Complex 3D surface structuring by means of laser chemical machining with modulated laser power

Laser chemical machining (LCM) utilizes the thermal induced chemical dissolution to remove the material far below the melting temperature. Material removal during LCM with modulated laser power depends on the modulation frequency applied. The spatial frequency of the depth’s oscillation corresponds to the spatial frequency of the laser power up to the threshold frequency. Above this threshold, the removal depth remains constant. The aim of this work is to investigate whether modulated laser power could be used for surface structuring and its influence on the wetting behavior. Therefore, line scans with different overlaps were generated to create a surface structure on titanium grade 1 using a rectangular function of the output power with frequencies below the threshold. In addition to the modulation frequency and the line overlap, the phase angle between two neighboring lines was also studied. Subsequently, a wide range of surface structures was achieved, including wavelike and braidlike structures. The wettability investigation highlighted the considerable impact of the line overlap on the wetting behavior of the surfaces produced. While higher overlaps caused an isotropic wetting, lower overlaps induced an anisotropic wetting. These results, thus, demonstrate for the first time the possibility of achieving anisotropic wetting behavior by LCM processing.