Development of carbon fibre reinforced carbon-silicon carbide composites for advanced friction brake applications

In the present study, different origins of recycled carbon fibre and carbon are evaluated against virgin-based alternatives as cost-effective constituents inside carbon fibre/carbon-silicon carbide (Cf/C-SiC) composites. These include: recycled, end-of-life or reclaimed carbon fibre and pyrolytic carbon (pyC), which are investigated inside these composites for potential friction materials to replace or extend the life of current high-end automotive, industrial and aircraft brake discs. The literature review begins by investigating the differences and implications of the applications on the requirements of the carbon fibre inside the composite and documents past and current progress made. The constituents that comprise these composites were investigated and the manufacture routes were reported in terms of their advantages and disadvantages. A three-step process was identified as the most costeffective and promising route to manufacture these new Cf/C-SiC composites with suitably high mechanical properties: 1). Polymer infiltration (PI) and hot pressing (HP) to create a carbon fibre reinforced plastic (CFRP), 2). Pyrolysis to convert the CFRP into a porous Cf/C composite, 3). Liquid silicon infiltration (LSI) to introduce the silicon carbide (SiC) matrix. Beyond this, the aims, feasibility and current progress of recycling carbon fibres were documented. It was found that current recycling technologies are in their infancy, in both academia and industry, although great commercial potential is recognised. Investigations herein revealed the capability to mechanically recycle carbon fibres from waste carbon fibre pre-pregs and CFRP spars, re-use end-of-life carbon fibre pre-pregs and reclaim carbon fibre from existing CFRP spars using pyrolysis. Testing and analysis were split into two stages: firstly, how the pre-preg architecture changes during pyrolysis and secondly, the resulting Cf/C-SiC composites: microstructural evolution after LSI; physical, mechanical and micro-mechanical properties; frictional performance. Pyrolysis of end-of-life pre-pregs revealed no significant difference in comparison to virgin carbon fibre pre-pregs. Instead, any differences were attributed to the: fibre orientation, preform architecture and resin carbon yield. Testing revealed that end-of-life pre-pregs and reclaimed CFRP’s were suitable for pyrolysis and further processing toward Cf/C-SiC composites. In addition, the architecture could be either customised or inherited from the original. Physical and mechanical property testing revealed that Cf/C-SiC composites incorporating recycled, end-of-life and re-claimed carbon fibre could achieve comparable densities, open porosities and flexural strengths compared to similarly processed virgin Cf/C-SiC composites. Microstructural examination by optical and electron microscopy revealed that the hierarchy order of the developed microstructure inside these composites by LSI was the same irrespective of the carbon fibre or carbon format. Combined TEM and XRD investigations indicated that the generated SiC and silicon belonged to the same polytypes regardless of the carbon format and that the most likely type was facecentered cubic (FCC) β 3C-SiC and cubic silicon respectively. Small-scale dyno in a disc-on-pad configuration revealed that a Cf/C-SiC composite comprising end-of-life fibre could achieve the required mechanical strength to perform dyno testing and that the surface topography had a significant influence on the coefficient of friction (COF), COF stability and wear rate.