Effect of powder structure on microstructure of the oxide scales formed on cold-sprayed NiCrAlY coatings

Commercially available, gas-atomized NiCrAlY powder was milled in Ar atmosphere to prepare nanostructured powder. The NiCrAlY coatings in the conventional microstructure and the nanostructure were subsequently deposited by cold spraying using the as-atomized powder and milled powder. The influence of the powder structure on the microstructure of cold-sprayed coating was investigated. It was found that dense NiCrAlY coatings can be cold-sprayed using two powders. Isothermal oxidation was performed at 1000°C in air for up to 500 hours. The results showed that the growth rate of the oxide on the nanostructured NiCrAlY coating was almost comparable to that of the conventional NiCrAlY coating. A uniform Al₂O₃ layer was formed on the surface of the nanostructured coating surface. Moreover, a dual-subscale oxide was formed on conventional coating composing of an inner Al₂O ₃ oxide and an external mixed oxide.