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Thermochemical Interaction of Thermal Barrier Coatings with Molten CaO–MgO–Al 2 O 3 –SiO 2 (CMAS) Deposits
Author(s) -
Krämer Stephan,
Yang James,
Levi Carlos G.,
Johnson Curtis A.
Publication year - 2006
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2006.01209.x
Subject(s) - thermal barrier coating , isothermal process , microstructure , materials science , coating , chemical engineering , deposition (geology) , phase (matter) , degradation (telecommunications) , silicate , mineralogy , metallurgy , chemistry , thermodynamics , nanotechnology , geology , paleontology , telecommunications , physics , organic chemistry , sediment , computer science , engineering
Thermal barrier coatings (TBCs) are increasingly susceptible to degradation by molten calcium–magnesium alumino silicate (CMAS) deposits in advanced engines that operate at higher temperatures and in environments laden with siliceous debris. This paper investigates the thermochemical aspects of the degradation phenomena using a model CMAS composition and ZrO 2 –7.6%YO 1.5 (7YSZ) grown by vapor deposition on alumina substrates. The changes in microstructure and chemistry are characterized after isothermal treatments of 4 h at 1200°–1400°C. It is found that CMAS rapidly penetrates the open structure of the coating as soon as melting occurs, whereupon the original 7YSZ dissolves in the CMAS and reprecipitates with a different morphology and composition that depends on the local melt chemistry. The attack is minimal in the bulk of the coating but severe near the surface and the interface with the substrate, which is also partially dissolved by the melt. The phase evolution is discussed in terms of available thermodynamic information.