A study on the multiple stages of oxidation kinetics in a single crystal nickel-based superalloy

Abstract Two stages of mass gain kinetics were observed in a single crystal nickel-based superalloy that corresponds to the growth of various layers. However, only one stage appeared in the intermediate layer, while the inner Al2O3 and outer NiO layers exhibited two stages. This abnormal kinetics behavior was attributed to the undermining effect of simple tetragonal structure Ta2O5 phases on the continuous hexagonal structure Al2O3. Furthermore, the Cr concentration gradient in the γ´-free zone transformed from depletion to enrichment with increase of exposure time, while Ni displayed a converse trend. This phenomenon further promoted the different growth kinetics of various layers.