Effects of Dy on Transient Oxidation Behavior of EB-PVD β-NiAl Coatings at Elevated Temperatures

β-NiAl is a potential oxidation-resistant coating material to be operated at temperatures above 1 150 °C. In this paper, β-NiAl coatings with 0–0.5 at% Dy are prepared by electron beam physical vapor deposition (EB-PVD). Transient oxidation behavior of the coatings is investigated. At 1 200 °C, only stable α-Al2O3 phase is observed on the 0.05 at% doped coating, whereas the phase transformation from θ-Al2O3 to α-Al2O3 occurs in the 0.5 at% Dy doped coating during 1 h oxidation. At 1 100 °C, all the coatings reveal the transient transformation of θ-α in the early 15 min and the transformation for the 0.05 at% Dy doped coating is completed within 45 min, much earlier than that for the 0.5 at% Dy doped coating. Overdoping of Dy retards the transformation of θ-α. The undoped and overdoped coatings reveal the whisker structure of θ-Al2O3 even after 20 h oxidation at 1 100 °C, while the 0.05 at% Dy coating reveals typical granulated structure of α-Al2O3.