Microstructural Characterisations and High Temperature Oxidation Studies of Nanostructured Co–Al Coatings Deposited on Superalloy

The microstructural characterizations and high temperature oxidation of magnetron sputtered Co–Al coatings on the superalloy substrate have been studied in the present work. FE-SEM/EDS and XRD were used to characterize the morphology and formation of different phases in the coatings, respectively. Thermo gravimetric technique was used to investigate the oxidation of the coatings, in air at 900°C. The growth kinetics of the oxide layers was predicted using weight change of the coated sample measured during oxidation. It was found that the oxidation rate of Co–Al coated superalloy was lower than that uncoated superalloy due to the formation of continuous dense, adherent and protective oxide scale such as CoO, Al2O3, Cr2O3, CoCr2O4, and CoAl2O4 over the surface of the coatings exposed to air at high temperature oxidation, 900°C. The microstructural features and phases of the oxidised coatings were used to elucidate the mechanism of high temperature oxidation.