Electrochemical deposition and mechanical property enhancement of the nickel and nickel-cobalt films

Electrochemical deposition is one of the effective and inexpensive processes in surface coating technology. It is of great interest to produce electrochemical deposits with dense structure and good mechanical properties. The electrochemical deposited nickel and nickel-cobalt are the most common materials used in decorative coatings and micro-fabrications. In this chapter, the authors will briefly review characteristics of nickel and nickel-cobalt deposits under different electrochemical treatments and introduce two effective procedures to enhance the strength of deposits: One is to vary the applying potential and the other to alter the temperature of the electrochemical cell. Both experimental and simulation results show that pulse electrodeposition leads to higher concentration of ions at cathodic surface and better penetration ability of ions than that by direct current (DC) one. More compact and hard deposits are formed during pulse electrodeposition compared to DC one. Moreover, usually electrodeposition is difficult to perform at low temperature due to ineffective mass transfer. Through careful control of the output power to the electrochemical cell, the resulting deposit at low temperature presents higher strength than those electrodeposited at relatively high temperatures. The possible mechanism of strengthening and the corresponding electrochemical phenomena are also introduced.