Symposium B
State-of-the-art Research and Applications of Shape Memory Alloys

ABSTRACTS

Session B-1 - Materials and Materials Design

B-1:IL02  High temperature SMA
A. LUDWIG, Inst. für Werkstoffe / Werkstoffe der Mikrotechnik (ICFO/03/225), Fakultät für Maschinenbau & Materials Research, Dept. Ruhr-Universität Bochum, Bochum, Germany

For the discovery and optimization of high temperature shape memory alloys (HTSMAs, operating temperatures >100°C) combinatorial and high-throughput thin film experimentation methods as well as MEMS tools for parallel materials science experiments were applied. Binary and ternary HTSMA systems were deposited in the form of thin film materials libraries by combinatorial sputter deposition processes. The obtained materials libraries were measured by automated high-throughput characterization methods (EDX, temperature-dependent XRD, temperature-dependent resistivity) in order to correlate compositional data with structural and functional properties. The obtained results were visualized in the form of composition-processing-structure-function diagrams (functional phase diagrams). Results from the systems Ti-Ta-X, Ti-Ni-Au, and Au-Cu-Al will be discussed. Funding from DFG (Forschergruppe FOR 1766) is acknowledged.


B-1:IL03  Hierarchical Twin Microstructure and Consequence for High Mobility of Twin Boundaries
O. HECZKO, Institute of Physics, Academy of Science of the Czech Republic, Prague, Czech Republic; H. SEINER, Institute of Thermomechanics, Academy of Sciences of Czech Republic, Prague, Czech Republic; S. FAEHLER, IFW Dresden, Dresden, Germany

Extreme high mobility of twin boundaries lies in the heart of the existence of magnetic shape memory effect. However, the reason for this high twin mobility, not seen in other materials, is still elusive. We will present the recent finding about twin mobility and discuss the hierarchical structure found in modulated 10M martensite of Ni-Mn-Ga as a precondition for that. In monoclinic martensite structure there are three different twinning systems forming hierarchical twin arrangement from highly mobile macroscopic a-c twin boundaries via modulation or monoclinic twinning to fine a-b twin laminate on microscale. Moreover, the macroscopic twinning comes in two forms, Type I and II, which strongly differs in their mobility. In addition the modulation on atomic scale can be considered as regular nanotwinning. This modulation of martensite lattice was considered as a necessary condition for the extreme mobility but recent observation suggests that the modulation is not always necessary. In the end we will compare the mobility of twin boundaries in the bulk single crystal and epitaxial thin films having approximately the same compositions in order to obtain better insight to the subject.


B-1:IL04  Magnetic Shape Memory Effect in Non-Modulated Ni-Mn-Ga-based Martensite
A. SOZINOV, N. LANSKA, K. ULLAKKO, Lappeenranta University of Technology, Material Physics Laboratory, Savonlinna, Finland

In magnetic shape memory (MSM) alloys crystallographic orientations of low symmetry martensite lattice and easy magnetization direction can be changed by application of a magnetic field or an external stress. Ni-Mn-Ga alloy is the most studied and most common MSM material. Several kinds of martensitic phases have been found in non-stoichiometric Ni2MnGa alloys. Giant magnetic field-induced strain (MFIS) of approximately 6% for 10M and 10% for 14M martensite has been reported 15 years ago. It has been argued that modulation of 10M and 14M crystal structures are a crucial property for MFIS occurring in MSM materials because the giant MFIS was never observed in Ni-Mn-Ga martensite with non-modulated (NM) crystal structure. We have reported recently the observation of 12% MFIS in non-modulated Ni-Mn-Ga-Co-Cu alloy [1]. The twinning stress has been decreased considerably by Co and Cu additives, compared to ternary Ni-Mn-Ga alloys. We present review of recent experimental results connected with Ni-Mn-Ga-Co-Cu alloy development and discuss different models for lowering of the twinning stress in NM martensites.
[1] A. Sozinov, N. Lanska, A. Soroka, W. Zou. 12% magnetic field-induced strain in Ni-Mn-Ga-based non-modulated martensite. Appl. Phys. Lett. 102 (2013) 021902.


B-1:L05  Role of Interstitial Oxygen Atom on Martensitic Transformation of Ti-Nb Alloy
M. TAHARA, T. INAMURA, H. HOSODA, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan; H.Y. KIM, S. MIYAZAKI, University of Tsukuba, Tsukuba, Ibaraki, Japan

Ti-Nb base alloys have been developed as new Ni-free biomedical shape memory alloys. The martensitic transformation behavior of Ti-Nb base alloys is highly sensitive to the interstitial impurities such as oxygen and nitrogen. In this study, the effect of oxygen addition on the martensitic transformation behavior of Ti-20mol%Nb alloy was investigated by DSC, XRD and TEM. Oxygen atoms in the parent beta phase (bcc) generated the nanosized lattice modulation and suppressed the martensitic transformation. On the other hand, the oxygen atoms in alpha″ martensite phase (orthorhombic) increased the axial ratio b/a of alpha″ and reverse martensitic transformation temperatures. These results means that the alpha″ martensite was stabilized by oxygen atoms, owing to the relaxation of strain filed introduced by interstitial oxygen atoms. The role of oxygen atoms on the martensitic transformation behavior of Ti-Nb alloy will be discussed based on the interstitial sites of oxygen atoms in beta and alpha″ phases.


B-1:L06  Bulk and Surface Properties of Ti-Nb-based Superelastic Implant Materials
YU. ZHUKOVA, S. DUBINSKIY, V. SHEREMETYEV, YU. PUSTOV, M. FILONOV, M. PETRZHIK, S. PROKOSHKIN, National University of Science and Technology “MISiS”, Moscow, Russia; V. BRAILOVSKI, Ecole de technologie superieure, Montreal, Canada

Metastable Ti-Nb-based alloys are known as perspective materials for bone implants since they combine outstanding bulk biocompatibility, resulting from the use of safe constituent elements, with favorable mechanical behavior which can be adjusted to reduce the stress shielding in a bone-implant system. These alloys exhibit pronounced superelastic behavior if they are subjected to a specific thermomechanical treatment (TMT). The final stage of this TMT comprises annealing in the 500 to 600°C temperature range and results in the formation of substantial surface oxide films. The aim of the present study is to characterize the effect of TMT on the bulk (mechanical, functional) properties and the surface layer features. The TMT-processed Ti-22Nb-6X (X = Ta or Zr, at.%) alloys were subjected to XRD, SEM, TEM microstructure analyses, mechanical, profilometry, microindentation, scratch and tribological testing, combined with wetting angle, corrosion and electrochemical characterization in simulated biological solutions. The general trend is that the TMT-processed Ti-Nb-based alloys combine the favorable mechanical behavior with superior corrosion resistance in simulated human body media.

 
Session B-2 - Basic Phenomena and Theory

B-2:IL01  First-principles and Monte Carlo Studies of Magnetocaloric Effects 
P. ENTEL, University of Duisburg-Essen, Faculty of Physics and CENIDE, Duisburg, Germany

We have performed ab initio electronic structure calculations and Monte Carlo simulations of frustrated ferroic materials where complex magnetic configurations and chemical disorder lead to rich phase diagrams. With lowering of temperature, we find a ferromagnetic phase which transforms to an antiferromagnetic phase at the magnetostructural (martensitic) phase transition and to a cluster spin glass at still lower temperatures. The Heusler alloys Ni-(Co)-Mn-(Cr)-(Ga, Al, In, Sn, Sb) are of particular interest because of their large inverse magnetocaloric effect associated with the magnetostructural transition and the influence of Co/Cr doping. Besides spin glass features, strain glass behavior has been observed in Ni-Co-Mn-In. The numerical simulations allow a complete characterization of the frustrated ferroic materials including the Fe-Rh-Pd alloys.


B-2:IL02  Phase Diagrams and Physical Properties of Ferromagnetic Shape Memory Heusler Alloys
R.Y. UMETSU1, XIAO XU2, RYOSUKE KAINUMA2, 1Institute for Materials Research, Tohoku University, Japan; 2Department of Materials Science, Graduate School of Engineering, Tohoku University, Japan

In the ferromagnetic shape memory alloys of Ni-Mn-based Heusler alloys, magnetic and structural phase transformations occur at the same time, and they show a rich variety of physical properties, such as large magnetoresistance, superelasticity and large inverse magnetocaloric effects, and drastic change of the thermal transport properties. In fact, drastic change of the density of states around the fermi revel has also been reported from the results of the photoemission spectroscopic experiments. For clarifying the mechanism of the unique phenomena in the ferromagnetic shape memory alloys, it is important to understand the physical properties both in the parent and the martensite phases. We have established phase diagrams for Ni-Mn-Z (Z = In, Sn, Sb and Ga) alloy systems and investigated their magnetic properties in wide composition range. In the presentation, magnetic properties approached by various methods, such as Mössbauer spectroscopy, ac magnetic measurements, neutron diffraction and x-ray magnetic circular dichroism, for the Ni-Mn-Z alloys will be introduced. In addition, results of low-temperature specific heat measurements in order to evaluate the electronic specific heat coefficient and the Debye temperature are presented.


B-2:IL03  Magnetic Shape Memory Materials: Martensitic Structures and Transformation Behaviour
L. RIGHI, Department of Chemistry, University of Parma, Parma, Italy; A. CAKIR, M. ACET, Faculty of Physics and Center for Nanointegration (CENIDE), Universitaet Duisburg-Essen, Duisburg, Germany; S. FABBRICI, F. ALBERTINI, IMEM-CNR, Parma, Italy

The present study summarizes the results obtained by the extensive investigation of martensitic transformations in different Ni-based Heusler alloys. In Ni-Mn-Ga ferromagnetic shape memory alloys the martensitic phases can typically assume different types of crystal structures depending upon composition and experimental conditions (temperature or mechanic loads). It is possible to recognize three different families of crystal structures labeled NM with tetragonal symmetry, 5M and 7M both showing lattice distortions combined with structural displacive modulation. The thermal stability and related crystal structures of such low-symmetry phases are tunable by tiny changes of the chemical composition. It is well known that the thermal stability of different martensitic phases is related to the e/a parameter. The detailed structural investigation accounts the complex interplay of a series of structural elements, apart from e/a level, contributing to the stabilization of martensitic phase and the selection of the corresponding crystal structure. In particular, the qualitative determination of the global volume change for the single lattice site showing mixed occupancy in off-stoichiometric alloys indicates the presence of local distortions responsible of martensitic transformation.


