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, Germany2 Key Lab of EPM, Northeastern University, Shenyang, China

3 Institute of Experimental Physics IV, Ruhr-University of Bochum, Bochum, Germany

2nd German-Chinese2nd German-Chinese Workshop on EPM Workshop on EPM, October, October 200 20055, , Dresden Dresden

Financed by Alexander von Humboldt Foundation

and by German Aerospace Center (DLR-Bonn)

OutlineOutline

• Motivation

• Experimental Setup

• Results

• Conclusions

Solidification of Nd-Fe-B alloys

800

1000

1200

1400

1600

1800

2000

707580859095100

Te

mp

era

ture

(K

)

Fe Concentration (at.%)

L + L

L +

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 Nd2Fe14B

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.

Previous work

1300

1350

1400

1450

1500

1550

Tem

pera

ture

(K

)

Time 10 s

TL=1503K

Tp=1453K

(a)T=35K

(b)T=60K

(c)T=75K

Nd14Fe79B7

L

L+

+ L+

(after Kurz)

EML

primary primary primary

=FeSS =Nd2Fe14B =Nd2Fe17Bx (x~1)

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.

Alloy Composition Table

800

1000

1200

1400

1600

1800

2000

707580859095100

Te

mp

era

ture

(K

)

Fe Concentration (at.%)

L + L

L + L +

L + +

+

+

Nd + +

Nd14Fe79B7

1665 K

928 K

1453 K

1353 K

1185 K

Nd:B=2:1

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.

Electromagnetic Levitation (EML)To chart recorder

R. F. Generator

He (6N)

CoilQuartztube

To vacuum pump

Sample (1g, 6mm)

Pyrometer

Vac:=10-6 mbarPHe=10-50 mbar

EML + low P + T>>TL large T

Nd2O3 (s)+ Nd (L) NdO (g)

Effects on Critical Undercoolings

Alloy base Co Dy Zr

TL(K) 1503 1518 1503 1503

(K) 45 50 25 40

(K) 60 65 35 60

Co adddition increases TL, and Dy addition lowers Ts.

Temp. Accuracy: 5K

Effects on Microstructure

T

Primary

Primary Primary

All three types of additions do NOT change the evolution of solidification microstructure with melt undercooling.

Change Due to Co Addition

Nd Fe CoBulk 14.7 74.2 11.1

1.0 92.1 6.9

12.6 77.5 9.9

10.9 79.3 9.8

20.8 68.2 11.0

Nd-rich

65.8 5.9 28.3

Co in , ,

X-ray Mapping of Nd-Fe-Co-B Alloys

“Homogeneous” distributin of Co

BSE

CoFe

Nd

Nd Fe CoBulk 14.7 74.2 11.1

1.0 92.1 6.9

12.6 77.5 9.9

10.9 79.3 9.8

20.8 68.2 11.0

Nd-rich

65.8 5.9 28.3

Change Due to Dy Addition

element Nd Fe DyBulk 13.2 84.6 2.2

0.8 99.2 0.0

11.4 86.4 2.2

9.6 88.7 1.7

21.2 76.7 2.1

Nd-rich81.7 16.8 1.5

Dy in and but not in.

X-ray Mapping of Nd-Dy-Fe-B Samples

BSE Nd

Dy Fe

Dy is segregated

in - and -phase.

Modification by Zr Addition

element

Nd Fe Zr

Bulk 14.7 84.7 0.6

0.7 99.3 -

12.3 87.7 -

11.0 89.0 -

22.0 78.0 -Nd-rich 88.3 11.7 -ZrFe2 4.0 65.7 30.3ZrB2 7.6 32.2 60.2

Concentration of Zr in ,, and is within the error of EDX.

Bulk

ZrFe2

ZrB2

X-ray Mapping of Nd-Fe-Zr-B Alloy

BSE

Fe

Nd

Zr

A large amount of Zr atoms are egregated on grain boundaries:ZrB2 and ZrFe2.

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

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.