Fabrication and characterization of Ti-Ni shape memory thin film using Ti/Ni multilayer technique

Alloying process and shape memory properties of a Ti/Ni multilayer thin film fabricated by a dual d.c. magnetron sputter-deposition method were investigated, and compared with those of a Ti-Ni amorphous thin film fabricated by an alloy target sputter-deposition method. The multilayer thin film was made by depositing Ti and Ni layers alternately on a SiO2/Si substrate. The Ti and Ni of the Ti/Ni multilayer thin film were crystalline after deposition. Alloying of the Ti/Ni multilayer thin film proceeded in multi steps. Amorphous phase was formed at the interfaces between the Ti and Ni layers by inter-diffusion of the Ti and Ni atoms during heating up to 640 K. Ni-rich Ti-Ni B2 phase was formed during heating up to 710 K. During further heating up to 750 K, the Ni-content of the Ti-Ni B2 phase decreased and Ti2Ni phase was formed. The Ti/Ni multilayer thin film exhibited shape memory effect after heat-treatment at 673 K where Ti-Ni amorphous thin films were not crystallized. The heat-treated Ti/Ni multilayer thin films exhibited the shape memory effect equivalent to that of the heat-treated Ti-Ni amorphous thin films when the heat-treatment temperature was above 873 K.