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Processing of alnico permanent magnets by advanced directional solidification methods

TitleProcessing of alnico permanent magnets by advanced directional solidification methods
Publication TypeJournal Article
Year of Publication2016
AuthorsZou, M, Johnson, F, Zhang, WM, Zhao, Q, Rutkowski, SF, Zhou, L, Kramer, MJ
JournalJournal of Magnetism and Magnetic Materials
Volume420
Pagination152-157
Date Published12
Type of ArticleArticle
ISBN Number0304-8853
Accession NumberWOS:000382218700023
Keywordsalnico, Directional solidification, Electron microscopy, Materials Science, permanent magnets, physics, transmission
Abstract

Sn bath at a withdrawal rate of at least 200 mm/h. However, higher Ti compositions did not result in further increases in magnet performance. Images of the microstructures collected by scanning electron microscopy (SEM) reveal a majority a phase with inclusions of secondary ay phase. Transmission electron microscopy (TEM) reveals that the a phase has a spinodally decomposed microstructure of FeCo-rich needles in a NiAI-rich matrix. In the 7.5% Ti composition the diameter distribution of the FeCo needles was bimodal with the majority having diameters of approximately 50 nm with a small fraction having diameters of approximately 10 nm. The needles formed a mosaic pattern and were elongated along one (001) crystal direction (parallel to the field used during magnetic annealing). Cu precipitates were observed between the needles. Regions of abnormal spinodal morphology appeared to correlate with secondary phase precipitates. The presence of these abnormalities did not prevent the material from displaying superior magnetic properties in the 7.5% Ti composition. Higher Ti compositions did not display the preferred spinodal microstructure, explaining their inferior magnetic properties. (C) 2016 Elsevier B.V. All rights reserved.

DOI10.1016/j.jmmm.2016.06.091
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Alternate JournalJ. Magn. Magn. Mater.