B-2:IL04  Magnetic Shape Memory Alloys: Lattice and Volume Instabilities
V.A. CHERNENKO, BCMaterials & University of Basque Country (UPV/EHU), Bilbao, Spain; and Ikerbasque, Basque Foundation for Science, Bilbao, Spain

The Heusler-type off-stoichiometric magnetic shape memory alloys (MSMAs) demonstrate the lattice spontaneous shear and volume instabilities resulting in the martensitic transformation (MT) giving rise to the extraordinary actuation abilities: a huge reversible deformation can be obtained under magnetic field, mechanical stress, temperature change or their combinations. In addition, the instability of the magnetic subsystem characterized by a complex interplay between ferro- and antiferromagnetic interactions is considered as the driving mechanisms of the inverse magnetocaloric effect in the so-called metamagnetic SMAs. The following aspects of transformation behavior and magnetoelasticity of MSMAs will be considered. (i) The nature of large non-hysteretic deformation of ferromagnetic Fe3Pt, Ni-Fe(Co)-Ga and Ni-Mn-Ga alloys. (ii) The influence of volume magnetostriction on the elastic and thermodynamic properties of ferromagnetic SMAs. (iii) The comparative analysis of the magnetic field induced magnetovolume and axial stresses on the stress-strain behavior of different MMSMAs. (iv) The role of the transformation volume change in the magnetocaloric effect. (v) Inverse elastocaloric effects in the MMSMAs ribbons.


B-2:IL05  Avalanche Criticality in Martenitic Transformations: An Acoustic Emission Study
A. PLANES, Departament d'Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Barcelona, Catalonia, Spain

In martensitic transitions, acoustic emission originates from local and sudden changes of the displacement field across the propagating interfaces. Acoustic emission reveals the jerky character of the dissipation of the elastic energy excess and establishes that the transition occurs through avalanches. In my talk I will show that the statistical analysis of the energy and duration of acoustic emission signals, and waiting times between signals reveal power law statistics over several decades which indicate the absence of length, energy and time scales during the transition and proves that martensitic transitions follow avalanche criticality. This behaviour will be illustrated with examples for non-magnetic and magnetic shape-memory alloys under selected external conditions. From these results I will conclude that avalanche criticality is characterized by exponents that mainly depend on the driving mechanism and on the change of symmetry at the transition expressed by variant multiplicity.


B-2:L06  High Mobility of Twin Interfaces in Ni-Mn-Ga at Ultrasonic Frequencies
H. SEINER, P. SEDLAK, M. LANDA, Institute of Thermomechanics, Czech Academy of Sciences, Prague, Czech Republic; V. KOPECKY, O. HECZKO, Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic

Laser-based resonant ultrasound spectroscopy (RUS) is applied to analyze vibrational properties of twinned samples of Ni-Mn-Ga 5M martensite. It is observed that the mechanical vibrations of these samples at the frequencies of the order of 100 kHz exhibit significant nonlinearity, which can be attributed to viscous motion of Type 2 interfaces in this alloy. A detailed theoretical analysis of the nonlinearity enables a construction of a dynamic stress-strain curve of the twinned material; this curve exhibits pronounced softening characteristics indicating the activity of the twin interfaces. The results prove that these interfaces retain their high mobility (i.e. low twinning stress) known from the quasi-static experiments even in the ultrasonic frequency range. In addition, the evolution of this high-frequency mobility of the interfaces is studied in the vicinity of the transition temperature: it is observed that while some of the elastic constants change dramatically in this temperature range (probably due to precursor phonon softening), the parameters of the nonlinearity of the vibrations exhibit only weak temperature dependences. This is, again, in agreement with very weak sensitivity of the mobility of Type 2 interfaces to temperature known from the quasi-static case.


B-2:L07  Elastic Anisotropy of Polycrystalline Martensite of NiTi-based Alloys
P. SEDLAK, M. THOMASOVA, H. SEINER, M. FROST, M. SEVCIK, M. LANDA, Institute of Thermomechanics of the CAS, Prague, Czech Republic

Several studies of strong elastic anisotropy of single crystals of both austenitic and martensitic phases of shape memory alloys have been reported in literature, but for theoretical and practical reasons it is also interesting to examine elasticity of polycrystalline samples used usually in SMA applications. In the present contribution, the laser-based resonant ultrasound spectroscopy complemented by ultrasonic pulse-echo measurements is applied to characterize the evolution of the full elastic tensor of martensite in polycrystalline NiTi and NiTiCu during stress-induced reorientation. Results show that in comparison to weak elastic anisotropy of polycrystalline austenite given by sample texture and weak anisotropy of temperature induced martensite, the anisotropy of stress-oriented martensite is huge and comparable to large anisotropy of martensite single crystals. Based on these results, a simple, heuristic algorithm which allows to unambiguously determine the elastic tensor of martensite from the undergone loading path was proposed and implemented to the constitutive model of NiTi.


B-2:L08  Isothermal B2 - B19’ Martensitic Yransformation in TiNi-based Shape Memory Alloy 
N. RESNINA, S. BELYAEV, Saint Petersburg State University, Saint Petersburg, Russia; A. SHELYAKOV, National Research Nuclear University “MEPhI” (Moscow Engineering Physics Institute), Moscow, Russia

The aim of the present work is a study of B2-B19' martensitic transformation under isothermal condition in TiNi-based alloy. The calorimetric data have shown that the forward transformation from cubic B2 phase to monoclinic B19’ phase occurs at a constant temperature that is higher than the start temperature of the forward martensitic transformation found during continuous cooling. The dependences of the alloy volume that underwent the transformation under isothermal condition on the holding temperature and time are found. The results obtained show that 70 % of the alloy may transform from the B2 phase to the B19’ phase under isothermal conditions before the Ms temperature. It is assumed that the nature of the observed phenomenon is due to quasi-static strain nanodomains forming in the studied alloy before the forward martensitic transformation on cooling. It results in an accumulation of elastic energy that prevents the forward martensitic transformation. This energy may decrease during holding at a constant temperature due to some relaxation processes, for instance, by reorientation of nanodomain structure. In this case, the thermodynamic condition for the forward martensitic transformation are fulfilled and as a result, the B19' phase appears at constant temperature


B-2:L10  Elasticity of Fe-Pd Single Crystals Under Unidirectional Prestress
M. LANDA, P. STOKLASOVÁ, H. SEINER, P. SEDLÁK, M. JANOVSKÁ, Institute of Thermomechanics, Czech Academy of Sciences, Prague, Czech Republic; T. FUKUDA, T. YAMAGUCHI, T. KAKESHITA, Dept. of Materials Science and Engineering, Graduate School of Eng., Osaka University, Suita, Osaka, Japan

We study the evolution of the second-order elastic constants of an iron-palladium FSMA single crystal (Fe-31at.%Pd) in the parent cubic phase under unidirectional prestress. In particular, the velocities of surface acoustic waves (SAWs) and bulk acoustic waves are measured for the compressive prestress ranging from zero to 200 MPa, which corresponds to compressive axial strains up to 4.3%. The ultrasonic datasets are then recalculated into full tensors of elastic constants, changing from cubic elasticity in the stress-free state to strongly tetragonal elasticity at 200MPa. It is observed that the shear moduli along the (110) austenite planes exhibit further softening with the prestress, which leads to an increase of the anisotropy up to A=52. Simultaneously, the soft acoustic phonon branches are stiffening, which indicates the stabilization of the lattice against the transition to fct martensite. The results are compared to behaviours of other SMAs (Cu-Al-Ni and Cu-Zn-Al) for which the softening of the corresponding phonon branches was observed, and discussed with respect to the ability of the Fe-Pd parent phase to exhibit large, non-hysteretic, elastic-like strains.


B-2:IL11  The Magnetovolume Transition of LaFe11.8Si1.2 as a Model System to Understand the Influence of Volume Expansion on Hysteresis During First Order Phase Transitions
A. WASKE1, A. FUNK1, B. WEISE1, A. RACK2, S. FÄHLER1, 1IFW Dresden, Germany, 2ESRF Grenoble, France

Understanding and reducing hysteresis is a key question for both shape memory alloys and magnetocaloric materials. A common criterion for low hysteresis during martensitic transformations is that the middle eigenvalue of the transformation matrix is close to one. However, also the change of volume during a first order transformation must be considered. As a model system to understand the consequences of a volume change alone we selected the magnetocaloric La(Fe,Si)13 system, which exhibits an isostructural first order transformation, without changing crystal symmetry but with a large volume change of 1.5 %. We apply low-temperature in-situ computed tomography and X-ray diffraction on magnetocaloric La(Fe,Si)13 to study the magnetovolume transition as a function of temperature. The in-situ experiments have been carried out at the beamline ID 19 at the ESRF in Grenoble and the PETRA III beamline 2.1 in Hamburg, respectively. Using these techniques, we i) clarify the effect of the volume change on both heating and cooling transition, ii) connect the observed virgin effect to changes in the microstructure and iii) find a strong dependence of nucleation and growth of the ferromagnetic phase on the surface morphology of the material.


