Quantitative Infrared Thermographic Nondestructive Testing of Thermal Barrier Coatings

In power production and aviation, thermal barrier coatings are widely used to improve performance of turbine blades. During deposition of plasma-sprayed coatings some discontinuities might appear to affect the ability of turbine blades to withstand high temperatures and protect primary parts. Thermal testing systems are increasingly used in the testing of thermal barrier coatings due to large surface, rapid and non-contact testing capabilities. In this work, the features of the thermal nondestructive testing (NDT) of thermal barrier coatings are summarized and the current problems, such as residual heating, spurious reflections and coating transparency, are addressed. The experimental data are presented along with advanced processing results obtained by using pulse phase thermography and principal component analysis. The comparison of the processing techniques is done in the detection of delaminations between the coating and substrate. The problem of the discrimination between the coating thickness variations and delaminations, as well as the sensitivity of thermal NDT, is discussed.