and low coercivity 62.1-106.6O_e）.The values ofε’andε″increase first and then decrease,and the maximum are simples of FeCo_0.6NiCu_0.5Al_0.4.The values ofμ′first rise(Al_0.2⁰.3)and then decrease(Al_0.3⁰.4),but finally still increase(Al_0.4⁰.5).The alloy powders have good absorbing ability and the maximum RL value is-23.13 dB.After annnealing,CoFe₂O₄ can be produced in all samples.But,AlFe₃ phase only can be generated in Al_x=0.3⁰.5 powders.The aspect ratios of fla Ky powders have also increased.Meanwhile,the values of electromagnetic parameters have also improved.These encouraging findings provide the potential advantages of high-entropy alloys for microwave absorption application.