Atomic-scale study on core-shell Cu precipitation in steels: atom probe tomography and ab initio calculations

TL;DR

This study combines atom probe tomography, DFT calculations, and molecular dynamics to understand the atomic interactions and formation mechanisms of core-shell Cu precipitates in steels, revealing insights into their stabilization and impact on mechanical properties.

Contribution

It introduces an integrated atomic-scale approach using APT, DFT, and MD to elucidate the formation and stabilization of core-shell Cu precipitates in steel, which was not previously detailed.

Findings

Ni and Al co-segregate with Cu in the steel matrix

The core-shell structure prevents rapid Cu precipitate growth

Stable co-segregation improves mechanical properties

Abstract

The present work investigates the atomic interactions among Cu, Al, and Ni elements in bcc-iron matrix, focusing on the formation mechanism of nano-sized core-shell Cu precipitates. Using a combination of atom probe tomography (APT), density functional theory (DFT) cal-culations, and molecular dynamics (MD) simulations, the study provides insights into the atomic-scale migration tendencies of these elements in the supersaturated solid solution sur-rounding Cu precipitate in the martensite phase of a medium-Mn steel. The results show that Ni and Al atoms were not expelled by Cu atoms but were instead attracted to the bcc iron matrix, forming a stable co-segregation in the outer shell. This phase effectively surrounded the nano-sized Cu precipitate and prevented its rapid growth, contributing to improved me-chanical properties. The findings offer a theoretical method for developing Cu-contaminated circular steels by utilizing DFT calculations to unravel bonding preferences and assess the po-tential for forming a stable precipitation phase around nano-sized Cu precipitates.