Isothermal and cyclic oxidation behaviour of Ni-25Cr-10Al-0.5Y coating deposited by AIP and magnetron sputtering at 1323 K

Two kinds of NiCrAlY coatings (Ni-25Cr-10Al-0.5Y) were prepared on K417 superalloy using ion plating (AIP) and magnetron sputtering (MS), respectively. The isothermal and cyclic oxidation behaviors of the two NiCrAlY coatings were evaluated at 1323 K in stair air. The results revealed that the nanocrystalline NiCrAlY coating exhibited better isothermal and cyclic oxidation resistance compared to the conventional NiCrAlY at 1323 K. The mass gain and parabolic rate constant K_p of the nanocrystalline NiCrAlY coating were 45.2% and 44.7% lower than those of the conventional NiCrAlY coating, respectively. During cyclic oxidation, the tendency for spallation of the oxide scale was evidently decreased by nanocrystallization due to the formation of a continuous, compact, adherent, and slow-growing exclusive α-Al₂O₃ scale. The mechanism responsible for the improvement of the nanocrystalline NiCrAlY coating was discussed.