Chemically complex ordered alloy enables electrochemically stable passivation for superior corrosion resistance

The nanoscale passive film on the alloy surface critically governs the corrosion resistance of alloys. An ideal passive film is expected to act as a protective barrier layer to effectively protect the alloy matrix by impeding the charge transfer reactions and diffusion of corrosive ions. Most traditional intermetallic alloys, however, face serious challenges when it comes to passivation or forming stable passive films in harsh/reactive environments. This is primarily due to limited elemental choices and single-atom occupancy tendencies, resulting in unsatisfactory aqueous corrosion resistance. Here, we develop a novel chemically complex intermetallic alloy (CCIMA) with a near-single-phase L1₂ structure, where tailored sublattice occupancy enables Co and Ni to occupy face-center sites and Al, V, Ta, and Ti to occupy corner sites. Electrochemical tests in 3.5 wt% NaCl solution demonstrate the superior comprehensive corrosion performance of CCIMA compared to most traditional intermetallic alloys, as evidenced by the higher pitting potential (E_pit), higher corrosion potential (E_corr), and lower corrosion current density (i_corr). This performance stems from the rapid formation of a ∼3.7 nm thick, non-stoichiometric amorphous passive film comprising multiple stable oxides (primarily Al₂O₃, TiO₂, Ta₂O₅, Co₃O₄, and minor V₂O₅, Co(OH)₂, Ni(OH)₂). Our work provides in-depth insights into the targeted design of passive films with desired properties towards better corrosion resistance and opens a new pathway for the optimization of damage-tolerant intermetallic alloys.