Phase transition induced inherent superhydrophobicity on Al alloys surface via femtosecond laser multi-scanning process

Fabrication of biomimetic superhydrophobic metals has attracted considerable interest because of their exceptional surface wettability. Conventional methods for achieving this property often rely on additional organic coatings to lower the surface energy; however, they are very prone to chemical decomposition and even flaking during practical usages. Here, we demonstrated that the laser-induced phase transition in hierarchical structures of metal surface can act as an effective approach to directly produce the superhydrophobic effect without any organic decorations. Through gradual increasing numbers of the femtosecond laser processing, we transfer the surface structures from the initial polycrystalline material into the super-nanometer-sized dual-phase and three-phase material that consists of nano and para-crystallinity embedded in amorphous substance, both of which contribute to lowering the surface energy. Meanwhile, the geometrical profiles of the surface structures become richer and more complicated for improving the stability of air pockets. Remarkably, it is found that both the mechanical and chemical durability of such superhydrophobic surfaces are enhanced significantly for the three-phase based material. This study describes the great value of the metal phase transition in achieving the inherent superhydrophobic properties, which provides a different route to develop high-performance coating-free superhydrophobic surfaces.