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In the present study, the effects of Sn content on microstructure, texture evolution, transformation behavior and superelastic properties of Ti–20Zr–9Nb‒(2–5)Sn (at.%) shape memory alloys were systematically investigated. After severe cold-rolling at room temperature, the sheet was annealed at 900 °C. A dominant α″ martensite and minor β phase were formed in the 2Sn alloy specimen. (Ti,Zr)5(Nb,Sn)3 s phase started to be detected in the 3Sn alloy specimen, and its area fraction increased from 0.02% to 1.75% with increasing Sn content from 3 at.% and 5 at.%. Increasing Sn content prevented recrystallization, affecting the texture evolution. A dominant ( 112 ) β [ 1 ‾ 3 ‾ 2 ] β and weak γ-fiber deformation textures were observed in the 5Sn alloy specimen and the 001 β 110 > β recrystallization texture was developed in the 3Sn alloy specimen. Also, increasing Sn content was found to effectively stabilize the β phase. 1 at.%‒Sn addition decreased the α″ → β reverse transformation start temperature (As) and finish temperature (Af) by 75 °C and 106 °C, respectively. The superelasticity was distinctly observed in the 900 °C annealed 5Sn alloy specimen at room temperature because its Af was below the room temperature.

LiCoO 2 thin films were fabricated using the metal-induced crystallization (MIC) method. The condition to create the MIC effect was investigated. The location and thickness of the Al coating used to manufacture the LiCoO 2 cathode thin film electrodes were varied, and the structural and electrochemical characteristics of the LiCoO 2 thin film electrode were investigated by Raman spectroscopy, field emission scanning electron microscopy and charge-discharge tests. The degree of crystallization of LiCoO 2 increased in the order of uncoated LiCoO 2 (lowest), Al(coating)/LiCoO 2 /Al foil, and LiCoO 2 /Al(coating)/Al foil (highest), for identical heat treatment condition (600 °C, 1 h). The crystallization of LiCoO 2 occurred more quickly as the Al thickness decreased, and it is considered that crystallization of LiCoO 2 is delayed owing to the formation of an alloy between Li-Al when there is more Al.

Micro carbon fibers (CFs) as a current collector were coated on sulfurized poly-acrylonitrile (SPAN) electrodes fabricated by using electrostatic flocking method. The alignment and flocking density of CFs and the electrochemical properties of SPAN electrodes were investigated with various flocking parameters of flocking distance, length of CF, and loading weight. A long flocking distance gave a sufficient space to rotate charged CFs and stand CFs on the surface of electrodes during flocking process. The flocking density was increased with a decrease of milling time and the increase of loading weight. The current collectors flocked with 12 h-milled carbon fibers (CFs) exhibited less weight than Al current collector. SPAN electrodes with CF current collector demonstrated better electrochemical performance than that with Al current collector. In particular, SPAN electrodes flocked with a loading weight of 0.3 g showed stable cycleability (76% of capacity retention until 100th cycle) and good rate capability (930 mAh/g_sulfur at 2.0 C-rate).

Functionally graded shape memory alloys have the advantage of combining the functionalities of the shape memory effect and those of functionally graded structures. By proper design, they can exhibit new and complex deformation behaviour that is unmatched in uniform shape memory alloys. One obvious advantage of functionally graded shape memory alloys is their widened transformation stress and temperature windows that provide improved controllability in actuating applications. This paper reports on the concept, fabrication, experimentation and thermomechanical behaviour of several designs of functionally graded NiTi alloys, including compositionally graded, microstructurally graded and geometrically graded NiTi alloys, and the various techniques that may be used to create these functionally graded materials. It is found that the property gradients created along the loading direction or perpendicular to the loading direction produce distinct thermomechanical behaviours. The property gradient along the loading direction provides stress gradient over stress-induced transformation, which can be adjusted by the property gradient profile. The property gradient through the thickness direction of plate specimens and perpendicular to the loading direction provides four-way shape memory behaviour during stress-free thermal cycling after tensile deformation. Keywords: Shape memory alloy (SMA), NiTi, Martensitic transformation, Functionally graded material (FGM), Pseudoelasticity, Heat treatment

This paper reports a complex four-way shape memory effect of a compositionally graded NiTi thin plate. The composition gradient is created by surface diffusion of Ni into the plate. After a 15% tensile deformation pre-treatment, the compositionally graded plate exhibits a complex four-way shape memory effect in bending mode, by which the metal exhibits a back-and-forth shape change upon a complete thermal cycle. This is analogous to a “fishtail-like” motion, resulting from the sequential transformation through the thickness of the plate as dictated by Ni content gradient. Such “four-way” shape memory effect has not been achieved in NiTi alloys before.

Shape memory alloys (SMAs) are commonly used for various applications, e.g., in the aerospace and automotive industries, robotics, and biomedical sciences. Although Ti–Ni SMAs are commercially available, the low biocompatibility of Ni has stimulated research into the development of Ti–Nb based SMAs as potential replacements of Ti–Ni alloys in biomedical applications. Ti–Nb alloys have attracted attention because of their low stiffness and superelasticity. Superelastic thin films can be used in medical applications, including the fabrication of stents for neurovascular blood vessels, which relies on a thin film and on the use of a Ti–Nb alloy coating for less biocompatible alloys. In this study, Ti–Nb thin films were prepared using magnetron sputtering. A Nb content in the range 12.2–35.9 at.% was used in the films, which was determined using energy-dispersive X-ray spectroscopy. X-ray diffraction measurement was used to analyze the crystal structure of the thin films, and their mechanical properties were investigated using nanoindentation.

