Professor Carlos Levi, University of California, Santa Barbara

The Challenges of Higher Temperature Coatings for Gas Turbines
When Jul 14, 2014
from 02:00 PM to 03:00 PM
Where LR8, IEB Building, Engineering Science
Contact Name
Contact Phone 01865-283490
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Gas turbine technology is at a cross-roads, with demands for increased engine performance and fuel flexibility translating into higher material temperatures, ≥1300°C, and more chemically aggressive environments for the gas path components.  All potential materials solutions, including the current Ni-based superalloys, involve thermal and/or environmental barrier coatings to enable their use under these conditions.  This presentation will start with a broad perspective on the problem, focusing primarily on thermal barrier coatings (TBCs) for metallic components.  Zirconia with 7±1wt%Y2O3 (7YSZ) has been the standard thermal barrier oxide since the commercial insertion of TBCs but is now reaching its limit of applicability.  Candidate new materials are mostly based on ZrO2 with rare earth and/or or transition metal additions.  Two groups emerge, one based on the non-transformable tetragonal (t’) form of ZrO2, and the other on rare earth zirconates.  Unfortunately no candidate in either group meets all the requirements for the more advanced applications.  Tetragonal materials are endowed with toughening mechanisms that underpin their durability.  However, as the engine temperature increases they are compromised by sintering, destabilization of the t’ phase, and by penetration of molten silicate deposits.  In contrast, the zirconate materials are phase stable and offer improved resistance to sintering and silicate penetration, but are limited by the absence of intrinsic toughening mechanisms, thermochemical interactions with the thermally grown oxide that protects the underlying alloy, and often by processability.  This presentation will discuss the scientific foundation of the design strategies for these materials and the challenges ahead.

Acknowledgments: The presentation benefits from various extramural collaborations and includes contributions from past and present graduate students (E.M. Donohue, M.R. Fisch, S.G. Heinze, J.A. Krogstad, R.M. Leckie, C.A. Macauley, D.L. Poerschke, T.A. Schaedler, K.M. Wessels, E.M. Zaleski) and post-docs (S. Burk, C. Carbogno, S. Krämer, R.W. Jackson, J.S. Van Sluytman and J.Y. Yang).  Research support provided by programs from the National Science Foundation (DMR-1105672), the Office of Naval Research (N00014-08-1-0522), AFOSR, and the UCSB-Honeywell Alliance for TBCs. 

About the speaker:  C.G. Levi received a Ph.D. in Metallurgical Engineering from the University of Illinois at Urbana-Champaign in 1981 and has been in the faculty at UCSB since 1984, where he is Professor of Materials and Mechanical Engineering. The overarching theme of his research is the fundamental understanding of microstructure evolution in inorganic materials, and the application of this understanding to the design and synthesis of improved coatings, thin films, composites and monolithic systems, with emphasis on high temperature applications.  Current areas of work include thermal and environmental barrier coatings for advanced gas turbine components, self-healing matrices and fibers for CMCs, environmental barrier layers for advanced nuclear energy systems, novel high temperature alloys and multi-phase functional materials.  His professional contributions have been recognized with election as Fellow of the American Ceramic Society (2012), the TMS Morris Cohen award (2014), the 2008 NIMS Award, the DLR Wissenschaftspreis (2004), the Alexander von Humboldt Forschungspreis (2002), the 1989 Grossman Award and the 1982 Howe Medal from ASM International.  For additional information please see: http://www.materials.ucsb.edu/~levic/levi.html