Optical measurements of stress in a thermally grown oxide (TGO) layer that has formed between a metallic bond coat and thermal barrier coating (TBC) have been previously demonstrated and shown useful in understanding aspects of TBC failure. These measurements have promise for nondestructive evaluation of coated turbine components. However, engine-run turbine parts collect significant surface contamination consisting of calcium-magnesium-alumina-silicate (CMAS). The deposited CMAS both blocks optical measurement of stress in the TGO and produces false stress signals. A recently developed laser ablation technique has enabled contaminant removal with minimal TBC damage. The locally cleaned engine run parts can then have their TGO stresses optically determined. In the present paper, it is shown that sporadic signals from contamination are still present due to CMAS infiltration into the TBC and due to local regions that cannot be cleaned without damaging the TBC. Methods for separating the contamination signal from the TBC signals are presented as needed for successful use of optical stress measurement on engine run turbine components. The stress measurements censored for false signals are compared to other destructive approaches and the methods are shown to provide robust nondestructive evaluation of the coating stress.
|Number of pages||8|
|Journal||Surface and Coatings Technology|
|State||Published - Feb 15 2012|
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation (CTS-0553623) and Rolls-Royce Corporation.
Copyright 2012 Elsevier B.V., All rights reserved.
- Photoluminescence piezospectroscopy
- Remaining life prediction
- Thermal barrier coatings
- Thermally grown oxide
ASJC Scopus subject areas
- Chemistry (all)
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films
- Materials Chemistry