Deconvoluting Mechanisms of Radiation-Induced Grain Boundary Segregation in Dilute Ni-X (X = Fe, Cr, Mn) Alloys via Ion Irradiation and Phase-field Modeling

Sohail Shah; Sourabh Bhagwan Kadambi; Anshul Kamboj; Benjamin Diaz; Xinchang Zhang; Jana Howard; Michael Moorehead; Boopathy Kombaiah; Lin Shao; Mukesh Bachhav

arXiv · 2610.05849

Deconvoluting Mechanisms of Radiation-Induced Grain Boundary Segregation in Dilute Ni-X (X = Fe, Cr, Mn) Alloys via Ion Irradiation and Phase-field Modeling

Sohail Shah·Sourabh Bhagwan Kadambi·Anshul Kamboj·Benjamin Diaz·Xinchang Zhang·Jana Howard·Michael Moorehead·Boopathy Kombaiah·Lin Shao·Mukesh Bachhav

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Abstract

Radiation-induced composition redistribution at grain boundaries (GBs) in Ni-based structural alloys poses a critical challenge for the long-term deployment of advanced nuclear reactors. The mechanisms governing solute-specific segregation remain poorly understood because defect-mediated transport, thermodynamic driving forces, and competing microstructural sinks can all contribute under irradiation. We perform systematic Ni2+ ion irradiations on dilute Ni-Fe, Ni-Cr, and Ni-Mn binary alloys at 500, 800, and 1000 K to 2 dpa and characterize GB chemistry using STEM-EDS. The segregation behavior is interpreted using rate-theory phase-field modeling informed by atomistic transport data. We find that Fe depletes at GBs across all temperatures via preferential vacancy-solute exchange (inverse Kirkendall effect). Cr segregation reflects a temperature-dependent competition between self-interstitial atom (SIA)-mediated transport toward GBs and vacancy-mediated transport away from GBs, yielding near-zero net segregation at 500 K and depletion at higher temperatures. In contrast, Mn exhibits distinct behavior dominated by thermodynamic segregation that drives local enrichment at the GB. We leverage depth-dependent characterization along the same GB, spanning irradiated and unirradiated regions, to separate radiation-induced and thermodynamic contributions and validate the unirradiated region as an internal thermodynamic reference. Void formation at 800 K and irradiation-induced GB migration at 800 and 1000 K further add mechanistic complexity by suppressing and redistributing the solute. Our combined experimental and computational assessments show that interpreting GB chemistry evolution under irradiation requires concurrent treatment of non-equilibrium kinetic transport, thermodynamic driving forces, bulk sink effects, and GB migration.

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Sohail Shah, Sourabh Bhagwan Kadambi, Anshul Kamboj, Benjamin Diaz, Xinchang Zhang, Jana Howard, Michael Moorehead, Boopathy Kombaiah, Lin Shao, Mukesh Bachhav. 2026-10-05. Deconvoluting Mechanisms of Radiation-Induced Grain Boundary Segregation in Dilute Ni-X (X = Fe, Cr, Mn) Alloys via Ion Irradiation and Phase-field Modeling. https://arxiv.org/abs/2610.05849

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