Synthesis And Electromagnetic Wave Absorption Properties Of Fe-based Amorphous/Nanocrystalline Soft Magnetic Alloy Powders With High Fe Content

With the rise of new generation wireless communication technology,more and more electronic devices are applied in the GHz frequency range,which results in serious electromagnetic?EM?interference and EM pollution.Therefore,it is of great practical significance to explore and develop new EM wave absorption materials with excellent properties in GHz frequency range.The saturation magnetization?M_s?of traditional ferrites absorption materials is relatively low,and the permeability???and EM wave absorption properties decreases greatly when the frequency increases to GHz range due to the restriction of Snoek's limit.The Fe-based nanocrystalline as represented by FeSiBCuNb series alloys have more outstanding advantages than the traditional magnetic materials at high frequency and attract increasing attention in the field of EM wave absorption due to the high?,low dielectric constant???,and better impedance matching.However,the M_s of FeSiBCuNb alloys is relatively low due to containing high content of Nb.If the M_s of the nanocrystalline alloy is increased by a proper composition design,the?at high frequency will be enhanced,which further improves the EM wave absorption properties.Therefore,in this paper,Fe_80.7Si₄B₁₃Cu_2.3.3 and Fe₉₀Si₇B₃ alloys with high Fe content but without Nb and other non-magnetic elements were designed,and the amorphous/nanocrystalline alloy powders were prepared by high-energy ball milling and annealing process.The microstructure,morphology,magnetic and EM wave absorption properties in 2-18 GHz of the powders were investigated under different preparation conditions.The results show that:?1?The near spherical powders with a bcc-Fe nanocrystalline/amorphous composite structure can be obtained after milling the Fe_80.7Si₄B₁₃Cu_2.3 alloy for 40-160 h.The average particle size decreases from about 9?m to 6?m.The grain size of bcc-Fe is about 10 nm after milling for 80 h.?2?The nanocrystalline alloy powders exhibit an excellent soft magnetic characteristic,and have high M_s of 183.4 emu/g after milling for 80 h.The powders possess high?and matchable?resulting in excellent impedance matching and attenuation characteristics.The powders?milled for 80 h?/paraffin composite sample with a thickness of 2.2 mm exhibits an optimal RL_min of-40.7 dB with an effective absorption bandwidth?f_{RL<-10 dB}L<-10 dB of 5.0 GHz?from8.2 to 13.2 GHz?covering the whole X-band.?3?The EM wave absorption properties of the nanocrystalline alloys can be further improved after an optimum heat treatment.The grain size of the bcc-Fe for the powders milled for 80 h remaind nearly a constant,while the RL_min can reach-48.0 dB after annealing at 623 K for 60 min.The EM wave absorption properties are deteriorated when the powders were annealed at higher temperature.?4?The Fe₉₀Si₇B₃ alloy can form nanocrystalline/amorphous composite structure with the grain size of bcc-Fe is about 5-15 nm after milling for proper time.The average particle size of the powders decreases from about 8.9?m at 30 h to 3.2?m at 150 h.?5?The M_s of the Fe₉₀Si₇B₃ nanocrystalline powders are in the range of 186.0-196.3emu/g.The composite samples composed of the nanocrystalline powders milled for 90 h and/paraffin with a thickness of 2.0 mm have the RL_min of-46.0 dB at 10.0 GHz and the?f_RL<-10dBL<-10dB is 6.1 GHz?from 7.4 to 13.5 GHz?.In addition,the optimal RL_minin reachs-46.0—-51.2 dB after annealing at 573-773 K for 30 min.