Carbon fiber-reinforced boron carbide friction materials

Ceramic matrix composites are being examined as an alternative to carbon/carbon (C/C) for high performance aircraft brake friction applications. In particular, carbon fiber-reinforced boron carbide (C/B 4 C) is of interest for next generation heat sinks due to its higher volumetric heat capacity. Composites were fabricated by chemical vapor infiltration processing of boron carbide into carbon fiber preforms. Thermal and mechanical properties of the resulting composites were then characterized. The effect of elevated temperature exposure, such as would be experienced during use as an aircraft brake friction material, was examined with regards to the stability of the composite microstructure and the effect of the heat treatments on the composite properties. Tribological properties were evaluated on sub-scale specimens at scaled energy conditions similar to an F-16 aircraft brake. Very low wear rates were measured at low rates of energy dissipation. Significantly higher wear rates resulted at higher rates of energy dissipation. Finite element modeling supports a thermal origin of the observed behavior.