Calorimetric and Volumetric Studies of Dislocations during Martensitic Transformations in TiNi Alloy with Shape Memory

An in-depth analysis of calorimetric and volumetric data for direct, reverse, and deformation martensitic transformations in the nanostructured alloy Ti_49.3Ni_50.7 with shape memory is carried out. The samples are obtained by cold rolling with the simultaneous action of a high-density pulsed current. A new technique for processing calorimetry spectra is applied, with the help of which, for the first time, the staging and kinetics of changes in the heat content are studied in detail, as well as thermal effects (enthalpy of individual stages) during direct and reverse martensitic transformations occurring under the influence of temperature. By processing volumetric data, using theoretical values of the dislocation density and elements of classical dislocation theory, it is shown that in the Ti_49.3Ni_50.7 alloy with shape memory subjected to cold plane deformation (rolling) accompanied by the action of a pulsed current, a strain-induced martensitic transformation occurs. This transformation results in a positive volume effect (∆V/V ≈ 3 × 10^–3), which can be largely due to dislocations. It is demonstrated that the possible contributions of dislocations to the enthalpy of direct and reverse martensitic transformations in the Ti_49.3Ni_50.7 alloy can and should be significantly lower in absolute value, but opposite in sign relative to the observed enthalpy of direct and reverse martensitic transformations in this alloy.