The effect of sliding speed and temperature on the tribological behaviour of carbon–carbon composites

Although the current use of carbon fibre reinforced composites (CFRC) as light weight mechanical resistant components in automotive and aircraft industries, namely in tribological systems such as high energy brake applications, there are few studies concerning the tribological behaviour of these materials in other sliding conditions. Sliding experiments were performed in a pin-on-disc tribometer in air, applying 100 N load, in the temperature range of 22–600°C, for three different sliding speeds (0.5, 2.0 and 3.5 m s−1). Unidirectional CFRC composite (PAN/resin carbon) pins and 2D-CFRC (rayon/resin carbon) composite discs were tested. The morphological features of the sliding surfaces were analysed by scanning electron and optical microscopies in order to understand the friction and wear mechanisms of carbon–carbon materials. At room temperature and low sliding speed (0.5 m s−1) the wear coefficient was extremely low (K<10−6 mm3 N−1 m−1). However, the wear values increased in three orders of magnitude for a sliding speed of 3.5 m s−1. The same trend was observed when comparing results taken at 22 and 300°C or above. At room temperature, the friction coefficient was almost independent of the sliding speed, with values around 0.25, while a decrease to near 0.10 was obtained from tests at higher temperatures. The main conclusion of this work is that carbon–carbon composites show unique properties as wear resistant materials at room temperature and moderate sliding speeds under unlubricated conditions. However, direct or frictional heating may deteriorate the tribological response of such materials due to fibre debonding and fracture.