Atomic oxygen(AO)is considered the most erosive particle to spacecraft materials in low earth orbit(LEO).Carbon fiber,carbon/carbon(C/C),and some modified C/C composites were exposed to a simulated AO environment to investigate their behaviors in LEO.Scanning electron microscopy(SEM),AO erosion rate calculation,and mechanical property testing were used to characterize the material properties.Results show that the carbon fiber and C/C specimens undergo significant degradation under the AO bombing.According to the effects of AO on C/C-SiC and CVD-SiC-coated C/C,a condensed CVD-SiC coat is a feasible approach to protect C/C composites from AO degradation.
Xiao-chong LiuLai-fei ChengLi-tong ZhangXin-gang LuanHui Mei
C/SiC composites prepared by chemical vapor infiltration(CVI) were subjected to a stationary loading of 160 MPa in a combustion gas environment with flame temperature of 1300 ℃.Lifetime of C/SiC composites in such environment was measured.Microstructures of the composites after the testing were also characterized by SEM.The experimental results indicate the lifetime of C/SiC composites is average 2.3 hours in combustion gas environments.The combustion gas flow accelerates the damage of carbon fibers and the failure of the composites by speeding up the diffusion of gas reactants and products,destroying the layer of SiO2 on the surface of SiC coating and bringing fused SiO2 inside the composites.The fracture face of C/SiC is uneven,i e,a flat area close to the windward side and a pulling-out of long fibers near the leeward side,which results from the directionality effect of the combustion gas flow.
