Wear-Corrosion Comparisons of Passivating vs Nonpassivating Alloys in Aerated 3.5% Aqueous Solutions of Sodium Chloride Available to Purchase

Metals and alloys that have the capability of forming passive films provide good corrosion resistance in many environments. Under localized wear-corrosion conditions, however, they undergo degradation, which greatly exceeds the metal loss expected from wear alone. Under such wear-corrosion conditions, potentiodynamic polarization curves determined in a 3.5 wt% aqueous solution of sodium chloride (NaCl) were displaced in the direction of more active potentials and much higher currents. Corrosion currents were increased by 2 or 3 orders of magnitude, although this is a qualitative estimate. Aluminum is an exception because, although it readily forms a protective oxide film in many environments, its wear-corrosion behavior in the present instance substantially corresponded to that of nonpassivating alloys. This behavior of aluminum is related to the instability of its oxide film in aqueous environments containing chloride ions and a resulting propensity for pitting. Nonpassivating alloys showed quite minor differences in the polarization curves for corrosion-only and wear-corrosion conditions under the experimental conditions used.