Micro-pits array structure, micro-gratings structure covered with finer nanostructures were generated on titanium surfaces using femtosecond laser pulse. The wetting behavior of the two types of surface structures were studied. Micropits array structure with a size of dozens of microns exhibits hydrophilic properties, and the hydrophilicity increased with increasing the number of laser pulses. Micro-gratings structure covered with finer nanostructures exhibits hydrophobic properties, and the hydrophobicity increased with decreasing the laser energy density. The results demonstrated that wettability of metallic surface can be facilely controlled by adjusting the femtosecond laser processing parameters. The formation processes of the two types of surface microstructures as well as the underlying mechanisms for their special wettability are also discussed. This research might provide a facile controllable strategy to realize special wettability for metal or other solid surfaces, even expand the functions and applications of metals.
Additive manufacturing of metal parts in space is one of the potential means to realize on-orbit maintenance of aircraft. However, the basic phenomena such as the rapid melting and solidification behavior of metallic materials under the action of high-energy beams in space are unclear. It is necessary to observe those phenomena and reveal basic laws through space experiments. Therefore, an experimental platform for rapid melting and solidification of metal materials is developed. There are two parts included in this platform. A detailed design of the manufacturing system in space is described at first while the in lab experimental system on the ground is introduced also. In order to simulate the vacuum environment in space, a vacuum chamber is used to contain the core unit of the experimental system. Laser is used to melt a metal wire during the experiment while a positioning stage is adopted to shape the melted wire. The melting and solidification process is controlled automatically while it is monitored by a machine vision system at the same time.