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Sample records for memory alloy ni-mn-ga

  1. Single-crystal growth of NiMnGa magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wang, Jingmin; Jiang, Chengbao

    2008-02-01

    The crystal growth of NiMnGa magnetic shape memory alloys was investigated by the optical zone melting method. Slightly macroscopic convex and planar solid-liquid interfaces were achieved by controlling the molten zone morphologies. Single crystals were successfully prepared in three typical series of NiMnGa magnetic shape memory alloys, including stoichiometric Ni 50Mn 25Ga 25, Ni-rich NiMnGa and Mn-rich NiMnGa alloys. Studies on the solute partition during crystal growth revealed the enrichment of Mn and deficiency of both Ni and Ga in front of the solid-liquid interface for both stoichiometric and Mn-rich NiMnGa alloys, while a slight enrichment of Ni for Ni-rich NiMnGa alloys. An initial transient stage was determined to be about 20 mm, and a uniform composition distribution existed along the axis of the crystals in the stable growth parts, which matches well with the proposed mathematic model.

  2. Microstructure and solidification behavior of Ni-Mn-Ga magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Chen, Jian; Gharghouri, Michael A.; Hyatt, Calvin V.

    2004-07-01

    In order to understand the solidification behavior of Ni-Mn-Ga alloys, ingots with different compositions were prepared by arc melting. Two series of compositions were investigated: Ni100-2xMnxGax (15<=x <=30) and Ni50Mn50-yGay (0<=y<=50). The microstructures obtained were observed and the compositions of the phases occurring in the ingots were identified by energy dispersive spectroscopy in the scanning electron microscope. Based on these observations, three solidification paths were identified: direct solidification of γ-Ni from the liquid, direct solidification of β-NiMnGa from the liquid, and solidification of β-NiMnGa phase via a peritectic reaction. It was found that the γ-Ni liquidus surface covers a large area of the ternary phase diagram. The γ-Ni liquidus boundary is located between Ni50Mn25Ga25 and Ni45Mn27.5Ga27.5 in the equal Mn and Ga alloy series, and between Ni50Mn5Ga45 and Ni50Mn10Ga40 in the 50 at.% Ni alloy series. The alloys with compositions close to the stoichiometric Ni2MnGa composition that show the magnetic shape memory effect are all covered by the γ-Ni liquidus surface. The β-NiMnGa liquidus surface covers the remaining alloy compositions.

  3. Quasi-static modeling of NiMnGa magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Couch, Ronald N.; Chopra, Inderjit

    2005-05-01

    A quasi-static model for NiMnGa magnetic shape memory alloy (MSMA) is formulated in parallel to the Brinson and Tanaka thermal SMA constitutive models. Since the shape memory effect (SME) and pseudoelasticity exist in both NiTi and NiMnGa, constitutive models for SMAs can serve as a basis for MSMA behavioral modeling. The quasi-static model for NiMnGa was characterized by nine material parameters identified by conducting a series of uniaxial compression tests in a constant field environment. These model parameters include free strain, Young"s modulus, fundamental critical stresses, fundamental threshold fields, and stress-influence coefficients. The Young"s moduli of the material in both its field and stress preferred configurations were determined to be 450 MPa and 820 MPa respectively, while the free strain was measured to be 5.8%. These test data were used to assemble a critical stress profile that is useful for determining model parameters and for understanding the dependence of critical stresses on magnetic fields. Once implemented, the analytical model shows good correlation with test data for all modes of NiMnGa quasi-static behavior, capturing both the magnetic shape memory effect and pseudoelasticity. Furthermore, the model is also capable of predicting partial pseudoelasticity, minor hysteretic loops and stress-strain behaviors. To correct for the effects of magnetic saturation, a series of stress influence functions were developed from the critical stress profile. Although requiring further refinement, the model"s results are encouraging, indicating that the model is a useful analytical tool for predicting NiMnGa actuator behavior.

  4. A quasi-static model for NiMnGa magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Couch, Ronald N.; Chopra, Inderjit

    2007-02-01

    A quasi-static model for NiMnGa magnetic shape memory alloy (MSMA) is formulated in parallel to the Brinson and Tanaka thermal SMA constitutive models. Since the shape memory effect (SME) and pseudoelasticity exist in both NiTi and NiMnGa, constitutive models for SMAs can serve as a basis for MSMA behavioral modeling. The simplified, linear, quasi-static model for NiMnGa was characterized by nine material parameters identified by conducting a series of uniaxial compression tests in a constant field environment. These model parameters include free strain, Young's modulus, fundamental critical stresses, fundamental threshold fields, and stress-influence coefficients. The Young's moduli of the material in both its field and stress preferred configurations were determined to be 450 MPa and 820 MPa respectively, while the free strain was measured to be 5.8%. These test data were used to assemble a critical stress profile that is useful for determining model parameters and for understanding the dependence of critical stresses on magnetic fields. Once implemented, the analytical model shows good correlation with test data for all modes of NiMnGa quasi-static behavior, capturing both the magnetic shape memory effect and pseudoelasticity. Furthermore, the model is also capable of predicting partial pseudoelasticity, minor hysteretic loops and stress-strain behaviors. To correct for the effects of magnetic saturation, a series of stress influence functions were developed from the critical stress profile. Although requiring further refinement, the model's results are encouraging, indicating that the model is a useful analytical tool for predicting NiMnGa actuator behavior.

  5. Influence of volume magnetostriction on the thermodynamic properties of Ni-Mn-Ga shape memory alloys

    NASA Astrophysics Data System (ADS)

    Kosogor, Anna; L'vov, Victor A.; Cesari, Eduard

    2015-10-01

    In the present article, the thermodynamic properties of Ni-Mn-Ga ferromagnetic shape memory alloys exhibiting the martensitic transformations (MTs) above and below Curie temperature are compared. It is shown that when MT goes below Curie temperature, the elastic and thermal properties of alloy noticeably depend on magnetization value due to spontaneous volume magnetostriction. However, the separation of magnetic parts from the basic characteristics of MT is a difficult task, because the volume magnetostriction does not qualitatively change the transformational behaviour of alloy. This problem is solved for several Ni-Mn-Ga alloys by means of the quantitative theoretical analysis of experimental data obtained in the course of stress-strain tests. For each alloy, the entropy change and the transformation heat evolved in the course of MT are evaluated, first, from the results of stress-strain tests and, second, from differential scanning calorimetry data. For all alloys, a quantitative agreement between the values obtained in two different ways is observed. It is shown that the magnetic part of transformation heat exceeds the non-magnetic one for the Ni-Mn-Ga alloys undergoing MTs in ferromagnetic state, while the elevated values of transformation heat measured for the alloys undergoing MTs in paramagnetic state are caused by large MT strains.

  6. Influence of volume magnetostriction on the thermodynamic properties of Ni-Mn-Ga shape memory alloys

    SciTech Connect

    Kosogor, Anna; L'vov, Victor A.; Cesari, Eduard

    2015-10-07

    In the present article, the thermodynamic properties of Ni-Mn-Ga ferromagnetic shape memory alloys exhibiting the martensitic transformations (MTs) above and below Curie temperature are compared. It is shown that when MT goes below Curie temperature, the elastic and thermal properties of alloy noticeably depend on magnetization value due to spontaneous volume magnetostriction. However, the separation of magnetic parts from the basic characteristics of MT is a difficult task, because the volume magnetostriction does not qualitatively change the transformational behaviour of alloy. This problem is solved for several Ni-Mn-Ga alloys by means of the quantitative theoretical analysis of experimental data obtained in the course of stress-strain tests. For each alloy, the entropy change and the transformation heat evolved in the course of MT are evaluated, first, from the results of stress-strain tests and, second, from differential scanning calorimetry data. For all alloys, a quantitative agreement between the values obtained in two different ways is observed. It is shown that the magnetic part of transformation heat exceeds the non-magnetic one for the Ni-Mn-Ga alloys undergoing MTs in ferromagnetic state, while the elevated values of transformation heat measured for the alloys undergoing MTs in paramagnetic state are caused by large MT strains.

  7. Quasi-static modeling of NiMnGa magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Couch, Ronald N.; Chopra, Inderjit

    2004-07-01

    A quasi-static model for NiMnGa magnetic shape memory alloy (MSMA) is formulated on the basis of NiTi SMA constitutive models such as the Brinson model, because of the similarities that exist in the behavior of both materials. NiMnGa shows a magnetically induced shape memory effect as well as a pseudoelastic behavior. Quasi-static tests at constant applied magnetic field and stress were conducted to identify the model parameters. The material parameters include free strain, Young's modulus, critical threshold fields and stress-influence coefficients. The Young's moduli of the material in its field preferred and stress preferred states were determined to be 450 MPa and 820 MPa respectively. Critical threshold fields as a function of stress were determined from constant stress testing. These test data were used to assemble a critical stress-temperature profile that is useful in predicting the various states of the material for a wide range of magnetic or mechanical loading conditions. Although the constant applied field and constant stress data have yet to be fully correlated, the model parameters identified from the experiments were used to implement an initial version of the quasi-static model. The model shows good correlation with test data and captures both the magnetic shape memory effect and pseudoelasticity. This introductory model provides a sound basis for further refinements of a quasi-static NiMnGa model.

  8. Size effects on magnetic actuation in Ni-Mn-Ga shape-memory alloys.

    PubMed

    Dunand, David C; Müllner, Peter

    2011-01-11

    The off-stoichiometric Ni(2)MnGa Heusler alloy is a magnetic shape-memory alloy capable of reversible magnetic-field-induced strains (MFIS). These are generated by twin boundaries moving under the influence of an internal stress produced by a magnetic field through the magnetocrystalline anisotropy. While MFIS are very large (up to 10%) for monocrystalline Ni-Mn-Ga, they are near zero (<0.01%) in fine-grained polycrystals due to incompatibilities during twinning of neighboring grains and the resulting internal geometrical constraints. By growing the grains and/or shrinking the sample, the grain size becomes comparable to one or more characteristic sample sizes (film thickness, wire or strut diameter, ribbon width, particle diameter, etc), and the grains become surrounded by free space. This reduces the incompatibilities between neighboring grains and can favor twinning and thus increase the MFIS. This approach was validated recently with very large MFIS (0.2-8%) measured in Ni-Mn-Ga fibers and foams with bamboo grains with dimensions similar to the fiber or strut diameters and in thin plates where grain diameters are comparable to plate thickness. Here, we review processing, micro- and macrostructure, and magneto-mechanical properties of (i) Ni-Mn-Ga powders, fibers, ribbons and films with one or more small dimension, which are amenable to the growth of bamboo grains leading to large MFIS, and (ii) "constructs" from these structural elements (e.g., mats, laminates, textiles, foams and composites). Various strategies are proposed to accentuate this geometric effect which enables large MFIS in polycrystalline Ni-Mn-Ga by matching grain and sample sizes.

  9. Multiscale twin hierarchy in NiMnGa shape memory alloys with Fe and Cu

    DOE PAGES

    Barabash, Rozaliya I.; Barabash, Oleg M.; Popov, Dmitry; Shen, Guoyin; Park, Changyong; Yang, Wenge

    2015-01-31

    X-ray microdiffraction and scanning electron microscopy studies reveal 10 M martensitic structure with a highly correlated multiscale twin hierarchy organization in NiMnGaFeCu shape memory alloys. In this paper, high compatibility is found at the twin interfaces resulting in a highly correlated twinned lattice orientation across several laminate levels. The lattice unit cell is described as monoclinic I-centered with a = 4.28 Å, b = 4.27 Å, c = 5.40 Å, γ = 78.5°. The modulation is found parallel to the b axis. Finally, thin tapered needle-like lamellae and branching are observed near the twin boundaries.

  10. Elastic Constants of Ni-Mn-Ga Magnetic Shape Memory Alloys

    SciTech Connect

    Stipcich, M.; Manosa, L.; Planes, A.; Morin, M.; Zarestky, Jerel L; Lograsso, Tom; Stassis, C.

    2004-01-01

    We have measured the adiabatic second order elastic constants of two Ni-Mn-Ga magnetic shape memory crystals with different martensitic transition temperatures, using ultrasonic methods. The temperature dependence of the elastic constants has been followed across the ferromagnetic transition and down to the martensitic transition temperature. Within experimental errors no noticeable change in any of the elastic constants has been observed at the Curie point. The temperature dependence of the shear elastic constant C' has been found to be very different for the two alloys. Such a different behavior is in agreement with recent theoretical predictions for systems undergoing multi-stage structural transitions.

