Thermal cycling of EB-PVD/NiCoCrAlYHf thermal barrier coatings

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 degrees C. Interfacial toughness of TBC systems was measured by indentation method. The results show that bond coat (BC) is composed of beta-(Ni,Co)Al and gamma solid solution at the initial cycles. beta phase is completely transformed into gamma 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 mu m when the TBCs spalled. Interfacial toughness decreases substantially at the initial stage of thermal cycling.