Radiation-induced segregation in dilute Fe-Cr: A rate-theory framework for the Cr enrichment-depletion transition at the grain boundary

Abstract

Radiation-induced segregation (RIS) poses a significant challenge for ferritic Fe-Cr alloys under irradiation, as it can compromise mechanical integrity and increase susceptibility to intergranular corrosion. Yet, the mechanisms governing Cr segregation remain incompletely understood. In this study, We present a physics-based rate-theory model parameterized using self-consistent mean field theory-based Onsager transport coefficients to investigate RIS at the grain boundary (GB) in dilute Fe-(0.1 at.%) Cr. Under equal production rates of vacancies and self-interstitial atoms (SIA), and their equal absorption rates by bulk dislocations, the model simulates the experimentally observed transition from Cr enrichment at low temperatures to depletion at higher temperatures. Under these unbiased conditions, systematic investigation reveals that while temperature-dependent transport properties dictate the segregation direction, dose rate, grain size, and dislocation density only influence the magnitude and spatial extent of Cr segregation. However, under more realistic conditions of preferential vacancy production within damage cascade and/or preferential SIA absorption by bulk dislocations, the enrichment-to-depletion transition shifts to lower temperatures. Our findings demonstrate that RIS predictions based solely on transport coefficients are valid only under symmetric point defect flux conditions, and that biases in defect production and absorption must be considered for accurate predictions. This work provides a mechanistic framework for understanding RIS in ferritic alloys and informs alloy design for advanced nuclear systems.

Figures (27)

• Figure 1: Temperature dependence of partial diffusion coefficient (PDC) ratios for vacancies and SIAs in Fe-0.1Cr. The PDC ratios are plotted from the Onsager coefficients obtained from KineCluE calculations of Messina et al. messina_OnsTran.
• Figure 2: (a) Dislocation capture efficiency Z for vacancies and SIAs as a function of dislocation density $\rho$, comparing the classical unbiased model with the DDD-based biased model from Kohnert et al. kohnert_DDD at 500 K and 700 K. (b) SIA absorption bias $B$ predicted by the DDD-based model as a function of dislocation density at 500 K and 700 K.
• Figure 3: Cr concentration profiles at 10 dpa as a function of normalized distance from the GB and irradiation temperature for a 5 $\mu$m grain with dislocation density of $10^{-4}$ nm$^{-2}$ irradiated at $10^{-7}$ dpa/s under unbiased conditions.
• Figure 4: Cr concentration at the GB versus temperature for dose rates ranging from $10^{-8}$ to $10^{-5}$ dpa/s for a system of 5 $\mu$m grain with dislocation density of $10^{-4}$ nm$^{-2}$ irradiated to 10 dpa under unbiased conditions.
• Figure 5: GB Cr concentration as a function of dislocation density $\rho$ for grain sizes ranging from 50 to 5 $\mu$m at (top) 500 K and (bottom) 700 K. Results correspond to irradiation up to 10 dpa at a dose rate of $10^{-7}$ dpa/s under unbiased conditions.