  11. Positron Annihilation Spectroscopy Study of Ni-Mn-Ga Ferromagnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Merida, David; Garcia, Jose Angel; Apiñaniz, Estibaliz; Plazaola, Fernando; Sanchez-Alarcos, Vicente; Pérez-Landazábal, Jose Ignacio; Recarte, Vicente

    We have studied the role that vacancy type defects play in the martensitic transformation of Ni-Mn-Ga ferromagnetic shape memory alloys by means of positron lifetime spectroscopy. The measurements presented in this work have been performed in five ternary alloys. Three of them transform to modulated and two to non-modulated martensitic phases. With these five samples we cover a large range in composition. Positron experiments have been performed at room temperature after subsequent isochronal annealing at different temperatures and up to a maximum temperature of 600°C. Results show a large variation of the average positron lifetime value with the isochronal annealing temperature in non-modulated samples. However, the response in the modulated samples is quite different. The results are discussed in term of different type of positron trapping defects and their evolution with the annealing temperature. The present work shows a correlation between vacancy concentration and martensitic transformation temperature of ferromagnetic shape memory alloys.

  12. Vacancy dynamic in Ni-Mn-Ga ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Merida, D.; García, J. A.; Sánchez-Alarcos, V.; Pérez-Landazábal, J. I.; Recarte, V.; Plazaola, F.

    2014-06-01

    Vacancies control any atomic ordering process and consequently most of the order-dependent properties of the martensitic transformation in ferromagnetic shape memory alloys. Positron annihilation spectroscopy demonstrates to be a powerful technique to study vacancies in NiMnGa alloys quenched from different temperatures and subjected to post-quench isothermal annealing treatments. Considering an effective vacancy type the temperature dependence of the vacancy concentration has been evaluated. Samples quenched from 1173 K show a vacancy concentration of 1100 ± 200 ppm. The vacancy migration and formation energies have been estimated to be 0.55 ± 0.05 eV and 0.90 ± 0.07 eV, respectively.

  13. Vacancy dynamic in Ni-Mn-Ga ferromagnetic shape memory alloys

    SciTech Connect

    Merida, D.; Sánchez-Alarcos, V.; Pérez-Landazábal, J. I.; Recarte, V.; Plazaola, F.

    2014-06-09

    Vacancies control any atomic ordering process and consequently most of the order-dependent properties of the martensitic transformation in ferromagnetic shape memory alloys. Positron annihilation spectroscopy demonstrates to be a powerful technique to study vacancies in NiMnGa alloys quenched from different temperatures and subjected to post-quench isothermal annealing treatments. Considering an effective vacancy type the temperature dependence of the vacancy concentration has been evaluated. Samples quenched from 1173 K show a vacancy concentration of 1100 ± 200 ppm. The vacancy migration and formation energies have been estimated to be 0.55 ± 0.05 eV and 0.90 ± 0.07 eV, respectively.

  14. Magnetic properties of single crystals of Ni-Mn-Ga magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Farrell, Shannon P.; Dunlap, Richard A.; Cheng, Leon M.; Ham-Su, Rosaura; Gharghouri, Michael A.; Hyatt, Calvin V.

    2004-07-01

    The magnetic shape memory (MSM) effect occurs in some ferromagnetic martensitic alloys at temperatures below the martensite finish temperature and involves the re-orientation of martensite variants by twin boundary motion, in response to an applied stress and/or magnetic field. The driving force for twin boundary motion is the magnetic anisotropy. In this study, magnetization measurements as a function of magnetic field were made on several oriented single crystals of Ni-Mn-Ga alloys using a vibrating sample magnetometer. The magnetization versus magnetic field curves were characteristic of magnetically soft materials with magnetic anisotropy consistent with literature estimates for the different martensite structures observed in Ni-Mn-Ga alloys. Differences in the slope of the curves were due to the martensite structure, the relative proportion of martensite variants present, and their respective easy and hard axis orientations. Thermo-magneto-mechanical training was applied in an attempt to transform multi-variant specimens to single variant martensite. Training of the orthorhombic 7M martensites was sufficient to produce a near single variant of martensite, while the tetragonal 5M martensite responded well to training and produced a single-variant state. The strength of the uniaxial magnetic anisotropy constant for single-variant tetragonal 5M martensite, Ni52.9Mn27.3Ga19.8, was calculated to be Ku=1.8 x 105 J/m3, consistent with literature values. To obtain single-variant martensites, heat-treatment of the specimens prior to thermo-magneto-mechanical training is necessary.

  15. Study of the transformation sequence on a high temperature martensitic transformation Ni-Mn-Ga-Co shape memory alloy

    NASA Astrophysics Data System (ADS)

    Recarte, V.; Pérez-Landazábal, J. I.; Sánchez-Alarcos, V.; Rodríguez-Velamazán, J. A.

    2014-11-01

    Ni-Mn-Ga alloys show the highest magnetic-field-induced strain among ferromagnetic shape memory alloys. A great effort is being done in this alloy system to increase the application temperature range. In this sense, the addition of small amounts of Cobalt to NiMnGa alloys has been proved to increase the MT temperatures through the increase of the electron per atom relation (e/a). In this work, the analysis of the crystal structure of the present phases and the phase transformations has been performed on a Ni-Mn-Ga-Co alloy by neutron diffraction measurements from 10 K to 673 K. The study has been completed by means of calorimetric and magnetic measurements. On cooling the alloy undergoes a martensitic transformation from a face centered cubic structure to a nonmodulated tetragonal martensite. The appearance of intermartensite transformations can be disregarded in the whole temperature range below the martensitic transformation. However, a jump in the unit-cell volume of the tetragonal martensite has been observed at 325 K. Since this temperature is close to the Curie temperature of the alloy both, the structural and magnetic contributions are taken into account to explain the results.

  16. Structural and dynamical fluctuations in off-stoichiometric NiMnGa shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Barabash, R. I.; Barabash, O. M.; Karapetrova, E. A.; Manley, M. E.

    2014-06-01

    Measurements and modeling of the 3D diffuse scattering from off-stoichiometric NiMnGa shape memory alloys reveal evidence of structural and dynamical precursors to the phase transition. A model of the diffuse scattering in the high temperature cubic L21 phase indicates that at temperatures tens of degrees higher than transition temperature, Tc, the lattice exhibits tetragonally distorted local regions that are clear precursors to the phase transition. The model also accounts for lattice deformation caused by precursor nanoregions of the martensite phase and thermal scattering from phonons and agrees well with the observed diffuse scattering maps in reciprocal space. A distinctive feature of the diffuse scattering is that it is highly anisotropic: Around (H0H) reflections, the diffuse scattering is strongly compressed along the [H0H] and enhanced along the [-H0H] direction. Additionally, localized intensity maxima associated with phasons are observed at temperatures 30-50 K above Tc. They clearly demonstrate that each phason corresponds to an individual point in reciprocal space, which is consistent with dynamical phase fluctuations of a well-formed charge density wave resulting from Peierls instability.

  17. Martensitic transformation in Cu-doped NiMnGa magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Li, Pan-Pan; Wang, Jing-Min; Jiang, Cheng-Bao

    2011-02-01

    This paper studies the martensitic transformation in the Cu-doped NiMnGa alloys. The orthorhombic martensite transforms to L21 cubic austenite by Cu substituting for Ni in the Ni50-xCuxMn31Ga19 (x=2-10) alloys, the martensitic transformation temperature decreases significantly with the rate of 40 K per Cu atom addition. The variation of the Fermi sphere radius (kF) is applied to evaluate the change of the martensitic transformation temperature. The increase of kF leads to the increase of the martensitic transformation temperature.

  18. Testing and modeling of NiMnGa ferromagnetic shape memory alloy for static and dynamic loading conditions

    NASA Astrophysics Data System (ADS)

    Couch, Ronald N.; Sirohi, Jayant; Chopra, Inderjit

    2006-03-01

    The response of NiMnGa ferromagnetic shape memory alloy to static and dynamic magnetic fields was studied. Tests involving excitation of the samples up to 10 Hz for constant stress and constant strain conditions were conducted. Based on these results, performance parameters were measured and discussed including power density, total power output and electromechanical efficiency. The effects of strain rate and material damping were also measured. It was shown that both power density and total power output were strong functions of applied stress. A maximum volumetric power density of 31 MW/m 3 was measured. Once the NiMnGa behavior was characterized, an analytical model based on four experimentally measured parameters was formulated to predict the induced strain in response to a dynamic magnetic field. Comparison of the analytical model to experimental data showed good correlation for applied stresses below 0.6 MPa and above 1.33 MPa. Although requiring further refinement, the model's results are encouraging, indicating that it could be developed into a useful analytical tool for predicting NiMnGa actuator behavior.

  19. The effect of doped elements on the martensitic transformation in Ni Mn Ga magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Guo, Shihai; Zhang, Yanghuan; Quan, Baiyun; Li, Jianliang; Qi, Yan; Wang, Xinlin

    2005-10-01

    Ni-Mn-Ga alloy is a new actuator material due to the fact that its shape memory effect can be controlled by magnetic field in addition to the conventional controls by temperature and stress. However, the alloy shows relatively low martensitic transformation and Curie temperatures. In this paper, we report the results of adding small amounts of Fe, Co and Tb to NiMnGa alloys. The effect of small additions of these doped elements on the martensitic transformation temperature is remarkable, but the Heusler structure of the alloys remains unchanged. For Ni50Mn27Ga23-xFex (x = 0,1,2) with partial replacement of Ga by Fe, the martensitic transformation temperatures increase with increase of the Fe content, and so does the Curie temperature. This phenomenon of increasing both the martensitic transformation temperatures and the Curie temperature was found for the first time. For Ni47Mn31X1Ga21 (X = Fe,Co), Fe and Co substitution for Mn, Fe increases the martensitic transformation temperature but decreases the Curie temperature, while Co has the opposite effect. For Ni48Mn33Ga18Tb1, the addition of the rare earth element Tb decreases the martensitic transformation temperature and the Curie temperature remarkably. Therefore, the transformation temperatures of the alloys can be improved by these doping methods.

  20. Extended investigation of intermartensitic transitions in Ni-Mn-Ga magnetic shape memory alloys: A detailed phase diagram determination

    SciTech Connect

    Çakir, Asli; Aktürk, Selçuk; Righi, Lara

    2013-11-14

    Martensitic transitions in shape memory Ni-Mn-Ga Heusler alloys take place between a high temperature austenite and a low temperature martensite phase. However, intermartensitic transformations have also been encountered that occur from one martensite phase to another. To examine intermartensitic transitions in magnetic shape memory alloys in detail, we carried out temperature dependent magnetization, resistivity, and x-ray diffraction measurements to investigate the intermartensitic transition in Ni{sub 50}Mn{sub 50–x}Ga{sub x} in the composition range 12≤x≤25 at. %. Rietveld refined x-ray diffraction results are found to be consistent with magnetization and resistivity data. Depending on composition, we observe that intermartensitic transitions occur in the sequences 7M→L1{sub 0}, 5M→7M, and 5M→7M→L1{sub 0} with decreasing temperature. The L1{sub 0} non-modulated structure is most stable at low temperature.

  1. Biocorrosion investigation of two shape memory nickel based alloys: Ni-Mn-Ga and thin film NiTi.

    PubMed

    Stepan, L L; Levi, D S; Gans, E; Mohanchandra, K P; Ujihara, M; Carman, G P

    2007-09-01

    Thin film nitinol and single crystal Ni-Mn-Ga represent two new shape memory materials with potential to be used as percutaneously placed implant devices. However, the biocompatibility of these materials has not been adequately assessed. Immersion tests were conducted on both thin film nitinol and single crystal Ni-Mn-Ga in Hank's balanced salt solution at 37 degrees C and pH 7.4. After 12 h, large pits were found on the Ni-Mn-Ga samples while thin film nitinol displayed no signs of corrosion. Further electrochemical tests on thin film nitinol samples revealed breakdown potentials superior to a mechanically polished nitinol disc. These results suggest that passivation or electropolishing of thin film nitinol maybe unnecessary to promote corrosion resistance.

  2. Optical and magneto-optical studies of martensitic transformation in Ni-Mn-Ga magnetic shape memory alloys

    SciTech Connect

    Beran, L.; Cejpek, P.; Kulda, M.; Antos, R.; Holy, V.; Veis, M.; Straka, L.; Heczko, O.

    2015-05-07

    Optical and magneto-optical properties of single crystal of Ni{sub 50.1}Mn{sub 28.4}Ga{sub 21.5} magnetic shape memory alloy during its transformation from martensite to austenite phase were systematically studied. Crystal orientation was approximately along (100) planes of parent cubic austenite. X-ray reciprocal mapping confirmed modulated 10 M martensite phase. Temperature depended measurements of saturation magnetization revealed the martensitic transformation at 335 K during heating. Magneto-optical spectroscopy and spectroscopic ellipsometry were measured in the sample temperature range from 297 to 373 K and photon energy range from 1.2 to 6.5 eV. Magneto-optical spectra of polar Kerr rotation as well as the spectra of ellipsometric parameter Ψ exhibited significant changes when crossing the transformation temperature. These changes were assigned to different optical properties of Ni-Mn-Ga in martensite and austenite phases due to modification of electronic structure near the Fermi energy during martensitic transformation.

