Megahertz Electromagnetic Properties Of FeCoNiCrCu High Entropy Alloy Powders

With the rapid development of electronic information technology,the signal processing of electronic equipment is becoming more and more high speed,reaching the megahertz(MHz)frequency range,which poses a greater challenge to absorbing materials.The key to improving the absorption performance of the absorbent is to improve impedance matching and energy attenuation.In the megahertz frequency range,the permeability of the material is usually much smaller than the dielectric constant.Therefore,it is required to increase the permeability of the material to improve impedance matching and increase energy attenuation.In this paper,a series of FeCoNiCr Cu high entropy alloy powders were successfully prepared by the mechanical alloying method.By changing the molar ratio of Cr and Cu elements and improving the alloy preparation process,the phase structure and microscopic morphology of the high entropy alloy powders were adjusted and the magnetic properties and electromagnetic wave absorption performance of the materials were adjusted.FeCoNiCr_(x=0.1-0.6)Cu_0.5 and FeCoNiCr_0.4Cu_(x=0-0.4)high entropy alloy powders were prepared by wet grinding in 70 hours.The crystal structure is body centered cubic(BCC)and face centered cubic(FCC)phases.By improving the preparation process,the FeCoNiCr_0.4Cu_0.2high entropy alloy powder is prepared as the FCC phase by the two step method of dry grinding and wet grinding.The FeCoNiCr Cu series high entropy alloy powder prepared by the mechanical alloying method has a flake structure,and the particle size is normally distributed.Thin thickness can be obtained by adding Cr element,and large particle size and aspect ratio can be obtained by adding an appropriate amount of Cu element and adopting a two step method.The average particle size of FeCoNiCr_0.4Cu_0.2 high entropy alloy powder prepared by dry grinding and wet grinding is 43.82?m.The experimental results show that the large particle size is beneficial to break through the magnetic limitation and increase the permeability.With the increase of Cr molar ratio,the saturation magnetization of FeCoNiCr_(x=0.1-0.6)Cu_0.5high entropy alloy powder prepared by wet grinding decreases from 119.73 emu/g to 102.45emu/g,and the coercive force Hc first decreases and then increases.The variation range is 57.6Oe?88.9 Oe.With the increase of Cu molar ratio,the saturation magnetization of FeCoNiCr_0.4Cu_(x=0-0.4)high entropy alloy powder prepared by wet grinding decreases from103.6 emu/g to 95.1 emu/g,and the coercivity ranges from 69.5 Oe to 83.4 Oe.The saturation magnetization of FeCoNiCr_0.4Cu_0.2 high entropy alloy powder prepared by dry grinding and wet grinding two step method is 102.5 emu/g,and the coercivity is 15.48 Oe,which is compared with FeCoNiCr_0.4Cu_0.2 high entropy alloy powder prepared by wet grinding method.The saturation magnetization is basically unchanged,while the coercive force is reduced by 57 Oe.The coercivity is related to the particle shape,internal stress,crystal structure,crystal grain size and other factors.The high entropy alloy powder prepared by the two step method of dry grinding and wet grinding has a larger aspect ratio,which will increase the shape anisotropy and reduce the coercivity.By adjusting the molar ratio of Cr and Cu,the real part of permeability for the FeCoNiCr_0.4Cu_0.2 high entropy alloy powder can reach 7.5,and the imaginary part of permeability can reach 2.7 at 708 MHz.It has larger permeability and smaller dielectric constant,and has better impedance matching and loss factor.Its reflection loss value can reach-33.6 d B at 484 MHz.The FeCoNiCr_0.4Cu_0.2 high entropy alloy powder prepared by the dry grinding and humidifying two step method has a relatively small coercivity,so it has large permeability,the real part of the permeability can reach 15.6,and the imaginary part of the permeability can reach 6.4,and the absorption bandwidth of the reflection loss value is lower than-5 d B(absorption rate is 68.4%)is larger than the high entropy alloy powder prepared by wet grinding.