Microstructure and functional fatigue of nanostructured Ti–50.26 at%Ni alloy after thermomechanical treatment with warm rolling and intermediate annealing

The effect of different thermomechanical treatments (TMTs) on the microstructure and functional fatigue of Ti–50.26 аt%Ni shape memory alloy (SMA) was studied. The TMTs evaluated were severe cold rolling (CR) in a strain range of е=0.75 to 1.2, and a combination of CR with warm rolling at 150 °C (WR) and intermediate annealing at 400 °С, 1 h (IA). The final step of all the TMT routes tested consisted of post-deformation annealing at 400 °С, 1 h (PDA). The resulting microstructure and crystallographic textures were studied using transmission electron microscopy and X-ray diffractometry. The processing-induced material damage was assessed by comparing edge cracks’ length and concentration measurements. Functional fatigue properties were measured after all the TMT routes using three multicycle testing modes: (a) stress-free strain recovery, (b) constraint stress recovery and (c) super elastic testing. The results of this study point to some promising technological avenues to improve the fatigue functional properties of Ti–Ni SMA.