Slide 1
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 1
Chapter 9:
Principles of Solidification
Chapter 9: Principles of Solidification
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Slide 2
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 2
Learning Objectives
1. Technological significance
2. Nucleation
3. Applications of controlled nucleation
4. Growth mechanisms
5. Solidification time and dendrite size
6. Cooling curves
7. Cast structure
8. Solidification defects
9. Casting processes for manufacturing components
10. Continuous casting and ingot casting
Chapter 9: Principles of Solidification
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Slide 3
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 3
Learning Objectives
11. Directional solidification [DS], single crystal growth, and epitaxial growth
12. Solidification of polymers and inorganic glasses
13. Joining of metallic materials
Chapter 9: Principles of Solidification
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Slide 4
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 4
Terminology for Mechanical Properties
Solidification process
Processing of materials involving solidification from the molten state
Primary processing Process involving casting of molten metals into ingots or semi-finished useful shapes such as slabs
Secondary processing
Processes such as rolling, extrusion, etc. used to process ingots or slabs and other semi-finished shapes
Chapter 9: Principles of Solidification
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Slide 5
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 5
Nucleation
Chapter 9: Principles of Solidification
Nucleation The formation of the first nanocrystallitesfrom molten material
Nuclei Small particles of solid that form from the liquid as atoms cluster together
Total change in energy (ΔG)
Embryo A tiny particle of solid that forms from the liquid as atoms cluster together
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Slide 6
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 6
Nucleation
Chapter 9: Principles of Solidification
Critical radius (r*) The minimum size that must be formed by atoms clustering together in the liquid before the solid particle is stable and begins to grow
Growth Refers to the formation of a stable solid as the liquid freezes
Undercooling (ΔT) The temperature to which the liquid metal must cool below the equilibrium freezing temperature before nucleation occurs
Superheat The difference between the pouring temperature and the freezing temperature
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Slide 7
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 7
Figure 9.1
Chapter 9: Principles of Solidification
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Slide 8
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 8
Nucleation
Chapter 9: Principles of Solidification
Homogeneous nucleation
Occurs when the undercooling becomes large enough to cause the formation of a stable nucleus.
whereHf latent heat of fusion
Tm equilibrium solidification temperature in kelvin
T = Tm- T undercooling when the liquid temperature is T
Heterogeneous nucleation Nucleation on preexisting surfaces.
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Slide 9
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 9
Figure 9.2
Chapter 9: Principles of Solidification
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Slide 10
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 10
Applications of Controlled Nucleation
Grain size strengthening
Process of intentionally introducing nucleating particles is called grain refinement or inoculation.
Chemicals added to molten metals to promote nucleation are known as grain refiners or inoculants.
Second-phase strengthening
Process of strengthening materials using ultra-fine precipitates. Also known as dispersion strengthening.
Solid-state phase transformation: A change in phase that occurs in the solid state.
Chapter 9: Principles of Solidification
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Slide 11
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 11
Applications of Controlled Nucleation
Glasses
Rapid solidification processing: Producing unique material structures by promoting unusually high cooling rates during solidification.
Photochromic glass: Glass that can change color or tint upon exposure to sunlight.
Glass-ceramics
Engineered materials that begin as amorphous glasses and end up as crystalline ceramics with an ultra-fine grain size.
Chapter 9: Principles of Solidification
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Slide 12
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 12
Figure 9.3
Chapter 9: Principles of Solidification
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Slide 13
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 13
Growth Mechanisms
Planar growth: A smooth solid-liquid interface grows with
little or no undercooling of the liquid.
Solidification front: Interface between a solid and liquid.
