The Relationship between Nano Crystallite Structure and Internal Stress in Ni Coatings Electrodeposited by Watts Bath Electrolyte Mixed with Supercritical CO₂

In this study, the internal stress of Ni coating electroplated in the supercritical-CO 2 (Sc-CO 2 ) mixed Watts bath was investigated with a focus on the effects of plating parameters and additives. Both the internal stresses of the Ni coatings and their corresponding microstructures were examined. A relationship is found that the internal stress of the Ni coating was inversely proportional to its grain size and the Ni{200}/Ni{111} peak fraction in the measured X-ray diffraction pattern. The smaller grain size, accompanied with higher Ni{111} intensity, resulted in the higher internal stress of the coating, and vice versa. A proposed theoretical model, which took both the grain size and preferred crystalline orientation into account, correlated closely with experimental results in the internal stress. As a result, the presence of surfactant in the Sc-CO 2 electrolyte increased the internal stress of Ni coating. However, a reduction of internal stress is made possible by varying four factors: the raising of current density, the increasing of plating temperature, the lowering of plating pressure, and the addition of saccharin into electrolyte. A comparison to the internal stress of Ni coatings plated by the conventional method was also discussed in this study.