Effects of Interfacial Diffusion Barriers on Thermal Stability of Ceramic Fibers
High-strength Si-N-C-O ceramic fibers have been made by pyrolysis of polymer fibers. The ceramic fibers are intended as reinforcement for high-performance composites and require good retention of mechanical properties after extreme thermal exposures. Strength retention of the fibers depends on growth of their critical flaws. This, in turn, can depend on the extent of decomposition reactions. These reactions require gas transport through the outer fiber surface and are subject to control by effective diffusion barriers at this interface. A new technique was used to study the effect on flaw growth from barrier coatings of carbon applied to a fiber fracture surface. A CVD coating of SiC applied to a strand of fibers can suppress gas diffusion through the fiber surface. The effectiveness of these barriers is reported in terms of the rate of flaw growth, the extent of chemical decomposition and gas diffusion, and the loss of fiber strength.
KeywordsDiffusion Barrier Flaw Growth Thermal Aging Fiber Strength Strength Loss
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