Nanoscale-oxide precipitation and microscale inclusion effects on strength and corrosion of laser powder bed fused 316L with trace Al2O3 additions

This study examines how trace Al 2 O 3 additions (0.5 and 1.0 wt%) influence the microstructure, mechanical performance, and corrosion behavior of laser powder bed fused (LPBF) 316L stainless steel. Nano-alumina was mechanically mixed with 316L powder and processed by LPBF under two laser power conditions. Microstructural features were characterized using SEM, EBSD, TEM, and STEM-EDS. Mechanical properties were evaluated by room-temperature and elevated-temperature tensile testing, and corrosion behavior was assessed through potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt.% NaCl. Rather than remaining as inert ceramic particles, Al 2 O 3 undergoes partial dissolution and re-precipitation, forming nanoscale Al–Mn–Cr–O-rich features that are coherent with the austenitic matrix. These nanoscale oxide precipitates provide consistent strengthening through dislocation impediment, increasing yield strength at both Al 2 O 3 contents. A second population of microscale agglomerates is also observed and is associated with reduced ductility and localized corrosion susceptibility, particularly at 1.0 wt% Al 2 O 3 . Electrochemical testing shows that 0.5 wt% Al 2 O 3 improves pitting resistance, whereas higher additions reduce repassivation capability. A nominal addition of 0.5 wt% Al 2 O 3 yields the most favorable balance of strength, ductility, and corrosion resistance by maximizing beneficial nanoscale oxide precipitation while limiting detrimental microscale agglomeration.