  3. Electronic structure and magneto-optical Kerr effect spectra of ferromagnetic shape-memory Ni-Mn-Ga alloys: Experiment and density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Uba, S.; Bonda, A.; Uba, L.; Bekenov, L. V.; Antonov, V. N.; Ernst, A.

    2016-08-01

    In this joint experimental and ab initio study, we focused on the influence of the chemical composition and martensite phase transition on the electronic, magnetic, optical, and magneto-optical properties of the ferromagnetic shape-memory Ni-Mn-Ga alloys. The polar magneto-optical Kerr effect (MOKE) spectra for the polycrystalline sample of the Ni-Mn-Ga alloy of Ni60Mn13Ga27 composition were measured by means of the polarization modulation method over the photon energy range 0.8 ≤h ν ≤5.8 eV in magnetic field up to 1.5 T. The optical properties (refractive index n and extinction coefficient k ) were measured directly by spectroscopic ellipsometry using the rotating analyzer method. To complement experiments, extensive first-principles calculations were made with two different first-principles approaches combining the advantages of a multiple scattering Green function method and a spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic, and MO properties of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases in the stoichiometric and off-stoichiometric compositions. The optical and MOKE properties of Ni-Mn-Ga systems are very sensitive to the deviation from the stoichiometry. It was shown that the ab initio calculations reproduce well experimental spectra and allow us to explain the microscopic origin of the Ni2MnGa optical and magneto-optical response in terms of interband transitions. The band-by-band decomposition of the Ni2MnGa MOKE spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified.

  4. Micro-processing of NiMnGa shape memory alloy by using a nanosecond fiber laser

    NASA Astrophysics Data System (ADS)

    Biffi, C. A.; Tuissi, A.

    2016-04-01

    The interest on Ferromagnetic Shape Memory Alloys (FSMAs), such as NiMnGa, is growing up, thanks to their functional properties to be employed in a new class of micro-devices. The most evident critical issue, limiting the use of these systems in the production of industrial devices, is the brittleness of the bulk material; its workability by using convectional processing methods is very limited. Thus, alternative processing methods, including laser processing, are encouraged for the manufacture of FSMAs based new devices. In this work, the effect of the nanosecond laser microprocessing on Ni45Mn33Ga22 [at%] has been studied. Linear grooves were realized by a nanosecond 30 W fiber laser; the machined surfaces were analyzed with scanning electron microscopy, coupled with energetic dispersion spectroscopy for the composition analysis. The morphology of the grooves was affected by the laser scanning velocity and the number of laser pulses while the measured material removal rate appeared to be influenced mainly by the number of laser pulses. Compositional modification, associated to the loss of Ga content, was detected only for the lower scanning velocity, because of the high fluence. On the contrary, by increasing the velocity up to 1000 mm/s no Ga loss can be seen, making possible the laser processing of this functional alloy without its chemical modification. The use of short pulses allowed also to reduce the amount of recast material and the compositional change with respect to long pulses. Finally, the calorimetric analysis indicated that laser nanosecond microprocessing could affect the functional properties of this alloy: a larger decrease of the characteristic temperatures of the martensitic transformation was observed in correspondence of the low scanning velocity.

  5. Isothermal oxidation study on NiMnGa ferromagnetic shape memory alloy at 600-1000 °C

    NASA Astrophysics Data System (ADS)

    Kök, Mediha; Pirge, Gürsev; Aydoğdu, Yıldırım

    2013-03-01

    Oxidation behavior of NiMnGa alloy has been investigated under isothermal temperature by thermo gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy equipped with an energy dispersive X-ray (SEM-EDX) spectroscope systems. The Ni-28.5Mn-20.5Ga alloy (composition in atomic percent) was exposed to oxygen atmosphere isothermally, i.e., between 600 °C and 1000 °C, for 1 h. A gravimetric method was used to determine the oxidation kinetics; weight gain per unit area as a function of time. It was determined that the oxidation constant increases significantly with isothermal temperature. Activation energy of the oxidation was found to be 152 kJ/mol. X-ray diffraction patterns of the heat-treated samples contain oxide peaks, mainly belonging to Mn3O4. X-ray analyses demonstrate that the amount of the oxide increases with isothermal temperature while that of martensite phase decreases. The scanning electron microscopy equipped with an energy dispersive X-ray (SEM-EDX) spectroscope analysis also gives the same result. According to magnetic measurements, the saturation of NiMnGa alloys decreases with rising isothermal oxidation temperature.

  6. Martensitic and magnetic transformation in Ni-Mn-Ga-Co ferromagnetic shape memory alloys.

    SciTech Connect

    Cong, D. Y.; Wang, S.; Wang, Y. D.; Ren, Y.; Zuo, L.; Esling, C.; X-Ray Science Division; Northeastern Univ.; Univ. of Metz

    2008-01-01

    The effect of Co addition on crystal structure, martensitic transformation, Curie temperature and compressive properties of Ni{sub 53-x}Mn{sub 25}Ga{sub 22}Co{sub x} alloys with the Co content up to 14 at% was investigated. An abrupt decrease of martensitic transformation temperature was observed when the Co content exceeded 6 at.%, which can be attributed to the atomic disorder resulting from the Co addition. Substitution of Co for Ni proved efficient in increasing the Curie temperature. Compression experiments showed that the substitution of 4 at.% Co for Ni did not change the fracture strain, but lead to the increase in the compressive strength and the decrease in the yield stress. This study may offer experimental data for developing high performance ferromagnetic shape memory alloys.

  7. Development of NiMnGa-based ferromagnetic shape memory alloy by rapid solidification route

    NASA Astrophysics Data System (ADS)

    Panda, A. K.; Kumar, Arvind; Ghosh, M.; Mitra, A.

    The ferromagnetic shape memory alloy with nominal composition of Ni 52.5Mn 24.5Ga 23(at%) was developed by the melt-spinning technique. The as-spun ribbon showed dominant L2 1 austenitic (cubic) structure with splitting of primary peak in the X-ray diffractogram indicating existence of a martensitic feature. The quenched-in martensitic plates were revealed from Transmission electron microscopy (TEM). Increase of magnetisation at low-temperature rise indicates martensite to austenite transformation and its reverse with a drop in magnetisation during cooling cycle. The martensite to austenite transformation can be made spontaneous at higher magnetic field.

  8. Effects of the substitution of gallium with boron on the physical and mechanical properties of Ni-Mn-Ga shape memory alloys

    NASA Astrophysics Data System (ADS)

    Aydogdu, Yildirim; Turabi, Ali Sadi; Kok, Mediha; Aydogdu, Ayse; Tobe, Hirobumi; Karaca, Haluk Ersin

    2014-12-01

    The effects of the substitution of gallium with boron on the physical, mechanical and magnetic shape memory properties of Ni51Mn28.5Ga20.5- xBx (at.%) ( x = 0, 1, 2, 3) polycrystalline alloys are investigated. It has been found that transformation temperatures are decreasing while hardness is increasing with boron addition. B-doping of NiMnGa alloys results in the formation of a second phase that increases its ductility and strength in compression. Moreover, saturation magnetization of austenite is decreasing, while Curie temperature of austenite is increasing with B-doping.

  9. Magneto-optical spectroscopy of ferromagnetic shape-memory Ni-Mn-Ga alloy

    SciTech Connect

    Veis, M. Beran, L.; Zahradnik, M.; Antos, R.; Straka, L.; Kopecek, J.; Fekete, L.; Heczko, O.

    2014-05-07

    Magneto-optical properties of single crystal of Ni{sub 50.1}Mn{sub 28.4}Ga{sub 21.5} magnetic shape memory alloy in martensite and austenite phase were systematically studied. Crystal orientation was approximately along (100) planes of parent cubic austenite. At room temperature, the sample was in modulated 10M martensite phase and transformed to cubic austenite at 323 K. Spectral dependence of polar magneto-optical Kerr effect was obtained by generalized magneto-optical ellipsometry with rotating analyzer in the photon energy range from 1.2 to 4 eV, and from room temperature to temperature above the Curie point. The Kerr rotation spectra exhibit prominent features typical for complexes containing Mn atoms. Significant spectral changes during transformation to austenite can be explained by different optical properties caused by changes in density of states near the Fermi energy.

  10. Temperature dependence of the giant magnetostrain in a NiMnGa magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Jiang, Chengbao; Wang, Jingmin; Xu, Huibin

    2005-06-01

    The temperature dependence of the magnetostrain was investigated in the Ni50Mn27.5Ga22.5 magnetic shape memory alloy with a five-layer martensitic (5M) structure in the temperature range from 110Kto300K. A temperature threshold at 166K was found for the magnetostrain. A giant magnetostrain of 6.3% was achieved above the temperature, while no magnetostrain was monitored below the temperature. No intermartensitic transformation was detected around the temperature threshold. The lattice parameter a slightly increases, c largely decreases, and the tetragonality (a/c-1) drastically increases with decreasing the temperature. The increase of the tetragonality is thought to be related to the temperature threshold of the magnetostrain by inducing a change of the electronic structure, twin structure, or the type of the variant with the same 5M martensitic structure below the temperature threshold. The interpretation is reasonably understood by the fact that only few samples with the same 5M martensitic structure exhibit a giant magnetostrain.

  11. Effect of Thermal Treatments on Ni-Mn-Ga and Ni-Rich Ni-Ti-Hf/Zr High-Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Santamarta, Ruben; Evirgen, Alper; Perez-Sierra, Aquilina M.; Pons, Jaume; Cesari, Eduard; Karaman, Ibrahim; Noebe, Ron D.

    2015-11-01

    Among all the promising high-temperature shape memory alloys (HTSMAs), the Ni-Mn-Ga and the Ni-Ti-Hf/Zr systems exhibit interesting shape memory and superelastic properties that may place them in a good position for potential applications. The present work shows that thermal treatments play a crucial role in controlling the martensitic phase transformation characteristics of both systems, but in different ways. On one hand, the equilibrium phase diagram of the Ni-Mn-Ga family allows selecting compositions with high transformation temperatures and outstanding thermal stability at relatively high temperatures in air, showing no significant changes in the transformation behavior for continuous aging up to ˜5 years at 500 °C. Moreover, the excellent thermal stability correlates with a good thermal cyclic stability and an exceptional oxidation resistance of the parent phase. On the other hand, precipitation processes controlled by thermal treatments are needed to manipulate the transformation temperatures, mechanical properties, and thermal stability of Ni-rich Ni-Ti-Hf/Zr alloys to become HTSMAs. These changes in the functional properties are a consequence of the competition between the mechanical and compositional effects of the precipitates on the martensitic transformation.

  12. Phase Transition and Texture Evolution in the Ni-Mn-Ga Ferromagnetic Shape-Memory Alloys Studied by a Neutron Diffraction Technique

    NASA Astrophysics Data System (ADS)

    Nie, Z. H.; Wang, Y. D.; Wang, G. Y.; Richardson, J. W.; Wang, G.; Liu, Y. D.; Liaw, P. K.; Zuo, L.

    2008-12-01

    The phase transition and influence of the applied stress on the texture evolution in the as-cast Ni-Mn-Ga ferromagnetic shape-memory alloys were studied by the time-of-flight (TOF) neutron diffraction technique. The neutron diffraction experiments were performed on the General Purpose Powder Diffractometer (Argonne National Laboratory). Inverse pole figures were determined from the neutron data for characterizing the orientation distributions and variant selections of polycrystalline Ni-Mn-Ga alloys subjected to different uniaxial compression deformations. Texture analyses reveal that the initial texture for the parent phase in the as-cast specimen was composed of {left\\{ {{text{001}}} right\\}}{left< {{text{100}}} rightrangle } , {left\\{ {{text{001}}} right\\}}{left< {{text{110}}} rightrangle } , {left\\{ {{text{011}}} right\\}}{left< {{text{100}}} rightrangle } , and {left\\{ {{text{011}}} right\\}}{left< {{text{110}}} rightrangle } , which was weakened after the compression deformation. Moreover, a strong preferred selection of martensitic-twin variants ( {left\\{ {{text{110}}} right\\}}{left< {{text{001}}} rightrangle } and {left\\{ {{text{100}}} right\\}}{left< {{text{001}}} rightrangle } ) was observed in the transformed martensite after a compression stress applied on the parent phase along the cyclindrical axis of the specimens. The preferred selection of variants can be well explained by considering the grain/variant-orientation-dependent Bain-distortion energy.

  13. Ni-Mn-Ga shape memory nanoactuation

    SciTech Connect

    Kohl, M. Schmitt, M.; Krevet, B.; Backen, A.; Schultz, L.; Fähler, S.

