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Regensburg 2002 – wissenschaftliches Programm

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M: Metallphysik

M 28: Wachstum

M 28.3: Fachvortrag

Freitag, 15. März 2002, 12:00–12:15, H8

Competitive phase formation in undercooled Nd16Fe76B8 alloys — •Jianrong Gao1,2, Thomas Volkmann1,3, Jörn Strohmenger1, and Dieter M. Herlach11Institut für Raumsimulation, Deutsches Zentrum für Luft- und Raumfahrt, D-51170 Köln — 2Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, China — 3Institut für Experimentalphysik IV, Ruhr-Universität Bochum, D-44780 Bochum

Alloy droplets with composition Nd16Fe76B8 were processed using the electromagnetic levitation technique for the purpose of studying competitive formation of the stable Nd2Fe14B and the metastable Nd2Fe17Bx phase in the undercooled melt. Bulk undercoolings ranging from 15 K to 72 K were achieved in the levitated samples prior to solidification. Microstructure examination of the as-solidified samples found that the primary formation of the stable Nd2Fe14B compound takes place for undercoolings up to 45 K, while that of the metastable Nd2Fe17Bx compound for undercoolings larger than 45 K. In the latter case, the stable Nd2Fe14B compound is also solidified but postponed. In-situ observations revealed that the solidification of the sample at smaller undercoolings is characterized by a strong recalescence, whereas that at larger undercoolings by a two-step recalescence. It was therefore suggested that the preferable formation of the metastable Nd2Fe17Bx compound to the stable φ-Nd2Fe14B compound at larger undercoolings may be controlled by a competitive nucleation mechanism.
This work is supported by the DLR Bonn under contract No. 50 WM9930 and the Deutsche Forschungsgemeinschaft under contract No. He 1601/14. J. G. is grateful to the financial support by the Alexander von Humboldt Foundation.

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