Exploring the functional capabilities of NiTi shape memory alloy thin films deposited using electron beam evaporation technique

Abstract

The viability of utilizing electron beam evaporation technique for the development of NiTi shape memory alloy (SMA) thin films on kapton polyimide (flexible substrate) has been investigated. The actuation characteristics of the SMA/polyimide structure were evaluated using shape recovery analysis and electrical actuation. The maximum shape recovery ratio of 1.375 was attained with butterfly configuration during shape recovery analysis. The SMA/polyimide stimulated via Joule heating has displayed a maximum displacement of 0.9 mm at 3 V. The surface morphology examined through scanning electron microscope shows the smooth surface without any pores. The thermal stability analyzed using thermogravimetric analysis shows the NiTi SMA thin film can withstand higher temperature above 550 °C without any damage to the SMA/polyimide structure. The stress/strain behavior of the SMA/polyimide structure was analyzed as a function of temperature. The differential scanning calorimetry has showed that the austenite phase transformation temperature lies in the range of 45°C-95 °C. The temperature sweep test performed using dynamic mechanical analyzer recorded a drastic drop in storage modulus in the same phase transformation temperature range as that of DSC. The UV–Vis spectroscopy reveals the NiTi/polyimide structure has high reflective surface in the visible region which aids in the application of reflectors. SMA/polyimide structure can be used as a smart optical mirror in interferometry technique owing to its optical reflectivity.