Atomistic Simulation of Microstructural Evolution of Ni50.8Ti Wires during Torsion Deformation

To explore the microstructural evolution of Ni50.8Ti wires during torsion deformation, single and polycrystalline models with various grain sizes (d = 9 nm, 5.6 nm, and 3.4 nm) were established on an atomic scale to explore their grain morphology evolution, stress-induced martensitic transformation, and dislocation movement. The results indicated that the grains were rotated and elongated to form long strips of grains during the torsion simulation. With the increase in torsion deformation, the elongated grains were further split, forming smaller grains. Stress-induced martensitic transformation took place and the martensite preferentially nucleated near the grain boundary, resulting in the formation of 30% austenites and 50% martensites. Additionally, a certain number of dislocations were generated during the torsion simulation. Under a low degree of torsion deformation, the main mechanism of plastic deformation was dislocation movement, while with a large degree of torsion deformation, the main mechanism of plastic deformation was grain rotation.