Unique twinning mode and extended twin boundary core structure associated with symmetry breaking in a multifunctional Ti-Nb-based alloy

Recently, a class of multifunctional Ti-Nb-based alloys has been developed, exhibiting exceptional mechanical and physical properties, such as high strength, high ductility, low-modulus superelasticity, and Invar/Elinvar anomalies. These properties are closely linked to the co-evolution of various microstructural defects, including dislocations, twins, and second-phase domains. In this study, we show the formation of unique defects, such as {3 9 10} twins and extended twin boundary core structures, in a cold-rolled Ti-24Nb-4Zr-8Sn-0.2O (wt.%) alloy. These defects arise from the intrinsic coupling between phase transformation and deformation twinning. Using a phase transition graph approach, we demonstrate that these high-index twins and extended defect core structures originate from the correlated broken symmetry associated with multiple crystal deformation processes. By establishing a symmetry-based link between deformation paths and characteristic defects, our work offers a new perspective for investigating the deformation mechanisms and unique properties of metallic materials.