Modification of surface characteristics and electrochemical corrosion behavior of laser powder bed fused stainless-steel 316L after laser polishing

Abstract

The development and growth of additive manufacturing (AM) processes have made the optimization of surface quality and properties of AM components critical. Laser polishing represents a recent and novel application of laser surface irradiation that can be used for precise, post-process smoothing of the rough surfaces commonly encountered on AM parts. Austenitic stainless steels are an important class of alloys frequently used in biomedical applications due to their corrosion resistance. Due to this, corrosion resistance advancements and improved bio-response to stainless steels are long-term active areas of research. In this study, the influence of laser polishing on surface modification and corrosion behavior of additively manufactured 316L has been investigated. Laser scanning speed and number of passes were varied to evaluate their effect on the surface quality and corrosion resistance of the experimental samples. The results indicated that laser polishing could enable reductions in surface roughness of over 92 % (from 4.75 μm to 0.49 μm Sa) while also incorporating partially melted powders originally on the as-printed surface layer. The X-ray diffraction (XRD) results indicated that there was no considerable phase change after laser polishing. Laser polishing was observed to refine the columnar structure within the as-printed sample into a fine cellular structure. Additionally, the sub-surface microhardness of the laser remelted layer increased from 1.82 GPa to 2.89 GPa. Moreover, the laser polished samples exhibited greater corrosion resistance, which was believed to be due to a combination of a decrease in surface roughness and grain refinement. These results show that laser polishing can improve the corrosion resistance of additive manufactured stainless steel while also decreasing surface roughness and increasing surface microhardness. Due to those enhancements, it represents a suitable multifaceted process for finishing additive manufactured parts.