Process optimisation of SiO2 interface coating on carbon fibre by RF PECVD for advanced composites

Abstract

Carbon fibre reinforced silicon carbide composites (Cf/SiC) are sought for high temperature application in areas of automobiles, aerospace and nuclear reactors. However they have low durability owing to oxidation of Cf hence to remove this draw back it's necessary to give an interface coating oxidation resistant layer to Cf prior to the development of Cf/SiC composites. In this study, we deposit SiO2 coatings onto a Cf using a Radio Frequency Plasma Enhanced chemical vapour deposition method (RF PECVD) technique with Tetraethyl orthosilicate (TEOS) as precursor. As part of optimizing the coating, we carried out a series of deposition experiments. These included investigating the effects of the chamber pressure in the range of 10−2, 10−3, 10−4 mbar, the effect of the bath temperature which was used to develop the monomer gas for the deposition of SiO2 layer. The coating was carried out at room temperature keeping rest of the parameters constant. The coated fibre was subjected to XRD and it was found that SiO2 films coated were amorphous in nature. Scanning electron microscope (SEM) and EDS was used to study the morphology and the elemental composition of the coated sample. It was observed that in the vacuum range of 10−2 mbar there was insitu formation of needle like nanostructures of SiO2 on the coated fibre. Further on the coated fibres were subjected to isothermal oxidation process and it was found that the coated fibre were showing better thermal resistant property then the uncoated counterparts, suggesting uniform coating of the SiO2 layer onto fibre.