4 D - Properties and Characterizations IV

18.1

Temperature dependent stress distribution in steel sheet around active NiTi inserts
B. Malard¹, V. Davydov², J. Pilch¹, D. J. Hughes³, P. Sittner⁴, P. Molnar¹, P. Lukas², (1)Institute of Physics of the ASCR, v.v.i., Praha, Czech Republic, (2)Nuclear Physics Institute, Rez, Czech Republic, (3)Institut Laue Langevin, Grenoble, France, (4)Institute of Physics Academy of Sciences of the Czech Republic, Prague, Czech Republic

This paper reports selected results of the research motivated by SMA application development in frame of European research project PROSTONE aimed at innovation in stone processing equipment. In many devices used in the stone sector, stress inhomogeneity in machine parts and tools seems to cause problems.

There is an idea to solve the problem of stress concentrations in metallic sheets occurring during operation through the insertion of small prestrained elliptical NiTi elements into elliptical holes in locations of maximum stress concentration which would counteract these stress concentrations.

In order to evaluate the effect of the temperature, compression force and on the stress distribution in the steel plate, three different neutrons strain scanning experiments have been carried out.

1. the effect of a prestrain insert at room temperature,

2. the effect of the temperature with in-situ heating experiment at 3 different temperature (25°C, 50°C, 70°C),

3. the effect of stress and temperature with in-situ compression up to 300MPa at temperature 70°C,

The deep penetration of the thermal neutrons in steel provides average data in the thickness with a gauge volume of about 1 to 8mm³. In the futur a complementary experiment using synchrotron x-ray radiation will performe to achieve high enough spatial resolution necessary for reliable evaluation of the internal stress gradient.

18.2

The Effect of Heat Treatment on SMA's Mechanical and Temperature Transition Region Properties
G. Paul, F. Sczerzenie, SAES Smart Materials, New Hartford, NY

In the processing of nitinol, there are four main parameters that control the superelastic and shape memory properties:  alloy composition, amount of cold work and time & temperature of thermal processing.  Alloy composition and the degree of cold work have been reported in the past.  To build on our knowledge, this paper aims to give a better understanding of the effect of heat treatment (time and temperature), on the mechanical and Temperature Transition Region (TTR) properties.  Two binary, A_s of -15oC and +95oC, nitinol alloy wires were selected to be tested.  Each wire tested had a diameter of 1mm and a cold work of 45%.  These wires were then heat treated at various times (ranging from 1min to 1hr) and temperatures (ranging from 400oC to 700oC).

A MTS tensile machine and a TA DSC were used to obtain the mechanical and temperature transition region properties.  Metallographic analysis was used to evaluate any microstructure changes that resulted from the heat treatments.

18.3

Characterization of Transformation Temperatures with the Bend and Free Recovery Technique: Parameters and Effects
M. J. Drexel¹, J. L. Proft², S. M. Russell³, (1)Confirmd LLC, San Carlos, CA, (2)Metallurgical Solutions, Foster City, CA, (3)Benchmark Nitinol Device Technologies, LLC, San Jose, CA

The Bend and Free Recovery (BFR) technique, as described in the ASTM F 2082 standard, is widely used in the medical device industry to determine the transformation temperature(s) of incoming material, partially processed devices, and finished devices. As described in the standard, factors such as the amount of prestrain and the prestraining temperature can potentially affect the result. In practice, these factors can be influenced by complicated device geometries and the availability of adequate cooling systems. This study will investigate the influence of several testing parameters on the resulting transformation temperature measurements. The effects of varying factors such as prestraining temperature, magnitude of prestrain, alloy transformation temperature, heat treatment, and repeated testing of a single part will be investigated.

18.4

Is the tensile test relevant to characterize NiTi Shape Memory alloy behaviour?
P. Schlosser¹, D. Favier², H. Louche³, L. Orgeas¹, Y. Liu⁴, (1)Grenoble universities, Grenoble Cedex 9, France, (2)Universités de Grenoble, Grenoble, France, (3)Polytech'Savoie, Annecy le Vieux Cedex, France, (4)University of Western Australia, Crawley, Australia

Tensile tests are widely used to characterize NiTi shape memory alloy superelastic behaviour. They are used by manufacturers in industrial production for quality control and by researchers to characterise the superelasticity and fatigue properties. Most models implemented in finite element software to aid design of NiTi applications and to predict their performances in use are also based on tensile test results. Analyses of tensile tests are often under the assumption of homogenous deformation. However, it is well known that NiTi may exhibit strong localisation during deformation via martensitic transformation.

This study carried out a comparative investigation of tensile and shear tests performed on Ti-50.8at% Ni plates using both thermal and kinematical full-field measurements. The kinematical measurement allows full-field detection of strain heterogeneity. Sample temperature changes due to the latent heat effect of the phase transformation were monitored during deformation. This measurement allows full-field detection of transformation heterogeneity.

It was found that in both tests the strain and temperature fields on the samples exhibited some level of heterogeneities. These heterogeneities are due to different origins. In tension the alloy exhibited some strongly localised bands, which were detected in both temperature and strain fields measurements. Homogeneous phase transformation precedes localised deformation. High strains observed in the localised bands are associated with high localised stress-induced phase transformation. In shear the heterogeneous strain fields are found to be more related to thermal and mechanical boundary conditions together with thermomechanical coupling. In this regard, the heterogeneities are reduced in shear when reducing the thermal effect by decreasing the deformation rate. Similar effect should be obtained by performing the test in a liquid bath.

To conclude, shear test performed at low deformation rate appears in a liquid bath to be more suitable for characterising mechanical behaviour and developing constitutive equations for superelastic NiTi.

18.5

Alternating current potential drop studies on localization phenomena in ultra fine grained NiTi shape memory alloys
A. Schaefer¹, M. F. X. Wagner¹, J. L. Pelegrina², J. Olbricht¹, G. Eggeler¹, (1)Ruhr-University Bochum, Bochum, Germany, (2)Centro Atomico Bariloche and Instituto Balseiro, Bariloche, Argentina

When a pseudoelastic NiTi specimen is subjected to uniaxial tension, it is often observed that the stress-induced martensitic transformation occurs in a localized manner, where macroscopic transformation bands form and propagate. Distinct transformation interfaces separate the specimen into regions of transformed martensite and austenite yet to transform. We have recently established alternating current potential drop (ACPD) measurements as a new experimental technique to characterize and track the positions of these interfaces during pseudoelastic cycling. In the present contribution, we apply this ACPD method to study localization events in ultra fine grained NiTi ribbons subjected to a wide range of thermo-mechanical load cases: (1) uniaxial tension at constant temperatures (pseudoelasticity), (2) cooling and heating through the transformation range under constant load (actuator load case), (3) combinations of mechanical and thermal loading. We monitor the ACPD signals in several zones along the gage length of our NiTi specimen, and we additionally characterize localized transformation events by thermal imaging and optical microscropy. Localization of transformation plays an important role under shape memory/actuator conditions, where stress-induced martensite is formed during cooling under a constant applied load. Moreover, changes in electrical resistance clearly highlight differences between thermally induced martensite (formed during cooling at no or very small loads), stress-indcued martensite (formed at higher loads), and reoriented martensite (formed when loads are applied at low temperatures). We discuss our results on a microstructural basis and we demonstrate that localized transformation events are a generic feature of pseudoelastic and shape memory deformation. We discuss the implications of our findings for actuator applications.

18.6

Experimental and theoretical aspects of the elastic properties of NiTi on several length scales
M. F. -. X. Wagner, A. Schäfer, C. Großmann, J. Pfetzing, Ruhr-University Bochum, Bochum, Germany

The most simple and fundamental characteristics of NiTi shape memory alloys, the elastic properties, are not well understood today: From an engineer's point of view, the slopes of stress-strain data during loading and unloading of austenite/martensite describe the macroscopic elastic behavior and hence need to be implemented in simulation codes. But thermo-mechanical testing and microstructural investigations reveal that these rather low macroscopic moduli are affected by localized transformation, and by additional inelastic deformation processes. In consequence, the “true” elastic moduli are expected to be larger. In this contribution, we discuss experimental data on the macrosopic elastic moduli below, in, and beyond the pseudo elastic plateau, which first decrease from the austenitic to the martensitic “end of plateau” modulus, but increase with further straining. We rationalize this behavior in the light of the dominant microstructural processes (e.g. further transformation beyond the pseudoelastic plateau, reorientation, detwinning, plasticity). We present complementary finite element results on the effect of localized transformation bands on macroscopic moduli. Nanoindentation experiments, where martensitic NiTi is subjected to a multiaxial stress-state, reveal that considerably higher elastic moduli govern the indentation response. Finally, we relate the rather low experimentally observed elastic moduli to novel atomistic first-principles simulations which yield the full set of elastic constants for NiTi martensite, and which demonstrate that the fundamental elastic stiffness of martensite is even larger than that of austenite. Our combined experimental and theoretical study provides a detailed picture of NiTi elasticity on the several length scales and points of view involved.

Closing Session

Opening Session

Plenary Session I

1.1

Functionalities of Shape Memory Alloys combined with Advantages of Textiles into the AVALON Project providing a Framework for the Creation of High Added-Value Networks
A. Monero¹, A. Querci¹, S. Carosio¹, R. De Laurentiis¹, T. Fischer², S. V. Rehm², (1)D'Appolonia S.p.A., Genova, Italy, (2)DITF-MR Denkendorf – Centre for Management Research of DITF Denkendorf, Denkendorf, Germany

This paper presents the EC-funded project AVALON, focussing on exploiting advantages provided by textiles, such as flexibility, light weight, low cost and high surface coverage, and combining those advantages with functionalities offered by SMAs towards the development of new industrial applications, opening up new perspectives in the highly competitive global textile industry, as well as for the market of Shape Memory Alloys. SMAs offer in fact a range of application perspectives, which could be more effectively and cost-efficiently exploited through the aid of textile architectures integrating thin and ultrathin SMA wires. Within this framework, applied research activities in AVALON are organized in networks, called Target Product Groups, with companies involved in many different types of businesses within the textile industry as well as within other manufacturing industries close to the application markets, pursuing the cooperative development of various new products applying hybrid textiles integrating SMA wires. As such, cross-sectoral industrial networking enables members of such networks to combine their complementary competencies and share specialised knowledge towards new product development. As such, the project aims to develop fundamental understanding on the behaviour of these materials, both when integrated within textile architectures and during textile processing, which is the key to develop performing products fully exploiting advantages provided by SMAs. This is achieved by integrating both the experience coupled with trial and error approaches typical of textile companies, with the expertise of excellent research centres on Shape Memory Alloys.

1.2

Recent developments in Nitinol surfaces for implantation
S. A. Shabalovskaya¹, G. Rondelli², M. Rettenmayr³, (1)Institute of Material Science and Technology, Jena, Germany, (2)Institute of Energy and Interphases CNR, Milano, Italy, (3)Friedrich-Schiller-University Jena, Jena, Germany

Nitinol as an implant material conquers steadily new areas of medical application as versatile as cardiovascular and orthopaedics. Because of the need to keep a low profile of miniature implant devices and considering the absence of compatibility between superelasticity of Nitinol and mechanical properties of various coatings, bare NiTi surfaces are of particular interest for implantation. Versatile applications require different in essence surface properties. In this paper, bare Nitinol surfaces were analyzed. Together dense and porous Nitinol offer the whole spectrum of topographies, chemistry, oxide thicknesses, and corrosion resistances. Native highly corrosion resistant oxides differ in structure from amorphous to crystalline and exhibit either conducting or semiconducting properties important for blood contacting applications. Various topographies can be designed both on nano and micro scales. These native surfaces free of stresses associated with coatings and interfaces are suitable for better cell attachment and migration, and thereby for faster implant healing and patient recovery. The disadvantages of mechanically polished finish surfaces are outlined. Surface chemistry in regard with lasting nickel release from Nitinol into biological solutions is analyzed and illustrated with examples. Various surface treatment and pre-treatment protocols contributing to lasting nickel release are discussed. Surface oxide thicknesses critical for the performances of superelastic implant devices are also evaluated.

