High-temperature oxidation and hot corrosion of Ni-based single crystal superalloy in the incubation stage

Early stages of high-temperature oxidation and hot corrosion of Ni-based single-crystal superalloy were studied at 900 degrees C by introducing sulfate coating. Detailed elemental and microstructural analysis revealed layered surface oxide, atomic diffusion, faceted Al-rich precipitation, and gamma '-phase depletion, together with grain coarsening and reorientation in the near-surface region. Undulated surface, multiple layered outer oxide scale, inner CrS scale (solely localized in gamma-matrix), and an additional gamma '-depleted region without crystal reorientation were observed in hot corrosion rather than in high-temperature oxidation. The corrosion behavior is discussed in terms of atomic diffusion and oxide growth. The impact of sulfate-coating is elucidated.