Download - Containerless Solidification of Multicomponent Nd-Fe-B Alloys by Electromagnetic Levitation
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
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1000
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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
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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
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1000
1200
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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.