1.3

Characterization of Non-Metallic Inclusions in Nitinol Tubes
A. Toro¹, M. H. Wu², F. Zhou², W. Van Geertruyden³, W. Z. Misiolek⁴, (1)National University of Colombia, Medellín, Colombia, (2)Edwards Lifesciences, Irvine, CA, (3)EMV Technologies, LLC, Bethlehem, PA, (4)Lehigh University, Bethlehem, PA

Non-metallic inclusions have been frequently shown to be linked to crack initiation in superelastic Nitinol fatigue specimens.  As the fatigue endurance of Nitinol draws increasing attention for improved device design guidelines in the medical device industry, the effect of inclusions on Nitinol fatigue endurance deserves a more in-depth comprehension. While prior studies have demonstrated that both carbide (TiC) and oxide (Ti₄Ni₂O_x) inclusions can develop in superelastic Nitinol alloys, questions remain on whether or how the chemistry and morphology of these non-metallic inclusions are affected by the melting and subsequent tube manufacturing process.  In the present study, samples of Ti-55.8wt.%Ni alloy were taken from forged and hot rolled bars converted from vacuum induction (VIM) and vacuum arc (VAR) ingots.  Additional samples were taken from tubes at various stages of the tube drawing process.  The chemistry and morphology of non-metallic inclusions in these specimens were analyzed using techniques of optical metallography, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD).  An emphasis focuses on the discussion of the experimental details developed to improve the identification of the different particles present in the material. In another aspect, the correlation between inclusion chemistry and the melting process as well as the influences of tube drawing process and inclusion chemistry on the final morphology of these particles will be analyzed and discussed.

1.4

SMA based high damping composite materials; microstructural characterization
G. A. Lopez, M. Barrado, J. San Juan, M. L. No, University of the Basque Country, Bilbao, Spain

In the last years absorption of vibration energy by mechanical damping have attracted much attention in several fields like vibration reduction in aircraft and machinery industries, nano-scale vibration isolations in electronic industry, vibration damping in civil engineering, etc. For structural applications, materials that combine a high damping capacity and high stiffness at moderate temperatures are required, but unfortunately this combination is not frequent. Usually, the most used high-damping materials are based on polymers due to their viscoelastic behaviour. However, polymeric materials typically show a low elastic modulus and are not stable at relatively low temperatures (≈ 323 K). Therefore, alternate materials for damping applications are needed. Metallic materials, which originally exhibit better mechanical properties (higher modulus and thermal stability) than polymers, with similar damping properties were proposed to replace polymeric ones. In particular, shape memory alloys (SMAs), thanks to the dissipative hysteretic movement of interfaces (martensite variant interfaces, twin boundaries) under external stresses, have found practical applications as high-damping metals.
Against this background, a completely new approach was applied to produce high-damping materials with relatively high stiffness. Cu-Al-Ni shape memory alloy powders were embedded with metallic matrices of pure In, a In-10 wt.% Sn alloy and In-Sn eutectic alloy. The production methodology is briefly described. A thorough characterization of the composites microstructures properties was carried out applying optical and scanning and transmission electron microscopy. A good particle distribution of the Cu-Al-Ni particles in the matrices was observed. Intermetallic phases were formed during the composite production. The nucleation of martensite at the interface between a Cu-Al-Ni particle and the matrices confirmed a strong interaction at the interfaces. The crystallographic structure of all phases was determined by electron diffraction. The methodology introduced provides versatility to control the temperature of maximum damping by adjusting the shape memory alloy composition.

Plenary Session II

10.1

Role and future of Shape Memory Alloy in automotive applications
S. Alacqua, M. Biasiotto, G. Capretti, T. Luchetti, A. Zanella, Centro Ricerche FIAT, Orbassano, Italy

In the past the main driver for the vehicle’s technological innovation was the cost reduction.  Nowadays priorities like legislative requirement (safety increase, emissions, fuel economy…) and customer satisfaction (comfort and ergonomics improvement, increasing of performances) are getting more and more important for a sustainable growth.  As a consequence the complexity of automobiles has increased as demonstrated by the growing number of actuations and on board sensors.
In this scenario SMs can give significant benefits and perform new functions with volume and cost reduction, an more design flexibility.  In the last years CRF has conduced a feasibility phase with interesting results in terms of integration of SMA devices into interior and exterior applications.  An activity to enhance the SMA’s characteristics has been also carried out in order meet the automotive requirements with particular focus on stability and the reliability improvement.
Nevertheless SMA devices’ design is still far from the point of view of automotive designers and engineers that traditionally use a mechanically oriented approach to face problems and to enhance performance and functionality of the automobile; very often the preferred solution is more bulky, massive and expensive than the new one.
Expanding the solution domain beyond the purview of traditional mechanical approaches is a CRF’s effort too. This presentation will give an historical overview of the use of SMA in the automotive field and a review of CRF’s approach to transitioning the technology into applications, highlighting standard and SMA’s design peculiarities.

10.2

Nitinol Implants in Orthopaedics: Review of past und current applications and concepts; discussion of boundaries for future applications
A. Schuessler, ADMEDES SCHUESSLER GmbH, Pforzheim, Germany

Although Nitinol has been used as an implant material in Orthopaedics for more than 20 years, it has never really penetrated the orthopaedic market like it did for vascular implants. Starting from early applications as osteosynthesis plates and staples, Nitinol implants underwent intensive clinical evaluations in China in the 80´s and early 90´s for spinal applications such as compression staples, intervertebral joints, scoliosis correction rods, anterior cervical fusion staples and posterior fixation devices.  These applications used predominantly the thermal shape memory effect of Nitinol. The success of current and future applications may hinge on whether they take advantage of the superelastic effect of Nitinol as well. The current commercial applications of Nitinol focus mainly on bone staples for the extremities and the spine.  The paper reviews the scientific and patent literature for the past 10 years which has been suggesting a broader use of the unique functional properties of the material: Examples include artificial spinal discs and spinal stabilization devices utilizing the superelastic transformation Austenite – Stress-Induced Marteniste), intervertebral annulus reinforcing  and nucleus augmentation devices using the enormous elastic deployment and porous Nitinol for spinal fusion and intervertebral body replacement making use of the excellent osteogenic cells integration and the low Elastic modulus. Finally the paper discusses boundaries for a broader use of Nitinol in the orthopaedics market including fatigue life, wear properties and corrosion behaviour.

10.3

Use of circular foldable Nitinol-blades for resecting calcified aortic heart valves
F. Hauck¹, D. Wendt², S. Stühle³, E. Kawa³, H. Wendt², W. Müller², M. Thielmann², B. Kipfmüller³, B. Vogel¹, H. Jakob², (1)Endosmart GmbH, Stutensee, Germany, (2)West-German Heart Center Essen, University Hospital Essen, Essen, Germany, (3)Fachhochschule Gelsenkirchen, Gelsenkirchen, Germany

Objectives:

Aortic valve replacement (AVR) using open heart surgery is a standardized cardiosurgical procedure with the disadvantage of 3 to 4 hours of cardiopulmonary bypass to resect the mostly calcified valve and to sew in the frame of the biological prosthesis.

The aim of the following device is to shorten this time by 75 %, using foldable Nitinol blades to create a circular annulus which allows the use of a self-fixating prosthesis. After further development, the device shall serve for minimally invasive surgery as part of transapical off-pump valve replacement through a trocar.

Methods:

Laser-cut T-structures of Nitinol sheet-material have been grinded to produce cutting edges which have been given the shape of half-circles afterwards. These have been connected to each other and to columns by using rivets which serve as articulating axes for the cutting ring.

To insert the cutting edges into the heart through the calcified leaflets, the blades are folded around theses axes and torn into a tube. Once released on the other side of the valve, they regain their shape due to the superelasticity of the material.

By combining rotation of the ring with a translating movement against a fix circular ring of hardly greater diameter on the instrument, a punching process is created which cuts the calcified valve leaflets and leaves a circular annulus.

Specially designed test-specimens have been created to simulate calcified valves. By using them, grinding and cutting parameters, as well as blade-shapes have been tested and optimized.

Conclusions:

Preliminary tests have shown that contraction and expansion of the Nitinol-cutting-rings are possible with acceptable shape stability. The results of the cutting-tests have shown sufficient stiffness and sharpness of the blades to obtain acceptable cutting results by using the rotating punching process. Resection time was very low with around 30 seconds per test-specimen.

Poster Session

“One-module”-actuators based on partial activation of shape memory components
S. Langbein, E. G. Welp, Ruhr-University Bochum, Bochum, Germany

An outstanding feature of shape memory alloys (SMAs) is their potential to generate integrated actuator systems with a shape memory component. This can be accomplished for example by activating the thermal shape memory effect in selected regions of the SMA-component. We refer to this process as partial activation. The purpose of the present study is to find a way to create universal actuators with properties adjustable for various applications solely by partial activation. Thus, an object of investigation is the analysis of properties and capabilities of partial activation. Furthermore this study also implicates the survey of possibilities for partial power supply and electrical contacting. One possibility to use partial activation in integrated systems is given by the agonist-antagonist design. This type of design offers the advantage that a return spring or a mechanical brake for clamping the position without feeding electrical power is not necessary. On the other hand retention force is limited by the martensitic plateau and positioning accuracy by the elastic portion of mechanical stress. To solve these problems with constructive or control-oriented solutions is furthermore an aim of this study. Another approach is to use partial activation for influencing passive superelastic structures like hinges, dampers or return elements by changing the austenitic plateau stress in integrated systems. To create a multifunctional integrated system, the NiTi-elements presented in this study offer various options since they apply partial activation both for thermal shape memory and for influencing superelasticity.

Investigation on the Hysteretic Behavior of NiTi Shape Memory Wires Actuated under Quasi-Equilibrium and Dynamic Conditions
A. Coda, M. F. Urbano, L. Fumagalli, F. Butera, SAES Getters S.p.A, Lainate, Italy

The functional characterization of SMAs for actuation is typically performed by measuring the specimen deformation under constant load during a controlled thermal cycling across the transformation temperatures.

Aim of this work is to better investigate and understand the hysteretic behavior under dynamic actuation, verifying whether transformation temperatures may be different from those measured in quasi-equilibrium conditions or not. Direct and indirect heating of shape memory wires under several loading conditions are examined in detail. Experimental results will be presented and discussed.  

Anti-tampering system: a novel application for shape memory alloy actuators
F. Stortiero, R. Gualandris, S. Gualandris, Technosprings Italia srl, Besnate, Italy

The spreading of shape memory alloys and related technology in the industrial field is often related to the lack of knowledge of the different opportunities for the application of SMA actuators.

In the present paper a novel application for shape memory alloy actuators will be presented. In particular way it will be illustrated the design of miniature anti-tampering system and related device for the unlocking of the same in manual valves.

