Journal
SURFACE & COATINGS TECHNOLOGY
Volume 188, Issue -, Pages 62-70Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.surfcoat.2004.08.001
Keywords
thermal barrier coatings; spallation failure; cyclic oxidation; bond coat
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The typical degradation mechanism of EB-PVD thermal barrier coatings (TBCs) that occurs during cyclic furnace testing of a commercial 7YSZ coating on a single-crystal nickel-base superalloy is analyzed. The mechanism includes local separation of the ceramic top coat from the thermally grown oxide (TGO), growth of the separated regions along the coating-substrate interface, and, upon reaching a critical size, large-scale TBC spallation. The extent of interface separation was evaluated by analyzing cross-section microstructures of the tested samples at different stages of TBC cyclic life. The morphological changes of the TGO as a result of roughening of the (Ni,Pt)Al bond coat surface were also quantified. Concurrently, the evolution of the TGO luminescence during cyclic oxidation and the development of TBC undulations, associated with large TBC-TGO interface separations, were monitored. It is demonstrated that there is a correlation between the extent of interface damage and the shift in TGO luminescence frequency, which can be evaluated nondestructively. (C) 2004 Elsevier B.V. All rights reserved.
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