Evaluation of coating thickness by thermal wave imaging: A comparative study of pulsed and lock-in infrared thermography - Part II: Experimental investigation

In this work, we focused on the experimental arrangement of thermal wave imaging (TWI) methods for the quantitative evaluation of non-uniform topcoat thickness of thermal barrier coatings (TBCs). Two TWI techniques, pulsed thermography (PT) and lock-in thermography (LIT) were implemented on plasma sprayed TBCs with varied topcoat ranging from 0.1 mm to 0.6 mm. In PT, a short and high energy light pulse was applied on a sample surface whereas, in LIT, the sample surface was excited by a sinusoidal heat flux at several modulation frequencies ranging from 2 Hz down to 0.01 Hz. Furthermore, an infrared camera was used to capture the surface temperature of a thermal wave that propagated into the sample and the effect of the applied heat flux in both techniques was analyzed by Fourier transform. The results of PT and LIT techniques were compared based on the evaluated accuracy of each technique. Finally, it was concluded that both the techniques could be applied to the fast and accurate evaluation of TBCs thickness.