Electrochemical behaviour in process of electrodeposition Ni–P alloy coating

An Ni–P alloy coating was obtained by electrodeposition on a 45 carbon steel substrate. The surface appearance of the coating was characterised by Hitachi S-4800 scanning electron microscope. The electrodeposition behaviour was investigated using electrochemical methods. The results showed that the Ni–P alloy coating was dense and smooth. The electrodeposition of the Ni–P alloy followed the mechanism of three-dimensional nucleation and subsequent grain growth. The main deposition process changed from heterogeneous nucleation/growth of Ni onto the 45 carbon steel substrate to heterogeneous nucleation/growth of Ni–P onto Ni film. There was low frequency scatter on electrochemical impedance spectroscopy plots, which can be attributed to the production of gas. With increasing negative bias voltage, the low frequency scatter became more obvious, and the charge transfer resistances R_ct and R_p increased.