This work presents the amorphization of metastable β phase and the phase stability of the amorphous phase and non-equilibrium phase in a Ti-Zr-Nb-Sn shape memory alloy (SMA). The amorphous phases with lenticular shape uniformly embedded in β matrix are observed in the twin-jet-electropolished thin foil specimen for transmission electron microscope (TEM) observations. Meanwhile, a co-existence of non-equilibrium athermal ω phase and nanodomain phases are found to be formed in the β matrix. These non-equilibrium phases could favorably compete with the amorphous phase formation and render the amorphous phases are not formed, leading to that the amorphous phase is not observed in the bulk specimens for X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) and also TEM specimen prepared by a focused ion beam (FIB). The formation of the amorphous phase in the twin-jet-electropolished TEM specimen is thought to be due to the hydrogen-related artifacts introduced during twin-jet electropolishing.

The structural and electrochemical properties of annealed Si film electrodes with titanium–nickel (TiNi) current collectors have been investigated to identify compounds and microstructures that improve electrochemical performances. The as-deposited Si/TiNi electrode consisted of amorphous Si (α–Si) and crystalline B2–TiNi alloy at room temperature. Only a thin oxide layer was formed at the interface, and any significant microstructural change was not found at 500 °C compared to the as-deposited electrode. The Ni atoms started to migrate from the TiNi alloy to the Si film at 600 °C, which resulted in the formation of a Ti-rich (Ti2Ni) layer at the interface. A large amount of Ni diffused into the Si film at 700 °C led to the formation of nickel silicide (NiSi2) particles being dispersed in the film. The Si/TiNi electrodes that were annealed at a temperature exceeding 600 °C showed improved electrochemical properties such as initial efficiency (~90%) and cycle performance (50% capacity retention after 300 cycles). The excellent electrochemical performance was achieved by enhancing the structural stability in annealed Si/TiNi electrodes.

Highly porous Ti-40Zr-8Nb-2Sn (at.%) shape memory alloy scaffolds were prepared by fiber metallurgy using rapidly solidified alloy fibers for the application of cancellous bone replacement. The phase constituents of alloy fibers and scaffolds were investigated by means of X-ray diffraction (XRD), superelastic behavior of alloy fibers was investigated by means of the dynamic mechanical analyzer (DMA), microstructures and mechanical properties of scaffolds were investigated by means of scanning electron microscopy (SEM) and compressive test, respectively. As-spun alloy fibers consisted of only β phase at room temperature. Clear superelastic behavior was observed in the as-spun alloy fibers at temperatures between 153 K and 298 K. The scaffolds showed three-dimensional networks with fiber-fiber bonds, whose porosity and pore size was about 80% and larger than 100 μm, respectively. The compressive yield stress and elastic modulus of the scaffold annealed at 973 K for 1.8 ks were about 4.0 MPa and 0.3 GPa, respectively, similar to those of cancellous bone. Recoverable strain in the scaffold was improved from 2.8% to 4.0% after annealed at 973 K due to the absence of α phase formed in the as-sintered scaffold. Stable cyclic superelastic behavior was observed in the annealed scaffolds at room temperature.

A low-temperature oxidation-reduction process was used to modify the surface of a Cu current collector (foil) for a Si film electrode. The surfaces of the modified Cu foils were investigated under various oxidation-reduction conditions, and the electrochemical properties of Si film electrodes containing the surface modified foils were evaluated. Various nanostructures were found to have formed on the surface; for example, Cu(OH)2 needles, CuO flowers, and CuO plates formed on Cu-foil surfaces oxidized at 313 K for 1, 10, and 30 min, respectively. Furthermore, these nanostructures were transformed to coral-like Cu2O structures after reduction at 673 K. The amount of Cu2O and the surface roughness decreased on increasing reduction time. The Si film electrode containing a Cu foil reduced for 6 h showed the best electrochemical performance (83.5% of the initial efficiency and 74.8% of capacity retention) due to the small amount of Cu2O and the formation of coral-like structures.

The effects of solvents on the preparation of sulfur cathodes were investigated by fabricating binder-free sulfur electrode films using three different solvents: 1-methyl-2-pyrrolidinone (NMP), acetonitrile, and deionized water. These solvents are commonly employed to dissolve binders used to prepare sulfur cathodes for lithium–sulfur batteries. The sulfur electrode fabricated with NMP had a higher discharge capacity and longer cycle life than the ones fabricated with acetonitrile and deionized water. Better adhesion between the current collector and the sulfur electrode accounted for the improved capacity and cycle life of the battery. In addition, the stability of the electrode in the electrolyte was a result of the solubility of sulfur in the solvent. We thus concluded that the solvents used in the fabrication of sulfur electrodes had a positive influence on the electrochemical properties of Li–S batteries.

