4.7 Article

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

Journal

INTERNATIONAL JOURNAL OF PLASTICITY
Volume 160, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijplas.2022.103486

Keywords

Itanium; {11(2)over-bar1} twinning; {11(2)over-bar2}-{11(2)over-bar1} double twinning; Interfacial structure; Coherent twin interface

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The twinning mechanisms in pure Ti, including {11 (2) over bar1} twinning and {11 (2) over bar2}-{11 (2) over bar1} double twinning, are systematically investigated using molecular dynamics simulations. The migration of {11 (2) over bar1} twin boundaries is mainly carried out by the slip of twinning dislocations. Two double twinning mechanisms, involving the formation and growth of {11 (2) over bar1} twin at the {11 (2) over bar2} twin tip, are discovered. The interfacial structures of {11 (2) over bar1} twins exhibit terraced character with short coherent facets and coherent twin boundary segments.
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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