End Plate Moment Connections with Superelastic Shape Memory Fasteners
M. Ghassemieh, University of Tehran, Tehran, Iran

In the Northridge earthquake more than 150 structures experienced brittle fractures in their welded moment connections.  The brittle failure of welded connections was also noticed in the Kobe earthquake.  Ductility in the components of structural systems has been demonstrated to be very effective in dissipating vibrations induced due to seismic activities. Researchers have identified that the ductility of structural components and systems would truly enhance structural performance subjected to dynamic or earthquake loads.  Recently, shape memory alloy (SMA) materials, which have two characteristics known as shape memory and superelasticity effects, have been used for seismic applications in structural systems. This is due to SMA’s high energy dissipating capabilities and their ability to endure large strains without undergoing permanent deformation.
This study compares the energy dissipative characteristics of end plate bolted moment connections using steel and SMA fasteners. The initial phase of the study focused on the calibration of the finite element model of the SMA superelasticity effect with the existing experimental results of the SMA rod.  Then the end plate moment connection models were subjected to cyclic loadings. Using the steel and/or SMA bolts, hysteresis results from the finite element analyses were compared in order to determine the effectiveness of the superelasticity capabilities of the SMA in dissipating energy.

Shape Memory Alloy Tension/Compression Device for Seismic Retrofit of Buildings
R. DesRoches¹, D. E. Hodgson², M. Speicher¹, (1)Georgia Institute of Technology, Atlanta, GA, (2)Nitinol Technology, Inc., Mountain View, CA

A Tension/Compression damper and recentering device is developed for applications as bracing elements in buildings.  The device is designed to allow Nitinol forms such as helical springs or Bellville washers to be used in compression or for rods and wires to be deformed in tension. The device allows both overall extension and compression while subjecting the Nitinol to the optimum deformation mode. It is possible due to the versatility of the design to adjust the force and stroke of the device without changing the overall configuration.

 The new device is tested using a full-scale loading frame, where it is subjected to increasing cyclical strains up to 10% strain.  The effect of loading rate, and loading history is also evaluated in the study.  An analytical study is performed, where the device is placed in bracing elements in 3 story, 2 bay steel framed building.  The results of the analysis show that the recentering and damping properties result in significant reductions in building displacements, and forces transmitted to columns.

The Influence of Overheating and Notches on TiNi Shape Memory Alloy Spherical Segments Functionality
M. A. Khusainov¹, A. B. Bondarev², D. A. Maslenkov³, V. A. Andreev⁴, (1)Yaroslav the Wise Novgorod State University, Velikiy Novgorod, Russia, (2)Industrial center “MATEKS”, Moscow, Russia, (3)Yaroslav the Wise Novgorod State University, Veliky Novgorod, Russia, (4)Industrial center "MATEKS", Moscow, Russia

The effect of spherical segment form recovery by leap under re-heating has put into practice in shutoff armature and thermoswitches. The main condition of reliability of devices containing spherical segments is guaranteeing of their stable functioning at multiple cycles of “bending in martensite ↔ re-heating up to austenite with an abrupt clap and, if a counter body presents, with an impact” for doing of operative action. That’s why the guaranteed reliability of such elements sort is necessary.

The research methods of the influence of overheating of spherical segments in free and built-in states after some number of cycles are represented in article.  It is shown, in particular, that the aging at temperatures of 100°Ñ, 150°Ñ during near an hour leads to clap effect intensification. Impact force is visibly increases. If the aging segment is in built-in state we can observe shape memory effect suppression and decrease of the impact force at the same time. In the previous articles we have found out that the edges are the most spherical segment stressed areas. The absence of stress concentrators on edges is, for example, a result of segment treatment by electro-spark machine tool. These concentrators initiate arising and development of cracks. These processes are controllable. It was found that the high stressed area during a bending, mirror-like to the initial form, in martensite and under re-heating is located at some distance from edge and depends on segments radius of curvature. The most stressed area, which is greatly sensitive to fracture, was found out using the specially made notches. Depending on radius of curvature, the interconnection between a crack resistance and notch dimensions is given in this work. We have made the scheme of arising and growth rate of cracks under mechanical cycling, which takes into account the specially made notch dimensions.

New stiff dampers based on shape memory alloys
J. San Juan, M. Barrado, G. A. Lopez, M. L. No, University of the Basque Country, Bilbao, Spain

Damping in structural applications require not only a high damping coefficient η but also a stiff behaviour in order to avoid the deformation of the structure, so the optimization of structural damping require a high merit index η·E. Using a patented technology of ultra-high damping composite materials based on SMA, we have developed some prototypes of dampers which exhibit both stiffness and high damping coefficient.
In this work we give a description of such dampers, as well as their characteristics and performances. We analyse some potential applications in several industrial sectors. Besides, these new dampers offer excellent performances at low frequencies, where the dynamic damping systems start to loose their good characteristics, and they also show a good potential to work in series with such devices to extend their performance at low frequencies.

Influence of carbon content on the rotary bending fatigue tests of NiTi SMA wires
W. M. M. Menezes¹, L. K. Kabayama², O. D. Rigo¹, J. Otubo¹, (1)Instituto Tecnologico de Aeronautica, S. J. dos Campos, Brazil, (2)Instituto Tecnologico de Aeronautica (ITA)., São José dos Campos,SP., Brazil

Superelastic NiTi shape memory alloys (NiTi SMA) are destined for applications in several areas such as aerospace, robotics and biomedical. In Biomedical applications include stents, orthopedics implants, arc wires and endodontic files for tooth root canal preparation. That last application the endodontic files upon rotation are subjected to both tensile and compressive stress in curved canals and unexpected failure may occur during rotary operation. Due to this problem, rotary bending fatigue tests to analyses fatigue resistance of shape memory wires are necessary. Recent work has shown that the influence of carbon content of NiTi SMA on its rotary bending fatigue resistance is an important factor. Aiming a future application as a raw material to produce endodontic files, NiTi wires produced with various carbon contents will be tested using rotary bending fatigue test varying wire curvature radius and rotational speed. Furthermore, special wire surface finish will be given to the wire in order to enhanceµ the real effect of carbon content on the fatigue resistance on the NiTi wires.

Carbon fiber reinforced smart laminates based on NiTiNOL microactuators: embedding techniques and interface analysis
P. Bettini, G. Sala, L. Di Landro, M. Riva, J. Cucco, Politecnico di Milano, Milano, Italy

In the last few years the Composite Materials Lab. of the Aerospace Engineering Department (DIA) of Politecnico di Milano has activated a research line on development of Smart Structures and their applications. Among the sensors and actuators that can be embedded in the composite laminates, generally, the shape memory alloys ones are preferred when large displacements are required (i.e. morphing for wing profiles tuning, buckling control, etc.).

Up to now one of the main limits for a large use of these smart structures in the aerospace industry is the lack of useful numerical tools for design. Otherwise some technological aspects still need a more detailed investigation.

This paper shows how to deal with issues regarding embedding of both NiTiNOL wires and strips in a carbon fibre/epoxy laminates. A crucial aspect of those structures is related to the load transfer capabilities between the SMA actuators and the host material during their activation.

In order to characterize the real conditions interface, pull-out tests have been conducted on NiTiNOL embedded in composite fiber laminates. The results have been compared to standard experiments on pure epoxy resin blocks. The reason of this correlation is due to the major difference between the two resin systems involved and boundary conditions. Other aim considered in this work is related to the embedding technologies in itself that have to take into account problems like thermal and electrical compatibility between actuators and host material and passive/active invasivity. Simple smart laminates with several actuators have been manufactured, tested and deeply analysed.

Construction of a Safety Clutch with Shape Memory Actuators
W. Predki, B. Bauer, Ruhr-Uni-Bochum, Bochum, Germany

This paper investigates the use of martensitic Nickel-Titanium within a safety clutch. This engineering application serves as a safety element within power trains to protect the components like motors, transmissions and the working machine against overload. The concept is based on a friction clutch that is able to transmit a defined torque. By exceeding this torque the clutch opens and the friction pads rub against each other. The increasing heat now can be used to activate the NiTi actuators. These are working under compression against steel disc springs according to the extrinsic two-way effect. The increasing heat leads to the phase transformation from martensite to austenite. This causes an elongation of the compressed NiTi-elements. The increasing stiffness leads to the movement of the clamped friction pad. The clutch opens and the transmittable torque decreases. After the cooling phase and the addicted martensitic phase transformation the initial axial force is reached and the initial torque can be transmitted. The analysis of the constructive solution of the safety clutch shows the practical behaviour of this concept. The transmittable torque can be adjusted continuously by screwing a shaft nut. With the help of measuring shafts the torque can be measured. The axial movement of the friction pad caused by the phase transformation of the NiTi can be measured with positioning sensors.

Wide range temperature memory effect of an in-situ NiTi alloys composite
J. Li¹, Y. Zheng², L. Cui², (1)China university of Petroleum,Beijing, Beijing, China, (2)China University of Petroleum, Beijing, China

An incomplete transformation cycle induces a kinetic stop in the following complete transformation cycle in shape memory alloys. Therefore, the kinetic stop can be regarded as a memory of the previous arrest temperature. Herein, we show that the temperature memory effect of a TiNi shape memory alloy can be expanded to be operational in a very wide temperature range by designing the shape of the original surface curve and cold rolling, which may be exploited for various practical applications.

The mechanical and thermal behaviors of heat treated NiTi orthodontic archwires
S. M. S. Aghamiri¹, M. Nili Ahmadabadi¹, S. Raygan¹, I. Haririan², M. S. A. Akhondi², (1)University of Tehran, Tehran, Iran, (2)Tehran University of Medical Science, Tehran, Iran

The near equiatomic nickel-titanium alloy is an outstanding intermetallic compound exhibiting distinctive properties associated with characteristic thermal and stress induced martensitic transformations. Some operations are applied in process of producing orthodontic wires so as to obtain the optimal shape memory behaviors. Phase transformation temperatures and load-deflection characteristics of this binary alloy are very significant variables in the application and can be manipulated by different thermomechanical treatments via inducing precipitation or dislocation networks in the matrix. More recently, heat activated NiTi wires have been marketed with clinically useful shape memory effect and higher transition temperature range (TTR). In this study, one brand of commercial heat activated nickel-titanium archwire (3M Unitek) was selected and solution treated. Then, The wires annealed at 400¢ªC for times of 10, 30 and 60 min. Thermal transformation temperatures were determined using differential scanning calorimeter and showed to alter as the time of heat treatment increased. The microstructures of wires were observed by scanning electron microscope. In order to evaluate mechanical parameters of heat treated archwires, they placed on an arch-form fixture simulating maxillary dentition and load-deflection curves were obtained by three point bending test at 37 ¢ªC. The results compared to as-received archwires and the changes were rationalized on the basis of microstructure.

The radiopacity of Ni-Ti alloys: A fundamental approach
S. M. Carr¹, S. A. M. Tofail¹, P. Devereux¹, T. McGloughlin¹, S. Lavelle², J. M. Carlson³, (1)University of Limerick, Limerick, Ireland, (2)Cook Ireland Ltd., Limerick, Ireland, (3)Cook Incorporated, Bloomington, IN

Binary Ni-Ti (Nitinol) alloys have been widely used in medical devices due to their superelastic and shape memory effects, in conjunction with their excellent biocompatibility. Despite these properties, there remain problems with the visibility of Nitinol devices during in-vivo deployment using e.g. an x-ray fluoroscope. Binary Nitinol possesses inferior radiopacity when compared to stainless steel and other major implantable metals and alloys. Our group has attempted to develop a fundamental approach towards a proper understanding of what constitutes the radiopacity of Ni-Ti. Here we calculate the radiopacity of Ni-Ti from first principles using Beer-Lamberts law of x-ray absorption, taking into account that x-ray fluoroscopy is performed with a poly-energetic x-ray under certain filtration conditions. We found that the photon distribution of the x-ray equipment, beam hardening from filtration, and the presence of absorption edges are the determining factors in defining the effective radiopacity of Ni-Ti. We then considered the addition of a ternary element to binary Ni-Ti to improve its radiopacity. The improvement of radiopacity due to the addition of Platinum, Tantalum and Tungsten are calculated using the same methods. We then compared our calculations with x-ray fluoroscopy experiments, carried out in the ambient environment and under a simulated body attenuation. Excellent agreement between the calculated and observed radiopacity was found.

