Raman and Rayleigh mapping of corrosion and mechanical aging in SiC fibres

SiC fibres are a complex system of heterogeneous nanophases. We used Raman microspectrometry to monitor the chemical changes of carbon phases and SiC nanocrystals in such fibres submitted to an alkali and oxidant environment (modelled by molten NaNO3). Specific study of Nicalon-NLM®, Tyranno SA3® and Sylramic® fibres allowed to evidence that surface and volume properties are different. Chemical and/or strain gradients change during corrosion. The important reactivity of the fibre's core is supposed to be linked to the easy intercalation of Na+ ions, which accelerates the oxidant species diffusion. Singular areas that were hardly strained during microindentation tests on SCS-6® fibres (a model for composites with self-healing interfaces like (SiC/C/BN)), were analysed using Rayleigh microspectrometry to determine the surface geometry.