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.