Abstract
The topcoat of the thermal barrier coating (TBC) applied to hot gas path parts of a gas turbine has a risk of delamination during operation. A nondestructive testing method based on active thermography has been developed to inspect for such delamination, using a laser beam as the heat source. With this technique, the laser beam is scanned over the surface to be inspected, and delamination is detected based on both the temperature peak attained when the delaminated part is heated, and a residual thermogram shaped with a trail behind it. This technique was applied to a disk-shaped TBC testpiece, in which simulated delamination was caused artificially. Inspection results with higher precision than conventional techniques were obtained, and it was shown that there are proper heating conditions for obtaining a high temperature peak and clear residual thermogram.
