Here, we compare corrosion behavior of 625 Inconel alloy manufactured by SLM to its wrought counterpart in the marine environment. We find that the initial polarization curves look almost identical for 625 AM and 625 wrought specimens both in 0.6 M NaCl and ASTM seawater (Fig. 1). However, the difference in open circuit potential (OCP) and microstructure of two specimens suggest different composition of surface oxides and potentially different rates of their dissolution. In order to understand how variations in microstructure and surface composition affect alloys’ long-term corrosion resistance, we perform ex-situ surface characterization and in-situ analysis of alloy dissolution while holding electrode potential at -1, -0.5, 0.5 and 1V vs Ag/AgCl reference electrode.
Electrochemical experiments were conducted in three-electrode flat electrochemical cells (PAR, Inc). Freshly polished coupons of 625 AM or 625 wrought Inconel alloys served as working electrodes (WEs), while platinum mesh and Ag/AgCl in 3 M NaCl (BioLogic, Inc) were used as a counter and reference electrodes, respectively. Initial corrosion properties of the alloy electrodes were characterized by linear polarization resistance and potentiodynamic measurements. Alloy dissolution experiments were conducted in potentiostatic conditions, and concentrations of dissolved metal species were determined by ICP-MS. X-Ray Photoelectron Spectroscopy was used to determine chemical speciation of the samples after exposure to OCP and carrying out alloy dissolution experiments.
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