Failure mechanism of gradient thermal barrier coating subjected to thermal cycling

Thermal cycling behavior of a new type gradient thermal barrier coating produced by electron beam physical vapor deposition (EB-PVD) was studied and its failure mechanism also analyzed. It is found that an α-Al₂O₃ scale was formed between NiCoCrAlY bond coat and gradient transition layer in the coating, which results from the selective oxidation of the NiCoCrAlY bond coat and Ni₃Al thin film on the surface of the bond coat. As the thermal cycling test went on, the thickness of the Al₂O₃ scale increased and under the action of thermal stress in the oxide scale, failure of the gradient coating eventually took place by cracking within the Al₂O₃ scale.