Effect of femtosecond laser processing parameters on microstructures and wetting properties of copper surface

In this work, the ablation characteristic, surface structure, and wetting property of the femtosecond laser-processed copper (Cu) surface are systematically studied. With the increase of laser pulse number, the area of the ablation crater increases and then tends to be stable, the period (0.62λ ∼ λ) of the generated ripple structures decreases, and the area of the periodic ripple structures in the Cu ablation crater first increases and then decreases. With the increase in laser fluence, the area of the ablation crater slightly increases, the period of the generated ripple structures varies oscillatively, and the area of the periodic ripple structures in the Cu ablation craters increases. Different columnar structures on the Cu surface are obtained through femtosecond laser cross-scanning processing. The height of columnar structures basically increases with the increase in laser power, laser scanning times, and laser scanning spacing. The wetting properties of the Cu columnar structure surfaces are also investigated. It reveals that the droplet contact angle obviously decreases with the increase in laser power and laser scanning times, and increases with the increase in laser scanning spacing. The variation of droplet contact angle on the laser-processed Cu surface is attributed to the different columnar structures and their different heights. It also reveals that the Cu surface changes from original hydrophobic to superhydrophilic with a contact angle of 8.9°. This work indicates the ability of femtosecond laser processing in regulating micro/nanostructure and wetting property of the Cu surface, which can be applicable to the surface treatment and performance control of other metallic materials.