Abstract
Electrodeposition of thin chromium layer on iron and steel sheets cathodically treated in dilute chromic acid solution was studied by electron microscopy. The results obtained were as follows: (1) At the early stage of electrodeposition, chromium epitaxially grew on the substrate, copying accurately the crystallographic orientation of base iron and steel sheets. (2) Even the thinnest film of such as about 15Å in thickness uniformly covered the substrate. (3) The rate and aspect of crystal growth seemed to depend on the crystallographic orientation of the chromium film. In the film of above 200Å in thickness, growth of pyramidal particles partitioned by four {011} planes was observed on the planes oriented within angle of 25° to the {011} planes. In the film of above 400A in thickness, the pyramidal particles changed to granular form, which deviated from the epitaxial growth. On the other hand, the planes oriented close to {111} or {011} planes showed uniform growth throughout each of the planes. The growth rate of {111} planes was found to be higher than that of {001} planes. (4) The dependence of chromium growth on crystallographic orientation could be interpreted in terms of epitaxial constraint of the substrate and the nucleation energy of electrodeposit.
