Temporal evolution of the nanostructure of AI(Sc,Zr) alloys:: Part I -: Chemical compositions of Al3(Sc1-xZrx) precipitatesy

Atom-probe tomography (APT) and high-resolution transmission electron microscopy are used to study the chemical composition and nanostructural temporal evolution of Al-3(Sc1-xZrx) precipitates in an Al-0.09 Sc-0.047 Zr at.%alloy aged at 300 degrees C. Concentration profiles, via APT, reveal that Sc and Zr partition to Al-3(Sc1-xZrx) precipitates and Zr segregates concomitantly to the alpha-Al/Al-3(Sc1-xZrx) interface. The Zr concentration in the precipitates increases with increasing aging time, reaching a maximum value of 1.5 at.% at 576 h. The relative Gibbsian interfacial excess (Gamma(Al-Sc)(Zr)) of Zr, with respect to Al and Sc, reaches a maximum value of 1.24 +/- 0.62 atoms nm(-2) after 2412 h. The temporal evolution of Al-3(Sc1-xZrx) precipitates is determined by measuring the time dependence of the depletion of the matrix supersaturation of Sc and Zr. The time dependency of the supersaturation of Zr does not follow the asymptotic t(-1/3) law while that of Sc does, indicating that a quasi-stationary state is not achieved for both Sc and Zr. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.