Morphological evolution of thermal barrier coatings with equilibrium (EQ) and NiCoCrAlY bond coats during thermal cycling

Morphology features and failure mechanisms of thermal barrier coating (TBC) systems under thermal cycling are very complicated as it is influenced by many factors. It is known that the imperfections existing along the interface between top coat and bond coat play a significant part in determining TBC spallation features. In the present study, the bond coat surface was polished prior to top coat deposition to remove the imperfections. In this case, different failure characteristics occurred. In order to see whether bond coat compositions influence failure mechanisms on the polished surface, two TBC systems were investigated. One is with a newly developed EQ (equilibrium) bond coat, designated as TMBC-1; the other is a commercially available NiCoCrAlY bond coat.