Influence of high temperature heat treatment on the friction properties of carbon/carbon composites under wet conditions

Under wet conditions, the influence of high temperature heat treatment on the friction properties of carbon/carbon (C/C) composites has been investigated. After C/C composite preforms prepared from 1 K PAN plain carbon cloth were densified up to the average density 1.75 g/m³ using the rapid directional diffusion (RDD) CVI processes, they were divided into four groups: A-D (each group has a rotor disc and a stator disc). The corresponding heat treatments were 1800, 1800 + 2000, 2000 and 2300 °C, respectively. A ring-on-ring specimen configuration was used to simulate aircraft brakes. Before the braking test of each time, the friction surfaces of specimens were watered using the artificial ocean water. The braking test were finished under different initial angular velocity, specific pressure and moment of inertia. The results showed the friction behaviors for RDD CVI C/C composites were strongly affected by the environment wetness. Their friction coefficients (FC) in wet decreased with increasing the brake specific pressure and moment of inertia. Under wet conditions high temperature heat treatment had a significant effect on the friction performances of the composites. It appeared that the most suitable heat treatment temperature (HTT) for the material was 2000 °C. The composites treated at this temperature kept still enough high FC under the present wet baking conditions. The wet FC of specimen A heated at 1800 °C was the lowest in all braking conditions researched. For four composites, their FC increased firstly with an increase of the brake angular velocity and energy until reaching the maximum values, and then a stepwise decrease occurred.