Discovering the nanoscale origins of localized corrosion in additive manufactured stainless steel 316L by in situ liquid cell TEM

TL;DR

This study uses in situ liquid cell STEM to directly observe nanoscale corrosion initiation in additive manufactured 316L stainless steel, revealing that corrosion begins at dislocation cell boundaries due to inclusion dissolution.

Contribution

It provides the first direct nanoscale visualization of corrosion initiation mechanisms in AM 316L stainless steel using in situ STEM.

Findings

Corrosion preferentially occurs at dislocation cellular boundaries.

Pit-like features form along cellular boundaries during corrosion.

Localized corrosion involves inclusion dissolution at dislocation boundaries.

Abstract

Additive manufacturing (AM) by laser powder bed fusion (L-PBF) leads to the formation of a rich, hierarchical microstructure, including dislocation cell structures and elemental segregation. This structure has profound impacts on the corrosion behavior and mechanical properties of printed materials. In this study, we use in situ liquid cell scanning transmission electron microscope (STEM) to directly characterize the nanoscale origins of corrosion initiation in AM 316L stainless steel. Under applied anodic potentials, we found that the dislocation cellular boundaries were preferentially corroded and that pit-like features formed along the cellular boundaries. We directly observed the earliest stages of corrosion by controlling the biasing parameters to decelerate the corrosion processes. The results show that highly localized corrosion occurs via inclusion dissolution along dislocation cell boundaries. More widespread corrosion initiates at the dislocation cell boundaries and spreads throughout the dislocation networks.