Chapter 4: DiffusionControlled Phase Transformations

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Chapter 4 Diffusion-Controlled Phase
Transformations

• 4.1 Examples of Diffusional Transformations
• 4.2 Driving Force, Gibbs-Thompson Effect
• 4.3 Diffusional Nucleation and Growth
• 4.4 Coarsening (Lifshiftz-Slyozov-Wagner
  Relation)
• 4.5 Spinodal Decomposition

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4.1 Examples of Diffusional Transformations
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4.2 Driving Force, Gibbs-Thompson Effect
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4.2 Driving Force, Gibbs-Thompson Effect
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Precipitation
Microstructures at different stages during ageing
of Al-Cu alloys. (a) GP zones 720 000. (b) ??
63 000. (c) ?' 18 000. (d) ? 8000.
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Precipitation
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Precipitation
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Precipitation
(a) The activation energy barrier to the
formation of each transition phase is very small
in comparison to the (b) barrier against direct
precipitation of the equilibrium phase (c)
Schematic diagram showing the total free energy
of the alloy v. time.
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Precipitation - Thermodynamics
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Precipitation - Thermodynamics
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4.4 Coarsening
The driving force for coarsening is the local
compositional gradient that is set up between
particles of equilibrium concentration of
different size. The reason for the local
compositional variation is the Gibbs-Thompson
effect.
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4.5 Spinodal Decomposition
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4.5 Spinodal Decomposition
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4.5 Spinodal Decomposition
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4.5 Spinoidal Decomposition
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4.5 Spinodal Decomposition
There is a potential difference due to the local
composition gradient
Compositional fluctuations
Strain energy due to compositional variation
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