Manipulating the interfacial structures in titanium alloys containing interstitial solutes delivers ultra-high strength and ductility

Design structural characteristics of interfaces is the key for ultra-strong titanium (Ti) alloys by tuning polymorphic α-precipitates. However, the conventional tri-modal structure, characterized by various interfaces, usually shows large ductility but low yield strength caused by numerous soft α-precipitates. This work focuses on manipulating multiple interfacial structures to endow a newly designed tri-modal Ti-4.9Al-4.4Cr-2.45Mo-1.6Zr alloys with the superior strength-ductility synergy assisted by interstitial solutes, beyond conventional high-strength Ti alloys. Here, an interstitial solute alloying strategy is utilized not only to form hard-yet-deformable α-precipitates, but also to achieve the controllably stepwise α-precipitation sequence to manipulate interfacial structures and thus slip transmission modes in Ti alloys. In particular, the coherent twin boundaries (CTBs) between secondary α-nanolamellae formed via dislocation-interstitial atom interactions can efficiently hinder dislocation motion but promote dislocation transmission in the soft transformed β-matrix. This strategy provides new insights into designing high-performance interstitial solute-tolerant alloys for cost-effective and lightweight applications.