Description:
<jats:p>Uncoated SiC fibres in SiC/SiC composites manufactured by the liquid-silicon infiltration (LSI) process show a strong degradation as a result of silicon attack. The goal of this research is the development of a SiN<jats:sub>x</jats:sub>-based fibre coating, which acts as a barrier against the liquid silicon. The coating is applied by means of low-pressure chemical vapour deposition (LPCVD) utilising the gaseous precursors silane (SiH<jats:sub>4</jats:sub>) and ammonia (NH<jats:sub>3</jats:sub>) on a commercial SiC multifilament yarn. The result is an amorphous fibre coating with an increasing coating thickness and a variable chemical composition from the middle of the yarn to the edges. The coated fibres exhibit a reduced characteristic Weibull strength in comparison to the uncoated fibres. In order to examine the stability of the films, the coated fibres undergo a heat treatment at 1450 °C in different environments (vacuum, argon and nitrogen). In all environments, the amorphous SiN<jats:sub>x</jats:sub>coatings crystallise to the trigonal Si<jats:sub>3</jats:sub>N<jats:sub>4</jats:sub>. Depending on the coating thickness cracks and defects develop. However, the best results and the lowest amount of damaging occurs during the treatment in nitrogen.</jats:p>