Ti 50 Ni 49.7 Mo 0.3 , Ti 50 Ni 49.6 Mo 0.4 and Ti 50 Ni 49.5 Mo 0.5 alloy fibers were prepared by a melt overflow process. Two-step B2-R-B19′ transformation was observed in the rapidly solidified Ti-Ni-Mo fibers. Upon increasing the Mo-content from 0.3 to 0.5 at.%, the austenite transformation finish temperature (A f ) of R → B2 decreased from 43 to −42 °C. Porous shape memory alloy pellets with 75% porosity were fabricated by a vacuum sintering technology, using the alloy fibers. Mechanical properties and shape memory effect of the highly porous Ti 50 Ni 49.6 Mo 0.4 alloy, of which A f is lower than room temperature, were investigated using a compressive test. The plateau of a stress-strain curve was observed at about 2 MPa and resulted in 5% elongation associated with stress-induced martensitic transformation. It was also found that a recovered strain was 1.8% on heating after the compressive deformation. Because of the high porosity of this specimen, an elastic modulus of 0.91 GPa could be obtained.

We prepared sulfur/active carbon composites via a simple solution-based process using the following commercial activated carbon-based materials: coal, coconut shells, and sawdust. Although elemental sulfur was not detected in any of the sulfur/activated carbon composites based on Thermogravimetric analysis, X-ray diffraction, and Raman spectroscopy, Energy-dispersive X-ray spectroscopy results confirmed its presence in the activated carbon. These results indicate that sulfur was successfully impregnated in the activated carbon and that all of the activated carbons acted as sulfur reservoirs. The sulfur/activated carbon composite cathode using coal exhibited the highest discharge capacity and best rate capability. The first discharge capacity at 1 C (1.672 A g−1) was 1240 mAh g−1, and a large reversible capacity of 567 mAh g−1 was observed at 10 C (16.72 A g−1).

Ti-Ni-Ag scaffolds were prepared by sintering rapidly solidified alloy fibers. Microstructures and transformation behaviors of alloy fibers and scaffolds were investigated by means of electron probe micro-analyzer (EPMA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The B2-R-B19′ transformation occurs in alloy fibers. The alloy fibers have good superelasticity with superelastic recovery ratio of 93% after annealing heat treatment. The as-sintered Ti-Ni-Ag scaffolds possess three-dimensional and interconnected pores and have the porosity level of 80%. The heat treated Ti-Ni-Ag scaffolds not only have an elastic modulus of 0.67 GPa, which match well with that of cancellous bone, but also show excellent superelasticity at human body temperature. In terms of the mechanical properties, the Ti-Ni-Ag scaffolds in this study can meet the main requirements of bone scaffold for the purpose of bone replacement applications.

Si film electrodes were fabricated on surface-modified Cu current collectors using an oxidation-reduction process. Flower-like nanostructures (FLNSs) with diameters of 2–3 μm and plate-like nanostructures (PLNSs) with lengths of 1 μm were formed on the Cu foil oxidized at 423 K for 0.5 h, but only the PLNSs remained after sonication. Reduction of the preoxidized Cu foil at 673 K resulted in the formation of plate-like and coral-like nanostructures on the Cu foils reduced for 1 and 3 h and a smooth surface without specific structures on the Cu foil reduced for 6 h. The best electrochemical properties in terms of the first columbic efficiency (85.4%) and the cycle performance (67.3% at 50 cycles) were obtained from the Si film electrode fabricated on the Cu foil that had been reduced for 3 h because the coral-like nanostructures on the Cu foil enhanced the adhesion of the Si film and improved the structural stability of the Si film electrode during the electrochemical reactions.

There has been a tremendous amount of research in the past decade to optimize the mechanical properties and degradation behavior of the biodegradable Mg alloy for orthopedic implant. Despite the feasibility of degrading implant, the lack of fundamental understanding about biocompatibility and underlying bone formation mechanism is currently limiting the use in clinical applications. Herein, we report the result of long-term clinical study and systematic investigation of bone formation mechanism of the biodegradable Mg-5wt%Ca-1wt%Zn alloy implant through simultaneous observation of changes in element composition and crystallinity within degrading interface at hierarchical levels. Controlled degradation of Mg-5wt%Ca-1wt%Zn alloy results in the formation of biomimicking calcification matrix at the degrading interface to initiate the bone formation process. This process facilitates early bone healing and allows the complete replacement of biodegradable Mg implant by the new bone within 1 y of implantation, as demonstrated in 53 cases of successful long-term clinical study.

Bulk nanocrystalline ( d = 20–40 nm) Ni–Ti shape memory alloy was produced via cold marforming, followed by optimum post-heat treatment. The total accumulative strain ( e ∼ 0.7) during the process was much lower than that typically imposed during severe plastic deformation operations (i.e., 5 ≤ e ≤ 12). In-situ heating transmission electron microscopy revealed that the present process was effective in promoting static recrystallization and limiting grain growth. The nanocrystalline alloy exhibited enhanced shape memory behaviors.

