PITTING BEHAVIOR OF ALUMINUM ION-IMPLANTED WITH NITROGEN

Ion implantation of approximate to 2 at9% N into aluminum increased th e pitting potential in 0.1 M sodium chloride (NaCl) by an average of 0 .35 V. Surface analysis by x-ray photoelectron spectroscopy (XPS) show ed implanted nitrogen was present as several species: NH4+, NO or NH, (as a ligand), AIN, and weakly bound or interstitial nitrogen. With an odic polarization, there was an increase in the total amount of nitrog en in the near-surface region, a decrease in the relative amount of ni tride, and an increase in the relative amount of NO or NH3. These chan ges resulted from migration of implanted nitrogen from the substrate i nto the near-surface region with partial conversion of the AIN species to NO or NH3. It was suggested that the effect of implanted nitrogen on pitting behavior of aluminum is similar to that in nitrogen-contain ing stainless steels (SS), where nitrogen at the metal surface inhibit s the dissolution kinetics or aids the repassivation process in the pi t by forming NH4+ ions that buffer the pit electrolyte.