Quality evaluation for air plasma spray thermal barrier coatings with pulsed thermography

Pulsed thermography (PT) as a non-contact non-destructive evaluation (NDE) technique was employed to examine as-sprayed air plasma spray (APS) thermal barrier coatings (TBCs) for quality evaluation. Thickness and microstructural characteristics play a vital role in determining the quality. In this paper, PT logarithmic peak second-derivative method was adopted to measure the thickness of top coat. Time dependent thermal images were used to characterize the microstructure which was confirmed by scanning electron microscope (SEM). The results showed that there was relationship between the temperature distribution of the surface and microstructure change in TBCs. Temperature distribution in thermal images and measurement results of thickness were in fairly good agreement with the microstructure change. It can be concluded that it was possible to employ these NDE methods as quality evaluation for as-sprayed TBCs.