Electrochemical characterization of electrodeposited chromium and nickel-chromium layers on a steel substrate

Chromium was deposited on steel specimens and on electroplated steel specimens covered with a Watts nickel layer. The influence of the substrate and of the crack pattern of the electrodeposited chromium layer on the passivation and the reactivation behaviour has been studied by means of potentiodynamic polarization curve measurements and cyclic voltammetry. In the results of the above mentioned electrochemical measurements a strong influence of the substrate was found for a cracked chromium layer deposited on the steel specimen and for a cracked chromium layer deposited on a 30 m Watts nickel layer. No influence of the substrate was found in the case of a crack-free chromium layer deposited on the steel substrate or on a Watts nickel layer. It is thus possible to determine whether the chromium layer is cracked or crack free by recording a polarization curve or a cyclic voltammogram for a chromium-plated system. A mechanism is proposed for the passivation and repassivation of cracked chromium layers electrodeposited on a steel substrate or on a Watts nickel layer.