Steps and {112¯1} secondary twinning associated with {112¯2} twin in titanium

Abstract

Abstract { 11 2 ¯ 2 } twinning commonly takes place in α-titanium (α-Ti). High-resolution transmission electron microscopies (HRTEM) explored various steps along { 11 2 ¯ 2 } coherent twin boundary. Topological model of { 11 2 ¯ 2 } twin revealed twinning disconnections (TDs) that are represented by (bi, i h { 11 2 ¯ 2 } ) corresponding to a step height i h { 11 2 ¯ 2 } and a shear vector bi. Atomistic simulations were conducted to study the energies and kinetics of TDs. Combining microscopies and atomistic simulations, we concluded that (b3, 3 h { 11 2 ¯ 2 } ) is the elementary TD and (b1, h { 11 2 ¯ 2 } ) is the reassembly TD. Steps observed in HRTEM thus can be treated as a reassembly of (b3, 3 h { 11 2 ¯ 2 } ) TDs and (b1, h { 11 2 ¯ 2 } ) TDs. In addition, Electron Backscatter Diffraction (EBSD) maps revealed { 11 2 ¯ 2 } → { 11 2 ¯ 1 } double twins in α-Ti. Using two-dimensional and three-dimensional atomistic simulations, we demonstrated the nucleation of (b1, h { 11 2 ¯ 2 } ) TD and { 11 2 ¯ 2 } → { 11 2 ¯ 1 } double twin through the interaction between basal dislocation and { 11 2 ¯ 2 } twin. Our results enrich the understanding of { 11 2 ¯ 2 } twinning including TDs, steps, and { 11 2 ¯ 1 } secondary twins in hexagonal metals.