Static friction properties of carbon/carbon composites

Preforms were made from 1K PAN plain carbon cloth and densified using the rapid directional diffusion chemical vapor infiltration (RDD CVI) processes. Four carbon/carbon (C/C) composite specimens treated at 1800 (specimen A), 1800+2000 (B), 2000 (C), and 2300 °C (D), respectively, were prepared, then machined into ring-on-ring specimen configurations. The influence of high-temperature heat treatment and the test temperatures on the static friction properties of the C/C composites has been researched. The results show that the high-temperature heat treatment processes has an important impact on the static friction behaviors of RDD CVI C/C composites. With raising the treatment temperature, the interlayer spacing of the matrix carbon in them becomes small, and the crystallite width as well as height increase. Under the test at room temperature, the static friction coefficients (FC) of the specimen treated at 1800 °C (A) are the lowest, but become very big and the highest under the test temperature of 260 °C due to desorption of the water absorbed on the friction surface. The composites treated at 2000 °C (C) exhibit enough high static friction coefficients under room temperature owing to their absorption of less water and the difficult delamination of the matrix carbon. However, in the test temperature of 260 °C or after the dynamic friction tests, their static FC is low. The specimen treated at 2300 °C (D) has a low FC at 260 °C heat condition, but its FC is higher than that of A and C under room temperature and largest after dynamic friction tests. No matter how high the heated temperatures are, the static FC of C/C composites decreases with an increase of the brake-specific pressure. When the specific pressure is very high and exceeds a certain value, the static FC is almost the same for specimens B, C, and D.