Abstract
Iron-zinc diffusion couples were annealed at temperatures from 320° to 412°C.
All the intermetallic phases in the iron-zinc system were observed in the diffusion zone, while the α solid solution of zinc in iron could not be detected in any specimens examined. The δ1 phase layer is composed of two parts: palisade and compact δ1 layers in the same manner as in the case of “Hot Dip Galvanizing”. At temperatures above 360°C the total width of both δ1 layers varies with time according to the parabolic rate law, but the growth of the palisade layer does not follow the rate law. It seems more likely that the material is transported through the palisade layer mainly along the grain boundary.
The activation energy for the growth of the total width of both δ1 layers is 21.2 kcal/mol, which is in good agreement with the activation energy for the δ1 phase layer growth obtained by Horstmann in his study on the reaction of solid iron with molten zinc.
Kirkendall markers exist always at the interface between the ζ and η(Zn) phases. Although this means that there is a one-sided diffusion of zinc to the iron, zinc penetration into grain boundary of the iron has not been detected. It appears that the intermetallic phases are formed in the interface between the iron and zinc disks at first and then zinc preferencially diffuses into the intermetallic phases.
