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Review on Effects of Static Magnetic Fields in Alloy Solidification

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Review on Effects of Static Magnetic Fields in Alloy Solidification

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  1. Solidification of Peritectic Cu-Ge Alloys in Strong Magnetic FieldJ. Gao, J. Fan, Y.K. Zhang, J.C. HeKey Lab of Electromagnetic Processing of Materials, Northeastern University, Shenyang 110004, ChinaS. Reutzel, D.M. HerlachInstitute of Space Simulation, German Aerospace Center,51170 Cologne, Germany

  2. Review on Effects of Static Magnetic Fields in Alloy Solidification • Lorentz force • Suppression of melt convection • Magnetization force • a. Texturing of materials • b. Phase separation • c. Shift of phase equilibrium

  3. T (K) GV (J/m3) Liquid TL Metastable solid Stable solid DT DT TLMS TLSS t (s) TN T (K) Solidification of Undercooled Melts Like rapid cooling, large undercooling can lead to the formation of a variety of metastable microstructure.

  4. 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?

  5. 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: DT=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 : DT= 26 K, aligned primary Co ― Co-B: DT= 20 K, primary ferromagnetic Co • Asai (2005): bismuth in SC magnetic field ― Remarkable recalescence for DT= 21 K

  6. Motivation Phase selection in peritectic alloys is of great technical 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.

  7. Experimental Set-Up Cu-Ge in B2O3 Small crucible Bmax=12 Tesla T max=1200°C Magnet Strong Magnetic Field Facility Big crucible Undercooling experiments were alse carried out in the absence of a magnetic field for comparision.

  8. Experimental Procedures alloy composition melting / solidification 1050°C×2h T (°C) 14.4 300°C/h B=10 T 1200°C/h B2O3: softening at 580°C Cu-Ge alloy Aluminia crucible t (h) Ge wt% 

  9. Microstructure of samples solidified in the 10 T magnetic field High Magnification Low Magnification All three samples were solidified into a single-phase microstructure.

  10. Element wt.% Cu K 85.56 Ge L 14.44 Compositional Analysis EDX anylasis Cu-14.4Ge Ge wt% 

  11. Ge wt%  X-ray Diffraction Analysis (Cu): fcc Not all diffractions are from CuSS!

  12. Ge wt%  Results of Comparision Exp. A two-phase microstructure with primary Cu for DT up to 120 K Implication: Magnetic Field promotes liquid undercooling!

  13. Ge wt%  Possible Mechanisms Ren (2004): • 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 Spaepen (1975): To verify them requires delicated experiments including measurements of liquid undercooling and susceptibility.

  14. 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.

  15. Acknowledgements 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.

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