Erosion-corrosion behavior of highly hydrophobic hierarchical nickel coatings

The effect of surface microstructure on erosion-corrosion resistance of hydrophobic rough and smooth nickel electrodeposited coatings was investigated using on site electrochemical impedance spectroscopy in dynamic solution of 3.5 wt.% NaCl + 40 wt.% sand. Atomic force microscopy (AFM) was used to track damage initiation at the surface of the coatings during erosion-corrosion. Changes in the hydrophobic behavior of the coatings during erosion-corrosion were recorded. It was observed that the rough nickel coating was not erosion resistant and about 65% of its initial average roughness was lost after 30 min of erosion-corrosion. This loss of roughness approached to about 80% after 1 h of erosion-corrosion. The water contact angle of the rough nickel coating after two weeks of storing in the air was about 131 degrees which decreased to about 115 degrees after 30 min of erosion-corrosion and to about 78 degrees after 1 h of erosion-corrosion. However, during erosion-corrosion tests, the polarization resistance of the rough nickel coating was constantly higher than that of the smooth nickel coating notwithstanding the significant loss of its surface microstructural features.