Abstract
The tribological performance of different C-fiber reinforced ceramic brake pads with a commercial ceramic brake disc as the counterpart were investigated on a full scale tribological dynamometer by the AK-Master test. Several types of reinforcements for the C/SiC pads (C/SiC = carbon fiber reinforcement in a SiC matrix) were applied, C-short fibres, C-fabrics and C-fleece. Four types of ceramic brake pads derived by these reinforcements, by different fabrication routes and additives (e.g. SiC powder). One type of short fibre reinforced ceramic brake pads were manufactured by the liquid silicon infiltration (LSI) process. For two types of friction pads the rapid- chemical vapour infiltration (r-CVI) of a porous C-fiber reinforced preform is combined with the liquid silicon infiltration. Finally, the last type of ceramic brake pads, with SiC particles as additives and C-fabric reinforcement, was fabricated by the LSI-process. Conventional organic brake pads (Low Mets) were chosen as a reference material, the current most suitable material for the ceramic brake disc. During the AK-Master test it’s obvious, that the reinforcements, the different microstructures and compositions of the ceramic brake pads, e.g. the porosity and amount of SiC influence the tribological behavior significantly. The most interesting behaviour show the C-short fiber reinforced ceramic brake pads, with CVI-derived pyrolytic-carbon and SiC, which is formed during liquid silicon infiltration. This material has a certain porosity of about 10 % and higher coefficient of friction (> 0.35)) during AK-Master and slightly higher amount of wear (0.49 mm), compared to the reference material (0.29 mm). Finally, friction and wear mechanisms were evaluated and a model about pure ceramic friction couples was created and compared with the conventional friction couple.
KEYWORDS – CMC, ceramic, C/SiC, AK-Master, friction pads