Fatigue and Corrosion Evaluation of L-PBF 316L Stainless Steel Having Undergone a Self-Terminating Etching Process for Surface Finish Improvement.

The poor surface finish of as-printed (AP) laser powder bed fusion (L-PBF) 316L stainless steels has detrimental impacts on the resulting fatigue and corrosion performance. One postprocessing method, a self-terminating etching process (STEP), can improve the surface finish of parts up to 76%, but the resulting effects on fatigue life and corrosion reliability remain unknown. This work evaluates the effect of the STEP on the fatigue and corrosion performance of L-PBF 316L. In addition, to determine the influence of changing the microstructures from the as-built condition, specimens having undergone a pre-STEP stress relief (SR + STEP) heat treatment and a pre-STEP solution anneal (SA + STEP) were evaluated. The results showed that a pre-STEP SR resulted in the best Sa roughness, while a pre-STEP SA had the biggest improvement in Sv roughness. Despite Sv roughness being a major indicator of fatigue performance, the coarse grains and internal porosity in the SA specimens resulted in the poorest fatigue performance. The SR + STEP specimens' fatigue lives were 10 × higher than the AP samples under a load of 275 MPa and 2-3 × higher under a 350 MPa load. The SR + STEP specimen also had the best corrosion performance in a sodium chloride electrolyte due to the smoother surface and least remnant surface carbides.