Novel concept of functional oxide coatings providing enhanced oxidation resistance to Ni-based superalloys

Graphical abstract: - Highlights: • New concept for providing extended oxidation resistance to Ni-based superalloys. • Oxygen-defective nanostructured oxide coatings reduce the oxygen partial pressure at the substrate interface. • Pre-oxidation of the substrate during annealing with the formation of alpha-alumina. • Growth of CeAlO₃ perovskite enhancing the adherence of the ceria top coat. • Microstructural stability of the coating system with no SRZ formation upon exposure. - Abstract: Aluminide-coated Ni-based superalloys are prone to microstructural instabilities during long-term exposure at high temperature with the growth of a secondary reaction zone (SRZ) detrimental from a mechanical viewpoint. This has been since overcome by the use of thermodynamically stable coatings (γ-Ni/γ′-Ni₃Al). However, additions of Pt and Hf are required to provide the formation of an exclusive α-Al₂O₃ scale and improved oxidation resistance in cyclic and isothermal regimes. The present work proposes a new coating system that relies on the use of a superficial nanostructured functional oxide providing the establishment of a stable alumina while avoiding SRZ formation. Tailored oxygen-defective and multi-cracked coatings were designed for 2nd generation Ni-based superalloys and generated by electrosynthesis using a water-based solution. Cyclic oxidation tests were carried out at 1100 °C in air and the oxidation properties and the microstructural stability of the coating system were demonstrated