The oxidation behavior of a nanostructured CoNiCrA1Y bond coat dispersed nano-sized alumina particles was compared to that of a conventional coarse-grained CoNiCrA1Y bond coat. It was found that after a 1000ºC/24 h oxidation a protective alumina layer was developed on the nanostructured coating, whereas a mixed and less protective oxide layer was observed on the conventional coating. Correspondingly, spallation of the oxide layer was not observed with the nanostructured coating but did occur with the conventional coating. The improvement in oxidation behavior observed in the nanostructured coating was suggested to be due to its fine-grained structure, which provides rapid pathways (grain boundaries) for A1 diffusion to form a protective scale of pure alumina. Furthermore, the dispersion of the nano-sized alumina particles was effective in suppressing grain growth and in promoting the rapid formation of a protective alumina scale and thus significantly improving the oxidation resistance of the bond coat.

Thermal barrier coating (TBC) systems protect turbine blades against high-temperature corrosion and oxidation. They consist of a metal bond coat (MCrAIY, M = Ni, Co) and a ceramic top layer (ZrO2/Y2O3). In this work the oxidation behavior of conventional and nanostructured HVOF NiCrAIY coatings has been compared. Commercially available NiCrAIY powder was mechanically cryomilled and HVOF sprayed on a nickel alloy foil to form a nanocrystalline coating. Free-standing bodies of conventional and nanostructured HVOF NiCrAIY coatings were oxidized at a 1000ºC for different time periods in order to form the thermally grown oxide (TGO) layer. The experimants show an improvement in oxidation resistance in the nanostructured coating when compared to that of the conventional one. This behavior is a result of the formation of a continuous AI2O3 layer on the top surface of the nanostructured HVOF NiCrAIY coating. This layer protects the coating from further oxide protrusions present in the conventional coating.