On the Super-Elastic and Phase Transformation of a Novel Ni-Rich/NiTiCu Bi-Layer Thin Film.

Shape memory Ni-Ti-based thin films were deposited on glass substrates at room temperature by DC magnetron sputtering system from alloy targets. Two discs of Ti-rich targets (Ni₄₁Ti₅₄Cu₅ and Ni₄₇Ti₅₃) were used to deposit two single-layers with chemical compositions of Ni₄₅Ti₅₀Cu₅ and Ni_50.8Ti_49.2 and one bi-layer thin films with different chemical compositions similar to the single layers on glass substrates. The as-deposited Ni-Ti thin films were annealed to transform the amorphous to a crystalline material. Subsequently, the structures, phase transformations, and mechanical properties were characterized using grazing incidence X-ray diffraction (GIXRD), field emission electron microscope (FESEM), electrical resistance, and nanoindentation. The developed bi-layer thin film exhibited a two-step transformation B2 ↔ R ↔ B19' during cooling and heating with a narrow thermal hysteresis as compared to the single-layers. Moreover, super-elasticity effect and partial permanent strain appeared in the bi-layer because of composite structure. [ABSTRACT FROM AUTHOR]