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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. Herlach1 — 1Institut 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.