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

TL;DR

This paper develops a physics-based rate-theory model to understand radiation-induced Cr segregation at grain boundaries in Fe-Cr alloys, revealing how defect production biases influence enrichment-depletion transitions under irradiation.

Contribution

It introduces a novel rate-theory framework parameterized with Onsager coefficients to predict RIS behavior, accounting for defect flux biases and temperature effects.

Findings

Cr segregation transitions depend on temperature and defect flux symmetry.

Biases in defect production shift the enrichment-depletion transition to lower temperatures.

Transport properties primarily determine segregation direction, while defect flux biases influence magnitude.

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.