Atomic scale investigation of Cr precipitation in copper

TL;DR

This study uses atom probe tomography to analyze the early stages of chromium precipitation in copper at the atomic level, revealing diverse precipitate shapes, compositions, and impurity segregation that challenge equilibrium phase diagram expectations.

Contribution

It provides detailed atomic-scale insights into Cr precipitation in copper, highlighting shape diversity, impurity effects, and non-equilibrium compositions during aging.

Findings

Nanoscale precipitates show various shapes including spherical, plates, and ellipsoids.

Precipitates contain up to 50% Cu, contrary to equilibrium predictions.

Fe impurities segregate at Cu/Cr interfaces, affecting precipitate evolution.

Abstract

The early stage of the chromium precipitation in copper was analyzed at the atomic scale by Atom Probe Tomography (APT). Quantitative data about the precipitate size, 3D shape, density, composition and volume fraction were obtained in a Cu-1Cr-0.1Zr (wt.%) commercial alloy aged at 713K. Surprisingly, nanoscaled precipitates exhibit various shapes (spherical, plates and ellipsoid) and contain a large amount of Cu (up to 50%), in contradiction with the equilibrium Cu-Cr phase diagram. APT data also show that some impurities (Fe) may segregate along Cu/Cr interfaces. The concomitant evolution of the precipitate shape and composition as a function of the aging time is discussed. A special emphasis is given on the competition between interfacial and elastic energy and on the role of Fe segregation.