Defect assessment in gas turbine blade coatings using non-contact thermography

Thermal Barrier Coatings (TBCs) are inevitably applied on combustion chamber liners, gas turbine buckets, gas turbine vanes, etc. for lowering the metal temperature. They play a major role in enhancing the life of components exposed to higher temperature during operation of gas turbines. Performance of TBCs is dependent on the coating procedure, type of coating material and bond strength between bond coat layer and TBCs. Amongst various techniques which are available for quantitative and quality assessment of the TBCs, non-contact thermography is one of the most promising techniques. The present work deals with simulating thermal cycling on coatings using Finite Element Methods (FEM) for understanding possible locations of residual stress development within the coatings due to thermal cycling. Subsequently, experimental thermal cycling of TBCs and their sequential study of defect formation using non-contact thermography are reported. Comparison of experimental studies and FEM results showed good correlation. Further, microstructural characterization of samples exposed to thermal cycling confirmed that the defects observed during thermography are due to delamination. These studies will be useful to predict defect formation in TBCs during operation of the gas turbine components.