Damage Assessment in Thermal Barrier Coatings Using Thermal Wave Imaging Technique

Thermal wave imaging (TWI) was used to investigate damage processes in electron beam-physical vapor deposited (EB-PVD) ZrO2-8% wt.%Y2O3 thermal barrier coatings (TBCs) during thermal cycling. TWI is a non-destructive and non-contact evaluation method. Small interfacial decohesions from manufacturing were captured by TWI after only two thermal cycles, but the decohesions did not grow with thermal cycling. No delamination was found in TBC specimens until failure, while surface temperature profiles of TWI indicated increases of thermal wave signal amplitude with thermal cycles. Local interfacial damage formed due to high thermal residual stresses during thermal cycling and induced thermal contact resistance in the TBCs, which resulted in the increases of thermal wave signal amplitude. The results of TWI confirmed the progressive damage evolution in TBCs observed by microscopy. The buckling propagation and spallation process were monitored by TWI.