Solute-point defect interactions, coupled diffusion, and radiation induced segregation in fcc nickel

TL;DR

This study investigates the atomic mechanisms driving radiation-induced segregation in fcc nickel alloys, revealing solute-specific diffusion behaviors and temperature-dependent segregation patterns through ab initio and kinetic modeling.

Contribution

It provides a detailed atomic-level understanding of solute-defect interactions and diffusion mechanisms in Ni-X alloys under irradiation, which was previously not well characterized.

Findings

P and Si are enriched at sinks during irradiation.

Cr prefers vacancy-mediated diffusion and shows temperature-dependent segregation.

Ti and Cr exhibit crossover from enrichment to depletion with increasing temperature.

Abstract

Radiation-induced segregation (RIS) of solutes in materials exposed to irradiation is a well-known problem. It affects the life-time of nuclear reactor core components by favouring radiation-induced degradation phenomena such as hardening and embrittlement. In this work, RIS tendencies in face-centered cubic (fcc) Ni-X (X = Cr, Fe, Ti, Mn, Si, P) dilute binary alloys are examined. The goal is to investigate the driving forces and kinetic mechanisms behind the experimentally observed segregation. By means of ab initio calculations, point-defect stabilities and interactions with solutes are determined, together with migration energies and attempt frequencies. Transport and diffusion coefficients are then calculated in a mean-field framework, to get a full picture of solute-defect kinetic coupling in the alloys. Results show that all solutes considered, with the exception of Cr, prefer vacancy-mediated over interstitial-mediated diffusion during both thermal and radiation-induced migration. Cr, on the other hand, preferentially migrates in a mixed-dumbbell configuration. P and Si are here shown to be enriched, and Fe and Mn to be depleted at sinks during irradiation of the material. Ti and Cr, on the other hand, display a crossover between enrichment at lower temperatures, and depletion in the higher temperature range. Results in this work are compared with previous studies in body-centered cubic (bcc) Fe, and discussed in the context of RIS in austenitic alloys.