solidification of electromagnetically levitated nd-fe-b melt droplets
DESCRIPTION
Sino-German Workshop on EPM 10-12 October, 2004, Shanghai. Solidification of electromagnetically levitated Nd-Fe-B melt droplets. J. Gao 1,2 , T. Volkmann 1 , J. Strohmenger 1 , S. Reutzel 3 , D.M. Herlach 1 1 Institute of Space Simulation, German Aerospace Center, Cologne, Germany - PowerPoint PPT PresentationTRANSCRIPT
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