TRIP/TWIP Networks Promoted via Multifunctional Nanoprecipitates-confined Specified Shear for Achieving Strong-yet-Ductile Titanium Alloys.

Abstract

Transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) are typically suppressed by precipitates and difficult to be significantly triggered under high yield stress. In titanium alloys, ω phase with intrinsic deformation heterogeneity localizes deformation to {112}〈111〉_β system, exactly aligning with the lattice shear in martensite transformation (MT). Therefore, beyond reported ω-nanoprecipitates functions, e.g., providing precipitation strengthening, maintaining strain compatibility and dynamically forming ω-free dislocation channels, new confining specific shear is proposed to integrate precipitates with TRIP/TWIP effects in this work. A de novo design scheme, consisting of Density Functional Theory, Cluster Expansion, Monte Carlo simulations and Ab Initio Molecular Dynamics, is employed for composition screening. β phase stability and β-ω continuous slip barriers are precisely tailored to provide large chemical driving force for MT while suppressing excessively slip priority. After simple thermomechanical processing, selected Ti-7.92Mo-3.22Cr-1.88Zr alloy exhibits dense TRIP/TWIP networks and record yield strength-ductility synergy (product exceeding 38 GPa%). Premature necking is delayed by ω-confined elevated local stress promoting MT followed by sequential transformation from strain-induced martensite to {332}〈113〉_β deformation twins, thus forming an extended ≈23.2% Lüders-type strain. These theoretical and experimental results provide implementable and individual strategies to overcome yield strength-ductility trade-off by reconciling precipitation strengthening with TRIP/TWIP effects.