Research On Microstructure,mechanical And Microwave Absorbing Properties Of Ni-doped Fe-based Metallic Microwires

Microscale Fe-based metallic microwires have unique microstructure and size effect,showing special mechanical,electrical properties and magnetic properties which makes it become a kind of absorbing agent for absorbing materials.Therefore,this article use rotate-dipping process to preparation of Fe-based metallic microwires,focus on effects of Ni-doping amount on the microstructure,mechanical properties and microwave absorption properties of metallic microwires,reveal the mechanism of Ni-doping on the microstructure and performance of microwires,in order to obtain a functional integrated material with stable structural and excellent performance,and to lay a theoretical foundation for its practical engineering application.The research results show that the microstructure of the as-prepared Ni doped Fe-based metallic microwires with amorphous/nanocrystalline two-phase structure,and the surface of the microwires are smooth,uniform and continuous.There are no obvious macro and micro defects,and the microwires have favorable thermal stability.Ni-doping can increase the degree of structure orderψof Fe-based metallic microwires,theψof FeSiBNi₂ metallic microwires reach 71.9%.Meanwhile,as-prepared Fe-based metallic microwires show favorable soft magnetic properties,FeSiBNi₂ metallic microwires has higher saturation magnetization M_S,permeabilityμ_m,and lower coercivity H_C.The soft magnetic properties of Fe-based metallic microwires are significantly improved after the modulation treatment,FeSiBNi₁ microwires have better soft magnetic properties,that is due to the change of stress anisotropy into magnetocrystalline anisotropy after annealing.An appropriate amount Ni-doping can improve the tensile strength of Fe-based metallic microwires,and FeSiBNi₃ have the largest average tensile strength R_m which reach 2554.47MPa.Based on the Weibull statistical analysis results,the fracture reliability of FeSiBNi₂microwires is better,and the fracture threshold valueσ_u,reach 1488.67 MPa.Simultaneously,Fe-based metallic microwires exhibit brittle fracture from macroscopically,the side fracture dip angleθdecreases with the increase of Ni-doping amount,a certain amount of nanocrystalline in the microwires tissue shows a certain plasticity.A large number of shear bands appear on the side fracture,vein-shaped pattern and a few molten drops appears on the section fracture.In the process of tensile deformation,the free volume aggregation and defect fusion lead to the formation of fine micropores,which promote the rapid expansion of microcracks,and fracture occurs under the action of shear stress.Based on the orthogonal experiment analysis,FeSiBNi₂ metallic microwires quality proportion is 40 wt.%,sample thickness is 2 mm,the composite has better microwave absorption performance,the maximum reflection loss R_L and electromagnetic wave absorption efficiency A_eff reached-54.89 d B,99.999%at 8.36 GHz respectively,there are two effective absorption peak,the corresponding frequency range are 7.49 GHz to 8.86 GHz and 15.01 GHz to 15.45 GHz respectively,effective absorption bandwidth EAB was detected as 1.81 GHz.At the same time,geometrical size,amount of Ni-doping and state of modulation treatment of the microwires have significant effects on the absorbing performance of composite.The variation of microwires length affects the resonance loss and ferromagnetic resonance in the dielectric loss,the shorter the microwires length is,the better the absorbing performance is;The variation of microwires diameter affects the polarization relaxation in the dielectric loss,the smaller the diameter is,the better the absorbing performance is.Ni-doping changes the interaction between atoms,The change of magnetic anisotropy leads to magnetic loss changed,which has a great influence on the microwave absorption property of composites.Modulated treatment state changed the microstructure of the microwires,with the increase of grain size and grain boundary,the polarization relaxation and conductance loss are effectively inhibited,while the magnetocrystalline anisotropy increased further enhances the magnetic loss of the composites.In a word,dielectric loss（resonance loss,conductivity loss,dipole polarization and interface polarization）and magnetic loss（natural resonance and exchange resonance）significant effect the microwave absorption characteristics of metallic microwires/paraffin matrix composites.