Adsorption and diffusion of atomic oxygen and sulfur at pristine and doped Ni surfaces with implications for stress corrosion cracking

Highlights: • Selective grain boundary oxidation mechanisms of Ni-Cr and Ni-Al alloys and competitive oxidation/sulfidation processes are examined by employing density-functional-theory (DFT) calculations. • Cr and Mn exhibit the strongest binding energies to both oxygen and sulfur. • Results help explain the observed tendency of Ni-Cr alloys to exhibit internal sulfidation in environmental conditions that do not allow internal oxidation. - Abstract: A density-functional-theory modeling study of atomic oxygen/sulfur adsorption and diffusion at pristine and doped Ni(111) and (110) surfaces is presented. We find that oxygen and sulfur feature comparable adsorption energies over the same surface sites, however, the surface diffusion of sulfur is characterized by an activation barrier about one half that of oxygen. Calculations with different alloying elements at Ni surfaces show that Cr strongly enhances surface binding of both species in comparison to Al. These results in combination with previous modeling studies help explain the observed differences in selective grain boundary oxidation mechanisms of Ni-Cr and Ni-Al alloys.