Enhancement of Surface properties of Metal substrates by Electroless Nickel Coating

Abstract

Ni plating, particularly electroless Ni plating or deposits, enjoys technological applicability in various industries, such as the electronic, oil and gas, aero-space, machinery, automobile and magnetic recording media industries. Present work reports the electroless coating of nickel-phosphorus on mild steel surface with increased coating rate. In this work the coating rate achieved was about 40 um/h against the reported literature value 25 um/h. To achieve the above coating rate various paramet-ers, namely bath compositions, pH, temperature, ratio of reducing agent and source of nickel were studied and a final optimum bath composition with controlled parameter was arrived at to achieve the enhanced coating rate around 40 um/h. Physical and chemical properties of the coating obtained were also studied. Thus, coating was essentially amorphous Ni-P coating when Na-hypophosphite was used as reducing agent. Micorhardness of the coating was -600Hv at room temperature but when it was annealed at 400oC, microhardness increased to -1059Hv. Corrosion resistant behaviour was also improved to that of electroplated nickel coatings.