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Abstract
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This study investigates the combined effects of temperature and point defects on the mechanical behavior of Ni-rich NiTi shape memory alloys under quasi-static uniaxial loading conditions using molecular dynamics simulations. A threedimensional polycrystalline model with random crystallographic orientations is constructed, incorporating point defects at concentrations ranging from 0 to 10%. The embedded atom method potential is employed to describe interatomic interactions, and simulations are conducted across temperatures from 250 K to 500 K under both tensile and compressive loading conditions. Results demonstrate that NiTi exhibits characteristic four-stage deformation behavior: initial elastic deformation of the B2 austenite phase, stress-induced martensitic transformation (B2→B19’), transformation plateau, and post-transformation plasticity. Temperature significantly influences mechanical properties, with increasing temperature causing systematic thermal softening, elevated transformation stresses, and reduced superelastic behavior. Point defects severely degrade the mechanical performance by suppressing the stress-induced martensitic transformation through interface pinning and local stress field creation. The combined effects of elevated temperature and point defects produce synergistic mechanical degradation exceeding individual contributions. Tension-compression asymmetry is observed in all conditions due to different martensite variant selection mechanisms. The study establishes critical defect tolerance thresholds for NiTi applications and demonstrates that maintaining low vacancy concentrations is essential for preserving shape memory functionality.
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