THE GROWTH AND MORPHOLOGY OF CHEMICALLY VAPOR-DEPOSITED SILICON-CARBIDE COATINGS ON CARBON CARBON COMPOSITES

Silicon carbide was chemically vapour deposited onto a carbon-carbon composite as a protective outer layer for oxidation resistance. The growth and morphology of the silicon carbide was investigated and scanning electron microscopy showed the coating to be cracked owing to the thermal expansion mismatch. Nodular growth had occurred with each nodule comprising fine faceted grains. Transmission electron microscopy revealed growth to have commenced as a microcrystalline layer. This developed into blocks of dendritic, spine-like crystals. Further from the interface the deposit consisted mainly of columnar grains with a layered structure. The layering was caused by microtwins and stacking faults on the {111} planes. There was also evidence of one-dimensionally disordered crystals.