Detection of Thermally Grown Oxide Layer in Thermal Barrier Coating for Gas Turbines by Photoluminescence

Eto

Electrical Engineering Japan

et al. 2014

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SUMMARYA compact, continuous wave laser was applied to detection of the thermally grown oxide (TGO) layer in a thermal barrier coating (TBC) for gas turbine hightemperature components by photoluminescence. Experiments were conducted using TBC specimens heated in air to artificially produce a TGO layer. For specimens heated at 1100 • C, the photoluminescence intensity increased with heating time, whereas for specimens heated at 1000 • C, the photoluminescence intensity did not increase beyond 100 h. The results indicate that the formation of the TGO layer is strongly dependent on the temperature. In addition, scanning electron microscope (SEM) observations of the specimen cross section confirmed the formation of the TGO layer after heating for 100 h at 1100 • C. The applicability of a compact laser to TGO layer detection allows the development of a simple TGO detection system, which can be used in screening for the detailed inspection of delamination. C⃝ 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 190(1): 1-8, 2015; Published online in Wiley Online Library (wileyonlinelibrary.com).

Section: Experimental Measurement Resultsmentioning

confidence: 84%

“…The result is shown in Fig. . The TGO layer appears as a dark region at the interface between the topcoat and bondcoat.…”

Section: Experimental Measurement Resultsmentioning

confidence: 95%

“…Relation between photoluminescence intensity (integrated over 690 nm to 698 nm) and excitation laser intensity .…”

Section: Experimental Measurement Resultsmentioning

confidence: 99%

“…Optical microscope observation result of cross section of specimen E (TGO layer appears at interface between topcoat and bondcoat) .…”

Section: Experimental Measurement Resultsmentioning

confidence: 99%

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Evaluation of Applicability of Compact Excitation Light Source to Detection of Thermally Grown Oxide Layer in Thermal Barrier Coating for Gas Turbines

Eto

Electrical Engineering Japan

et al. 2014

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“…Previous system transmits laser beam in the air, and photoluminescence is received by an independent optical system [12,13], but for operability improvement, it is necessary to integrate the optical fiber transmission of laser beam and the laser receiving and transmitting systems into a single probe. …”

Section: Problems For Practical Realizationmentioning

confidence: 99%

Development of a Portable System for Detection of Thermally Grown Oxide Layer in Thermal Barrier Coating

Fujii

2017

Elect Comm in Japan

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Thermal barrier coating (TBC) is applied to high temperature components in gas turbines. The thermally grown oxide (TGO) layer, which forms at the interface between the topcoat and the bondcoat, is an origin of topcoat damage, which can lead to delamination of the topcoat. In order to detect the TGO layer in in-service components, a portable detection system based on photoluminescence was developed. The system consists of a compact, continuous wave Nd:YAG laser of wavelength 532 nm to excite Cr 3+ included as an impurity in Al 2 O 3 and a compact spectrometer with a two-dimensional CCD array for enhanced sensitivity to detect the photoluminescence from Cr 3+ at 694.3 nm (R 1 ) and 692.9 nm (R 2 ). An optical probe is used to illuminate the specimen with laser light and to collect the photoluminescence. The probing region is a circle of diameter 5 mm. The optical probe is coupled to the main body by an optical fiber, which allows flexibility to match specimens with curved surfaces or complex structures. The system performance was tested using TBC specimens heated at 1000°C and 1100°C, and an as-sprayed, unheated TBC specimen. Photoluminescence (R 1 and R 2 ) was observed from heated specimens and was not observed from the unheated specimen, and agreed with previous measurement results. This system can be used for screening test of topcoat delamination inspection, since delamination is likely to occur at locations where the TGO layer has grown. C⃝ 2017 Wiley Periodicals, Inc. Electron Comm Jpn, 100(2): 76-82, 2017; Published online in Wiley Online Library (wileyonlinelibrary.com).

Topcoat Transmission Measurement and Sensitivity Evaluation for Detection of Thermally Grown Oxide Layer of Thermal Barrier Coating

Eto

et al. 2016

Elect Comm in Japan

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SUMMARY The thermally grown oxide (TGO) layer, which forms below the topcoat of thermal barrier coating (TBC), is an important factor that causes topcoat delamination, and its detection is important for health monitoring of TBC. Photoluminescence detects the emission from Cr3+ in the TGO layer upon laser excitation, and is an effective, nondestructive method to detect the TGO layer. In this method, the laser light and Cr3+ photoluminescence must transmit through the topcoat, so the topcoat transmittance is a limiting factor of the measurement sensitivity. In this report, the topcoat transmittance was measured by comparing the photoluminescence intensities from the TGO layer in the presence and absence of the topcoat. The round‐trip transmittance of the topcoat of thickness 300 μm was 1.26%, corresponding to an attenuation coefficient of 7.3 mm‐1. The sensitivity of the luminescence measurement was evaluated by placing ND filters of known attenuation in front of the TGO layer, to simulate the attenuation for different topcoat thickness. The results showed that luminescence measurement is possible for a maximum topcoat thickness of about 700 μm. A method to adjust the photoluminescence intensity for different topcoat thickness is presented.