Effects of Co and W alloying elements on the electrodeposition aspects and properties of nanocrystalline Ni alloy coatings

Depending on deposition current density and alloying elements, various types of surface structure (surface morphology and grain orientation) were observed for Ni and Ni alloy nanocrystalline coatings. It was found that the variation of surface morphology with current density is in a good agreement with the variation of grain orientation. An increase in the current density produced larger grains and also reduced the charge transfer resistance and growth inhibition intensity which may change the surface structure of the coatings. For Ni coatings, the effect of surface structure on the corrosion resistance was detected to be superior to that of grain size. In the case of Ni-Co coating and at different deposition current densities, Co content and surface structure were recognized as the major factors influencing the corrosion resistance. Surface structure was also a more important factor determining the corrosion resistance of Ni-W coatings. In Ni-Co-W coatings, surface structure and grain size of the coatings were found to be independent of deposition current density. This is believed to be due to the simultaneous contrary effects of Co and W elements.