Effect of external stress on the high-temperature corrosion behavior of GH4169 alloy

The influence of the applied tensile elastic stresses on the corrosion behavior of GH4169 Ni-based superalloy, 75 wt% Na₂SO₄ + 25 wt% NaCl salt, 650 or 850 °C and 24 h, is investigated. The corrosion surface tend to exhibit serious peeling of the oxide scale and uneven morphology when stress applied, and the main corrosion products are identical with or without stress. With the increment in stress, the corrosion layer deepens, and more voids (or cracks) can be observed and their distribution as a function of stress and corrosion depth is further discussed with respect to linear density. Apart from the transverse extension of the corrosion area from grain boundaries to grain interior, the stress enhanced corrosion also demonstrates longitudinal extension along grain boundaries perpendicular to the stress direction into the alloy interior. Local mechanical properties in thermal etched region obtained by nanoindentation demonstrate that the alloy yields worse properties resulted from the negative effect of high stress and hot corrosion on internal microstructure. The mechanism of stress enhanced hot corrosion is further analyzed combining both experimental and molecular dynamics simulation results with respect to vacancies, distribution and bonding situation of atoms, and morphology and thickness of the transition layer.