Degradation behavior of magnetron sputtered Cr/CoAlTa/YSZ nanostructured coating on nickel super-alloy

To improve Superni-718's oxidation resistance at high temperatures, a nanostructured Cr/CoAlTa/YSZ multilayer coating was deposited by magnetron sputtering. The effects of substrate deposition temperatures (100°C, 150°C, and 200°C) on the coating microstructure, phase stability, and oxidation kinetics were systematically evaluated under cyclic oxidation for 100 cycles at 900°C in air. Post-exposure characterization examined the development of thermally grown oxide (TGO), phase constitution, and microstructural degradation mechanisms. Oxidation behavior was governed by the formation of an adherent, continuous Cr 2 O 3 scale, which was strengthened by spinel oxides that effectively prevented oxygen infiltration and metal-ion transport. Yttria-stabilized zirconia (YSZ) helped preserve microstructural integrity by limiting phase change and crack development during heat cycling. In coatings deposited at 200°C, a finer nanostructure, lower defect density, and better oxidation resistance were associated with a dense, slow-growing TGO layer with improved adhesion. Increased adatom mobility during deposition likely contributed to improved coating densification and reduced defect density. The observed oxidation behavior is consistent with reduced oxygen transport through the coating and the beneficial influence of reactive elements reported in previous studies.