Pitting Behavior of Aluminum Ion Implanted with Nitrogen

Ion implantation of ≈ 2 at% N into aluminum increased the pitting potential in 0.1 M sodium chloride (NaCl) by an average of 0.35 V. Surface analysis by x-ray photoelectron spectroscopy (XPS) showed implanted nitrogen was present as several species: NH4+, NO or NH3 (as a ligand), AIN, and weakly bound or interstitial nitrogen. With anodic polarization, there was an increase in the total amount of nitrogen in the near-surface region, a decrease in the relative amount of nitride, and an increase in the relative amount of NO or NH3. These changes resulted from migration of implanted nitrogen from the substrate into 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-containing stainless steels (SS), where nitrogen at the metal surface inhibits the dissolution kinetics or aids the repassivation process in the pit by forming NH4+ ions that buffer the pit electrolyte.