Influence of laser hardening on laser induced periodic surface structures on steel substrates

Laser-induced periodic surface structures (LIPSS) are used to structure surfaces for functionalization. Thus, hydrophilic states are generated using LIPSS. However, these nanostructures do not withstand mechanical loads and therefore cannot be used for most tribological applications. Within this work the approach of laser hardening of LIPSS is investigated. It is shown that laser hardening leads to an alteration of prior structured surfaces. That effects the wetting behaviour. The higher the laser power during hardening, the more increases the contact angle of a single droplet on the surface and the more the surface lacks in terms of wetting behaviour. This phenomenon is attributed to changes in LIPSS' aspect ratio. A high ratio leads to low contact angles and is shifted to low values when the laser power increases resulting in high contact angles. Hence, it is concluded that the thermal load during laser hardening, and it's influence on the wettability must be taken into account when LIPSS are subjected to laser hardening.