Tuning Yttrium {\Sigma}7(0001) Twist Grain Boundary Properties through Segregation and Co-segregation of Low Neutron Absorption Elements: First-Principles Insights

TL;DR

This study uses first-principles calculations to explore how low neutron absorption elements, especially silicon, co-segregate at yttrium grain boundaries to enhance stability and strength for nuclear materials.

Contribution

It provides detailed insights into the segregation behaviors and electronic effects of multiple elements at yttrium grain boundaries, guiding alloy design for nuclear applications.

Findings

Si stabilizes and strengthens the grain boundary effectively.

Co-segregation of Si with Mg or Al enhances electronic stability.

Silicon's covalent bonds improve fracture resistance.

Abstract

Elements with low thermal neutron absorption cross-sections are ideal for enhancing structural materials in nuclear systems. In this study, We systematically investigate the segregation and co-segregation behaviors of eleven elements at the {\Sigma}7(0001) twist grain boundary in yttrium and their effects on stability and strength. The {\Sigma}7(0001) grain boundary exhibits weakening, with fracture occurring preferentially along path I. Segregation energy calculations show that Si, Cu, Cr, Mo and Fe prefer interstitial sites, while others occupy substitutional ones. Si, Al, Zn, Cu, Mg and Fe stabilize the boundary, while Mo, Fe, Si, Cr, Cu, Nb and Ti strengthen it, with Si offering the most balanced improvement. Co-segregation studies reveal that Si induces the enrichment of other solutes at the boundary, promoting synergistic stabilization and turning embrittling elements (Al, Mg, Zn, Zr) into strengthening agents. Electronic structure analysis shows that Si-Y covalent bonds enhance electron localization, and Si+Mg co-segregation optimizes electronic distribution through metallic-covalent cooperation, significantly improving fracture resistance. The density of states analysis indicates new low-energy deep states in the Si, and Si+Al, Si+Mg systems, which lower grain boundary energy and improve stability. This study provides guidance for designing high-performance, low-neutron-absorption Y-based alloys.