Microstructure and properties of C/C composites prepared by thermal gradient CVI process

With the carbon fiber integrated felts used as preforms, two different types of carbon-carbon(C/C) composites, namely, rough laminar (RL) structure materials and smooth laminar (SL) structure materials were fabricated by thermal gradient CVI process. The microstructure and thermal and physical properties of the materials under different conditions were investigated by means of optical microscopy, X-ray diffractometer, hardness tester, thermal conductivity tester respectively. Furthermore, the mechanical, frictional and wear properties of the materials were also investigated. It is shown that the effects of microstructure of pyrocarbon on the mechanical and frictional properties outweigh by far the effects of bulk density on the corresponding properties when the bulk density amounts to a certain degree. It is also shown that, the frictional properties of both as-deposited RL structure material and heat-treated one are obviously superior to those of the SL structure material, which implies that the decisive factor in determining the frictional behavior of C/C composites turns to be the microstructure of pyrocarbon.