Novel Structural Design Strategies in Ceramic-Modified C/C Composites

With the increasing improvement of aerospace, the servicing environments of thermal structural materials are complicated and harsh, featuring ultrahigh temperatures (>2000 degrees C), large thermal gradients and stresses, highly chemically active airflows, and complex thermal-mechanical loads. Carbon fiber reinforced carbon matrix (carbon/carbon, C/C) composites have become promising candidates for high-temperature thermal structure materials in aerospace fields, owing to their excellent structural merits, such as low density, low coefficient of thermal expansion (CTE), high thermal conductivity, excellent mechanical properties, good thermal shock, and ablation resistance. However, when applied in a high-temperature oxygen-containing environment, C/C composites are highly susceptible to oxidation above 450 degrees C, and the oxidation is intensified with the rising of temperature, further leading to the failure of C/C composites. High oxidation sensitivity of C/C composites would seriously limit their applications in oxygen-containing environments at ultrahigh temperatures and high-speed gas flow. Matrix modification with Si-based ceramics or ultrahigh temperature ceramics (UHTCs) offers an effective approach to further enhance the oxidation and ablation resistance performance of C/C composites. Si-based ceramics and UHTCs usually possess high melting points, high thermal conductivity, good oxidation and ablation resistance, and high hardness, which are potential candidate materials for extreme environments containing oxygen. However, their application is restricted by low fracture toughness and poor thermal shock resistance. Introducing ceramics into C/C composites to modify the carbon matrix can combine the above two materials and give play to their respective advantages, which has proved very effective in meeting the increasing requirements of thermal protection materials. Published research confirms that ceramics modification could not only significantly enhance the oxidation and ablation resistance of C/C composites but also improve the mechanical and functional performance in some cases. In this Account, we highlight the improvements and progress on ceramic-modified C/C composites in our research group in the past few years, from the view of "structural design strategies", as well as some critical advancements acquired in other teams, which incorporate our insights and thoughts in this field. Additionally, we describe the methods of material preparation and structural design and discuss the relationship between structure and properties in detail. Finally, the prospects and challenges of ceramic-modified C/C composites in the future are discussed. We believe that this Account can not only provide a universal design method for ceramic-modified C/C composites that can provide theoretical and technical guidance for other researchers but also give new ideas of structural design for other materials, such as ceramics, ceramic matrix composites, metallic matrix composites, etc.