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Transformation behavior and shape memory characteristics of temperature gradient anneal (TGA) treated and thermo-mechanically treated (TMT) Ti–47Ni–3Cu(at.%) alloys were investigated by means of differential scanning calorimetry and thermal cycling tests under constant load. Both TGA treated and TMT Ti–47Ni–3Cu alloys showed B2–B19' transformation behavior. The change in Ms * by 23 K was developed in the TGA treated Ti–47Ni–3Cu alloy along the length of the sample (150 mm). TGA treated Ti–47Ni–3Cu alloy showed perfect shape memory effects. The temperature dependence of elongation (de/dT) of a TGA treated specimen was in the range of 0.02–0.09% K−1 depending on the amount of applied stress, which was small compared to that of a TMT specimen (0.01–0.18% K−1). The temperature dependence of elongation (de/dT) of the TGA treated specimen on cooling is almost the same as that on heating, while de/dT of the TMT specimen on cooling is much smaller than that on heating (0.68% K−1).

Six batches of Ti50Ni50-xCux alloy (x=0–25) were prepared by a melt overflow process and strips of about 550 μm thickness were fabricated by rapid solidification. Microstructures and shape memory characteristics were investigated by means of x-ray diffraction (XRD), optical microscopy, differential scanning calorimetry and thermal cycling tests under a constant load. The microstructures of the as-cast strips exhibited columnar grains normal to the strip surface. XRD showed B2–B19' martensitic transformation in the Ti50Ni50 binary alloy strip, while B2–B19 martensitic transformation in all the ternary alloy strips. The transformation temperature (Ms) increased with Cu-content. During cycle deformation with an applied stress of 60 MPa, the smallest transformation hysteresis and the largest elongation associated with the B2–B19 transformation were observed to be 3.5% in Ti50Ni25Cu25 alloy strip and 3.02% in Ti50Ni40Cu10 alloy strip.

Li0.98Ni0.7Ti0.3O1.92 (LNTO) cathode material for Li ion batteries was thermally synthesized using Ni/Li/TiNi film and Li/TiNi film. Structural and electrochemical properties of the synthesized electrodes were investigated by means of x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and galvanostatic charge?discharge half-cell test. A large amount of LNTO was synthesized in a Ni/Li/TiNi system compared to a Li/TiNi system, and the Ni film in the Ni/Li/TiNi system restrained Li leakage during thermal synthesis at high temperature. The surface of the annealed Ni/Li/TiNi film consisted of a peel-off layer part (Li2O2) and an exposed surface part (LNTO). A cell with LNTO electrode synthesized in the Ni/Li/TiNi system showed 103?mAh?cm?2 initial discharge capacity and 83% of capacity retention after 10 cycles.

A novel design of the functionally graded near-equiatomic NiTi shape memory alloys that exhibit expanded ranges of transformation temperature and stress is developed. The approach utilises the sensitivity of the alloys' thermomechanical properties with respect to heat treatment conditions. The functionally graded properties are achieved by anneal within a temperature gradient after cold work, thus to create a continuous structural variation. The optimum annealing temperature range for the Ti–50.5 at.% Ni alloy is determined to be 630–800 K. Gradient-anneal of the alloy wire in this temperature range resulted in varying thermal transformation behaviour along its length and unique Luders-type deformation behaviour with a positive stress gradient for both the forward and the reverse transformations. Such behaviour enhances the functionality of the alloy for actuation applications.

Ni sulfides were formed on a Ni-deposited Ti–50.0Ni(at) alloy by annealing under a sulfur pressure of 100 kPa at 673 K for 0.36 ks. Martensitic transformation, superelasticity and electrochemical properties were characterized using different techniques. Ni sulfides consisting of NiS and NiS2 of thickness 0.8 μ m were formed by a reaction between Ni and S. Some spherical particles and pores were found in the sulfides. A Ti–50.0Ni alloy with Ni sulfide surface layers showed a two-stage B2–R–B19' transformation behavior. A partial superelasticity with a superelastic recovery ratio of 78% found in a current collector showed a clear discharge behavior with a voltage plateau between 1.3–1.6 V. Discharge capacities of the Ni sulfide cathode decreased largely from 700 to 510 mAh(g-NiS2)−1 with increasing number of cycles up to 3, above which it decreased gradually.

