Health and Durability of Protective and Thermal Barrier Coatings Monitored in Service by Visual Inspection

Protective and Thermal Barrier Coatings (TBC) applied on gas-turbine blades gradually degrade due to oxidation, aluminum depletion impacts of environmental particles. Among various non-destructive coating testing methods (NDT), visual inspection can be undertaken regularly in service, but it provides little quantitative information, only surface defects detected. This work aims at in-service monitoring turbine with multilayer coatings by atmospheric plasma spraying (APS) a few variants. They were validated during series accelerated mission tests retired military turbofan engine test cell together five other technologies. The fifty-hour rainbow focused assessing durability. Between runs, 12 borescope inspections conducted monitor the health blades. Finally, disassembled examined using computed tomography (CT) metallographic methods. Throughout testing, 31 newly-coated (66%) withstood tests, producing results comparable reference However, 16 suffered intolerable failures observed as increased roughness, gradual loss topcoat, spallation minor foreign object damage. Visual generally agreement subsequent laboratory tests.