Thermokinetics of shape recovery of nanostructured titanium nickelide

Abstract

The microstructure, martensitic transformations (MTs), functional characteristics and thermokinetics of shape recovery of Ni-rich titanium nickelide was studied. Post-deformation annealing at a temperature of 823 K (30 min) after cold drawing with the accumulated logarithmic strain of 0.6 forms a mixed nano-sized grain / subgrain structure of B2 austenite. The training procedure was carried out using isothermal and non-isothermal bending modes. The loading-unloading temperatures were associated with the characteristic temperatures of MTs; the loading strain was varied in the range of 13 –19 %. The specific features of the evolution of functional characteristics when using various loading modes are described. The strain-temperature conditions for the realization of the total shape recovery 17 % and TWSME value 4 % are revealed. The two-stage character of shape recovery after unloading is revealed; the hypothesis of its origin is suggested. The start and finish temperatures of shape recovery vs loading strain are measured. When using the non-isothermal mode with deep cooling under load, the temperature range for shape recovery expands from 35 to 77 K with increasing loading strain. When using the isothermal mode with loading-unloading at a start temperature of the direct MT, the temperature range of shape recovery degrades from 66 to 54 K.