Influence of temperature range on NiTi SMA actuator performance during thermal cycling

The aim of the study was to find the temperature range of thermal cycling of the NiTi alloys, which would provide the most stable actuator performance. The pre-deformed NiTi samples were subjected to thermal cycling in various temperature ranges with different relevant positions of the maximum (Tmax) and minimum (Tmin) cycle temperatures compared to the finish temperatures of the reverse (Af) and forward (Mf) transformations. It was shown that the closer the Tmax value to the Af temperature and the further the Tmin value from the Mf temperature, the better the stability of the recoverable strain, recovery stress and work output and the less the irrecoverable strain accumulation during thermal cycling. However, if Tmax value exceeded the Af temperature, then the stability of the parameters was worse and the irreversible strain increased more intensive. Thus, the optimal temperature range with Tmax = 410 K and Tmin = 324 K was found where the smallest accumulation of irreversible strain and the smallest decrease in work output were observed during thermal cycling. It was discussed how the position of the Tmax and Tmin temperatures compared to the transformation temperatures affected the dislocation density variation during thermal cycling.