Fabrication of superhydrophobic NiTi shape memory alloy surface with inclined microstructure by wire electrical discharge machining

The anisotropic microstructure of the biological surface has the characteristics of direction-relatedness. This characteristic provides the basis for various functions such as water harvesting of rice leaves and cactus spine, water strider locomotion, water repellency of butterfly wings, and plant pollination. Capturing these natural features in the field of biomimetic functions is an active area of research. However, it is still a challenge to use a simple method to prepare anisotropic microstructured surfaces accurately. Inspired by the microstructure of butterfly wings, a superhydrophobic Nitinol shape memory alloy (NiTi-SMA) surface with a controllable anisotropic inclined micropillar structure was prepared by wire electric discharge machining (WEDM). The surface morphology and chemical composition of the inclined microstructured NiTi-SMA surface were characterized. The wetting mechanism of the inclined micropillar structure NiTi-SMA surface was analyzed, and the static contact angle of the surface with the spacing of the inclined micropillars was discussed. The results show that the maximum contact Angle of NiTi-SMA surface with inclined microstructure reaches 160.1°, which is about 78% higher than that of smooth surface, and the controllable preparation of the superhydrophobic surface is realized. At the same time, the influence of micropillar spacing on the contact angle is analyzed. When the number of micropillars supporting the water droplets is the same, the contact angle of the water droplets decreases with the increase of micropillar spacing. This study provides a new idea for NiTi-SAM to develop new multifunctional components.