**4. Conclusions**

This paper presents the first atomistic study of the effect of linear complexions on the mechanical behavior of metallic alloys, with Fe-Ni used as a model system. A strong pinning effect of linear complexions on their host dislocations is observed, which is connected to the alteration of the dislocation's stress field in the crystal. This pinning effect leads to a substantial increase in the initial breakaway stress with a pronounced initial peak stress, aligning with experimental observations from alloys with similar complexion structures. Dislocation motion away from the nanoparticle arrays leads to an L10-to-B2 lattice distortive transformation as the stress field, which stabilized the original complexion structure, is removed. These findings provide additional understanding and context for nanoscale phase transformations induced by dislocation stress fields and their effect on the mechanical properties of materials. Additional studies to obtain a complete understanding of linear complexion thermodynamics and the deformation physics associated with dislocation complexion-interactions are needed to enable "defects-by-design," which can be used to tailor mechanical response.

**Author Contributions:** Conceptualization, Methodology, Data curation, Formal analysis, and Writing-original draft, V.T. Conceptualization, Methodology, Resources and Writing—review & editing, T.J.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the U.S. Army Research Office, grant number W911NF-16-1-0369.

**Acknowledgments:** The authors express appreciation to Daniel S. Gianola (University of California, Santa Barbara) for fruitful discussions on this topic.

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