    2014-01-27

    To probe finite size effects in ferromagnetic shape memory nanoactuators, double-beam structures with minimum dimensions down to 100 nm are designed, fabricated, and characterized in-situ in a scanning electron microscope with respect to their coupled thermo-elastic and electro-thermal properties. Electrical resistance and mechanical beam bending tests demonstrate a reversible thermal shape memory effect down to 100 nm. Electro-thermal actuation involves large temperature gradients along the nanobeam in the order of 100 K/μm. We discuss the influence of surface and twin boundary energies and explain why free-standing nanoactuators behave differently compared to constrained geometries like films and nanocrystalline shape memory alloys.

  14. Ferromagnetic shape memory in the NiMnGa system

    SciTech Connect

    Tickle, R.; James, R.D.; Shield, T.; Wuttig, M.; Kokorin, V.V.

    1999-09-01

    Strain versus field measurements for a ferromagnetic shape memory alloy in the NiMnGa system demonstrate the largest magnetostrictive strains to date of nearly 1.3%. These strains are achieved in the martensitic state through field-induced variant rearrangement. An experimental apparatus is described that provides biaxial magnetic fields and uniaxial compressive prestress with temperature control while recording microstructural changes with optical microscopy. The magnetostrictive response is found to be sensitive to the initial state induced by stress-biasing the martensitic variant structure, and exhibits rate effects related to twin boundary mobility. Experiments performed with constant stress demonstrate work output capacity. Experimental results are interpreted by using a theory based on minimization of a micromagnetic energy functional that includes applied field, stress, and demagnetization energies. It is found that the theory provides a good qualitative description of material behavior, but significantly overpredicts the amount of strain produced. Issues concerning the martensitic magnetic anisotropy and variant nucleation are discussed with regard to this discrepancy.

  15. Defects structure characterization of NiMnGa alloys by PALS

    NASA Astrophysics Data System (ADS)

    Merida, David; Garcia, Jose Angel; Plazaola, Fernando; Sanchez-Alarcos, Vicente; Pérez-Landazábal, Jose Ignacio; Recarte, Vicente

    2013-06-01

    We have studied the behaviour of defects in off-stoichiometric Ni-Mn-Ga ferromagnetic shape memory alloys by means of positron lifetime spectroscopy. The measurements presented in this work have been performed in six ternary alloys. The studied samples cover a large composition range. Positron experiments have been performed at room temperature after subsequent isochronal annealing at different temperatures up to a maximum temperature of 700°C. Results show a large variation of the average positron lifetime value with the isochronal annealing temperature in three of these samples, with significant differences between them. In the other three, the response is quite different. The results are discussed in terms of different types of positron trapping defects and their evolution with the annealing temperature. The present work shows a high dependence of recovery behaviour with composition in NiMnGa ferromagnetic shape memory alloys.

  16. The effects of alloying elements Al and In on Ni-Mn-Ga shape memory alloys, from first principles.

    PubMed

    Chen, Jie; Li, Yan; Shang, Jia-Xiang; Xu, Hui-Bin

    2009-01-28

    The electronic structures and formation energies of the Ni(9)Mn(4)Ga(3-x)Al(x) and Ni(9)Mn(4)Ga(3-x)In(x) alloys have been investigated using the first-principles pseudopotential plane-wave method based on density functional theory. The results show that both the austenite and martensite phases of Ni(9)Mn(4)Ga(3) alloy are stabilized by Al alloying, while they become unstable with In alloying. According to the partial density of states and structural energy analysis, different effects of Al and In alloying on the phase stability are mainly attributed to their chemical effects. The formation energy difference between the austenite and martensite phases decreases with Al or In alloying, correlating with the experimentally reported changes in martensitic transformation temperature. The shape factor plays an important role in the decrease of the formation energy difference.

  17. Effect of Heat-Treatment on the Phases of Ni-Mn-Ga Magnetic Shape Memory Alloys

    SciTech Connect

    Huq, Ashfia; Ari-Gur, Pnina; Kimmel, Giora; Richardson, James W; Sharma, Kapil

    2009-01-01

    The Heusler alloys Ni50Mn25+xGa25-x display magnetic shape memory effect (MSM) with very fast and large reversible strain under magnetic fields. This large strain and the speed of reaction make MSM alloys attractive as smart materials. Our crystallographic investigation of these alloys, focused on non-stoichiometric composition with excess of manganese. Using neutron diffraction, we revealed the necessary processing parameters to achieve and preserve the homogeneous metastable one-phase martensitic structure that is needed for an MSM effect at room temperature.

  18. Magnetic and mechanical properties of Ni-Mn-Ga/Fe-Ga ferromagnetic shape memory composite

    NASA Astrophysics Data System (ADS)

    Tan, Chang-Long; Zhang, Kun; Tian, Xiao-Hua; Cai, Wei

    2015-05-01

    A ferromagnetic shape memory composite of Ni-Mn-Ga and Fe-Ga was fabricated by using spark plasma sintering method. The magnetic and mechanical properties of the composite were investigated. Compared to the Ni-Mn-Ga alloy, the threshold field for magnetic-field-induced strain in the composite is clearly reduced owing to the assistance of internal stress generated from Fe-Ga. Meanwhile, the ductility has been significantly improved in the composite. A fracture strain of 26% and a compressive strength of 1600 MPa were achieved. Projects supported by the National Natural Science Foundation of China (Grant Nos. 51271065 and 51301054), the Program for New Century Excellent Talents in Heilongjiang Provincial Education Department, China (Grant No. 1253-NCET-009), the Youth Academic Backbone in Heilongjiang Provincial Education Department, China (Grant No. 1251G022), the Projects of Heilongjiang, China, and China Postdoctoral Science Foundation.

  19. Energy harvesting using martensite variant reorientation mechanism in a NiMnGa magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Karaman, I.; Basaran, B.; Karaca, H. E.; Karsilayan, A. I.; Chumlyakov, Y. I.

    2007-04-01

    Magnetic shape memory alloys demonstrate significant potential for harvesting waste mechanical energy utilizing the Villari effect. In this study, a few milliwatts of power output are achieved taking advantage of martensite variant reorientation mechanism in Ni51.1Mn24Ga24.9 single crystals under slowly fluctuating loads (10Hz) without optimization in the power conversion unit. Effects of applied strain range, bias magnetic field, and loading frequency on the voltage output are revealed. Anticipated power outputs under moderate frequencies are predicted showing that the power outputs higher than 1W are feasible.

  20. Magnetic transitions and structure of a NiMnGa ferromagnetic shape memory alloy prepared by melt spinning technique

    NASA Astrophysics Data System (ADS)

    Panda, A. K.; Ghosh, M.; Kumar, Arvind; Mitra, A.

    A ferromagnetic shape memory alloy with nomial composition Ni 52.5Mn 24.5Ga 23 (at%) was developed by a melt spinning technique. The as-spun ribbon showed dominant L2 1 austenitic (cubic) structure with a splitting of the primary peak in the X-ray diffractogram indicating the existence of a martensitic feature. The quenched-in martensitic plates were revealed in transmission electron microscopy. An increase of magnetization at low temperature indicated a martensite to austenite transformation and its reverse with a drop in magnetization during the cooling cycle. Higher magnetic fields propel martensite-austenite transformation spontaneously.

  1. Internal variable model for magneto-mechanical behaviour of ferromagnetic shape memory alloys Ni-Mn-Ga

    NASA Astrophysics Data System (ADS)

    Hirsinger, L.; Lexcellent, C.

    2003-10-01

    In this paper, a predictive model of field-induced strain in Ferromagnetic Shape Memory Alloy (FSMA) is proposed. This phenomenological scalar magneto-mechanical model is built in the frame of thermodynamic of irreversible process. The strain mechanism corresponds to the reorientation process of twinned martensite platelets at constant temperature. In this model, physical microstructure parameters are chosen as variables: volume fraction z of one martensite variant and ratio α of magnetic domain width. Pure mechanical behaviour of FSMA is supposed to be decomposed in reversible (or anhysteretic) part and irreversible one. From dissipation, a yield function written in terms of energy, has been introduced to determine when reorientation of twinned martensite platelets (via internal variable z) could occur. Pure magnetic behaviour is supposed to be non-liner reversible. The coupling between magnetism and mechanics is introduced in the expression of magnetisation via microstructure parameters z and a. The good prediction capability of the proposed model is shown by an identification made on experiments performed by O'Handley & Murray: simulations of strain induced by pure mechanical loading or by applied magnetic field under constant compressive stress, are presented and compared with these experiments. These first results are very promising.

  2. Latent heat contribution to the direct magnetocaloric effect in Ni-Mn-Ga shape memory alloys with coupled martensitic and magnetic transformations

    NASA Astrophysics Data System (ADS)

    Caballero-Flores, R.; Sánchez-Alarcos, V.; Recarte, V.; Pérez-Landazábal, J. I.; Gómez-Polo, C.

    2016-05-01

    We report the direct magnetocaloric response of materials that present a second-order phase transition in the temperature range where a first-order structural transition also occurs. In particular, the influence of the latent heat on the field-induced adiabatic temperature change has been analyzed in a Ni-Mn-Ga alloy with coupled martensitic and magnetic transformations. It is found that discrepancies around 20% arise depending on whether the latent heat is taken into account or not. From the observed results, a general expression for the indirect determination of the adiabatic temperature change, that takes into account the contributions of both the martensitic and magnetic transformations, is proposed and experimentally confirmed. The observed key role of the latent heat allows us to understand why materials with first-order transformations do not present adiabatic temperature changes as higher as those which would correspond to materials undergoing second-order transformations with similar isothermal entropy change.

  3. Microstructural Development and Ternary Interdiffusion in Ni-Mn-Ga Alloys

    NASA Astrophysics Data System (ADS)

    Zhou, Le; Kammerer, Catherine; Giri, Anit; Cho, Kyu; Sohn, Yongho

    2015-12-01

    NiMnGa alloys functioning as either ferromagnetic shape memory alloys or magnetocaloric materials have both practical applications and fundamental research value. In this study, solid-to-solid diffusion couple experiments were carried out to investigate the phase equilibria, microstructural development, and interdiffusion behavior in Ni-Mn-Ga ternary alloys. Selected diffusion couples between pure Ni, Ni25Mn75 and four ternary off-stoichiometric NiMnGa alloys ( i.e., Ni52Mn18Ga30, Ni46Mn30Ga24, Ni52Mn30Ga18, Ni58Mn18Ga24) were assembled and annealed at 1073 K, 1123 K, and 1173 K (800 °C, 850 °C, and 900 °C) for 480, 240, and 120 hours, respectively. At these high temperatures, the β NiMnGa phase has a B2 crystal structure. The microstructure of the interdiffusion zone was examined by scanning electron microscopy and transmission electron microscopy. Concentration profiles across the interdiffusion zone were determined by electron probe micro analysis. Solubility values obtained for various phases were mostly consistent with the existing isothermal phase diagrams, but the phase boundary of the γ(Mn) + β two-phase region was slightly modified. In addition, equilibrium compositions for the γ(Ni) and α' phases at 1173 K (900 °C) were also determined for the respective two-phase region. Both austenitic and martensitic phases were found at room temperature in each diffusion couple with a clear boundary. The compositions at the interfaces corresponded close to valence electron concentration (e/a) of 7.6, but trended to lower values when Mn increased to more than 35 at. pct. Average effective interdiffusion coefficients for the β phase over different compositional ranges were determined and reported in the light of temperature-dependence. Ternary interdiffusion coefficients were also determined and examined to assess the ternary diffusional interactions among Ni, Mn, and Ga. Ni was observed to interdiffuse the fastest, followed by Mn then Ga. Interdiffusion flux

  4. Deformation twinning in polycrystalline NiMnGa alloys

    NASA Astrophysics Data System (ADS)

    Chulist, R.; Pötschke, M.; Lippmann, T.; Oertel, C.-G.; Skrotzki, W.

    2010-07-01

    The texture and local orientation after compression of a NiMnGa polycrystal and a bicrystal with 5M modulated structure were measured with synchrotron radiation and electron backscatter diffraction (EBSD), respectively. Compression of both samples leads to motion of those twin boundaries changing the volume fraction of particular martensitic variants in such a way that the shortest axis (c-axis) becomes preferentially aligned parallel to the compression axis. EBSD directly confirms the motion of twin boundaries within individual grains.

  5. A model for giant magnetostrain and magnetization in the martensitic phase of NiMnGa alloys

    NASA Astrophysics Data System (ADS)

    Pei, Yongmao; Fang, Daining

    2007-06-01

    A model on the basis of transformation kinetics is developed in this paper in which magnetic-field-induced stress is introduced and the equivalence principle is employed for mechanical and magnetoelastic deformation. An exponential expression is given to describe the field dependence of magnetization for martensitic variants. A good agreement between the theoretical calculations and the experimental results is achieved for the non-stoichiometric Ni2MnGa alloys. The proposed simple model is acceptable for describing magnetization and magnetic-field-induced strain behavior of ferromagnetic shape memory NiMnGa alloys.