This study investigates the recovery stress and pullout resistance of crimped fiber made by cold drawn shape memory alloy (SMA) wires considering the geometry of the crimped fiber, namely, wave height/depth. Moreover, it assesses how the shape memory effect influences the pullout resistance of the crimped fiber. For this purpose, four types of crimped fibers with different wave heights as well as the as-received fiber without any crimping are prepared with six specimens, and half of them are heated to induce the shape memory effect. The recovery stress is measured with several heating temperatures ranging from 100℃ to 300℃, and the residual stress at room temperature is also measured. When the crimped fibers are heated to induce phase transformation, the ratio of wave height to wire diameter is reduced from 33% to 48%. In this study, two types of crimped fibers with relatively small wave height do not show yielding, while the other two fibers with relatively large wave height show yielding of the fiber. Thus, this study suggests a critical wave depth for yield of the fiber. If the difference between wave height and thickness, namely wave depth, exceeds 0.1 mm, the crimped fibers experiences yield.

Achieving a combination of good superelastic performance and high strength in the bio-functional nickel-free Ti-based shape memory alloys is always required for the superelastic biomedical devices. For achieving this combination, in this paper, the thermo-mechanical treatment's influence on the microstructural development, mechanical performance and superelastic behavior of a Ti–45Zr–8Nb–2Sn (at.%) shape memory alloy was studied by using X-ray diffraction (XRD), transmission electron microscope (TEM), and tensile tests. 773 K and 823 K annealed specimens after cold rolling showed (β+α) two-phase microstructure. The grain size increased from 0.11 μm in 773 K annealed specimen to 125 μm in 1173 K solution-treated specimen. A maximum recovery strain of 5.4% was achieved at room temperature in the 1073 K annealed specimen due to some extent of the favorable recrystallization texture together with reasonable grain size but the tensile strength was 830 MPa. A combination of a large recovery strain of 5.0%, a high tensile strength of 1030 MPa and good ductility with fracture strain of 13.2% was achieved at room temperature in the 823 K annealed specimen due to the fine β grains of 0.74 μm, which can be beneficial for biomedical applications.

Ni-free Ti-based shape memory alloy with superior superelasticity is promising and attractive for biomedical applications. In this study, Ti-18Zr-12.5Nb-2Sn (at.%) alloy fibers were prepared by rapid solidification method and then the effect of various heat treatments on phase constitutions, microstructures, mechanical properties, and superelasticity was investigated by means of X-ray diffraction (XRD), optical microscope (OM), transmission electron microscope (TEM) and tensile test. α phase was observed in the 673 K and 773 K annealed alloy fibers, leading to the degraded ductility. The total recovery strain at room temperature decreased, grain size and transformation temperature increased with increasing annealing temperature from 873 K to 1173 K. Athermal ω was observed in the 1173 K annealed alloy fibers. A good combination of clear superelasticity and high yield stress was achieved by annealing at 873 K followed by aging at 573 K due to the combined effect of the age-hardening caused by isothermal ω phase and small grain size, which indicates these alloy fibers have a good potential in biomedical applications.

The framework of addiction as an attachment disorder has been used widely in recent years to explain various technological addictions. However, research that explores the association between attachment and Internet gamining disorder is still limited. The purpose of this study was to investigate the potential mediating effects of stressful events on the relationship between attachment styles and Internet gaming addiction. Three hundred and thirty-seven Korean university students in provincial South Korea participated in the study. The hypothesized model was tested using structural equation modeling. Results indicated that the relationships between attachment styles (both attachment anxiety and avoidance) and Internet gaming addiction were fully mediated by stressful events. These results contribute to understanding the etiology of gaming addiction and may guide development and delivery of treatment for problematic gaming behaviors.

Highly porous Ti–18Zr-12.5Nb–2Sn (at.%) scaffolds with porosities of 70%, 75% and 80% were prepared by sintering rapidly solidified alloy fibers. Superelastic behavior of alloy fiber was investigated by the dynamic mechanical analyzer (DMA). Phase identifications of alloy fiber and scaffold were studied by X-ray diffraction (XRD). Precipitates in alloy fiber were investigated by transmission electron microscope (TEM). Porous structure of alloy scaffold was observed by scanning electron microscope (SEM). Mechanical properties and the superelasticity of alloy scaffold were investigated using compressive test. The superelasticity of alloy fibers was improved after aged at 673 K for 3.6 ks due to α precipitates. The sintered scaffolds showed three-dimensional networks with fiber-fiber sintering joints. The compressive yield stress and elastic modulus of the alloy scaffolds aged at 673 K for 3.6 ks were in the range of 5.0–16.7 MPa and 0.33–1.05 GPa, respectively. These values were a close match to those for cancellous bone. The recoverable strain increased from 3.2% to 3.7% with the increase in porosity from 70% to 80% in aged Ti–Zr–Nb–Sn scaffolds when tested at human body temperature (310 K).

The microstructures and transformation behavior of Ti-49Ni-20Hf, Ti-49.5Ni-20Hf and Ti-50.3Ni- 20Hf alloys, when prepared by conventional casting, were investigated and compared with the properties of the alloys prepared by melt spinning. The area fraction of (Ti,Hf)2Ni in Ti-Ni-Hf alloys decreased to 3.9% from 9.4% as Ni content rose to 50.3 at% from 49 at%. Several cracks were observed in the hot-rolled Ti-49Ni-20Hf alloy sheet but none were found in the Ti-50.3Ni-20Hf alloy sheet. The B2-B19' transformation start temperature (Ms) decreased to 476 K from 580 K as Ni content increased to 50.3 at% from 49 at%. All the as-spun ribbons were amorphous, and the activation energy for crystallization ranged from 167.8 kJ/mol to 182.7 kJ/mol based on Ni content. When annealing temperature ranged from 810 K to 873 K, crystalline Ti-Ni-Hf alloys without (Ti,Hf)2Ni particles were obtained. At annealing temperatures higher than 873 K, very fine (Ti,Hf)2Ni particles, less than 20 nm in size, were found embedded in a crystalline matrix.

