Interface velocity-driven non-equilibrium nitrogen supersaturation in additive manufacture: a universal strategy for breaking strength-corrosion trade off

Achieving synergistic high strength and corrosion resistance in high-nitrogen stainless steels remains challenging due to inherent trade-offs: dispersion strengthening enhances strength, but heterogeneous interfaces often act as micro-galvanic corrosion or pitting nucleation sites, compromising corrosion resistance. Laser powder bed fusion (LPBF) with its extreme thermal cycles, offers a non-equilibrium strategy to address this limitation. Here, using multi-scale microstructural characterization and thermo-kinetic simulations methods, we report that during melt pool solidification, interface velocity-regulated kinetics trap excess nitrogen in the ferritic matrix, inducing non-equilibrium nitrogen supersaturation. Subsequently during fast cooling process, this supersaturated nitrogen combines with chromium to form dense superfine CrN lamella. Coupled with fine grain structures from rapid solidification, this two-stage non-equilibrium process achieves a synergy of high tensile strength (~1700 MPa) and pitting resistance (~1000 mV), breaking the classical strength-corrosion trade-off. Key mechanisms include: (1) superfine CrN lamellae minimizing adjacent Cr-depleted zones, (2) grain refinement suppressing precipitate-free zones (PFZ), and (3) nitrogen-stabilized grain boundaries enhancing corrosion resistance. By controlling interface velocity in LPBF non-equilibrium solidification, we establish a nitrogen supersaturation pathway that tailors hierarchical microstructures (grains, boundaries, nanoprecipitates), resolving the strength-corrosion trade-off in additively manufactured high-nitrogen alloys.