Microstructural observation and wear properties of thin chrome layers prepared by pulse plating

Microstructural observation of chrome layers prepared by various pulse plating were studied and correlated with the wear properties. The chrome was electrodeposited from an electrolyte bath containing 500 g l(-1) of chromic acid, 10 g l(-1) of sulfuric acid and 10-20 mg l(-1) of methane sulfuric acid at a direct current density of 1.6 mA mm(-2) and a pulse current of 6.2 mA mm(-2) with on/off time of 2-60 ms. Flake-shaped nodules were formed after pulse plating, the size of which at an equal on/off time ratio increased with increasing on/off time ratio. A shorter off- than on-time led to larger nodules. The deposition rate of chrome with an equal on/off time ratio increased with the value of the on/off time. The chronic growth kinetics determining the nodule size and shape significantly depends on the value of the on/off time ratio. Microstructural observations using transmission electron microscopy and scanning electron microscopy, as well as microhardness measurements, revealed that the reduction in wear resistance of the chrome deposited by pulse plating compared to that deposited by DC plating resulted from an increase in residual stress relief and the formation of large flake-shaped nodules during the off-time. (C) 2001 Elsevier Science B.V. All rights reserved.