Mechanistic investigation into the role of aluminum diffusion in the oxidation behavior of cryomilled NiCrAlY bond coat

High temperature oxidation behavior of the bond coat layer is a critical factor that controls the failure mechanism of thermal barrier coatings (TBCs). Previous work reveald that TBCs with cryomilled NiCrAlY bond coats exhibited an improved oxidation behavior compared to equivalent TBCs with conventional bond coats. The cryomilled NiCrAlY bond coats contributed to a slower growth rate of thermally grown oxides (TGO) with a final thinner thickness and enhanced homogeneity in TGO composition. To better understand the improved oxidation behavior, a mechanistic investigation based on diffusion theory and quantum mechanics is performed to elucidate the role of aluminum diffusion in the oxidation behavior and how the microstructural features of the cryomilled NiCrAlY bond coats, i e, the creation of a thermally stable, uniform distribution of ultrafine Al-rich oxide dispersoids, affect the diffusion kinetics of Al and the migration of free electrons. It is revealed that these Al-rich oxide dispersoids result in a uniform diffusion of Al and slow migration of free electrons within the NiCrAlY bond coat, consequently leading to the improved oxidation behavior.