Investigation Of Shape Memory and Supper Elastic Effects Of Ni-Ti Bi-Layers Thin Films

Shape memory thin films are candidates for micro-electro-mechanical-systems because of their strong recovery force and large deformation. In the present study Ni-Ti thin films have been deposited on Si (111) substrates by RF magnetron sputtering. The two targets (NiTi and Ti) were prepared by vacuum arc re-melting (VAR), used for co-sputtering. In this study, two mono Ni-rich and Ti-rich and two bi-layers (Ni-rich/Ti-rich and Ti-rich/Ni-rich) thin films have been deposited on Si (111) substrates. The as-deposited Ni-Ti thin films were annealed to transform the amorphous to a nano-structured material. Subsequently, shape memory and super elastic behavior were characterized. The compositions of the films were determined by energy dispersive X-ray spectroscopy. Crystallization and transformation temperatures were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and electrical resistance. Nanoindentation was used to characterize the mechanical properties. The results show that the mechanical properties of bi-layer are different of the mono layers. Also, the two way shape memory effect has been seen in the bi-layers.