B-2:L12  Localization of Phase Transformation in NiTi Shape Memory Alloy Studied by the Finite Element Method Employing a Nonlocal Averaging Technique
M. FROST, P. SEDLAK, Institute of Thermomechanics, CAS, Prague, Czech Republic; P. SEDMAK, L. HELLER, P. SITTNER, Institute of Physics, CAS, Prague, Czech Republic

Martensitic phase transformation in NiTi shape memory alloys (SMA) can spread either homogenously or in localized shear bands. Shear band propagation often occurs in particular loading modes (tension) and geometries of specimen (wire, thin ribbon). In-situ observation of temperature changes or surface deformation during the transformation brings partial information on the morphology of the shear band. However, it is more difficult to determine experimentally the internal state of the material (phase fraction or stress distribution) inside the specimen. Continuum mechanics-based modeling can provide such information. In this work, a well established NiTi SMA constitutive model is enhanced to account for softening of the material response during the phase transition (i.e. stress needed for further promotion of the transformation decreases with increasing strain). The characteristic length parameter is introduced and a nonlocal integral averaging technique is adopted in the finite element implementation of the model so that well-posedness of the problem is recovered. Then, we study morphology of localization patterns in some geometries and compare them to experimental data. Our simulations reveal inhomogenous stress distribution within the specimens undergoing simple tensile loading.

 
Session B-3 - Functional Properties

B-3:IL01  Caloric and Multicaloric Effects in Ferroic and Multiferroic Materials
L. MANOSA, Dept. ECM. Facultat de Física. Universitat de Barcelona, Barcelona, Spain

A caloric effect refers to the isothermal entropy or to the adiabatic temperature changes experienced by a material when subjected to the application of an external field. These effects are enhanced in the vicinity of a phase transition and to date several caloric effects have been reported (mangetocaloric, electrocaloric, barocaloric and elastocaloric) depending on the nature of the order parameter and of its conjugated external field [1,2]. Many caloric materials posses a strong coupling between different degrees of freedom, and they may also be sensitive to fields not conjugated to the order parameter. Such a cross-response opens-up the possibility of tuning the phase transition by a variety of external stimuli giving rise to a variety of caloric effects in a single material. A multicaloric effect refers to the case when more than one type of caloric effect is driven simultaneously or sequentially in a single sample [2]. In my talk I will report on recent experiments which provide experimental evidences for multicaloric effects in materials with first-order magnetostructural phase transitions.  References: [1] L. Mañosa et al. J. Mater. Chem. A 1 (2013) 4925. [2] X. Moya et al. Nature Mater. 13 (2014) 440.


B-3:IL02  Heusler Alloys for Solid State Refrigeration
O. GUTFLEISCH, T. GOTTSCHALL, S. ENER, K. SKOKOV, TU Darmstadt, Materialwissenschaft, Darmstadt, Germany

Magnetocaloric materials based on LaFeSi-, Heusler- and Fe2P-type compounds are the most promising amongst many candidates to be utilized in magnetic refrigeration. All three systems show some specifics in terms of synthesis, efficiency, cyclability and sustainability. Heusler alloys are fascinating as their multifunctional nature can provide pathways to at least minimize if not eliminate hysteresis. Hysteresis is typical for first-order magnetostructural transitions and detrimental to the cooling cycle. The MCE properties of NiMnInCo compounds are investigated, and intrinsic and extrinsic contributions to hysteresis are analyzed. We find a high irreversible adiabatic temperature change of −8 K in a magnetic field change of 1.95 T. Due to the large thermal hysteresis of 10 K, this high ΔTad cannot be maintained upon cycling. However, the reversible MCE amounts to −3 K when using inner magnetization loops, in which martensite and austenite coexist. Different magnetic field sweeping rates reveal the dynamic features of the martensitic transformation, relevant when discussing non quasi-static application conditions. These results are put into a broader context when in a MCE material´s library the (cyclic) adiabatic temperature of large number of candidate materials is compared.


B-3:L03  Magnetostructural Coupling and Magnetocaloric Effect in Ni-Mn-Ga-Cu Microwires
X.X. ZHANG, M.F. QIAN, H.H. ZHANG, L. GENG, J.F. SUN, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, China

Ni-Mn-Ga-X microwires were successfully produced by melt-extraction technique on a large scale. Their shape memory effect, superelasticity and damping capacity have been demonstrated. Here, the excellent magnetocaloric effect was revealed in Ni-Mn-Ga-Cu microwires produced by melt-extraction and subsequent annealing. The overlap of the martensitic and magnetic transformation, i.e. magnetostructural coupling, was achieved in the annealed microwires. The magnetostructural coupling and wide martensitic transformation temperature range contribute to a large magnetic entropy change of -8.3 J.kg-1×K-1 with a wide working temperature interval of ~13 K under a magnetic field of 50000 Oe. Accordingly, a high refrigeration capacity of ~78 J×kg-1 was produced in the annealed microwires.


B-3:IL04  Elastocaloric Effect in an Iron-Palladium Shape Memory Alloy
TOMOYUKI KAKESHITA, FEI XIAO, TAKASHI FUKUDA, Osaka University, Suita, Osaka, Japan

A disordered Iron-palladium alloy containing palladium content of 31.2 at% exhibit a weak first order martensitic transformation from a cubic structure (FCT) to a tetragonal structure (FCT) at 230 K (=T0). Since the transformation is associated with a significant softening of the elastic constant C’, the elastic strain caused by a compressive stress applied in the [001] direction depends strongly on temperature. Therefore, considering the Maxwell relation for thermodynamics, we can expect a large isothermal entropy change and adiabatic temperature change (elastocaloric effect) by the application and removal of the external stress. In fact, we confirmed a large temperature change of more than 1.5 K in a wide temperature range of between 175 K (< T0) and 335 K (> T0) by applying compressive stress of 200 MPa in the [001] direction. The refrigeration capacity calculated in this temperature range is 5 MJ/m3.


B-3:IL05  Functional Fatigue of Elastocaloric NiTiCu-based Thin Films
C. CHLUBA1, WENWEI GE2, R. LIMA DE MIRANDA1, J. STROBEL1, L. KIENLE1, M. WUTTIG2, E. QUANDT1, 1Institute for Materials Science, Faculty of Engineering, University of Kiel, Germany; 2Department of Materials Science and Engineering, University of Maryland, USA

Caloric materials have the potential to serve as an environmentally friendly and more efficient alternative substitute in conventional vapor compression cooling. The principle of ferroic cooling is based on a solid state phase transformation initiated by an external field, in the case of elastocalorics by an external stress field. Combined with thin film processes this technology enables the development of small scale cooling devices required for mobile applications. Up to now, the major obstacle for the implementation of elastocaloric materials in cooling devices are the functional degradation and structural failure of the material. To investigate the underlying microstructural mechanisms TEM and synchrotron analyses of NiTiCu- based thin films are conducted in the pristine state and after superelastic cycling. A strong difference of superelastic degradation for Ti-rich compositions compared to near equiatomic compositions is found. While near equiatomic compositions already degrade severely during the first cycles, Ti-rich compositions are functionally stable for 107 full superelastic cycles (1). Using stress dependent in situ synchrotron investigations the change of lattice constants of B2 phase and stress induced B19 phase during the superelastic transformation can be quantified. This measurement enables the compatibility calculation of austenite and martensite phases which is known to have a strong influence on the superelastic hysteresis and the thermally induced transformation stability. The microstructural influences of grain size, precipitates and crystallographic compatibility on the functional degradation of NiTiCu-based thin films will be discussed.
(1) Chluba, C.; Ge, W.; Lima de Miranda, R.; Strobel, J.; Kienle, L.; Quandt, E.; Wuttig, M.: Ultralow-fatigue shape memory alloy films, Science, 348 (2015), 1004-1007.


B-3:L06  Effects of Pseudoelastic Cycling under Different Temperatures on Physical and Mechanical Properties of a NiTi Alloy
M.C.M. RODRIGUES, G.C. SOARES, V.T.L. BUONO, L.A. SANTOS, Department of Metallurgical and Materials Engineering, Universidade Federal de Minas Gerais, Belo Horizonte-MG, Brazil 

The effects of pseudoelastic cycling at different temperatures on physical and mechanical properties of a superelastic NiTi wire were investigated by uniaxial tensile testing. A universal testing machine with an attached heating chamber was used to cycle the wires. The number of cycles was established as 20. The samples were cyclically deformed up to 6% strain at different temperatures: 25, 40, 55, 70, 85, and 100 °C. The effects of the pseudoelastic cycles on the physical properties were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Three-point bending and flexural fatigue tests were performed to analyze the influence of the pseudoelastic cycles on the mechanical behavior of the NiTi wire. It was found that increasing the test temperature promotes the hysteresis stability in fewer cycles. XRD patterns showed that the intensity of austenite peaks increased with the test temperature, what may indicate the recovery of defects and residual stresses in the structure during cycles at higher temperatures. No significant changes were detected in the transformation temperatures measured by DSC. Flexibility and fatigue life were increased after cycling at different temperatures.


B-3:IL07  Mechanical Behaviour, Shape Memory Effect and Micro-structures of Ti-based Shape Memory Alloys
SHUICHI MIYAZAKI, HEE YOUNG KIM, Division of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, Japan

The beta Titanium alloys exhibit shape memory effect, superelasticity, low Young’s modulus, high strength, non-linear large elastic deformation, Inver behavior, etc. These unique properties are closely related with the martensitic transformation, microstructure and added interstitial atoms. The martensitic transformation of beta Titanium alloys occurs between the parent beta phase and the alpha” martensite. Interstitial atoms such as oxygen and nitrogen strongly affect the martensitic transformation. Lattice distortion around an oxygen tends to the martensite phase structure, but is suppressed to form a nano-domain which is an intermediate state from the beta to the alpha”. There are 6 nano-domain variants similarly to the martensite variants. The most favorable nano-domain variant grows and changes its lattice constants by stressing or cooling under stress. These characteristics of the nano-domain cause the unique properties of Gum metals: nonlinear large elastic deformation and Invar behavior. Another unique phenomenon, heating-induced martensitic transformation, appears at high temperatures where oxygen moves easily. These topics of the beta Titanium alloys will be reviewed.


