Effect of environmental sulfur on the structure of alumina scales formed on Ni-base alloys

摘要: Short-term oxidation exposures of an alumina-scale forming γ′-Ni 3 Al-based model alloy in air and O 2  + 0.1%SO at 900 °C revealed that the presence sulfur can affect kinetic competition between θ α structural isomorphs Al . After 2 h exposure, metastable θ-Al growth predominated alone; whereas, a much larger percentage stable α-Al formed during This promotion establishment was due to enrichment on surface, which occurred even when samples were exposed low-temperature, pre-test position (∼150 °C), i.e., prior insertion into hot zone. It determined from XPS measurements mainly S 6+ valence state and, correspondingly, form NiSO 4 Cross-sectional scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) corroborated results by detecting ∼20 nm zone within surface region ∼90 nm oxygen-rich layer exposure. A systematic explanation for this intriguing observation promoting is provided perspective kinetics α. supported calculations complementary tests low p atmosphere.