Processing-driven microstructural refinement and tribocorrosion performance of SS316L: A comparative study of laser powder bed fusion and spark plasma sintering

This study presents a comprehensive comparison of the microstructural evolution, mechanical performance, and fretting tribocorrosion behavior of 316 L stainless steel fabricated by laser powder bed fusion (LPBF) and spark plasma sintering (SPS). The influence of processing route on densification, grain morphology, and passive-film stability was examined using X-ray diffraction (XRD), electron back scattered diffraction (EBSD), scanning electron microscope (SEM), three-dimensional optical profilometry and X-ray spectroscopy (XPS) analyses. LPBF produced a highly dense material (99.6%) with fine cellular–columnar grains and elevated dislocation density (4.7 ± 2.2 × 10¹⁴ m⁻²), whereas SPS yielded an equiaxed, coarser-grained structure with slightly lower density (98.8%) and larger pore size. The refined LPBF microstructure resulted in superior hardness (224 ± 7.8 HV) and maximum compressive stress at 50% strain (2286 ± 13.1 MPa) compared with SPS (164 ± 6.7 HV; 2100 ± 11.4 MPa). Fretting tribocorrosion tests and electrochemical impedance spectroscopy (EIS) in phosphate-buffered saline (PBS) revealed that LPBF exhibited a smaller OCP drop (∼117 mV), lower coefficient of friction (∼0.9), and a pronounced increase in polarization resistance after fretting. In contrast, SPS showed larger potential fluctuations, deeper wear scars, a higher estimated wear volume (∼1.3 × 10 −3 mm 3 ), and minimal changes in Rp. The LPBF specimen exhibited a lower estimated wear volume (∼0.9 × 10 −3 mm 3 ), indicating reduced material loss during fretting tribocorrosion. Surface chemical analyses confirmed the formation of a dense Cr₂O₃–Fe₂O₃–phosphate tribofilm on LPBF, enabling sustained passivity through self-regenerative reoxidation. SPS, however, developed a hydrated hydroxide-rich layer prone to rupture and unstable electrochemical behavior. Overall, the findings demonstrate that rapid solidification in LPBF enhances both mechanical integrity and tribochemical stability, establishing LPBF as a superior processing route for producing corrosion and wear-resistant biomedical-grade stainless steel components.