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Annealed NiTi thin films (∼51.2 at.%Ni) were implanted with carbon and nitrogen ions with 80 keV energy and 3×1017 cm-2 ion dose. X-ray photoelectron spectroscopy confirmed the existence of implanted ions in the surface structure of the films. Atomic force microscopy showed an increase of roughness and decrease of grain size after ion implantation. Grazing incidence X-ray diffraction showed the formation of new phases in the films such as TiN, Ti2N, TiC and different kinds of oxides. Nanoindentation and nanoscratching tests revealed the improvement of wear behaviour of NiTi thin films after ion implantation via increasing nanohardness (3.1-6.2 and 7.3 GPa after carbon and nitrogen ion implantation, respectively) and decreasing of scratch coefficient (0.22-0.18 and 0.17 after carbon and nitrogen ion implantation) and wear depth. [ABSTRACT FROM AUTHOR]

Abstract: Copper nanowire arrays were synthesized on NiTi shape memory alloy thin films to improve thermal actuation. To grow the forest of Cu nanowires, an Al film was deposited on top of the NiTi by DC sputtering, anodized in oxalic acid to form anodic aluminum oxide (AAO), and then the copper was electrodeposited inside the nanochannels of the template. Growth of these Cu nanowires was studied by electrochemical methods: anodization and electrodeposition rates were characterized using current density versus time diagrams. The morphology and crystal structure of Cu nanowires were evaluated by field emission scanning electron microscopy and X-ray diffraction. [Copyright &y& Elsevier]

Abstract: In this paper, the corrosion behavior of NiTi thin films implanted with argon, carbon and nitrogen ions was investigated by potentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS) methods. PDS results showed that the icorr was decreased after implantation with carbon and nitrogen and increased with argon ions. EIS measurements also indicated that the corrosion resistance (Rp) of the films implanted with carbon and nitrogen was increased and with argon implantation decreased. Scanning electron microscopy (SEM) images showed a lesser amount of corrosion defects in nitrogen and carbon implanted thin films and more amounts in argon implanted and unimplanted film surfaces. The cracks are also observed on argon implanted surface. [Copyright &y& Elsevier]

Abstract: Actuation frequencies in thermally triggered Shape Memory Alloy (SMA) thin films are limited by the slow heat transport into/out of the films. Carbon Nanotubes (CNTs) are known to exhibit an exceptionally high thermal conductivity. Thus, we propose to thermally contact SMA films with CNTs to increase SMA actuation frequencies by enhanced heat transport through the CNTs. The basic requirement for this envisaged nanotube application is to obtain CNT forest growth on a SMA material while retaining a reversible martensitic transformation, as required for Shape Memory Effect exploitation. We show how such growth can be achieved on thin films of the SMA material NiTi. Future work is needed to measure thermal properties and obtainable cycling frequencies of CNT-SMA structures. [Copyright &y& Elsevier]

Abstract: In this paper the corrosion behavior of NiTi thin films fabricated by sputtering from Ni and Ti targets has been studied by cyclic potentiodynamic polarization tests in Hank''s and Ringer''s solution at 310 K. For comparison, bulk NiTi Shape Memory Alloy (SMA) has also been studied to elucidate the different corrosion behavior of bulk and thin film material. The electrochemical experiments reveal that thin film NiTi SMA has comparable corrosion current density (i corr), much higher pitting corrosion potentials and wider passive range than the bulk NiTi. We show that NiTi SMA vapour deposited thin films are less susceptible to pitting corrosion than the bulk. [Copyright &y& Elsevier]

Abstract: Thin sputtered films of binary (Ni–Ti) and ternary (Ni–Ti–Hf and Ni–Ti–Cu) shape memory alloys have been subjected to nanoindentation over a range of temperature (up to 400 °C), using a small diameter spherical indenter. The load-displacement plots obtained during these experiments have been interpreted so as to reveal whether the imposed strain was being at least partly accommodated by the martensitic phase transformation, ie whether superelastic deformation was taking place. This was done by evaluating the remnant indent depth ratio (depth after unloading/depth at peak load), which is expected to have a relatively small value if superelastic deformation and recovery are significant. It is confirmed that this procedure, which has previously been validated for bulk material, can be applied to these thin films (~2 µm in thickness). The results indicate that ternary alloys with up to about 20 at.%Hf or 10 at.%Cu can exhibit superelastic behaviour over suitable temperature ranges. [Copyright &y& Elsevier]

In the present paper, the fabrication and characterisation of typical high temperature Ni(Ti+Hf) alloyed thin films produced by simultaneous sputter deposition from separate elemental Ni, Ti and Hf targets are presented. Film composition, determined by energy dispersive X-ray spectroscopy, was controlled by adjusting the ratio of powers applied to each target. Films deposited at room temperature had an amorphous structure and subsequent annealing at 550°C was carried out in a high vacuum environment, based on crystallisation temperature evaluation by differential scanning calorimetry (DSC). High temperature martensitic transformation, confirmed by DSC and variable temperature X-ray diffraction (XRD), was achieved by deposition of (Ti+Hf) rich Ni–Ti–Hf films. Any slight change of composition towards Ni rich reduced the transformation temperature. Atomic force microscopy and XRD illustrated that the films had a fine grain structure (∼100 nm). One way shape memory effect was observed at ∼200°C in a film with composition of 15·6 at.-%Hf. [ABSTRACT FROM AUTHOR]

A transition of film surface morphology between wrinkling and surface relief during heating/cooling is reported for a sputtered TiNiCu thin film shape memory alloy. The mechanisms for this transition are discussed based on film stress evolution. During annealing surface wrinkling occurs to relieve compressive stress in the film, while the surface relief morphology occurs during cooling due to the martensitic transformation, which relieves tensile stress. [ABSTRACT FROM AUTHOR]

Abstract: TiNiCu films were deposited on a (100) type Si substrates by co-sputtering of TiNi and Cu targets at room temperature, and then post-annealed at 450 °C for crystallization. Significant surface relief due to martensitic transformation occurred on the film surface after cooling, and variations in surface relief morphology (the size and density of martensite crystals) have been quantified with atomic force microscopy. Energy dispersive X-ray analysis showed that the surface relief morphological difference in the TiNiCu films is due to the change in composition. It was proposed that the crystallization of the amorphous thin film during annealing behaved differently with chemical composition, which in turn induced fluctuations in phase transformation temperatures at various regions, as confirmed by differential scanning calorimeter measurements. [Copyright &y& Elsevier]