Towards multifunctional thermal-barrier and environmental-barrier coatings

Conference Dates

June 24-29, 2018


Gas-turbine engines are ubiquitous in aircraft propulsion, and land-based ones are used to generate ~20% of world’s electricity. Ceramic thermal barrier coatings (TBCs) are used to insulate and protect hot-section metallic components in these gas-turbine engines. However, the higher temperatures and extreme conditions in high-efficiency engines are making TBCs prone to deposition of undesirable silicates ingested by the engines, engendering new materials issues that are becoming critical for the development of more efficient engines. The undesirable silicates (calcium-magnesium-alumino-silicate glass or CMAS) can be in the form of sand and volcanic ash in the case of aircraft engines, and coal fly ash in the case of syngas-fired engines used for electricity generation. The understanding of mechanisms by which molten CMAS deposits damage conventional yttria-stabilized zirconia TBCs is presented. Demonstration and understanding of approaches to mitigate this type of CMAS-induced damage in new TBCs are also presented, together with a discussion of guidelines for the development of new TBCs. However, state-of-the-art TBC-coated metallic components may not have the necessary high-temperature capabilities required for the next-general engines with even higher operating temperatures and more demanding efficiency standards. In this context, ceramic-matrix composites (CMCs), combined with environmental barrier coatings (EBCs), are being implemented in gas-turbine engines. But the CMAS issue will need to be addressed in the context of EBCs-coated CMCs. Strategies for CMAS-attack mitigation of EBCs, which are different from those used in TBCs, are discussed and demonstrated. Finally, new concepts in CMAS-resistant T/EBCs that combine the thermal-barrier and environmental-barrier functions are discussed and demonstrated.

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