Abstract
The topcoat thickness of thermal barrier coating (TBC) applied to metal substrates was measured using terahertz waves. The method is based on the difference between the arrival times of the waves reflected from the topcoat surface and from the interface between the topcoat and bondcoat. The refractive index of the topcoat, which is necessary to convert the time difference to thickness, is obtained from the frequency characteristics of the reflected waves. The method was applied to yttria stabilized zirconia (YSZ) specimens, and the obtained specimen thickness was in agreement with measurements using a contact thickness gauge. The method was also applied to a TBC specimen, and the obtained topcoat thickness was in agreement with microscope observation of the cross section of the specimen. The results showed that terahertz waves are useful for nondestructive measurement of the topcoat thickness.
