Grain boundary interstitial segregation in substitutional binary alloys

TL;DR

This study reveals significant interstitial segregation at grain boundaries in Al-Ni alloys, challenging previous assumptions, and introduces a new method combined with machine learning to predict segregation behavior and energies.

Contribution

It presents the first detailed atomistic analysis of interstitial segregation in substitutional alloys and develops a novel site identification method combined with machine learning for accurate predictions.

Findings

Ni atoms preferentially segregate to interstitial sites in GBs.

Interstitial segregation can induce GB structural transitions.

A new method accurately predicts interstitial segregation energies.

Abstract

Grain boundary (GB) segregation is a powerful approach for optimizing the thermal and mechanical properties of metal alloys. In this study, we report significant GB interstitial segregation in a representative substitutional binary alloy system (Al-Ni) through atomistic simulations, challenging prevailing assumptions in the literature. Our findings show that Ni atoms preferentially segregate to interstitial sites within numerous kite-like GB structures in the Al bicrystals. An intriguing interplanar interstitial segregation pattern was also observed and analyzed. Additionally, interstitial segregation can induce unexpected GB transitions, such as kite transitions and nano-faceting, due to the existence of small interstitial sites. Building upon these observations, we developed a robust method to systematically identify the interstitial candidate sites for accommodating solutes at GBs. This approach combines site detection with structural filtering to produce distributions of interstitial sites that closely match atomistic simulation results. Applied to nanocrystalline alloys, this method enabled the calculation of interstitial segregation energies, significantly improving GB segregation predictions for the Al-Ni system. Furthermore, machine learning models using smooth overlap of atomic positions descriptors successfully predicted per-site interstitial segregation energy. This study highlights the critical role of GB interstitial segregation in advancing our understanding of solute behavior and provides valuable insights for designing next-generation alloys.