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Wednesday, 18 September 2019
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Raw materials & technologies, Production and testing

Measuring the topcoat thickness of thermal barrier coating of gas turbine blade

Wednesday, 16 July 2014

The topcoat thickness of thermal barrier coating (TBC) applied to a gas turbine blade was measured using terahertz waves.

The topcoat thickness was obtained from the refractive index and the time separation between the reflected waves Source: fotohansel-Fotolia.com

The topcoat thickness was obtained from the refractive index and the time separation between the reflected waves Source: fotohansel-Fotolia.com

The Japanese researchers obtained the refractive index of the topcoat by frequency analysis of the waves reflected from the topcoat surface and the interface between the topcoat and bondcoat. They considered the roughness of the topcoat surface 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.

Terahertz waves are effective for nondestructive measurement

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.

The study is published in: Electrical Engineering in Japan, Volume 189, Issue 1, pages 1-8, October 2014.

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