When 3:30 PM - 5:00 PM Jan 25, 2008
Where 1670 CSE
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Carlos Levi, UC Santa Barbara

Understanding the Role of Chemical Composition in Novel Thermal Barrier Oxides for Gas Turbines

Thermal barrier coating systems (TBCs) for high performance gas turbines are one of the most demanding applications for advanced ceramics in modern technology. These engineered surfaces are multifunctional, providing both thermal and environmental protection to the superalloy components, but the thermal barrier itself is also subject to multiple requirements that go beyond its basic function of thermal insulation efficiency to influence both its durability and performance. Zirconia partially stabilized with 7±1wt%Y2O3 (7YSZ) has been the standard material for TBCs since their commercial insertion. The demands for increased engine performance and fuel flexibility in advanced gas turbines translate into higher temperatures and more aggressive operating environments for TBCs, motivating the search for alternate materials, most of which retain ZrO2 as the base oxide with rare earth and/or or transition metal additions. Because a key element in the durability of current TBCs is their non-transformable tetragonal (t’) structure, which is metastable, one must tread carefully in the design space to achieve desired targets in functionality such as lower thermal conductivity or increased corrosion resistance, while maintaining adequate toughness, phase stability, compatibility with the underlying thermally grown oxide (TGO) and morphological stability of the strain-tolerant microstructure. These challenges and the necessary scientific understanding are discussed in this presentation in light of current work on alternate TBCs driven by desired improvements in higher temperature stability, resistance to erosion, cyclic life and attack by molten siliceous deposits that are commonly encountered in advanced engines for aircraft propulsion and industrial power generation.
Acknowledgments: The presentation includes contributions from past and present graduate students and post-docs notably T.A. Schaedler, R.M. Leckie, F.M. Pitek N.R. Rebollo, S. Krämer and A.S. Gandhi, and benefits from various extramural collaborations. The research was sponsored by programs from the National Science Foundation (DMR-0099695 and 060605700) and the Office of Naval Research (N00014-99-1-0471 and MURI/N00014-00-1-0438).

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