Surface Texture Properties of Co-Ni Alloys Formed with Unipolar and Bipolar Plating

Mixed chloride-sulfate electrolytes are used to plate Co-Ni alloys under stagnant conditions. Pulse reverse enables to control mass-transfer and kinetics of Co(II) and H⁺ reduction, in order to suppress the anomalous behavior and improve current efficiency. Variations of cathodic and anodic amplitudes, frequency, and duty cycle are discussed to determine their influence in alloy composition, textural properties, and current efficiency. Higher nickel contents and current efficiencies are obtained with pulse reverse: 80% duty cycle, 5Hz, and anodic amplitudes of 120Am⁺². Chemical analysis revealed that atomic absorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy are able to determine an accurate alloy composition. XRD suggests the formation of an alloy in the whole composition range. Atomic force microscopy and scanning electron microscopy analyses reveal that pulse reverse generates finer grains and smoother surfaces if compared to dc plating. Although, parasitic reactions and nickel content exert some influence in the micro-structure of Co-Ni alloys, plating mode is more overriding than the aforementioned parameters due to a better control of mass-transport and electrocrystallization phenomena. Frequency is also a crucial factor to fabricate Co-Ni alloys with enhanced features, since it removes unstable regions of the deposit (dendrites) and create more nuclei more often during plating.