1. 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 2 Key Lab of EPM, Northeastern University, Shenyang, China 3 Institute of Experimental Physics IV, Ruhr-University of Bochum, Bochum, Germany 2nd German-Chinese Workshop on EPM, October 2005, Dresden Financed by Alexander von Humboldt Foundation and by German Aerospace Center (DLR-Bonn)

2. Outline Motivation Experimental Setup Results Conclusions

3. Solidification of Nd-Fe-B alloys 800 1000 1200 1400 1600 1800 2000 707580859095100 Temperature (K) Fe Concentration (at.%)  L +  L    +   +   +  Nd +  +  1665 K 928 K 1453 K 1353 K 1185 K Nd:B=2:1  L  Nd-Fe-B phase diagram L +  -Fe   Nd 2 Fe 14 B The composition of Nd-Fe-B magnets falls into the primary field of  -Fe phase. For this reason, precursor ingots often contain undissolved  -Fe dendrites leading to reduced magnetic properties of sintered magnets.

4. Previous work L  L+L+ ++ L+  (after Kurz) EML primary  primary  primary   =Fe SS  =Nd 2 Fe 14 B  =Nd 2 Fe 17 B x (x~1) 

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

6. Alloy Composition Table Base alloy (at%): Nd 14 Fe 79 B 7 Co for Fe: Nd 14 Fe 69 Co 10 B 7 Dy for Nd: Nd 13 Dy 1 Fe 69 B 7 Zr for Fe: Nd 14 Fe 78.5 Zr 0.5 B 7 Original sampels were prepared by arc-melting elemental materials.

7. Electromagnetic Levitation (EML) To chart recorder R. F. Generator He ( 6N ) Coil Quartz tube To vacuum pump Sample (1g, 6mm) Pyrometer Vac:=10 -6 mbar P He =10-50 mbar EML + low P + T>>T L  large  T Nd 2 O 3 (s)+ Nd (L)  NdO (g)

8. Effects on Critical Undercoolings Alloy baseCoDyZr T L (K) 150315181503     (K) 45502540     (K) 60653560 Co adddition increases T L, and Dy addition lowers  Ts. Temp. Accuracy:  5K

9. Effects on Microstructure TT Primary  Primary  Primary  All three types of additions do NOT change the evolution of solidification microstructure with melt undercooling.

10. Change Due to Co Addition NdFeCo Bulk 14.774.211.1  1.092.16.9  12.677.59.9  10.979.39.8  20.868.211.0 Nd- rich 65.85.928.3 Co in , , 

11. X-ray Mapping of Nd-Fe-Co-B Alloys “Homogeneous” distributin of Co BSE CoFe Nd   FeCo Bulk 14.774.211.1  1.092.16.9  12.677.59.9  10.979.39.8  20.868.211.0 Nd- rich 65.85.928.3

12. Change Due to Dy Addition element NdFeDy Bulk 13.284.62.2  0.899.20.0  11.486.42.2  9.688.71.7  21.276.72.1 Nd-rich 81.716.81.5 Dy in  and  but not in .

13. X-ray Mapping of Nd-Dy-Fe-B Samples BSENd Dy Fe Dy is segregated in  - and  -phase.  

14. Modification by Zr Addition elem ent NdFeZr Bulk 14.784.70.6  0.799.3-  12.387.7-  11.089.0-  22.078.0- Nd-rich 88.311.7 - ZrFe 2 4.065.730.3 ZrB 2 7.632.260.2 Concentration of Zr in , , and  is within the error of EDX. Bulk ZrFe 2 ZrB 2

15. X-ray Mapping of Nd-Fe-Zr-B Alloy BSE Fe Nd Zr   A large amount of Zr atoms are egregated on grain boundaries: ZrB 2 and ZrFe 2.

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 2.Addition of 1.0 at.% Dy : — lower critical undercoolings — preferential segregation in  and  — increased stability of  against decomposition 3.Addition of 0.5 at.% Zr: — no significant effect on phase formation — preferential segregation on GB by formation of minor phases — increased stability of  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.