PS–PVD Alumina Overlayer on Thermal Barrier Coatings Against CMAS Attack

Abstract

Glassy deposits mainly comprising of calcium–magnesium–alumina–silicate (CMAS) accelerate the spallation of thermal barrier coatings (TBCs). In this work, an Al2O3 layer was produced on yttria-stabilized zirconia (YSZ) coating by plasma spray–physical vapor deposition (PS–PVD). The effects of processing parameters during PS–PVD process on the microstructures of the deposited Al2O3 coatings were investigated. A homogeneous Al2O3 coating with porosity less than 1% was deposited at the spray distance of 1400 mm, which is much denser than the coating produced by atmospheric plasma spray (APS) and other PS–PVD coatings sprayed at 1000 and 1900 mm. The CMAS corrosion test at 1250 °C showed that the APS Al2O3 layer was dissolved in CMAS after 24 h thermal exposure, whereas a dense reaction layer mainly composed of anorthite formed on the top region of the PS–PVD Al2O3 layer effectively protected the underlying Al2O3 layer from CMAS infiltration. Thermal cycling behavior of the PS–PVD Al2O3/YSZ TBC and the APS Al2O3/YSZ TBC at 1050 °C was compared. Bulk spallation of the APS TBC occurred within 300 h thermal cycling, while little spallation was observed on the PS–PVD TBC even after 500 h thermal cycling, indicating superior durability of the PS–PVD coating.