The Superelastic Stability of Nanocrystalline Ni-51 At.% Ti Shape Memory Alloy

NiTi shape memory alloys have been extensively studied owing to its superelasticity. However, the application of coarse-grained NiTi alloys is limited due to their low superelastic stress and poor superelastic stability after cyclic deformation, which mainly because of their low yield strength. In this study, large deformation cold-drawing and low-temperature annealing were used to obtain nanocrystalline (NC) Ni 51 Ti 49 (at.%) wire specimen (average grain size ~ 14 nm). After twenty cycles of loading (up to 6%)–unloading, the Ni 51 Ti 49 alloy has a superelastic stress of 1051 MPa, a residual strain of 0.66% and a superelastic stress reduction rate of 9%, which is obviously superior to NC NiTi with the same grain size, as well as previous coarse-grained NiTi alloys. We have suggested that this mainly stems from the NiTi matrix that was considerably improved by the synergistic enhancement of high-density grain boundaries and doped Ni atoms in NC Ni 51 Ti 49 SMAs, reducing plastic deformation and showing high superelastic stability.