Effect of Ceramic-Media Tumbling Duration on the Surface Characteristics and Corrosion Behavior of SLM-Manufactured AISI 316L Stainless Steel Under Simulated Microbial-Induced Corrosion Conditions

Surface finishing of SLM-manufactured AISI 316L aims to reduce recessed features that may retain deposits and create occluded corrosion environments. This study evaluates whether extending ceramic-media tumbling provides electrochemical benefits beyond initial surface smoothing. An as-built reference and specimens tumbled for 30–120 min were characterized using Ra, Rz, Sa, and Sz, confocal microscopy, SEM, metallographic cross-sections, and wettability measurements. Electrochemical impedance spectroscopy and potentiodynamic polarization were performed after 100 h in 0.1 M H2SO4, an abiotic surrogate for acidification associated with sulfur-oxidizing microorganisms. After 120 min, Ra and Rz decreased from 7.2 and 32.2 to 1.9 and 11.0 µm, while Sa and Sz decreased from 21.1 and 216.9 to 8.9 and 102.2 µm, respectively. The Tafel-derived corrosion rate decreased from 9.8 to 2.5 µm year−1, and the Stern–Geary polarization resistance increased from 32 to 68 kΩ cm2. The largest profile roughness reductions occurred during the first 30 min, whereas the polarization results showed limited additional improvement between 90 and 120 min. The impedance modulus at 0.1 Hz varied non-monotonically. The combined assessment reveals different duration-dependent topographical and electrochemical responses, supporting evaluation of finishing duration using both. Effects on microbial colonization require further biological validation.