B-3:IL08  Surface Modification of NiTi Shape Memory Alloy by Hafnium Ion Implantation
YAN LI, T.T. ZHAO, School of Materials Science and Engineering, Beihang University, Beijing, China

NiTi shape memory alloy was modified by Hf ion implantation to improve its mechanical properties, corrosion resistance and biocomparability. The auger electron spectroscopy and x-ray photoelectron spectroscopy results indicated that the oxide thickness of NiTi alloy was increased by the formation of TiO2/HfO2 nanofilm on the surface. The lower coefficient of friction with much longer fretting time indicated the remarkable improvement of wear resistance. Moreover, Hf implanted NiTi exhibited larger pseudoelastic recovery strain and retained better surface integrity even after being strained to 10%. Potentiodynamic polarization tests displayed that the corrosion resistance of NiTi alloys was significantly improved by Hf ion implantaiton. The Ni ion release rate was remarkably decreased during 60 days immersion in 0.9NaCl. The water contact angle increased and surface energy decreased after Hf implantation. Hf implanted NiTi expressed enhanced osteoblasts adhesion and proliferation, especially after 7 days culture. Platelets adhesion and activation were suppressed significantly and the hemolysis rate was decreased by at least 57%. The improved biocomparability can be ascribed to the modified surface composition and morphology and decreased surface energy by Hf ion implantation.


B-3:L09  Thermo-mechanical Properties of NiTi Alloy after High Strain Rate Tension and COMPRESSION
V. GRIGORIEVA, E. OSTROPIKO, A. RAZOV, Saint-Petersburg State University, Saint-Petersburg, Russia; A. MOTORIN, Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, Saint-Petersburg, Russia

The results of the comparative study of a near equiatomic NiTi alloy’s thermo-mechanical response to high strain rate (103s-1) and quasi-static (10-3s-1) tension and compression in the temperature range of 20–300 °C are considered. The existence of B2-B19' and B2-R-B19' martensitic transformations, associated with the Ni4Ti3 precipitates heterogeneous distribution is shown to result in appearance of martensitic and austenitic two-way shape memory effects, the simultaneous presence of which leads to the formation of the reversing two-way shape memory effect. It was found that the shape memory effect after the high-strain-rate loading at different temperatures up to 10-25% residual strain is less than after quasi-static loading.


B-3:L09b  Influence of Softening on Martensitic Transformation During Ti50Ni50 Alloy Thermal Cycling
A. SIBIREV, S. BELYAEV, N. RESNINA, Saint-Petersburg State University, Saint-Petersburg, Russia

The aim of the present study was to investigate the influence of softening on variation in martensitic transformations parameters. As the softening was controlled by the maximum temperature attained during thermal cycling then, the influence of this parameter on the variation in transformation temperatures and defect density was studied. The value of maximum temperature was varied in range of 120 to 220 °C. It was found that the higher maximum temperature, the less a change in transformation temperatures and in defect density during thermal cycling. To find the softening phenomenon kinetics, the samples preliminary subjected to thermal cycling were hold at a constant temperature from 120 to 240 °C. During holding variations in physics properties such as resistivity and heat flow were studied. After holding, the sample was subjected to one thermal cycle to find the influence of holding on a variation in martensitic transformation parameters. The higher the holding temperature and larger the duration the less change in transformation temperatures and defect density were found.
 

B-3:IL11  Microstructural Evaluation of NiMnGa Ferromagnetic Shape Memory Alloy Particles Embedded in Polymer Using X-ray Computed Tomography
H. HOSODA, H. KAWABE, P. SRATONGON, T. INAMURA, Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama, Japan; V.A. CHERNENKO, BCMaterials & Dpto de Electricidad y Electronica, Universidad del Pais Vasco UPV/EHU, Bilbao, Spain, Ikerbasque, Basque Foundation for Science, Bilbao, Spain

NiMnGa single crystals are novel high-frequency actuator materials. The magnetic-field-induced twin-boundary motion effect as a reason of large strains was shown to persist down to microscale whereby facilitating a design of new materials, such as composites. A short overview of NiMnGa single-crystal-like particles and polymer matrix composites will be presented. The particles can be easily produced by a mechanical crush utilizing fact of the intrinsic grain boundary brittleness by Bi addition. This processing implies intergranular crush ensuring mobility of the interfaces in the particles under magnetic field. The composites were fabricated by mixing the NiMnGa particles with a polymer followed by the curing under magnetic field. Recently, we have established a method for three-dimensional microstructural observation under magnetic field and/or mechanical stress combined with an evaluation of micrometer-level deformation of individual particle using nano-focused X-ray computed tomography, and the latest achievements will be presented.
This work is supported by Grant-in-Aid of Scientific Research Kiban S26220907 from Japan Society for the Promotion of Science, and VC is also grateful to JSPS for financial support of his visit Tokyo Institute of Technology.


B-3:L12  Superelasticity and Shape Memory Effect in Laser Welded NiTi Shape Memory Alloys
J.P. OLIVEIRA, F.M. BRAZ FERNANDES, CENIMAT/I3N, Faculdade de Ciência e Tecnologias, Universidade Nova de Lisboa, Portugal; R.M. MIRANDA, UNIDEMI, Faculdade de Ciência e Tecnologias, Universidade Nova de Lisboa, Portugal

Joining of NiTi shape memory alloys is of great interest as it allows increasing flexibility for different applications in the biomedical, aerospace or civil engineering industries. However, for taking advantage of the functional properties of NiTi (superelasticity and shape memory effect) it is mandatory to preserve them after the joining process. In this work, similar NiTi butt joints were produced using a Nd:YAG laser. Superelasticity was assessed by means of cycling behavior at high strains (total of 600 cycles up to 10% strain) without rupture of the joints. The shape memory effect was found to be preserved after welding and even after the mechanical cycling tests. Microstructural characterization performed using X-ray synchrotron radiation allowed to understand the singularities of the functional properties exhibited by these laser welded NiTi joints. Due to the preservation of both superelasticity and shape memory effect after joining, it is apparent that laser welding is a suitable and promising welding technique for industrial applications involving joining of NiTi to itself or to other materials.


B-3:L13  Functional Degradation in Novel Shape Memory Alloys: On the Role of Dislocation Formation and Diffusion During Thermomechanical Cycling
P. KROOSS1, M. VOLLMER1, P.M. KADLETZ2, C. SOMSEN3, Y.I. CHUMLYAKOV4,  H.J. MAIER5, T. NIENDORF6, 1Institut für Werkstofftechnik, TU Bergakademie Freiberg, Freiberg, Germany; 2Applied Crystallography, Dept. of Earth and Environmental Sciences, Ludwig Maximilians Universität, Munich, Germany; 3Institut für Werkstoffe, Ruhr-Universität Bochum, Bochum, Germany; 4Tomsk State University, Siberian Physical Technical Institute, Tomsk, Russia; 5Institut für Werkstoffkunde, Leibniz Universität Hannover, Garbsen, Germany; 6Institut für Werkstofftechnik, Metallische Werkstoffe, Universität Kassel, Kassel, Germany 

Shape memory alloys (SMAs) attract a lot of attention due to their unique properties since decades. Conventional SMAs, such as Ni-Ti alloys, often lose their functional properties at about 100 °C and/or are high in processing costs. To overcome current limitations and widen the fields of application, novel alloy systems, i.e. high-temperature (HT-) SMAs for applications at temperatures well above 100 °C and Fe- based alloy systems allowing for cost efficient processing, have been developed recently. HT-SMAs, such as Ti-Ta-Al and Co-Ni-Ga show good functional properties at elevated temperatures. Fe‑Ni‑Co‑Al‑X (X=Ta, Ti, Nb) as well as Fe-Mn-Al-Ni are characterized by low processing cost and high transformation strains. Cyclic stability of all these alloys is crucial for an intended industrial application. However, data reporting on functional degradation are rare. In order to close this gap, the current study characterizes and discusses the elementary degradation mechanisms in different alloys revealing a complex interplay between dislocation activity, formation of secondary phases and changes in the degree of chemical order. The actuation response under different stress states as well as the evolution of the pseudoelastic response at different temperatures were characterized for novel SMAs, amongst others by in-situ techniques. Detailed microstructure analyses were performed using electron-microscopy and neutron diffraction.


B-3:L14  Functional Properties and Structure of Ti-Ni SMA After Multi-Axial Isothermal Quasi-continuous Deformation
I.YU. KHMELEVSKAYA1, V.S. KOMAROV1, R. KAWALLA2, S.D. PROKOSHKIN1, G. KORPALA2, 1NUST“MISIS”, Moscow, Russia; 2Freiberg University of Technology and Mining, Germany

Severe plastic deformation (SPD) of Ti-50.2 at.%Ni alloy was carried out using the multi-axial deformation Max-Strain module of Gleeble system at 400, 370, 350, 330°C with accumulated true strain from e=3.5 to 9.5. Kinetics of martensitic transformations was studied by DSC method, the structure features using X-ray and TEM. The recoverable strain was studied using a bending mode for strain inducing. A mixed nanocrystalline and nanosubgrained structure with average grain/subgrain size below 100 nm has been formed as a result of SPD at as low as 330°C. Lowering of the deformation temperature from 370oC to 330oC with increasing of accumulated strain from 4.5 to 9.5 leads to a refinement of the structural elements and formation of mixed nanosubgraine and nanocrystalline structure with high dislocation density and average grain/subgrain size of 85 nm after deformation at the lowest temperature with the highest strain. The nanostructure resulting from Max-Strain deformation of e=9.5 allows obtaining a very high completely recoverable strain, er 1max = 9.3%, and a maximum recoverable strain ermax = 10 -11% with shape recovery rate of 80%, which is comparable with the best performance characteristics attained for equiatomic Ti-Ni alloys.


B-3:L15  A Large Elastic Deformation of a Partly Ordered Iron-Platinum Shape Memory Alloy
T. YAMAGUCHI, T. FUKUDA, T. KAKESHITA, Osaka University, Suita, Osaka, Japan

A partly ordered (S = 0.75) Fe3Pt alloy exhibits a second-order-like martensitic transformation from an L12-type cubic structure to an L60-type tetragonal structure at 90 K. This transformation is caused by the band Jahn-Teller effect and associated with softening of the elastic constant C'. We have investigated elastic behaviors of this alloy by mechanical tests and neutron diffraction using single crystals. As a result, we found that the alloy exhibits a large elastic strain of more than 6% when compressive stress is applied in the [001] direction near the transformation temperature. We also found that the Young's modulus decreases linearly on approaching the transformation temperature. It also decreases significantly as the elastic strain increases.

