Thermomechanical treatment to achieve stable two-way shape memory strain without training in Ti-49.8 at.% Ni alloy

Two-way shape memory (TWSM) strain for the Ti-49.8 at.% Ni alloy after rolling (40 % thickness reduction) at temperatures 470 870 K is studied. It is found that rolling at 470 and 570 K produces samples showing the dilatation jump in the rolling direction of 0.9 and 1.3 %, respectively, that does not change upon thermal cycling through the martensite transformation temperature range. The dilatation jump in the direction normal to the rolling plane is even two to three times higher. The TWSM dilatation jump demonstrated by the samples rolled at higher temperatures stabilizes only after 30 cycles. Stability of the TWSM strain of the samples rolled at 470 and 570 K is explained from the consideration of the alloy microstructure. Material which is sufficiently large and stable with respect to thermal cycling dilatation jump is ideal for the use in actuators.