Ti-based Shape Memory Alloys Research Articles

Shape memory and superelastic behavior of Ti–7.5Nb–4Mo–1Sn alloy

In the present work, a Ti-based shape memory alloy with the composition of Ti–7.5Nb–4Mo–1Sn was designed based on the d-electron orbit theory. The shape memory and superelastic behavior of the alloy were investigated. It is found that the martensitic transformation temperature of the alloy is near 261 K. The tensile and the thermal cycling testing results show that the alloy exhibits the stable shape memory effect and superelasticity at room temperature. The maximum recovered strain of the alloy is 4.83%.

パルス通電焼結によるTi基形状記憶合金の創製に関する研究

Recently, the fabrication of Ti-based shape memory alloys (SMAs) has been tried using the powder metallurgy (PM) process. The fabrication conditions of Ti-based SMAs by PM process and their important shape memory characteristics for applying to the elements, however, have not been discussed enough. The target of this study is to develop Ti-based SMAs having superior shape memory characteristics by PM process. At first, the fabrication conditions and shape memory characteristics of Ti-Ni alloys were examined. Next, in order to improve the critical stress for slip deformation and the shape memory characteristics of Ti-Ni alloys, the effects of aging treatment, densification processing and addition of Cu and Zr as third elements on the shape memory characteristics were investigated. In this paper, the effects of Cu addition on phase transformation behavior and thermo-mechanical properties of Ti-Ni-Cu alloy were introduced. As a result, Ti-based SMAs having superior shape memory characteristics could be developed by establishment of fabrication conditions of the alloy by the PM process.

New Internalized Distraction Device for Craniofacial Plastic Surgery Using Ni-Free, Ti-Based Shape Memory Alloy

This study was undertaken to examine effects and biocompatibility of a new internalized distraction device made from newly developed Ti-Nb-Al shape memory alloy (SMA). Crania of Wistar rats were expanded using a U-shaped wire of this SMA set on each cranium in an experimental group. At 2 or 4 weeks after operation, the rats were killed; width measurements and three-dimensional observations of crania were conducted using soft x-ray and microfocus x-ray computed tomography photography. After photography, histologic sections were made and stained with hematoxylin and eosin. No pathologic change in the experimental duration was observed macroscopically or histologically. Significantly increased size was found for the rat crania in the experimental group compared with the control group. Results demonstrated the feasibility and biocompatibility of internalized distraction osteogenesis using Ni-free, Ti-based SMA in craniofacial plastic surgery for craniofacial deformities.

Design of a New Biocompatible Ti-Based Shape Memory Alloy and Its Superelastic Deformation Behaviour

Titanium-nickel (Ti-Ni) shape memory alloys have been widely used for biomedical applications in recent years. However, it is reported that Ni is allergic and possibly carcinogenic for the human body. Therefore, it is desirable to develop new Ni-free Ti-based shape memory alloys for biomedical applications. In the present study, a new Ti-18Nb-5Mo-5Sn (wt.%) alloy, containing only biocompatible alloying elements, was designed with the aid of molecular orbital method and produced by vacuum arc melting. Both β and α″ martensitic phases were found to coexist in the alloy after ice-water quenching, indicating the martensitic transformation. The phase transformation temperatures of the Ti-18Nb-5Mo-5Sn alloy were Ms = 7.3 °C, Mf = −31.0 °C, As = 9.9 °C, and Af = 54.8 °C. Superelasticity was observed in the alloy at a temperature higher than the Af temperature. A totally recovered strain of 3.5 % was achieved for the newly designed Ti-based shape memory alloy with a pre-strain of 4 %.

<I>In Vitro</I> Biocompatibility of Ni-Free Ti-Based Shape Memory Alloys for Biomedical Applications

This study was undertaken to evaluate the in vitro biocompatibility of newly developed Ni-free Ti-based shape memory alloys (SMAs) in comparison to that of commercial pure titanium (cpTi). This study compared Ti-24 mol%Nb-3 mol%Al (Ti-Nb-Al) and Ti-7 mol%Cr-3 mol%Sn (Ti-Cr-Sn) to cpTi from a cell-compatibility perspective. In all, 63 samples (21 samples for each group) were prepared, which were machined into 10-mm-diameter, 0.15-mm-thick, mirror-polished disks. Their surface morphology was evaluated using scanning electron microscopy (SEM). The chemical composition of the sample surface was determined using an energy dispersive X-ray analyzer (EDX). Sample surface roughness was measured using a non-contact 3D profiler. After sample surface observations, the cell proliferation and viability of African green monkey kidney fibroblast cell line COS7 in direct contact with these new alloys were evaluated by DNA quantification, by live cell imaging using CelLuminate Red fluorescent cell stain as a new method, and by cytoskeletal observations by immunofluorescent actin labelling. Cell proliferation was examined after 1, 3, and 5 days of culture. Results were the following. (i) Each sample showed high purity and a very smooth surface, showing no morphological differences among groups. (ii) The COS7 cells took in sufficient CelLuminate Red to visualize the cells using epifluorescent microscopy, and (iii) cell proliferation with Ti-Cr-Sn was lower than with either cpTi or Ti-Nb-Al. These results suggest that Ti-Nb-Al alloy showed biocompatibility as high as that of cpTi and that it is more suitable for biomedical applications.

