The effect of immersion time on the electrochemical characterization of additively manufactured 316L stainless steel exposed to artificial seawater

Additive manufacturing (AM) encompasses a range of production processes in which complex 3-dimensional components are fabricated in a layer-by-layer manner directly from a digital model. These processes involve the use of a powder feedstock and a high energy density source, such as a laser, to melt the feedstock. The AM process can provide a means for rapidly producing replacement parts and also has the potential to create new alloys and composites that were not previously possible with conventional processing methods. However, the differences in processing between conventional and AM parts lead to differences in the microstructure and morphology of the resulting components, even though they may be fabricated from the same alloy system. These corresponding microstructural differences can have a significant impact on the electrochemical and corrosion behavior of a traditional range of corrosion-resistant alloys, such as austenitic grade stainless steels (SS). This work compares the electrochemical corrosion behavior of two different AM 316L alloys fabricated through powder bed fusion using argon and nitrogen atomized feedstock powders to that of wrought 316L stainless steels as a function of immersion time in artificial seawater. The AM 316L specimens produced for this research were essentially pore-free. Corrosion characteristics of the specimens were investigated using anodic and cyclic polarization techniques. All of the wrought 316 L specimens exhibited well defined pitting potentials, protection potentials (for pitting) a few hundred millivolts above open circuit potential, and pitting on the surface of the specimens. In contrast to this, the AM 316L specimens did not show a pitting potential or pitting on the specimen surfaces, at high potentials transpassive dissolution of the oxide film was noted instead of pitting corrosion. Cyclic polarization experiments revealed the initiation of crevice corrosion for the AM 316L specimens in the transpassive region and the AM 316L specimens exhibited low or no protection potential for crevice corrosion. Figure 2 b and c. Again, none of the AM specimens exhibited a pitting potential or pitting on the surface of the specimens. However, after 2 weeks of immersion all of the AM specimens underwent crevice corrosion when polarized to the highest potential (in the transpassive region) and essentially no E _{protect crevice} (for crevice corrosion) was present. In the initial (0 day data), 2 of the 3 AM (N) specimens did not initiate crevice corrosion at the highest potentials (in the transpassive region), suggesting that the AM (N) appears to be a bit more resistant to crevice corrosion initiation than the AM (Ar). All of the wrought 316L specimens showed well defined pitting and protection potentials, E _{protect pitting} ,(for pitting) .