Research Progress on Phase Design at Micro and Nano Scales of Low-cycle-fatigue NiTi Based Superelastic Alloys

The cycle fatigue of functional characteristics of shape memory alloys is a general key issue in restricting its functional application under long-term service conditions.Under cyclic loading-unloading conditions, stress-induced plastic deformation in austenite affects the cycling stability of stress-driven superelasticity.The recent research advances show that reasonable alloy design results in the introduction of a second phase with an appropriate volume fraction, which can dramatically enhance the cyclic stability of superelastic response.In this article, the phase design strategy of three low-cycle-fatigue NiTi based superelastic alloys was reviewed, ranging from NiTi based alloy film, additive manufactured bulk alloy to severely plastic deformed alloy pillar.The phase structure, phase interface, volume fraction and modulus of both the matrix phase and the second phase in each alloy were discussed.Finally, the potential application fields of the low-cycle-fatigue phase design strategy were highlighted.