A Study Of Influence Of Microstructure Of Pyrocarbon On The Properties Of C/C Composites

On the base of the experimental investigation and theoretical analyses, the microstructure of pyrocarbon and the C/C composites have been researched, and the influences of microstructure and texture of pyrocarbon on structure and properties of C/C composites were investigated and studied systematically.1. The basic principles of polarized light microscopy observation used for the extinction angle(Ae) and phase shift were studied. Pyrocarbon may be classified into rough laminar, smooth laminar and isotropic structures according to the extinction angle, which can't reflect the misorientation of the aromatic layers. So Ae has no physical meaning, but it gives numerical values easy to collect, however, the physical meaning of phase shift is clear, it is inversely proportional to the misorientation by tilt of the aromatic layers.By transmission electron microscopy and selected area electron diffraction techniques, 002 reflection arc represents the twist misorientation of the aromatic layers. The orientation angle measured from 002 arc reflects the twist angle of aromatic layers. And the pyrocarbon may be classified into high texture, medium texture, low texture and isotropic according to the orientation angles.2.icromechanism of graphitization of pyrocarbon was proposed. At about 2100℃ and 2600 ℃, the Lc value and La value of aromatic layers increased significantly. The graphitization process model was proposed; The microstructure models of high texture and low texture pyrocarbons were established; The ability of graphitization of pyrocarbon was explained on micromechanism view.3. The influence of microstructure of pyrocarbon on thermal conductivity and thermal expansion of C/C composites was studied.The thermal properties from room temperature to 800℃ of high texture, medium texture and low texture pyrocarbons in C/C composites were investigated. The basic causes of thermal conductivity difference of three textures pyrocarbons were explained from microstructure; thermal ability tendency model of different texture composites was proposed; and the thermal property increased with the increasing of open porosity of C/C composites was explained and the model was proposed.The thermal expansion properties of high texture and medium texture C/C composites from room temperature to 800℃ were investigated. The basic reasons of great difference of two kinds of textures composites were explained at the view of microstructure. The tendency model of thermal expansion property varied with the changing of temperature of different texture composites was put forward.4. The influence of microstructure of pyrocarbon on mechanical properties of C/C composites was researched. The micromechanisim of near catastrophic failure model of low texture composites and stepwise failure model of medium texture and highHItexture composites was proposed.5. The influence of thermal properties such as thermal expansion and conductivity on the friction and wear properties of C/C composites was analyzed; The influence of microstructure of pyrocarbon on friction and wear property of C/C composites was studied.6. The oxidation property of C/C composites was investigated. The oxidation mechanism of C/C composites was proposed. The influence of micropore of carbon fiber on oxidation property of C/C composites was analyzed. The influence of macropore and surface area of C/C composites on oxidation property was studied. The influence of microstructure of pyrocarbon on oxidation property was researched.