Localized corrosion of low-carbon steel at the nanoscale

Steven C Hayden,Rachael O Grudt,Daniel C Bufford,Paul G Kotula,Jeffery A Aguiar,Tatiana S Pilyugina,Khalid Hattar,Timothy J Kucharski,William M Mook,Ihsan M Taie,Claire Chisholm,Katherine L Jungjohann,Michele L Ostraat

doi:10.1038/s41529-019-0078-1

Abstract

Mitigating corrosion remains a daunting challenge due to localized, nanoscale corrosion events that are poorly understood but are known to cause unpredictable variations in material longevity. Here, the most recent advances in liquid-cell transmission electron microscopy were employed to capture the advent of localized aqueous corrosion in carbon steel at the nanoscale and in real time. Localized corrosion initiated at a triple junction formed by a solitary cementite grain and two ferrite grains and then continued at the electrochemically-active boundary between these two phases. With this analysis, we identified facetted pitting at the phase boundary, uniform corrosion rates from the steel surface, and data that suggest that a re-initiating galvanic corrosion mechanism is possible in this environment. These observations represent an important step toward atomically defining nanoscale corrosion mechanisms, enabling the informed development of next-generation inhibition technologies and the improvement of corrosion predictive models.

Highlights

The ubiquity of steel in infrastructure makes aqueous steel corrosion a global concern, with negative repercussions impacting most industrial sectors.[1]
These predictive models have been continually updated since their initial development in the early 1970s;3 even the models employed today often rely on semi-empirical correction factors derived from field observations or bulk-scale experiments to fill gaps in basic scientific understanding.[4]
The first evidence of localized corrosion was visible after 40 min of exposure to liquid electrolyte (Fig. 2c), indicated by triple junction formed by Fe3C/αB/αC (TJ2) and at the triple junction formed by Fe3C/αE/αF (TJ3)

Summary

Introduction

The ubiquity of steel in infrastructure makes aqueous steel corrosion a global concern, with negative repercussions impacting most industrial sectors.[1]. Myriad self-compounding environmental factors can completely alter the mechanisms by which corrosion progresses, even when only one factor is changed. This complexity presents a formidable problem for the scientific community to approach, resulting in gaps in the mechanistic understanding of how corrosion progresses in certain environments. Recent studies have suggested that nanoscale processes at heterogeneous sites in materials are a likely culprit for deviation between predictive models and observed corrosion rates from the field.[6] A timedependent understanding of accelerated nanoscale processes in steel corrosion under aqueous flow will help to narrow this knowledge gap

Methods

Results

Conclusion