Superior corrosion resistance and its origins in an additively manufactured Co-Cr-Ni-Al-Ti high-entropy alloy with nano-lamellar precipitates

L1₂-strengthened high-entropy alloys (HEAs) are promising materials for advanced structural applications in harsh environments due to their outstanding mechanical properties. However, the Cr-depleted L1₂ particles usually increase the alloy's galvanic corrosion susceptibility, thus resulting in a decrease in pitting resistance. In this work, the corrosion behavior and associated passive film characteristics of a novel Co₄₀Cr₂₀Ni₃₀Al₅Ti₅ HEA (at.%) additively manufactured by selective laser melting (SLM) were systematically characterized and investigated. It was found that the precipitation of coherent nano-lamellar L1₂ phase significantly refined the grain structure of the aged alloy, which leads to an anomalously improved corrosion resistance compared to the as-printed single-phase counterpart. Such excellent corrosion resistance of the aged alloy originated from the thin amorphous passive film with Cr₂O₃, Al₂O₃, and TiO₂ as the main constituents that were firmly adhered to the alloy matrix. Moreover, the corrosion morphologies revealed that the dense and large-sized pits on the as-printed alloy were in sharp contrast to the sparse and irregularly-shaped pits on the aged alloy, which can be attributed to the potential difference and/or the refined grain structure. These findings will effectively advance the development of corrosion-resistant additively manufactured alloys and provide new insights into the innovative design of high-performance damage-tolerant L1₂-strengthened HEAs. © 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.