I have been researching plating issues on Copper Plated Zinc Cents. The information I have found has been both interesting and challenging. My research has resulted in some papers I prepared to organize the information in a way that I can understand. Unfortunately, I have only scratched the surface! It seems that I continue to find significant related aspects that I may yet include in future revisions. I am sharing one of those papers here in .pdf format. SUMMARY Since copper is a Nanocrystalline (NC) metal, it has a face-centered cubic crystal structure that is prone to exhibit plastic deformation. During plating, stress gradients are formed within the plating and may be amplified by various elements of the plating process. As the crystalline lattice structure of the plating reorients to release the stress, ridges and valleys are created by the grains rotating out of plane.
The papers you reference are referring to dislocations in a crystal. This is very very small. These lines are very very large and all travel in the same direction. All te crystals would need to be orientated in the same direction
Thanks for your comment! You are focusing on a key question I have about my findings. The STM images of these crystalline structures, along with the descriptions, appear to be applicable to the surface morphology visible on these "corrugated" cents. However, I have found no references to how the build-up of the crystalline structure would form on plating surfaces to a size visible without magnification. I am making the assumption that the patterns continue to build, but have no research evidence to verify either that such happens or does not happen. I would appreciate any references about this question with links to resources!
There are two primary areas still to be addressed. One is the applicability of studies (as discussed in the paper) of copper deposition at the crystalline level to the corrugation features easily and commonly seen on many CPZ cents. The other is the mechanism by which the ridges and valleys are oriented in approximately the same direction on both sides of the planchet/coin. In addition to crystal behavior at the atomic level Current Density and Electrolyte Flow influence the formation, direction and orientation of the ridges and valleys of a corrugated surface. In research carried out by the Bureau of Mines to develop new technology for electrorefining metals, the hydrodynamics of electrolyte flow were studied: “The cathode deposits are relatively smooth but with striations or grooves running parallel to the electrolyte flow. Many of the striations were continuous along the entire length of the cathodes. Their origin is believed to reflect the hydrodynamic flow conditions close to the surface. It appears that either a ridge or groove, once initiated at the front edge of the cathode, propagates along the entire length.” (https://www.911metallurgist.com/blog/electrorefining-copper/) {In barrel electroplating, the object being plated acts as the cathode} A barrel plating process is used by the supplier of Cent Ready-to-strike (RTS) planchets for the US Mint. Barrel rotation is likely a key factor contributing to the formation of ridges and valleys and in their alignment in the same direction on both sides of the planchet/coin. ►Current density varies, resulting in thicknesses that vary. ►An electrolyte flow pattern is driven by the rotation of the barrel, resulting in striations or grooves running parallel to the electrolyte flow. ►The result of these dynamics builds on the crystal orientation patterns developed at the atomic level. ►The tumbling action of a metal disc in the barrel plating bath, as the barrel rotates, is most likely to be end over end, resulting in electrolyte flow patterns being in approximately the same orientation on both sides of the planchet.
