Tuning residual stress in electrodeposited nickel films via pulse current

The pulse current electrodeposition has proved to be effective in the preparation of metal films with a low residual stress, while the formation mechanism of residual stress under the pulse current remains unclear. In this study, in situ measurements of residual stress in electrodeposited nickel films was performed. Nickel films with the lowest average stress were obtained under the frequency of 800 Hz, average current density of 1 A/dm2 and duty cycle of 50%. Based on X-ray diffraction and TEM analysis, the relationship between dislocation density and residual stress was studied, revealing that a high dislocation density contributed to the formation of cross slip, as well as the release of residual stress. Furthermore, charge time of the electric double layer was measured by multi-current step tests, and the possible mechanism for residual stress formation under pulse currents was proposed. The results indicated the stress was modulated by two competing factors: overpotential and fraction of the charge time. The overpotential played a leading role on average stress at low frequency and high current density, while fraction of the charge time played a dominant role at high frequency and low current density (less than 1 A/dm2). Our study provides a valuable insight to understand how pulse current parameters influence the residual stress in electrodeposited nickel films.