Thermal shock failure mechanism of thermal barrier coating with thermal gradient across the coating

Thermal fatigue (thermal shock lifetime) of thermal barrier coatings is considered a key factor in performance of aero gas turbines and, thus, there is a need to simulate and perform thermal shock tests with near-actual operation in turbines. By using burner rig tests, for applying the simultaneous cooling from backside of the substrate along with cooling shocks at constant periods, the practical thermal shock conditions in aero turbines were designed and applied. In this research, two-layer conventional TBC with APS NiCoCrAlY bondcoat (BC) and APS YSZ topcoat (TC) were studied. The microstructure of coatings after 10 and 40 thermal shock cycles were evaluated for failure analysis. The interlamellar TGO with planar morpholohgy revealed detrimental effects on protection performance of BCs. Actually, the non-beneficial consumption of aluminum not only limits the oxidation protection of the bondcoat, but also the interlamellar APS-TGO intensified the harmful stresses at the TC/BC interface. The detrimental effects of Ratcheting at BC and TGO surfaces were higher than the stresses from growth of both interlamellar and interfacial TGOs at thermal shock performance of the coating.