Effects of controlled shot peening on multi-scale morphology and hydrophobicity of 316L stainless steel

In this study, we used shot peening-etching method to construct the multi-scale morphology on the surface of 316L stainless steel, assisted by surface modification to improve hydrophobicity. The effects of the diameter of projectile (0.2, 0.3, 0.4 mm) and shot peening time (1, 1.5, 2, 2.5 min) on the multi-scale morphology and hydrophobicity of the samples were studied. Meanwhile, the surface morphology was examined by metallographic microscope (OM) and scanning electron microscope (SEM). The surface profile and roughness were characterized by laser scanning confocal microscope (LSCM). The fractal dimension D was calculated by data analysis software, and the static contact angle measuring instrument was used to evaluate the hydrophobic performance. The results show that the smaller the diameter of projectile is, the stronger the hydrophobicity of the sample is, and there is the best time for shot peening. Moreover, the size and distance of pits on the surface decrease as the diameter of projectile decreases. The roughness of the surface shows a tendency to increase first and decrease with the increase of shot peening time, and the contact angle has the same tendency. The contact angle of the sample surface increases as the fractal dimension D increases. When the diameter of the projectile is 0.2 mm and the shot peening time is 2 min, after etching and surface modification, the static contact angle is 137.4° and the solid-liquid contact area is only 15.4%. This method has the advantages of low cost, high efficiency and environment-friendly, which is beneficial to the large-scale production of hydrophobic materials.