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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. Gao 1,2 , T. Volkmann 1 , J. Strohmenger 1 , S. Reutzel 3 , D.M. Herlach 1 1 Institute of Space Simulation, German Aerospace Center, Cologne, Germany

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Solidification of electromagnetically levitated Nd-Fe-B melt droplets

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  1. 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. B 60 (BH)max 50 Nd-Fe-B 40 Ferrite 30 (BH)max H 20 0 10 0 1990 1940 1950 1960 1970 1980 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. L f g 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. Overheated L g T(K) TL TP L+ g f TL 82.3 76.5 Undercooled f L+ f Fe (at.%) (Nd:B=2:1) 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 Vac:=10-6 mbar PHe=10-50 mbar 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.

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