Solidification of electromagnetically levitated Nd-Fe-B melt droplets

1
Solidification of electromagnetically levitated
Nd-Fe-B melt droplets
Sino-German Workshop on EPM 10-12 October, 2004,
Shanghai

• J. Gao1,2, T. Volkmann1, J. Strohmenger1,
• S. Reutzel3, D.M. Herlach1
• 1 Institute of Space Simulation, German Aerospace
  Center, Cologne, Germany
• 2 Key Laboratory of Electromagnetic Processing of
  Materials, Northeastern University, Shenyang,
  China
• 3 Institute of Experimental Physics IV,
  Ruhr-University of Bochum, Bochum, Germany

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Outline

• Motivation
• Experimental-Setup
• Solidification experiments
• Microstructural examination
• Conclusions outlook

3
Introduction to Nd-Fe-B alloys
Nd2Fe14B
(MGOe)
Sm2Co17
max
(BH)
SmCo5
Ba-Ferrite
DS-Alnico
AlNiCo5
Year
F-Nd2Fe14B cell
Hysteresis loops
Development of PMM
4
Peritectic formation of f
Fabrication of sintered Nd-Fe-B magnets requires
casting of bulk ingots for powder precursors.
Peritectic formation of f
Nd-Fe-B phase diagram
Residual Fe dendrites lead to reduced magnetic
properties.
5
Motivation - direct f formation
Peritectic f-phase might be solidified directly
from an undercooled liquid. It is a big
challenge to undercool Nd-Fe-B melt droplets
because of their high chemical reactivity!
6
Electromagnetic Levitator
To chart recorder
Pyrometer
Sample (1g, 6mm)
R. F. Generator
Coil
Vac10-6 mbar PHe10-50 mbar
Quartz tube
He (6N)
To vacuum pump
EML low P TgtgtTL ? large DT
Nd2O3 (s) Nd (L)? NdO (g)
7
In-situ X-ray diffraction analysis
X-ray Synchrotron radiation highly
penetrating Beamtime ID 15A, ESRF, Grenoble,
France
8
Cooling curves during solidification
Recalescence occurs due to rapid latent heat
release!
9
In-situ diffraction analysis
MS c-Nd2Fe17Bx Th2Zn17-type rhombohedral
structure Decomposition of Nd2Fe17Bx into Fe
plus Nd2Fe14B.
10
Primary phase selection map
?g-Fe f-Nd2Fe14B ?c-Nd2Fe17Bx
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Solidification microstructure
12
Thermomagnetic analysis
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Summary

• Chemically reactive Nd-Fe-B melt droplets could
  be undercooled by electromagnetic levitation
  under controlled conditions.
• Solidification of levitated Nd-Fe-B droplets
  depends on melt undercooling, and three
  metastable solidification pathways have been
  determined for Nd-rich compositions.

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Outlook Fe-rich compositions
Preliminary drop tube experiments
Fe phase is not harmful any longer! EM-levitation
for in-situ studies.