Microelectrochemical studies on the influence of Cr and Mo on nucleation events of pitting corrosion

Nucleation events of pitting corrosion for Fe-Cr and Fe-Cr-Mo alloy series, enabling a single-parameter variation in the alloy composition, was studied with microelectrochemistry. The main effect of Cr and Mo additions in Fe-Cr alloys on the microtransient activity in NaCl solution is a decrease of the transient heights. As a consequence, fewer transients are detected for alloys with higher Cr and Mo contents. However, it cannot be excluded that a high number of small nucleation events takes place on these alloys, leading to undetectable transients. A single transient analysis reveals that Cr and Mo lead to an earlier start of repassivation, but they do not accelerate the repassivation kinetics of the small nucleation events detected by microelectrochemistry. The higher the Cr and Mo content in the alloy, the faster the decrease in the microtransient activity as a function time. The type of transients does not essentially change as a function of time. Hence, only the nucleation activity but not the repassivation behavior are influenced by aging.