Oxidation behavior of NiCrAlY coatings prepared by arc ion plating using various substrate biases: Effects of chemical composition and thickness of the coatings

NiCrAlY coatings with various Cr and Al contents were prepared on Ni-based superalloy K438G from a single NiCrAlY target by adjusting the substrate bias during high vacuum arc ion plating. The oxidation behavior of the coatings follows the oxide map laws proposed by Wallwork and Hed rather than the guide line based on Cr/Al = 4. As the coatings degrade due to Al depletion, formation of Cr2O3 scales beneath the external α-Al2O3 scales was observed. The mechanism for the oxidation of Ni-Cr-Al alloys is discussed.