Exact localization of debonding defects in thermal barrier coatings

The existence of debonding defects in thermal barrier coatings is one of the key problems that result in the premature failure of blades. In this paper, a line heat-source scanning thermography method for locating the defects in blades with unpainted thermal barrier coatings is developed. Compared with planar specimens, uneven temperature distribution in the blade surface is an unavoidable problem when using a line heat source because the complex shape of the blade makes the heat absorbed nonuniform. This unevenness shields the thermal response features of the defects and disturbs the identification of the defects. The developed window-averaged carrier postprocessing algorithm can solve this problem to achieve nondestructive testing of debondings. Apart from inspecting defects, a projected infrared fringe method is developed to reconstruct the three-dimensional morphology of the blade surface by analyzing the relationship between the temperature fringes modulated by surface morphology and surface height. In addition, a new manufacturing technique of artificial debondings is proposed by filling a groove with ceramic hollow particles. Nondestructive testing experiments on a blade with artificial debondings show that the methods and technique developed here have the potential to locate the three-dimensional spatial position of debondings in a scanning process.