Polymeric ablative materials (PAMs) are widely used in spacecraft currently for thermal insulation. However, it is challenging to find a single filler that can improve both ablative and mechanical properties of PAMs. In this study, a new type of hybrid cross-linked polyphosphazene microspheres (PHC) is added to ethylene propylene diene monomer (EPDM) composites as a filler for the first time and its influence on the ablation, mechanical, and thermal properties of EPDM is investigated. The results show that the addition of 3 phr PHC increases the ablation performance by about 10% and enhances the mechanical properties by 20% approximately. In addition, the ablation mechanism is studied in accordance with SEM, FTIR, and Raman spectroscopy. On the one hand, PHC has the effect of catalyzing carbonization, thus increasing the rate of residual carbon; on the other hand, PHC changes the morphology of the char layer, forming a cross-linked structure containing P─O─Si bonds on the surface. The findings regarding catalyzing carbonization and the special char layer structure could guide the design of ablative materials.
A (ZrC/SiC) 35 multilayer alternating coating with 500∼700 nm sublayers thickness and 70 interfaces was deposited on sharp leading edge C/C composites by continuous CVD method. Its mechanical property and ablation resistance were assessed by scratch test and oxy-acetylene flame respectively and compared with ZrC monolayered coating. The (ZrC/SiC) 35 multilayer alternating coating exhibited a high bonding strength via the regulation of sub-micro alternating stress field and the inhibition of crack propagation by 70 interfaces, showing a high critical load L C3 of 22.521 N, which was higher than that of ZrC monolayered coating of 5.688 N. Furthermore, the coating revealed excellent ablation resistance evidenced by its intact oxide layer, and the mass and linear ablation rates were only 0.17 mg/s and 0.87 μm/s respectively. The layer-by-layer oxidation behavior allowed the advantages of ZrC and SiC sublayers to be fully utilized, thus maintaining the layered oxide structure. Furthermore, the total 35 layers of thin ZrO 2 layers improved the fault tolerance ability of coating in harsh ablative environments.
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