The Early Oxidation of Vacuum Heat Treated Nanostructured NiCoCrAlY Coatings

Conventional and vacuum heat treated nanostructured NiCrAlY coatings were applied using the high-velocity oxy-fuel (HVOF) process. The microstructural examinations of the as-received and nanostructured powders as well as their developed coatings were then analyzed using field emission scanning electron microscope (FESEM) equipped with energy-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. For investigating oxidation behavior, the coated specimens were subjected to isothermal oxidation testing at 1050 ºC up to 5 h under air atmosphere. The results indicated that the nanostructured NiCrAlY coating has a lower oxide growth rate compared with the conventional coating due to the controlling the diffusion of Al-ions by the higher volume fraction of grain boundaries in the coating structure.