THE RELATIONSHIP AMONG MICROSTRUCTURES,PROCESSING PARAMETERS AND PROPERTIES FOR CARBON-CARBON COMPOSITES

Various kinds of microstructures under polarized light for carbon carbon composites made by Chemical Vapor Infiltration (CVI) were discussed, with its appearance features and the basic physical properties of the corresponding matrix pyrolytic carbon, the relationship between processing parameters, microstructures and material properties were summarized. There are three kinds of basic microstructures under polarized light illumination on C/C composite, i.e. RL, SL and ISO. Due to the different optical morphological characteristics, the carbons with these kinds of basic microstructures can be distinguished by its characteristics of extinction crosses, optical activity and reflectivity, growth features, surface texture, preferred orientation and circumferential cracks etc. There are no invariable regularities to follow with the effect of processing parameters on microstructures of deposited carbons under polarized light illumination during the CVI process, it is not only influenced by temperature, pressure, gas composition and flow rate, but also affected by geometric sizes of furnaces and packing sizes of specimens. A set of optimal processing parameters must be explored for different CVI deposition systems, which matches them well respectively. The properties of C/C composites are considerably decided by its microstructures under polarized light illumination, such as physical, mechanical and thermal properties. All these are the most important basic knowledge to fabrication of a carbon carbon composite, which has certain type of homogeneous polarized microstructure and the properties that are expected.