Carbon fiber reinforced carbon-based composites are considered to be an ideal lightweight material with exceptional high-temperature mechanical performance. Nevertheless, their high conductivity result in a strong reflection rather than absorption of electromagnetic wave (EMW) for the stealth application. To address this challenge, a novel carbon-based composite made of multi-scale lossy phases (Carbon nanotubes (CNTs), SiC nanowires (SiC_nws), and Carbon fiber (C_f)) and impedance matching phase (SiOC ceramic) was fabricated by the precursor-derived method. The prepared SiC_nws/CNTs/C_f-C/SiOC (SCC-CS) composites exhibit an effective absorption (EAB) of 2.4 GHz at a thickness of 1.9 mm and a minimum reflection loss (RL_min) of −58.44 dB (99% absorption) in the X band. The EMW absorption of the composite is attributed to the multiple loss mechanisms and favorable impedance matching with free space, caused by the multi-conductive phase and SiOC in the composite. In addition, the fabricated composites also have thermal insulation properties and can effectively achieve radar cross-sectional (RCS) reduction, which are promising aerospace composites with the integration of structure and function.

HfC–SiC-modified carbon/carbon composite (C/C–HfC–SiC) sharp leading edges (SLEs) were prepared via precursor infiltration and pyrolysis for potential hypersonic applications. The effect of SiC proportion on the ablation behavior of the SLEs under oxyacetylene flames with 2.38 MW/m² and 4.18 MW/m² was investigated. The preferred sample with a volume ratio of HfC to SiC of 0.74 possessed almost zero degradation (linear recession rate 0.6 μm/s) up to a temperature of 2371 ℃. As the temperature increases to 2527 ℃ in the latter condition, the SLE with less SiC (the volume ratio of HfC to SiC is 1.10) exhibited a linear recession rate of 1.03 μm/s during cyclic ablation of 3 × 40 s. Relatively more SiC addition is favorable under lower heat flux due to the better oxygen barrier performance of the scale. However, superior ablation resistance is available under higher heat flux with less SiC addition due to the higher thermal stability of the resulting oxide scale.

For the inadequate interlaminar strength of 2D carbon/carbon (C/C) composite, in-situ grown carbon nanotubes (CNTs) reinforcing strategy was put forward to strengthen the interlaminar matrix at the nanoscale and inhibit the interlaminar cracking. CNT morphology is an essential factor in influencing the enhancement effect. Herein, the influence of in-situ grown CNT morphology on the microstructure and mechanical properties of C/C composite was deeply studied. The radially-aligned straight CNTs could induce the formation of highly-ordered pyrolytic carbon (PyC), while PyC in randomly-distributed curved CNTs concentrated area exhibits an isotropic structure. Further, radially-aligned straight CNTs show better improvement on the flexural and shear strength of C/C composites. According to the fine structural characterization and finite element simulation, the influence mechanism of CNT morphology was revealed. CNT morphology can influence the stress distribution in the PyC protective layer, and compared with radially-aligned straight CNTs, randomly-distributed curved CNTs induce higher tensile stress in the PyC protective layer, which has a detrimental impact on the flexural and shear properties of C/C composite. This work provides novel insights into the effect of CNT morphology on the microstructure and mechanical properties of C/C composites, which gives a basis for the structural design and preparation of CNTs reinforced C/C composites.

To repair the damaged SiC coated C/C composites, a double-layer system including a Sm-doped borosilicate glass external layer and a SiSiC inner layer was prepared by a slurry-based laser cladding technique. Isothermal oxidation experiment and indirect/direct thermal-radiation measurements were performed. The results showed that the absorbance of borosilicate glass to the laser at 900–1200 nm was improved significantly by Sm-doping. Consequently, the repaired coating with a more compact structure and better oxidation resistance was obtained. After oxidation at 1773 K for 10 h, the mass loss of the damaged sample could be reduced by 74.98% with repairing. By increasing laser-absorption and reducing viscosity, the thermal-radiation property of the repaired coating was enhanced to decrease the surface temperature greatly. A repair system with excellent thermal protection performance was achieved.