On the mechanisms of wetting characteristics modification for selected metallic materials by means of high power diode laser radiation

This work elucidates and analyzes the factors responsible for modifications to the wettability characteristics of metallic materials after high power diode laser (HPDL) treatment. It was found that interaction of EN3 and EN8 mild steel with HPDL radiation resulted in the wettability characteristics of the mild steels altering to various degrees depending upon the laser processing parameters. Such changes in the wettability characteristics of the mild steels were found to be due essentially to: (i) modifications to the surface roughness; (ii) changes in the surface O₂ content; and (iii) the increase in the polar component of the surface energy. All of these factors were seen to influence the wettability characteristics of the mild steels, however, the degree of influence exerted by each was found to differ. Work was therefore conducted to isolate each of these influential factors, thereby allowing the magnitude of their influence to be determined. This analysis revealed that surface roughness was the primary influential factor governing changes in θ and hence the wettability characteristics of the mild steels. Surface energy, by way of microstructural changes, was also shown to influence to a lesser extent changes in the wettability characteristics, while surface O₂ content, by way of process gas, was found to play a minor role in inducing changes in the wettability characteristics of the mild steels.