  6. An anisotropic micromechanical-based model for characterizing the magneto-mechanical behavior of NiMnGa alloys

    NASA Astrophysics Data System (ADS)

    Wang, Xingzhe; Li, Fang; Hu, Qiang

    2012-06-01

    As a typical ferromagnetic shape memory alloy (FSMA), NiMnGa alloy at room temperature is a heterogeneous material with martensitic variants and a high magnetic anisotropy property to produce a giant magnetic-induced strain and high frequency response. A theoretical model based on micromechanical and thermodynamic theory is proposed to describe the magneto-mechanical behavior of single-crystal FSMAs during the reorientation process of martensitic variants. It follows the well-established Eshelby equivalent inclusion method and the Mori-Tanaka scheme, and incorporates the influence of the material anisotropy and the variant inclusion morphology on the reorientation of the martensite variants. The modified micromechanical model is further applied to characterize the stress-strain behavior and magnetic-field-induced strain during the martensite variant rearrangement process in a single-crystal NiMnGa rod under applied magnetic field and/or mechanical loading. The simulation results show good agreement with the experimental data. The effects of the material anisotropy and inclusion morphology on the magnetoelastic constitutive behavior of FSMAs are discussed.

  7. Microstructure characterization of the non-modulated martensite in Ni-Mn-Ga alloy

    SciTech Connect

    Han, M. Bennett, J.C.; Gharghouri, M.A.; Chen, J.; Hyatt, C.V.; Mailman, N.

    2008-06-15

    The microstructure of the non-modulated martensite in a Ni-Mn-Ga alloy has been characterized in detail by conventional transmission electron microscopy. Bright field images show that the martensite exhibits an internal substructure consisting of a high density of narrow twins. Using electron diffraction, it is found that the martensite has a tetragonal crystal structure. The lattice correspondence between the parent phase and the non-modulated martensite is investigated. Furthermore, the four twinning elements describing the microtwinning have been graphically and quantitatively determined. The results indicate that the microtwinning within the non-modulated martensite belongs to the compound type.

  8. Complex magnetic interactions in off-stoichiometric NiMnGa alloys

    NASA Astrophysics Data System (ADS)

    Ghosh, Subhradip; Sanyal, Biplab

    2010-09-01

    Using first-principles density functional theory, the magnetic pair interactions between various pairs of chemical specie have been calculated and the trends in magnetism with varying compositions and chemical ordering are analyzed for three off-stoichiometric NiMnGa alloys in their austenite phases. The experimentally observed trend of decreasing magnetization with increasing Mn concentration is attributed to the antiferromagnetic interactions among Mn atoms occupying sublattices other than the original Mn one. The role of chemical ordering on magnetization is also analyzed by total energy results and exchange interactions. We are able to explain the recently published neutron scattering experiments with our theoretical analyses.

  9. Reverse magnetostructural transformation in Co-doped NiMnGa multifunctional alloys

    NASA Astrophysics Data System (ADS)

    Fabbrici, S.; Albertini, F.; Paoluzi, A.; Bolzoni, F.; Cabassi, R.; Solzi, M.; Righi, L.; Calestani, G.

    2009-07-01

    We studied the composition dependence of the structural and magnetic properties of Co-doped Ni-Mn-Ga alloys around the Mn-rich composition Ni50Mn30Ga20. By varying the Co and Mn content we have been able to tune the critical temperatures. In particular, in a suitable composition range, the Curie temperature of martensite is lower than Curie temperature of austenite and lower than martensitic transformation temperature, giving rise to a paramagnetic gap between magnetically ordered martensite and austenite and to the occurrence of a reverse magnetostructural transformation.

  10. Complex magnetic interactions in off-stoichiometric NiMnGa alloys.

    PubMed

    Ghosh, Subhradip; Sanyal, Biplab

    2010-09-01

    Using first-principles density functional theory, the magnetic pair interactions between various pairs of chemical specie have been calculated and the trends in magnetism with varying compositions and chemical ordering are analyzed for three off-stoichiometric NiMnGa alloys in their austenite phases. The experimentally observed trend of decreasing magnetization with increasing Mn concentration is attributed to the antiferromagnetic interactions among Mn atoms occupying sublattices other than the original Mn one. The role of chemical ordering on magnetization is also analyzed by total energy results and exchange interactions. We are able to explain the recently published neutron scattering experiments with our theoretical analyses. PMID:21403266

  11. Enhanced magnetic hysteresis in Ni-Mn-Ga single crystal and its influence on magnetic shape memory effect

    SciTech Connect

    Heczko, O. Drahokoupil, J.; Straka, L.

    2015-05-07

    Enhanced magnetic hysteresis due to boron doping in combination with magnetic shape memory effect in Ni-Mn-Ga single crystal results in new interesting functionality of magnetic shape memory (MSM) alloys such as mechanical demagnetization. In Ni{sub 50.0}Mn{sub 28.5}Ga{sub 21.5} single crystal, the boron doping increased magnetic coercivity from few Oe to 270 Oe while not affecting the transformation behavior and 10 M martensite structure. However, the magnetic field needed for MSM effect also increased in doped sample. The magnetic behavior is compared to undoped single crystal of similar composition. The evidence from the X-ray diffraction, magnetic domain structure, magnetization loops, and temperature evolution of the magnetic coercivity points out that the enhanced hysteresis is caused by stress-induced anisotropy.

  12. Structural and magnetic investigations in the vicinity of first-order transformations in Ni-Mn-Ga-Co ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Satish Kumar, A.; Ramudu, M.; Seshubai, V.

    2012-12-01

    Among the series of alloys derived from Ni50Mn29Ga21 on selective substitution of Co for Ni and Mn, two alloys Ni49.8Mn27.2Ga21.2Co1.8 and Ni46.9Mn28.8Ga21Co3.3 referred to as CoMn-1.8 and CoNi-3.3, respectively, are found to exhibit an additional first-order transformation below their martensitic transformation temperatures. Systematic studies on temperature and field dependence of magnetic properties of these alloys are carried out, through the transformations, to understand their origin. An examination of these results in conjunction with those from structural investigations reveals that the transformation in the CoMn-1.8 alloy is an intermartensitic transformation and has a structural origin, while that in the CoNi-3.3 alloy is not of the structural origin and is attributed to local spin inversion of Co moments, which is of the magnetic origin.

  13. Effect of composition on the magnetic and elastic properties shape-memory Ni-Mn-Ga

    NASA Astrophysics Data System (ADS)

    Malla, Aayush; Dapino, Marcelo J.; Lograsso, Thomas A.; Schlagel, Deborah

    2003-08-01

    The growing interest in ferromagnetic shape-memory Ni-Mn-Ga for implementation in actuator applications originates from the fact that this class of materials exhibits large strains when driven by a magnetic field. Large bidirectional strains up to a theoretical 6% are produced in these materials by twin boundary motion as martensite variants rotate to align respectively parallel or perpendicular to applied magnetic fields or stresses. These strains represent a significant improvement over piezoelectric and magnetostrictive materials. In this paper, we report on experimental measurements conducted on Ni-Mn-Ga cylindrical rods subjected to uniaxial stresses and uniaxial magnetic fields which were applied collinearly along the magnetic easy axis direction of the rods. To this end, a test apparatus was developed which consists of a water-cooled solenoid actuator and a loading fixture. Despite the lack of a readily recognizable mechanism for reversible deformations, bidirectional strains as large as 4300 ppm (0.43%) were observed, or three times the saturation magnetostriction of Terfenol-D. This paper presents room-temperature data including magnetization hysteresis, strain versus field and peak strain versus stress curves collected over a range of stresses between 0-65 MPa. From the latter set of curves, blocking force values are estimated as those for which the strain is 1% of the maximum (zero-load) strain. The results illustrate the sensitivity of material behavior with respect to composition at different driving conditions and offer insight on the choice of material compositions at which maximum actuation performance is achieved.

  14. Experimental Characterization of the Magnetomechanical Response and Power Harvesting Suitability of a NiMnGa Alloy

    NASA Astrophysics Data System (ADS)

    Nelson, Isaac D.

    NiMnGa is a relatively new metallic alloy that exhibits the shape memory effect in the presence of a magnetic field, hence its name of magnetic shape memory alloy (MSMA). MSMAs are considered to be smart materials that are characterized by magneto-mechanical coupling which can be used to induce and recover reorientation strain of up to 10%. The amount of recoverable strain varies depending on the training and chemical composition of the alloy [11]. Over the past decade, while material development was ongoing, MSMAs have been investigated extensively to determine their magneto-mechanical properties and response, primarily under constant compressive stress-variable magnetic field, and under constant magnetic field -- variable compressive stress (with the stress and field directions mutually perpendicular). These loading conditions may be exhibited by the material in practical applications such as actuation, sensing and or power harvesting. However, as other loading cases may be envisioned for practical applications, further magneto-mechanical characterization of the material was required, which motivated the work performed for this thesis.

  15. Neutron diffraction study of a non-strichiometric Ni-Mn-Ga MSM alloy

    SciTech Connect

    Ari-Gur, Pnina; Garlea, Vasile O

    2013-01-01

    The structure and chemical order of a Heusler alloy of non-stoichiometric composition Ni-Mn-Ga were studied using constant-wavelength (1.538 ) neutron diffraction at 363K and the diffraction pattern was refined using the FullProf software. At this temperature the structure is austenite (cubic) with Fm-3m space group and lattice constant of a = 5.83913(4) [ ]. The chemical order is of critical importance in these alloys, as Mn becomes antiferromagnetic when the atoms are closer than the radius of the 3d shell. In the studied alloy the refinement of the site occupancy showed that the 4b (Ga site) contained as much as 22% Mn; that significantly alters the distances between the Mn atoms in the crystal and, as a result, also the exchange energy between some of the Mn atoms. Based on the refinement, the composition was determined to be Ni1.91Mn1.29Ga0.8

  16. Microstructure and twinning in epitaxial NiMnGa films

    NASA Astrophysics Data System (ADS)

    Mahnke, Guido J.; Seibt, M.; Mayr, S. G.

    2008-07-01

    Although magnetic shape memory alloys have attracted large scientific interest, miniaturization as single-crystalline thin films is still a greatly unresolved issue. In the present work we investigate the microstructure of epitaxial NiMnGa thin films which are fabricated by sputter deposition on magnesium oxide substrates at elevated temperatures. Transmission and scanning electron microscopy as well as atomic force microscopy studies are employed to relate surface topography to twin formation in 7 M martensitic NiMnGa films. Additional findings include pore formation in substrate proximity as well as minor precipitation with reduced nickel and gallium contents.

  17. Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Yang; Wang, Y. D.

    2015-07-08

    The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.

  18. Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Yang; Wang, Y. D.

    2015-06-03

    The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.

  19. Phase Transformation and Magnetic Property of Ni-Mn-Ga Powders Prepared by Dry Ball Milling

    NASA Astrophysics Data System (ADS)

    Tian, B.; Chen, F.; Tong, Y. X.; Li, L.; Zheng, Y. F.

    2012-12-01

    This study investigated the phase transformations and magnetic properties of Ni-Mn-Ga alloy powders prepared by dry ball milling in argon atmosphere. The Fe and Cr elements were found to be introduced in the alloy after ball milling, which should result from the severe collision and friction among the particles, balls, and vial. The x-ray diffraction result indicated that the Fe and Cr elements should have alloyed with the Ni-Mn-Ga matrix. The martensitic transformation temperature and Curie temperature of the 800 °C annealed powders decreased by ~33 °C and increased by ~28 °C, respectively, as compared to that of the bulk alloy. The comprehensive effect of the changing of valence electron concentration of the alloy due to the introduction of Fe and Cr and the grain refinement of the alloy caused by ball milling should be responsible for the reduction of martensitic transformation temperature. The saturation magnetization of the 800 °C annealed powders became larger (~5 emu/g) than that of the bulk alloy. The enhancement of magnetic properties, such as the increase of Curie temperature and enhancement of saturation magnetization of the annealed Ni-Mn-Ga powders, should be attributed to the increase of magnetic exchange caused by introduction of Fe in the alloy. The contaminations of Fe and Cr elements emerging from the dry ball milling process changed the phase transformation and magnetic properties of the Ni-Mn-Ga alloy. Therefore, the dry ball milling process is difficult to control the contamination from the milling medium and not suitable to prepare Ni-Mn-Ga powders. On the contrary, the wet ball milling method under liquid medium should be a better method to prevent the contamination and fabricate pure Ni-Mn-Ga ferromagnetic shape memory alloy powders.

