Synergistic effects of Cu alloying on mechanical properties, corrosion resistance, and antibacterial behavior in ultra-high strength maraging stainless steel

• Cu promotes co-precipitation of Cu-rich, Mo-enriched, and refined Cr-rich nanoscale phases. • Cu accelerates austenite reversion and enhances TRIP, improving strength and ductility. • Cu addition refines Cr-rich and Mo-enriched precipitates, reducing Cr and Mo depletion and improving corrosion resistance. • Cu-rich precipitates enable controlled Cu 2+ release, achieving 98.6% antibacterial efficiency. High-performance steels that combine superior mechanical properties, corrosion resistance, and antibacterial functionality are increasingly required for medical instruments. In this study, we designed a novel Cu-containing maraging stainless steel that integrates these properties through Cu-mediated control of precipitation and phase evolution. Atomic-scale characterization reveals that Cu addition promotes the formation of dense nanoscale Cu-rich precipitates, while simultaneously suppresses Cr-rich precipitates spinodal decomposition. This co-precipitation behavior accelerates aging hardening and enhances mechanical performance, enabling the aged alloy to achieve a yield strength of 1263 MPa and tensile strength of 1432 MPa with improved uniform elongation of ∼ 10% and superior impact toughness of 68 J. Beyond mechanical strengthening, the nanoscale galvanic interaction with the matrix facilitates Cu 2+ release, leading to a strong antibacterial efficiency of 98.6% against E. coli . In parallel, the suppression of Cr-rich precipitates and refinement of Mo-enriched precipitates reduce local compositional gradients, leading to higher corrosion and pitting potentials and the formation of a more uniform and stable passive film. Overall, this work clarifies the synergistic effect of Cu alloying on tensile properties through co-precipitation, assisted austenite reversion, and an enhanced TRIP effect; on antibacterial performance via Cu 2+ release, and on corrosion protection via passive-film stabilization.