Making a low-cost duplex titanium alloy ultra-strong and ductile via interstitial solutes

Abstract

Interstitial solutes (e.g. O, N) often enhance strength; however, their poisoning effect leads to markedly decreased ductility and even embrittlement in titanium (Ti) alloys. Thus, using unavoidably interstitial O and N atoms to achieve low-cost, ductile Ti alloys with ultrahigh-specific-strength is significant for industrial applications. Here, taking the Ti-4.1Al-2.5Zr-2.5Cr-6.8Mo-0.17O-0.10N (wt.%) alloy as a model material, we successfully achieved an ultra-high yield strength of ∼1800 MPa in this low-cost Ti alloy by a hierarchically heterogeneous microstructure consisting of micron-scaled primary α, nano-scaled secondary α and ultrafine α-Widmanstätten nano-precipitates in the β-matrix. In particular, utilizing grain boundary engineering (GBE), the percolative nano-precipitates network directly precipitated from β-GBs, which not only strengthens GB cohesion, but also effectively blunts the crack tip and hinders crack propagation, rendering enhanced ductility. This strategy combining GBE and interstitial solutes opens an avenue to design ultra-strong and ductile Ti alloys with increased tolerance to interstitial impurities.