Temperature Effect on Early Oxidation Behavior of NiCoCrAlY Coatings: Microstructure and Phase Transformation

Initial oxidation behavior of NiCoCrAlY coating prepared by arc-ion plating has been studied in air at 900, 1000 and 1100 °C. The results showed that phase transformation from transient θ-Al2O3 to α-Al2O3 was highly related to the temperature and oxidation time. The oxide scale in the initial stage was mainly composed of θ-Al2O3 at 900 °C. Instead, more amount of α-Al2O3 emerged out with increasing oxidation temperature. The elemental distribution after oxidation confirmed that faster chromium diffusion to the oxide scale played an important role in the speedy transformation from θ-Al2O3 to α-Al2O3. Y segregation at scale/coating interface resulted in less cavity formation and hence improved the oxide scale adherence.