The Effect of the Underlying Metal on the Internal Stress and Formation of Microcracks in Electrodeposited Chromium

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Abstract
The surface texture of the underlying metal has been shown to influence the type of crack pattern produced in the chromium overlay although the chromium was deposited from the same microcracked solution. Zoned crack patterns were found to be characteristic of bright unpolished copper or nickel surfaces but were not observed in chromium deposited on polished undercoats. Cracks were preferentially orientated at right angles to the polishing direction on soft undercoats such as copper and silver. Cracking, even on a macro scale, did not take place so readily on matt surfaces. The surface texture of the undercoat has also been shown to influence the internal stress in the chromium layer. When a step occurred in the curves relating instantaneous stress and chromium thickness, this was indicative of the point at which microcracking took place. Compressive stresses were observed in thin chromium deposits plated from the microcracked, crack-free and bright chromium solutions on to nickel undercoats. These initial compressive stresses could be accounted for on the basis of hydrogen adsorption by the surface of the underlying metal.

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