Effects of temperature and stress on the oxidation behavior of a 3D C/SiC composite in a combustion wind tunnel

High-temperature oxidation of a 3D C/SiC composite has been conducted under various tensile creep loads in a combustion wind tunnel at 1200-1500 degrees C. The effects of temperature and stress on the oxidation behavior were evaluated according to length change, lifetime and morphology of the specimens. The damage mechanisms of the composite are changed from superficial oxidation to non-uniform even uniform oxidation by a tensile stress. The stressed oxidation process is controlled by a normalized threshold stress (NTS), which is increased with rising temperature. When the normalized stress (NS) is below the threshold value, the oxidation of carbon fibers is controlled by the in-crack diffusion, starts from the windward and develops region by region along the combustion gas flow. The specimen displays a multiple creep behavior because the applied tensile load is borne by several load-bearing regions in turn and each region manifests a typical creep behavior after the tensile load transferred from an oxidized region to it. When NS is above NTS, the oxidation of carbon fibers is limited by the boundary layer diffusion, and the specimen exhibits a typical creep behavior. (C) 2009 Elsevier Ltd. All rights reserved.