Ti-Ni shape memory alloy (SMA) thin films are very attractive material for industrial and medical applications such as micro-actuator, micro-sensors, and stents for blood vessels. An important property besides shape memory effect in the application of SMA thin films is the adhesion between the film and the substrate. When using thin films as micro-actuators or micro-sensors in MEMS, the film must be strongly adhered to the substrate. On the other hand, when using SMA thin films in medical devices such as stents, the deposited alloy thin film must be easily separable from the substrate for efficient processing. In this study, we investigated the effect of substrate roughness on the adhesion of Ti-Ni SMA thin films, as well as the structural properties and phase-transformation behavior of the fabricated films. Ti-Ni SMA thin films were deposited onto etched glass substrates with magnetron sputtering. Radio frequency plasma was used for etching the substrate. The adhesion properties were investigated through progressive scratch test. Structural properties of the films were determined via Feld emission scanning electron microscopy, X-ray diffraction measurements (XRD) and Energy-dispersive X-ray spectroscopy analysis. Phase transformation behaviors were observed with differential scanning calorimetry and low temperature-XRD. Ti-Ni SMA thin film deposited onto rough substrate provides higher adhesive strength than smooth substrate. However the roughness of the substrate has no influence on the growth and crystallization of the Ti-Ni SMA thin films.

Functionally graded NiTi structures benefit from the combination of the smart properties of NiTi and those of functionally graded structures. This article provides experimental data for thermomechanical deformation behaviour of microstructurally graded, compositionally graded and geometrically graded NiTi alloy components, related to the research article entitled “Functionally graded shape memory alloys: design, fabrication and experimental evaluation” (Shariat et al., 2017) [1]. Stress–strain variation of microstructurally graded NiTi wires is presented at different heat treatment conditions and testing temperatures. The complex 4-way shape memory behaviour of a compositionally graded NiTi strip during one complete thermal cycle is demonstrated. The effects of geometrical design on pseudoelastic behaviour of geometrically graded NiTi plates over tensile loading cycles are presented on the stress–strain diagrams. Keywords: Shape memory alloy (SMA), NiTi, Martensitic transformation, Functionally graded material (FGM), Pseudoelasticity, Heat treatment

Nano Ni particle embedded Ni 3 S 2 powders (Ni-Ni 3 S 2 ) are prepared by means of melt spinning and 10 h-ball milling processes. The Ni particles with 10–20 nm size are dispersed over all the Ni 3 S 2 powders with 3.28 μm. Reversibility and rate capability of the Ni-Ni 3 S 2 electrode are investigated at various current densities from 0.1 C to 5 C by comparing with a conventional Ni 3 S 2 electrode. The Ni-Ni 3 S 2 electrode exhibits the remarkably improved reversibility of the redox reactions under high current density and 40% of discharge capacity retention at the current density of 2310 mA g −1 , corresponding to 5 C-rate. The improved electrochemical performances are mainly ascribed to ultra fine Ni particles that supplement the loss of Ni and promote the recovery of Ni 3 S 2 during charge process.

A hot forging process of an as-cast NiTi shape memory alloy was designed by processing maps and a finite element method analysis. The NiTi alloy samples used in this study were made using a vacuum plasma arc melting process. In order to analyze the microstructural change and flow behavior of the as-cast NiTi alloy during the ingot breakdown process, high temperature compression tests were carried out at different temperatures and strain rates up to a true strain level of 0.9. Deformation processing maps were generated by using the dynamic materials model approach developed by Prasad to search for the optimum hot forging process conditions. The flow instability criterion proposed by Ziegler was utilized to evaluate the unstable deformation region in the processing map. The grain refinement was achieved by recrystallization during high temperature deformation of the NiTi alloy. Finally, the optimum hot forging design to obtain a sound NiTi billet without forging defects was identified with the actual ingot breakdown process.

Inhomogeneous deformation is one of the essential characters of shape memory alloy. Specimen is composed of many variants which have different strain. There exist a phase interface between two different phases and its mobility will depend on several factors such as curvature and orientation of the interface. The shape memory alloys exhibit hysteresis and one of the main reasons to cause hysteretic behavior is thought to be the internal inhomogeneity. It is thought that the phase interfaces display irregularities in the motion and the resultant state is metastable one which requires a very long relaxation time. In this work, spatially inhomogeneous frictional force to the volume change of the variants is assumed to account for the irregular behavior of the phase transformation. Its effect on the production of the macroscopic strain of a shape memory alloy is investigated using finite element calculation. Load-biased thermal cycling of a shape memory alloy is considered. The numerical result is compared with experimental data of Ti-44.5Ni-5Cu-0.5V (at.%) alloy. A better agreement is obtained for the experimental data when the inhomogeneous friction is assumed.

