Understanding Coarsening of a Post-Corrosion Microstructure in a Molten Salt by Combining Phase-Field Modeling and In Situ Tomography

September 1, 2025

The Science 

In emergent nuclear reactor systems, corrosion in molten salts produces complex porous structures. Their long-term evolution affects material integrity, but the mechanisms controlling this evolution are not well understood. Researchers combined in situ X-ray nanotomography with phase-field simulations to study how a dealloyed Ni–Cr alloy coarsens in molten KCl–MgCl₂. By directly comparing experimental and simulated microstructures, they evaluated competing transport mechanisms and their kinetics. Different mechanisms resulted in qualitatively similar evolution, with densification near the surface and coarsening of internal features. Coarsening via surface diffusion provided the best agreement between experiment and simulation with realistic material properties. 

The Impact 

Understanding how porous structures evolve after corrosion is critical for predicting material degradation in molten salt systems. This work provides a framework for quantitatively connecting experimental observations to fundamental transport properties. The approach enables extraction of kinetic parameters and improves predictive understanding of corrosion-driven microstructural evolution. 

Summary 

This study combined in situ X-ray nanotomography with phase-field simulations to investigate coarsening of a dealloyed Ni–20Cr structure in molten KCl–MgCl₂. 

Simulations were initialized directly from experimental 3D microstructures and used to evaluate surface diffusion, solid-state diffusion, and liquid-phase transport mechanisms. All mechanisms reproduced general coarsening behavior, including ligament growth and surface densification. 

Quantitative comparison using morphological metrics and time scaling yielded kinetic parameters corresponding to each mechanism, and the kinetic parameter for surface diffusion was most consistent with material properties (e.g., surface diffusivity) reported in previous literature. Analysis of curvature distributions revealed that material transport is driven by gradients in surface curvature, causing densification near the surface and coarsening of internal features. 

The results also suggest that additional processes, such as residual chromium dissolution, may influence long-term evolution beyond idealized coarsening behavior. 

Overall, the study linked the time-dependent structural evolution of porous metal structures in molten salts to fundamental material properties and found that surface diffusion was the most likely governing mechanism for coarsening. 

Contact 

Katsuyo Thornton, University of Michigan, kthorn@umich.edu 
Yu-chen Karen Chen-Wiegart, Stony Brook University / Brookhaven National Laboratory, Karen.Chen-Wiegart@stonybrook.edu 

Funding 

This work was supported by the Molten Salts in Extreme Environments Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. This research used resources of the National Synchrotron Light Source II at Brookhaven National Laboratory and computational resources at Purdue University (ACCESS) and other DOE-supported computing facilities. 

Citation 

Hendrix, E. J., W. B. Andrews, X. Liu, Y.-c. K. Chen-Wiegart, and K. Thornton. “Understanding Coarsening of a Post-Corrosion Microstructure in a Molten Salt by Combining Phase-Field Modeling and In Situ Tomography.” Acta Materialia 297 (2025): 121299. https://doi.org/10.1016/j.actamat.2025.121299 

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