First-Principles Investigation of Grain Boundary Effects on Fluorine-Induced Initial Corrosion of NiCr Alloys
Chromium depletion at grain boundaries (GBs) due to selective attack is a critical issue in the molten salt corrosion of NiCr alloys. Despite the importance of GBs in this process from numerous experimental studies, most theoretical work has predominantly focused on fluorine interactions with ideali...
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Zusammenfassung: | Chromium depletion at grain boundaries (GBs) due to selective attack is a
critical issue in the molten salt corrosion of NiCr alloys. Despite the
importance of GBs in this process from numerous experimental studies, most
theoretical work has predominantly focused on fluorine interactions with
idealized crystalline surfaces, neglecting the complexity of GB local
environments. This study aims to bridge that gap by employing density
functional theory (DFT) to investigate the atomic interactions and Cr
dissolution mechanisms at GB in NiCr alloys under molten fluoride salt
environments. Specifically, a $\Sigma$5(210)/(001) symmetrical tilt GB is
constructed to explore the adsorption energies of fluorine on Ni(100) and
Cr-doped Ni(100) surfaces. We find that fluorine exhibits a strong preference
for binding at GB sites, with Cr doping amplifying this effect, leading to
higher adsorption energies compared to bulk Ni surfaces. Fluorine bonding with
Cr significantly alters the interaction between Cr-F complexes and Ni
substrate, and the consequent dissolution barriers for Cr atoms; the formation
of CrF$_3$ largely reduces the energy barrier for Cr dissolution. This work
highlights the essential role of GBs in enhancing fluorine adsorption and
accelerating Cr depletion, providing new insights into the mechanisms of
early-stage corrosion in NiCr alloys. |
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DOI: | 10.48550/arxiv.2411.00673 |