Structural and microhardness changes during long-term storage of Ti-Ni shape memory alloys after plastic deformation

Abstract
Quenched Ti-50.26at.%Ni and Ti-50.6at.%Ni shape memory alloys samples were subjected to cold rolling (CR) with true strains from moderate (logarithmic thickness reduction e = 0.25) to severe (e = 2.1). The evaluation of structural changes in the material during its long-term storage was performed using Vickers microhardness (HV), Differential Scanning Calorimetry (DSC) and X-ray diffraction techniques. It was shown that during storage, microhardness varied following a dome-shaped trend, thus reflecting the commonly encountered interaction between two concurrent time-dependent phenomena, the first responsible for material post-deformation hardening, and the second, for material post-deformation softening.