Topcoat Thickness Measurement of Thermal Barrier Coating of Gas Turbine Blade Using Terahertz Wave

Fukuchi, Tetsuo; Fuse, Norikazu; Okada, Mitsutoshi; Ozeki, Takayuki; Fujii, Tomoharu; Mizuno, Maya; Fukunaga, Kaori

doi:10.1002/eej.22624

Cited by 38 publications

(21 citation statements)

References 16 publications

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“…In view of the fact that the characteristics of the ceramic layer of the TBC specimen used in the present experiments and those of the YSZ specimens used for THz‐TDS did not necessarily coincide, and in view of the error of the refractive index (a calculation error of ±0.1 for the refractive index, compared with a calculation error of ±0.01 for

R_{S}

), the two results can be regarded as consistent. Furthermore, the refractive index of the ceramic TBC layer of gas turbine blades calculated from the frequency characteristics of the reflected waves was

n = 4.66 \pm 0.10

, and the refractive index obtained in the present experiments is

n = 4.7

, which agrees with this value.…”

Section: Measurement Experimentssupporting

confidence: 89%

“…Terahertz waves pass through plastic, ceramics, wood, and paint relatively easily. Consequently, there are reports of applications such as the visualization of interior structure (tomography), the detection of internal defects, and the measurement of film thickness .…”

Section: Introductionmentioning

confidence: 99%

“…However, there are no such reports involving dielectrics. For TBCs, we have previously proposed a method of finding the refractive index by compensating the reflection coefficient on the basis of assumptions regarding the surface roughness . However, the use of a surface roughness gage or microscopic observation of a cross section is needed in order to verify the assumptions about surface roughness.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Measurement of Refractive Index of Thermal Barrier Coating using Reflection of Terahertz Waves and Variable Aperture

et al. 2014

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SUMMARY A method to measure the refractive index of the ceramic layer of a thermal barrier coating (TBC) using the intensity ratio between the reflection of terahertz waves from the ceramic surface and a reference metal plate is proposed. This method uses a variable aperture to change the relative proportions of specular refraction and scattering from the ceramic surface. The refractive index is calculated based on the specular reflectivity, which is obtained from the intensity ratio when the field of view is extrapolated to zero. Measurement of a TBC specimen resulted in a refractive index of 4.7, which was in good agreement with the refractive index of the ceramic material obtained by terahertz time‐domain reflectometry. In addition, the surface roughness of the ceramic surface was obtained based on the frequency characteristics of the reflections from the ceramic surface and a reference metal plate. A surface roughness of 14 μm was obtained, which matched the results of microscopic observation of a TBC specimen whose coating was applied using the same lot as the specimen used in the measurement.

show abstract

R_{S}

n = 4.66 \pm 0.10

, and the refractive index obtained in the present experiments is

n = 4.7

, which agrees with this value.…”

Section: Measurement Experimentssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Measurement of Refractive Index of Thermal Barrier Coating using Reflection of Terahertz Waves and Variable Aperture

et al. 2014

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“…To protect the blade metal from oxidation, a thermal barrier coating (TBC) is applied to the blades, which typically consists of a ceramic layer-topcoat, an alloy layer-bond coat, and a bulk metal substrate. In [49], the authors demonstrated the use of THz pulse reflection to measure the topcoat thickness; the results were verified with microscopic imaging to be within measurement error. In [50], a similar measurement was carried out with a custom erosion platform to simulate topcoat erosion in the real operating environment.…”

Section: Thermal Barrier Coatingsmentioning

confidence: 90%

Non-Contact, Non-Destructive Testing in Various Industrial Sectors with Terahertz Technology

Tao

Fitzgerald

Wallace

2020

Sensors

180

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In this article, we survey various non-contact, non-destructive testing methods by way of terahertz (THz) spectroscopy and imaging designed for use in various industrial sectors. A brief overview of the working principles of THz spectroscopy and imaging is provided, followed by a survey of selected applications from three industries—the building and construction industry, the energy and power industry, and the manufacturing industry. Material characterization, thickness measurement, and defect/corrosion assessment are demonstrated through the examples presented. The article concludes with a discussion of novel spectroscopy and imaging devices and techniques that are expected to accelerate industry adoption of THz systems.

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“…Here, I j ′ is photoluminescence intensity in the case that the layer thickness at site j is d ′.

I_{j}^{'} (λ_{L}) = I_{j} (λ_{L}) e^{2 α (d_{j} - d^{'})}

As regards the measurement of topcoat thickness, a method using terahertz waves has been established and applied for TBC on gas turbine blades . For qualitative evaluation for TGO detection, there is no need to proceed precise measurement of thickness, and an electromagnetic coating thickness meter can be used as well.…”

Section: Topcoat Thickness Correctionmentioning

confidence: 99%

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

Fukuchi

Eto

Okada

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.

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Topcoat Thickness Measurement of Thermal Barrier Coating of Gas Turbine Blade Using Terahertz Wave

Cited by 38 publications

References 16 publications

Measurement of Refractive Index of Thermal Barrier Coating using Reflection of Terahertz Waves and Variable Aperture

Measurement of Refractive Index of Thermal Barrier Coating using Reflection of Terahertz Waves and Variable Aperture

Non-Contact, Non-Destructive Testing in Various Industrial Sectors with Terahertz Technology

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

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