Response of Carbon-Carbon Composites to Challenging Environments

Abstract

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.

Advanced Oxidation Protection System for Carbon-Carbon Composites

“…The basic features of an advanced oxidation protection system are shown in Figure 1 [1,2]. The system consists of an external barrier coating (typically Sic or Si 3N4 ) which is the primary barrier to the diffusion of oxidizing species to the substrate.…”

“…The transition layers contain substantial amounts of boron and silicon compounds to form sealant glasses upon oxidation. A recent test series with time-temperature-pressure exposures as shown in Figure 4 was conducted to simulate the type of conditions expected for the National Aerospace Plane [2]. Humidity exposures consisted of 90 percent relative humidity at 80°F for 16 hours.…”