Synthesis And Electromagnetic Shielding Properties Of Soft Magnetic FeCoNi(Al,Si,B) High Entropy Amorphous And Nanocrystalline Alloy Powder

Soft magnetic high entropy alloy powders have attracted much attention due to their high temperature stability,corrosion resistance,oxidation resistance and excellent electromagnetic properties thus are expected to become a new kind of electromagnetic shielding materials.The p of crystalline materials is much higher than their permeability,and the shielding（absorption）performance of electromagnetic wave is limited.The formation of amorphous/nanocrystalline phase can reduce the permittivity and improve the permeability at the same time,thus improve the impedance matching between the permittivity and the permeability and improve the absorption performance of electromagnetic waves.Based on traditional FeSiAl alloy,FeCoNi(Al_0.2Si_0.6B_0.2)high entropy alloy was designed by adding Co,Ni and B to increase the entropy of the alloy while improving its amorphous forming ability.The HEA powders have been fabricated by melt-spun and subsequent ball-milling methods.The morphology,microstructure,EM parameters and EM wave absorption properties of the powders with different synthesis methods have been investigated.1.FeCoNi(Al_0.2Si_0.6B_0.2)high entropy alloy powders with flaky shapes of 14.7-17.6μm in mean particle size and 8.2-14.9 in aspect ratio have been prepared by melt-spun and subsequent ball-milling for 10-50 h.The powders possess a mixing structure of BCC nanocrystalline and amorphous phases with average grain sizes of 6-20 nm.The powders exhibit soft magnetic characteristic with saturation magnetization of 78.6-88.1 emu/g and coercivity（H_c）of 63.3-79.5 Oe.The powders/paraffin（mass ratio 3:2）composites have high permeability,matchable permittivity,and excellent electromagnetic wave absorption properties in X-and Ku-bands.The composites with thicknesses（d_m）of 1.2-2.0 mm possess minimum reflection losses(RL_min)of-38.1^-44.1 dB with effective absorption bandwidths(Δf_{RL<-10 dB})of 2.5-3.8 GHz^[1].2.FeCoNi(Al_0.2Si_0.6B_0.2)high entropy alloy powders with flaky shapes of 18.8–19.8μm in mean particle size and 7.6–20.9 in aspect ratio have been prepared by a two-step ball milling（dry milled for 10–50 h in vacuum,then wet ball-milled for 5 h adding ethanol）.The structure of powders transformed from a mixing structure of BCC/FCC nanocrystalline and amorphous phases to the total amorphous phases.The powders exhibit soft magnetic characteristic with M_s of 75.8–76.6 emu/g.The powders/paraffin composites with d_m of 2.1-2.9 mm possess RL_min of-34.3^-45.9 dB andΔf_{RL<-10 dB} of 2.6-2.9 GHz.3.After annealed at 623 K and 673 K for an hour,the BCC phases of FeCoNi(Al_0.2Si_0.6B_0.2)high entropy alloy powders fabricated by two step ball-milling method increased and the average grain size increased to 10 nm.The powders possess M_s of 89.5 and 92.8 emu/g.The powders/paraffin（mass ratio 3:2）composites with d_m of 1.3 and 1.2 mm possess RL_min of-33.7and-21.0 dB at the matching frequency of 16.6 and 17.7 GHz.