Film evolution and growth mechanism of a Ni-based superalloy in the two models at the different temperatures

Two types of oxidation behavior were observed in a Ni-based superalloy that corresponds to a single stage of parabolic law for Type I and multiple subparabolic laws for Type II. In the type I model, the Cr content was matched in the external oxidation of the Cr2O3 layer, thereby favoring the formation of a continuous and compact Cr2O3 layer. Since Ni cannot readily diffuse through Cr2O3, it tends to remain in the alloy leading to the Ni is enriched at the metal/oxide interface. Moreover, the enrichment of Ni increased with the increase of exposure times. In comparison, the depletion degree of chromium in the gamma'-free zone fails to maintain the growth of Cr2O3, NiO to precipitate in the Cr2O3 layer and increasing the formation of voids in the surface film. Beyond the microstructural results, we explore the oxidation mechanism in the two types of oxidation behavior.