Laser surface treatment of stainless steel and environmental dust effects

Laser texturing of the surface of 304 stainless steel is carried out under the high pressure N2 assisting gas. Morphology, elemental composition and wetting state of the surface are analysed using the analytical tools. Free energy of the laser textured surface is measured using the droplet method. The influence of environmental dust particles on the laser textured surface in a humid air ambient is examined. It is found that laser texturing results in micro/nanopillars with presence of nitride compounds at the surface and the formation of micro/nanopillars changes the wetting state of the surface from hydrophilic to hydrophobic. The dust particles possess alkaline (Na, K) and alkaline earth (Ca) metals and their compounds dissolve in water while forming chemically active liquid on the laser textured surface. The liquid solution wets the entire textured surface and once it dries and forms crystal structures and strongly adheres to the surface. The tangential force required to remove the dried solution from the laser textured surface is almost three-times of the frictional force. The liquid solution results in small and shallow pit sites on the as-received surface; however, this behavior is not observed for the laser textured surface.