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Abstract:
A recent development in composite processing at the Air Force Research Laboratory (AFRL) in Edwards, CA, drastically reduces both the cost of and processing time required for high performance carbon-carbon (C-C) composites. These composites possess a unique set of properties that make them ideal materials for high temperature structural uses, such as in rocket propulsion components, hypersonic vehicles, and aircraft brakes. C-C composites are stronger and stiffer than steel, while less dense than aluminum. In addition, they not only maintain their mechanical properties to temperatures in excess of 3000 degrees centigrade, the composite's material properties actually improve with heating as the non-ordered carbon is converted to the ordered graphite structure through the process of graphitization. In spite of their excellent properties, the use of carbon-carbon composites has been limited because of their high cost and oxidation at elevated temperatures. AFRL's In- Situ Densification Process is an impregnation process that, in contrast to commercial processes, is able to rapidly densify the composite uniformly because it addresses the conflicting requirements of the impregnant's low viscosity and good wettability and the need for a high char yield carbon precursor. This is accomplished by using a low viscosity impregnant that wets the fiber preform surface in the first step of the process. The impregnant is sucked into the fiber preform like water into a sponge. This not only results in a uniform density, but there also is no need for machining after densification to open up the surface pores. After the impregnant has filled the preform, it is polymerized into a carbon matrix precursor that has a high carbon yield, which means that fewer cycles are needed to bring the composite to final density. The carbon matrix precursor is then pyrolyzed to produce a high quality carbon matrix. The in situ process also seems to have no size limitations.
| Limitations: |
 APPROVED FOR PUBLIC RELEASE |
| Description: |
Technical paper |
| Pages: |
4 |
| Report Date: |
31 OCT 2001 |
| Report Number: |
A745014 |
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