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

A new Fabrication method for Ni-Ti thin films showing martensitic phase tra nsformation is presented. A multilayer of up to 100 alternating pure Ni and pure Ti layers is deposited in an automated DC magnetron sputter system op timized for homogeneous deposition on large substrate. The single layer thi ckness is in the range of 10-20 nm. The multilayer is subjected to differen t heat treatments in order to allow for interdiffusion of Ni and Ti and sub sequent recrystallization as a Ni-Ti intermetallic compound. The martensiti c and austenite phase in the resulting films could be identified by means o f X-ray diffraction. Differential scanning calorimetry (DSC) measurements m onitor the transformation behavior of films with different composition and indicate the existence of an R-phase. The microstructure of the annealed fi lms is investigated by transmission electron microscopy (TEM). The composit ion and transformation temperatures can be adjusted by varying the thicknes s ratio of the initial Ni and Ti layers. These films show a well pronounced shape memory effect for certain annealing procedures. (C) 1999 Elsevier Sc ience S.A. All rights reserved.