Controlling the Surface Properties of Electrodeposited Ni Films

Abstract

Polymer/metal composites, including polymer films deposited on metallic layers, are very important because of the increasing demand of these advanced materials in multiple applications, such as in microelectronics, automotive, aerospace, and medical devices [1]. The surface topography of the metal substrate is a critical factor in producing a good adhesion surface, particularly for polymer films. In this work, electrodeposition was used to create a micro/nano-structured Ni surface with specific engineered properties, with Ni selected as it has excellent abrasion, erosion, and corrosion resistance and can therefore be used in many aggressive environments. While previous work [e.g., 2,3] has examined the effect of electrodeposition conditions on the resulting Ni surface morphology and crystallite size, particularly to achieve a high surface areas [4,5], our goal was to determine the optimum surface properties to enhance the adhesion of various elastomeric coatings, while also ensuring that a high strength Ni layer was produced. In the present work, a Watt’s bath was employed for Ni electrodeposition [2], with the main variables being the applied current density, temperature, stirring rate, and chemical additives, resulting in microstructures of a range of shapes and roughness [6, 7], where the surfactant was used to minimize hydrogen bubble adhesion under negative polarization [8]. A range of Ni substrates was examined, including Ni plates, rods and electroformed Ni, having a thickness of ca. 0.1 mm and a complex shape, intended for use particularly in aerospace applications. For our purposes, it was found that low current densities of ~ 5 mA/cm2 and a temperature of 40 oC produced surface morphologies having the desired characteristics. An example of SEM and 3D optical profilometry images of an electrodeposited Ni deposited on a Ni plate is shown in Fig. 1, with the applied current density clearly affecting the surface roughness and crystallite shape. At lower current densities, the electrodeposited Ni surface exhibited pyramidal-like structures, interconnected with a finer matrix and having a high roughness factor, while at higher current densities, the surface is fully covered by a very fine structure with a small grain size and a lower degree of roughness. The results also showed that the adhesion of the electrodeposited Ni films on the Ni substrate is better for samples prepared at lower current densities. This presentation will also discuss the results of pulsed electrodeposition and electrodeposition-dissolution methods to produce the desired Ni surface morphology and strength characteristics, as well as the results of elastomer adhesion testing.