Preparation And Performance Study Of SiBON_f/Si₃N₄ Wave-transparent Composite Materials

With the development of aerospace and national defense technology,wave-transparent material has become a research and development hotspot.Si BON material combines the advantages of Si O2 and BN wave-transparent material.While maintaining the excellent dielectric properties of Si O2 and BN,has excellent dielectric properties and stable mechanical properties,and meets the requirements of radome wave-transparent materials for carrying,protection,and wave-transparent.It can be used as a new generation of radome materials.In this thesis,the sol-gel method is used to synthesize the Si BONC fiber precursor,the low carbon content Si BONC fiber precursor is prepared by carbon removal,and the high temperature nitridation is performed in a nitrogen atmosphere to obtain the Si BON fiber;Si BONf/Si₃N₄ wave-transparent material was prepared with Si BON fiber and Si₃N₄ as raw materials.With the help of Thermogravimetric Analysis（TG）,Fourier Transform Infrared Spectroscopy（FT-IR）,Scanning Electron Microscope（SEM）,Elements Spectral Analysis（EDS）and X-ray Diffractometer Analysis（XRD）and other test methods were used to study the influence of the synthesis,carbon removal and nitridation process of Si BONC fiber precursor on the composition and morphology of Si BON fiber,and explore the Si BONf/Si₃N₄ penetration,the relationship between the mechanical properties,dielectric properties and microstructure of wave materials.The factors affecting the performance of Si BONf/Si₃N₄ wavetransparent material are: Si BON fiber pretreatment,Si BON fiber content,molding system and sintering temperature.When the Si BON fiber content is 30 wt.%,the Si BONf/Si₃N₄ wavetransparent material has a dielectric constant of 3.41,a dielectric loss tangent value of 0.0085,flexural strength of 152.6 MPa and fracture toughness property of 5.67 MPa·m1/2 at 2-10 GHz.The internal solid melt-stereoscopic network structure of Si BONf/Si₃N₄ wave-transparent material is an important factor affecting the dielectric properties,mechanical properties,porosity and shrinkage of the materials.The structure is formed by the sintering aids Al2O3 and Y2O3,and the Si BON fibers are bonded and contracted to form a solid network structure and combined with silicon nitride to form a replacement solid melt,resulting in pores.This structure reduces the dielectric constant of the material and increases the porosity and shrinkage of the material.The formula for calculating the relative constant of Si BONf/Si₃N₄ wave-transparent material was established by Monte Carlo and finite element method:By studying the wave-transparent material mechanism of Si BONf/Si₃N₄ wave-transparent material,it is believed that the solid melt-stereoscopic network structure and pore phase will reduce the loss of the wave-transparent material,reduce the dielectric constant,and improve the dielectric properties of the material.It has a certain reference for the development of silicon nitride-based wave-transparent material.