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Influencing the Martensitic Phase Transformation in NiTi through Point Defects

Equiatomic nickle-titanium (NiTi) is investigated to determine the consequences of point defects on the Martensitic phase transformation. Using molecular dynamics (MD) simulations, NiTi with 0.1%, 0.5%, 1%, 2%, and 3% of Schottky-type defects (vacancies) have been modeled with the temperature of structural transformation elucidated. Increasing the concentration of point defects leads to this transformation occurring at lower temperatures than the perfect structure while the final monoclinic unit cell angle ($γ$) substantially decreases. Modeling anti-site defects at the 0.1%, 0.5%, and 1% concentration level indicates the cubic to monoclinic structural transformation temperature decreases even faster with a more dramatic change in $γ$ compared to the vacancy structure. The change in this Martensitic transformation stems from pinning due to the structural defects.