Wednesday  |  Monongahela  |  04:40 PM–05:00 PM

#13403, Insights from X-ray Computed Tomography into the Relationship between Pit Morphology and Growth Kinetics During Atmospheric Corrosion

There is strong evidence that the morphology of pits evolves significantly during atmospheric corrosion. However, there is limited understanding of how this affects pit growth kinetics and pit stability. Conventional approaches to characterizing pit growth such as mass-change measurements provide limited insight into this question, but X-ray computed tomography allows these effects to be unraveled by allowing pit growth to be observed directly in-situ. This work presents present new findings on how changes in pit morphology affect growth kinetics and how this enables certain pits to grow significantly larger than average. Atmospheric corrosion damage in high-purity Al wires exposed to chloride salts in humid air was studied. The 1.3 hour temporal resolutions used in these studies indicated that the rate of pit growth can be non-linear and that this is related to pit morphology. Pit morphology as a result of preferential microstructural attack appears to allow certain pits to continue growing for much longer than average, resulting in certain pits being 2-3 times larger than average. The evolution of the droplet was also observed to affect pit growth kinetics. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Philip Noell   Sandia National Labs
Michael Melia   Sandia National Labs
Eric Schindelholz   The Ohio State University
Ian Cambell   The University of Washington