  20. Three dimensional experimental characterization of a NiMnGa alloy

    NASA Astrophysics Data System (ADS)

    Nelson, Isaac; Ciocanel, Constantin; LaMaster, Doug; Feigenbaum, Heidi

    2013-04-01

    Magnetic shape memory alloys (MSMAs) are materials that can display up to 10% recoverable strain in response to the application of a magnetic field or compressive mechanical stress. The recoverable strain depends on the magnitude of the stress and magnetic field that is applied to the material. Due to their large strains as well as fast response, MSMAs are suitable for actuation, power harvesting, and sensing applications. Broadening the range of applications for MSMAs requires an understanding of their magneto-mechanical behavior beyond 2D loading cases that have been studied to date. The response of MSMAs is primarily driven by the reorientation of martensite variants. During the reorientation process a change in material's magnetization occurs. Using a pick-up coil (placed around, or on the side, of the specimen) one may convert this change in magnetization into an electric potential/voltage, making the material act as a power harvester. The magnitude of the output voltage depends on the number of turns of the pick-up coil, the amplitude of the reorientation strain, the magnitude and direction of the biased magnetic field, and the frequency at which the reorientation occurs. This paper presents experimental results for the material behavior under 3D loading conditions, including power harvesting data generated under such loading conditions. The 3D experimental data includes the material's response to two compressive mechanical stresses, applied in perpendicular directions, simultaneously with the application of a magnetic field applied in the remaining orthogonal direction. The power harvesting data includes magnetic fields in multiple directions and different orientations of the pick-up coil. Results indicate that the presence of a bias magnetic field along the specimen length (i.e. the direction of application of the compressive stress) in addition to that applied normal to the specimen length, leads to an increase in the electric potential output.

  1. A less expensive NiMnGa based Heusler alloy for magnetic refrigeration

    NASA Astrophysics Data System (ADS)

    Mejía, C. Salazar; Gomes, A. M.; de Oliveira, L. A. S.

    2012-04-01

    We present a study of the substitution of Mn by Cu on the compound Ni2 Mn1-x Cux Ga0.9 Al0.1, showing that the substitution of a small amount of Al on the Ga site does not affect the magnetic and magnetocaloric potential compared to Ni2(Mn,Cu)Ga alloy. The samples were prepared with 10% substitution of Al and with Cu concentrations of x = 0.0, 0.2, and 0.3. Magnetization measurements as a function of temperature performed from 10 to 400 K, with an applied field of 0.02 T showed a ferromagnetic state, with critical temperature Tc = 295 and 300 K for the samples with Cu, x = 0.2 and 0.3, respectively. For the sample without Cu, a complex behavior is observed at Tc = 370 K, with martensitic transition at 220 K and a premartensitic at 250 K. Analysis of x-rays diffractograms at room temperature show a L 21 structure for x = 0.0, while for x = 0.2 a mixture of L 21 and martensitic is present, and the sample with x = 0.3 it is in a fully martensitic phase. Heat capacity measurements were performed in order to calculate magnetocaloric effect in the samples. The results indicate that in Ni(Mn,Cu)Ga alloys, a partial substitution of Ga by Al still produce a high refrigerant capacity while reducing the costs of fabrication.

  2. Adjusting the crystal structure of NiMnGa shape memory ferromagnets

    NASA Astrophysics Data System (ADS)

    Gaitzsch, U.; Roth, S.; Rellinghaus, B.; Schultz, L.

    2006-10-01

    The compound Ni2MnGa is known to exhibit large magnetic field induced strain (MFIS) due to magnetically switching the shape memory effect within a large composition range. Samples of Ni50Mn30Ga20 were prepared by induction melting of the elements under argon. Annealing at and below the ordering temperature ( 740C, B2'- L21-type) followed by water quenching was found to have an influence on the martensite structure, which was analyzed using XRD. For powder samples, the structure was found to be tetragonal or orthorhombic with some monoclinic distortion of the unit cell, indicating seven-layered (7M) type of martensite (Ni50Mn30Ga20). The structures could be selected by appropriate thermal treatment.

  3. The kinetic relation for twin wall motion in NiMnGa

    NASA Astrophysics Data System (ADS)

    Faran, Eilon; Shilo, Doron

    2011-05-01

    A complete description of magnetically induced strains in ferromagnetic shape memory alloys (FSMAs) requires knowledge of the constitutive equation describing twin wall motion, commonly referred to as the kinetic relation. Here we present a unique experimental setup that allows for direct measurement of individual twin wall velocities as a function of a magnetically induced driving force in a NiMnGa FSMA, i.e., the kinetic relation. Our results demonstrate the validity of a general kinetic law that is typical of a viscous interface motion in a periodic potential. Values of basic material properties that govern twin wall motion, such as the Peierls energy barrier and the crystal viscosity, are extracted, and a simple model suggests that the viscosity measured in NiMnGa represents the magnitude of this property in other non-ferromagnetic shape memory alloys.

  4. Phase transition processes and magnetocaloric effects in the Heusler alloys NiMnGa with concurrence of magnetic and structural phase transition

    NASA Astrophysics Data System (ADS)

    Long, Y.; Zhang, Z. Y.; Wen, D.; Wu, G. H.; Ye, R. C.; Chang, Y. Q.; Wan, F. R.

    2005-08-01

    The Ni2MnGa-based Heusler alloys with high magnetocaloric effect have attracted considerable attention as a promising magnetic refrigerant. The phase-transition processes and magnetic entropy changes in the NiMnGa alloys with the concurrence of magnetic and structural phase transitions were studied. The ac magnetic susceptibility results showed the magnetic transition occurred during the reverse martensitic phase transition in the Ni55.5Mn20Ga24.5 alloy and the direct transition from the ferromagnetic matrensitic phase to the paramagnetic austenitic phase occurred in the Ni54.9Mn20.5Ga24.6 alloy. When the magnetic field had changed to 2 T, a comparable large magnetic entropy change was observed in both the Ni55.5Mn20Ga24.5 and Ni54.9Mn20.5Ga24.6 alloys, which is speculated as the result of the discontinuous change of magnetization near the phase transition.

  5. Numerical predictions versus experimental findings on the power-harvesting output of a NiMnGa alloy

    NASA Astrophysics Data System (ADS)

    Nelson, Isaac; Dikes, Jason; Feigenbaum, Heidi; Ciocanel, Constantin

    2014-03-01

    Magnetic shape memory alloys (MSMAs) can display up to 10% recoverable strain in response to the application of a magnetic field or compressive mechanical stress. The amount of recoverable strain depends on the amount and direction of the applied stress and magnetic field as well as manufacturing, chemical composition, and training of the material. Due to their relatively large strains and fast response, MSMAs are suitable for a wide range of applications, including power harvesting, sensing, and actuation. The response of MSMAs is primarily driven by the reorientation of martensite variants. Power harvesting is possible due to this reorientation process and the accompanying change in material's magnetization, which can be changed into an electric potential/voltage using a pick-up coil placed around (or on the side of) the specimen. The magnitude of the output voltage depends on the number of turns of the pick-up coil, the amplitude of the reorientation strain, the magnitude and direction of the biased magnetic field, and the frequency at which the reorientation occurs. This paper focuses on the ability of a two dimensional constitutive model, developed by the group to capture the magnetomechanical response of MSMAs under general two dimensional loading conditions, to predict the power harvesting output of a Ni2MnGa specimen. Comparison between model predictions of voltage output and experimental measurements of the same indicate that, while the model is able to replicate the stress-strain response of the material during power harvesting, it is unable to accurately predict the magnitude of the experimentally measured voltage output. This indicates that additional features still need to be included in the model to better capture the change in magnetization that occurs during variant reorientation.

  6. Successive occurrence of ferromagnetic and shape memory properties during crystallization of NiMnGa freestanding films

    NASA Astrophysics Data System (ADS)

    Rumpf, H.; Craciunescu, C. M.; Modrow, H.; Olimov, Kh.; Quandt, E.; Wuttig, M.

    2006-07-01

    Ni 50Mn 30Ga 20 films of 13 μm thickness were fabricated by DC magnetron sputtering on unheated glass substrates. The As-deposited films are partially crystalline and crystallize during rapid annealing. The successive appearance of ferromagnetic and shape memory properties was observed as the annealing temperature was increased. Ferromagnetic properties evolved after annealing at 400 °C for 0.5 h, while thermal annealing of at least 600 °C for 0.5 h led to polycrystalline films that transformed reversibly and martensitically as shown by structural analysis and differential scanning calorimetry and confirmed by mechanical spectroscopy data. Magnetic measurements also revealed the influence of the post deposition annealing on the ferromagnetic hysteresis. Transition temperatures and reaction enthalpies of the martensitic phase transformation were strongly influenced by the temperature of the rapid annealing process. X-ray absorption fine-structure (XAFS) spectroscopy proved these changes to be related to the change in the chemical order. It is proposed that the annealing data reflect the evolution of the crystalline state. Ferromagnetic order is established already in nano-grained samples whereas the shape memory effect is only observed above a critical grain size.

  7. Relation between martensitic transformation temperature range and lattice distortion ratio of NiMnGaCoCu Heusler alloys

    NASA Astrophysics Data System (ADS)

    Wei, Jun; Xie, Ren; Chen, Le-Yi; Tang, Yan-Mei; Xu, Lian-Qiang; Tang, Shao-Long; Du, You-Wei

    2014-04-01

    In order to study the relation between martensitic transformation temperature range ΔT (where ΔT is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a) of martensitic transformation, a series of Ni46Mn28-xGa22Co4Cux (x = 2-5) Heusler alloys is prepared by arc melting method. The vibration sample magnetometer (VSM) experiment results show that ΔT increases when x > 4 and decreases when x < 4 with x increasing, and the minimal ΔT (about 1 K) is found at x = 4. Ambient X-ray diffraction (XRD) results show that ΔT is proportional to c/a for non-modulated Ni46Mn28-xGa22Co4Cux (x = 2-5) martensites. The relation between ΔT and c/a is in agreement with the analysis result obtained from crystal lattice mismatch model. About 1000-ppm strain is found for the sample at x = 4 when heating temperature increases from 323 K to 324 K. These properties, which allow a modulation of ΔT and temperature-induced strain during martensitic transformation, suggest Ni46Mn24Ga22Co4Cu4 can be a promising actuator and sensor.

  8. Effect of magnetizing field on the martensitic transformations in a melt spun NiMnGa alloy

    NASA Astrophysics Data System (ADS)

    Panda, A. K.; Singh, Satnam; Das, S. K.; Mitra, A.; Koblischka, M.; Jamieson, Brice; Roy, Saibal

    2009-12-01

    The investigation addresses the effect of magnetizing field on the magnetic properties of melt spun Ni52.84Mn19.6Ga27.56 (at%) alloy ribbons. Magnetization behaviour at different fields was observed using a superconducting quantum interference device magnetometer for heating and cooling cycles. The plots showed distinct changes in magnetization around the characteristic temperatures at austenitic start and finish (AS, AF), martensitic start and finish (MS, MF). With increasing field AS, MF were unaffected. In the range of martensitic start and its finish temperature, the zero field cooled and field cooled measurements indicated magnetization drops indicating antiferromagnetic interactions, which is characteristic of the martensitic phase formation. It was shown from x-ray diffraction analysis that the low martensitic fraction in the majority austenite phase induced the splitting in the L21 austenitic ordering. This was further corroborated by the evidence of a few martensitic plates around grain boundaries at room temperature which is close to martensitic start temperature.

  9. Transformation twinning of Ni-Mn-Ga characterized with temperature-controlled atomic force microscopy.

    PubMed

    Reinhold, Matthew; Watson, Chad; Knowlton, William B; Müllner, Peter

    2010-06-01

    The magnetomechanical properties of ferromagnetic shape memory alloy Ni-Mn-Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni-Mn-Ga single crystal. Experiments were performed in the martensite phase at 25 degrees C and in the austenite phase at 55 degrees C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature (55 degrees C), the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25 degrees C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys.

  10. A discrete twin-boundary approach for simulating the magneto-mechanical response of Ni-Mn-Ga

    NASA Astrophysics Data System (ADS)

    Faran, Eilon; Shilo, Doron

    2016-09-01

    The design and optimization of ferromagnetic shape memory alloys (FSMA)-based devices require quantitative understanding of the dynamics of twin boundaries within these materials. Here, we present a discrete twin boundary modeling approach for simulating the behavior of an FSMA Ni-Mn-Ga crystal under combined magneto-mechanical loading conditions. The model is based on experimentally measured kinetic relations that describe the motion of individual twin boundaries over a wide range of velocities. The resulting calculations capture the dynamic response of Ni-Mn-Ga and reveal the relations between fundamental material parameters and actuation performance at different frequencies of the magnetic field. In particular, we show that at high field rates, the magnitude of the lattice barrier that resists twin boundary motion is the important property that determines the level of actuation strain, while the contribution of twinning stress property is minor. Consequently, type II twin boundaries, whose lattice barrier is smaller compared to type I, are expected to show better actuation performance at high rates, irrespective of the differences in the twinning stress property between the two boundary types. In addition, the simulation enables optimization of the actuation strain of a Ni-Mn-Ga crystal by adjusting the magnitude of the bias mechanical stress, thus providing direct guidelines for the design of actuating devices. Finally, we show that the use of a linear kinetic law for simulating the twinning-based response is inadequate and results in incorrect predictions.

