Abstract
Internal stress of chromium coatings has been investigated by means of a spiral contractometer and an X-ray stress analyzer. In the spiral contractometer method, an increase in the deflection of dial pointer is observed with thin coatings less than 5μm in thickness, irrespective of their deposition conditions. Thus these coatings are characterized by high tensile stress. A peak deflection value is obtained, in the region of 8-10μm thickness, with the bright coatings deposited at the temperatures of 40, 50 and 55°C. After the peak value is reached, the deflection gradually decreases and eventually shifts to the negative side. However, the deflection of the dial pointer for the grey chromium coatings deposited at 30°C increases linearly. A decrease in deflection is caused by compressive stress of build-up layers formed after the peak value is reached. Measurements by the X-ray stress analyzer reveal that the internal stress of thin layers of less than 3μm thickness is also tensile. This finding coincides with that obtained from the measurements by the spiral contractometer. But, as the thickness of deposit increases, the stress measurable within the depth of X-ray penetration changes to compression. This can explain the peak and the subsequent decrease in deflection as measured by the spiral contractometer. The values measured by these two different methods are found to agree closely. The internal stress of chromium electrodeposited by applying direct current is very different from that of chromium obtained by applying a single phase full-wave rectified direct current.
