Parallel Imaging of Thickness Variations and Disbonding of Thermal Barrier Coatings by Time-Resolved Infrared Radiometry (TRIR)

Pulsed photothermal radiometry has been shown to be a useful thermally-based nondestructive evaluation technique for various thin films and layered specimens [1,2]. In this method the time development of the surface temperature is studied for both heating and cooling, during and after the application of a step heating pulse of duration, T. In this paper, we show that the method gives quantitative information about layered materials including measurement of coating thickness and the detection and characterization of disbonding between layers. Since all times are monitored, it is not necessary to know the thickness of the coating provided the heating pulse is set longer than the thermal transit time of the coating. As a result, both coating thickness and the integrity of the coating-substrate bond can be determined simultaneously.