High temperature oxidation behaviour of CVD β-SiC seal coated SiC f /SiC composites in static dry air and combustion environment

Abstract

Abstract A composite with SiC matrix and 40 vol% of SiC fibres with a β-SiC coating (SiC f /SiC) was prepared by the isothermal chemical vapour infiltration process. Oxidation of the SiC f /SiC composite was investigated at 1200 °C, 1300 °C and 1400 °C, for up to 100 h in static dry air, and for up to 24 h in combustion environment. In static dry air, the composite showed mass gain with nearly parabolic oxidation kinetics. The uniform oxide scale developed cracks as oxidation progressed. Oxidation in combustion environment was performed using an oxy-acetylene flame containing CO 2 and H 2 O gases. The chemical erosion by the reaction of H 2 O with oxide scale was the likely ablation mechanism. At 1200 °C and 1300 °C, the oxidation rate was higher than that of ablation and the composite showed a net mass gain. However, at 1400 °C, significant ablation was observed. Localised attack by the combustion gases caused pitting of the β-SiC seal coating. The present study shows that β-SiC seal coating remains intact at relatively lower temperatures (below 1300 °C) for a shorter period of time (~24 h) and is lost it at higher temperatures (~1400 °C) by ablation.