Dual Ni/Ni-Co electrodeposited coatings for improved erosion-corrosion behaviour

Industrial applications of hydrophobic metallic coatings are limited to durability of their surface structures against detrimental effects of the surrounding environments. In the present research, the life-long of the hierarchical structure of hydrophobic nickel coating in an erosive-corrosive solution was investigated. The effect of alloying with cobalt on strengthening the hierarchical structures was also investigated. In this regard, highly hydrophobic Ni/Ni, Ni-Co/Ni-Co, dual Ni/Ni-Co and dual Ni-Co/Ni coatings with rough hierarchical structures were electrodeposited. In situ electrochemical measurements were performed to investigate changes in corrosion resistance and hydrophobicity of the coatings with damage initiation to their morphology. Damage to the hierarchical structure of the coatings during erosion-corrosion tests was followed by a decrease in their real surface area in contact with solution and as a result an increase in the charge transfer resistance of the coatings. The Ni/Ni coating showed the highest increase of polarization resistance after erosion-corrosion test, and therefore, it had the lowest erosion-corrosion resistance. On the other hand, the Ni-Co/Ni experienced the lowest degradation during erosion-corrosion test, but it showed higher loss in water contact angle due to flattening of top Ni cones. Although, the coatings with second Ni-Co layer had more degradation, but they revealed less contact angle loss denoting better preservation of hierarchical structures and thus hydrophobicity.