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On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

TitleOn spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study
Publication TypeJournal Article
Year of Publication2018
AuthorsZhou, L, Guo, W, Poplawsky, JD, Ke, LQ, Tang, W, Anderson, IE, Kramer, MJ
JournalActa Materialia
Volume153
Pagination15-22
Date Published07
Type of ArticleArticle
ISBN Number1359-6454
Accession NumberWOS:000437391500003
Keywordsalloys, Atom-probe tomography, heat-treatment, Magnetic, magnetic-field application, Materials Science, Metallurgical Engineering, Microstructure, permanent-magnets, Spinodal decomposition, STEM HAADF, TEM, titanium
Abstract

Alnico is a prime example of a finely tuned nanostructure whose magnetic properties are intimately connected to magnetic annealing (MA) during spinodal transformation and subsequent lower temperature annealing (draw) cycles. Using a combination of transmission electron microscopy and atom probe tomography, we show how these critical processing steps affect the local composition and nanostructure evolution with impact on magnetic properties. The nearly 2-fold increase of intrinsic coercivity (H-ci) during the draw cycle is not adequately explained by chemical refinement of the spinodal phases. Instead, increased Fe-Co phase (alpha(1)) isolation, development of Cu-rich spheres/rods/blades and additional alpha(1) rod precipitation that occurs during the MA and draw, likely play a key role in H-ci enhancement. Chemical ordering of the Al-Ni-phase (alpha(2)) and formation of Ni-rich (alpha(3)) may also contribute. Unraveling of the subtle effect of these nano-scaled features is crucial to understanding on how to improve shape anisotropy in alnico magnets. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI10.1016/j.actamat.2018.04.042
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