Carbon nanotubes (CNTs) have been synthesized through chemical vapor deposition in argon gas atmosphere using Fe–2.5%Mo alloyed nanoparticles as a catalyst and H2/CH4 gas mixture as a reaction gas. Fe–2.5 wt.%Mo alloyed nanoparticles with average diameter of 7, 20, 45 and 85 nm are prepared by the chemical vapor condensation process using the pyrolysis of iron pentacarbonyl (Fe(CO)5) and molybdenum hexacarbonyl (Mo(CO)6). The morphologies of the CNTs are controlled by adjusting the nanoparticle size, reaction gas ratio and reaction temperature. With decreasing nanoparticle size under the same experimental conditions, the degree of crystalline perfection increases gradually and the morphologies of the carbon nanotubes vary from multi wall carbon nanotubes to single wall carbon nanotubes. Also, the ratio of reaction gas has an effect on the morphology and the degree of crystallinity of CNTs. In this work, it is suggested that morphology, diameter and degree of crystallinity of CNTs could be controlled by adjusting the reaction gas ratio, reaction temperature and catalyst size.

Four batches of Ti?Ni?Cu strips (Ti49Ni21Cu30, Ti50Ni20Cu30, Ti51Ni19Cu30 and Ti52Ni18Cu30) were prepared by an arc melt overflow technique. The microstructure of as-cast strips exhibited columnar grains normal to the strip surface. XRD analysis showed that B2?B19 martensitic transformation occurred in all alloy strips. The martensitic transformation start temperature (Ms) of the Ti49Ni21Cu30 strip was 54.6??C and continued to increase with increasing Ti-content. During cycle deformation with an applied stress of 120?MPa, transformation hysteresis and elongation associated with the B2?B19 transformation were observed to be 4.1??C and 1.84% in the Ti49Ni21Cu30 strip. The transformation hysteresis associated with the B2?B19 transformation increased with increasing Ti-content, while the elongation decreased with increasing Ti-content. Even though it is known that Ti?Ni?Cu alloys with high Cu-content (more than 13?at?% Cu) are too brittle to deform plastically, the rapidly solidified Ti?Ni?Cu alloy strips, which contain 30?at?% Cu, have excellent shape memory characteristics and mechanical properties.

A temperature gradient of 75–188 K was developed in a Ti–45Ni–5Cu(at %) alloy wire with 30 mm length by Joule heating, depending on electrical power. The shape change rate increased from 0.022 to 0.045% K−1 on increasing the electrical power from 4.8 to 6.2 W. The change in the stress required for the B2–B19' transformation increased from 60 to 103 MPa on increasing the electrical power from 4.8 to 10.1 W.

For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, consolidation of TiNi alloy powders is more useful than that of elemental powders of Ti and Ni. In the present study, TiNi shape memory alloy powders were prepared by inert gas atomization, and martensitic transformation temperatures and microstructures of those powders were investigated as a function of powder size. The size distribution of the powders was measured by conventional sieving, and sieved powders with the specific size range of 0–200 μm were chosen for this examination. XRD analysis showed that the B2–B19' martensitic transformation occurred in powders smaller than 200 μm. In DSC curves of the as-atomized Ti50Ni50 powders as a function of powder size, only one clear peak was found on each cooling and heating curve. The martensitic transformation start temperature (Ms) of the 0–20 μm powders was 21.9 °C. The Ms increased with increasing powder size, and the difference in Ms between 0 and 20 μm powders and 150–200 μm powders is only 1 °C. The typical microstructure of the rapidly solidified TiNi powders showed cellular/dendrite morphology and exhibited a small volume fraction of Ti2Ni phase, which is located in interdendritic/intercellular regions.

This study used prestrained NiTiNb and NiTi shape memory alloy (SMA) wires to confine concrete cylinders. The recovery stress of the wires was measured with respect to the maximal prestrain of the wires. SMA wires were preelongated during the manufacturing process and then wrapped around concrete cylinders of 150 mm×300 mm (×L). Unconfined concrete cylinders were tested for compressive strength and the results were compared to those of cylinders confined by SMA wires. NiTiNb SMA wires increased the compressive strength and ductility of the cylinders due to the confining effect. NiTiNb wires were found to be more effective in increasing the peak strength of the cylinders and dissipating energy than NiTi wires. This study showed the potential of the proposed method to retrofit reinforced concrete columns using SMA wires to protect them from earthquakes.

For the accurate and dexterous operation of mechanical systems, continuous-type actuation, rather than on/off-type actuation, is an indispensable function. However, conventional Ti–Ni alloys present difficulties for continuous positioning control, due to their hysteretic and abruptly changing relationship between strain and temperature. Therefore, this paper proposes a new linearity-enhanced SMA actuator using a temperature-gradient annealed alloy and an inverse hysteresis controller. In comparative experiments, the proposed controller and alloy exhibit superior performance for continuous actuation.