This study was carried out to develop a new concrete reinforcing fibers using the shape memory alloy wires. Conventional steel reinforcing fibers have hooked ends to provide anchoring and induce plastic deformation at the hooked ends to dissipate energy. However, the hooked shape produces negative effects during concrete mixing. For the shape memory alloy fibers, the shape memory effect of martensitic shape memory alloys can be exploited. An elongated shape memory alloy wire in a martensitic state recovers the deformed length upon heating. During this process, the diameter of the wire is also recovered because of Poisson’s effect. The diameter recovery of the shape memory alloy fibers can provide anchoring action for the shape memory alloy fibers in concrete since bulging of the shape memory alloy fibers inside concrete produces confining pressure around the fiber. In this study, martensitic NiTi wires with 1.0 mm diameter were prepared. The wires were elongated by cold drawing until a diameter of 0.93 mm was achieved; this process reduced the cross-sectional area by 13.5%. Two methods were applied to recover the diameter, namely, heating of the shape memory alloy fibers after they were embedded in concrete and recovery of the diameter of both ends of the fibers in air, where the fiber-shape resembles that of a dog-bone. Thus, the following four types of fibers were prepared: (I) as-built fiber of 1.0 mm diameter, (II) cold-drawn fiber of 0.93 mm diameter, (III) cold-drawn fiber in concrete with heating, and (IV) dog-bone-shaped cold-drawn fiber. The cold-drawn shape memory alloy fiber showed higher bond strength than the as-built fiber because of the difference in the stress–strain curve of the cold-drawn fiber. The shape memory alloy fiber in Case III showed increased bond strength compared with the fiber in Case I because of confining pressure around the fiber. The fibers in Case IV showed increased bond strength and energy dissipation capacity compared with the other types of the fibers and are, therefore, the most desirable type.

Microstructures and martensitic transformation behavior of Ti–Ni–Ag alloys prepared by arc melting were investigated by means of scanning electron microscopy (SEM), electron probe micro analysis (EPMA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and thermal cycling tests under constant load. Ti–Ni–Ag alloys consisted of Ti–Ni–Ag matrices, Ti 2 Ni and TiAg phases. Ti–Ni–Ag matrices contained 0.27–0.52 at.% of solute Ag atoms depending on alloy compositions. The B2–B19′ transformation occurred in Ti–50.1Ni–0.7Ag, Ti–49.2Ni–0.9Ag, Ti–49.2Ni–0.6Ag and Ti–49.0Ni–0.7Ag alloys, while the B2-R-B19′ transformation did in Ti–47.5Ni–1.3Ag and Ti–44.4Ni–1.1Ag alloys. Thermo-mechanical treatment separated the B2-R from the R–B19′ transformation clearly and improved shape recovery by increasing the critical stress for slip deformation in a Ti–50.0Ni–0.7Ag alloy.

We designed a novel layer-built rechargeable lithium ribbon-type battery intended for textile or cloth based applications. The ribbon-type battery, 2.4 mm (or 1 mm) wide and 10 cm long, is composed of a double layer LiFePO4 cathode and an amorphous silicon nanofilm. The double layer LiFePO4 and amorphous silicon electrodes were prepared using the doctor blade method and a vertical deposition technique, respectively. The structure and morphology of the LiFePO4 and the silicon thin film were characterized by Rietveld refinement, SEM and TEM. At room temperature the ribbon-type battery exhibited an initial discharge capacity of 166.4 and 132.7 mA h g−1 at 0.5 and 1 C-rate, respectively. A reasonably good cycling performance and high coulombic efficiency under the high current density of 1 C-rate could be obtained with the Si/LiFePO4 ribbon-type battery. Also, a high volumetric capacity of 336 mA h cm−3 at 0.5 C-rate was achieved, which makes the ribbon-type battery suitable for practical use.

β-type Ni-free Ti-based alloys are promising materials for biomedical applications. In this study, highly porous Ti-18Zr-12.5Nb-2Sn (at.%) alloy scaffolds with a porosity of about 80% were fabricated by a process of combining rapid solidification method and fiber metallurgy technique for the replacement of damaged human cancellous bone. Alloy fibers were produced by melt overflow technique. Phase identifications of alloy fiber and scaffold were studied by X-ray diffraction (XRD). Transformation behavior and microstructure of alloy fiber were investigated by differential scanning calorimetry (DSC) and transmission electron microscope (TEM), respectively. Superelastic behavior of alloy fiber was investigated by the dynamic mechanical analyzer (DMA). Porous structure of scaffold was observed by scanning electron microscope (SEM). The mechanical properties and superelasticity of scaffold were investigated by compressive test. The rapidly-solidified fiber consisted of β phase, athermal ω phase and nanodomains. Clear superelastic behavior with the recoverable strain of 4.5% for 5% pre-strain was observed in rapidly-solidified alloy fiber. Three-dimensional networks with fiber-fiber sintering joints were observed in the as-sintered scaffold which consisted of predominant β phase, α phase and isothermal ω phase. The scaffold annealed at 973 K consisted of single β phase. Stress-induced martensitic transformation of β→α" occurred during the compressive test. The compressive plateau stress and elastic modulus of the as-sintered and annealed scaffold were found to be 7.9 MPa and 0.43 GPa, 7.4 MPa and 0.41 GPa, respectively, similar to those of cancellous bone. A recoverable strain of 3.4% was observed in the annealed scaffold at body temperature (310 K).

