Grain size dependence of TRIP/TWIP synergy and its impact on the mechanical response in an oil-quenched Ti–10Mo alloy

The deformation behavior of an oil-quenched Ti-10Mo alloy with β grain sizes (GS) ranging from 18 to 155 μm was systematically investigated, focusing on the evolution of stress-induced martensitic α″ (SIM α″) transformation and {332}<113> twinning. Emphasis was placed on elucidating the TRIP/TWIP synergy and its influence on mechanical properties (TRIP: transformation-induced plasticity; TWIP: twinning-induced plasticity). The tensile results reveal a pronounced grain size dependence of discontinuous yielding, with the yield drop becoming increasingly evident as the β grain size decreases. A clear Hall-Petch relationship is established between the lower yield strength and the β grain size, yielding a high Hall-Petch coefficient of 1456 MPa·μm 1/2 . Although the TRIP/TWIP synergy enhances the work hardening capacity, its contribution varies with β grain size. Coarse-grained samples exhibit higher work hardening rates owing to a higher volume fraction of SIM α″. Moreover, the rapid intersection of SIM α" variants and the formation of internal twins at these intersections further enhance the work hardening capacity in the GS155 sample. The GS48 sample achieves the highest ductility, which is attributed to a more balanced contribution between SIM α" transformation and {332}<113> twinning under the TRIP/TWIP synergy, characterized by the highest twin fraction among all samples. These findings demonstrate that β grain size control is an effective strategy for tailoring the TWIP/TRIP synergy and then optimizing the comprehensive mechanical properties of metastable β-Ti alloys.