Study on the internal stress of nickel coating electrodeposited in an electrolyte mixed with supercritical carbon dioxide

This study focuses on the internal stress in the nickel deposit during electroplating through the additive-free Watts bath electrolyte mixed with and without supercritical carbon dioxide (Sc-CO2). The results showed that the Ni films plated in Sc-CO2 had brighter, smoother surface and higher hardness than plated in conventional electrolyte without Sc-CO2. However, there existed more nano-sized pinholes via TEM and AFM measurements in the Sc-CO2 specimens. It was found that during electroplating the Sc-CO2 occluded into the coating through the nano-sized pinholes/voids influenced the internal stress of the deposit. On the other hand, the periodic plating characteristics of the Sc-CO2 electroplating led to higher relative peak magnitude of Ni {111} over {200} in crystalline orientation revealed in X-ray diffraction patterns. As a result, the internal stress in the nickel film plated through the Sc-CO2 method was significantly higher than that in the conventional one. Moreover, the more CO2 volume fraction used in Sc-CO2 electroplating resulted in even higher internal stress of nickel film.