In this study, Ti-xZr-8Nb-2Sn (x = 40, 45, 50) (at.%) alloys were fabricated by arc melting method and then microstructures, martensitic transformation behavior, superelasticity and mechanical properties were investigated by means of optical m icroscopy, electron microscopy, X-ray diffraction, tensile test and Vickers hardness test. The alloys consisted of β phase only at room temperature and exhibited strong (200)β texture after solution treated at 1173 K for 1.8 ks. Athermal ω phase was not observed from transmission electron microscopy in the alloys. The stress induced β→α″ transformation and the reverse transformation occurred on loading and unloading, respectively. Transformation temperature (Ms(C-C)) decreased from 188 K to 77 K with increasing Zr content from 40 at.% to 50 at.%. The maximum recoverable strains for 40Zr, 45Zr and 50Zr alloys were 7.1%, 7.5% and 7.3%, respectively, which was due to a combined effect of the large lattice deformation and a strong recrystallization texture. All alloys were fractured in ductile manner with fracture strains larger than 25%. Ultimate tensile strength of 835 MPa and superelastic recovery strain of 5.5% were obtained at room temperature in the solution treated Ti-40Zr-8Nb-2Sn alloy.

Stress vs. strain curves of two kinds of Ti–Ni shape memory alloys under dynamic compressive loading condition were obtained by the split Hopkinson pressure bar experiment. One is Ni-rich, 50.75Ni–49.25Ti (at%), alloy and the other is Ti-rich, 49.5Ni–50.5Ti (at%). The former exists as austenite phase to show superelastic behavior at the room temperature, and the latter is martensitic phase at the room temperature. The dynamic stress–strain curves were compared with quasi-static compressive test results. The Ni-rich specimen displayed a much higher stress level at the high strain rate than at the quasi-static test, but the Ti-rich specimen exhibited a stress level alike in the two types of tests. Temperature measurement on the surface of the impact specimens was carried out during the impact test. The temperature rising was about 3–5 °C in the considered test conditions.

This paper presents a three-dimensional calculation model for martensitic phase transformation of shape memory alloy. Constitutive model based on thermodynamic theory was provided. The average behavior was accounted for by considering the volume fraction of each martensitic variant in the material. Evolution of the volume fraction of each variant was determined by a rate-dependent kinetic equation. We assumed that nucleation rate is faster for the self-accommodation than for the stress-induced variants. Three-dimensional finite element analysis was conducted and the results were compared with the experimental data of Ti–44.5Ni–5Cu–0.5 V (at.%) alloy under bias loading.

Graphical abstract: - Highlights: • Amorphous Si-coated TiNi powders were prepared successfully by ball milling. • Ti{sub 4}Ni{sub 4}Si{sub 7} was formed at the interface between Si and TiNi after annealing. • Si-coated Ti–Ni powders displayed the R phase after annealing. - Abstract: Si was coated on the surface of Ti–49Ni (at%) alloy powders by ball milling in order to improve the electrochemical properties of the Si electrodes of secondary Li ion batteries and then the microstructure and martensitic transformation behavior were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Ti–Ni powders coated with Si were fabricated successfully by ball milling. As-milled powders consisted of highly deformed Ti–Ni powders with the B2 phase and amorphous Si layers. The thickness of the Si layer coated on the surface of the Ti–Ni powders increased from 3–5 μm to 10–15 μm by extending the milling time from 3 h to 48 h. However, severe contamination from the grinding media, ZrO{sub 2} occurred when the ball milling time was as long as 48 h. By heating as-milled powders to various temperatures in the range of 673–873 K, the highly deformed Ti–Ni powdersmore » were recovered and Ti{sub 4}Ni{sub 4}Si{sub 7} was formed. Two-stage B2–R–B19′ transformation occurred when as-milled Si-coated Ti–49Ni alloy powders were heated to temperatures below 873 K, above this temperature one-stage B2–B19′ transformation occurred.« less

Prepared by the deposition of a solid electrode and electrolyte, all-solid-state batteries are a promising next generation battery system. Aerosol deposition (AD) offers many advantages compared to the conventional thin film deposition methods, including the deposition of a crystallized thin film with no heat treatment and a fast deposition rate. In this study, a LiFePO 4 /C composite thin film is directly fabricated using a LiFePO 4 /C composite raw powder. SEM and EDS results show the successful deposition of a LiFePO 4 /C composite thin film on a stainless steel substrate and X-ray diffraction patterns reveal that the as-deposited thin film has a crystalline structure, corresponding to the olivine phase, without any heat treatment. In a CV test, oxidation and reduction peaks appear at 3.51 and 3.36 V, corresponding closely to the peaks of bulk olivine LiFePO 4 . Furthermore, the profiles of the charge and discharge curves are similar to those of the bulk electrode and the discharge capacity is 31.1 μAh cm −2 μm −1 in the first cycle. After 20 cycles of 10.65 and 106.5 μA cm −2 μm −1 , the capacity is recovered to 30.7 μAh cm −2 μm −1 . Aerosol deposition can potentially be used in the fabrication of all-solid-state batteries.

