Design of micro-scale periodic surface textures by pulsed laser melting and its influence on wettability

Micro-and nano-scale surface texture plays a major role in the wetting behavior of various metallic and non-metallic components. Modifying surfaces using lasers has been widely explored to induce periodic surface textures and thus modify the wetting behavior. Most of these modifications are either through addition or ablation material, making the process uneconomical for the industries. This work presents the pulsed laser surface melting (pLSM) based modification of metallic surfaces to change the wetting behavior, wherein the material is neither removed nor added but is redistributed to create micro-scale features. The size and geometry of the redistributed material depend on the incident laser power and pulse duration and thus affect the wetting behavior. Detailed experimental study on an initially near-flat titanium alloy (Ti6Al4V) surface at various laser powers and pulse durations are presented to understand their influence on the wetting behavior. Experiments are carried out at various laser powers ranging from 120W to 300W and various pulse durations ranging from 3-s to 20-s to understand the size and geometry achievable through pLSM. The highest peak to valley height of the pLSM induced feature (2.3-m) was achieved with 10-s long laser pulses at 210W power. This single spot feature was then rastered across the surface with varying spot spacing and line spacing to generate nine textured surfaces. The corresponding transverse contact angles and the orthogonal contact angles are reported. The results show that the textured surfaces are more wettable or hydrophilic than the near-flat untextured surface of Ti6AL4V. In addition, line spacing of the raster scan in the transverse direction has a more significant impact on the contact angle than the spot spacing in the orthogonal direction. The transverse direction has uniform groove-like features, which aid wettability more than the periodic circular features in the orthogonal direction. Nonetheless, pLSM is demonstrated as a potential method to develop micro-scale surface textures to increase the wettability (hydrophilicity) of the Ti6Al4V surface.