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Containerless Solidification of Multicomponent Nd-Fe-B Alloys by Electromagnetic Levitation

2nd German-Chinese Workshop on EPM , October 200 5 , Dresden. Containerless Solidification of Multicomponent Nd-Fe-B Alloys by Electromagnetic Levitation. J. Gao 1,2 , T. Volkmann 1 , S. Reutzel 3 , D.M. Herlach 1 1 Institute of Space Simulation, DLR , Cologne, Germany

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Containerless Solidification of Multicomponent Nd-Fe-B Alloys by Electromagnetic Levitation

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  1. 2nd German-Chinese Workshop on EPM, October 2005, Dresden Containerless Solidification of Multicomponent Nd-Fe-B Alloys by Electromagnetic Levitation J. Gao1,2, T. Volkmann1, S. Reutzel3, D.M. Herlach1 1 Institute of Space Simulation, DLR, Cologne, Germany 2 Key Lab of EPM, Northeastern University, Shenyang, China 3 Institute of Experimental Physics IV, Ruhr-University of Bochum, Bochum, Germany Financed by Alexander von Humboldt Foundation and by German Aerospace Center (DLR-Bonn)

  2. Outline • Motivation • Experimental Setup • Results • Conclusions

  3. L f g Solidification of Nd-Fe-B alloys 2000 1800 d L L + 1665 K 1600 g L + Temperature (K) 1453 K 1400 f L + 1353 K g f + 1200 1185 K f h L + + f a f + 1000 928 K f h Nd + + 800 100 95 90 85 80 75 70 Fe Concentration (at.%) Nd:B=2:1 Nd-Fe-B phase diagram L + g-Fe f-Nd2Fe14B The composition of Nd-Fe-B magnets falls into the primary field of g-Fe phase. For this reason, precursor ingots often contain undissolved g-Fe dendrites leading to reduced magnetic properties of sintered magnets.

  4. Previous work (after Kurz) L L+g c f g+f L+ f EML primary g primary f primary c g=FeSS f=Nd2Fe14B c=Nd2Fe17Bx (x~1)

  5. Motivation Nd-Fe-B magnets often contain 4th element such as cobalt, dyprosium, and zironium. We wonder to what extentandhow they affect phase formation in undercooled melts.

  6. Alloy Composition Table Base alloy (at%): Nd14Fe79B7 Co for Fe: Nd14Fe69Co10B7 Dy for Nd: Nd13Dy1Fe69B7 Zr for Fe: Nd14Fe78.5Zr0.5B7 Original sampels were prepared by arc-melting elemental materials.

  7. Electromagnetic Levitation (EML) 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)

  8. Effects on Critical Undercoolings Temp. Accuracy: 5K Co adddition increases TL, and Dy addition lowers DTs.

  9. Effects on Microstructure DT Primaryc Primaryf Primaryg All three types of additions do NOT change the evolution of solidification microstructure with melt undercooling.

  10. Change Due to Co Addition Co in a, f, c

  11. X-ray Mapping of Nd-Fe-Co-B Alloys BSE Nd f c Fe Co “Homogeneous” distributin of Co

  12. Change Due to Dy Addition Dy in f and c, but not in a.

  13. BSE Nd Fe Dy X-ray Mapping of Nd-Dy-Fe-B Samples f c Dy is segregated in f- and c-phase.

  14. Modification by Zr Addition Bulk ZrFe2 ZrB2 Concentration of Zr in a ,c, and f is within the error of EDX.

  15. Nd BSE f c Zr Fe X-ray Mapping of Nd-Fe-Zr-B Alloy A large amount of Zr atoms are egregated on grain boundaries: ZrB2 and ZrFe2.

  16. Summary • By EML, we have investigated effects of alloying addition on phase formation in undercooled Nd-Fe-B alloy melts. • Addition of 10 at.% Co : • — no effect on phase formation • — homogeneous distribution • Addition of 1.0 at.% Dy : • — lower critical undercoolings • — preferential segregation in f and c • — increased stability of c against decomposition • Addition of 0.5 at.% Zr: • —no significant effect on phase formation • —preferential segregation on GB by formation of minor phases • —increased stability of c against decomposition

  17. The attendance of the speaker at this workshop is supported by the Alexander von Humboldt Foundation and by the Institute of Safety Research, FZ-Rossendorf.

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