Inter-diffusion and oxidation behavior in electron-beam evaporated NiAl coatings

In this work, by electron-beam physical vapour deposition (EB-PVD), grit blasting and vacuum heat treatment, a two-phase [NiAl+Ni₃Al] coating was fabricated. Rather than the column grain boundaries, the small voids formed on the surface of the columnar grains serve as the fast diffusion route for chromium of the substrate. In order to evaluate the oxidation resistance of this coating, an isothermal oxidation test at 1100 °C in air was conducted. The oxidation resistance of the as-coated specimen was improved approximately twice that for a substrate without coating.