SOLIDIFICATION

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SOLIDIFICATION

• Fundamentals and applications

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Fundamentals

• Solidification is change from liquid to solid
  state
• Recall the atomic arrangements in a liquid and
  solid
• 2 step process of NUCLEATION and GROWTH

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Thermodynamic concept

• Energy of an isolated system tends toward a
  MINIMUM
• Spontaneous and Non-spontaneous processes

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Spontaneous processes
1.
2.
Na Cl NaCl
Involves reduction in energy Or Energy change is
negative
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Non-spontaneous processes
2.
1.
Qactivation energy
State 1
State 2
Involves reduction in energy Or Energy change is
negative
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Solidification(cooling) curves
Pure metal
Alloy
L
Soldification begins
L
TL
L S
L
S
Tm
TS
Solidification complete
S
S
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HOMOGENEOUS NUCLEATION
Cluster formation
Cluster stability depends on whether Energy
change is positiveinstable cluster Or Energy
change is negativestable cluster
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Conditions for nucleation
Stable cluster nucleation
solidification Assume spherical cluster of
radius R Total energy ET Volume energy
(negative) Surface energy (positive) Total
energy ET 4/3pR3 Gv 4pR2 g dET/dR 0 for
energy to be minimum dET/dR 4 pR2 Gv 8pR
g0 R -2 g/ Gv R is the critical radius for a
stable nucleus
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GROWTH
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QUESTIONS
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METALLOGRAPHY
1. SAMPLE MOUNTING 2. GRINDING 3. POLISHING 4.
ETCHING 5. OPTICAL MICROSCOPY
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MICROSTRUCTURES
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MICROSTRUCTURES
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MICROSTRUCTURES