Effects of thermal and mechanical properties of Hf and Ta-doped NiCoCrAlY bonding layer alloys on the high-temperature oxidation resistance of thermal barrier coatings

The MCrAlY bonding layer alloy was prepared by vacuum melting, and the alloy composition was NiCoCrAlY and NiCoCrAlYHfTa. The high-temperature cyclic oxidation experiment was carried out in air at 1050 degrees C until it failed. The results show that Hf and Ta have a significant influence on the oxidation resistance of the alloy. The doped specimens have longer oxidation lifetimes compared to the undoped samples. The study also found that the Hf would diffuse out and combine with O to form HfO2 in the thermally grown oxide (TGO) layer, which would improve the adhesion and reduce the wrinkles of the oxide layer. Ta in the doped specimens hinders the diffusion of Al and reduces the oxidation rate, while improving the thermal mismatch. Therefore, the specimens doped with both Hf and Ta have the highest oxidation lifetimes, though the oxidation lifetime was 10 times longer than that of the undoped specimens. It is indicated that the doping of Hf and Ta is an important method to improve the oxidation lifetime of thermal barrier coatings (TBCs).