A new fabrication process for Ni-Ti shape memory thin films

A new fabrication method for Ni-Ti thin films showing martensitic phase transformation is presented. A multilayer of up to 100 alternating pure Ni and pure Ti layers is deposited in an automated DC magnetron sputter system optimized for homogeneous deposition on large substrates. The single layer thickness is in the range of 10-20 nm. The multilayer is subjected to different heat treatments in order to allow for interdiffusion of Ni and Ti and subsequent recrystallization as a Ni-Ti intermetallic compound. The martensitic and austenite phase in the resulting films could be identified by means of X-ray diffraction. Differential scanning calorimetry (DSC) measurements monitor the transformation behavior of films with different composition and indicate the existence of an R-phase. The microstructure of the annealed films is investigated by transmission electron microscopy (TEM). The composition and transformation temperatures can be adjusted by varying the thickness ratio of the initial Ni and Ti layers. These films show a well pronounced shape memory effect for certain annealing procedures. (orig.)