The dominant mechanisms for the formation of solute-rich clusters in low-Cu steels under irradiation

TL;DR

This paper investigates the atomic-scale mechanisms behind the formation of solute-rich clusters in low-Cu steels under irradiation, highlighting the dominant role of self-interstitial atom loops through a new modeling approach.

Contribution

It introduces a new object kinetic Monte Carlo model to explain NSRC formation, emphasizing the role of SIA loops, and validates it against experimental data.

Findings

SIA loops dominate NSRC nucleation

Model aligns well with experimental observations

Solute clustering occurs without Cu precipitates

Abstract

The formation of nano-sized, coherent, solute-rich clusters (NSRC) is known to be an important factor causing the degradation of the macroscopic properties of steels under irradiation. The mechanisms driving their formation are still debated. This work focuses on low-Cu reactor pressure vessel (RPV) steels, where solute species are generally not expected to precipitate. We rationalize the processes that take place at the nanometre scale under irradiation, relying on the latest theoretical and experimental evidence on atomic-level diffusion and transport processes. These are compiled in a new model, based on the object kinetic Monte Carlo (OKMC) technique. We evaluate the relevance of the underlying physical assumptions by applying the model to a large variety of irradiation experiments. Our model predictions are compared with new experimental data obtained with atom probe tomography and small angle neutron scattering, complemented with information from the literature. The results of this study reveal that the role of immobilized self-interstitial atoms (SIA) loops dominates the nucleation process of NSRC.