Florian Reichert

5.1 Design Objectives and Design Philosophies, Interphases and Interfaces in Fiber-Reinforced CMCs

Ceramic matrix composites are a unique and relatively new class of structural materials. Depending on the processing route and the type of interphase, respectively, a wide variability of mechanical as well as thermophysical properties can be achieved and result in new applications. All CMC materials are characterized by a porous and/or micro-cracked matrix, by a high anisotropy and by a high fracture toughness. These properties can be used in new designs of novel hybrid structures, where the favorable properties of CMC materials are combined with those of conventional materials like metals or monolithic ceramics.

The Evaluation of Thermoplastic Precursors for C/C-SiC Manufactured by Liquid Silicon Infiltration (LSI)

C/C-SiC composites, fabricated by the Liquid Silicon Infiltration process (LSI), typically use phenolic resin-based thermosets as carbon precursors. In contrast to this, two different thermoplastics (Polyetheretherketone PEEK and Polyetherimide PEI) were examined for their suitability as carbon precursors for C/C-SiC composites. The carbon fiber surfaces were pretreated between 400 °C and 800 °C in nitrogen atmosphere to modify the fiber/matrix bonding. The microstructures of the materials show an increasing SiC content with increasing fiber pretreatment temperature. The flexural strength of the resulting material was determined by 4-point-bending tests.