Secondary twinning and twin–twin interaction mechanisms of {112¯1} deformation twins in rhenium

Deformation twinning plays a central role in the plasticity of hexagonal close-packed (hcp) metals, and twin–twin interactions together with secondary twinning can strongly influence their mechanical response. Yet these phenomena remain insufficiently understood, especially for the less common { 11 2 ¯ 1 } extension twins. This study investigates these mechanisms in single-crystal rhenium using in-situ transmission Kikuchi diffraction tensile testing along the [0001] axis. We observe two distinct secondary twinning phenomena. First, native secondary twins form abundantly within primary twins, independent of twin interaction sites. Their nucleation is rationalized by their high Schmid factor and the energetically favorable dissociation of basal dislocations at primary twin boundaries. Second, specific twin-twin interactions trigger a distinct secondary variant selection producing a crossing-like morphology. While these twin crossing configurations violate classical geometric criteria, we show that variant selection is governed by the local stress state and plausibly facilitated by the dissociation of non-basal dislocations. These findings establish a stress- and dislocation-based framework for secondary twinning in { 11 2 ¯ 1 } extension twins, offering new insights into deformation anisotropy of hcp metals.