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Determination of Creep Behavior of Thermal Barrier Coatings Under Laser Imposed Temperature and Stress Gradients
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
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In the present study, a laser sinteringcreep technique has been established to quantitatively determine the creep behavior of thermal barrier coatings under steady state high heat fluxhigh thermal gradient conditions. An approach is proposed to separate the strong influence of stress relaxation, based on the deduced strain rate changes with respect to time and temperature during testing. For a plasma sprayed zirconia-8wt. yttria ceramic coating, a large primary creep strain and a low creep activation energy were observed. The significant primary creep stage and low apparent creep activation energy for the coating are attributed to stress induced mechanical sliding, and temperature and stress enhanced cation diffusion through the splat and grain boundaries. Possible creep mechanisms for the ceramic coating are also discussed. The elastic modulus evolution, the stress response and the total accumulated creep strain variation across the ceramic coating under laser imposed temperature and stress conditions are simulated using a finite difference approach. The modeled creep response is consistent with experimental observations.
APPROVED FOR PUBLIC RELEASE