The effect of reactive element species and concentrations on the isothermal oxidation of β-NiAl coating fabricated by spark plasma sintering

The Hf, Zr, and Y doped β-NiAl coatings with controlled compositions were deposited onto Hastelloy substrates by spark plasma sintering with improved specimen protection method. The microstructures and oxidation behavior of β-NiAl coatings with different reactive element species and concentrations were investigated. It was shown that the 0.05 at.% Hf-doped coatings exhibited the best spallation resistance with the lowest scale growth rate, while the 0.05 at.% Zr-doped coatings had the worst spallation resistance. The 0.05 at.% Y-doped coatings exhibited the highest scale growth rate while maintaining a good spallation resistance. With an increase of the Y concentrations, the scale growth rate was reduced and the spallation resistance increased. The effect by doping Hf, Zr, Y, and by varying Y concentrations on the scale growth rate, the residual stress in the scale, the interface roughness, and the spallation resistance of the scales was discussed. Further analysis also pointed to the fact that the NiAl oxidation behavior was not only associated with the intrinsic properties of the reactive elements but also the chemical compositions of the substrates.