Atomic-scale study of the 11(2)over-bar1 twinning and 11(2)over- bar2-11(2)over-bar1 double twinning mechanisms in pure titanium

H Zhang and XQ Ou and S Ni and HG Yan and XZ Liao and M Song, INTERNATIONAL JOURNAL OF PLASTICITY, 160, 103486 (2023).

DOI: 10.1016/j.ijplas.2022.103486

The 11 (2) over bar1 twinning and 11 (2) over bar2-11 (2) over bar1 double twinning mechanisms in pure Ti are systematically investigated using molecular dynamics (MD) simulations. MD simulation results indicate that a 11 (2) over bar1 twin embryo is composed of a group of pyramidal stacking faults (PSFs) with 6d(11 (2) over bar1) or 8d(11 (2) over bar1), caused by the successive slip of partial dislocations with the Burgers vector of 1/36<11<(26)over bar>>(M). The migration of 11 (2) over bar1 twin boundaries (TBs) is mainly carried out by the slip of twinning dislocations (TDs) (b) over right arrow (1) = 1/6(4 gamma(2)+1)<<(11)over bar>26> +/- 1/2 <1<(1)over bar>00>. Two 11 (2) over bar2-11 (2) over bar1 double twinning mechanisms are discovered. One is that a 11 (2) over bar1 twin forms and grows at the 11 (2) over bar2 twin tip through the dissociation of the TD (b) over right arrow ((11 (2) over bar2))(1) at the 11 (2) over bar2 twin tip, forming the 11 (2) over bar2-11 (2) over bar1 double twin structure. The other is that a basal (T) dislocation interacts with a 11 (2) over bar2 TB, forming a twin embryo composing of a group of PSF with the 6d(11 (21) over bar) and leaving a step at the 11 (2) over bar2 TB, eventually forming the 11 (2) over bar2-11 (2) over bar1 double twin structure. The interfacial structures of 11 (2) over bar1 twins have the terraced character with short coherent (11 (2) over bar2)parallel to(11 (2) over bar0) facets and coherent twin boundary (CTB) segments. In addition, (0001)parallel to(11 (2) over bar4) facets with a disclination dipoles feature can form at twin tips. The coherent twin interfaces form at their intersected interfaces during the 11 (2) over bar2-11 (2) over bar1 double twinning process. Our present findings may provide clues for designing Ti alloys with excellent strength-ductility properties through obtaining a high-volume fraction of coherent interfaces in terms of 11 (2) over bar2-11 (2) over bar1 double twins.

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