Dual regulation of crystallographic orientation and internal stress of electroplated nickel

Abstract

Electrodeposited nickel is widely used in high-precision manufacturing, where both crystallographic orientation and internal stress critically affect the mechanical performance and dimensional stability of coatings. However, achieving simultaneous control over crystallographic orientation and internal stress remains a significant challenge in electroforming processes. In this study, a dual-additive strategy is proposed by combining PEG of various molecular weights (200, 2000, and 20,000) with sodium naphthalene-1,3,6-trisulfonate (NTS) to regulate both crystal orientation and internal stress in nickel coatings. Experimental results show that high-molecular-weight PEG-20,000 promotes (111) and (220) preferred orientations while suppressing the (200) plane, thereby improving coating hardness. Molecular dynamics simulations confirm that the polymerization degree of PEG correlates positively with its adsorption energy on Ni (111), which hinders vertical grain growth and promotes lateral expansion. However, PEG also significantly increases tensile stress by inhibiting the migration of nickel atoms and expanding interplanar spacing, as evidenced by both simulation and stress measurement. The introduction of NTS effectively compensates for this effect, reducing tensile stress and enabling the attainment of zero internal stress within the concentration range of 0–1 g/L. Furthermore, COMSOL simulations were conducted to optimize the circumferential current density distribution during the electroforming of Wolter-I type X-ray focusing mirrors. The results show that uniform anode configuration improves current uniformity, reduces stress fluctuations, and helps prevent mirror deformation. This work provides an effective approach for the simultaneous regulation of texture and stress in nickel electroplating and offers practical guidance for fabricating high-performance, low-stress nickel coatings in high-precision manufacturing, such as X-ray optics.