New Design of NT Memory Connector for fractures and nonunion of distal radius
B. Yu, C. Zhang, J. su, S. Xu, Changhai Hospital, The Second Military Medical University, Shanghai, China

Objective   To find a new method for the management of fractures and nonunion on distal radius. Methods   According to the anatomical feature, mechanism of fracture and stress sustained on the fracture site of distal radius, a new type of nitinol shape memory alloy connector was designed by taking the advantage of its special mechanics action. The biomechanics test included photoelasticity, electrometric method and three dimensional finite element analyses. In clinical applications, 25 cases were treated by the procedure, of which 5 cases were fresh fractures of distal radius and 20 cases nonunion. The duration of postoperative follow-up was from 6 moths to 2 years (1.3 years on average).   Results The biomechanics study showed that the connector was characteristic of good anti-fatigue and reuse. The initiative memorial bone holding and  longitudinal compressive forces were 98.40N~125.05N and 152N~196N correspondingly for maintaining axial stability. All the cases had primary healing without infection, angulationer and dislocation. Fracture line disappeared 9~14 weeks later postoperatively.  Conclusion The newly designed NT memory device that matches optimally the anatomy of the distal radius. It not only can maintained longitudinal compressive force continuously, but also has efficacious fixation effect with anti-shearing, bending and distracting stress. It can shorten the duration of bone healing and improve the healing quality of bone.

Treatment of severely comminuted patellar fractures with Nitinol Patellar Concentrator
X. Shuogui, Second Military Medical University, Shanghai, China

XU Shuo-gui,ZHANG Chun-cai,NIU Yunfei

Combined effects of different heat treatments and alloying elements on transformation behavior of NiTi orthodontic wires
S. M. S. Aghamiri, M. Nili Ahmadabadi, S. Raygan, University of Tehran, Tehran, Iran

The shape memory nickel-titanium alloy has been applied in many fields due to its unique thermal and mechanical performance. One of successful applications of NiTi wires is in orthodontics because of its good characteristics providing low stiffness, high spring back, high stored energy, biocompatibility, superelasticity and shape memory effect. The mechanical properties of wires are paid special attention which can result in achieving continuous optimal forces and eventually causing rapid tooth movement without any damage. The behaviors can be controlled by chemical composition and thermo-mechanical treatment during the manufacturing process. In this study two kind of NiTi archwires of 0.016 in. diameter investigated: shape memory wire (Copper NiTi) and superelastic wire (TruFlex). The chemical analysis of Both wires was determined by EDS and shape memory wire contained copper and chromium in its composition. They exposed to different heat treatment conditions at the temperatures of 400 and 500°C for 10 and 60 min. Using differential scanning calorimetry, phase transformation temperatures were clarified and three point bending tests in the certain designed fixture in form of maxillary dentition were perfomed at 37°C to evaluate mechanical behaviors. Finally, the behaviors after aging treatment  were compared to as-received wires. The results showed presence of alloying additions gave distinctive transformation features to Copper NiTi wire.

Stress Induced Martensitic Transformation in the Crack Tip Region of NiTi Alloy
A. Falvo, F. furgiuele, A. Leonardi, C. Maletta, University of Calabria, Arcavacata Rende (CS), Italy

In recent years, Nickel Titanium based shape memory alloys (NiTi), have received much attention from scientific and engineering communities, owing to their unique characteristics, namely shape memory effect (SME) and superelastic effect (SE) [1]. These properties are due to a reversible solid state phase transformation between austenite and martensite; which can be activated by a temperature change (TIM, Thermally Induced Martensite) or by the application of external forces (SIM, Stress Induced Martensite). Up to now, a lot of researchers have studied the thermo-mechanical behavior of SMAs, but a very limited number of works has been devoted to study the fracture behavior of SMAs [2-4].
The evolution of stress induced martensitic transformation in front of the crack tip in a NiTi alloy is numerically analyzed in this investigation, by 2-D finite element simulations of single edge-crack specimens. In particular, the transformation start and finish contours, i.e. the boundaries of the transformation zone, were obtained by using plasticity concepts, and the effects of the temperature were taken into account by using the Clausius-Clapeyron relation. Furthermore, comparisons between numerical and analytical results, obtained by modified linear elastic fracture mechanics relations, were carried out. These comparisons show that the analytical approach is able to describe the stress field in the crack tip region outside the phase transformation zone, i.e. in the austenitic region.
References
[1]    K. Otsuka and C.M. Wayman, in: Shape memory materials, edited by Cambridge University Press, Cambridge, UK (1998).
[2]    S. Yi and S. Gao: Int. J. Solids Struct. Vol. 37 (2000), pag. 819
[3]    K. Gall, N. Yang, H. Sehitoglu and Y.I. Chumlyakov: Int. J. Fract. Vol. 109 (2001), p. 271
[4]    J.H. Chen, W. Sun and G.Z. Wang: Metall. Mater. Trans. Vol. 36A (2005), p. 941

Numerical simulation of SMA structures using interior-point methods
J. P. Seguin, M. Peigney, LCPC, Paris, France

This Communication addresses the numerical simulation of quasi-static evolutions in monocrystalline SMA structures. Following the works of Govindjee and Miehe (2001), Anand and Gurtin (2003), the phase transformation is described locally by an internal vectorial variable representing the volume fractions of the n variants of martensite. That internal variable is physically constrained to satisfy n+1 inequalities at each point. This is a major difference with the framework of plasticity, in which the internal variable is usually subjected to equality constraints. From a structural simulation point of view, handling such local constraints in the evolution problem is not obvious. Robustness and computational time are particularly sensitive issues. Most of the strategies used so far rely on active set strategies and regularization. Here we propose a new approach, which consists in reformulating the incremental problem as a Linear Complementarity Problem (LCP). This allows one to use a Interior-point method (such as the algorithm of Ye) for the resolution. Such methods are indeed known to be very efficient for solving large-scale LCPs. This approach has been implemented in Matlab (using the finite element toolbox OpenFem) and validated by comparison with the experimental results of Shield (1995). Comparison of computational costs with other resolution techniques from the literature shows the relevancy of the proposed approach. 

Design and characterization of new Ti-Nb-Hf alloys
M. González¹, J. Peña², J. M. Manero¹, M. Arciniegas¹, F. J. Gil¹, (1)Universitat Politècnica de Catalunya, Barcelona, Spain, (2)Elisava Escola Superior de Disseny, Barcelona, Spain

NiTi alloys are the only shape memory alloys that have been used in biomedical applications. However, in recent studies, it has been demonstrated that the release of Ni ions produces adverse reactions in the surrounding tissue which can generate different kinds of allergy. The objective of this work is to design, produce and characterize new Ni-free Ti alloys as possible substitutes of the NiTi materials and also, enhance bone regeneration by presenting a similar bone elastic response.

 For that, a method based on the molecular orbital theory has been implemented to design three new Ti-Nb-Hf system alloys. A vacuum arc melted button of each alloy was heat treated at 1100 ºC during 2 hours and quenched with a mixture of ethanol/water at 0 ºC. Finally, the alloys were microstructurally and mechanically characterized elastic modulus was obtained as well as the thermoelastic behaviour, which were evaluated by means of nanoindentation tests using a Berkovich and a spherical tip, respectively.

 X-Ray diffraction results show the presence of β phase in the three studied alloys. Moreover, one of the alloys exhibits reversible phase transformation due to the presence of thermoelastic martensitic α” plates inside the β grains observed by transmission electron microscopy. Results show a low elastic modulus in all the studied alloys with values between 70-90 GPa, which are values lower than those of the commercial alloys used in bone implants load transfer.

 Keywords: Ni-free Ti alloys, shape memory effect, low elastic modulus, nanoindentation.

The modeling of the magnetocaloric effect in the shape memory Heusler Ni-Mn-Ga alloys by Monte-Carlo simulations
V. D. Buchelnikov¹, S. Vladimir V², T. Sergey V², (1)Chelyabinsk State University, Chelyabinsk, Russia, (2)Chelyabinsk State university, Chelyabinsk, Russia

The magnetocaloric effect (MCE) has a significant technical importance since magnetic materials with large MCE values can be used as refrigerants in the devices working on principles of magnetic refrigeration. Recent researches have shown that Heusler Ni-Mn-Ga alloys are also the perspective materials as refrigerants in cooling devices. These alloys have approximately the same properties as the best MCE materials. The aim of the present work is the modeling of the magnetic entropy change and other magnetic properties of Ni-Mn-Ga alloys by classical Monte-Carlo simulations. In the proposed model we use the three-dimensional cubic lattice with periodic boundary conditions and consider interactions only between nearest sites of the lattice. The whole system can be representing as two interacting parts – magnetic and structural subsystems. The magnetic part is describes by the “q-state” Potts model for the first order magnetic phase transition from ferromagnetic to paramagnetic phases. The structural part is describes by the degenerated three – state Blume – Emery – Griffiths model for the structural transformation from cubic (austenitic) phase to tetragonal (martensitic) one. In our model we considered the alloys with compositions at which the first order coupled magnetostructural phase transition takes place. For the modeling lattice we use the standard Metropolis algorithm. The isothermal magnetic entropy change upon variation of the magnetic field from 0 to 5 T and other magnetic properties, such as the structural and the magnetic order parameters, the magnetic specified heat, and the magnetic part entropy were theoretically calculated. It is shown that the theoretical results are in good agreement with available experimental ones.

The investigation of the phase transformations in the shape-memory Heusler Ni-Mn-X (In, Sn,Sb) alloys by Monte-Carlo simulations
S. V. Taskaev¹, V. V. Sokolovsky¹, V. D. Buchelnikov¹, P. Entel², (1)Chelyabinsk State University, Chelyabinsk, Russia, (2)University of Duisburg-Essen, Duisburg, Germany

The Heusler Ni-Mn-X (such X=In, Sb, Sn) alloys, which relate to the class of shape-memory alloys, attract much attention because they have also the giant magnetocaloric effect and the giant magnetoresistance. These properties are applicable in developing actuator materials and materials for magnetic refrigeration. The aim of this work is the theoretical description and the modeling magnetic properties in Ni-Mn-X (such X=In, Sb, Sn) alloys by the classical Monte Carlo method. In the proposed theoretical model for description of the phase transformation in Ni-Mn-X alloys the phase transitions from the mixed antiferromagnetic – ferromagnetic martensitic states to the ferromagnetic austenitic state and from ferromagnetic austenitic state to paramagnetic austenitic state are considered. The whole three – dimensional cubic lattice with periodic boundary conditions included the magnetostructural interaction between the magnetic and the structural subsystems. The magnetic part is described by the “q-state” Potts model with local interactions. The structural part is described by the degenerated three-state Blume-Emery-Griffiths model for the structural phase transformation. The configuration of antiferromagnetic clusters on the ferromagnetic lattice was set random and the clusters concentration was determined from experimental compositions of the Ni-Mn-X (X=In, Sb, Sn) alloys. By the help of theoretical model the temperature dependences of the normalized magnetization, strain order parameter, magnetic heat capacity and internal energy are obtained. All quantities are in good agreement with the available experimental data.

