TBC Bond Coat Properties and Dynamics

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This grant undertakes an experimental study to elucidate and model the mechanical behavior and thermal stability of a new class of bond coat materials for thermal barrier coatings (TBCs). One of the key components of a TBC is its bond coat, and there is clear empirical evidence that platinum additions to aluminide bond coats enhance the overall performance and reliability of these coatings. Other platinum group metals (Pd, Ru, Ir, Rh, and Os) are believed to provide similar or even greater benefits, but the mechanisms that govern bond coat performance are currently not well understood. The proposed study will parallel and compliment a larger NSF-EC collaborative program on the dynamics of layered multifunctional surfaces. One aspect of the NSF-EC study involves processing and phase equilibria aspects of platinum group metal bond coats, and the current study will be conducted in close collaboration with the NSF-EC team to characterize the mechanical behavior and microstructural evolution of Ru-based alloys and bond coats. The grant supports for the principal investigator and graduate students to participate in annual workshops and collaborations with the NSF-EC team with extended reciprocal visits of students between European Countries and US. The overall focus of this research program will be to measure single-phase Ru-Ni-Al-Xn and ruthenium modified bond coat properties, to develop a fundamental understanding of the substrate-bond coat interactions that occur during thermal cycling (inter-diffusion, viscoplasticity, morphological evolution, crack formation, etc.) and to derive a science-based protocol for assessing the potential and assisting in the development of ruthenium modified bond coats. The microsample tensile testing approach to be used in this study permits characterization of small-scale and highly scale-specific coatings and properties (elastic modulus, yield and creep strength) in a way not possible by conventional means. The technological motivation for this proposal is rooted in the fact that TBCs offer tremendous opportunities for increasing the temperature capabilities and durability of gas turbine engines. Through the proposed participation in annual workshops and extended reciprocal visits, the students working on this project will gain valuable experience into how research is conducted in both the U.S. and Europe.