Plasma electrolytic polishing of additively manufactured parts: The role of initial surface topography

Laser powder bed fusion (L-PBF) enables the production of geometrically complex metallic components but inherently produces rough surfaces that require post-processing for most engineering applications. Plasma electrolytic polishing (PeP) offers an environmentally friendly and contactless route for surface finishing in which dilute salt-based electrolytes rather than concentrated acids are used. In addition to the process parameters, the initial surface roughness is one of the major factors that has an effect on the final surface quality after PeP treatment. In this work, a multi-step voltage strategy in an NH₄Cl + NH₄F-based electrolyte was applied directly to as-built L-PBF 316L stainless steel samples without any prior surface roughness reduction process. Three topographically different surfaces co-existing in the as-built samples, namely, side, top, and machined were simultaneously polished, isolating the effect of starting topography from the process variables. After eight polishing steps, the Arithmetic Mean Roughness (R_a) values of the side surfaces dropped from 10.64 to 0.47 μm, approaching the machined-reference quality, whereas the top surfaces saturated at 1.5 μm. The machined surface exhibits a mirror-like finish within the early polishing steps. The chemical analyses of the PeP-treated sample revealed the surface has higher oxide contents compared to the ground surface, without localized oxidation.