A study of NiMnGa high temperature shape memory alloys
Y. Li, F. Liu, H. Xu, Beijing University of Aeronautics and Astronautics, Beijing, China

NiMnGa shape memory alloys (SMAs) have recently drawn more attention as promising high temperature SMAs (HTSMA) due to large shape memory effect (SME), pseudoelasticity (PE), high thermal stability and interesting aging effect. A systematic substitution of Ni for Ga has been performed in the non-stoichiometric NiMnGa alloys. The relationship among the composition, structure and martensitic transformation temperatures was studied in detail. The martensitic transformation temperatures increase with increasing Ni content from lower than 0^oC up to 400^oC until the appearance of the second phase. A high-temperature shape-memory alloy, Ni₅₄Mn₂₅Ga₂₁, was subsequently developed with a shape-memory effect of 6.1% and a martensitic transformation temperature higher than 250 °C for single crystals. The measured compressive strength and strain were 845 MPa and 20.5%. It was also found that the martensitic structure, the transformation temperatures and the enthalpy of this alloy almost keep invariable even after 1000 thermal cycles. In general, polycrystalline NiMnGa alloys have an extremely brittle feature. The results show that the second phases in Ni₅₈Mn₂₅Ga₁₇ and Ni₅₆Mn₁₇Fe₈Ga₁₉ alloys can raise the strength and plasticity. The shape memory effect of the former is 5.1%, which is better than the latter due to the favorable γ phase distribution. Moreover, a plate with the thickness of 1.5mm has been made by Pack-Hot-Rolling method for Ni₅₆Mn₁₇Fe₈Ga₁₉ alloy.

Structure and Functional Properties of Precipitation-Hardening Fe-Mn Alloys with Controlled Shape Memory Effect
V. V. Sagaradze, E. V. Belozerov, N. L. Pecherkina, M. L. Mukhin, Institute of Metal Physics, Ekaterinburg, Russia

The structure and physical-mechanical properties of new high-strength alloys of the Fe-20Mn-2Si-2V-0.2(1.0)C type, in which the shape memory effect (SME) can be controlled by carbide aging at different temperatures (with precipitation of VC particles of different fineness) and gamma-epsilon-gamma transformations, have been studied. Maximum strengthening (the yield stress  = 1600-1900 MPa) of the Fe-20Mn-2Si-0.4Ñ shape memory alloy (SMA) was achieved after aging and fractional rolling (30-90%) at 400-600C. Also, ultrathin nanostructured strips 1.5-3 mm wide were made by the melt spinning method. An insufficient amount of the epsilon-martensite (20-40%) is formed in the low-strength austenitic alloys like Fe-18Mn and Fe-20Mn-2Si-0.2(0.4)Ñ at small degrees of cold deformation (4-5%). Oppositely, small deformation of aged alloys like Fe-20Mn-2Si-0.4Ñ  with uniformly distributed VC nanocarbides leads to formation of 70-90% epsilon-phase. VC particles contribute to splitting of perfect dislocations to partial dislocations, leading to the formation of stacking faults and the epsilon-phase. Authors [1] found that b-Mn nanoparticles increased SME from 1.8 to 2.3%  in Fe-31Mn-6Si SMA. This increase can be explained (analogously to the effect of VC particles) by the formation of a large amount of the strain-induced e-martensite in the decomposed solid solution of the austenite.

This work was partially financed by RFBR (project No. 03-06-32715).

1.      Gavriljuk V.G., Bliznuk V.V., Shanina V.D., Kolesnik S.P.  MSE(A), 2005, v.406, 1, p.1-10.

The stress-induced martensitic transformation of aged ferromagnetic shape memory Fe-Ni-Co-Ti-Cu alloys
A. N. Titenko, Institute of Magnetism, Kiev, Ukraine

Under certain conditions, alloys with thermoelastic martensite exhibit superelastic properties. The necessury conditions for the realization of superelastic deformation are a small volume effect DV/V of the martensitic transformation (MT), the presence of a shear strain component, and a high yield strength s^s of matrix phase.

Two polycrystalline Fe-Ni-Co-Ti-Cu alloys, namely Fe-15,2Ni-37,0Co-8,0Ti-6,17Cu, Fe-15,2Ni-36,6Co-6,72Ti-7,62Cu (wt.%) were investigated. The MT temperatures were determined from the temperature dependences of the electrical resistance r(T) and low-field magnetic susceptibility c(T). The influence of austenite ferromagnetism on the volume change DV/V at the starting temperature M_s of forward a«g MT was studied using dilatometric technique. Small elasticity modulus of the austenite below Curie temperature T_c is favoured superelastic behaviour of investigated alloys. The superelastic characteristics are affected also by the duration of austenite annealing and deformation temperature. 

The effect of thermo-mechanical treatment on the microstructure and properties of NiTiNb shape memory alloys
E. Wang, G. Yang, Z. Zhao, Beijing Institute of Aeronautical Materials, Beijing, China

Because of the wide transformation hysteresis upon proper pre-deformation in martensite state, Ni₄₇Ti₄₄Nb₉ shape memory alloy (SMA) has applied as coupling or sealing components. Actually, in above application situations, the NiTiNb SMA is subjected to a constrained state in the service. In the present work, a thermo-mechanical treatment was applied in attempt to improve the mechanical properties and to enhance the recovery force of NiTiNb SMA under constrained state. A systematical study has made of the microstructure evolution, mechanical properties and recovery force of the NiTiNb SMA upon cooled deformation followed by annealing treatment at different temperature (400 ~ 900 °C). In particular, the dependence of recover force on the raising temperature and the transformation temperature dependence of the pre-deformation were investigated. It was indicated that the thermo-mechanical treatment can significantly improve the mechanical properties and the recovery force of NiTiNb SMA after pre-deformation in martensite state. The relationship between the pre-deformation and the reversed martensitic transformation temperature was reported. In this context, the corresponding mechanisms for the enhancement of the recovery forces and for the transformation temperature change were discussed.
Keywords: NiTiNb, shape memory alloys, thermo-mechanical treatment, mechanical properties
Corresponding author, Ermin Wang, Associated Prof., Email:genlin.yang@biam.ac.cn

Modification of an Fe-14Mn-5Si-9Cr-5Ni alloy by adding Copper
H. Bao-Quan, North University of China, Taiyuan, China

Abstract
The modification of an Fe-14Mn-5Si-9Cr-5Ni shape memory alloys (SMAs) by copper addition has been carried out in the present paper, aiming at further enhancing its corrosion resistance. The results of electrochemical potentiodynamic measurement and immersion test showed that copper remarkably improved its corrosion resistance behavior in Cl^- solution. On the other hand, it was found not to markedly affect the mechanical properties or the shape memory effect (SME). The multiple effects of copper on Fe-Mn-Si based alloys were discussed in view of that the strengthen austenite is one of key factor to improve SME.
Key words: FeMnSiCrNi, shape memory effect, corrosion resistance, strengthen, Copper

Electrochemical deposition of Fe-Pd thin films with 30% at Pd
M. Bestetti, M. Villa, C. Borioli, S. Franz, P. L. Cavallotti, Politecnico di Milano, Milano, Italy

Ferromagnetic Shape Memory Alloys (FSMA) are smart materials able to change shape and size by rearrangement of the crystallographic variants as a response to an external magnetic field, and exhibiting reversible martensitic transformation. FePd alloys (Pd ~ 30% at) are interesting FSMA, and in the present work we present original results about the electrodeposition of Fe-Pd alloy films. Fe-Pd films were electrodeposited by using an aqueous solution containing Fe₂(SO₄)₃ and PdCl₂ as metallic ions sources, ammonium hydroxide and 5-sulfosalicylic acid as complexing agents. Composition of the films was analysed by means of Energy Dispersive Spectroscopy (EDS) and X-Ray Fluorescence (XRF). The crystallographic structure and the surface morphology of the sample were determined by X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM), respectively. The magnetic properties were assessed by Vibrating Sample Magnetometer (VSM). The influence of temperature, current density, electrolyte hydrodynamics, PdCl₂ and (NH₄)₂SO₄ concentration on the electrodeposited film quality and composition and on the current efficiency of the process were investigated. Either by increasing the electrolyte temperature or agitation, or by reducing the current density, an increase in Pd content in the alloy was observed. The Pd content in the film also showed a linear dependence on PdCl₂ concentration in the electrolyte. Improvement of the film quality were observed by increasing the (NH₄)₂SO₄ concentration, or reducing the current density. The deposition parameters were optimized in order to obtain electrodeposited films with Pd content around 30% at.

Development of texture and microstructure during cold Rolling and annealing of a Fe-based shape memory alloy
B. C. Maji¹, V. Hiwarkar², M. Krishnan¹, I. Samajdar², R. K. Ray³, (1)Bhabha Atomic Research Centre, Mumbai, India, (2)Indian Institute of Technology, Mumbai, India, (3)Tata Steel, Jamshedpur, India

The shape memory effect (SME) observed in Fe-based shape memory alloys is governed by the g to e martensitic transformation and strongly dependent on the crystallographic orientation. Therefore, introducing proper texture and microstructure by processing could be an effective approach for improving the imperfect SME shown by these alloys. With this objective, the development of texture and microstructure in cold rolling and annealing of Fe-14Mn-6Si-9Cr-5Ni shape memory alloy was studied. Vacuum arc melted ingots of the Fe-14Mn-6Si-9Cr-5Ni alloy were hot rolled into strips and solution annealed at 1050^oC temperature for 1 hr. The strips were subjected to different extents of reduction (0-45%) by cold rolling. The effect of annealing was studied on specimens cold rolled to 45% reduction at different temperature between 700-1100^oC for time ranging from 2 minutes to 8 hrs. The microstructural evolution was characterized by optical microscopy, transmission electron microscopy and electron back scatter diffraction (EBSD). The bulk texture measurement was carried out at the mid thickness of the specimens using X-ray of MoK_a1 ( l = 0.7093 A^o) radiation. Pole figure and orientation distribution function (ODF) methods were used to study the texture development in the parent austenite phase. The solution treated material has a nearly random texture and cold deformation induces a strong alloy type texture with Brass {011}<211> and Goss {011}<100> components. It is observed that annealing of the cold deformed material in the single phase austenite region (1000-1100^oC) produces a nearly random recrystallization texture. Annealing in the two-phase region (700-1000^oC) also produces random recrystallization texture but is kinetically a slower process. This is perhaps related to the precipitation of the Fe₅Ni₃Si₂  intermetallic phase.

The martensitic microstructure of modulated 5M martensite in off-stoichiometric Ni₂MnGa ferromagnetic shape memory alloys
P. Sontakke, A. Gupta, M. Krishnan, Bhabha Atomic Research Centre, Mumbai, India

Ni-Mn-Ga alloy system has attracted considerable attention during the past few years and is expected to become a promising potential for fast-responsive and compact actuators owing to its large magnetic field induced strain (upto 10%) along with other interesting properties like premartensitic transition, large magnetocaloric effect, high transformation temperature and low stress for twin variant rearrangement. Depending upon the composition, the most important martensites that exist in off-stoichiometric Ni₂MnGa alloys are the modulated 5M and 7M, and, the non-modulated tetragonal NM ones. In this study, a systematic investigation was carried out on the 5M martensite in a well characterised Ni₅₀Mn_28.9Ga_21.1 alloy using transmission electron microscopy (TEM) and x-ray diffractometry for determining its crystal structure, substructure, intervariant interfaces and self-accommodating microstructure. It was established that the 5M martensite is a monoclinic crystal structure with internally faulted substructure. Figs1-3. The crystallographic features of the martensitic microstructure as observed by TEM are found to be in agreement with those predicted by computations based on the phenomenological theory of martensite crystallography.

