  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.
