Berlin 2005 – wissenschaftliches Programm

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M: Metallphysik

M 23: Phasenumwandlung III

M 23.3: Vortrag

Samstag, 5. März 2005, 15:15–15:30, TU H1058

In-situ Determination of Phase Formation in Undercooled Nd-Fe-B-melts – Identification of a Metastable Phase with Synchrotron Radiation — •Jörn Strohmenger¹, Thomas Volkmann¹, Jianrong Gao², Sven Reutzel³, Dirk Holland-Moritz¹, Oliver Heinen¹, and Dieter M. 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 — ³Institute of Experimental Physics IV, Ruhr-University Bochum, D-44780 Bochum

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 was investigated using electromagnetic levitation combined with in-situ X-ray diffraction experiments at the ESRF. Under equilibrium conditions for alloys near the stoichiometric composition the Φ-phase is formed by a peritectic reaction from pro-peritectic γ-Fe. For Nd-contents between 10 and 18at% at the ratio Nd/B=2/1 it is shown that the crystallization of primary phase is affected by undercooling, e.g a metastable phase can be directly observed which initiates the formation of the Φ-phase. It can be identified as a ternary extension of the rhombohedral Nd₂Fe₁₇ phase being stable in binary Nd-Fe alloys. A phase selection diagram showing the different solidification pathways as a function of undercooling and alloy composition will be analysed within theories of nucleation and crystal growth. This work was supported by DFG under contract No. HE1601/14.