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

2. Outline Motivation Experimental-Setup Solidification experiments
Microstructural examination
Conclusions & outlook

3. Introduction to Nd-Fe-B alloysB H
(BH)max
Nd-Fe-B
Ferrite 10 20 30 40 50 60
Nd2Fe14B
(MGOe)
Sm2Co17
max
(BH)
SmCo5
Ba-Ferrite
DS-Alnico
AlNiCo5
1940
1950
1960
1970
1980
1990
Year
Hysteresis loops
Development of PMM
F-Nd2Fe14B cell

4. Peritectic formation of f
Fabrication of sintered Nd-Fe-B magnets requires
casting of bulk ingots for powder precursors. g L f
Peritectic formation of f
Nd-Fe-B phase diagram
Residual Fe dendrites lead to reduced magnetic properties.

5. Motivation - direct f formation
T (K)
Fe (at.%) (Nd:B=2:1)
82.3
76.5
L+ g
L+ f
Undercooled
Overheated f TL g L TP
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
Vac:=10-6 mbar
PHe=10-50 mbar
Coil
Quartz
tube He
(6N)
To vacuum pump
EML + low P + T>>TL  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

11. Solidification microstructure

12. Thermomagnetic analysis

13. 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.

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