Chapter 9: Principles of Solidification
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Slide 14
© 2011 Cengage Learning Engineering. All Rights Reserved. 9 - 14
Figure 9.4
Chapter 9: Principles of Solidification
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Slide 15
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 15
Solidification Time and Dendrite Size
Chapter 9: Principles of Solidification
Chvorinov’s rule
where
V volume of the casting and represents the amount of heat that must be removed before freezing occurs
A surface area of the casting in contact with the mold and represents the surface from which heat can be transferred away from the casting
n constant (usually about 2)
B mold constant
Rate of solidification
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Slide 16
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 16
Figure 9.5
Chapter 9: Principles of Solidification
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Slide 17
© 2011 Cengage Learning Engineering. All Rights Reserved. 9 - 17
Figure 9.8
Chapter 9: Principles of Solidification
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Slide 18
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 18
Figure 9.9
Chapter 9: Principles of Solidification
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Slide 19
© 2011 Cengage Learning Engineering. All Rights Reserved. 9 - 19
Figure 9.10
Chapter 9: Principles of Solidification
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Slide 20
© 2011 Cengage Learning Engineering. All Rights Reserved. 9 - 20
Cast Structure
Equiaxed zone
A region of randomly oriented grains in the center of a casting produced as a result of widespread nucleation.
Skin-forming alloys
Alloys with a microstructure that shows an outer skin of small grains
in the chill zone followed by dendrites.
Mushy-forming alloys
Alloys that produce castings with a macrostructure consisting
predominantly of equiaxed grains.
Superheat
The difference between the pouring temperature and the freezing temperature.
Chapter 9: Principles of Solidification
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Slide 21
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 21
Figure 9.11
Chapter 9: Principles of Solidification
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Slide 22
© 2011 Cengage Learning Engineering. All Rights Reserved. 9 - 22
Figure 9.13
Chapter 9: Principles of Solidification
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Slide 23
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 23
Figure 9.14
Chapter 9: Principles of Solidification
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Slide 24
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 24
Figure 9.15
Chapter 9: Principles of Solidification
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Slide 25
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 25
Figure 9.16
Chapter 9: Principles of Solidification
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Slide 26
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 26
Figure 9.17
Chapter 9: Principles of Solidification
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Slide 27
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 27
Figure 9.18
Chapter 9: Principles of Solidification
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Slide 28
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 28
Figure 9.20
Chapter 9: Principles of Solidification
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Slide 29
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 29
Figure 9.21
Chapter 9: Principles of Solidification
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Slide 30
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 30
Figure 9.22
Chapter 9: Principles of Solidification
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Slide 31
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 31
Figure 9.23
Chapter 9: Principles of Solidification
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Slide 32
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 32
Figure 9.24
Chapter 9: Principles of Solidification
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Slide 33
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 33
Key Terms
Solidification
Primary processing
Secondary processing
Nucleation
Nuclei
Embryo
Critical radius
Growth
Undercooling
Superheat
Homogeneous nucleation
Heterogeneous nucleation
Grain refinement or inoculation
Inoculants
Dispersion strengthening or second-phase strengthening
Solid-state phase transformations
Rapid solidification processing
Photochromic glass
Glass-ceramics
Specific heat
Chapter 9: Principles of Solidification
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Slide 34
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 34
Key Terms
Latent heat of fusion
Solidification front
Planar growth
Dendrite
Chvorinov’s rule
Mold constant
Secondary dendrite arm spacing
Recalescence
Thermal arrest
Total solidification time
Local solidification time
Ingot structure
Chill zone
Columnar zone
Equiaxed zone
Skin-forming alloys
Mushy-forming alloys
Shrinkage
Cavities
Interdendritic shrinkage or microshrinkage or shrinkage porosity
Glass-ceramics
Gas porosity
Sievert’s law
Gas flushing
Chapter 9: Principles of Solidification
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Slide 35
© 2011 Cengage Learning Engineering. All Rights Reserved.9 - 35
Key Terms
Stainless steel
Argon oxygen decarburization
Sand casting
Investment casting
Lost wax process
Lost foam process
Permanent mold casting
Pressure die casting
Ingot casting
Continuous casting
Directional solidification
Epitaxial growth
Lamellar
Spherulite
Preform
Brazing
Soldering
Fusion welding
Fusion zone
Chapter 9: Principles of Solidification
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