Oxidation resistance of highly porous CVD-SiC coated Tyranno fiber composites

Oxidation tests have been carried out on highly porous ceramic matrix fiber composites consisting of Tyranno Lox M fibers coated with Pyro C and CVD-SiC thin layers. TGA experiments carried out at 900 °C confirm that mass loss rates are higher for materials with thicker Pyro C layers. At higher temperatures (i.e. 1250 °C) such differences are not significant likely due to the interaction between SiC oxidation and Pyro C burnout. These tests clearly show that the oxidation kinetics of Tyranno fibers are much faster than those of CVD-SiC coatings. Therefore, the CVD-SiC coatings protect the Tyranno fibers against oxidation, although this is less effective as the thickness of the Pyro C layer increases. Finally, it has been found that the oxidation kinetics of the CVD-SiC layers are faster as the coating thickness increases and are different for the inner and the outer coating surfaces.