Effect of Amine Additive on Properties of Electrodeposited Nickel

Nickel and its alloys are commonly used as materials for electroforming process, and the electroforming of nickel alloys has been conducted to manufacture three-dimensional micro-structures and micro-components with high precision. Many studies have been performed to minimize internal stress of the electrodeposited nickel layer using pulse plating and/or various additives, as the internal stress and the hardness of the nickel layer are very important factors. This study was performed to investigate changes in the internal stress and the hardness of the electrodeposited nickel layer by amine additive. Effect of amine additive was investigated using in-situ measurements of pH values adjacent to the electrode surface with a gold mesh electrode in the nickel sulfamate electrolyte. The internal stresses of the nickel layer from the same electrolyte were measured with bent strip test. Polarization curves and adjacent to surface pH values showed that the amine additive provided hydronium ion to lower the pH value adjacent to the electrode surface in the electrolyte. The zero internal stress of the nickel layer could be obtained with a small amount of amine additive. The hardness of the nickel layer also increased up to 550 Hv. X-ray diffraction and transmitted electron microscope analyses were adopted to evaluate the microstructure of the nickel layer.