  11. Changes in magnetic domain structure during twin boundary motion in single crystal Ni-Mn-Ga exhibiting magnetic shape memory effect

    NASA Astrophysics Data System (ADS)

    Kopecký, V.; Fekete, L.; Perevertov, O.; Heczko, O.

    2016-05-01

    The complexity of Ni-Mn-Ga single crystal originates from the interplay between ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure in the vicinity of single twin boundary was studied using magneto-optical indicator film and magnetic force microscopy technique. The single twin boundary of Type I was formed mechanically and an initial magnetization state in both variants were restored by local application of magnetic field (≈40 kA/m). The differently oriented variants exhibited either stripe or labyrinth magnetic domain pattern in agreement with the uniaxial magnetocrystalline anisotropy of the martensite. The twin boundary was then moved by compressive or tensile stress. The passage of the boundary resulted in the formation of granular or rake domains, respectively. Additionally, the specific magnetic domains pattern projected by twin boundary gradually vanished during twin boundary motion.

  12. Growth and magnetic properties of NiMnGa thin films prepared by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Zhu, T. J.; Lu, L.; Lai, M. O.; Ding, J.

    2005-10-01

    Ni-Mn-Ga alloys have attracted increasing attention due to their large magnetic-field-induced stresses and the potential applications in sensors and actuators. In the present work, NiMnGa half-Heusler alloy films have been deposited on Si(100) substrates by the pulsed laser deposition technique at temperatures ranging from 450 to 650 °C. X-ray diffraction and atomic force microscopy observation show the phase structure and surface morphology of these films are different, and energy dispersive spectroscopy analysis shows compositions of the films remain nearly unchanged, independent of the deposition temperature. Vibrating sample magnetometer measurement indicates that good magnetic properties are obtained. All the films exhibit the same coercive field, about 250 Oe. The thermomagnetic curve shows that the Curie temperature of NiMnGa films is higher than room temperature, which is crucial for the room-temperature application.

  13. Magnetocaloric effect in NiMnGa particles produced by spark erosion

    NASA Astrophysics Data System (ADS)

    Tang, Y. J.; Solomon, Virgil C.; Smith, D. J.; Harper, H.; Berkowitz, A. E.

    2005-05-01

    The magnetic entropy change of tetragonal and orthorhombic NiMnGa fine particles made by spark erosion was investigated in this paper. It was found that the structure and crystalline phase transformation temperatures can be strongly affected by the compositions of the particles, while Curie temperature is less sensitive to the compositions. Due to the possible distribution of the particle size and compositions in these particles, the magnetic entropy changes observed are much broader and smaller than those of bulk NiMnGa alloys. The maximum absolute value of entropy change ΔS =2JKg-1K-1 was observed for tetragonal structure NiMnGa particles at 95°C in a field of 2T.

  14. Fabrication of magnetic shape memory alloy/polymer composites

    NASA Astrophysics Data System (ADS)

    Ham-Su, R.; Healey, J. P.; Underhill, R. S.; Farrell, S. P.; Cheng, L. M.; Hyatt, C. V.; Rogge, R.; Gharghouri, M. A.

    2005-05-01

    NiMnGa-based magnetic shape memory (MSM) alloys have attained magnetic-field-induced strains up to approximately 10%, making them very attractive for a variety of applications. However, for applications that require the use of an alternating magnetic field, eddy current losses can be significant. Also, NiMnGa-based MSM alloys' fracture toughness is relatively low. Using these materials in the form of particles embedded in a polymer matrix composite could mitigate these limitations. Since the MSM effect is anisotropic, the crystallographic texture of the particles in the composites is of great interest. In this work, a procedure for fabricating NiMnGa-based MSMA/elastomer composites is described. Processing routes for optimizing the crystallographic texture in the composites are considered.

  15. Structural and Dynamical Fluctuations in Off-Stoichiometric NiMnGa Shape-Memory Alloys

    SciTech Connect

    Barabash, Rozaliya; Barabash, Oleg M; Karapetrova, Evgenia; Manley, Michael E

    2014-01-01

    3D diffuse scattering dataset in the temperature region of the existence of high temperature cubic L21 phase reveals localized intensity maxima related to phason modes. Peierls instability induced tetragonal distortions in the pre-martensitic phase cause strong diffuse scattering. Around (H0H) reflections diffuse scattering is strongly compressed along the [H0H] and enhanced along the [-H0H] direction.

  16. Effect of Mn incorporation for Ni on the properties of melt spun off-stoichiometric compositions of NiMnGa alloys

    NASA Astrophysics Data System (ADS)

    Panda, A. K.; Singh, Satnam; Roy, R. K.; Ghosh, M.; Mitra, A.

    2011-05-01

    The investigation addresses the effect of Mn incorporation for Ni on the properties of a series of Ni 77- xMn xGa 23 ( x=22-29; at%) ferromagnetic shape memory alloys prepared in the form of ribbons by a melt spinning technique. Phase transformation studies in these ribbons by differential scanning calorimetry revealed that austenitic start and martensitic start temperatures decreased with the increase in Mn content. The Curie temperature ( TC) of these alloys determined from thermal variation of magnetisations was found to rise with increasing Mn content. The martensitic transformation temperatures were above TC in low Mn containing ( x=22 and 23) alloys. Morphology observed through transmission electron microscopy manifested complex martensitic features in the alloy with x=22 while x=29 had an austenitic phase. The alloys with intermediate Mn content ( x=24, 25) had overlapping magnetic and martensitic transformations close to room temperature. The thermal lag between austenitic and martensitic characteristic temperatures in these alloys has been corroborated to their structural state. X-ray diffraction indicated a predominant martensite phase and austenite phase in low and high Mn containing alloys respectively. In-situ diffraction studies during thermal cycle indicate martensite-austenite transformations.

  17. Thermal and damping behaviour of magnetic shape memory alloy composites

    NASA Astrophysics Data System (ADS)

    Glock, Susanne; Michaud, Véronique

    2015-06-01

    Single crystals of ferromagnetic shape memory alloys (MSMA) exhibit magnetic field and stress induced strains via energy dissipating twinning. Embedding single crystalline MSMA particles into a polymer matrix could thus produce composites with enhanced energy dissipation, suitable for damping applications. Composites of ferromagnetic, martensitic or austenitic Ni-Mn-Ga powders embedded in a standard epoxy matrix were produced by casting. The martensitic powder composites showed a crystal structure dependent damping behaviour that was more dissipative than that of austenitic powder or Cu-Ni reference powder composites and than that of the pure matrix. The loss ratio also increased with increasing strain amplitude and decreasing frequency, respectively. Furthermore, Ni-Mn-Ga powder composites exhibited an increased damping behaviour at the martensite/austenite transformation temperature of the Ni-Mn-Ga particles in addition to that at the glass transition temperature of the epoxy matrix, creating possible synergetic effects.

  18. Effect of gallium alloying on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary Ni-Mn-Ga alloys

    NASA Astrophysics Data System (ADS)

    Belosludtseva, E. S.; Kuranova, N. N.; Marchenkova, E. B.; Popov, A. G.; Pushin, V. G.

    2016-04-01

    The effect of gallium alloying on the structure, the phase composition, and the properties of quasibinary Ni50Mn50- z Ga z (0 ⩽ z ⩽ 25 at %) alloys is studied over a wide temperature range. The influence of the alloy composition on the type of crystal structure in high-temperature austenite and martensite and the critical martensitic transformation temperatures is analyzed. A general phase diagram of the magnetic and structural transformations in the alloys is plotted. The temperature-concentration boundaries of the B2 and L21 superstructures in the austenite field, the tetragonal L10 (2 M) martensite, and the 10 M and 14 M martensite phases with complex multilayer crystal lattices are found. The predominant morphology of martensite is shown to be determined by the hierarchy of the packets of thin coherent lamellae of nano- and submicrocrystalline crystals with planar habit plane boundaries close to {011} B2. Martensite crystals are twinned along one of the 24 24{ {011} }{< {01bar 1} rangle _{B2}} "soft" twinning shear systems, which provides coherent accommodation of the martensitic transformation-induced elastic stresses.

  19. Application of a bi-stable chain model for the analysis of jerky twin boundary motion in NiMnGa

    NASA Astrophysics Data System (ADS)

    Benichou, Itamar; Faran, Eilon; Shilo, Doron; Givli, Sefi

    2013-01-01

    The "jerky" motion of a twin boundary in the ferromagnetic shape memory alloy NiMnGa is studied experimentally and theoretically. We employ a bi-stable chain model in order to interpret macroscopic stress-strain experiments and extract important micro-level properties. The analysis reveals the existence of a periodic barrier for type I twin boundary motion with an average distance of 19 μm and amplitude of 0.16 J/m2. Further, we show that the macroscopic mechanical response depends on the length of the crystal and predict a significant decrease of the hysteresis in sub-mm length specimens.

  20. A fabrication technology for epitaxial Ni-Mn-Ga microactuators

    NASA Astrophysics Data System (ADS)

    Khelfaoui, F.; Kohl, M.; Buschbeck, J.; Heczko, O.; Fähler, S.; Schultz, L.

    2008-05-01

    This paper reports on the fabrication and characterization of epitaxial Ni-Mn-Ga microactuators. Ni-Mn-Ga films are grown on heated single-crystalline MgO substrates by DC magnetron sputtering. X-ray diffraction measurements demonstrate epitaxial growth of the films. At room temperature, the crystal structure is identified to be non-modulated (NM) tetragonal martensite. Electrical resistance measurements confirm that the films display the martensitic phase transformation well above the Curie temperature TC of 325 K. Orientation-dependent magnetization measurements are performed to determine magnetic film properties. Micromachining of the Ni-Mn-Ga films is performed on an alumina substrate covered by a temporary adhesive layer. A transfer bonding process is developed to finally integrate the micromachined Ni-Mn-Ga structures to a target substrate in order to obtain NiMnGa microactuators having freely movable microparts. Temperature-displacement characteristics demonstrate the actuation performance of epitaxial NiMnGa microactuators for the first time.

  1. Hysteresis and magnetocaloric effect at the magnetostructural phase transition of Ni-Mn-Ga and Ni-Mn-Co-Sn Heusler alloys

    NASA Astrophysics Data System (ADS)

    Basso, Vittorio; Sasso, Carlo P.; Skokov, Konstantin P.; Gutfleisch, Oliver; Khovaylo, Vladimir V.

    2012-01-01

    Hysteresis features of the direct and inverse magnetocaloric effect associated with first-order magnetostructural phase transitions in Ni-Mn-X (X = Ga, Sn) Heusler alloys have been disclosed by differential calorimetry measurements performed either under a constant magnetic field, H, or by varying H in isothermal conditions. We have shown that the magnetocaloric effect in these alloys crucially depends on the employed measuring protocol. Experimentally observed peculiarities of the magnetocaloric effect have been explained in the framework of a model that accounts for different contributions to the Gibbs energy of austenitic gA and martensitic gM phases. Obtained experimental results have been summarized by plotting a phase fraction of the austenite xA versus the driving force gM-gA. The developed approach allows one to predict reversible and irreversible features of the direct as well as inverse magnetocaloric effect in a variety of materials with first-order magnetic phase transitions.

  2. Phase transition in a multiferroic Ni-Mn-Ga single crystal

    NASA Astrophysics Data System (ADS)

    Veřtát, P.; Drahokoupil, J.; Perevertov, O.; Heczko, O.

    2016-08-01

    We studied martensitic phase transformation, crystal structure and twinned microstructure of resulting martensite of a Ni-Mn-Ga single crystal as essential conditions for magnetic shape memory effect. Thermal dependence of electric resistivity, magnetic susceptibility and dilatation measurements were measured to characterise kinetics of the transformation. With the help of XRD analysis and optical microscopy we evaluated the hierarchical twinning microstructure in the 10M martensite.

  3. Achieving giant magnetically induced reorientation of martensitic variants in magnetic shape-memory Ni-Mn-Ga Films by microstructure engineering.

    PubMed

    Ranzieri, Paolo; Campanini, Marco; Fabbrici, Simone; Nasi, Lucia; Casoli, Francesca; Cabassi, Riccardo; Buffagni, Elisa; Grillo, Vincenzo; Magén, Cesar; Celegato, Federica; Barrera, Gabriele; Tiberto, Paola; Albertini, Franca

    2015-08-26

    Giant magnetically induced twin variant reorientation, comparable in intensity with bulk single crystals, is obtained in epitaxial magnetic shape-memory thin films. It is found to be tunable in intensity and spatial response by the fine control of microstructural patterns at the nanoscopic and microscopic scales. A thorough experimental study (including electron holography) allows a multiscale comprehension of the phenomenon.