 
Session B-4 - Thin Films and Micro Nano-systems

B-4:IL01  Elastocaloric Microcooling: From Basic Effects to Miniature Cooling Devices
M. KOHL1, H. OSSMER1, C. CHLUBA2, E. QUANDT2, 1Karlsruhe Institute of Technology, IMT, Karlsruhe, Germany; 2University of Kiel, IMS, Kiel, Germany

Shape memory alloys (SMAs) undergoing a stress-induced first-order phase transformation exhibit a large entropy change, which is highly attractive for cooling applications. Elastocaloric cooling in film devices is expected to enable fast heat transfer, high cycling frequencies as well as tunable temperature change. Major challenges in this research are the effect size and long-term fatigue properties. Local strain and temperature profiles of pseudoelastic TiNi-based films and foils of 20 μm thickness are investigated during tensile load cycling with respect to strain, strain-rate and cycle number by in-situ infrared digital image correlation and infrared thermography. The investigation is complemented by finite element simulations using a thermodynamics-based model. Main features of the elastocaloric effect can be understood in terms of the local effects of mesoscale stress and temperature fields on the kinetics of phase transformation. Results on novel quaternary TiNiCuCo films are presented showing negligible functional fatigue over millions of load cycles. A first generation of miniature cooling devices is presented showing a cooling power of about 50 mW. The coefficient of performance (COP) is 2.8 on the device level, whereas the theoretical COP of the material is 10.5.


B-4:IL02  Multicaloric Effects in Mn-Ga-Co Films on Ferroelectric Substrates
B. SCHLEICHER1,2, R. NIEMANN1,2, S. SCHWABE1, A. DIESTEL1, A. WASKE1, R. HÜHNE1, P. WALTER3,4, L. SCHULTZ1,2, S. FÄHLER1,2, 1IFW Dresden, Dresden, Germany; 2TU Dresden, Institute for Solid State Physics, Dresden, Germany; 3Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany; 42nd Institute of Physics B and JARA-FIT, RWTH Aachen University, Aachen, Germany

One of the today’s challenges is a more efficient use of energy in general and in particular industrial and private cooling applications offer a large potential for improvement. For this issue various solid-state cooling cycles had been proposed, which rely on magnetocaloric, electrocaloric or elastocaloric effects. Giant caloric effects are observed in these ferroic material in vicinity of a first order phase transition. A drawback, however, is the narrow usable temperature range. In order to tune the transition temperature we present multicaloric heterostructures consisting of magnetocaloric Ni-Co-Mn-Ga epitaxial films on a ferroelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMN-PT) substrates. Applying an electric voltage to the substrate allows straining the film and by a stress induced martensitic transformation the transition temperature can be controlled. To probe the suitable magnetic and electric field range at different temperatures we present in-situ synchrotron diffraction experiments as well as by SQUID. We consider these multicaloric films are of particular interest for solid state refrigeration since their high surface to volume ratio allows fast heat transfer and high cycling frequencies which leads to higher cooling power using less material.
Supported by SPP1599.


B-4:IL03  Giant Inverse Magnetocaloric Effect of NiCoMnAl Films
N. TEICHERT, L. HELMICH, A. HÜTTEN, Department of Physics, Bielefeld University, Bielefeld, Germany

Epitaxial magnetocaloric Ni40Co10Mn50-xAlx thin films are deposited on heated MgO (001) substrates with sacrificial V seed layers by adjusting the alloy concentration via co-sputtering from elemental sources. After deposition, these films are released from their substrates by chemical wet etching of the V layers, which enables to study both, the freestanding and substrate constraint films regarding crystal structures, transformation temperatures, magnetic and resulting magnetocaloric properties. We measure remarkable magnetocaloric properties with ΔSM up to 7.5 Jkg-1K-1 for μ0ΔH = 2 T for both films. With a corresponding relative cooling power of 130 Jkg-1 Ni-Co-Mn-Al classifies as one of the most promising magnetocaloric thin film materials, known so far. In order to be able to validate the adiabatic temperature change ∆T of freestanding films a new device is set up, which detects ∆T by infrared thermography, giving access to a temperature range between 120 K and 470 K in vacuum. Magnetic fields up to 1.1 T can be applied with a rate of 1.2 T/s. Literature values for bulk Gadolinium (Gd) samples are well reproduced with our device. ΔT – values of all relevant thin film systems are determined and will comparatively be discussed.


B-4:IL04  Size Effects and Orientation Dependence in Superelastic Cu-Zn-Al Micro/Nano-pillars
J. FORNELL, Department of Materials Science and Engineering, MIT, Cambridge, MA, USA and Departament de Física, Facultat de Ciències, Universitat Autònoma de Barcelona, Bellaterra, Spain, N.TUNCER, C.A. SCHUH, Department of Materials Science and Engineering, MIT, Cambridge, MA, USA


Cu-Zn-Al shape memory alloys exhibit good superelastic behavior at the macro scale but their behavior at the micro and nano scale remains unexplored. In this work, the superelastic behavior of Cu-Zn-Al micro- and nano-pillars is studied under compression: (i) as a function of the crystallographic orientation and (ii) as a function of the pillar diameter size. In order to study the orientation dependence, pillars of ~2 mm diameter are milled in different crystallographic orientations. Pillars oriented close to the [001] direction show the largest total strain (~4.5%) while plastic deformation dominates the compressive response in the pillars milled close to the [111] direction. Pillars covering a wide range of size diameters, from 250 nm to 5 mm, oriented along the [001] direction, were also studied. The experimental results reveal a slight increase in the critical stress to induce the transformation and a clear increase in the transformation strain with a decrease in the pillar size. An effect of size on the shape and hysteresis of the stress-strain superelastic curve is also noticed: higher damping is observed for pillars smaller than 1 mm in diameter while much narrower hysteresis is observed at larger diameters. The size effects observed in Cu-Zn-Al pillars can be attributed to several factors (i.e. machining and testing procedure, pillar bending, dislocation activity, martensite type, etc). These issues will be discussed in detail. Nevertheless, it is interesting and technologically relevant that superelasticity is achieved in these alloys at the nanoscale.

 
B-4:L05  High Temperature Ti-Ni-Pd Shape Memory Alloys Subjected to High Pressure Torsion
S. TULIĆ, M. KERBER, A. PANIGRAHI, T. WAITZ, University of Vienna, Faculty of Physics, Physics of Nanostructured Materials, Vienna, Austria; MITSUHIRO MATSUDA, Kumamoto University, Department of Materials Science and Engineering, Kumamoto, Japan

A grain size on a nanoscale strongly impacts martensitic phase transformations and functional properties of shape memory alloys (SMA). Nanocrystalline SMA can be achieved via devitrification of an amorphous phase induced by severe plastic deformation. In the present work, a coarse grained Ti50Ni25Pd25 high temperature SMA showing a B2 to B19 transformation was subjected to high pressure torsion. This yields a nanoscale mixture of amorphous phase and strongly fragmented crystallites of the parent B19 martensite. As compared to its undeformed counterpart, the severely strained martensite shows a considerable larger thermal stability. Isochronal heating of the severely deformed samples yields relaxation of the amorphous phase that is followed by the reverse B19 to B2 transformation, crystallization, and, finally, the formation of an ultrafine-grained structure. Upon cooling, B19 martensite forms in the small grains. As compared to the case of coarse grains, the forward transformation is hindered (i.e. shifted to lower temperatures and is incomplete). Martensite formed in the ultrafine grains shows a lower thermal stability since the reverse transformation occurs at lower temperatures than in the case of the coarse grains.


B-4:IL06  Microstructure – Functional Property Relationships of NiTi Filaments
J. PILCH, O. TYC, P. SITTNER, L. KADERAVEK, L. HELLER, Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic; J.E. Schaffer, Fort Wayne Metals Research Products Corp, Fort Wayne, IN, USA; J. STRASKA, K. HORVATH, Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic; P. BUBLIKOVA, Research Centre Rez, Husinec-Rez, Czech Republic; P. STRUNZ, V. RYUKHTIN, Nuclear Physics Institute, Husinec-Rez, Czech Republic; B. MALARD, CIRIMAT, Toulouse, France; R. Delville, SCK•CEN, Mol, Belgium

Since its discovery in late 1960s, Nitinol metallurgy involving ingot casting, extrusion and wire processing up to final cold working/heat treatment has developed to produce high quality thin filaments. For a fixed melt technology, the final cold working and heat treatment in an environmental furnace constitutes the most critical processing steps in which functional and fatigue properties are adjusted. We have developed an alternative nonconventional heat treatment method by electric current which does the same in a very short time (down to 1 ms) with high precision and repeatability. Our research has shown that short annealing time prevents precipitation which is essential in some applications for functional and fatigue enhancement. Hence, we started to beneficially combine the rapid electrical treatment and prolonged aging treatments. Synchrotron x-ray diffraction was used to characterize the recovery of microstructure upon heating and small angle neutron scattering was employed to track down the precipitation kinetics during aging. The results helped us to develop a novel heat treatment technology which leads to unique precipitate-microstructural architecture of NiTi filaments with desired functional properties. The key strategies will be overviewed in the presentation.


