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Durable, CMAS resistant, thermal/environmental barrier coatings for metallic and CMC hot section components of gas turbine engines

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OBJECTIVE: Develop and validate durable, Calcia-Magnesia-Alumina-Silicate (CMAS) resistant thermal/environmental barrier coatings for metallic and CMC hot section components of turbine engines DESCRIPTION: Gas turbine metallic combustor liner walls, along with turbine blades, vanes and shrouds are typically coated with an intermediate bond coat and a porous, ceramic-based thermal barrier coating (TBC) system to enable effective high temperature operation. Similarly, with the development of advance ceramic matrix composite (CMC) materials to replace metallic versions of these components, environmental barrier coatings (EBCs) are used in place of the TBCs for protection against temperature/moisture-induced degradation leading to spallation. Gas turbines engines that ingest sand are subject to the accumulation of deposits of Calcia-Magnesia-Alumina-Silicate (CMAS) on the TBC surfaces. The CMAS deposits are viscous, or possibly become molten, at the high combustor temperatures (>2100F). The high temperatures provide the potential for the CMAS deposits to wick into the TBC/EBC. In the case of conventional yittria-stabilized zirconia TBCs, the coating structure is columnar, which allows the CMAS material to wick between the columns. Upon cooling and subsequent hot-cold cycles, the CMAS-filled TBC/EBC is unable to handle the thermal expansion mismatch between the coating and the substrate. These stresses are often relieved by TBC/EBC spallation. Therefore, there is a need to identify CMAS resistant TBC/EBC technologies. This could be accomplished by a completely different coating micro-structure that is not columnar and is resistant to CMAS or by adding a protective layer to more conventional TBCs that stops the CMAS from getting into the columnar structure. The objective of this topic is to develop and validate durable, Calcia-Magnesia-Alumina-Silicate (CMAS) resistant thermal/environmental barrier coatings for metallic and CMC hot section components of turbine engines. The coefficient of thermal conductivity of the new TBC should be better than that of yittria-stabilized zirconia (less than 2 W/mK). The small business is encouraged to work with and establish a clear transition path with a turbine engine manufacturer. PHASE I: Assess the feasibility of promising CMAS resistant thermal/environmental barrier coatings in the presence of CMAS. TBC coated metallic or EBC coated CMC specimens will be thermal cyclic tested at greater than 2100F with the presence of CMAS on the surface to evaluate the relative durability performance. PHASE II: Apply CMAS resistant TBC or EBC technology to high (>2100F) temperature engine component(s) for evaluation in a full-scale cyclic endurance test with sand ingestion of the appropriate constituents to promote CMAS. PHASE III: The optimized coating technology shall be applied to hot section component(s) for full engine test validation to TRL 6. Validation will include a sand test demonstration with appropriate cyclic content. DUAL USE APPLICATIONS: The resulting technology will enable significantly enhanced durability of hot section components of future advanced engines with high turbine inlet temperatures operating in sandy environments. Both military and commercial aircraft applications are likely to encounter such an environment and thereby will derive benefit from this technology. REFERENCES: 1. Krmer, S., Yang, J., Johnson, C., and Levi, C. Thermochemical Interaction of Thermal Barrier Coatings With Molten Cao-Mgo-Al2o3-Sio2 (CMAS) Deposits. (http://www.materials.ucsb.edu/MURI/papers/Kraemer-JAcerS1205.pdf) 2. Drexler, J.M., et al. Air-Plasma-Sprayed Thermal Barrier Coatings that are Resistant to High-Temperature Attack by Glassy Deposits. Acta Materialia. 58. pp. 6835-6844. 2010. 3. Li, L. Hitchman, N., and Knapp, J. Failure of Thermal Barrier Coatings Subjected to CMAS Attack. Journal of Thermal Spray Technology. 19 (1-2). pp. 148-155. 2010. 4. Kramer, S., et al. Mechanisms of Cracking and Delamination within Thick Thermal Barrier Systems in Aero-Engines Subject to Calcium-Magnesium-Alumino-Silicate (CMAS) Penetration. Materials Science and Engineering A. 490. pp. 26-35. 2008. 5. Kendra M. Grant, Stephan Krmer, Jan P.A. Lfvander, Carlos G. Levi, CMAS Degradation of Environmental Barrier Coatings. (http://www.materials.ucsb.edu/MURI/papers/Grantetal_CMASonEBC.pdf)
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