Factors influencing the reversion of stress-induced martensite to austenite in a Fe-Mn-Si-Cr-Ni shape memory alloy
L. G. Bujoreanu¹, S. Stanciu¹, R. I. Comaneci¹, M. Meyer², V. Dia³, C. Lohan¹, (1)The Gheorghe Asachi Technical University from Iasi, Iasi, Romania, (2)NETZSCH, Selb/ Bavaria, Germany, (3)S.C.MITTAL STEEL Iasi S.A., Iasi, Romania

It is well-known that one way shape memory effect (SME) in Fe-Mn-Si based shape memory alloys (SMAs)  is related to the thermally-induced reversion of ε (hexagonal close packed, hcp) stress induced martensite (SIM) to γ (face centered cubic , fcp) austenite. In the case of a Fe-Mn-Si-Cr-Ni SMA this reverse martensitic transformation was analyzed  in regards to the critical temperature for the beginning of austenite formation (A_s) and the percentage of permanent deformation recovered by heating (SME). For this purpose, a dilatometric study, dynamic mechanical analyzer (DMA) measurements and scanning electron microscopy (SEM) observations were employed aiming to determine a relationship between permanent strain, ε SIM, A_s and SME.

Examination of the Cu-13,4Al-5Ni Shape Memory Alloy
M. Benke¹, V. Mertinger¹, L. Daroczi², (1)University of Miskolc, Miskolc, Hungary, (2)University of Debrecen, Debrecen, Hungary

Cu based shape memory alloys exhibit relatively high transformation temperatures and low price compared to the other shape memory alloy systems. In spite of their advantages, their brittle behavior and ageing processes limits their applications. To increase ductility, Mn and Fe were added to the CuAlNi alloy. To examine the effect of the Mn and Fe addition and to characterize the ageing processes, the base Cu-13,4Al-5Ni alloy was investigated. After performing the needed heat treatments on the single crystal samples, equilibrium (α and γ₂) and non-equilibrium (martensite) phases and transformations were also examined on the alloy. Transformation processes were examined using heat flux DSC, structure examinations were performed using optical microscope and SEM devices, phase identifications were carried out by XRD method. Identification of the equilibrium α phase using XRD method was not possible on the single crystal samples. Texture examinations revealed the textured structure of the α phase. According to the results the equilibrium phases (α and γ₂) form only after long term heat treatments. Because of that, ageing processes do not affect the thermoelastic martensitic transformation of the CuAlNi alloy. This phenomena is probably caused by the high Ni content that decreases the diffusion rate in CuAlNi alloys.

Study of shape memory effect developed by helical springs made from Cu-Al-Ni base alloy by lost-wax casting
S. Stanciu, L. G. Bujoreanu, N. Cimpoesu, I. Ionita, The Gheorghe Asachi Technical University from Iasi, Iasi, Romania

By means of displacement-temperature variation curves, the occurrence of both free-recovery and work-developing shape memory effects (SME) were revealed in the case of compression helical springs made from a Cu-Al-Ni based shape memory, by lost-wax casting. The corresponding critical temperatures of the martensitic transformation, determined during heating-cooling cycling, were compared to the results obtained during thermal cycling performed by dilatometry and differential scanning calorimetry (DSC). The results showed a decreasing tendency of critical temperatures. The corresponding microstructure was analyzed by scanning electron microscopy (SEM) in order to reveal the formation of β₁’ martensite and its morphological changes produced by cycling.

Effect of pulsed heat treatment on microstructure of rapidly quenched TiNiCu alloys
A. V. Shelyakov¹, A. A. Korneev², (1)National Research Nuclear University MEPhI, Moscow, Russia, (2)Moscow Engineering Physics Institute (State University), Moscow, Russia

In the present research, TiNiCu alloys were produced in amorphous state by melt spinning technique at the cooling rates around 10⁶ K/s. Crystallization of the alloys was performed by single pulse of electric current or laser radiation with duration from 10^-1 s to 10^-6 s. TEM investigations shown that the martensite transformation B2-B19 occurred after all heat treatment regimes but average grain size varied from 500 nm to 80 nm with decreasing the time of heat exposure. The effect of thermal treatment on structural parameters, morphology and transformation temperatures of the alloys is discussed.

In situ XRD study of the transformation charcaterisitics of severely plastic deformed NiTi SMA
F. M. Braz Fernandes¹, A. Pereira¹, K. K. Mahesh¹, R. J. Cordeiro Silva¹, C. Gurau², (1)FACULDADE DE CIÊNCIAS E TECNOLOGIA / UNL, CAPARICA, Portugal, (2)"Dunarea de Jos” University of Galati, Galati, Romania

Severe plastic deformation by High Pressure Torsion (HPT) of NiTi alloys (Ni-rich and Ti-rich) has been performed. The samples have been studied by in situ X-ray diffraction (XRD) in order to get information about (i) the transformation characterisitics and (ii) the structural evolution during annealing.

The effect of magnetoelectropolishing on corrosion and fatigue resistance of NiTi endodontic rotary files
R. Rokicki¹, T. Hryniewicz², K. Rokosz², (1)Electrobright, Macungie, PA, (2)Politechnika Koszalinska, Koszalin, Poland

Abstract

In recent decade Nitinol have become the main material for production of endodontic rotary files where fatigue resistance, elasticity and resistance to torsional fracture are highly desirable. But in spite of this mechanical attributes fracture of NiTi rotary files during clinical use occur. The corrosion and fatigue resistance of endodontic files are influence by many interconnected factors namely: presence of hydrogen in starting material, surface quality, hydrogen introduce to files during finishing processes as eching, electropolishing, hydrogen introduce during sterilization and disinfect ion. To overcome these obstacles and improve corrosion and fatigue resistance many processes have been proposed including: electropolishing, cryogenic treatment, nitriding (etc). In present work we have evaluated “magnetoelectropolishing” (electropolishing under influence of uniform magnetic field) as alternative process for improvement of corrosion and fatigue resistance of Nitinol endodontic rotary files and compared this new technique with conventional electropolishing process. To evaluate influence of “magnetoelectro-

polishing” process we used electrochemical tests: (Open Circuit Potential (OPC), Polarization Curves (PC), Electrochemical Impedance Spectroscopy (EIS) and mechanical bending test (number of bending cycles required to fracture). To evaluate surface condition and fracture morphology scanning electron microscope (SEM) was used. The study has shown essential improvement in corrosion resistance of “magnetoelectropolished” files, which most probably arise from enrichment of passive layer in Ti by selectively dissolved Ni. The number of bending cycles necessary to break files was increased of about 40% when compared to conventionally electropolished files.

The main factor, which influence improved fracture resistance of “magnetoelectro-

polished” files were created by remarkable ability of this new process to degas of hydrogen from the files. 

Effect of aging on superelastic behavior and transformation temperatures of Ti-50.5 at.% Ni shape memory alloy
F. Naghdi¹, M. Nili-Ahmadabadi¹, H. Shahmir², I. Haririan³, (1)University of Tehran, Tehran, Iran, (2)Tehran University, Tehran, Iran, (3)Tehran University of Medical Science, Tehran, Iran

Abstract: In the present study the effect of aging treatment on the superelastic behavior and transformation temperatures of NiTi shape memory alloy was studied. The wire with composition of Ti-50.5 at.% Ni was prepared via VAR and rolling followed homogenization. After solution annealing, aging treatment was carried out at 400 and 500 °C for 30 and 60 min. Three point bending test was used to investigate the superelastic behavior and transformation temperatures was determined by differential scanning calorimetry. It was found that the superelastic characteristics including level of bending stress on louding and unloading, mechanical hysteresis, slope of plateau and amount of permanent deflection are sensitive to aging treatment. Also, transformation temperatures and thermal hysteresis change and R phase appears as result of this treatment.

Temperature full-field measurement and heat sources estimation during superelastic tests of NiTi samples
P. Schlosser¹, H. Louche², D. Favier³, L. Orgeas¹, (1)Grenoble universities, Grenoble Cedex 9, France, (2)Université Montpellier 2, Montpellier, France, (3)Universités de Grenoble, Grenoble, France

Intensive experimental investigations have been carried out to characterise and understand the deformation mechanisms associated with the superelasticity of SMAs. In that respect, thermal and kinematical full-field measurement are increasingly performed during mechanical tests of NiTi samples [1-4]. They have allowed to bring new information to analyse the mechanical behaviour of this alloy, including localisation phenomena.

In order to obtain a quantitative energy information and a better recognition of the deformation mechanisms involved, an estimation of the local heat sources based on an image processing of the heat balance equation has been achieved. In the poster, we will present first the theoretical equations and the hypotheses used to estimate the heat sources from the measured thermal fields. The software and the validation of the method will be presented in the second part. Finally, typical results showing the heat sources (local latent heat) distribution during mechanical tests will be given.

[1] S. Daly, G. Ravichandran, K. Bhattacharya, Acta Mater., 55 3593–3600, (2007).

[2] E.A. Pieczyska, S.P. Gadaj, W.K. Nowacki, H. Tobushi, Exp Mech., 46, pp 531–542, (2006).

[3] D. Favier , H. Louche, P. Schlosser, L. Orgéas, P. Vacher and L. Debove, Acta Mater., Vol. 55, 16, pp 5310-5322, (2007).

[4] P. Schlosser, H. Louche, D. Favier and L. Orgéas, Strain, Vol 43, 3, pp 260-271, (2007).

Nitrogen plasma immersion ion implantation on NiTi SMA
S. C. Baldissera¹, E. N. D. Camargo¹, M. M. D. Silva¹, M. Ueda², J. Otubo¹, (1)Instituto Tecnologico de Aeronautica, S. J. dos Campos, Brazil, (2)National Institute for Space Research, S. J. dos Campos, Brazil

NiTi alloys are considered as ‘‘smart functional materials’’ exhibiting shape memory and superelasticity effects with applications in many areas such as aerospace, robotic and medicine. Although the NiTi alloy is an intermetallic compound with strong atomic bonding, but for medical application the Ni ion release is still a major concern due to its eventual toxicity.  This work will show the effects of the surface modification by nitrogen plasma immersion ion implantation. Recently published literatures indicate that Ni release can be suppressed by this technique and successful “in vivo” tests have been performed. Other surface improvements (mechanical as well as tribological) are expected by obtaining subsurface TiN formation. The nitrogen implanted samples will be analyzed by DSC, Auger Spectroscopy, SEM, tribometer, nanoindenter and AFM.

Comparison of the Effects of Strain Rate in Three Different Environments on the Results of Tension Testing of Superelastic Nickel-Titanium (Nitinol)
M. Platt¹, J. Ritchey¹, D. Norwich², (1)Instron, Norwood, MA, (2)Memry Corporation, Bethel, CT

Mechanical testing provides important materials properties data during the physical evaluation of superelastic NiTi specimens. Typically, ASTM F2516-06 Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials is employed and lists specific test rates to be utilized. In order to allow for heat dissipation that occurs during the austentite to martensite transformation portion of the test, slow test rates are required within this method to ensure that test results are not affected. This study will compare three different test rates (1X, 2X, and 3X of the ASTM test method rate) for two different diameter NiTi wire materials at two different temperatures (ambient and 37C). Additionally, the tests will be replicated in a water bath at 37C. The data will be examined to determine if the heat effect is a valid phenomenon and if test speeds could be increased within a particular test environment without influencing the materials properties and subsequent results.

