Time‐Dependent Oxidation and Scale Evolution of a Wrought Co/Ni‐Based Superalloy

Understanding how protective oxide scales evolve over time is necessary for improving the long term resistance of superalloys. This work investigates the time‐dependent oxidation behavior of an ingot‐processable Co/Ni‐based superalloy oxidized in air at 800°C for 20, 100, and 1000 h. Mass‐gain and white‐light interferometry measurements quantified oxidation kinetics, surface roughness, and spallation, while high‐resolution STEM‐EDX characterized oxide morphology and nanoscale elemental partitioning. Atom probe tomography captured the key transition regions between the chromia and alumina scales, and X‐ray diffraction was used to identify a gradual transition from (Ni, Co)‐spinel phases to a compact, chromia and alumina‐rich scale. The oxidation rate evolved with parabolic behavior over time, consistent with diffusion‐controlled growth once a continuous CrO/AlO scale formed. These observations help link kinetics, structure and chemistry, showing how an originally porous spinel layer transforms into a dense, adherent chromia + alumina scale that provides long‐term protection in wrought Co/Ni‐based superalloys.