Electrodeposition of nanocrystalline chromium coatings from Cr(III)-based electrolyte using pulsed current

Abstract

The effect of the pulse ratio on the current efficiency of the chromium electrodeposition reaction and the properties of coatings obtained from sulfate-formate electrolyte based on Cr(III) salts is studied. It is shown that the dependences of the current efficiency on the relative pulse duration feature a maximum that corresponds to a relative pulse duration of 2 (at τpulse = τp = 1 s). Light chromium coatings with good adhesion to the substrate are formed under pulsed electrolysis and their thickness is several tens of μm. In order to prevent pitting formation, it is expedient to introduce a special wetting surfactant additive into the electrolyte. As follows from the data of small-angle X-ray scattering, the deposited coatings are nanocrystalline. An increase in the relative pulse duration promotes a decrease in the nanocrystal size. The application of pulsed electrolysis leads to a decrease in the anodic dissolution rate of coatings in an acidic medium. Chromium electrodeposition decrease under pulsed current results in a decrease in internal stresses and in an increase in microhardness of coating.