Combined Femtosecond Laser and Electrodeposition Process to Prepare Stainless-steel Superhydrophobic Surfaces with Reduced Drag

In long-distance pipeline transportation, the relative motion of the solid and liquid phases generates a large frictional drag between them, which is a problem that cannot be ignored. The shark-like ribbed groove microstructure, commonly used to reduce resistance, has poor drag-reduction stability, low efficiency, and is difficult to prepare. Therefore, based on the bionic concept, microstructures were constructed and modified through self-assembly to produce superhydrophobic surfaces that reduce the frictional drag between the solid and liquid phases. A superhydrophobic surface was constructed on the surface of 3Cr13 stainless steel using a composite process of femtosecond laser etching and electrodeposition, and the surface was modified using a self-assembled fluorosilane coating. The effects of the laser etching and electrodeposition parameters on the morphology and surface wettability of the frame-cone multilevel microstructures were analyzed. Additionally, the drag reduction performance of the superhydrophobicsurface of the frame-cone multilevel structure was investigated underwater. The results showed that periodically distributed micron frame structures can be obtained using a femtosecond laser, with an irregularly grooved metal build-up forming inside the micron frame structure as the laser power increases. An increase in the off-light delay produces a unilateral regular distribution of microporous structures, which damages the overall strength of the substrate. At 35% laser power and 180 mu s off delay, the micron frame structure was constructed with an intact surface. Moreover, the depth of the micron frame structure increased linearly with the number of femtosecond laser etchings. When the laser etching was conducted 10 times, the frame structure depth and the static contact angle of the surface were 4.23 mu m and 138.6 degrees, respectively. The nano/submicron cone structure of the nickel coating was prepared using electrodeposition, and both the current density and deposition time affected the microstructure morphology of the nickel coating. With an increase in the current density and deposition time, the surface microstructure of the nickel coatings changed from small to large cones and finally to a broad leaf-like structure. The surface of the microstructure was transformed from hydrophobic to superhydrophobic using a self-assembled fluorosilane coating. The optimum electrodeposition process parameters were a current density of 3 A/dm2 and a deposition time of 10 min, where the percentage of 800-1200 nm cones was 72.5%, and the static contact angle of the surface was 158.73 degrees Compared with the conventional micro-nano needle cone structure, the superhydrophobic surface of the micro-nano frame-cone multilevel structure prepared using the laser etching and electrodeposition composite process enhanced the boundary slip effect and improved the underwater drag-reduction performance. Compared with the 10-times laser-etched self-assembled fluorosilane-coated samples, the contact angle of the self-assembled fluorosilane-coated samples prepared using combined laser etching and electrodeposition increased from 138.6 degrees to 156.7 degrees, and the drag reduction rates for water and 30 wt.% glycerol increased from 8.17% and 14.38% to 27.74% and 23.69%, respectively. The superhydrophobic surface was prepared using combined laser etching and electrodeposition to construct micro-and nanostructures using self-assembly, providing a new technical method of reducing the frictional resistance between solid and liquid phases in pipeline transportation; however, its preparation technology is more demanding.