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

Nucleation events of pitting pitting corrosion for Fr-Cr and Fe-Cr-Mo alloy series, enabling a single-parameter variation in the alloy composition, wa s studied with microelectrochemistry. The main effect of Cr and Mo addition s in Fe-Cr alloys on the microtransient activity in NaCl solution is a decr ease of the transient heights. Asa consequence, fewer transients are detect ed for alloys with higher Cr and Mo contents. However, it cannot be exclude d that a high number of small nucleation events takes place on these alloys , leading to undetectable transients. A single transient analysis reveals t hat Cr and Mo lead to an earlier start of repassivation, but they do nor ac celerate the repassivation kinetics of the small nucleation events detected by microelectrochemistry. The higher the Cr and Mo content in the alloy, t he faster the decrease in the microtransient activity as a function rime. T he type of transients does nor essentially change as a function of time. He nce, only the nucleation activity but not the repassivation behavior are in fluenced by aging. (C) 2000 The Electrochemical Society. S0013-4651(99)03-1 23-7. All rights reserved.