Abstract
Ni-Ti-Nb and Ni-Ti shape memory thin films were sputter-deposited onto silicon substrates and annealed at 600°C for crystallization. X-ray diffraction (XRD) measurements indicated that all of the annealed Ni-Ti-Nb films were composed of crystalline Ni-Ti (Nb) and Nb-rich grains. X-ray photoelectron spectroscopy (XPS) tests showed that the surfaces of Ni-Ti-Nb films were covered with Ti oxides, NiO and Nb2O5. The corrosion resistance of the Ni-Ti-Nb films in 3.5wt.% NaCl solution was investigated using electrochemical tests such as open-circuit potential (OCP) and potentio-dynamic polarization tests. Ni-Ti-Nb films showed higher OCPs, higher corrosion potentials (Ecorr) and lower corrosion current densities (icorr) than the binary Ni-Ti film, which indicated a better corrosion resistance. The reason may be that Nb additions modified the passive layer on the film surface. The OCPs of Ni-Ti-Nb films increased with further Nb additions, whereas no apparent difference of Ecorr and icorr was found among the Ni-Ti-Nb films.
Highlights
Ni-Ti based shape memory alloys (SMAs) have received extensive commercial attention owing to their high damping capacity, high working efficiency and sufficient corrosion resistance [1, 2]
Results showed that thermal hysteresis of phase transformation decreased to near zero when the Ni-Ti(Nb) grain size was reduced to ~50 nm, which was attributed to the increased volume fraction of grain boundaries, reduced transformation friction and spontaneous lattice distortion [14]
Ni-Ti-Nb and Ni-Ti thin films have been prepared by sputter deposition
Summary
Ni-Ti based shape memory alloys (SMAs) have received extensive commercial attention owing to their high damping capacity, high working efficiency and sufficient corrosion resistance [1, 2]. Their mechanical and physical properties can be adjusted by adding ternary or even quaternary alloying elements such as Fe, Cu and Pd [3]. Micro-actuators based on shape memory thin films generally show increased actuation frequencies, improved mechanical and fatigue properties, and enhanced working outputs per volume compared with their bulk counterparts [12, 13]. The corrosion behavior of the films was characterized using various methods including open circuit potential (OCP) and potentio-dynamic polarization tests [20]. After the OCP tests, potentio-dynamic polarization tests were conducted by scanning from -500 mV to 500 mV vs. OCP, with a scan rate of 1 mV/s
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