MICROSTRUCTURE OF WORN PITCH RESIN/CVI C-C COMPOSITES

This paper describes the microstructure of nonworn and worn samples of a pitch/resin/CVI carbon-carbon composite. Optical microscopy, scanning, and transmission electron microscopy techniques were used to characterize the structure of the composites. The friction and wear properties of the composites were tested under different energy conditions using a laboratory dynamometer. Results indicate that both a particulate-type (type I) and a film-type (type II) of wear debris coexisted on the worn surfaces. Under low energy test conditions, the type I debris predominates the worn surface, with only limited coverage of the type II debris. This dominance of the particulate debris and the lack of the film debris is thought responsible for the observed higher coefficient of friction and wear rates. Under high energy conditions, the predominance of the smooth type II debris, which serves as a self-lubricant, yields a lower coefficient of friction and wear rate than under low energy conditions. The type II debris is comprised of plastically deformed and fractured components of the composite, including fibers, CVI carbon, and resin char. A thin, nonuniformly distributed amorphous film, identified by selected area diffraction, is also formed during the wear process. Possible wear mechanisms are discussed.