Title

Electrochemical impedance spectroscopy of thermal barrier coatings as a function of isothermal and cyclic thermal exposure

Authors

Authors

B. Jayaraj; S. Vishweswaraiah; V. H. Desai;Y. H. Sohn

Comments

Authors: contact us about adding a copy of your work at STARS@ucf.edu

Abbreviated Journal Title

Surf. Coat. Technol.

Keywords

thermal exposure; electrochemical impedance spectroscopy; thermal; barrier coatings; non-destructive evaluation; OXIDATION; FAILURE; EVOLUTION; ZIRCONIA; Materials Science, Coatings & Films; Physics, Applied

Abstract

yElectrochemical impedance spectroscopy (EIS) is being developed as a non-destructive evaluation technique of thermal barrier coatings (TBCs) for life-remaining assessment and quality control. In this investigation, EIS was employed to non-destructively examine TBCs, as a function of thermal exposure during isothermal and cyclic oxidation in air at 1121 degreesC. TBCs examined in this study include electron beam physical vapor deposited (EB-PVD) and air-plasma sprayed ZrO2-7wt.%Y2O3 (YSZ) on NiCoCrAlY or (Ni,Pt)Al bondcoat. Electrochemical impedance response of TBC specimens at room temperature were acquired and analyzed with an AC equivalent circuit based on the multi-layered micro-constituents of TBCs. Microstructural characteristics of TBCs were also examined by optical and electron microscopy. Initial increase in the resistance of YSZ with thermal exposure was observed and related to the high temperature sintering of YSZ. The parabolic growth of TGO during high temperature oxidation was inversely proportional to the capacitance of TGO. An explanation based on electrolyte penetration into sub-critical damage is proposed for the gradual decrease in the resistances of YSZ and TGO with prolonged thermal exposure. Observation of exposed metallic bondcoat surface on the fracture surface, which provides conduction readily through electrolyte contact, was related to the abrupt and large increase in the capacitance of YSZ and TGO. (C) 2003 Elsevier Science B.V. All rights reserved.

Journal Title

Surface & Coatings Technology

Volume

177

Publication Date

1-1-2004

Document Type

Article; Proceedings Paper

Language

English

First Page

140

Last Page

151

WOS Identifier

WOS:000189038100021

ISSN

0257-8972

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