Effect of heat treatment on the tribological behavior of 2D carbon /carbon composites

The effect of high temperature heat treatment on the tribological behavior of carbon/carbon (C/C) composites has been investigated. C/C composite preforms were made from 1K PAN plain carbon cloth, and densified using rapid directional diffusion (RDD) CVI processes. Four specimens treated at 1800, 1800+2000, 2000, and 2300 degreesC, respectively, were prepared. A ring-on-ring specimen configuration was used to simulate aircraft brakes. The brake initial angular velocity ranged from 1800 to 7500 rpm (6.2-26.0 m s(-1) average linear sliding velocity). The specific pressure and moment of inertia were 392-784 kPa and 0.25-0.31 kg m(2), respectively (1.9-42.3 MJ m(-2) kinetic energy loading per unit friction surface area). The results showed that the stability of the brake moment-time curves increased with increasing heat treatment temperature (HTT) for the four composites, and those treated at 2300 degreesC possessed the lowest initial brake moment peak ratio values (from 1.1 to 1.3). The high degree of graphitization and low shear forces of the matrix carbon resulting from the high HTT could allow friction films to develop and reduce those values under the present brake conditions. The friction coefficients of four RDD CVI C/C composites decreased with an increase in specific pressure. The resulting changes in the friction coefficient of the four composites due to the specific pressure changes have basically nothing to do with the interface temperature under those conditions. According to the practical brake conditions, the friction properties of RDD CVD C/C composites could be improved by regulating the structure of the brake discs, changing the specific pressure exerted on the discs and the heat treatment. The linear wear rates of the four materials increased with increasing HTT. The composites treated at 2000 degreesC had both high enough friction coefficients and the lower linear wear rates. The different heat treatment methods at 2000 degreesC had no obvious effect on the friction and wear properties of RDD CVI C/C composites. (C) 2003 Elsevier Ltd. All rights reserved.