A Chemo-Thermo-Mechanics Theory: Application to High-Temperature Thermal Barrier Coatings

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Thermal barrier coatings are applied to superalloy turbine blades to provide thermal insulation and oxidation protection. A typical coating consists of an oxide/metal bilayer: the outer oxide layer (top-coat) imparts thermal insulation, while the metallic layer (bond-coat) affords oxidation protection through the formation of a thermally-grown-oxide at elevated temperatures. Bond-coat oxidation is the primary cause of coating failure. The goal of this research is to develop a simulation-based design capability to predict the stability and durability of thermal barrier coatings. The specific aims are to: (i) Develop a continuum-level chemo-thermo-mechanics theory for modeling the coupled diffusion-oxidation-deformation and degradation of coating systems. (ii) Numerically implement the theory and develop a robust simulation-based capability for predicting coating performance. (iii) Conduct an experimental research program to validate the predictive capabilities of the theory and simulation-based design capability. Over the past 40 years, natural-gas-combined-cycle turbine-technology has evolved to dominate large scale power generation. The main technological challenges for this technology going into the future are: (i) to improve the combustion design to reduce emissions, while raising firing temperatures beyond 1430°C (the current standard); (ii) to extend operation time between maintenance intervals; and (iii) to further improve the reliability of these complex systems. The stability and durability of single-crystal turbine blades and thermal barrier coatings in such advanced applications is not very well understood or modeled. This research will provide a theoretical basis for life-prediction and performance improvement of thermal barrier coatings in such severe environments.