Oxidation behavior of NiCoCrAlY coatings deposited by double-Glow plasma alloying

Highlights: • The NiCoCrAlY coatings were deposited on Inconel 718 alloy by a novel method called double-glow plasma alloying (DG). • Dense homogeneous NiCoCrAlY coatings with fine microstructure (approximately 500 nm in size) were obtained. • The result of the scratch test showed that excellent plasticity, toughness and good adhesion to substrate was achieved. • The coating oxidation mechanism was hypothesized based on the concentration profiles and oxidation kinetics. The NiCoCrAlY coatings were deposited on the Inconel 718 alloy substrates by a novel method called double-glow plasma alloying (DG). The phases and microstructure of the coatings were investigated by X-ray diffraction analysis while their chemical composition was analyzed using scanning electron microscopy. The morphology of the NiCoCrAlY coatings was typical of coatings formed by DG, with their structure consisting of uniform submicron-sized grains. Further, the coatings showed high adhesion strength (critical load >46 N). In addition, the oxidation characteristics of the coatings and the substrate were examined at three different temperatures (850, 950, and 1050 °C) using a muffle furnace. The coatings showed a lower oxidation rate, which was approximately one-tenth of that of the substrate. Even after oxidation for 100 h, the Al₂O₃ phase was the primary phase in the surface coating (850 °C), with the thickness of the oxide film increasing to 0.65 μm at 950 °C. When the temperature was increased beyond 1050 °C, the elemental Al and Ni were consumed in the formation of the oxide scale, which underwent spallation at several locations. The oxidation products of Cr, which were produced in large amounts and had a prism-like structure, controlled the subsequent oxidation behavior at the surface.