Phase Transformation Behaviour And Mechanical Properties Of TiNiTa Memory Alloys

In recent years,NiTi shape memory alloys（SMAs）has been widely used in the field of medical biology due to its unique shape memory effect,superelasticity and good biocompatibility.In order to facilitate medical application and follow-up examination,its X-ray visibility needs to be improved,and TiNiTa SMAs will provide better X-ray visibility.Therefore,TiNiTa SMAs has great potential to be applied in the field of medical biology.In this paper,amorphous TiNiTa SMAs were obtained by severe deformation of cold drawing.The phase transformation behavior of TiNiTa SMAs after heat treatment was studied by DSC,electrical resistivity and DMA.The microstructure of TiNiTa SMAs after heat treatment was studied by SEM and XRD,and the mechanical properties of TiNiTa SMAs after heat treatment were investigated by tensile machine.Ni₅₀Ti₄₆Ta₄,Ni_50.5Ti_45.5Ta₄and Ni₅₁Ti₄₅Ta₄exhibit B2-R phase transformation after annealing at low temperature,while B2-B19’phase transformation occurs after annealing at high temperature.With the increase of Ni content,the phase transformation temperature decreases and the strength increases.With the increase of annealing temperature,the phase transformation temperatures of the materials increase.When annealing at low temperature,the ductility of the material is poor due to the small grain size of the material.The ductilities of Ni₅₀Ti₄₆Ta₄and Ni_50.5Ti_45.5Ta₄were improved after annealing at high temperatures.After annealing at 400℃for 20 min,the critical stress of the material increased with the increase of the test temperature,and the material has superelasticity at 0℃.Aging treatment had little effect on Ni_50.5Ti_45.5Ta_4,but Ni₄Ti₃precipitated along grain boundaries in Ni₅₁Ti₄₅Ta₄was observed.Although the material aged at room temperature does not have superelasticity,the ductility of the material can be adjusted by adjusting the aging temperature.Ni₅₀Ti₄₆Ta₄SMAs showed two-way shape memory effect after certain pre-strain.The material showed stable two-way shape memory effect over the temperature range of 50-110°C.