Atomic insights into corrosion of Fe-Cr alloy in chloride contaminated environment: Development of JAX-ReaxFF force field

Abstract

This study provides atomic-level insights into the chloride-induced corrosion of Fe-Cr alloy, using the newly developed JAX-ReaxFF force field. Fe/Cr/Cl parameters were generated from density functional theory (DFT)-derived data on chromium-chloride and iron-chloride molecular clusters. These parameters were validated against DFT results, showing strong agreement in bond dissociation energies, angular distortions, atomic charges, and adsorption energies. Reactive molecular dynamics simulations revealed that chloride ions accumulate on the Fe-Cr alloy surface, destabilizing the passive film and leading to metal ion dissolution, forming soluble chlorides. As the process advances, metal oxides and hydroxides deposit, further accelerating corrosion. The charge transfer between Fe and Cr plays a critical role (Fe loses approximately 1 electron, while Cr loses only 0.5 electrons), with Fe exhibiting higher diffusivity (diffusion coefficient = 5.54 ×10⁻¹² m²/s) due to significant charge loss, while Cr forms a protective oxide layer that slows its dissolution. These findings provide valuable insights into the corrosion resistance of Fe-Cr alloy, particularly in chloride-contaminated environments.