Professor Ruirun Chen's team from the School of Materials Science and Engineering at Harbin Institute of Technology has made significant progress in the composition design and deformation behaviors of metastable titanium alloys

Recently, Professor Ruirun Chen’s team achieved important advances in the deformation mechanisms of novel ω-enhanced TRIP/TWIP titanium alloys. The research has been published in Acta Materialia under the title “Dynamic stress/strain partitioning of distinct early plastic deformation behaviors in ω-enhanced TRIP/TWIP titanium alloys”. This work provides crucial guidance for composition optimization of metastable alloys and design strategies for metastability engineering.

Metastability engineering, namely transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects, has been extensively introduced as effective plastic carriers beyond dislocation slip in metallic structural materials, aiming to achieve considerable ductility while maintaining high strength. In titanium alloys, the ω phase demonstrates high tolerability with both dislocation slip and TRIP/TWIP effects, establishing ω-enhanced TRIP/TWIP titanium alloys as a promising new family of high strength-ductility titanium alloys. However, the deformation anisotropy of ω phase leads to localized dislocation activity, while TRIP effect also exhibits strain localization tendency, both posing crucial impacts on deformation behaviors.

To systematically reveal the influence of abundant deformation mechanisms on plastic deformation behaviors, the research team employed a comprehensive theoretical calculations methodology incorporating density functional theory, cluster expansion, Monte Carlo simulations, and ab initio molecular dynamics. β phase stability, β-ω continuous slip barriers, solid-solution strengthening, and precipitation strengthening effects were focused for composition screening. For the first time, the intrinsic mechanisms of distinct early deformation behaviors (Lüders-type strain and uniform deformation) were analyzed under nearly overlapping engineering stress-strain curves. The results indicate that the insufficient work-hardening capacity caused by the ineffectiveness of stress-induced martensite-mediated dynamic Hall-Petch (DHP) effect constituted the critical factor for Lüders-type strain formation. Meanwhile, uniform deformation could be stabilized by deformation twins (DT) through pinning intergranular deformation and mediating DHP effect. Furthermore, local stress concentrations at DT intersections could be relaxed via triple mechanisms synergy: twinning splitting, dislocation activation, and secondary twinning. This research provides theoretical calculations methods for composition design of metastable alloys with mechanical/dynamical instability, while offering fundamental insights for metastability engineering strategies.

Harbin Institute of Technology serves as the sole corresponding institution for this paper. Doctoral candidate Xiaofu Zhang is the first author, with Professor Ruirun Chen and Assistant Researcher Shu Wang as co-corresponding authors.

This research was supported by the National Natural Science Foundation of China for Distinguished Young Scholars Continuation Funding Project and Regional Joint Key Project.

‌Paper Link: https://doi.org/10.1016/j.actamat.2025.121506

Figure 1 Two alloys screened through comprehensive theoretical calculations exhibit similar initial microstructures, strength, ductility, and the same uniform elongation after identical preparation and thermomechanical processing, yet demonstrate distinct early plastic deformation behaviors (Lüders-type strain vs. uniform deformation).