APS Y2O3 environmental barrier coatings for oxide ceramic matrix composites

Authors

Peter Mechnich, DLR, GermanyFollow

Conference Dates

November 5-9, 2017

Abstract

Similar thermal expansion, microstructural stability, good adherence, and corrosion resistance are key issues for environmental barrier coatings (EBC) for oxide ceramic matrix composites (CMC) such as Al₂O₃/Al₂O₃. Laboratory-scale specimen as well as prototypic engine components were coated with Y₂O₃ by means of air plasma spraying (APS). Cubic -Y₂O₃ exhibits favorable properties such as thermal expansion close to that of Al₂O₃ and phase stability up to melting. The high thermal stability and low diffusivity of Y₂O₃ provides an exceptional microstructural stability of APS Y₂O₃ coatings. Although Y₂O₃ and Al₂O₃ are not thermodynamically compatible, the interdiffusion and reaction zone consisting of Y-aluminates is growing only slowly under relevant thermal conditions and does not seriously affect coating adherence. Consequently, APS Y₂O₃-coated Al₂O₃/Al₂O₃ CMC exhibited a high durability versus thermal cycling. APS Y₂O₃ coatings showed a high recession resistance in water vapor-rich, high-velocity combustion atmospheres. Moreover, APS Y₂O₃-coatings exhibited a high resistance against thermos-chemical attack by inorganic particles commonly referred to as CMAS corrosion. Infiltration of molten CMAS is mitigated by a dense reaction layer as well as by a quasi-impermeable coating microstructure. The outstanding combination of properties was the rationale for selecting APS Y₂O₃ as EBC material for Al₂O₃/Al₂O₃ combustor liners. Two can-type demonstrators with 0.5 and 1 mm thick APS Y₂O₃ EBC were manufactured and tested under engine conditions. Both EBCs passed high-pressure combustor rig tests without visible damages, emphasizing the fundamental viability of the concept.

Recommended Citation

Peter Mechnich, "APS Y2O3 environmental barrier coatings for oxide ceramic matrix composites" in "Ceramic Matrix Composites: Science and Technology of Materials, Design, Applications, Performance and Integration", Yutaka Kagawa, Tokyo University of Technology, Japan Dongming Zhu, NASA Glenn Research Center, USA Ram Darolia, GE Aviation (retired), USA Rishi Raj, University of Colorado, Boulder, USA Eds, ECI Symposium Series, (2017). https://dc.engconfintl.org/acmc/18