Local chemical and topological order in Al-Tb and its role in controlling nanocrystal formation

TitleLocal chemical and topological order in Al-Tb and its role in controlling nanocrystal formation
Publication TypeJournal Article
Year of Publication2012
AuthorsKalay YE, Kalay I, Hwang J, Voyles PM, Kramer MJ
Journal TitleActa Materialia
Volume60
Pages994-1003
Date Published02
Type of ArticleArticle
ISBN Number1359-6454
Accession NumberWOS:000301157900022
Keywordsalloy, CRYSTALLIZATION, diffraction, diffraction (XRD), electron microscopy (STEM), FLUCTUATION MICROSCOPY, medium-range order, metallic glasses, Nanocrystalline materials, PHASE-SEPARATION, probe, refinement, Scanning/transmission, Three-dimensional atom probe (3DAP), x-ray
Abstract

How the chemical and topological short- to medium-range order develops in Al-Tb glass and its ultimate effect on the control of the high number density of face-centered-cubic-Al (fcc-Al) nuclei during devitrification are described. A combined study using high-energy X-ray diffraction (HEXRD), atom probe tomography (APT), transmission electron microscopy and fluctuation electron microscopy (FEM) was conducted in order to resolve the local structure in amorphous Al90Tb10. Reverse Monte Carlo simulations and Voronoi tessellation analysis based on HEXRD experiments revealed a high coordination of Al around Tb atoms in both liquid and amorphous states. APT results show Al-rich and Al-depleted regions within the as-quenched alloy. A network structure of Tb-rich clusters divides the matrix into nanoscale regions where Al-rich clusters are isolated. It is this finely divided network which allows the amorphous structure to form. Al-rich regions are the locus for fcc-Al crystallization, which occurs before the intermetallic crystallization. FEM reveals medium-range ordered regions similar to 2 nm in diameter, consistent with fcc-Al and trigonal-like Al3Tb crystal structures. We propose that the high coordination of Al around Tb limits diffusion in the intermetallic network, allowing for the isolated Al-rich regions to form at high density. These regions are responsible for the extremely high density of Al nanocrystal nuclei. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

URL<Go to ISI>://WOS:000301157900022
DOI10.1016/j.actamat.2011.11.008
Alternate JournalActa Mater.