Mechanical Properties of Electrodeposited Ni-W ThinFilms with Alternate W-Rich and W-Poor Multilayers

Nickel-tungsten (Ni-W) alloys with tailored composition were electrodeposited by controlling the pH of electrolytes and the applied current density. The current efficiency for the electrodeposition of Ni-W alloys was dependent on the pH of the employed electrolytes. The surface morphology and crystallinity of the electrodeposited Ni-W with controlled compositions were characterized. Based on the electrochemical studies of Ni-W alloys, Ni-W thin films with alternate W-rich and W-poor multilayers were produced by applying alternate current densities. The number and dimensions of the deposited layers were well controlled by the programmed frequency of the applied current and period time, respectively, in the electrochemical cell. In addition, the mechanical properties, such as hardness and internal stress of the Ni-W electrodeposits, were investigated as a function of the composition and number of deposited layers. Compared to the single layer Ni-W films showing the increase of cracks and interal stress with increasing the hardness, the modulated Ni-W multilayers without surface cracks demonstrated the enhanced hardness without an increase in the internal stress.