Electrochemical Corrosion of the Stainless Steel 15-5PH and 17-4PH Passivation in Citric Acid

Abstract

Corrosion, the product of the oxidation-reduction reactions of a metallic material with its environment, generates in modern military aircraft manufactured mainly with titanium and stainless steels: deterioration, maintenance and even impact on safety. Within the methods of protection against corrosion are the coatings. The passivation is a conversion coating for stainless steels to increase the surface oxide layer that reduces the effects of corrosion. The objective of this work is to study the formation of a passive layer in steels 15-5 and 17-4PH using the electrochemical technique of potentiodynamic polarization curves (PPC), using as a passivating agent citric acid at a temperature of 25 ° C with a time of immersion of 30, 60 and 90 min and exposed in a sodium chloride medium. The passive layer was evaluated by the technique of X-ray photoelectron spectroscopy (XPS). The results obtained by PPC indicate a mixed activation control for both steels. Passive layers with corrosion current density (Icorr) of the order of 10-5mA / cm2 for 15-5PH while for the 17-4PH the passive layer presents Icorr 10-4mA / cm2 at a time immersion of 30min. The corrosion kinetics indicates a passivation mechanism for the 15-5PH steel while for the 17-4PH passivation-pseudopassivation, which indicates less stable passive layers for the latter steel. The XPS technique allows to define passive layers of up to 12.5nm, constituted by Cr2O3.