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

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 similar to 1800 MPa in this low-cost Ti alloy by a hierarchically heterogeneous microstructure consisting of micron-scaled primary alpha, nano-scaled sec-ondary alpha and ultrafine alpha-Widmanstatten nano-precipitates in the beta-matrix. In particular, utilizing grain boundary engineering (GBE), the percolative nano-precipitates network directly precipitated from beta-GBs, which not only strengthens GB cohesion, but also effectively blunts the crack tip and hinders crack propa-gation, 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.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.