The Investigation Of NiTiNb(Fe) Shape Memory Alloys With High Superelastic Stress At Wide Temperature Range

In recent years,with the demanding requirements of intelligent and lightweight in various industrial devices,new challenges have been put forward on the mechanical properties and service temperatures of Shape Memory Alloys(SMAs).For example,the spacecraft,which is used in Mars(-190℃ to 30℃),are required to have high superelastic stress at low temperatures and wide temperature range.However,the existing SMAs is difficult to overcome the challenge.In this paper,NiTiNbFe and NiTiNb alloy of wide temperature range and high superelastic stress were designed and fabricated.The microstructure,phase transition characteristics and superelastic behavior were studied.In this paper,NiTiNbFe and NiTiNb alloy wires were prepared by vacuum induction melting,forging,drawing and heat treatment.It was found that cold drawn wire of NiTiNbFe was annealed at 380 °C,and the average grain size is10 nm.It can achieve 8% recoverable strain from-60 °C to-196℃(temperature range of 136℃).In particular,the superelastic stress is above 1.5 GPa,which is higher than previously reported.When the stretching temperature is lower than-160℃,the relationship between the superelastic stress and the stretching temperature no longer satisfies the thermodynamic Clausius-Clapeyron(C-C)equation.It is also found that the cold-drawn wire of NiTiNb alloy annealed at 350 °C,average grain size of 15 nm,the superelastic temperature range is widened to 346°C(150°C to-196°C),and a superelastic stress of 0.6-1.5 GPa.The superelastic stress is much higher than that reported in the previous report.The relationship between the superelastic stress and the tensile temperature in the range of 150°C to-100°C is 3.26 MPa/°C,which is lower than Ni Ti alloy(6 MPa/℃).When the stretching temperature is lower than-100 °C,the relationship between the superelastic stress and the stretching temperature no longer satisfies the thermodynamic C-C equation,is "V" shaped.However,its mechanism of deviation from the thermodynamic C-C equation needs further exploration.