Effects of thermal cycling on the temperature memory effect of TiNiNb alloys
D. Jiang¹, L. Cui², Y. Zheng², X. Jiang², Y. Yan¹, J. Jiang¹, (1)China University of Petroleum, Beijing, Beijing, China, (2)China University of Petroleum, Beijing, China

The temperature memory effect (TME) in Ti₅₀Ni₁₅Nb₃₅ and Ti₄₈Ni₁₇Nb₃₅ alloys was investigated by using differential scanning calorimeter (DSC). After several incomplete thermal cycles upon heating to the arrest temperature, the TME appeared in the next 30 complete thermal cycles. This is contradictive to the previous understanding, that is, TME could be erased totally by one complete thermal cycle. In our research, we also found that the numbers of the incomplete thermal cycle plays an important role in inducing this repeatable TME. However, with increasing of heating rate, the memory effect became weaker and disappeared within fewer cycling numbers. These were considered closely relating to the existence of a large number of interfaces between the TiNiNb and (Nb, Ti) phases.

Effects of hydrogen on Ni47Ti44Nb9 shape memory alloy
Z. Yan, L. Cui, Y. Zheng, T. Liu, X. Jiang, China University of Petroleum, Beijing, China

The effect of hydrogen on the transformation characteristic and microstructure of NiTiNb shape memory alloy was investigated. Samples were charged with hydrogen by electrolysis for different time. DSC results showed that new reversible transformation peaks around 110°C appeared, and the transformation enthalpies of the thermal peaks increased with the increasing charging time. They had a narrow hysteresis (almost 5°C) which was quite a novel characteristic for large hysteresis NiTiNb alloy. X ray diffraction (XRD) results illustrated that the {110} diffraction peak of the b-Nb phase shifted to lower angles with a corresponding lattice parameter increased from 2.3356 Å to 2.4427 Å (corresponding to nearly 14% of volume increase), while the lattice parameter of the {110}_B2 diffraction peak of NiTi alloy increased from 2.1361 Å to 2.1453 Å (corresponding to just 1.3% of volume increase).

SME and TWSME Study in Ti-Ni Alloy after Strain Aging
A. A. Chernavina¹, E. P. Ryklina², S. D. Prokoshkin¹, N. N. Perevoshchikova², (1)Moscow Institute of Steel and Alloys, Moscow, Russia, (2)Moscow State Institute of Steel and Alloys (Technological University), Moscow, Russia

Abstract ID#: 20366
Password: 834182
Title: SME and TWSME Study in Ti-Ni Alloy after Strain Aging
Session Selection: SMA Properties and Characterizations
Presentation Format: Oral
Lead Presenter's E-mail Address: dreams_sea@mail.ru
Summary: This paper focuses on the optimization of shape memory effect (SME) training parameters bringing maximum one-way and two-way recovery strain. The joint effect of isothermal annealing at 430 deg.C after Low-Temperature Thermomechanical Treatment (LTMT) and external training parameters on functional properties of Ti-50.7%Ni alloy is studied. The homogenizing annealing at 700 deg.C, 20 min is chosen as a reference heat treatment (RHT). Under experiment procedure, the bending loading mode, strain state, loading value and loading time were varied. Increasing of strain aging time from 10 min to 10 hr affects characteristic temperatures A_s and A_f after aging and RHT, however, in the case of LTMT the A_s - A_f temperature range is significantly wider than after RHT. The TEM and X-ray studies testify that it is caused by two factors: heterogeneity of nano-size subgrain structure and nano-phase Ti₃Ni₄ precipitates. The evolution of SME and two-way TWSME parameters is studied as well. The recovery strain e_r and TWSME amplitude e_TW increase with aging time. Variation of loading time is effective for e_TW regulation; the achievement of required TWSME value is possible after minimum number of training cycles owing to exposure time increasing in a constrained condition. The loading mode and constraining strain e_t strongly affect all studied SME and TWSME parameters. Variation of training parameters enables additional precise regulation of final functional properties. The obtained results can be used for development elements functioning under TWSME realization.

Martensitic transformation behaviors of TiNi alloys with non-homogeneous strains
J. Li¹, Y. Zheng², L. Cui², (1)China university of Petroleum,Beijing, Beijing, China, (2)China University of Petroleum, Beijing, China

In-situ shape memory alloys (SMAs) composites had been produced by designing the shape of the original surface curve and cold rolling. If the heterogeneous in a SMA is magnified in such a way that macroscopic distinct domains are aligned regularly, then the SMA has a structure similar to those of composites. As a result, two peaks appeare on the DSC curves in the first heating process, which correspond to different deformation regions in these in-situ SMAs composites respectively. In this paper it has been shown that in-situ composites of TiNi alloys can overlap a desirable (also adjustable) strong negative strain over a moderate negative strain compared to directly cold-deformed TiNi alloys. Composites with a small prestrain level show a larger hysteresis upon heating than those with a large prestrain level. We presumed that the interactions between the dislocation texture and martensite variants were introduced when the TiNi martensite was cold rolled at room temperature might be responsible to the phenomena. All the phenomena above showed it is feasible to the method for controlling the thermal properties of a material by a proper design of the dislocation texture.

Kinetics of failure rate accumulation and TiNi shape memory alloy fracture under the cycling
V. A. Andreev¹, A. B. Bondarev², M. A. Khusainov³, A. A. Larionov⁴, G. V. Plastinina⁴, (1)Industrial center "MATEKS", Moscow, Russia, (2)Industrial Center "MATEKS", Moscow, Russia, (3)Yaroslav the Wise Novgorod State University, Velikiy Novgorod, Russia, (4)Yaroslav the Wise Novgorod State University, Veliky Novgorod, Russia

Researches were carried out on wire samples of 0.4 mm diameter made of shape memory alloy of Ti – 50.0 at % Ni and Ti – 50.8 at % Ni with pseudoelastic effect under mechanical cycling and thermochanges at martensitic transformations intervals (MT).

After annealing at temperature 550 ºC for 30 minits, MT characteristic temperatures of these alloys are: Ti-50.0 at. %Ni  (M_s =  42 ºC,   M_f = 39 ºC  A_s =  74 ºC,   A_f  =  65 ºC);   Ti – 50,8 at. % Ni (A_s = (-28 ºC), A_f = (-17 ºC)).

The mechanical cycling was carried out according to the scheme: tensioning-unloading, one-sided and two-sided bendings and torsion bending. Failor rate accumulation during the cycling was measured by electrical resistance change and mechanical characteristics qualities changes. Fracture was estimated according to data of optical and electronical mocroscopy investigation.

Resistivity was shown to increase before the hysteresis loop stabilization period (4-7 cycles) during the mechanical cycling at strain (ε < ε_pl) where ε_pl – pseudoelastic strain at the plateau-shaped area. Resistivity changes a little during the cycling. Such behavior is a result of deformation hardening. At the stage of full strain returning after unloading the following hardening is absent; it is connected with initiation of reversible austenite – martensite transformation.

Plastic strain at cooling stage takes place already under thermocycling of shape memory alloys. The alloy did not accumulate defects during a heating. Full shape memory effect reversibility is an evidence of this.The paper deals with systematized data of fracture research during the process of different types of cycling deforming. Equations of linear regression showing results of the alloy low-cycle fatigue are represented here. Due to the results of measuring of electrical resistance togeather with mechanical characteristics, we have fixed the period of material critical state, after which the fracture evidently occurs.

Thermal diffusivity of porous Ni-Ti SMAs
C. Zanotti¹, A. Tuissi², P. Giuliani³, P. Bassani⁴, (1)Consiglio Nazionale delle Ricerche, Milano, Italy, (2)CNR IENI, LECCO, Italy, (3)CNR IENI Istituto per l'Energetica e le Interfasi, Milano, Italy, (4)CNR IENI Istituto per l'Energetica e le Interfasi, Lecco, Italy

Porous NiTi alloy were tested to define the thermal diffusivity dependence on temperature in the range from 300 up to 1300 K.
Samples were produced by combustion synthesis technique (diameter 8 mm) and characterized by different porosity values (30-68 %).
An  experimental-numerical approach, adopted for this scope, is described and the obtained results have been compared with the ones relevant a full dense NiTi alloy.
The experimental work is based on the capability to heat one side of the NiTi cylindrical sample by means of laser radiation and to record the temperature history at different positions along the sample.
Tests were featured by different heating rates, ranging from 2 to 120 K/s, and maximum temperature values of1 300 K at the heated side of the NiTi sample.
The experimental curves have been reproduced by numerical code assuming an uniform heating of one of the cylinder bases while the opposite end is supposed in contact with a massive ceramic holder. This makes reasonable the assumption of quasi one-dimensional heat transfer along the sample axis and reduced heat loss through the sample holder.
The mathematical model used is thus based on the 1D unsteady heat diffusion equation with additional terms accounting for energy losses by radiation and convection. The energy input is defined by the time-dependent surface temperature (experimentally detected) provided as a boundary condition at the heated surface.
The numerical  computations was observed to be in very good agreement with the experimental results and the obtained thermal diffusivity value showed a significant change during the phase transition that occurred during the martensitic transformation.

Apparatus for SMA transition temperatures measurement
Z. O. Jedlicka, Technical University of Ostrava, Ostrava, Czech Republic

An accurate measurement of a Shape Memory Alloy's (SMA) transition temperatures is necessary for the development of actuators.

The apparatus is used to obtain SMA transition temperatures associated with changes in alloy chemical composition, fabrication process and forming method. The apparatus consist of “pushrod dilatometer”, contact-less resistance measurement, heating/cooling unit and sample temperature measurement. Time/temperature dependence of tested sample can be used as thermal analysis, so three characteristics are sensed simultaneously. Temperature span of the measurement is from temperature of liquid nitrogen up to 473 K. Peltier cooling unit is used if so low negative temperature is not required.

There is little data directly correlating a material's thermal properties with its performance in an actuator, particularly for durations of thousands thermal cycles.

Material Characterization of Manufactured NiTi SMAs
S. Dilibal¹, N. Cansever², (1)Yeditepe University, Istanbul, Turkey, (2)Yildiz Technical University, Istanbul, Turkey

Shape memory alloys (SMAs) are successfully used for their great potential use as functional materials in many engineering and medical applications. The technological importance of shape memory alloys is coming from their shape memory effect (SME) and superelastic (SE) capability. SME and SE capability are due to martensitic transformation (MT), that is triggered by changing temperature and applied stress resulting in a transformation of the crystal structure from austenite parent phase to martensite phase.
In this study, commercially pure nickel and titanium are cast in vacuum arc and vacuum induction furnace, to produce equiatomic structure. After successful manufacturing, DSC and microscopically analysis was applied to alloys NiTi 12-3, NiTi 7-3, NiTi 4-3 and NiTi 3-2 for material characterization, to determine their transformation temperature and phase structure. Additionally, Vickers hardness and X-Ray diffraction phase analysis were performed and the shape memory capabilities of the alloys were studied with shape memory training experiments.
Among the produced nickel-titanium alloys, the one with highest shape memory capability is determined to be the one cast in zirconia crucible in three remelting castings, in 4mm.x4mm.x65mm dimensions, namely NiTi 12-3. EDS analysis showed the atomic percentage to be 50.10 % Ti and 49.90 % Ni. DSC analysis was done to find out the phase transformation temperatures.The optical micrograph observations have been carried out to illustrate
the variation of the microstructures in the same heating/cooling rate for each samples. The effects of annealing on the transformation behavior of
NiTi 12-3 shape memory alloy have been extensively studied and well characterized.

