Combating Localized Corrosion in Additively Manufactured 316L Using Ceramic Dopants

In laser additively manufactured 316L, enhanced pitting susceptibility has been discussed in the context of the cellular microstructure that forms during printing. Interestingly, some studies also report on laser printed samples with seemingly enhanced stability against pitting relative to wrought 316L. The complexity of these highly heterogeneous microstructures has thus made it difficult to identify the mechanisms governing localized attack, and in turn design printed alloys with performance exceeding their wrought counterparts. In this study, we explore the microstructural underpinnings of localized corrosion in laser additively manufactured 316L using multi-modal synchrotron characterization techniques combined with correlative electron microscopy imaging. The dislocation density and its dependence on printing conditions are correlated to chemical heterogeneities formed at the nanoscale. On this basis, accelerated pitting is attributed to depletion of Cr and carbide formation in regions of high dislocation density. Finally, we show that the addition of ceramic dopants to the 316L feedstock powder, which decompose and mix with the alloy to form a series of complex second-phase nanoprecipitates, inhibit accelerated pitting corrosion by augmenting the chemical state of the cellular walls.