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.

· 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.