Effects of Pretreatment on the Structure And Properties of Electroless Nickel Coatings

The pretreatment process can significantly affect the corrosion resistance of electroless nickel (EN) coatings One of the most important reasons is that different pretreatment processes can give different surface morphologies of the substrate. The scanning electron microscope (SEM) and the scanning tunneling microscope (STM) have been used to investigate the structure and properties of EN coatings in the as-plated condition for various deposition times, in relation to different mechanical/chemical pretreatment processes. The morphology of the substrate surface is found to be a key factor in control of the porosity of EN coatings. It can significantly affect the formation of EN deposits, not only in the early stage but also in the morphology/structure during the continued growth of the deposit. Possible porosity is associated with the morphology of the substrate and the coalescence of the nodules in the coating.