Investigation of CMAS Resistance of Sacrificial Suspension Sprayed Alumina Topcoats on EB-PVD 7YSZ Layers

Abstract

Molten calcium-magnesium-aluminum-silicate (CMAS) mineral particles cause significant degradation of thermal barrier coatings (TBCs) in aero-engines. One approach to protect the TBC coating against the CMAS attack is the application of a sacrificial coating on top of the TBC coating. In this work sacrificial Al2O3 coatings were deposited on top of EB-PVD 7YSZ layers using suspension thermal spraying starting from an aqueous Al2O3 suspension. Spray parameters were varied in order to produce sacrificial topcoats with two different microstructures and porosities levels. The coating systems were tested under CMAS attack by performing short and long-time infiltration tests at 1250 °C. It was found out that the porosity and morphology of Al2O3 coatings strongly influenced the CMAS infiltration kinetics and the formation of various phases. CMAS mitigation depended on the interaction between the coating morphology which rules the driving force for infiltration, as well as on the reaction speed between alumina and the CMAS deposit.