316L stainless steel is widely used in the aerospace, biomedical, and nuclear power industries owing to its high corrosion resistance, ease of processing, adequate strength, and reasonable cost. Laser directed energy deposition (LDED) is an additive manufacturing technology that has the advantages of high flexibility, high processing efficiency, and high degrees-of-freedom, making it suitable for manufacturing fine and complex components. However, fields such as aerospace, biomedical, and nuclear power require components that achieve low surface roughness. The main objective of this study is to utilize the jet electrochemical polishing method to post-polish an LDEDed 316L stainless steel surface. Before polishing, this study elucidates the anisotropy of the microstructure of the LDEDed front, top, and side faces, and analyzes the differences in their anodic dissolution behavior in a sodium chloride-glycol electrolyte, which provides a sufficient theoretical basis for the subsequent jet electrochemical polishing. The surface morphologies and microstructures of the different faces were analyzed in detail after polishing. The aim of this study is to provide an empirical and technical support for the polishing of LDEDed components to improve their surface quality.

The microstructural anisotropy of three faces—front, top, and side—of LDEDed 316L stainless steel was analyzed using optical microscopy (OM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) techniques. Then, the open-circuit potentials, polarization curves, and alternating current (AC) impedance curves of the three faces were measured using an electrochemical workstation to assess the anodic dissolution behavior of the individual surfaces in a sodium chloride-glycol electrolyte. A jet electrochemical polishing device was then utilized to polish the three faces with the face-scan mode to reduce their roughness. The three-dimensional morphology and surface roughness of the three faces were measured using a laser confocal microscope to evaluate the effect of polishing. Finally, scanning electron microscopy (SEM) was used to analyze the micromorphology and chemical composition.

The LDEDed 316L stainless steel shows significant anisotropy in the microstructure (Fig. 4), physical phase (Fig. 5), and texture (Fig. 6). The results of the open-circuit potential (Fig. 7), potentiodynamic polarization curves (Fig. 8), and electrochemical impedance spectra (Fig. 9) indicate that the corrosion-dissolution behavior of the three different faces of the LDEDed 316L stainless steel exhibits anisotropy. Specifically, the corrosion resistance of the three faces decreases in the following order: top face < front face < side face. Scratches on the front, top, and side faces disappear after the jet electrochemical polishing surface sweep, all of which show good mirror effect (Fig. 10). The roughness decreases from the original 1.057 μm to 0.177 μm, 0.200 μm, and 0.171 μm, respectively (Fig. 11). Bright and dark zones exist on all three faces after polishing (Fig. 10), which are caused by the different microstructures of the bright and dark zones (Fig. 12). SEM and energy-dispersive X-ray spectroscopy (EDS) results (Fig. 14) show that after jet electrochemical polishing, a large number of dendrites exist in the dark zone; dendrites in the bright zone are basically dissolved.

In this study, LDEDed 316L stainless steel was subjected to jet electrochemical polishing to reduce its roughness. First, the anisotropy of the microstructures of the front, top, and side faces was analyzed. Subsequently, the electrochemical anodic dissolution behaviors of the three faces in a sodium chloride-glycol electrolyte were analyzed. Finally, the three faces were subjected to jet electrochemical polishing with surface sweep mode to reduce their roughness to less than 0.2 μm. The reasons for the appearance of bright and dark areas on the polished surfaces were elucidated by analyzing the microstructure and chemical composition of the bright and dark zones.