Abstract
Chromium coatings electrodeposited from Sargent bath (50°C) at a current density of 30A/dm2 by using rippled direct current of various frequencies were investigated by hydrogen gas analysis method, microscope, and X-ray stress analyser. Heating the chromium coatings, consisting of both hcp and bcc crystals, caused generation of hydrogen gas and disappearance of the X-ray diffraction line due to the hcp crystals. A close correlation was observed between the quantity of hydrogen gas and the content ratio of hcp crystals. In the transition state from mixed crystals to bcc crystals only, the cracks seemed to be caused by a shrinkage force, which overcomes the bonding force of the chromium. And the number of cracks on the surface observed was also proportional to the content ratio of hcp crystals. The cracked coatings became almost free from stress. However, the surface and the stress of as-electrodeposited chromium consisting of only bcc crystals did not show any change after heating. Crack-free coatings of relatively high hardness were obtained in the range of 1.4kHz to 5.0kHz ripple frequency of the direct current.
