High Temperature Shape Memory Effect In Titanium-Based Alloys After Isothermal Treatment

In alloys of Ti-Ta, Ti-Nb, Ti-Ta-Zr, Ti-Ta-Mo-V, in which the shape memory effect (SME) is realized by martensitic transformation (first effect), after isothermal treatment at deforming load above temperature of the first effect (~ 450⁰C), is first discovered high-temperature shape memory effect (second effect). Deformation of the samples were performed on tensile and torsion deformation for 5-20 minutes. Researches of deformed samples were performed by X-ray diffraction, differential thermal analysis and dilatometry. The same effect was observed after repeated cycling under load in the temperature range of the first effect. It is found that after short-term (up to 5 minutes) isothermal deformation under load and then cooled to room temperature when heating, is manifested both the first and the second effect. After a prolonged deformation (~ 20 minutes) and then cooled to room temperature, both with load and without it, is revealed only the second effect. The second effect is manifested in the case when, after the isothermal treatment  the load is removed by heating above the temperature of treatment. On the example of the alloy Ti-50Ta-6Zr (wt%) it is shown that at the residual deformation of 6% degree, shape recovery is ~ 90%.

Keywords: Ti - alloys, Shape Memory Effect.