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.