B-4:IL07  Nucleation and Growth of Martensite by In-situ Experiments
R. NIEMANN1,2, A. DIESTEL1, B. SCHLEICHER1,2, S. KAUFFMANN-WEISS1*, C. BEHLER1,2, A. BACKEN1**, U.K. RÖßLER1, H. SEINER3, O. HECZKO4, S. HAHN5, M.F.-X. WAGNER5, L. SCHULTZ1,2, S. FÄHLER1,2, 1IFW Dresden, Dresden, Germany; 2Technische Universität Dresden, Dept. of Physics, Institute for Solid State Physics, Dresden, Germany; 3Institute of Thermomechanics, Academy of Sciences of Czech Republic, Prague, Czech Republic; 4Institute of Physics, Academy of Science of the Czech Republic, Prague, Czech Republic; 5Technische Universität Chemnitz, Institute of Materials Science and Engineering, Chemnitz, Germany; *now at KIT, Karlsruhe, Germany; **now at CNRS, Grenoble, France

Magnetic shape memory alloys can be used in magnetocaloric regenerators of solid-state cooling devices and as large-strain actuator materials. The energy efficiency of both applications depends strongly on the microstructure developing during the martensitic transformation. A martensitic microstructure that forms with as low elastic energy as possible and contains only weakly pinned twin boundaries is optimal for applications. Often, the martensite shows a complex hierarchical microstructure. We use sputter-deposited epitaxial Ni-Mn-Ga and Ni-Mn-Ga-Co films to study the nucleation and growth of martensite by field-, temperature-, and time-dependent magnetization measurements and in-situ in the scanning electron microscope. The final microstructure is also analyzed by means of transmission electron microscopy and X-ray diffraction. We explain the observed nucleation- and growth process using a model derived from the phenomenological theory of martensite crystallography and finite element calculations. We conclude that the hysteresis is dominated by nucleation and discuss its influence on the magnetocaloric effect. Finally, we present a way to reduce the energy barrier of the nucleation by nanoindentation.
We acknowledge funding by DFG SPP 1599.


B-4:IL09  Recent Advances in Magnetic Shape Memory Thin Films
S. FABBRICI, P. RANZIERI, M. CAMPANINI, L. NASI, F. CASOLI, E. BUFFAGNI, R. CABASSI, V. GRILLO, F. ALBERTINI, IMEM-CNR, Parma, Italy; C. MAGÉN, Instituto de Nanociencia de Aragón, Zaragoza, Spain; F. CELEGATO, G. BARRERA, P. TIBERTO, INRIM, Torino, Italy

Ni_2MnGa Heusler alloys are promising materials potentially exploitable for the fabrication of microdevices based on novel actuation mechanisms. In bulk materials, giant strains, higher than magnetostriction and state-of-the-art piezoelectric values, can be obtained by magnetic field induced twin variant reorientation. Thin films have recently attracted much interest as they offer the further possibility of tuning properties by thickness and by the choice of suitable substrates and underlayers. In the present contribution we review a series of epitaxial thin films of NiMnGa of thickness ranging from 10 to 200 nm, grown by r.f. sputtering on MgO substrates with and without a Cr underlayer. A multiscale structural and magnetic study was performed by means of electron transmission microscopy, (HREM, STEM-HAADF, electron diffraction, Lorentz microscopy), X-ray diffraction, AFM/MFM, AGFM and SQUID magnetometry. It was found that the film thickness and the underlayer determine the occurrence of the martensitic transformation and the type and orientation of martensitic variants. We will also review how in well-defined conditions a proper thermo-mechanical training can induce outstanding values of Magnetic Field Induced twin-variant reorientation.

 
Session B-5 - Engineering

B-5:IL01  Design of Multifunctional SMA Devices Using Finite Element Simulation Methods
T. BEN ZINEB, LEMTA Université de Lorraine CNRS, Vandoeuvre les Nancy, France

Developed constitutive models describing various kinds of SMAs behaviors were integrated in a finite element code. This made possible to use finite element method for SMA devices design. The shape of each part could be numerically optimized by maximizing the superelastic or shape memory effect behaviors. Applications were studied using the obtained numerical tool. As examples, the response of endodontic file in single crystal Cu-based under bending or torsion-bending loading was analyzed by finite element method. A connection ring in NiTiNb. The geometry was numerically analyzed in order to maximize the tightening pressure by considering effects of ductile niobium precipitates on preventing the tightening pressure decreasing after cooling. Micro devices etched in NiTi SMA thin films could be designed using this numerical tool. As an example, a NiTi SMA micro-actuator composed of two membranes operating in an antagonistic way. Other SMA applications were analyzed by this numerical tool among them fish-plates in low cost Fe-based SMA or endodontic parts subjected to properties modifications dues to hydrogen diffusion.


B-5:IL02  Enviromentally Assisted Fatigue of NiTi
P. SITTNER, J. RACEK, B. MARESOVA, L. KADERAVEK, L. HELLER, Institute of Physics of the ASCR, Prague, Czech Republic

Superelastic NiTi devices and implants suffer from preliminary fatigue failure when transforming cyclically in body fluids. We have developed original in-situ electrochemical methods which are beneficially employed to characterize fatigue performance of superelastic NiTi wires and springs subjected to superelastic loadings in simulated body fluid environment. Several in-situ methods were developed, such as open circuit potential, potentiodynamic and potentiostatic polarization, electrochemical impedance spectroscopy to characterize the passive layer, surface oxides, interface between austenite and stress induced martensite relevant for mechanically loaded surface matrix/oxide layers. The results will be overviewed and a new mechanism of environmental fatigue degradation of NiTi will be presented.


B-5:L04  High Speed Smart Soft Composite (SSC) Structure Actuator with Large Deformation
SUNG-HYUK SONG, J.Y. LEE, H. RODRIGUE, S.H. AHN, Department of Mechanical & Aerospace Engineering, Seoul National University, Seoul, Korea

Shape memory alloys (SMAs) have a high power density; however, their slow actuation speed restricts adoption in a wide range of applications. The use of heat sinks, forced air convection, and heat pumps to increase the actuation speed of SMAs has been investigated, but the proposed designs are bulky and offer limited actuation rate increase. In this paper, we present a smart soft composite (SSC) actuator that is capable of fast, large-scale deformation in simple structures. To increase the rate of cooling, the proposed SSC structures comprise multiple small-diameter SMA wires, rather than a single thick wire. In addition, a 3D printed scaffold structure is embedded in the actuator to control its characteristics. According to the desired motion, scaffold structures can be modified by changing the orientation of each scaffold layer. SMA wires and scaffold structures are combined into a composite using a rubber-like soft polymer to protect the thin SMA wires and to enable precise positioning of each component during large deformation. This study expands the applicability of SMA-based actuators in robotics technologies, in particular, those that require fast-action motion such as flying or swimming.


B-5:L05  Structural Effects of Thermomechanical Processing on the Static and Dynamic Responses of Powder Metallurgy Fe-Mn-Si Based Shape Memory Alloys
E. MIHALACHE, B. PRICOP, R.I. COMANECI, M.G. SURU, N.M. LOHAN, M. MOCANU, L.G. BUJOREANU, “Gheorghe Asachi” Technical University of Iasi, Romania; B. ÖZKAL, Istanbul Technical University, Istanbul, Turkey

Fe-14Mn-6Si-9Cr-5Ni (wt. %) shape memory alloys (SMAs) were produced by powder metallurgy combined with Mechanical Alloying(MA). The specimens were pressed (500 MPa) and sintered under Ar atmosphere (1423 K for 2 x 3.6 ks) from as blended powders and from mixtures of as blended and 10, 20, 30 and 40 vol. % MA’ed powders, respectively. Sintered specimens were hot-rolled (1373 K), spark-erosion cut and solution treated (1273K/ 300 s/ water) in order to obtain the initial state (I) of the five specimens under study. Tensile loading-unloading tests were performed in order to obtain stress-induced martensite (SIM). The static responses of the five specimens were evaluated by means of the areas under unloading curve (E2) and between loading and unloading curves (E1 + E2) which were used for determining energy storage efficiency, E2/(E1+E2) and internal friction, E1. The dynamic responses were determined by Dynamic Mechanical Analysis (DMA) performed, at room temperature, with a three-point-bending specimen holder in strain sweep mode. The structure of the five specimens, I and SIM states, was analyzed by optical and scanning electron microscopy as well as X-ray diffraction. The effects of MA fraction were correlated with static and dynamic responses via structural changes.

 
Session B-6 - Applications

B-6:L01  Shape Memory Alloy Rods with Variable Flexural Stiffness for Spine Correction: Manufacturing, Modeling and Biomechanical Evaluation
V. BRAILOVSKI, Y. FACCHINELLO, M. BRUMMUND, Y. PETIT, Ecole de Technologie Superieure, Montreal, Quebec, Canada; J-M. MAC-THIONG, Department of Surgery, Faculty of Medicine, University of Montreal, Montreal, Quebec, Canada

A new concept of monolithic spinal rods with variable flexural stiffness is proposed to reduce the risk of adjacent segment degeneration and vertebral fracture while providing adequate stability to the spine. The variability of mechanical properties is generated by locally annealing hardened Ti-Ni shape memory alloy rods. Ten minute Joule-effect annealing allows restoring the superelasticity in the heated portion of the rod. Such processing also generates a mechanical property gradient between the heated and the unheated zone. A numerical model simulating the annealing temperature and the mechanical property distributions was developed to optimize the Joule-heating strategy and to modulate the rod’s overall flexural stiffness. Subsequently, the rod model was included in a finite element model of the porcine lumbar spine to study the effect of the rod’s stiffness profiles on the spinal kinematics, intradiscal pressure, and pullout forces on the upper anchors. In vitro testing was performed on six porcine spine segments to assess the stabilization capacity of the rods and to validate the numerical model. VAR rods with transverse hooks as proximal anchors were found to reduce the stress on the adjacent segment as well as the pullout force at the upper instrumented level.


B-6:L02  A New Design of a Nitinol Ring-like Wire for Suturing in Deep Surgical Field
A. NESPOLI1, V. DALLOLIO2, E. VILLA1, F. PASSARETTI1, 1Consiglio Nazionale delle Ricerche, Istituto per l'Energetica e le Interfasi (CNR-IENI), Lecco, Italy; 2ProMev, Lecco, Italy

The present work proposes a new suturing procedure based on self-accommodating suture points. Each suture point is made of a commercial NiTi wire hot-shaped in a single loop ring; a standard suture needle is then fixed at one end of the NiTi suture. According to this simple geometry, several NiTi suture stitches have been prepared and tested by tensile test to verify the closing force in comparison to that of commercial sutures. Further experimental tests have also been performed on anatomic samples from animals to verify the handiness of the NiTi suture. Moreover, surface quality of sutures has been carefully investigated via microscopy. Results show that the NiTi suture expresses high stiffness and a good surface quality. In addition, the absence of manual knotting allows for a simple, fast and safe procedure.


