Interfacial fracture behavior of a thermal barrier coating system under four-point bend loading

A newly designed thermal barrier coating (TBC) system, consisting of a detonation-sprayed top coat (TC) and a high velocity oxygen fuel sprayed NiCrAlY bond coat (BC), was used for four-point bend tests in air at room temperature. It was found that cracks generated in the TC layer penetrated through the TC/BC interface in the as-sprayed coatings, while they deflected into the TC/BC interface in the oxidized coatings (1100 °C, 100 h). The stress in the thermally grown oxide (TGO) was measured by the shift of the photo-stimulated luminescence spectrum from Cr3+ incorporated into the TGO. The fracture behavior of the TBC system was discussed on the basis of the change of the stress state and microstructure around the TC/BC interface caused by high temperature oxidation.