Thermomechanical Fracture of Compositionally Graded Thermal Barrier Coatings with Time-Dependent Behavior

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ABSTRACTThermal barrier coatings (TBCs) offer the potential of increased performance for high temperature applications such as diesel engines, gas turbines and aircraft engines. Compositionally graded TBCs offer an excellent alternative to enhance the resistance to thermomechanical damage by providing a gradual transition in properties through the coating thickness. The objective of this project is to study analytically and experimentally, compositionally graded material systems of similar thermal resistances, but different architectures. At high temperatures, thermally activated time-dependent (viscoplastic) effects in the lower layers comprised of ceramic/bond coat alloy mixtures are expected to become significant. Therefore it is proposed to: (1) develop new models that allow the prediction of viscoplastic behavior of zirconia-bond coat alloy mixtures; (2) to use these models to study the time-dependent behavior, crack initiation and propagation in compositionally graded TBC systems of similar thermal resistances; (3) to perform controlled experiments with high heat fluxes that provide verification of the analytical predictions. The results are expected to yield design guidelines that would allow TBC designers to optimize the architecture of graded TBC systems to achieve improved durability for specific temperature loading conditions. In addition, these investigations will enhance basic scientific knowledge in the areas of viscoplastic deformation and fracture in two-phase and compositionally graded material systems. This new knowledge will be incorporated in undergraduate and graduate courses and help in the education of women and minority undergraduate students with the possibility they may embark on graduate studies.