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° which decreased to about 115° after 30 min of erosion-corrosion and to about 78° 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.