Solidification Processing

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Solidification Processing

• L23 Solidification under electropulsing

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Solidification under electropulsing
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Solidification under electropulsing
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Solidification under electropulsing

• Misra found that passing direct electrical
  current during alloy solidification resulted
  refined microstructure and improved mechanical
  properties (1986).
• Makada et al. investigated the influence of the
  pulse electrical current (electropulsing,
  hereafter) on the solidification of Sn-15wtPb
  alloy and found that the primary phase was
  globular instead of dendrite (1990).
• Li et al investigated 60Sn40Pb alloy
  solidification and they found that the eutectic
  structure is modified by electropulsing (1994).
• Barnak et al. utilizes high current density
  electropulsing and found that the colony grain
  size is reducing as the increasing of the current
  density (1995).

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Solidification under electropulsing
Grain size vs. current density.
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Side effects

• Joules heat

?0, ?m and c are the conductivity, mass density
and specific heat of liquid metal, respectively.
In order to reduce Joules heat, short-duration
electric current pulse is used.
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Side effects

• Skin

where ? and ? are magnetic permeability and
current pulse wave frequency, respectively. The
skin effect raises the temperature of the molten
metal near the mold wall which suppresses
heterogeneous nucleation there ?2.5 mm for
experiment by Barnak et al.
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Side effects

• Pinch

The pinch squeezes the liquid metal and reduced
heterogeneous nucleation at the mold wall and
disperse any nuclei which may have formed at or
near the mold wall. The maximum stress calculated
for experiments of Barnak et al. is 1 kPa
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Side effects

• Electron wind
• Shielding effect
• Electrical migration
• Active energy

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Solidification under electropulsing
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Solidification under electropulsing
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Solidification under electropulsing
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Solidification under electropulsing
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Nucleation

• Work needed for nucleation

We ?
Free energy change induced by passing electric
current
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Thermodynamics of current carrying body

• Current distribution

In uniform liquid
With nucleus
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Thermodynamics of current carrying body

• Current distribution

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Thermodynamics of current carrying body
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Thermodynamics of current carrying body
For the following format of integration
where ? and ? represent integral domain (within
nucleus or within liquid matrix). It is very
difficult to calculate the above equation
directly due to the domain coherent factor of
r-r. Therefore, the method of physical
replacement was used
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Thermodynamics of current carrying body
U(q) is the electrical potential generated by
electrostatic q at a distance r-r
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Thermodynamics of current carrying body
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Nucleation under electropulsing
Nucleation rate
Grain size
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Solidification under electropulsing
For Sn-Pb alloy
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Solidification under electropulsing
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Conductivity vs. grain size

• S.H. Liu, D. R. Poirer and P.N. Qansry, Metall.
  Trans. 26A, (1995) 741

R.S. Qin, Nanostructured Materials 10 (1998)
71-76
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Solidification under pulse electric field
Electrical field treatment causes the
disappearance of bulk silicon phases. (a) no EF,
(2) 30 second
X.D Shi et al, Rare Earth Metals, 24 (2005) 288
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Solidification under pulse electric field
Eutectic phase is refined by pulse electric field
X.D Shi et al, Rare Earth Metals, 24 (2005) 288
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Further reading

• MISRA A.K, Metall. Trans. 17A, (1986) 358.
• NAKADA M, ISIJ International 30 (1990) 27.
• LI J.M. et al, Scripta Metall. Mater. 31
  (1994)1691.
• J. P. Barnak, A. F. Sprecher and H. Conrad,
  Scripta Metall. Mater. 32 (1995)879.
• X.D Shi et al, Rare Earth Metals, 24 (2005) 288.