Cost Reduction
Carbon-carbon composites are often referred to as “black gold.” The high cost of carbon fiber and the lengthy densification process are the primary factors contributing to the high cost of carbon-carbon composites.
Production costs have always been the primary factor limiting the development of carbon fiber. To reduce carbon fiber production costs, manufacturers are focusing on transitioning from small-bundle filaments to large-bundle filaments to lower the cost of the filaments themselves, thereby enhancing the market competitiveness of carbon fiber. Only by significantly reducing carbon fiber costs while maintaining quality can the conditions be created for the widespread application of carbon-carbon composites, thereby ensuring the rapid development of the carbon-carbon composite industry.
Currently, the main methods for preparing carbon-carbon composites include liquid-phase impregnation pyrolysis and isothermal CVI. The liquid-phase impregnation pyrolysis method typically uses large-scale hot isostatic pressing equipment, with purchase costs exceeding 10 million yuan, and requires multiple impregnation pyrolysis processes, resulting in high equipment operating costs. The traditional isothermal CVI method for preparing carbon-carbon composites requires 1,000–2,000 hours of densification time, and severe surface crusting occurs, necessitating multiple high-temperature heat treatments and surface peeling processes during preparation. The density of carbon-carbon composites produced by this method generally falls below 1.75 g/cm³. Therefore, to shorten the densification cycle of carbon-carbon composites, various new equipment processes have been proposed, such as ultra-high-pressure asphalt impregnation-carbonization, thermal gradient chemical vapor deposition, pulse chemical vapor deposition, forced flow thermal gradient chemical vapor deposition, and liquid-phase vaporization deposition.
Improving Performance Stability
The manufacturing process for carbon-carbon composite materials is highly complex. Changes in factors such as preform structure, densification temperature, pressure, gas flow rate, gas residence time, heat and mass transfer mechanisms, heating power, cooling water temperature and flow rate, and initial gas temperature can all affect the performance and microstructure of the final product. Additionally, in mass production, differences in product shape and batches require corresponding adjustments to process parameters and tooling fixtures. If these factors are not properly controlled or controlled with insufficient precision, it will result in significant variability in the performance of carbon-carbon composite materials, leading to unstable performance during service.
The density and structure of the preform have a significant impact on the performance of carbon-carbon composite materials. Carbon-carbon composite materials produced using different densification processes also exhibit significant performance differences, primarily due to variations in the matrix carbon texture obtained from different processes and differing interface bonding states with the fibers.
To enhance the performance stability of carbon-carbon composite materials, efforts should focus on improving density uniformity, controlling matrix microstructure, optimizing interface structure, and standardizing processes. For specific shapes, densities, and performance requirements of carbon-carbon composite materials, strict process specifications should be established for preform quality, preform heat treatment processes, densification processes, mold design, graphitization, matrix modification techniques, and anti-oxidation coatings. Additionally, efficient process combinations and optimizations must be implemented to ensure that products manufactured under the same process conditions but at different times or in different batches exhibit uniform microstructures and stable performance.
Enhancing Antioxidant and Ablation Resistance
Since carbon-carbon composites are composed of a carbon matrix and reinforcing carbon fibers, carbon is prone to oxidation at high temperatures. Research has shown that carbon-carbon composites undergo rapid oxidation in an air environment above 370°C, leading to a significant decline in various properties. In recent years, the rapid development of China’s aerospace industry has created an urgent demand for high-temperature resistant and ablation-resistant carbon-carbon composite materials. Addressing the high-temperature oxidation and corrosion resistance issues of carbon-carbon composite materials has become particularly important and is a key focus of research in this field.
Currently, there are two primary methods to prevent oxidation of carbon-carbon composite materials: the first is internal matrix modification technology, which relies on the material itself to inhibit oxidation reactions; which involves modifying carbon fibers and the matrix during the preparation process to enhance the material’s inherent oxidation resistance; and external oxidation-resistant coating technology, which prevents oxygen-containing gases from contacting and diffusing into the material. This involves applying a high-temperature oxidation-resistant coating to the surface of the carbon-carbon composite material, using the high-temperature coating to isolate the carbon-carbon composite material matrix and achieve oxidation resistance.