Dependence of Radiation Induced Segregation of Cr on Sink Dimensionality and Morphology in Fe-Cr Alloys

TL;DR

This study addresses radiation-induced segregation (RIS) of Cr in Fe-Cr alloys under irradiation by examining how sink dimensionality and morphology influence Cr redistribution. It combines kinetic Monte Carlo (KMC) simulations, finite-difference (FD) solutions, and analytical approaches, leveraging the Wiedersich relation $\nabla c_{\text{Cr}}(z) = \alpha(z) \frac{\nabla c_v(z)}{c_v(z)}$ to connect vacancy gradients to Cr concentration, across spherical and Cartesian sink geometries with a defect production rate $G$. The key findings show that Cr segregation toward planar sinks (1D/2D/3D) scales nearly linearly with interface density $\rho_I$, while spherical domains exhibit a nonlinear, dose-rate dependent relationship; FD results agree well with KMC and analytical expressions. These insights advance understanding of RIS control in radiation environments and provide guidance for designing more radiation-tolerant Fe-Cr alloys by tailoring sink topology and morphology.

Abstract

Radiation-induced segregation (RIS) and chemical redistribution in structural alloys can significantly degrade material performance, ultimately leading to failure. In this study, building on previous work by the authors [1], we investigate how the dimensional characteristics of sinks influence solute concentration distributions and segregation behavior. Specifically, we utilize a kinetic Monte Carlo (KMC) model to simulate atomic-scale diffusion and analyze segregation processes in an Fe-3Cr alloy. Our analysis includes three representative sink geometries: one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) planar sinks to capture the effects of sink dimensionality on Cr segregation at grain boundaries (GBs). We also found solutions of concentration and segregation profiles in these cases as well as for a 3D spherical sink. KMC simulations are performed over a range of temperatures to assess thermal effects on Cr redistribution. The results reveal distinct segregation profiles and concentration gradients, although the dependence with sink density seems to remain linear in all cases with planar sinks. The analytical results show that this is not the case in spherical domains, with a more complex dependence of segregation on sink density. Our finite difference solutions for domains including 2D and 3D planer sinks show agreement with corresponding KMC results.

Figures (11)

• Figure 1: Schematic of planar GBs (gray surfaces) acting as sinks in a) 1D, b) 2D c) 3D. d) Spherical domain with the outer boundary acting as an ideal sink.
• Figure 2: Steady-state chromium concentration distributions (3 at% nominal composition) at 500 K, influenced by a spherical sink located at the interface under an irradiation dose rate of $10^{-6}$ dpa/s
• Figure 3: steady-state distribution of vacancy concentration, showing the effect of planar sinks oriented normal to the x and z directions at 500 K under an irradiation dose rate of $10^{-6}$ dpa/s
• Figure 4: Steady-state Cr concentration with 3 at% nominal composition, showing the effect of planar sinks oriented normal to the x and z directions at 500 K under a displacement rate of $10^{-6}$ dpa/s
• Figure 5: Three-dimensional steady-state distribution of vacancy concentration at 500 K under an irradiation dose rate of $10^{-6}$ dpa/s