Microstructure and Shape Memory Properties of Biomedical Ti-(40-65) Ta (wt. %) Alloys

Recently Ni-free Ti-based shape memory alloys have been actively studied for biomedical applications in order to replace Ti-Ni alloys which bear the possibility of Ni-hypersensitivity. In this paper, The Ti-(40-65) Ta (wt. %) alloys have been studied with regard to their microstructure, mechanical and shape memory properties, as well as the effect of heat treatment on their shape memory behaviors. The results show that Ti-40wt. %Ta exhibits single orthorhombic structure (''), Ti-55wt. %Ta mainly '' and a little BCC structure (β), and Ti-65wt. % Ta mainly β and a little '' at room temperature. The tensile strengths of Ti-Ta alloys are all over 550 MPa, and the elongations over 17%. The Young’s modulus of Ti-Ta alloys ranges from 66 to 75 GPa, which are closer to the modulus of human bone as compared with that of Ti-6Al-4V alloy. The maximal shape memory strain of 3.32% was obtained in Ti-55wt. %Ta alloy quenched at 1273 K followed by aging at 723 K for 10min. The obtained results will be beneficial for developing Ti-Ta alloys for biomedical applications.

ニッケルフリーチタン基形状記憶合金を利用したラットの矯正学的歯の移動に関する研究

The purpose of this study was to evaluate the performance and the usefulness of a newly developed Ni-free Ti-based shape memory alloy (SMA) wire in orthodontic tooth movement by comparing with a nickel-titanium (Ni-Ti) alloy wire. A Titanium-niobium-aluminum (Ti-24Nb3Al) SMA wire, which was considered to be biocompatible because it contained no nickel, was newly developed and mechanical property of this new alloy was improved by severe cold rolling reduction. Twenty-one male Wistar-strain rats (age; 6 weeks) were used in the animal experiment. A Ti-Nb-Al alloy wire and an orthodontic superelastic wire (Ni-Ti alloy wire) were set in the oral cavities of rats, and orthodontic palatal movement of maxillary first molars was performed with an initial load of 15 gf. The amount of tooth movement was measured and periodontal structures were histologically examined. The Ti-Nb-Al alloy wire was effective for palatal tooth movement without any adverse reaction in rats. There was no significant difference in the amount of tooth movement between the Ti-Nb-Al group and the Ni-Ti group. Histological observation of the periodontal tissues revealed no differences between the two groups. These results indicate that Ti-Nb-Al alloy wire has excellent mechanical properties suitable for orthodontic tooth movement, suggesting that Ti-Nb-Al wire may be used as a practical nickel-free shape memory and superelastic alloy wire for orthodontic treatment as a substitute for Ni-Ti alloy wire. [doi:10.2320/matertrans.48.367]

Nanoindentation of binary and ternary Ni–Ti-based shape memory alloy thin films

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.

TiNi-Base and Ti-Base Shape Memory Alloys

The basic characteristics of TiNi-based and Ni-free Ti-based shape memory alloys are reviewed. They include the crystal structures of the parent and martensite phases in both the alloys, the recoverable strain associated with the martensitic transformation, the transformation temperatures, the temperature and orientation dependence of deformation behavior, etc. The sputter-deposited Ti-Ni thin films are also reviewed briefly because of their possibility of expanding into micromechanical system applications as the most powerful microactuator.

