Tailor-designed Phenolic Resins as C-Precursors applied in Liquid Silicon Infiltration (LSI) Process

Abstract

The key step in the manufacture of C-fibre reinforced SiC composites (C/C-SiC) via liquid silicon infiltration of porous C/C structures is the manufacture of CFRP composites. In this step fibre matrix bonding (FMB) is determining the microstructure in C/C state: strong FMB leads to a block structure of dense C/C segments which are hardly accessible to complete reaction with liquid silicon, whereas weak FMB leads to a porous C/C structure which is easily accessible to reaction with liquid silicon. Consequently, different C/C-SiC materials with low  and high SiC content, high and low fracture toughness as well as bending strength are obtained. Within the framework of fundamental research several novel C-precursors based on phenolic resins were selected, screened and thoroughly characterised with respect to their suitability of application within the LSI-process in order to obtain C/C-SiC with respect to microstructure and SiC content. Characterization includes thermal analysis and especially rheological investigations of precursors prior to composite manufacture. Furthermore, the effect of interaction of precursors with various C-fibres is investigated. Since processing routes like resin transfer moulding (RTM) or autoclave technique strongly influence matrix evolution and final SiC formation phenolic resins are investigated accordingly. Microstructure and properties are monitored along the complete processing chain from polymer infiltration via pyrolysis and resulting C/C phase to the final siliconised state. Microstructural composition is characterised by SEM and phase analysis. With these results it is expected that final composition as e.g. content of SiC can be defined accurately by the choice of precursors and adjustment of processing routes and parameters.