Corrosion behavior and effect of bath parameters on plating rate of electroless Ni-Co-P ternary alloy coatings

Electroless Ni-P coatings have found a variety of applications due to their unique properties. For improvement of the electroless nickel-phosphorous binary coatings qualities, addition of a third element is being developed. Meanwhile, Cobalt as an effective element in improving the coatings characteristics such as corrosion and wear resistance, hardness, electromagnetic properties, etc., has attracted attentions of many researchers. In this study, applying the electroless Ni-Co-P alloy deposit on St37 substrate was considered and the achieved coating was heat treated at 400oC for 1 hour. Influence of bath parameters such as pH, concentration of cobalt sulphate and reducing agent on plating rate was investigated. Morphology and composition of the coatings were characterized by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Corrosion behavior of the binary and ternary alloy deposits were characterized using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) confirming the effect of cobalt addition on improvement of the coatings corrosion resistance.