The influence of cyclic potentiodynamic passivation (CPP) of 316L stainless steels (SS) of different crystallographic orientation produced by laser powder bed fusion (LPBF) on the resulting general and pitting corrosion resistance is discussed. CPP was performed by cyclic voltammetry in aqueous 0.1 M NaNO3. Electrochemical tests including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and linear potentiodynamic polarization were employed to evaluate the resulting corrosion properties of the surfaces in aqueous 3.5 wt.% NaCl. It was found that the CPP method enables the formation of a passive oxide surface film which significantly improved the materials' general and pitting corrosion resistance in comparison to the naturally‐formed passive film under the experimental conditions investigated. It was also found that the general corrosion resistance, for both the unmodified (naturally‐passivated) and CPP‐modified LPBF 316L samples, decreased in the order of {111} > {100} > polycrystalline > {110}. Although the CPP‐modified samples showed a significantly lower current in the passive region and higher pitting potentials, in comparison to the unmodified samples, their crystalline structure was found not to have any influence on the corresponding behaviours.
Metal additive manufacturing techniques have been recognized for their capability of controlling the crystallographic orientations of stainless steels. However, the inherent anisotropic corrosion behavior has not been extensively studied. In this study, the corrosion properties of 316L stainless steels prepared by Laser Powder Bed Fusion (LPBF) additive manufacturing were investigated. The effects of different crystallographic textures, namely {100}, {110} and {111} on both general and pitting corrosion were characterized by several electrochemical measurements, including Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization and Mott-Schottky analysis. The results were also compared to the polycrystalline and wrought 316L counterparts. It was found that the LPBF-{111} sample offered the highest general corrosion resistance, followed by the LPBF-{100}, LPBF-polycrystalline and LPBF-{110} samples (Figure 1). The origin of this trend was related to the atomic surface density. The LPBF-{111} surface exhibited a stronger atomic bonding than that of LPBF-{100} and LPBF-{110} samples, resulting in a higher corrosion activation energy and thus a higher general corrosion resistance. All the LPBF samples also offered a significantly higher pitting corrosion resistance (Figure 2), which was attributed to the lower concentration of oxygen vacancies (donor levels) in the passive film that serve as pits nucleation sites, as observed by the Mott-Schottky analysis (Figure 3).
Figure 1
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