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Kinetics and Microstructural Control | |||||||||||||||
Heterogeneous
Nucleation
· In a heterogeneous nucleation process, an additional surface term, due to the loss of grain boundary area in the polycrystalline alpha-matrix, must be taken into account. |
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·
The
total Gibbs function change associated
with the formation of a nucleus of radius, r, is: ΔGT
(het) = (4πr3/3)ΔGV
+ 4πr2
γαβ
- πr2
γαα .
· The last term is the decrease in α - α grain boundary energy and causes both r*het and ΔG*het to be smaller than their homogeneous values. |
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