Effect of vacuum annealing on initial oxidation behavior and alumina transition of NiCoCrAlY coatings

NiCoCrAlY coatings were prepared using arc-ion-plating on a second generation Ni-base single crystal superalloy, in which some of them underwent vacuum annealing treatment while the others did not. Early oxidation behavior of the two coatings, including phase pattern and morphological evolution of oxide scale during the short term oxidation, has been studied in static air at 1000 °C. The results showed that the vacuum treatment was not only efficient in inhibiting the cavity formation, but also significantly increased the adhesion between oxide scale and coating. Compared with those without vacuum annealing, the NiCoCrAlY coatings with vacuum treatment exhibited slower phase transformation from metastable θ-Al2O3 to stable α-Al2O3. Initial oxidation behavior of as-received and annealed coatings, especially the effect of vacuum annealing on morphology evolution and adhesion of oxide scale, are particularly discussed.