Thermal cycling of EB-PVD/NiCoCrAlYHf thermal barrier coatings

Abstract

Microstructural evolution, interfacial toughness and damage initiation of Y₂O₃ partially stabilised ZrO₂ thermal barrier coatings (TBCs), which have been deposited by electro-beam physical vapour deposition on NiCoCrAlYHf coated superalloy substrate, were studied as a function of thermal cycles at 1150°C. Interfacial toughness of TBC systems was measured by indentation method. The results show that bond coat (BC) is composed of β-(Ni,Co)Al and γ solid solution at the initial cycles. β phase is completely transformed into γ at 185 cycles. The thermally grown oxide (TGO), which consists of an Al₂O₃ layer and a thin spinel layer, has a high growth rate and grows irregularly because of preferential oxidation of Hf rich phases in the BC. This TBC system has a larger critical TGO thickness for failure. The thickness of TGO at planar place is approximately 10 μm when the TBCs spalled. Interfacial toughness decreases substantially at the initial stage of thermal cycling.