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, Germany2 Key Laboratory of Electromagnetic Processing of Materials, Northeastern University,

Shenyang, China3 Institute of Experimental Physics IV, Ruhr-University of Bochum, Bochum, Germany

Sino-German Workshop on EPM Sino-German Workshop on EPM 10-12 October, 2004, Shanghai10-12 October, 2004, Shanghai

OutlineOutline

• Motivation

• Experimental-Setup

• Solidification experiments

• Microstructural examination

• Conclusions & outlook

Introduction to Nd-Fe-B alloysIntroduction to Nd-Fe-B alloys

0

10

20

30

40

50

60

1940 1950 1960 1970 1980 1990

(BH

)m

ax

(MG

Oe

)

Year

AlNiCo5

Ba-FerriteDS-Alnico

SmCo5

Nd2Fe14B

Sm2Co17

0

B

H

(BH)max

(BH)max

Nd-Fe-B

Ferrite

-Nd2Fe14B cellHysteresis loops Development of PMM

Peritectic formation of

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

CommercialMagnets

L

Nd-Fe-B phase diagram Peritectic formation of

Residual Fe dendrites lead to reduced magnetic properties.

Fabrication of sintered Nd-Fe-B magnets requires casting of bulk ingots for powder precursors.

Motivation - direct formationT

(K)

Fe (at.%) (Nd:B=2:1)

82.3 76.5

L+

L+ Undercooled

Overheated

TL

TL L

TP

Peritectic -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!

Electromagnetic Levitator

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)

In-situ X-ray diffraction analysisIn-situ X-ray diffraction analysis

X-ray Synchrotron radiation: highly penetratingBeamtime: ID 15A, ESRF, Grenoble, France

Cooling curves during solidification

1300

1350

1400

1450

1500

1550T

em

pe

ratu

re

(K)

Time 10 s

TL=1503K

Tp=1453K

(a)T=35K

(b)T=60K

(c)T=75K

Nd14Fe79B7

Recalescence occurs due to rapid latent heat release!

In-situ diffraction analysisIn-situ diffraction analysis

MS= -Nd2Fe17Bx; Th2Zn17-type rhombohedral structure;

Decomposition of Nd2Fe17Bx into Fe plus Nd2Fe14B.

Primary phase selection map

●-Fe ■-Nd2Fe14B ♦-Nd2Fe17Bx

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

Solidification microstructure

1300

1350

1400

1450

1500

1550

Te

mp

era

ture

(K

)

Time 10 s

TL=1503K

Tp=1453K

(a)T=35K

(b)T=60K

(c)T=75K

Nd14Fe79B7

Thermomagnetic analysis

1300

1350

1400

1450

1500

1550

Te

mp

era

ture

(K

)

Time 10 s

TL=1503K

Tp=1453K

(a)T=35K

(b)T=60K

(c)T=75K

Nd14Fe79B7

SummarySummary

1. Chemically reactive Nd-Fe-B melt droplets could be undercooled by electromagnetic levitation under controlled conditions.

2. Solidification of levitated Nd-Fe-B

droplets depends on melt undercooling, and three metastable solidification pathways have been determined for Nd-rich compositions.

Outlook – Outlook – Fe-rich compositionsFe-rich compositions

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

Fe phase is not harmful any longer!EM-levitation for in-situ studies.

Preliminary drop tube experiments