Effects of strain rate and c-axis orientation on microscale α-Ti compression: From kink bands to twinning

The plastic deformation behavior of high-purity alpha-titanium (α-Ti) single crystals is investigated through micropillar compression experiments over a wide range of strain rates (10 −3 to 10 3 𝑠 −1) at room temperature. For c-axis compression, where prismatic slip is geometrically unfavorable, two distinct deformation regimes emerge. At low to intermediate strain rates (𝜀̇< 10 2 𝑠 −1) plasticity is governed by a non-classical kink band-type mechanism. Deformation is accommodated within broad, localized bands exhibiting significant continuous lattice rotation and internal < 𝑐 + 𝑎 > dislocation structures. These bands lack discrete slip traces and show features distinct from conventional slip or twinning. At higher strain rates (𝜀̇≥ 10 2 𝑠 −1) a transition to deformation twinning is observed, characterized by exhaustive {112 ̅ 2} < 1 ̅ 1 ̅ 23 > twinning and twin-twin interactions. This shift in deformation mode coincides with a notable increase in flow stress. In contrast, for compression perpendicular to the c-axis, plastic deformation is consistently accommodated by prismatic {101 ̅ 0} < 112 ̅ 0 > slip across the entire range of strain rates, without showing any evidence of twinning or kink band formation. Additionally, the flow stress is significantly (7x) lower than that under c-axis loading. This work provides direct experimental evidence of strain rate-induced transitions in deformation mechanisms of α-Ti at the microscale.