Phase Tranformation Hysteresis And Shape Memory Strain Of NiTi(Nb) Alloys

The electronic structure of crystal material can be changed by elastic strain,thereby regulating its electrical,thermal,optical,magnetic,properties.In recent years,NiTi shape memory alloy,which is used as the Nano-film substrate,regulated physical and chemical properties of Nano-film,by its shape memory effect applying to elastic strain of Nano-film.It has attracted widespread attention of many experts.The substrate of shape memory alloy needs to satisfy the wide phase transition hysteresis,and large the one-way and two-way shape memory recovery strain,in order to facilitate the application of elastic strain to the Nano-film.Ni₅₀Ti₅₀,Ni₅₀Ti₄₈Nb₂ and Ni₄₅Ti₄₅Nb₁₀ alloy sheet were prepared in this paper.The effects of pre-strain,heat treatment temperatures and Nb element on phase transition hysteresis and shape memory strain were studied.It is found that the phase transition hysteresis of NiTi?Nb?alloy increases with the increase of pre-strain.When the pre-strain is lower than 13%,the growth rate of phase-change hysteresis is larger.When the pre-strain is higher than 13%,the phase-change hysteresis increases,and the rate is small.Under the same pre-strain,the phase transition hysteresis of NiTi?Nb?alloy annealed at 400°C is always narrower than that of NiTi?Nb?alloy annealed at 600°C,and the phase transition hysteresis of Ni₅₀Ti₄₈Nb₂ and Ni₄₅Ti₄₅Nb₁₀ alloy is always larger than the phase transition of the Ni₅₀Ti₅₀ alloy.At annealed 600°C and 15%pre-strain,the phase transition hysteresis of Ni₅₀Ti₅₀,Ni₅₀Ti₄₈Nb₂ and Ni₄₅Ti₄₅Nb₁₀ alloy are 68°C,104°C and 126°C,respectively.The one-way shape memory strain of NiTi?Nb?alloy increases first and then decreases with the increase of pre-strain.When the annealing temperature is 400°C and the pre-strain is 13%,the maximum one-way shape memory strain of Ni₅₀Ti₅₀ and Ni₄₅Ti₄₅Nb₁₀ alloy is 6.4%and 5.2%;when the pre-strain is 15%,the Ni₅₀Ti₄₈Nb₂ alloy exhibits the maximum one-way shape memory strain of 7.1%;the one-way shape memory strain of Ni₅₀Ti₅₀ alloy is always smaller than that of Ni₅₀Ti₄₈Nb₂ alloy and larger than Ni₄₅Ti₄₅Nb₁₀ alloy under the same pre-strain.The two-way shape memory strain of NiTi?Nb?alloy increases first and then decreases with the increase of pre-strain.When the annealing temperature is 600°C and the pre-strain is 13%,the Ni₅₀Ti₅₀ alloy exhibits the maximum two-way shape memory strain of3.4%.When the pre-strain is 15%,the Ni₅₀Ti₄₈Nb₂ alloy and Ni₄₅Ti₄₅Nb₁₀ alloy exhibit the maximum two-way shape memory strain of 1.8%and 2.2%,respectively.Under the same pre-strain,the two-way shape memory strain of Ni₅₀Ti₅₀ alloy is always larger than that of Ni₅₀Ti₄₈Nb₂ alloy and Ni₄₅Ti₄₅Nb₁₀ alloy.