Laser surface texturing on curved geometries

Abstract

This study investigated the use of nanosecond laser pulses to induce hydrophobicity on flat and curved 316L stainless steel surfaces. Laser surface texturing is a surface modification technique used to change the morphology of a surface, which could potentially change the properties of a surface. The main gap that this study serves to investigate is the change in hydrophobicity of curved surfaces as little research has been done for laser texturing on curved geometries. Hydrophobic surfaces with stable water contact angles of ~120° were achieved by direct laser surface texturing using a nanosecond short-pulsed laser on flat and curved geometries. Varying laser parameters are known to affect the wettability of a laser textured surface. It was observed that the laser scanning speed, laser scan line separation, and textured patterns are factors that determine the wettability of a surface. The time dependency after exposure to ambient conditions also causes the wettability of the surface to change. The changes in surface morphology after laser processing was analysed and compared with surfaces processed with different laser parameters. There were significant changes in the surface morphology, which likely affected the wettability of the surfaces. The surface chemistry of the laser processed surface changes as the surface oxide created by laser ablation reacts with carbon dioxide in the air to form non-polar bonds, increasing the hydrophobicity of a surface. EDS analysis indicated the presence of elements that are present in the surface oxide which likely contributes to the change in wettability of the surface overtime as chemical bonds change. The WCA of all surfaces remained stable after a certain period of exposure to ambient conditions. Moreover, the results showed that a lower scanning speed (300mm/s) and smaller hatch distance (50μm) are ideal to create hydrophobic surfaces on flat and curved surfaces. It has also been identified that groove patterns are more suitable to create hydrophobic surfaces on flat surfaces instead of on curved surfaces.