The polymer derived SiBCN has excellent electromagnetic wave absorbing performance, but the impedance matching characteristics of single SiBCN component are poor. The composite powder system of Mullite matrix and SiBCN absorbing agent was designed. The powders was uniformly dispersed in the water-soluble resin glue by ball milling method, the Mullite-SiBCN absorbing coating with different mullite content was prepared on the surface of epoxy resin plate by slurry brushing method. The reflectivity of the coating was tested by the bow method, and the effect of mullite content on the absorbing performance of the coatings was studied. The results showed that the absorption performance of the coatings first increased and then decreased with the mullite content increased. When the content is 70wt.%, the absorption performance of the coating is relatively the best, The frequency range of reflection loss less than-4dB can reach 3.5GHz. When the mullite content is lower than 70wt.%, the matching performance between the coating and the free space impedance was poor, most of the incident waves on the coating surface were reflected, thus when the mullite content exceeded 70wt.%, the SiBCN content of the coating was too low, resulting in insufficient microwave absorbing performance of the coating.

with the advantages of low textile processing cost, short period and excellent in-plane mechanical properties, the 2D SiC/SiC composites has become one of the most potential structure in engineering application. In this article, base on automatic CNC sewing system and lock stitch method, the SiC fiber preform is sewed by SiC fibers with different sewing density. The sewing 2D SiC fiber preform with PyC interface is densified by polymer infiltration and pyrolysis (PIP) method. The microstructure of 2D SiC/SiC composites is characterized by micro-CT and scanning electron microscope (SEM). Specifically, for the sewing densities of 5mm, 7.5mm, 10mm, 12.5mm, and 15mm, the average flexural strength at room temperature was 378.8 MPa, 447.1 MPa, 485.6 MPa, 504.0 MPa, and 521.5 MPa, and the average tensile strength at room temperature was 261.6 MPa, 286.4 MPa, 293.8 MPa, 300.5 MPa, and 306.5 MPa, respectively. The average interlayer shear strength at room temperature was 84.7 MPa, 76 MPa, 70.2 MPa, 63 MPa and 54.4 MPa, respectively. The results show that with the increase of sewing density, the densification process is affected by the bending of the preform, which leads to the decrease of the in-plane tensile and flexural strength of the composites at room temperature, but the increase of interlaminar shear bearing fibers increases the interlaminar shear strength of the composites at room temperature.

SiC/SiC composites were prepared by precursor infiltration and pyrolysis process combined with three matrix modification methods. The effect of matrix modification on the high temperature oxidation resistance of SiC/SiC composites was analyzed by morphology analysis and mechanical property test. The results showed that the flexural strength of the matrix-modified composites hardly decreases after 100h static oxidation at 1200℃. After 200h oxidation, the retention rates of flexural strength reached 80%. After 300h oxidation, the internal structure of the composites was not oxidized and the oxidation degree of the interface layer in the surface area decreases. The B element in the modified matrix was oxidized to form liquid phase to seal the surface of SiC coating, which delayed the oxidation process of SiC coating, preventing the oxidation medium from entering the interior of the compo-site and protects the fiber and interface layer, so that the long-term static oxidation resistance of SiC/SiC composites was improved significantly.

SiC_f/SiBCZr composites were prepared by polymer precursor impregnation and pyrolysis process with near stoichiometric ratio SiC fiber preform as reinforcement phase and SiBCZr multiphase ceramic precursor as impregnating reagent. The results highlighted that the SiC_f/SiBCZr composites exhibited excellent ablative properties after ablative tests at 1200 ℃/3600 s and 1400 ℃/3600 s, and the strength retention rates of the composites reached 90% and 85%, respectively. This was mainly due to the liquid sealing effect of the ablative products represented by B₂O₃ and SiO₂∙B₂O₃, which inhibited the ablative reaction by reducing the diffusion rate of the oxidation medium, and the solid pinning effect of the substances represented by SiO₂, ZrO₂, and ZrSiO₄, which could play high viscosity and high strength characteristics to improve anti-erosion ability. The above-mentioned SiC_f/SiBCZr composites with corrosion resistance, oxidation resistance, and ablative resistance provided a solid material foundation and technical support for the development of reusable spacecraft hot-end components.