Probe into deposition mechanism of double pulse electrodepositing Ni-W-P matrix composite coatings containing CeO2 and SiO2 nano-particles

Ni-W-P matrix composite coatings reinforced by CeO2 and SiO2 nano-particles were prepared on common carbon steel surface by double pulse electrodeposition and the deposition mechanism was discussed. The results showed that the composite coatings with amorphous structure were obtained as-deposited. The initial growth behavior had alternatives and the nucleation was inhomogeneous because of obvious composition fluctuation. With the pulse deposition time increasing, some pearlite microstructures of the substrate were covered by some deposits and the composition fluctuation disappeared. Forward pulse currents promoted to form a great number of atomic beams composed of Ni, W and P atoms or CeO2 and SiO2 nano-particles as the core, which inhabited the growth of atomic beams. Reverse pulse currents eliminated concentration polarization and dissolved some surface boss of atomic beams. The solution of W and P atoms within Ni grains and embedding of CeO2 and SiO2 nano-particles within Ni-W-P matrix metal made atomic arrangement disordered. Finally, the atomic beams grew to amorphous small particles.