Solidification of Peritectic Cu-Ge Alloys in Strong Magnetic Field

  J. Gao, J. Fan, Y.K. Zhang, J.C. He

Key Lab of Electromagnetic Processing of Materials, Northeastern University, Shenyang 110004, China

S. Reutzel, D.M. Herlach

Institute of Space Simulation, German Aerospace Center,51170 Cologne, Germany

Review on Effects of Static Magnetic Fields in Alloy Solidification

1. Lorentz force Suppression of melt convection

2. Magnetization force a. Texturing of materials b. Phase separation c. Shift of phase equilibrium

Solidification of Undercooled MeltsT

(K

)

t (s)

TL

TStable solid

Liquid

Metastable solid

GV (

J/m

3 )

T (K)TLMS TL

SSTN

T

Like rapid cooling, large undercooling can lead to the formation of a variety of metastable microstructure.

Question

• Both strong magnetic field and undercooling are attractive for fabrication of advanced materials by solidification.

• If we apply a strong static magnetic field to solidification processing, how will it affect or interact with liquid undercooling?

Undercooling in Magnetic Fields

• Hasegawa (1994): copper in 0.5 T ― Increase of maximum undercooling ― More regular change of undercooling during repeated solidification

• Tagami (1999): water in 17.9 T ― Containerless crystallization by magnetic levitation: T=10 K

• Aleksandrov(2000): water in 0.5 T ― Decrease of undercooling with increasing field ― Neglegible undercooling above 0.5 Tesla

• Gaucherand (2001, 2004): cobalt alloys in 3T ― Co-Sn : T= 26 K, aligned primary Co ― Co-B: T= 20 K, primary ferromagnetic Co

• Asai (2005): bismuth in SC magnetic field ― Remarkable recalescence for T= 21 K

Motivation

Phase selection in peritectic alloys is of greattechnical interest as introduced in my first talk.

If a static strong magnetic field influences liquid undercooling, it will also influence phase selection.

In present work, we did undercooling experiments on peritectic Cu-Ge alloys using the glass fluxing method in a 10 T magnetic field to check this point.

Experimental Set-Up

Big crucible

Magnet

Small crucible

Cu-Ge in B2O3

Undercooling experiments were alse carried out in the absence of a magnetic field for comparision.

Strong Magnetic Field Facility

Bmax=12 TeslaT max=1200°C

Experimental Procedures

T (

°C)

t (h)30

0°C

/h 1200°C/h

1050°C×2h

B=10 T

B2O3: softening at 580°C

Cu-Ge alloy

Aluminia crucible

alloy composition melting / solidification

Ge wt%

14.4

Microstructure of samples solidified in the 10 T magnetic field

Low Magnification High Magnification

All three samples were solidified into a single-phase microstructure.

Compositional Analysis

Element wt.%Cu K 85.56Ge L 14.44

EDX anylasis

Ge wt%

Cu-14.4Ge

X-ray Diffraction Analysis

0

500

1000

1500

2000

30 40 50 60 70 80 90

Inte

nsity

(a.u

.)

2 (deg.)

Not all diffractions are from CuSS!

Ge wt%

(Cu): fcc

Results of Comparision Exp.

A two-phase microstructure withprimary Cu for T up to 120 K Ge wt%

Implication: Magnetic Field promotes liquid undercooling!

Possible Mechanisms

• Possible mechanisms for the promotion of liquid undercooling:

1) shift of phase equilibrium

2) enhanced purification

3) increased liquid viscosity

4) reduced nucleation barrier

for peritectic phase by

modification of liquid/solid

interfacial energy

Ge wt%

To verify them requires delicated experiments including measurements of liquid undercooling and susceptibility.

Ren (2004):

Spaepen (1975):

Conclusions and Outlook

• Peritectic Cu-Ge alloys were solidified into a single-phase microstructure by glass fluxing in a strong magnetic field.

• The results imply the promotion of liquid undercooling by the strong magnetic field.

• Several possible mechanisms have been proposed, and further investigations will be done in cooperation with partners from DLR, Cologne.

Thanks to E.G. Wang, Q. Wang, L. Zhang, F. Li, and Z.M. Zhou for useful discussions and help in experimental work.

Thanks to the Alexander von Humboldt Foundation and the Institute of Safety Research, FZ-Rossendorf for kind support to the present presentation.

Acknowledgements