Effect of Point Defects on the Phase Transformation of NiTi Shape Memory Alloy

A. Mansouri Tehrani, J. Brgoch

amansouritehrani at uh.edu

Department of Chemistry, University of Houston, Houston, TX, 77204, USA

Shape memory alloys are a fascinating class of smart materials with applications ranging from stents to actuators. Among the known materials displaying this phenomenon, NiTi alloys have attracted the most attention due to their efficient shape recovery, mechanical robustness, and biocompatibility. The phase transformation between the cubic B2 and monoclinic B19’ crystal structures are responsible for the shape memory and pseudoelasticity behavior within these alloys. Although the composition-transformation relationship has been extensively studied, the influence of point defects that are undoubtedly present in NiTi are not well understood. Here, we have employed Molecular Dynamic (MD) simulations using LAMMPS to determine the origin of changes on both thermal and stress induced phase transformations in NiTi upon point defect incorporation. Our results suggest that increasing the defect concentration hinders the transformation through a pinning mechanism, leading to a predicted 80 K change in the transformation temperature with 3% of vacancies. Moreover, anti-site defects have a greater impact than vacancies causing a more substantial shift in the transformation temperatures. The results presented here provide insights into the shape memory behavior and pseudoelasticity mechanisms while allowing for a more fine-tune control over the transformation temperature and elastic recovery.