Residual elastic strain and survivability of stabilized zirconia coated carbon-carbon (C/C) composite

Carbon-carbon (C/C) composites require protective coatings for prolonged use in elevated temperature, oxidizing environments. Ceramic coatings can provide oxidation protection; however, thermal expansion mismatch in conjunction with thermal events and interfacial constraint during coating deposition can result in residual stress, which can affect the lifetime and performance of the system. This work leveraged high energy synchrotron X-ray diffraction to determine the depth resolved residual elastic strain in two rare-earth oxide stabilized zirconia (12 mol% yttria and 6 mol% samaria) coatings, applied to a carbon-carbon composite substrate. The experimental characterization of the as-deposited coatings indicated a tension to compression residual elastic strain gradient, which was consistent with an energy-based model that illustrated the crystal structure dependence of the residual stress state. Via an oxyacetylene torch exposure, the ablation behavior and crack propagation were correlated to the measured residual elastic strain state and highlighted the influence of processing and exposure induced residual stress on coating performance. These experimental residual elastic strain measurements and relation to failure mechanisms support the survivability of these coating systems in applications that require thermal protection systems (TPS).