Fabrication and coating adhesion study of superhydrophobic stainless steel surfaces: The effect of substrate surface roughness

Abstract

In this study, superhydrophobic 17–4 PH stainless steel surfaces were fabricated for applications in harsh marine environment. The impacts of the substrate's surface roughness on the fabrication and durability of the developed superhydrophobic coating, comprised of a Zn electrodeposited layer capped with 0.05 M stearic acid, were investigated for the first time in this study. Various micron and sub-micron scale finished surfaces with different surface roughness, namely as-received (Ra ~ 4.62 μm), sandblasted (Ra ~ 11.93 μm), and ground (Ra ~ 0.39 μm) surfaces, were fabricated, followed by applying Zn electrodeposited coating to improve the water-repellent properties of the stainless steel substrate. The adhesion durability of the coating and corrosion behavior of the electrodeposited Zn layer were deliberated by studying the combined impacts of the initial surface roughness, and super-hydrophobicity of the surfaces. The cyclic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) results measured in aerated 3.5 wt.% NaCl electrolyte at room temperature along with salt spray testing highlighted a significantly better uniformity and adhesion durability of the coating on the as-received substrate correlated to its optimum surface roughness. The best coating adhesion was obtained on surfaces with an initial surface roughness of 4.62 ± 0.15 µm. The coated 17–4 pH stainless steel surfaces were also found to be effective in preventing the aggressive chloride ions from approaching the substrate, leading to the improved corrosion performance of the material.