Effect of macro- and microstructural features on the corrosion behavior of additively manufactured alloy 625

The aim of the work is to investigate the general and localized corrosion behavior of Alloy 625 obtained via different AM technologies, namely laser powder bed fusion (LPBF) and metal fused filament fabrication (MFFF). The outcomes of these evaluations were compared with the traditionally manufactured material (hot rolling). The macro- and microstructures as well as unique surface features of the AM-produced specimens were assessed in terms of digital optical microscopy and scanning electron microscopy. Intergranular corrosion susceptibility tests, in compliance with ASTM G28 method A (1), potentiodynamic and potentiostatic polarization tests were performed. The electrochemical tests were carried out in sulfuric acid according to the ASTM G5 standard (2) and in deaerated chloride solutions. The results demonstrated that the surface features, porosity, as well as the microstructure are strictly dependent upon the manufacturing technology. Corrosion morphologies change significantly in function of the unique macro- and microstructural features. Susceptibility to intergranular corrosion tests carried out on the MFFF alloy only revealed not penetrating attack. The results of potentiostatic and potentiodynamic tests showed a passive behavior over a wide range of potentials, thus confirming the very high corrosion resistance to localized corrosion of the additive manufacturing Alloy 625 in neutral chloride solutions. In acidified chloride solution (pH = 3) the presence of crevice attacks on MFFF specimens was detected.