**4. Conclusions**

Molecular dynamics simulations performed on the compressive loading of axially twinned [110] BCC Fe nanowire indicate that the deformation is dominated by a de-twinning mechanism involving the migration of a twin–twin junction. In the present study, two types of twin–twin junctions were observed. One is Y-junction where three TBs meet at an angle of 120◦ with respect to each other and the other is an arrow (↓)-like junction, where TBs meet at an angle of 60 and 240◦. The results indicate that compared to the Y-junction, the arrow like junction participates more actively in de-twinning mechanisms. In all the nanowires, the de-twinning mechanism results in a complete annihilation of pre-existing TBs along with a change in nanowire orientation from initial <110> to <001>. Further, it was observed that the annihilation of pre-existing TBs occurs through two different mechanisms, one without any resolved shear stress and other with a finite and small resolved shear stress. The annihilation of pre-existing TBs without any resolved shear stress has occurred through the step-by-step movement of the twin–twin junction due to the glide of 1/6<111> partial dislocations on newly formed twin boundaries. The annihilation of pre-existing TBs with finite shear stress occurred due to the slight bending of twin boundaries at higher strains. The present study significantly improves our understanding of de-twinning and also the stability of twin boundaries in BCC nanowires.

**Author Contributions:** G.S.: Conceptualization, Methodology, Data curation, Formal analysis and Writing-original draft; S.G.: Resources and Writing - review & editing; A.N.: Resources and Writing-review & editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
