Modification of wetting property of Inconel 718 surface by nanosecond laser texturing

Topographic and wetting properties of Inconel 718 (IN718) surfaces were modified via nanosecond laser treatment. In order to investigate surface wetting behavior without additional post treatment, three kinds of microstructures were created on IN718 surfaces, including line pattern, grid pattern and spot pattern. From the viewpoint of surface morphology, the results show that laser ablated grooves and debris significantly altered the surface topography as well as surface roughness compared with the non-treated surfaces. The effects of laser parameters, such as laser scanning speed and laser power, on surface features were also discussed. We have observed the laser treated surfaces of IN718 showed very high hydrophilicity just after laser ablation under ambient air condition. And this hydrophilic property has changed rapidly to the other state, very high hydrophobicity over about 20 days. Further experiments and analysis have been carried out so as to investigate this phenomenon. Based on the XPS analysis, the results indicate that the change of wetting property from hydrophilic to hydrophobic over time may be due to the surface chemistry modifications, especially carbon content. After the contact angles reached steady state, the maximum water contact angle (WCA) for line-patterned and grid-patterned surfaces increased to 152.3 ± 1.2° and 156.8 ± 1.1° with the corresponding rolling angle (RA) of 8.8 ± 1.1° and 6.5 ± 0.8°, respectively. These treated IN718 surfaces exhibited superhydrophobic property. However, the maximum WCA for the spot-patterned surfaces just increased to 140.8 ± 2.8° with RA above 10°. Therefore, it is deduced that laser-inscribed modification of surface wettability has high sensitivity to surface morphology and surface chemical compositions. This work can be utilized to optimize the laser processing parameters so as to fabricate desired IN718 surfaces with hydrophobic or even superhydrophobic property and thus extend the applications of IN718 material in various fields.