Deformation Induced Hierarchical Twinning Coupled with Omega Transformation in a Metastable β-Ti Alloy.

Hierarchical twinning, at multiple length scales, was noted in a metastable body-centered cubic (bcc) β-titanium alloy on tensile deformation. Site-specific characterization within the deformation bands, carried out using EBSD and TEM, revealed {332} <113> type primary bcc twins, containing different variants of secondary and tertiary twins, as well as the formation of stress-induced martensite (α"). Within the primary {332} <113> type twin, "destruction" of the prior quenched-in athermal ω phase was observed, while a stress-induced ω phase reforms within the tertiary twins, revealing the intricate nature of coupling between deformation twinning and displacive ω transformation.