KINETICS AND MECHANISMS OF OXIDATION OF 2D WOVEN C SIC COMPOSITES .1.EXPERIMENTAL APPROACH/

The oxidation behavior of a 2D woven C/SiC composite partly protected with a SiC seal coating and heat-treated (stabilized) at 1600-degrees- C in inert gas has been investigated through an experimental approach based on thermogravimetric analyses and optical/electron microscopy. R esults of the tests, performed under flowing oxygen, have shown that t he oxidation behavior of the composite material in terms of oxidation kinetics and morphological evolutions is related to the presence of th ermal microcracks in the seal coating as well as in the matrix. Three different temperature domains exist. At low temperatures (<800-degrees -C), the mechanisms of reaction between carbon and oxygen control the oxidation kinetics and are associated with a uniform degradation of th e carbon reinforcement. At intermediate temperatures, (between 800-deg rees and 1100-degrees-C), the oxidation kinetics are controlled by the gas-phase diffusion through a network of microcracks in the SiC coati ng, resulting in a nonuniform degradation of the carbon phases. At hig h temperatures (>1100-degrees-C), such diffusion mechanisms are limite d by sealing of the microcracks by silica; therefore, the degradation of the composite remains superficial. The study of the oxidation behav ior of (i) the heat-treated composite in a lower oxygen content enviro nment (dry air) and (iii) the as-processed (unstabilized) composite in dry oxygen confirms the different mechanisms proposed to explain the oxidation behavior of the composite material.