Percolating Corrosion Pathways of Chemically Ordered NiCr Alloys in Molten Salts

TL;DR

This study reveals that long-range chemical ordering in NiCr alloys creates percolating pathways that significantly accelerate corrosion in molten salts, providing a mechanistic understanding of the process.

Contribution

It demonstrates that chemical ordering alone, through percolation pathways, enhances corrosion rates in NiCr alloys in molten salt environments, independent of residual stresses.

Findings

Ordered Ni2Cr pathways facilitate faster Cr dissolution.

Corrosion rate is significantly higher in long-range ordered alloys.

Percolation pathways are key to understanding corrosion mechanisms.

Abstract

Recent experiments have shown that chemical ordering in NiCr alloys can significantly accelerate corrosion in molten salt environments. However, the underlying mechanisms remain poorly understood. Using reactive molecular dynamics and first-principles calculations, we show that long-range ordered Ni$_2$Cr in Ni-33at.%Cr alloys corrodes far more rapidly in FLiNaK salt at 800{\deg}C than short-range ordered or random solid solutions. This accelerated attack originates from percolating Cr pathways that enhance near-surface diffusion and a lowered energetic barrier for Cr dissolution, as confirmed by first-principles calculations. Contrary to earlier explanations that attributed this behavior to residual stresses, our stress-free simulations demonstrate that ordering alone accelerates the degradation. These results establish percolation as a critical link between chemical ordering and corrosion kinetics, offering a mechanistic basis for experimental observations.