Corrosion Behavior of Nickel-Copper-Phosphorous Electroless Coating

CuSO 4 was added into electroless Ni-P bath to prepare Ni-Cu-P ternary alloy coating so as to improve the corrosion resistance of Ni-P electroless coating.The surface morphology of the coating was observed using a scanning electron microscope,and its corrosion resistance in 5.0 % H 2 SO 4,5.0 % NaOH and 3.5 % NaCl solutions was evaluated by measuring the potentiodynamic polarization curves.It was found that Ni-Cu-P coating had finer nodular structure and better compactness than Ni-P coating.In the meantime,Ni-Cu-P coating showed better resistance to general corrosion and pitting in the three kinds of corrosive solutions than Ni-P coating.The reason lay in that the ternary coating contained amorphous phase,which reduced the amount of defects thereby reducing the amounts of corrosion positions and corrosion microcells.Moreover,the Ni-Cu-P coating composed of finer grains with better compactness was more liable to be passivated and remain passivating status,thereby more effectively preventing the corrosive mediums from penetrating into the substrate.