Porosity, roughness, and passive film morphology influence the corrosion behavior of 316L stainless steel manufactured by laser powder bed fusion

The development of additively-manufactured (AM) 316L stainless steel (SS) using laser powder bed fusion (LPBF) has enabled near net shape components from a corrosion-resistant structural material. In this article, we present a multiscale study on the effects of processing parameters on the corrosion behavior of as-printed surfaces of AM 316L SS formed via LPBF. Laser power and scan speed of the LPBF process were varied across the instrument range known to produce parts with >99 % density, and the macroscale corrosion trends were interpreted via microscale and nanoscale measurements of porosity, roughness, microstructure, and chemistry. Porosity and roughness data showed that porosity 9 decreased as volumetric energy density E(v )increased due to a shift in the pore formation mechanism and that roughness S-q was due to melt track morphology and partially fused powder features. Cross-sectional and plan-view maps of chemistry and work function phi(s) revealed an amorphous Mn-silicate phase enriched with Cr and Al that varied in both thickness and density depending on E-v. Finally, the macroscale potentiodynamic polarization experiments under full immersion in quiescent 0.6 M NaCl showed significant differences in breakdown potential Eb and metastable pitting. In general, samples with smaller 9 and S-q values and larger phi(s) values and homogeneity in the Mn-silicate exhibited larger Eb. The porosity and roughness effects stemmed from an increase to the overall number of initiation sites for pitting, and the oxide phase contributed to passive film breakdown by acting as a crevice former or creating a galvanic couple with the SS.