NDI of interfaces in coating systems using digital interferometry

This paper describes a new application of two laser interferometry techniques to the non-destructive inspection (NDI) of coated surfaces. The purpose is to detect interfacial disbond between the coating and the substrate. Debonding is detected by properly exciting the surface of the object under inspection in such a way that the interference fringe pattern is modified rendering the disbond readily visible. The fringe patterns resulting from the associated images were captured using electronic speckle pattern interferometry (ESPI) and shearography. Image processing techniques are applied to enhance the detection and better definition of the debonded layer. Some results and discussions are presented to illustrate the applicability of these two optical techniques to thermal barrier coatings.