Increasing Corrosion Resistance of Passivating Metals by Electrochemical Application of Local Nanosized Coatings

A method is proposed for increasing the resistance of passivated metals (in particular, stainless steels) to corrosion that is based on the use of the principle of cathodic alloying by electrolytic deposition of local palladium nanocoatings. It was found that the corrosion potential of AISI 321 steel samples in a 0.1 M NaCl solution electrochemically treated at a current density of 1 μA/cm2 and a frequency of 0.06 Hz in chloride-containing solutions with 0.1% Pd2+ shifts towards more positive values by almost 150 mV. It was also shown by scanning electron microscopy and Auger spectroscopy that, in the process of electrochemical polarization, subindividuals of a new phase (Pd) with sizes of the order of 5–80 nm are deposited on the surface of AISI 321 steel, the formation of which causes the potential improvement of the samples under study. It was found that the largest accumulation of subindividuals of the new phase (Pd) is observed in areas with artificially created surface defects (scratches).