Wettability and Tribological Performances of the Textured F-DLC Coating Surface

At low temperatures, the surface of the substrate is prone to freezing, resulting in losses. With the development of nanotechnology and biomimetic technology, hydrophobic surfaces are widely used in the field of surface frosting/ice protection. The hydrophobic surface can greatly inhibit the penetration and adhesion of liquid on the surface to achieve the effect of anti-icing, which is mainly affected by the surface micro-nano structure and low surface energy. At the same time, the durability of hydrophobic coatings in low-temperature and high-humidity environments is crucial. The construction of an integrated lubricating and hydrophobic coating on the substrate surface imparts excellent wetting and tribological properties to the substrate surface at the same time. The hydrophobic surface on 304 stainless steel was constructed by laser texture treatment combined with fluorine-doped diamond-like carbon (F-DLC) coating deposited by plasma enhanced chemical vapor deposition technology. The effects of micro-texture treatment and F-DLC coating on the wettability and tribological performances of the 304 stainless steel surface were investigated carefully. The results showed that fluorine doping could reduce the surface energy of diamond-like carbon (DLC) coating, resulting in the increase of the static water contact angle from 57° to 104° for the 304 stainless steel surface, which successfully realized the transition from hydrophilic surface to hydrophobic surface. The pattern of laser texture and the small particles formed by laser ablation during the process of laser texture contributed to the formation of a structure similar to cauliflower clusters after the deposition of the coating, which could further improve the hydrophobic performance of the surface. And thus, the static water contact angle could be raised to 144° resultantly. In this paper, two different types of texture patterns were selected, namely circular dot matrix pattern and grid pattern, and the arrangement spacing of the texture pattern and the laser texture process had an effect on the surface wettability. By depositing F-DLC coatings on the texture surface with different spacing and different texture processes, two texture patterns with the highest static water contact angles were selected in their respective types, namely 0.1 mm (spacing) ×0.1 mm (diameter) laser lattice and grid laser lattice with line spacing of 0.2 mm, and the static water contact angles reached 132° and 144°. The tribological properties of the F-doping DLC coatings could be tailored by designing different micro-weaving patterns. The F-DLC textured coating treated with 0.1 mm (spacing) ×0.1 mm (diameter) laser lattice had the best tribological properties with a stable friction coefficient of only 0.2. This was because the pits formed by the circular pass texture in this pattern could be used to store the abrasive debris generated during the friction process, reducing the friction coefficient of the coating as a result. However, even though the groove formed by the grid pattern texture with 0.2 mm spacing could also store the wear debris, the deposition of F-DLC surface textured by the 0.2 mm spacing pattern possessed a rough surface which is not so flat. And thus, the convex structure would affect the friction process, resulting in stress concentration, and the friction coefficient was slightly higher than that of the lattice pattern texture as a consequence. Therefore, the hydrophobic and tribological properties of the 304 stainless steel surface could be significantly improved by optimizing the laser lattice structure for micro-texture treatment combined with fluorine-doped DLC coating.