Eddy Current Thermography with Adaptive Carrier Algorithm for Non-destructive Testing of Debonding Defects in Thermal Barrier Coatings

Interfacial defects can cause the premature failure of thermal barrier coatings (TBCs). An Eddy current thermography (ECT) method under the transmission mode in the heating phase is developed in this study to detect the artificial debonding defects in TBCs samples. When ECT is used, the temperature distribution of specimen surface is uneven on account of geometric heating effect, skin effect, edge effect and abnormal emissivity. Among them, the influence of the surface emissivity is the smallest, because the background noise is subtracted before the thermal images are processed. The uneven temperature distribution shields the weak thermal response characteristics of the defects and interferes with the identification of the defects. Adaptive carrier algorithms are established as post-processing algorithms to resolve this problem. The feasibility and validity of the developed methods are verified by simulation and validation tests using TBCs samples with a 2 mm artificial debonding defect and a 0.5 mm blind-hole defect.