This paper describes recent developments of the thermal barrier sensor concept for nondestructive evaluation (NDE) of thermal barrier coatings (TBCs) and online condition monitoring in gas turbines. Increases in turbine inlet temperature in the pursuit of higher efficiency will make it necessary to improve or upgrade current thermal protection systems in gas turbines. As these become critical to safe operation, it will also be necessary to devise techniques for online condition monitoring and NDE. The authors have proposed thermal barrier sensor coatings (TBSCs) as a possible means of achieving NDE for TBCs. TBSCs are made by doping the ceramic material (currently yttria-stabilized zirconia (YSZ)) with a rare-earth activator to provide the coating with luminescence when excited with UV light. This paper describes the physics of the thermoluminescent response of such coatings and shows how this can be used to measure temperature. Calibration data are presented along with the results of comparative thermal cycle testing of TBSCs, produced using a production standard air plasma spray system. The latter show the durability of TBSCs to be similar to that of standard YSZ TBCs and indicate that the addition of the rare-earth dopant is not detrimental to the coating. Also discussed is the manufacture of functionally structured coatings with discreet doped layers. The temperature at the bond coat interface is important with respect to the life of the coating since it influences the growth rate of the thermally grown oxide layer, which in turn destabilizes the coating system as it becomes thicker. Experimental data are presented, indicating that dual-layered TBSCs can be used to detect luminescence from, and thereby the temperature within, subsurface layers covered by as much as of standard TBC material. A theoretical analysis of the data has allowed some preliminary calculations of the transmission properties of the overcoat to be made, and these suggest that it might be possible to observe phosphorescence and measure temperature through an overcoat layer of up to approximately 1.56 mm thickness.
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November 2008
Research Papers
Optical Nondestructive Condition Monitoring of Thermal Barrier Coatings
A. L. Heyes,
A. L. Heyes
Department of Mechanical Engineering,
Imperial College London
, Exhibition Road, London, SW7 2AZ, UK
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J. P. Feist,
J. P. Feist
Southside Thermal Sciences Ltd.
, c/o IC Innovations, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
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X. Chen,
X. Chen
Solar Turbines Inc.
, 2200 Pacific Highway, P.O. Box 85376, San Diego, CA 92186-5376
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Z. Mutasim,
Z. Mutasim
Solar Turbines Inc.
, 2200 Pacific Highway, P.O. Box 85376, San Diego, CA 92186-5376
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J. R. Nicholls
J. R. Nicholls
Cranfield University
, College Road, Cranfield, Bedfordshire, MK43 0AL, UK
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A. L. Heyes
Department of Mechanical Engineering,
Imperial College London
, Exhibition Road, London, SW7 2AZ, UK
J. P. Feist
Southside Thermal Sciences Ltd.
, c/o IC Innovations, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
X. Chen
Solar Turbines Inc.
, 2200 Pacific Highway, P.O. Box 85376, San Diego, CA 92186-5376
Z. Mutasim
Solar Turbines Inc.
, 2200 Pacific Highway, P.O. Box 85376, San Diego, CA 92186-5376
J. R. Nicholls
Cranfield University
, College Road, Cranfield, Bedfordshire, MK43 0AL, UKJ. Eng. Gas Turbines Power. Nov 2008, 130(6): 061301 (8 pages)
Published Online: August 28, 2008
Article history
Received:
April 27, 2007
Revised:
September 4, 2007
Published:
August 28, 2008
Citation
Heyes, A. L., Feist, J. P., Chen, X., Mutasim, Z., and Nicholls, J. R. (August 28, 2008). "Optical Nondestructive Condition Monitoring of Thermal Barrier Coatings." ASME. J. Eng. Gas Turbines Power. November 2008; 130(6): 061301. https://doi.org/10.1115/1.2940988
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