Abstract: The presence of excess Ta in high-temperature protective coatings can compromise the integrity of the Al₂O₃ scale on the surface, which has a negative impact on the oxidation behavior and reduces the service life. The effects of oxygen doping on the isothermal oxidation of three sputtered nanocrystalline coatings were investigated at 1100 °C. The results indicated that oxygen doping inhibited the diffusion of Ta from the coating to the oxide scale, which was primarily attributed to the preferential oxidation of the Al in the coating. However, excess oxygen doping decreased the amount of Al available for the formation of the Al₂O₃ scale on the coating, thus reducing the inhibitory effect on Ta oxidation. Moreover, doping with excess O caused spalling of the oxide scale. Therefore, the right balance in O doping is crucial for suppressing Ta oxidation while maintaining the integrity of the oxide scale.

Key words: High-temperature oxidation, Oxygen doping, Nanocrystalline coating, Ta-rich phase, Residual stress