Microelectrochemical Studies on the Influence of Cr and Mo on Nucleation Events of Pitting Corrosion

Abstract

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.

Corrosion and erosion–corrosion behaviour of activated combustion high-velocity air fuel sprayed Fe-based amorphous coatings in chloride-containing solutions

“…6d), and this trend is more obvious at high potentials. These microtransients in the current-time curve are formerly defined as metastable pits induced by local breakdown of the passive film [28,30]. Clearly, compared with that in the HVOF AMC, the microtransients in the AC-HVAF AMC are less abundant and smaller (Fig.…”

“…6a, c, and e). The background currents were usually retained in tens of nano-amperes (nA) with an acceptable variation [28,29]. Many current transients, which are characterised by a sharp rise followed by a slow decay in the current, can be detected on the 316L SS (Fig.…”

Pit growth in a Ni–Nb metallic glass compared with its crystalline counterpart

“…There exhibits nanoampere current transients and only a small number of current transients can be detected without transients overlapping. It has been recognized that metastable pitting behavior is closely associated with the current micro-transients [22,23]. When passive film breakdown occurs, there undergoes the initiation of metastable pits and the growth of pits, correspondingly, the transient heights vary from pA to mA and a larger transient height relates to further growth of metastable pits.…”

“…The transient heights in our potentiostatic measurements are mainly in the range of nA, reflecting an early stage of pit growth. A single transient in the current-time curves was characterized by a sharp rise followed by a slow decay in the current, which has been illustrated in many references [22,23]. Herein, the current transient is defined as follows: the transient height should be 3 times larger than the background noise; the life times (pit growth times plus repassivation times) of the transient should be longer than 10 s.…”

Local electrochemical investigation of single grains of polycrystalline Cu-16%Zn-8%Al alloy

“…Thus, the study and understanding of their activities (e.g., electrochemical) in a local point of view are needed. Local electrochemistry via electrochemical microcell has been, and continues to be, extensively employed in numerous fields such as corrosion studies, [14][15][16] batteries, 17-19 electrodeposition [20][21][22] and biological environments. [23][24][25] Besides local resolution, the use of electrochemical microcell has significant advantages compared to conventional one.…”