Orthodontic Tooth Movement in Rats Using Ni-Free Ti-Based Shape Memory Alloy Wire

The purpose of this study was to evaluate the performance and the usefulness of a newly developed Ni-free Ti-based shape memory alloy (SMA) wire in orthodontic tooth movement by comparing with a nickel-titanium (Ni-Ti) alloy wire. A Titanium-niobium-aluminum (Ti-24Nb-3A1) SMA wire, which was considered to be biocompatible because it contained no nickel, was newly developed and mechanical property of this new alloy was improved by severe cold rolling reduction. Twenty-one male Wistar-strain rats (age; 6 weeks) were used in the animal experiment. A Ti-Nb-Al alloy wire and an orthodontic superelastic wire (Ni-Ti alloy wire) were set in the oral cavities of rats, and orthodontic palatal movement of maxillary first molars was performed with an initial load of 15 gf. The amount of tooth movement was measured and periodontal structures were histologically examined. The Ti-Nb-Al alloy wire was effective for palatal tooth movement without any adverse reaction in rats. There was no significant difference in the amount of tooth movement between the Ti-Nb-Al group and the Ni-Ti group. Histological observation of the periodontal tissues revealed no differences between the two groups. These results indicate that Ti-Nb-Al alloy wire has excellent mechanical properties suitable for orthodontic tooth movement, suggesting that Ti-Nb-Al wire may be used as a practical nickel-free shape memory and superelastic alloy wire for orthodontic treatment as a substitute for Ni-Ti alloy wire.

Smart Glass Epoxy Laminates with Embedded Ti-based Shape Memory Alloy

Growing attention has been given in the last years to the development of smart materials and structures. Among them, composite materials play evidently a leading role. In tract, it is relatively easy, taking in account their processing techniques, to embed in the structural material itself some sensors, processors and actuators at a mesoscopic scale. Shape memory alloys (SMA) are particularly fitted as actuators because they can be easily drawn into thin wires and incorporated in polymeric and metallic matrices or in classical fibre epoxy laminate structure. To test the influence of the materials and processing conditions on the actuation properties of adaptive hybrid composites four sets of asymmetric composite systems based on a glass epoxy laminate with embedded wires of a shape memory Ti-Ni-Cu alloy were processed. The SMA wires in One Way Shape Memory Effect (OWSME) or (Two Way Shape Memory Effect TWSME) conditions were incorporated as far as possible away from the neutral plan. These asymmetric hybrid laminate beams were tested in clamp-free conditions. With the actuators heated by Joule effect undergoing a reversible martensite to austenite transformation, the reversible bending was induced due to the recovery strain in relation with the shape memory effect. The most important deflection of the composite was obtained for the material, processed with embedded wires in TWSME conditions. Nevertheless, for samples just prestrained for the OWSME, a self-training effect occurred in relation to the reverse polarised austenite to martensite transformation, during cooling after actuation. In order to follow the phase transitions in the embedded SMA wires, resistance measurements have been performed during actuation. Describing the macroscopic behaviour in the frame of the unidirectional approach de Liang and Rogers and using metallurgical parameters defined from a Clausius-Clapeyron diagram, a description of the temperature-deflection curves can be obtained. Nevertheless some parameters have to be mastered in order to process real structural parts.

Electronic structure of binary and ternary Ti-based shape-memory alloys

The electronic and structural properties for TiMe (Me=Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) alloys are studied using the full-potential linearized augmented plane wave (FLAPW) method. The alteration of electronic structure with disorder and alloying with a third element is analyzed. The calculated emission, absorption X-ray and electron energy-loss spectra are found to be in good agreement with experiments.

Electronic structure and stability of Ti-based B2 shape-memory alloys: By LMTO-ASA

The electronic and structural properties for TiM alloys (where M stands for Fe, Co, Ni, Pd, Pt, Cu, Ag and Au) with B2 (CsCl) structure are systematically studied using an LMTO-ASA method. Our discussion gives a detailed explanation of correlations between B2 phase stability and electronic structure for these alloys. Using two parameters, (1) overlapped area of site and momentum decomposed DOS, (2) shift of the center of partial band, the mechanism of interbonding which strongly determines phase stability can be explored further. The difference electron densities contour maps also help to give a clear picture of the interbonding situation in some of these alloys. Our results may give a direction to the work of designing new B-structured functional materials.

Irradiation induced stress relaxation and high temperature deformation behavior of neutron irradiated Ti based shape memory alloys

Several tools using Ti based shape memory alloys (SMA) such as SMA coupler, connector, jack system and in-vacuum gate valve, have been developed to promote the remote maintenance and the quick replacement technology for fusion core parts. Recently, irradiation induced stress relaxation (IISR) has become a concern for components of the fusion core. IISR may be a severe problem for SMAs as well as the structural materials in the fusion reactor. The IISR of TiNi SMA and TiPd high temperature shape memory alloys (HTSMA), which have both transformation temperatures and working temperatures 400 K higher than those of TiNi alloys, may be controlled by the migration of vacancies rather than interstitials. This mechanism facilitates restoration of the damaged state to normal state under irradiation. TiPd HTSMAs may be used to fabricate irradiation-resistant shape memory devices for temperatures up to 800 K if proper heat treatments can be developed.