INTERPHASE PHENOMENA IN SILICON-CARBIDE SINGLE FILAMENT COMPOSITES

A heat-treated SiC Nicalon NLP 201 fibre and four single-filament composites have been characterized by means of transmission electron microscopy techniques. Phenomena occurring before and during the chemical vapour deposition process have been investigated. First, the thermal decomposition of the fibre is explained. The SiC microcrystals which are in the fibre decompose giving a solid carbonaceous porous residue and a gas phase containing mainly silicon. A catalytic reaction is noticed. This reaction explains the reorganization of carbon when silica is present. Another reaction between silica and carbon, giving rise to the formation of SiC, also explains the formation of an SiC interphase when depositing a carbon matrix. The non-stability of the SiC Nicalon fibre explains all of these transformations, the major consequence of them being a decrease in its mechanical properties when used in a composite material. © 1990 Chapman and Hall Ltd.