B-6:L03  Manufacturing and Processing of New Ni-free SMA for Biomedical Implants
S. DUBINSKIY1, V. BRAILOVSKI2, S.PROKOSHKIN1, K. INAEKYAN2, YU. ZHUKOVA1, V. SHEREMETYEV1, A. KONOPATSKIY1, 1National University of Science and Technology “MISIS”, Moscow, Russia; 2Ecole de Technologie Superieure, Montreal, Quebec, Canada

Commonly used metallic materials for orthopedic implants, such as Ti-CP and Ti-6Al-4V, exhibit excellent biochemical compatibility, but their mechanical behavior differs drastically from that of bones. Ti-Ni superelastic shape memory alloys (SMA) are much closer to bone tissues in terms of biomechanical compatibility due to their plateau-like behavior and low elastic modulus. However, Ti-Ni alloys contain toxic nickel, which compromises their use as a material for permanent implants. New generation Ti-Nb- and Ti-Zr-based SMA exhibit both excellent biochemical and biomechanical compatibility, and are therefore the most promising candidates for load-bearing implant applications. These alloys are commonly produced by vacuum induction melting and vacuum arc remelting. Their functional properties, such as superelastic behavior and effective elastic modulus, can be controlled via structure modification by methods of thermomechanical treatment. Nanostructure formation is also beneficial for the improvement of the functional properties of these Ni-free SMA. Foams produced from Ti-Nb and Ti-Zr SMA promote bone ingrowth and firm fixation of an implant, and their elastic modulus comes closer to that of bone than that of any other metallic implant material.


B-6:IL05  Advances in Single Crystal Technology of Magnetic Shape Memory Materials
E. PAGOUNIS, ETO MAGNETIC GmbH, Stockach, Germany
 
Magnetic shape memory (MSM) alloys generate stroke and force when inserted in moderate magnetic fields (< 1T). Because of their ultrafast response times they are very well suited for advanced actuators and sensors. Single crystalline Ni-Mn-Ga alloys have shown the best performance for application in MSM-driven devices. However, their production process represents many challenges. In the present work we report on the Bridgman-type single crystal growth of Ni-Mn-Ga MSM alloys, using industrial production machinery. The crystals have a diameter ranging from 12-60 mm, and a length of 120-220 mm. Various process parameters and compositions have been used during production. The single crystals were characterized utilizing optical and DIC microscopy, SEM-EBSD, EDX and XRF techniques. It is proven that the applied Bridgman-type casting process significantly improves the chemical homogeneity and minimizes low-angle boundaries. Rectangular actuator elements cut from the single crystals demonstrate a reduced twinning stress, and an increased work output and efficiency. Furthermore, MSM alloys with increased operating temperature and magnetic field-induced strains above 10% were produced, using advanced manufacturing technologies.


B-6:IL06  A Magnetic Shape Memory Micropump and Other Applications
K. ULLAKKO, A. SAREN, D. MUSIIENKO, A. SOZINOV, J. TELLINEN, Lappeenranta University of Technology, Material Physics Laboratory, Savonlinna, Finland

The magnetic shape memory (MSM) material Ni-Mn-Ga can strain up to 12 percent by an applied magnetic field due to the motion of twin boundaries. We have measured a twin boundary velocity greater than 30 m/s, actuating velocity greater than 4.5 m/s and actuation acceleration of 70 km/s2. We have also shown that magnetic-field-induced stress decrease with decreasing thickness of the Ni-Mn-Ga sample. These unique characteristics of the Ni-Mn-Ga samples enable the development of several micro devices such as micropumps. We present a self-priming integratable contactless micropump made from Ni-Mn-Ga. The working principle of the micropump is based on the motion of a local shrinkage which is driven by a changing magnetic field distribution in the sample. The micropump consists primarily of a piece of the Ni-Mn-Ga alloy and it does not need electrical contacts. Most of the micropump characteristics are superior as compared to the existing technologies in the flow rate range of 0-1800 microliters/minute. We also present MSM microvalves, manifolds, manipulators, and optical and electronic switches.

 
Poster Presentations

B:P01  Experimental Study and Modeling of Pseudoelastic Systems for the Design of a Complex Passive Damper
A. NESPOLI1, D. RIGAMONTI2, M. RIVA3, E. VILLA1, F. PASSARETTI1, 1Consiglio Nazionale delle Ricerche - Istituto per l’Energetica e le Interfasi (CNR-IENI) Unità di Lecco, Lecco, Italy; 2Politecnico di Milano, Italy; 3INAF, Osservatorio di Merate, Lecco, Italy

The dissipated energy that is associated with the load/unload cycle of a pseudoelastic element is suitable for the damping or the prevention of oscillations of any physical system. In this paper, the damping response of some systems of NiTi pseudoelastic wires is investigated. First, standard tensile tests were accomplished to evaluate the global damping capacity, the energy dissipated per cycle and the maximum attenuated force of some basic systems based on two pseudoelastic wires. On the basis of the results of the mechanical test, a complex bi-directional damper was designed and tested. Furthermore, the experimental results were employed to validate the XY model (implemented by Matlab code) that was utilized to predict the damping esponse of more complex dampers. It was found that 0.09 is the upper limit of the damping capacity of the presented pseudoelastic systems; this value is independent from the number and the length of the NiTi components. In addition, the energy dissipated per cycle is related to the strain and to the number of the NiTi components; furthermore, the system composed by NiTi wires with different length shows the highest dissipated energy .


B:P02  Mechanical and Superelastic Properties of Au-51Ti-18Co Biomedical Shape Memory Alloy Heat-treated at 1173K to 1373K
T. BUASRI, H. SHIM, M. TAHARA, T. INAMURA, K. GOTO, H. HOSODA, Tokyo Insititute of Technology, Yokohama, Kanagawa, Japan; H. KANETAKA, Tohoku University, Sendai, Miyagi, Japan; Y. YAMABE-MITARAI, National Institute for Materials Science, Tsukuba, Ibaraki, Japan

Development of novel Ni-free biomedical shape memory alloys (SMAs) has been encouraged due to the Ni-toxicity issues of NiTi practical SMAs. Recently, AuTiCo alloys have attracted a large number of research interests due to their excellent biocompatibility and high X-ray radiocapacity. In the present study, the effect of heat treatment condition from 1173K to 1373K for 3.6ks on mechanical and superelastic properties of Au-51Ti-18Co alloy (mol%) was investigated. The stress for inducing martensitic transformation (SIMT) and the critical stress for slip deformation (CSS) slightly decrease with increasing the heat treatment temperature. Good superelasticity was definitely recognized with the maximum shape recovery ratio up to 95% in all the specimens. Regardless of heat treatment temperature, furthermore, the Au-51Ti-18Co alloy also exhibited 4% superelastic shape recovery strain at room temperature. As the mentioned reasons, the Au-51Ti-18Co alloy is promising for biomedical materials.
This work was supported by Grant-in-Aid for Scientific Research Kiban S 26220907 and Challenging Exploratory Research 26630343 from Japan Society for the Promotion of Science (JSPS).


B:P03  Influence of Intermediate Layer Formation on Properties of Bimetallic Shape Memory Alloy Composites Produced by Explosion Welding
S. BELYAEV, N. RESNINA, E. DEMIDOVA, I. LOMAKIN, O. MEDVEDEV, Saint Petersburg State University, Saint Petersburg Russia; V. RUBANIK, V. RUBANIK jr., Institute of Technical Acoustics NAS of Belarus, Vitebsk, Belarus Vitebsk State Technological University, Vitebsk, Belarus

The aim of the present work was a study of the intermediate layer formation during explosion welding on structure, martensitic transformation and recoverable strain in bimetallic shape memory composites produced by explosion welding. Four different bimetal composites were produced: two of them "TiNi - stainless steel" and "TiNi - TiNi" were not able to form the intermediate layer during explosion welding whereas, "TiNi – Ti-6%Al-4%V" and "TiNi - C17200 (copper beryllium alloy)" composites might form the intermediate layer. It was found that the intermediate layer consisted of solid solution and intermetallics phases. It was shown that if the intermediate layer did not formed in the bimetallic composite during explosion welding then, the layers were subjected to a high plastic deformation. It resulted in a significant change in grain structure in the vicinity to the joint, depressed the martensitic transformation and decreased in recoverable strain. To recover the grain structure and properties of the layers an annealing at high temperatures was needed. If the intermediate layer was formed during the explosion welding then, the plastic strain was less and the bimetal composite kept their physical and functional properties.


B:P05  On the Nanostructures Gradation in Thermomechanically Treated Ti-Ni SMA
S. PROKOSHKIN1, V. BRAILOVSKI2, S. DUBINSKIY1, K. INAEKYAN2, A. KREITCBERG2, 1National University of Science and Technology “MISIS”, Moscow, Russia; 2Ecole de Technologie Superieure, Montreal, Quebec, Canada

Different nanostructures formed in Ti-Ni shape memory alloys (SMA) as a result of post-deformation annealing (PDA) in the 200-450°C temperature range after cold rolling (CR) in a e=0.3-1.9 true strain range are studied and classified. A statistical analysis of the nanostructure parameters obtained from the TEM analysis of bright and dark field images and selected area diffraction patterns is carried out. The results of this analysis alongside the visual observations allows establishment of the following regularities. Two types of nanostructure form in Ti-Ni SMA as a result of PDA after CR: (a) a nanosubgrained structure (NSS), which consists of subgrains separated by low-angle boundaries formed as a result of polygonization of the initially highly-dislocated substructure; (b) a nanocrystalline structure (NCS), which consists of grains separated by high-angle boundaries, and represents a combination of the deformation-induced nano-grains grown during PDA and the new nano-grains formed during crystallization of the amorphous phase. After CR of moderate intensity (e=0.3), mainly NSS forms as a result of PDA. After CR of moderate-to-high intensity (e=0.5-1.0), the structure is mixed (NS+NC). After high-intensity CR (e=1.2-2), the structure is mainly NC.


