Study on corrosion behavior and mechanism of Fe-Cr alloy in chloride- containing environments based on reactive molecular dynamics

Y Guo and MH Li and L Yang and GJ Liu, ELECTROCHIMICA ACTA, 543, 147576 (2025).

DOI: 10.1016/j.electacta.2025.147576

Reactive molecular dynamics (ReaxFF MD) simulations were employed to systematically investigate the effects of chloride ion concentration (Cl-, 1-10 mol/L), pH (12.5-14.0), and temperature (100-700 K) on the corrosion performance of Fe-Cr alloy (9 wt% Cr). Analysis of charge transfer mechanisms, radial distribution functions, and atomic diffusion revealed that Cl- significantly accelerates the corrosion and dissolution of Fe-Cr alloy surfaces primarily by weakening the bonding strength between surface metal atoms, which in turn remarkably promotes their desorption; when Cl- concentration increases from 1 mol/L to 10 mol/L, its intrusion amount into the matrix is over 400 % higher than that at 1 mol/L, the corrosion morphology transitions from localized pitting (1-3 mol/L) to general corrosion (5-10 mol/L), and the Cr2O3-rich passive film is preferentially degraded with increasing Cl- concentration. The alkaline environment exhibited an inhibitory effect on corrosion propagation, as pH rising from 12.5 to 14.0 weakened Cr-Cl coordination bonding and enhanced competitive adsorption of OH- ions, with only isolated micro-pits appearing on the alloy surface at pH 14.0. Elevated temperatures significantly increased the reaction frequency and rate of Cr and Fe atoms, with the number of reactive Fe/Cr atoms at 700 K increasing by 99.6 % and 100 % respectively compared to 100 K, and the corrosion reaction rate rising from 0.1 to 0.21, thereby accelerating oxidation and corrosion of the alloy matrix. This research quantifies the underlying atomic corrosion mechanism of Fe-Cr alloys under multi- factor coupling conditions, clarifies critical regulatory thresholds for corrosion behavior including Cl- concentration >= 5 mol/L, pH >= 13.5, and temperature >= 500 K, and proposes a three-stage corrosion mechanism of "passive film formation - Cl--induced dissolution - loose product deposition". It establishes a quantitative correlation between atomic- scale bond breaking and macroscopic passive film failure, providing fundamental theoretical insights for the design of low-Cr corrosion- resistant Fe-Cr alloys and protection strategies in extreme chloride- containing environments such as marine infrastructure.

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