Mechanical and electrical properties of Au-Ni-C alloy films produced by pulsed current electrodeposition

Au-Ni-C alloys films electrodeposited by a pulsed current method were investigated to assess the crystalline structure, sheet resistance, and wear resistance, for use as an electronic contact material. In particular, we have analyzed the effects of citric acid concentration and pulse off-time on the mechanical and electrical properties of the electrodeposited Au-Ni-C alloy films. The electrodeposition bath used in this study was composed of K[Au(CN)₂] and NiSO₄ · 6H₂O as precursors, and citric acid as the complexing agent. The film microstructure and composition were controlled by adjusting the interval of pulse off-time and the concentration of citric acid. With the prolongation of the pulse off-time interval, XRD results indicated that the amorphous structure with high Ni and C contents was transformed into a nanocrystalline structure, followed by the formation of crystals with small Ni and C contents. The amorphous and nanocrystalline films showed a high Knoop hardness of ca. 500 kg mm ^-2, while that of the crystalline films was found to be 300 kg mm^-2. The wear resistance of the film electrodeposited by the pulsed current method was remarkably good compared to that of the direct-current electrodeposition films, even though both films exhibited essentially identical microstructure and composition. The wear property was considered to be relevant to the restoration of the surface flatness of the film by the galvanic displacement deposition of Au during the pulse off time.