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Topcoat Thickness Measurement of Thermal Barrier Coating of Gas Turbine Blade Using Terahertz Wave
Author(s) -
Fukuchi Tetsuo,
Fuse Norikazu,
Okada Mitsutoshi,
Ozeki Takayuki,
Fujii Tomoharu,
Mizuno Maya,
Fukunaga Kaori
Publication year - 2014
Publication title -
electrical engineering in japan
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.136
H-Index - 28
eISSN - 1520-6416
pISSN - 0424-7760
DOI - 10.1002/eej.22624
Subject(s) - materials science , thermal barrier coating , refractive index , optics , surface roughness , composite material , turbine blade , terahertz radiation , coating , turbine , mechanical engineering , optoelectronics , engineering , physics
SUMMARY The topcoat thickness of thermal barrier coating (TBC) applied to a gas turbine blade was measured using terahertz waves. The refractive index of the topcoat was obtained by frequency analysis of the waves reflected from the topcoat surface and the interface between the topcoat and bondcoat. The surface roughness of the topcoat surface was considered for improving the accuracy of the refractive index calculation. The topcoat thickness was obtained from the refractive index and the time separation between the reflected waves. The validity of the method was confirmed using a TBC sample with variable topcoat thickness, and the obtained topcoat thickness was in agreement with measurement results using a contact thickness gauge. Error analysis showed that the measurement error of the topcoat thickness was about 3%. The method was applied to a gas turbine blade with TBC, and the measured topcoat thickness agreed with microscope observation results of the cross section to within 6%, which was within the range of measurement error. The effect of curvature of the gas turbine blade surface did not result in significant measurement error. The results showed that terahertz waves are effective for nondestructive measurement of the topcoat thickness of TBC applied to gas turbine blades.