Lead P.I. - Dr. Jason R. Trelewicz

Laser based additive manufacturing (AM) techniques, such as laser powder-bed fusion (L-PBF), produce highly heterogeneous microstructures due to the layer-by-layer nature of the build process coupled with rapid solidification from large thermal gradients. Common microstructural features include solidification structures and fusion boundaries at the macroscale and subgrain cellular structures at nanoscale due to the high density of dislocations produced during rapid solidification.  A key observation accompanying an enhanced pitting susceptibility specifically in L-PBF 316L is the presence of the cellular microstructure within surface pits, which suggests that the defect microstructure accelerates localized attack.  The hypothesis of this research is that chemical heterogeneities deriving from elemental segregation to the dislocation network structures combined with surface tensile residual stresses enhances the susceptibility of L-PBF 316L to localized attack.  Two enabling research thrusts are involved in this project with a focus on microstructural origins of anomalous corrosion behavior and tailoring microstructure for enhanced corrosion performance. The figure above demonstrates multi-modal characterization (TEM with synchrotron x-ray fluorescence and diffraction) of AM 316L and the implications of the dislocation microstructure for corrosion performance.