Influence of Fiber Type on the Properties of Short-Fiber Based C/C-SiC

Kurzfassung

Originally developed for heat shields and hot structures of space vehicles, C/C-SiC materials were adapted to be applied as lightweight, high performance brake discs for automotive use. Thereby, costly fiber preforms based on woven fabrics, typically used for thin walled aerospace structures, were replaced by cut fiber rovings, leading to economic as well as technical advantages. Press masses with randomly oriented short fibers and powdery phenolic resin offer a high flowability and even thick-walled parts with complex shaped geometries, like internally ventilated brake discs in single piece design, can be manufactured economically in near net shape technique. In a new approach, short-fiber based C/C-SiC materials have been further developed for the use in space propulsion systems, where high mechanical and thermal loads are a challenge. In order to meet these requirements, the commonly used high tenacity (HT) fibers were replaced by intermediate modulus (IM) and pitch based ultrahigh modulus (UHM) carbon fibers with a fiber length of 10 mm. The resulting C/C-SiC materials showed different microstructures with significantly different phase composition. Compared to HT based C/C-SiC, strength an elastic modulus were increased by UHM fibers, whereas the use of IM fibers lead to higher fracture strain. The manufacture of the sample plates as well as the influence of the fiber type on the mechanical properties is presented in detail.