High resolution characterization of sulfur-assisted degradation in alloy 800

Environmentally assisted cracking (EAC) initiation tests were carried out by subjecting Alloy 800 tensile specimens to 0.55 mol/kg SO42− solution, pH280°C 3, at 280 °C using slow rise-time cyclic loading and in-situ crack detection. EAC, intergranular corrosion (IGC), and pitting were observed. Transmission electron microscopy analysis revealed Ti- and Cr-rich oxides in cracks, and sulfur incorporated in oxide(s) or as sulfide compound(s). This oxide/sulfide film is likely impaired, producing a slip dissolution-type EAC mechanism. For pitting, only a nano-scale sulfur layer was identified at pit-metal interfaces. This high surface coverage of adsorbed sulfur limited oxide nucleation and accelerated metal dissolution.