Simultaneously enhancing the strength and ductility of medium-entropy alloys via manipulating ordered oxygen complexes

Abstract Oxygen solute strengthening is an effective strategy to harden metallic materials, yet, it usually deteriorates the ductility. Ordered oxygen complexes, a state between regular random interstitials and oxides, can simultaneously enhance strength and ductility in high-entropy alloys. However, if such strengthening media can be created and if this particular strengthening mechanism still holds in other alloys remain unclear. Here, we demonstrated that OOCs can be obtained in the single bcc (body-centered-cubic) Ti-Zr-Nb medium-entropy alloys (MEAs) via tailoring the content of bcc-stabilizer Nb and oxygen. It was found that decreasing the bcc phase stability (i.e., lowering the Nb content) enhances the degree of chemical short-range orderings, particularly those enriched in Ti and Zr, and then favors the formation of ordered complexes after doping oxygen. Moreover, the number density of OOCs increases with oxygen contents (\(\le 3.0\)at.%) in a given alloy, but addition of excessive oxygen (\(>3.0\)at.%) leads to grain boundary segregation. As a result, the tensile yield strength is appreciably enhanced by ~ 75% and ductility is substantially improved by ~ 164% when doping the Ti-30Zr-14Nb MEA with 3.0 at.% oxygen. Our work not only manifests the universality of the novel interstitial strengthening mechanism, but also offers insights into developing advanced metallic materials with localized atomic orderings.