Deformation twinning-induced single-variant ω-plates in metastable β-Ti alloys containing athermal ω-precipitates

The omega-phase in metastable beta-titanium (Ti) alloys attracts great research interests owing to the metastability and the involved microstructural complexity upon straining, while the fundamental understanding on its formation mechanism is still insufficient. In this study, deformation-induced omega-plates have been systematically investigated using Ti-10 wt% Cr metastable beta-Ti alloy containing athermal omega-precipitates. It is found that single-variant omega-plates form either along {332}(beta) twin interfaces or in the twin interiors, which closely depends on twin morphologies. For the acicular beta-twin, the omega-plate appears in the twin interiors accompanied by high density of parallel straight dislocations, while for the lenticular twin, the omega-plate attaches to the twin interface without the surrounding dense parallel straight dislocations. These unique formation characteristics result from local stress field induced by the twinning itself and the passive transformation of athermal omega-precipitates. It is further revealed that the passive transformation of athermal omega-precipitates dominates the formation of omega-plates inside the acicular twins, while it is the locally preferential twin thickening that promotes the omega-plates to form along the lenticular twin interfaces. These findings provide new insight into deformation-induced omega-phase transformation and the intricate deformation microstructures in metastable beta-Ti alloys.