Abstract
Understanding the mechanistic relationship between the environment, microstructure, and local kinetics of atmospheric corrosion damage remains a central challenge. To address this challenge, this study used laboratory-based X-ray tomography to directly observe attack in-operando over an extended period, enabling insights into the evolving growth kinetics and morphology of individual pits over months of exposure. Damage progression associated with nine pits in a 99.9% pure aluminum wire exposed to chloride salts in humid air was characterized. Most pits grew at a nominally linear rate up until pit death, which occurred within 12–24 h of nucleation. Exceptions to this were observed, with three pits exhibiting bimodal growth kinetics and growing for 40 or more hours. This was explained by secondary droplets that formed near the pits, increasing the cathode area. A corrosion-driven drying mechanism likely contributed to pit death in both cases. Pits first grew into the material followed by lateral expansion.
Highlights
Predicting the kinetics and morphology of the localized damage produced during corrosion of passive alloys is a foundational challenge
The growth kinetics of atmospheric corrosion damage was characterized using in-situ XCT observations of a 1.02 mm diameter Al wire having a nominal purity of 99.9% Al, see Supplementary Fig. 1 for a schematic
Electron backscatter diffraction (EBSD) data, see these pits was not captured by the scan schedule used for this
Summary
Predicting the kinetics and morphology of the localized damage produced during corrosion of passive alloys is a foundational challenge This is especially the case for atmospheric corrosion, wherein the complex mechanistic interrelationships between environment, material microstructure and the electrochemical processes driving corrosion remain poorly understood. Several studies in the past decade demonstrated that X-ray tomography (XCT) can be used to characterize corrosion-related damage non-destructively in-operando[1,2,3,4,5,6]. This study applies this tool to elucidate the long-term growth kinetics of atmospheric corrosion pits in aluminum
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