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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)
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Outline Motivation Experimental Setup Results Conclusions
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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.
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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)
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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.
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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.
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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)
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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
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Effects on Microstructure TT Primary Primary Primary All three types of additions do NOT change the evolution of solidification microstructure with melt undercooling.
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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 , ,
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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
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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 .
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X-ray Mapping of Nd-Dy-Fe-B Samples BSENd Dy Fe Dy is segregated in - and -phase.
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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
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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.
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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
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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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