Regensburg 2004 – wissenschaftliches Programm

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M: Metallphysik

M 12: Phasenumwandlungen II

M 12.3: Vortrag

Dienstag, 9. März 2004, 10:45–11:00, H16

Metastable Phase formation in electromagnetically levitated Nd-Fe-B-melts investigated by in-situ diffraction experiments with synchrotron radiation. — •Jörn Strohmenger¹, Thomas Volkmann¹, Jianrong Gao², Sven Reutzel¹, Dirk Holland-Moritz¹, Oliver Heinen¹ und Dieter Herlach¹ — ¹Institute of Space Simulation, German Aerospace Center (DLR), D-51170 Cologne — ²Key Lab of Electromagnetic Processing of Materials (EMP), Northeastern University, Shenyang 110004, China

Nd-Fe-B alloys are of special interest due to the excellent hardmagnetic properties of the intermetallic compound Nd₂Fe₁₄B₁ (Φ-phase). Competitive crystallisation of stable and metastable phases in undercooled Nd-Fe-B melts with Nd-contents between 11.8 and 18.0 at.% at the ratio of Nd/B=2/1 was investigated by the electromagnetic levitation technique in combination with in-situ diffraction experiments at the European Synchrotron Radiation Facility (ESRF) in Grenoble. Under equilibrium conditions the solidification sequence is primary γ-Fe followed by the peritectic formation of the Nd₂Fe₁₄B₁ phase. It is shown that in the undercooled melt the crystallisation of the γ-Fe-phase is suppressed in favour of the Φ phase. Moreover, the crystallisation of a metastable phase could be directly observed. A phase selection diagram showing the different solidification pathways as a function of undercooling and alloy composition will be presented.
Financial support by the Deutsche Forschungsgemeinschaft under contract No. HE1601/14 and the European Synchrotron Radiation Facility is gratefully acknowledged. J.G. appreciate support from AvH-foundation.