Spectroscopic Properties of Carbon Fibre Reinforced Silicon Carbide Composites for Aerospace Applications

Abstract

The use of Ceramic Matrix Composites (CMCs) such as carbon fibre reinforced silicon carbide composites (C/SiC), carbon fibre reinforced carbon composites (C/C) but also silicon carbide fibre reinforced silicon carbide composites (SiC/SiC) is mandatory within the aerospace sector whenever the transfer of mechanical loads at high temperatures (up to 1900 K in air) is required and any metallic material (e.g. refractory metals) or intermetallic materials cannot be employed. CMCs are constituted by the coupling of long fibres reinforcement (usually carbon fibres) and a refractory ceramic matrix (i.e. carbon, or silicon carbide) and represent a class of ceramic materials characterized by good mechanical properties, thermo-mechanical stability and fracture toughness: their fracture behaviour sets them apart from conventional monolithic ceramics, allowing for a variety of uses in which damage tolerance is the main requirement. The extremely good high temperature fracture toughness of CMCs is provided by the crack bridging effect of the carbon fibres: stress concentrations, e.g. notches or holes, are reduced by stress redistribution and inelastic deformation. In case of overloading, monolithic ceramics break immediately, while CMC materials are still able to carry load even if the elastic mechanical load range is exceeded. Such a damage tolerant behaviour constitutes an important point for the safety issues in particular for space re-entry vehicles. Typical applications for CMCs within aerospace sector include thermo stable satellite structures for optical components, ultra lightweight scanning mirrors (Harnisch et al., 1998), hot structures for atmospheric re-entry vehicles (Laux et al., 2001), and very high temperature parts for hypersonic and rocket engines (Muhlratzer & Leuchs, 2001 Naslain & Schneider, 2002). One of the most relevant application fields of carbon fibre reinforced silicon carbide composites (C/SiCs) concerns the manufacturing of structural thermal protection systems (TPSs) for planetary re-entry vehicles, where good thermo-mechanical properties at high temperature associated with oxidation resistance are required. During the re-entry phase in Earth’s atmosphere nose tips and leading edges are the structural parts of spacecrafts subject 10