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 ( ε ˙ < 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 ( ε ˙ ≥ 10 2 s − 1 ) a transition to deformation twinning is observed, characterized by exhaustive { 11 2 ¯ 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 { 10 1 ¯ 0 } 〈 11 2 ¯ 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.