Relative grain size influence on the mechanical behavior in shape memory material in flexion test
J. Cortés-Pérez¹, F. N. García C.¹, G. González R.², A. Reyes S.¹, H. Flores Z.³, (1)Universidad Nacional Autónoma de México, Cd. Nezahaualcoyotl, Mexico, (2)Universidad Nacional Autónoma de México, D. F., Mexico, (3)Centro de Investigaciones en Materiales Avanzados, Chihuahua, Mexico

An experimental study on a Cu-Al-Be shape memory alloy in cantilever flexion arrangement is presented. The samples tested were thin plate of shape memory material polycristallynes with M_S near to -20^oC and a monocrystallyne sample with M_S near to -40 ^oC. The samples were instrumented with electrical strain gauges on top and they were subject to variable load and strain-load curves were plotted. The curves were employed to obtain the critical stress.

A polycrystalline sample was instrumented and tested and then it was cut in three samples to the wide thing. After, these samples were instrumented and tested also. 

The obtained results shown a hard variation in the critical stress for each sample; the three samples obtained of the pattern sample presented lower critical stress than the pattern. 

A results’ analysis showed that the Ms calculated with the critical stress correspond with good agreement with the Ms Measurement by DSC in the case of monocrystalline sample and it present major deviation in the case of pattern sample mentioned before.  

A relation between sample's wide-grain's size was found but don't correspond with the relation: sample's thickness-grain's size reported in the literature for polycristallyne subject to simple tension test. It is because the last relation was constant in pattern sample and the three samples obtained of him. The effect observed in the present work is due to grains constrain condition and could be the responsible of an effect reported in a previous papers.

Characterization of a New Precipitate Phase and its Effect on the Work Characteristics of a Near-Stoichiometric Ni30Pt20Ti50 High-Temperature Shape Memory Alloy
A. Garg¹, D. Gaydosh¹, R. D. Noebe¹, S. Padula II¹, G. S. Bigelow¹, D. Diercks², S. McMurray³, M. J. Kaufman⁴, P. Sarosi⁵, M. J. Mills⁵, (1)NASA Glenn Research Center, Cleveland, OH, (2)University of North Texas, Denton, TX, (3)Western Kentucky University, Bowling Green, KS, (4)Colorado School of Mines, Golden, CO, (5)The Ohio State University, Columbus, OH

A new phase observed in a nominal Ni₃₀Pt₂₀Ti₅₀ (at.%) high temperature shape memory alloy has been characterized using transmission electron microscopy and 3-D atom probe tomography.  This phase forms homogenously in the B2 austenite matrix by a nucleation and growth mechanism and results in a concomitant increase in the martensitic transformation temperature of the base alloy.  Although the structure of this phase typically contains a high density of faults making characterization difficult, it appears to be trigonal (-3m point group) with a_o~1.28 nm and c_o~1.4 nm.  Precipitation of this phase increases the microhardness of the alloy substantially over that of the solution-treated and quenched single-phase material.  The effect of precipitation strengthening on the work characteristics of the alloy has been explored through load-biased strain-temperature testing in the solution-treated condition and after aging at 500 ºC for times ranging from 1 to 256 hours.  Work output was found to increase in the aged alloy as a result of an increase in transformation strain, but was not very sensitive to aging time.  The amount of permanent deformation that occurred during thermal cycling under load was small but increased with increasing aging time and stress.  Nevertheless, the dimensional stability of the alloy at short aging times (1-4 hours) was still very good making it a potentially useful material for high-temperature actuator applications. 

On the Influence of Alloy Composition on the Microstructures, Workability and functional Stability of NiTiZr Shape Memory Alloys
J. Frenzel¹, L. Gerke², K. Neuking³, G. Eggeler³, (1)Ruhr University Bochum, Bochum, Germany, (2)Ruhr-Universitaet Bochum, Bochum, Germany, (3)Ruhr-University Bochum, Bochum, Germany

NiTiZr alloys provide a shape memory effect at high temperatures. While the costs for Zr are relatively low as compared to those of other elements (like Pt, Pd or Hf) which can be added to yield high phase transformation temperatures, the limited workability of NiTiZr represents a general drawback of this alloy system. In the present work, we show how microstructures, workability and functional stability of NiTiZr depend on the alloy composition. A variety of shape memory alloys (SMAs) on the basis of NiTiZr with various Zr and Ni levels was characterized by electron microscopy, compression testing and differential scanning calorimetry (DSC). It was found that higher Zr concentrations result in elevated transformation temperatures but also in strongly decomposed microstructures with brittle secondary phases. The Zr level strongly affects the ductility of the alloy. As a consequence, the benefit of elevated transformation temperatures has to be well balanced against a sufficient workability. The functional stability of the alloys was evaluated by thermal cycling. It was found that the stability of solution annealed NiTiZr SMAs is lower than in the case of binary NiTi but can be significantly improved by aging in Ni-rich alloys. In the present study, we identified one alloy composition which shows elevated phase transformation temperatures, an acceptable workability and a wide thermal hysteresis comparable to conventional NiTiNb SMAs. This alloy might by attractive for coupling devices which only require a small number of cycles.

Electrochemical reaction mechanism of nitinol in the amidosulphonic acid- formamide system
W. Miao, Y. Hu, Z. Feng, J. Wang, Z. Yuan, General Research Institute for Nonferrous Metals, Beijing, China

Cyclic voltammetry and polarization curves were used for a study of the electrochemical reaction mechanism of the NiTi alloy in the amidosulphonic acid-formamide system. The anodic polarization curves and the Tafel curves were obtained. The dynamical parameters of the NiTi alloy are: a�F5.6399,b�F0.7229,i₀�F1.5784×10^-8 A/cm²,nβ�F0.08. The results of cyclic voltammetry show that the NiTi alloy dissolves in the solution as an intermetallic instead of titanium and nickel separately, the anodic reaction of the NiTi alloy in the system belongs to an inreversible process, the anodic peak on the CV curve corresponds with an one step seven electrons oxidation process, and the anodic reaction is:  NiTi - 7e → Ti4⁺ + Ni3⁺. For Ni3⁺ is very instable in the acid solution, then a reduction process happens: Ni3⁺ + e → Ni2⁺.

Self accommodating microstructure of the B19 martensites in Ni-Ti-Cu alloys
M. Krishnan, Bhabha Atomic Research Centre, Mumbai, India

The microstructure of shape memory alloys is characterized by the self accommodating arrangement of martensite variants. While the self accommodating microstructures of the B19’ martensite in Ni-Ti alloys has been established to be the <111>_C 3-variant plate group, there is insufficient information regarding that of the orthorhombic B19 martensite found in Ni-Ti-Cu alloys. In this study, we investigated the martensitic microstructures in the Ni₄₁Ti₅₀Cu₉ alloy using transmission electron microscopy (TEM) and observed that the self accommodating arrangement consists of stacks of 3-variant plate groups. This paper examines the driving force for the formation of such unusual self accommodating plate groups on the basis of the crystallographic information provided by TEM.

High energy milling powder preparation of equiatomic Ni-Ti shape memory alloy
F. Ambrozio Filho, Centro Universitario da FEI, São Bernardo, Brazil

A 50Ni50Ti at % powder mixture, by using commercially pure elemental powders, was prepared by mechanical alloying in an Attritor with the following conditions: the milling speed and the ball charge were 1500 rpm and 10:1 respectively. No process control agent was used in the processing.  The milling time was 1,2,4,8 and 16h, under a nitrogen atmosphere at room temperature. After milling it was determined the particle size distribution to determine the effect of milling time on powder particle size, the phases by X-ray diffractions (XRD) and the powder morphology by scanning electron microscopy (SEM). The high energy milling promotes dissolution of Titanium in Nickel and continuous amorphization by increasing the milling time. The powders after milling were compacted and heat treated at heat treated at 500, 650 and 800°C under vacuum microstructural evolution was characterized by X-ray diffractions (XRD). Different phases were detected in the heat treated samples showing the effect of temperature treatment and heterogeneity in the alloy.

Wire drawing and functional characterization of thin NiTi wires
S. Armaboldi¹, P. Bassani², R. Casati¹, F. Passaretti¹, E. Villa³, A. Tuissi¹, (1)CNR IENI, LECCO, Italy, (2)CNR IENI Istituto per l'Energetica e le Interfasi, Lecco, Italy, (3)IENI, CNR, Lecco, Italy

NiTi shape memory alloy (SMA) shows unique properties, the so called “shape memory effect” (SME) and “superelasticity” (SE), which have been applied with success in several biomedical applications and many other devices; smart actuators or SE antennas among them. New applications, based on SMA properties could be developed by integrating low dimension SMA wires in fabric products. In this case very thin NiTi material, with controlled characteristics, is required for textile processing.
In this work an experimental drawing equipment was tested to manufacturing SE and SME NiTi wires with diameter down to 30 microns. Drawing procedures were optimized and the process parameters were correlated with the functional properties of NiTi products. Material characterization was carried out throughout DSC, DMA, Stress-Strain and SEM analyses.
This work was developed in the framework of AVALON Project an European Community project NMP2-CT-2005-515813-2

Development of wire drawing and surface treatment of NiTi shape memory alloys
L. K. Kabayama, W. M. M. Menezes, O. D. Rigo, J. Otubo, Instituto Tecnologico de Aeronautica, S. J. dos Campos, Brazil

Wires of NiTi shape memory alloys (SMA) are largely used in aerospace, robotics and biomedical applications and their performance depend upon the wire surface finishing. By its turn, in order to obtain a NiTi wire with good surface finishing a complex fabrication process is required. This work present the special wire drawing process developed to produce NiTi with good surface quality taking into account the impurity content such as carbon, wire surface treatment, intermediary annealing temperature etc.

Thermomechanical properties of porous NiTi alloy produced by SHS
P. Bassani¹, A. Tuissi², P. Giuliani³, C. Zanotti⁴, (1)CNR IENI Istituto per l'Energetica e le Interfasi, Lecco, Italy, (2)CNR IENI, LECCO, Italy, (3)CNR IENI Istituto per l'Energetica e le Interfasi, Milano, Italy, (4)Consiglio Nazionale delle Ricerche, Milano, Italy

Self-propagating High temperature Synthesis (SHS) was proposed as a suitable route for the production of porous NiTi alloys that show promising potential in biomedical applications.
Samples obtained from relatively large powders (<150 mm), with total porosity in the range 30-55%, were characterized mainly from a morphological point of view. Total porosity, as well as pore size, shape and distribution were analyzed.   Sample microstructure  was also investigated indicating that the main phase produced during the SHS reaction is Ti reach NiTi phase, as confirmed by DSC calorimetric analyses.
Moreover,  the present of secondary phases, suggested by the low transformation enthalpy, was confirmed by SEM observations. Infact, EDS microanalyses and EBSD mapping, helped in the identification of such secondary phases, such  as Ni3Ti, Ti2Niand Ti4Ni2Ox .
Other samples were successively produced starting from the same powders but introducing a different powder compression methodology and operating conditions. In this way, the obtained samples showed higher porosity featured by more uniform size, shape and distribution while from a micro-structural point of view no significant differences were observed. 
Mechanical compression tests were carried out at room temperature and selected sample also above Af in order to highlights the influence of pore shape and distribution. Results, obtained at room temperature, show that the mechanical properties decrease with the porosity augmentation.  For higher temperatures the sample presented a pseudoelastic behavior.
Dilatometric tests were performed on selected  porous samples and the results well indicated the martensite to austenite transformation at the same temperature showed by the DSC analysis.