LiCoO2 single-layer and LiCoO2/LiNiO2 multi-layer thin film electrodes were successfully fabricated by magnetron sputtering. Their microstructure and electrochemical properties were investigated. Once annealed, both films had the (0 0 3) preferred orientation to minimize the surface energy. The initial discharge capacity of the multi-layer thin film was approximately 53.1 μAh/cm2 μm, which was higher than that of the LiCoO2 single-layer thin film having similar thickness. The capacity retention of the multi-layer thin film was superior to that of the single-layer thin film. These findings indicate that the multi-layer thin film is a promising cathode material for the fabrication of high-performance thin film batteries.

The electrochemical and structural properties of Si thin film electrodes using a TiNi shape memory alloy as a current collector (substrate) are investigated with and without annealing. Annealed Si film electrodes exhibit an initial efficiency of 87% and a charge capacity retention (at the 50th cycle) of 85%. XRD results of the annealed Si film electrode during the charge–discharge process reveal the phase transformation (stress accommodation) of the TiNi substrate: cubic TiNi (initial) to monoclinic TiNi (after charge) and back to cubic TiNi (after discharge). SEM results of the annealed Si electrode show a remarkable reduction in structural damage of the Si film as compared to the as-deposited Si film electrode. The good electrochemical performances are ascribed to the high structural stability enhanced by both the post-annealing and stress accommodation of the TiNi substrate.

Three batches of Ti–Ni–Cu powders (Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 ) were prepared by gas atomization and porous specimens were fabricated by spark plasma sintering (SPS). The microstructure of as-solidified powders exhibited a cellular structure. XRD analysis showed that one-step martensitic transformation of B2–B19 occurred in all alloy powders and SPS specimens. DSC measurements of as-atomized powder, sintered bulk specimens and as-cast ingots were performed in order to study the effect of rapid solidification on martensitic transformation behaviors. The dependence of powder size on martensitic transformation temperature is very small in the rapidly solidified powders. However, the transformation temperatures were strongly dependent on the Cu-content. The martensitic transformation starting temperatures ( M s ) of Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 powders ranging between 25 and 150 μm are −4.9, −17.6 and 32.1 °C and the austenite transformation finishing temperatures ( A f ) of Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 powders were 15.6, −4.4 and 38.3 °C, respectively. The M s and A f of the as-atomized powders are much smaller than those of SPS specimens and as-cast ingots for all Ti 50 Ni 45 Cu 5 , Ti 50 Ni 40 Cu 10 and Ti 50 Ni 30 Cu 20 alloy systems. The temperature hysteresis ( A f − M s ) of Ti 50 Ni 45 Cu 5 powders was 20 °C and continued to decrease with increasing Cu-content. The temperature hysteresis of Ti 50 Ni 30 Cu 20 powders was only 7 °C.

Microstructural features and martensitic transformation behavior of Ti–Ni–Sn alloys were investigated by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). In a Ti–49.5Ni–0.5Sn alloy, Ti 2 Ni phase embedded in Ti–Ni matrix containing 0.7 at%Sn was observed. In a Ti–49.0Ni–1.0Sn alloy, Ti 2 Ni, unknown phase and Ti–Ni matrix containing 1.1 at%Sn were observed, while Ti 2 Ni and two different Ti–Ni matrices with 2.1 at%Sn and without Sn were observed in a Ti–50.0Ni–1.0Sn alloy. In a Ti–48.5Ni–1.5Sn alloy, Ti 2 Ni, Ti 3 Sn and Ti–Ni matrix containing Sn about 1.2 at% were observed. The B2–R–B19′ transformation occurred in Ti–49.5Ni–0.5Sn, Ti–49.0Ni–1.0Sn and Ti–48.5Ni–1.5Sn alloys, while the B2–B19′ transformation occurred in a Ti–50.0Ni–1.0Sn alloy. Substitution of Sn for Ni of an equiatomic TiNi alloy was effective to induce the R phase transformation.

Discontinuous Si film electrodes with 400, 800, and 1700 μm discontinuous lines (break lines) were fabricated by a simple masking and etching process. The structural and electrochemical properties of continuous and discontinuous Si film electrodes were investigated by means of optical microscopy, field emission scanning electron microscopy, X-ray diffraction, and charge–discharge tests. Although all electrodes showed similar first-charge capacities in the range of 210–230 μAh/g, the discontinuous electrode exhibited improved coulombic efficiency and cyclability when compared to the continuous electrode. Up to 100 cycles, the discontinuous electrode with the shortest line distance of 400 μm demonstrated the highest efficiency (95.2%) and capacity retention (89%). Observation of the cycled Si film electrodes revealed that discontinuity enhanced the structural stability of the electrode during the charge–discharge process.

Microstructures and martensitic transformation behavior of 52.7Ti–Ni, 52.0Ti–Ni, 51.1Ti–Ni and 49.7Ti–Ni (at%) alloy ribbons were investigated by means of optical microscopy, transmission electron microscopy, differential scanning calorimetry, X-ray diffraction and thermal cycling tests under constant load. Very fine Ti2Ni particles less than 20 nm which induced the B2-R transformation by suppressing the B2–B19′ transformation were observed in the ribbons. A temperature difference (ΔT) between TR* and Ms* almost kept constant with increasing Ti content from 49.7 at% to 52.0 at% (∼8 K), above which it increases largely (∼17 K), which was ascribed to the fact that volume fraction of Ti2Ni particles almost kept constant with increasing Ti content from 49.7 at% to 52.0 at% (∼8%), above which it increases largely (∼18%).