Carbon-carbon composites are an emerging class of composite materials having a unique combination of high-temperature properties and low densities. These properties are attractive for hot structure and thermal protection system applications in future aerospace vehicles. Aerospace service environments of particular interest are cyclic temperature, oxidizing environments to 3000°F. For carbon-carbon composites to serve as practical engineering materials in such challenging environments, their long-term mechanical and chemical stability is essential.Many aspects of proposed service environments for these composites pose significant challenges to their satisfactory performance. Among these aspects are the oxidizing nature of the environments (including both high and low oxygen partial pressures), high temperatures, moisture, cyclic temperature service, and foreign-object impact. This paper presents results from materials performance evaluations which cover each of these parameters. The focus is on oxidation-resistant carbon-carbon composites intended specifically for multi-use aerospace applications. Results are presented for the carbon-carbon material currently in use on Space Shuttle and for newer, more advanced structural forms of these composites.
Functionally gradient coatings have the potential to eliminate sharp interfaces between the coating layer and substrate resulting in a great ability to tailor the thermo-mechanical properties of the coating systems to a variety of substrates. Primary examples of beneficial use of the functionally gradient materials are the crack free CVD C-SiC coatings that were recently produced by a number of researchers on C-C composites. Inherent limitations of the CVD technique make it practically difficult to obtain high deposition rates on very complex and large shapes combined with good coating uniformity. A new process termed Chemical Vapor Reaction (CVR) has been employed to produce virtually crack free SiC coatings on 2–D C–C composites. Properties of this new class of functionally gradient coatings will be presented and discussed.
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