Comparative investigation of deformation mechanisms in Ti-6Mo-3.5Cr-1Zr metastable β titanium alloy subject to cold rolling strain paths

Metastable β-titanium alloys exhibit excellent room-temperature ductility due to their complex deformation structure, yet the microstructural responses to different rolling strain paths remain unclear. This study comparatively investigated the deformation mechanisms of a novel metastable β titanium alloy (Ti-6Mo-3.5Cr-1Zr) deformed via two distinct strain paths: unidirectional rolling (UDR) and multi-step cross rolling (MSCR). The results demonstrate that MSCR provides diverse strain paths, which facilitate uniform deformation band distribution across variously oriented grains while promoting the formation of a reticular structure. Additional investigation using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) revealed that the deformation bands predominantly consist of stress-induced ω (SIω) phase and a minor fraction of β twins. MSCR facilitates greater SIω phase formation than UDR during early deformation stages (61.1 % vs 50.3 % mass fraction at 5 % deformation), attributed to its enhanced activation of multiple slip systems in individual grains. During subsequent heat treatment, the high-density reticular SIω phase forms abundant interfaces and a higher dislocation density, which provides additional nucleation sites and driving forces. Consequently, unlike the predominantly banded β grains observed in the UDR sample, equiaxed recrystallized grains in the MSCR sample nucleate and gradually develop. The room-temperature tensile test results reveal that MSCR samples not only retain elevated yield strength (YS ∼898 MPa) and elongation after fracture (EL ∼32.4 %) but also reduce the anisotropy of mechanical properties, as evidenced by 41.3 % and 37.0 % reductions in the corresponding index of plane anisotropy (IPA) for YS and EL, respectively.