B:P06  The Magnetic States of Co and Cr Ni-Co-Mn-In(Sn) Heusler Alloys
V. BUCHELNIKOV1, V.V. SOKOLOVSKIY1, P. ENTEL2, 1Chelyabinsk State University, Chelyabinsk, Russia; 2University of Duisburg-Essen, Duisburg, Germany

The functional properties of Mn excess Ni-Mn-Z (Z = Ga, In, Sn, Sb) Heusler alloys with addition of fourth and fifth elements like the magnetic shape memory effect, exchange bias effect and the magnetocaloric effect are promising for future technologies [1]. These effects are associated with the complex magnetic ordering in Heusler alloys. The strong antiferromagnetic correlations start to appear with the Mn excess atoms which occupy sites of the Z sublattice, causing the nearest neighbor Mn-Mn distances to shrink. This is responsible for the appearance of antiferromagnetic interactions. The competing magnetic interactions lead to the characteristic drops of magnetization curves in martensite. In this work we have focused on the Co- and Cr-doped Ni-Co-Mn-In(Sn) alloys. The equilibrium lattice parameter and magnetic reference state in the austenite with cubic structure have obtained by the lattice relaxation calculations with 16 and 32 atoms in the supercells. The four magnetic configurations with different orientation of magnetic moments of Ni, Co, Cr, and Mn atoms have been considered. We have done also energy calculations with tetragonal distortion c/a of cubic supercells.
1. A. Planes, L. Manosa, and M. Acet, J. Phys.: Condens. Matter 21, 233201 (2009).


B:P08  Contributions to Transformation Entropy Change in Magnetic Shape Memory Alloys
C. SEGUI, E. CESARI, Dept. de Física, Universitat de les Illes Balears, Palma de Mallorca, Spain

Mn-rich Ni-Mn-X (X = In, Sn, Sb, Ga, + Co) alloys, derived from Heusler Ni2MnX, show a martensitic transformat. (MT), usually between ferromagnetic austenite and nonmagnetic or weakly magnetic martensite. These so-called metamagnetic shape memory alloys (MetaMSMAs), owing to the large drop in the magnetization (DM) across the MT, can show the magnetic shape memory effect, large inverse magnetocaloric effect, giant magnetoresistance, etc. In these effects, the entropy change due to the MT (DS) is one of the important issues. A clear correlation between DS and the atomic order degree -which in turn modifies the Curie temperature of austenite, TC,a, and the MT temperature, Tm- has been observed. The strong decrease of DS with (TC,a - Tm ) has been attributed to the magnetic contribution to the entropy change, DSmag, attributing a minor role to changes in the vibrational entropy term, DSvib. Recently it has been fully clarified that the most relevant factor for the decrease of DS with (TC,a - Tm ) is, in fact, the temperature dependence of austenite magnetization. The role of intrinsic effects related atomic order seems to be small. On the other hand, the vibrational contribution to DS, and its influence on the temperature extension of the MT needs further discussion.


B:P10  Calorimetric Study of Hysteresis Effects on the Magnetocaloric Effect in Ni-Co-Mn-Sn Alloys
B. EMRE1, E. STERN-TAULATS2, S. YUCE3, N. BRUNO4, A. PLANES2, L. MAÑOSA2, I. KARAMAN4, 5, 1Ankara University, Faculty of Eng., Dept. of Eng. Phys., Ankara, Turkey; 2Dept. ECM. Ftat. Física. Universitat de Barcelona, Barcelona, Catalonia; 3Ondokuz Mayis University, Faculty of Arts&Science, Dept. Phys., Samsun, Turkey; 4Dept. of Mechanical Engineering, Texas A&M University, College Station, TX, USA; 5Dept. of Materials Science and Engineering, Texas A&M University, College Station, TX, USA

Ni-Co-Mn-X (X=In, Ga, Sn) alloys were the subjects of intensive investigations due to interplay between structure and magnetism, which causes various properties: magnetic superelasticity, giant magnetocaloric effects, and giant magnetoresistance [1]. This alloy system is reported as a proper magnetic shape memory alloy without expensive element and with one and two-way magnetic shape memory effect, furthermore some of these alloys were reported to exhibit low hysteresis [2]. However, hysteresis shows its detrimental effects through successive cycles across the transition. On the other hand, a marked sensitivity of the transition temperature to an applied field heals the detrimental effects of the hysteresis on magnetocaloric properties. It is reported that the most suited technique to measure heat is differential scanning calorimetry [3]. In this work we study the magnetocaloric effect, hysteresis and relative cooling power in Ni-Co-Mn-Sn metamagnetic shape memory alloy by differential scanning calorimetry under magnetic fields up to 6 T.
References: [1] Planes A. et al., J. Phys.:Condens. Matter, 2009, 21: 233201. [2] V. Srivastava, X. Chen and R. D. James, ApplPhysLett., 2010, [3] L. Mañosa, A. Planes, X. Moya, Advanced Materials, 2009, 21 (37), 3725-3726


B:P12  Design and Experimental Testing of a NiTi-based, High Frequency, Centripetal Multiple Actuator
E. BORLANDELLI, D. SCARSELLI, P. BETTINI, G. SALA, M. QUADRIO, Politecnico di Milano, Milano, Italy; A. NESPOLI, D. RIGAMONTI, E. VILLA, CNR IENI, Lecco, Italy

The purpose of this work is to analyze complex systems with multiple SMA actuators working at frequencies greater than 1 Hz, which are higher than those typical of NiTi actuators. In particular, we show the design, the development and the testing of a peristaltic experimental rig actuated by multiple shape-memory NiTi wires. Each centripetal actuator is designed to radially and cyclically shrink a compliant silicone pipe containing fluid. The actuation device converts a linear contraction of a heated SMA wire into a radial displacement: four rigid, aluminum-made circular sectors are placed along the pipe circumference and provide the required NiTi wire housing. The aluminum assembly acts as geometrical amplifier of the wire contraction and as heat sink required to dissipate the thermal energy of the wire during the cooling phase. The NiTi re-arm force is provided by the fluid pressure inside the pipe. The positioning of 200 of this SMA devices along the external surface of the compliant test section, has allowed to create sinusoidal waves of wall-normal deformation traveling along the pipe. The pipe wall displacement is monitored by means of laser transducers. The performance of all the actuators is analyzed and compared with the authority of the single actuator.


B:P14  Mechanical Properties of Nanoceramic Zirconia Coatings on Superelastic NiTi Strips
N.I.A. LOPES, V.T.L. BUONO, UFMG, Belo Horizonte, MG, Brazil

Nickel titanium (NiTi) alloys have been largely applied in biomechanical devices and implants due to their special properties. Mechanical fatigue and fretting-corrosion resistance remain important challenges in a number of such applications of superelasticity and shape memory behavior. This study aimed at developing appropriate coatings to help delaying crack nucleation and corrosion in NiTi alloys. Zirconia (ZrO2) coating stands as a good candidate to improve the corrosion and wear resistance of metallic substrates and was obtained by electrodeposition on a electropolished NiTi superelastic alloy wire. The surface morphology and the chemical composition of the coated samples were evaluated using scanning electron microscopy with energy dispersive X-ray spectrometry. X-ray diffraction, nanoindentation analyses, and deformation tests were also performed. The results showed that the ZrO2 coating deposited was uniform and well adhered to the NiTi subtract. Additionally, it was observed that this coating was capable of undergoing severe deformation without cracking, indicating a potential increase in fatigue resistance of the conjugate.


B:P15  Application of TiNi Alloy Coils as a Filtration Rating Controller for Three Dimensional Filter Made of a Stainless Steel Wire
YOICHI KISHI, Z. YAJIMA, Advanced Materials Systems Research and Development Center, Kanazawa Institute of Technology, Hakusan, Ishikawa, Japan; C. SHIOMI, T. MATSUMOTO, T. OHIGASHI, Y.NISHIMOTO, Fuji Filter Manufacturing Co. Ltd., Tokyo, Japan

We propose a new filtering device which is composed of a tube-like filter element and a TiNi shape memory alloy (SMA) coil spring. The proposed new filtering device achieves the variable filtering performance due to the temperature changes. The filter element, which can be made of stainless steel wire, shows superior bending resistance and excellent elasticity. The filtration performance of the filter element can be regulated depending on the elastic deformation. Because the size of the mesh in a filter element, that is to say the filtration rating, can be controlled according to the elastic deformation of the filter element. If the filter element is stretched elastically, the filtration rating is decreasing with increasing of the elastic deformation of the filter element. After the tube-like filter element was placed in the inside of a TiNi SMA coil spring, the new filtering device was manufactured by bonding the filter element to the SMA coil spring. In this report, the fundamental properties of the filter element were investigated. The trial product of a new filtering device, which was made with the filter element and the SMA coil spring, were evaluated for its filtration performance due to the temperature changes.


B:P17  Intelligent Shape Memory Device for Clipping Vessels
E.P. RYKLINA, A.V. KOROTITSKIY, I.YU. KHMELEVSKAYA, S.D. PROKOSHKIN, National University of Science and Technology “MISIS”, Moscow, Russia; M.V. SOUTORINE, A.N. CHERNOV, Globetek 2000 PTY LTD, Brighton, Victoria, Australia

Traditional clips for the blood vessels used in clinical practice are made of common materials and operate under mechanical force; that often leads to over-tightening and damaging the vessels. A newly developed device has an original design; its functioning is based on one-way and two-way shape memory effects (SME and TWSME, respectively). The clip remains in the ready-to-closure position before it is heated up to 42 - 45°C. Once heated by a specially developed clip-holder device, it closes immediately due to SME, thus softly clipping the vessel. Under cooling, the device manifests a partial unclosing due to TWSME realization and can be removed easily without any trauma of the vessel. Various types of clips dimensions were developed for the vessels of various calibres and blood pressures. The special regimes of the clip thermomechanical treatment were developed to obtain the best combination of the functional properties. Bench test of clips was performed using a specially developed vessel phantom with possibility of verification the liquid pressure under the human body temperature. The obtained results can be used for development of implants and elements with one-way SME and two-way SMEs.
 

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