NDE of degradation of thermal barrier coating by means of impedance spectroscopy |
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Authors: | Ogawa Kazuhiro Minkov Dorian Shoji Tetsuo Sato Minoru Hashimoto Hideo |
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Affiliation: | a Research Institute for Fracture Technology, Tohoku University Aoba 01, Aramaki, Aoba-ku, Sendai, 980-8579, Japan;b Tohoku Electric Power Co. Inc. 3-7-1 Ichibancho, Aoba-ku, Sendai, 980-0811, Japan |
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Abstract: | Nondestructive evaluation of thermal barrier coating (TBC) degradation during service operation has received a wide attention for service life prediction of advanced gas turbines. In this work, TBC on nickel base superalloy degraded at various degrees by thermal aging is investigated. Particularly, TBC and Metal–Chromium–Aluminum–Yttrium alloy (McrAlY) (M indicates iron (Fe), cobalt (Co), nickel (Ni) or these combinations) bond coating interface where a detrimental reaction takes place and forms various reaction products during thermal aging, is studied in detail. Formation kinetics and physical properties of the reaction layer are evaluated by means of Impedance Spectroscopy (IS). Specimens aged at higher temperature and a longer aging time shows larger impedance. The impedance behavior of TBC and bond coating is found to be markedly changed by the formation of the reaction layer. Physical properties and thickness of the reaction layer are evaluated using the change of the impedance. A mechanistic interpretation of the cause of change in the physical properties and IS behavior are described. |
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Keywords: | Nondestructive examination Gas turbines Protective coatings Thermal insulating materials Interfaces (materials) Aging of materials Nickel alloys Superalloys Spectroscopy Service life Thermal effects Thermal barrier coatings Impedance spectroscopy |
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