316L stainless steel fabricated by selective laser melting and spark plasma sintering: A comparative analysis on their microstructural, mechanical, and electrochemical performance

This work presents a comparative analysis of SS316L stainless steel fabricated via two different powder-based techniques: laser powder bed fusion (LPBF) and spark plasma sintering (SPS), emphasizing their microstructural evolution, mechanical behavior, and time-resolved electrochemical degradation in phosphate-buffered saline (PBS). LPBF samples exhibited superior densification (∼99.58%) and a refined microstructure characterized, in contrast, a relatively higher residual porosity is observed in the SPS samples (∼1.25%). Mechanical testing revealed an enhanced yield strength (505±12.4 MPa), ultimate tensile strength (686±13.6 MPa), and hardness (237 ± 8.1 HV) in the LPBF samples due to high dislocation density and subgrain refinement, while SPS offered improved ductility (39%) owing to larger, equiaxed grains. Time-dependent corrosion evaluation was conducted at four stages: post-electrochemical polarization (EP), EP+15 min, EP+30 min, and full half-cycle (FHC), revealing a significantly more stable Cr 2 O 3 -enriched passive film on the LPBF surface, with delayed chloride-induced breakdown (breakdown potential ∼1302.8 mV) and lower pit depth and volume. Conversely, SPS samples showed early passivity breakdown (∼386.3 mV), elevated corrosion product accumulation, and pronounced pitting, attributed to microstructural heterogeneities and residual porosity. In addition, the 72h immersion study and EIS (Electrochemical Impedance Spectroscopy) analysis further confirmed the superior long term passivation stability of LPBF 316L, which developed a more stable oxide film, whereas SPS exhibited unstable passivation and sustained pit growth. The findings establish that LPBF SS316L exhibits superior microstructural integrity, mechanical performance, and long-term electrochemical stability, rendering it a more viable candidate for applications in chloride-rich and physiologically corrosive environments.