Electromagnetic Wave Absorbtion Properties Of Flaky Fe (Ti,Ni)-Si-Al Nanocrystalline Composites

Electromagnetic interference(EMI) in quasi-microwave frequency band has become an increasingly serious problem between electronic and digital equipments due to the rapid improvement of wireless telecommunication technology.Sendust alloy(Fe-Si-Al) has been regarded as a good candidate to suppress EMI in gigahertz frequencies because of its excellent soft magnetic properties such as high saturation magnetization,high permeability,low magnetocrystalline anisotropy,and nearly zero magnetostriction.However,eddy current loss and skin effect in high frequencies restrict its further application.In this paper,nanocrystalline Fe(Ti,Ni)-Si-Al flaky powders have been fabricated by high-energy planetary milling melt-spun ribbons.Effects of milling time and annealing temperature on the micrographs,phase structure,soft magnetic properties and wave absorption properties of(Fe_1-xTi_x)₈₅Si_9.6Al_5.4(wt.%)(x=0,0.005, 0.010,0.015,0.020) and Fe_86.73Ni_3.27Si₆Al₄ were investigated.It was found that a homogeneous distribution of powder sizes was achieved after milling for 70 h.The powders were nearly oblate,with a thickness of～800 nm and a length of～20μm.The corresponding aspect ratio was about 25:1.In addition,no agglomerated powders were detected and no in-plane fragmentation occurred.But the D0₃ structure disappeared with long milling time.After subsequent annealing,partial ordering phase appeared.According to M(o|¨)ssbauer spectra,partial ordering phase was identified as D0₃ structure.When the Ti addition x is 0.010,saturation magnetization and Curie temperature were the biggest in all five samples,which was 127.59 emu·g^-1 and 580.42℃,respectively.Toroidal(Φ_out:19,Φ_in:10,thickness:3 mm) and disk(Φ19,thickness:3 mm) magnetic composites were fabricated by compacting the magnetic slurry made of annealed(Fe_1-xTi_x)₈₅Si_9.6Al_5.4 powders and epoxy resin.The resistivity of Fe(Ti) -Si-Al alloy could be enhanced after Ti addition,as a result,eddy current loss could be effectively reduced,which enhanced the cut-off frequency of magnetic composites.Meanwhile,compared to the Ti-free composites,reflection loss of the Ti-doped composites(3 mm in thickness) was lower than -10 dB in the frequency range from 593 MHz to 1.83 GHz,indicating that the composites could effectively work in a wider frequency bandwidth.In addition,the relative content of Fe in the as-milled powders increased,which enlarged the magnetostriction coefficient.Ni with a negative magnetostriction coefficient was added to compensate for the enlargement of positive magnetostriction by Fe.Flaky powders of Fe_86.73Ni_3.27Si₆Al₄ were got after 90 h milling time. Saturation magnetization of Fe_86.73Ni_3.27Si₆Al₄ was higher than that of the Ni free one. Meanwhile,the magnetic composites also exhibtied good wave absorption properties at high-frequencies.