Size effect on shape recovery and induced strain of NiTi nanowires

The nanomechanical properties, the mechanism of fracture, and the shape recovery of NiTi nanowires under the nanobending test by an atomic force microscope tip are studied using molecular dynamics simulations. The effects of the nanowire diameter and heat treatment are evaluated in terms of atomic trajectories, loading force, adhesion, stress, slip vector, centro-symmetry parameter, Youngʹs modulus, and yield strength. Simulation results show that the occurrence of initial adhesion deformation depends on the nanowire diameter. The nanomechanical strength of a NiTi nanowire can be enhanced by decreasing its diameter. NiTi nanowires in the high-temperature austensite phase have better nanomechanical strength than those of nanowires in the low-temperature martensite phase. During deformation, dislocations glide along the {1 1 0} planes inside the nanowire. The shape recovery after loading on the (1 0 0) surface is faster than that on the (1 1 0) surface.