Elemental decoration design with metastable cellular substructures for additively manufactured high-strength and high-corrosion resistant austenitic stainless steel

Multi-level chemical-structural heterogeneities extensively exist in additively manufactured (AM) metals due to the intrinsic layer-by-layer non-equilibrium solidification process. Strategies designed with particular metastable substructures aiming at advanced performances are significant for AM counterparts. In this work, Si and Mo additions are conducted based on the regulations of dislocation cell substructures and stacking fault energies for stainless steel (SS) 316L fabricated by laser powder bed fusion (PBF-LB). Their load-bearing performance and corrosion behavior are characterized. Results show that additional Mo segregation at cellular boundaries contributes a stronger strengthening effect than Si, which periodically hinders dislocation slip during deformation. Addition of Si triggers deformation twinning at an early stage due to decreased stacking fault energy, and subsequent dynamic Hall-Petch effects improve strain-hardening capability and plasticity for PBF-LB SS 316L+Si. Meanwhile, addition of Mo enhances pitting corrosion resistance of PBF-LB 316L+Mo SS in chloride-containing solutions, especially the pitting re-passivation, which is opposite in the Si addition case due to the increased quantiy of undesired Si/Mn-rich oxides. Underlying deformation and corrosion mechanisms for Mo/Si-added PBF-LB SSs are discussed. Our work is anticipated to motivate the alloy design concept based on particular metastable substructures for advanced AM alloys.