Dynamic CMAS–TBC Interactions: Infiltration and Degradation in APS YSZ Coatings

During operation, gas-turbine engines may ingest siliceous particulate matter that deposits on the hot surfaces of thermal barrier coatings (TBCs) and forms molten calcium–magnesium–alumino–silicate (CMAS). At temperatures above approximately 1200 °C, molten CMAS can infiltrate the coating microstructure, reduce its strain tolerance, and promote premature failure. Previous studies have suggested that dynamically deposited CMAS may exhibit limited infiltration because of insufficient exposure time at elevated temperatures. In the present study, a model CMAS composition (AFRL-03) was dynamically deposited onto conventional air-plasma-sprayed 8 wt.% yttria-stabilized zirconia (8YSZ) TBCs using an atmospheric plasma spray process. The substrate temperature was maintained above 1200 °C, followed by a 10-minute dwell period, to simulate severe service conditions and facilitate CMAS–TBC interactions. CMAS infiltration and the resulting microstructural degradation were systematically examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Particular attention was given to identifying the reaction products and degradation mechanisms associated with CMAS infiltration and coating failure. The findings provide further insight into the behavior of APS 8YSZ coatings under severe dynamic CMAS-deposition conditions.

Keywords: thermal barrier coating; dynamic CMAS deposition; atmospheric plasma spraying; 8YSZ; CMAS infiltration; AFRL-03