Passivity breakdown of 316L stainless steel during potentiodynamic polarization in NaCl solution

• 316L stainless steel was potentiodynamically polarized in NaCl solution.
• ToF SIMS depth profiles of surface film on 316L stainless steel were analysed.
• Cl− ions penetrated and accumulated at the metal/film interface.
• Cl− ion intensities increased with the potential and charge density.
• The results support passivity breakdown at the metal/film interface.

Time-of-flight secondary ion mass spectroscopy (ToF SIMS) analysis was performed on 316L stainless steel polarized potentiodynamically up to different potentials in NaCl solution. The surface film thickness increased with the ending potential of the potentiodynamic polarization, when estimated by the oxygen ion depth profiles. The chloride ion intensities at the film/metal interface were correlated with the ending potentials during the potentiodynamic polarization and cumulative anodic charge densities that govern the pit initiation. The results and analysis support the passivity breakdown mechanisms considering the role of chloride ions at the metal/film interface, rather than at the film/solution interface.