  4. XAS and XMCD study of the influence of annealing on the atomic ordering and magnetism in an NiMnGa alloy.

    PubMed

    Chaboy, J; Lázpita, P; Barandiarán, J M; Gutiérrez, Jon; Fernández-Gubieda, Maria Luisa; Kawamura, N

    2009-01-01

    The proper annealing of Ni(51)Mn(28)Ga(21) ribbon alloy gives rise to an increase of the saturation magnetization and of the magnetic order T(C) (up to 20 K) and martensitic transition T(M) (up to 10 K) temperatures. The combined x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies indicate that the annealing treatment drives the alloy to a more ordered structure without significantly affecting the local structure in terms of interatomic distances and bonding geometry. By contrast, the annealing strongly affects the near-edge absorption at the Mn K-edge while no effect is observed at either the Ni or Ga K-edge. These results suggest that annealing leads to a modification of the electronic structure of the Mn atoms while that of Ni and Ga atoms remains unvaried. However, strong XMCD signals are detected at both Ni and Ga K-edges whose amplitude increases after annealing. These results point out that despite the change of the magnetic properties of the system being mainly associated with the modification of the electronic properties of the Mn atoms, both Ni and Ga may play a non-negligible role through the polarization of the conduction band. PMID:21817239

  5. XAS and XMCD study of the influence of annealing on the atomic ordering and magnetism in an NiMnGa alloy

    NASA Astrophysics Data System (ADS)

    Chaboy, J.; Lázpita, P.; Barandiarán, J. M.; Gutiérrez, Jon; Fernández-Gubieda, Maria Luisa; Kawamura, N.

    2009-01-01

    The proper annealing of Ni51Mn28Ga21 ribbon alloy gives rise to an increase of the saturation magnetization and of the magnetic order TC (up to 20 K) and martensitic transition TM (up to 10 K) temperatures. The combined x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies indicate that the annealing treatment drives the alloy to a more ordered structure without significantly affecting the local structure in terms of interatomic distances and bonding geometry. By contrast, the annealing strongly affects the near-edge absorption at the Mn K-edge while no effect is observed at either the Ni or Ga K-edge. These results suggest that annealing leads to a modification of the electronic structure of the Mn atoms while that of Ni and Ga atoms remains unvaried. However, strong XMCD signals are detected at both Ni and Ga K-edges whose amplitude increases after annealing. These results point out that despite the change of the magnetic properties of the system being mainly associated with the modification of the electronic properties of the Mn atoms, both Ni and Ga may play a non-negligible role through the polarization of the conduction band.

  6. Characterization of preferential orientation of martensitic variants in a single crystal of NiMnGa

    NASA Astrophysics Data System (ADS)

    Liu, Guodong; Chen, Jinglan; Cui, Yuting; Liu, Zhuhong; Zhang, Ming; Wu, Guangheng; Brück, E.; de Boer, F. R.; Meng, Fanbin; Li, Yangxian; Qu, Jingping

    2004-06-01

    We report the detailed observation of martensitic variants in NiMnGa single crystals. The variants that are twinned with each other in different ways can be clearly identified in our single crystals by optical observation. We also investigated the preferential orientation of the martensitic variants in NiMnGa single crystals. We observed the motion of the variant boundary in response to application of a magnetic field. This observation can be used to explain phenomenologically the magnetic-field-induced strain. In the single crystal with composition Ni 52Mn 24Ga 24, martensite with seven modulated layers (7M) shows preferentially oriented variants. A completely recoverable two-way shape-memory behavior was also observed by measuring the free sample in three different directions during a complete temperature cycle. It was found that the largest strains in the [001] and [010] directions occur in different temperature ranges.

  7. Transformation behavior of Ni-Mn-Ga in the low-temperature limit.

    PubMed

    Pérez-Landazábal, J I; Recarte, V; Sánchez-Alarcos, V; Chernenko, V A; Barandiarán, J M; Lázpita, P; Rodriguez Fernández, J; Righi, L

    2012-07-11

    The magnetic, magnetocaloric and thermal characteristics have been studied in a Ni(50.3)Mn(20.8)Ga(27.6)V(1.3) ferromagnetic shape memory alloy (FSMA) transforming martensitically at around 40 K. The alloy shows first a transformation from austenite to an intermediate phase and then a partial transformation to an orthorhombic martensite, all the phases being ferromagnetically ordered. The thermomagnetization dependences enabled observation of the magnetocaloric effect in the vicinity of the martensitic transformation (MT). The Debye temperature and the density of states at the Fermi level are equal to θ(D) = (276 ± 4) K and 1.3 states/atom eV , respectively, and scarcely dependent on the magnetic field. The MT exhibited by Ni-Mn-Ga FSMAs at very low temperatures is distinctive in the sense that it is accompanied by a hardly detectable entropy change as a sign of a small driving force. The enhanced stability of the cubic phase and the low driving force of the MT stem from the reduced density of states near the Fermi level.

  8. Damping behavior of polymer composites with high volume fraction of NiMnGa powders

    NASA Astrophysics Data System (ADS)

    Sun, Xiaogang; Song, Jie; Jiang, Hong; Zhang, Xiaoning; Xie, Chaoying

    2011-03-01

    Polymer composites inserted with high volume fraction (up to 70 Vol%) of NiMnGa powders were fabricated and their damping behavior was investigated by dynamic mechanical analysis. It is found that the polymer matrix has little influence on the transformation temperatures of NiMnGa powders. A damping peak appears for NiMnGa/epoxy resin (EP) composites accompanying with the martensitic transformation or reverse martensitic transformation of NiMnGa powders during cooling or heating. The damping capacity for NiMnGa/EP composites increases linearly with the increase of volume fraction of NiMnGa powders and, decreases dramatically as the test frequency increases. The fracture strain of NiMnGa/EP composites decrease with the increase of NiMnGa powders.

  9. Magnetoelastic coupling in nickel manganese gallium ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Zhao, Peng

    NiMnGa alloys have attracted extensive attention because their ferromagnetic characteristic provides an additional degree of freedom to control both the shape memory effect and the multi-stage phase transformations in this Heusler system. Technically, along with the large magnetic-field-induced strains, NiMnGa alloys exhibit giant magnetocaloric effect due to their magnetic entropy changes associated with the coupled magnetostructural transitions. Fundamentally, a sequence of phase transformations, manifesting itself by a rich variety of physical anomalies on cooling to the martensitic transformation (MT) temperature TM, has been established. However, in comparison to the intensive studies of structural transformations, the magnetic properties of NiMnGa premartensite were hardly touched. The purpose of this research is to (i) investigate the temperature dependence of the magnetic driving force of martensitic NiMnGa, which is a critical factor to determine the actuation temperature window of this material; and (ii) understand the magnetoelastic coupling enhanced precursor effects, especially the unique magnetic behavior of NiMnGa premartensite. The singular point detection technique has been applied to determine the magnetic anisotropy constant K1 of a martensitic Ni49.0 Mn23.5Ga27.5 (wt%) crystal. As expected, K 1 increases with decreasing temperatures below TM of 276 K, following a magnetization power law K1(T)/K1(0)=(M s(T)/Ms(0))3. However, the force required to initiate twin boundary motion increases exponentially with decreasing temperature. The combination of both temperature dependences leads to a very restricted temperature window for magnetic actuation using this alloy. The premartensitic transformation has been established by means of neutron powder diffraction and measurements of elastic constants of C44 and C'. The premartensitic phase has been verified by the stiffening of C 44 prior to the MT. The slope change of C' at TC positively confirms that the

  10. Anomalous magnetoresistance in NiMnGa thin films

    NASA Astrophysics Data System (ADS)

    Golub, Vladimir O.; Vovk, Andriy Ya.; Malkinski, Leszek; O'Connor, Charles J.; Wang, Zhenjun; Tang, Jinke

    2004-10-01

    The origin of anomalous negative magnetoresistance and its temperature dependence in polycrystalline Ni -Mn-Ga films prepared by pulse laser deposition was studied. The investigation of structural, transports, magnetic, and ferromagnetic resonance properties of the films suggests contributions of different mechanisms in magnetotransport. At low magnetic fields the main contribution to magnetoresistance is due to the transport between the areas with different orientation of magnetic moments, while at high fields it is an electron scattering of in spin-disordered areas.

  11. Compressive Response of Polycrystalline NiCoMnGa High-Temperature Meta-magnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Karaca, H. E.; Turabi, A. S.; Basaran, B.; Pathak, A. K.; Dubenko, I.; Ali, N.; Chumlyakov, Y. I.; Li, P.

    2013-10-01

    The effects of the addition of quaternary element, Co, to polycrystalline NiMnGa alloys on their magnetic and shape memory properties have been investigated. NiCoMnGa polycrystalline alloys have been found to demonstrate good shape memory and superelasticity behavior under compression at temperatures greater than 100 °C with about 3% transformation strain and low-temperature hysteresis. It is also possible to train the material to demonstrate a large two-way shape memory effect.

  12. A free energy model for magneto-mechanically coupled NiMnGa single crystals

    NASA Astrophysics Data System (ADS)

    Morrison, P.; Seelecke, S.; Krevet, B.; Kohl, M.

    2008-05-01

    This paper presents a one-dimensional magneto-mechanical model for NiMnGa. Following a modeling approach developed by the authors for conventional shape memory behavior and ferroelectricity, a constitutive Helmholtz free energy landscape with strain and magnetization as order parameters is constructed for a representative meso-scale lattice element. The landscape includes three paraboloidal energy wells representing the two easy-axis and one hard-axis martensite variants distinguishable in the chosen coordinate system. The resulting stress- and magnetic-field-dependent Gibbs free energy expressions are then used within the theory of thermally activated processes to derive a series of phase-fraction evolution equations. The phase fractions subsequently determine the macroscopic strain and magnetization of a sample of NiMnGa by a standard averaging procedure. Results from the model are compared to experimental data and demonstrate the model's ability to reproduce constitutive behaviors of the material. Future work includes an extension to a full thermo-magneto-mechanical model accounting for the occurrence of austenite and inhomogeneity effects and configured to function within the tensile-stress regime.

  13. Development of magnetic shape memory alloy actuators for a swashplateless helicopter rotor

    NASA Astrophysics Data System (ADS)

    Couch, Ronald Newton

    Actuator concepts utilizing NiMnGa, ferromagnetic shape memory alloy are investigated for potential use on a smart rotor for trailing edge flap actuation. With their high energy density, large dynamic stroke, and wide operating bandwidth, ferromagnetic shape memory alloys (FSMA) like NiMnGa, seem like attractive candidates for smart rotor actuators, potentially able to fulfill the requirements for both primary rotor control and vibration suppression. However, because of the recent discovery of the material, current experimental data and analytical tools are limited. To rectify these shortcomings, an extensive set of detailed experiments were conducted on samples of NiMnGa to characterize the response of the alloy for a wide variety of mechanical and magnetic loading conditions. Measurements of the material performance parameters such as power density, damping properties, magneto-mechanical coupling, and transduction efficiency were included. Once characterized, the experimental data were used to develop a series of analytical tools to predict the behavior of the material. A model, developed in parallel to thermal shape memory alloy models is proposed to predict the quasi-static stress-strain behavior. A simple, low frequency, parameter based model was also developed to predict the alloy's dynamic strain response. A method for developing conceptual actuators utilizing NiMnGa as the actuation element was proposed. This approach incorporates experimental data into a process that down-selects a series of possible actuator configurations to obtain a single configuration optimized for volumetric and weight considerations. The proposed actuator was designed to deliver 2 mm of stroke and 60 N of force at an actuation frequency of 50 Hz. However, to generate the 1.0 T magnetic field, the actuator mass was determined to be 2.8 kg and required a minimum of 320 Watts of power for operation. The mass of the NiMnGa element was only 18.3 g. It was concluded that although the NiMnGa

  14. Magnetotransport in NiMnGa thin films

    NASA Astrophysics Data System (ADS)

    Vovk, Andriy; Malkinski, Leszek; Golub, Vladimir; O'Connor, Charles; Wang, Zhenjun; Tang, Jinke

    2005-05-01

    The influence of substrate temperature and annealing conditions on structure, magnetic, and magnetotransport properties of NiMnGa films was investigated, and the crucial effect of substrate temperature was confirmed. It was found that amorphous disordered films are formed during deposition on a substrate held at room temperature. Postdeposition annealing leads to partial recrystallization and recovery of magnetic properties. Annealing at 773 K does not allow the formation of crystal structure, which is created during deposition on substrates held at the same temperature. The highest values of magnetoresistance were observed in the films with a well-defined crystal structure.

  15. The effect of antiphase boundaries on the elastic properties of Ni-Mn-Ga austenite and premartensite.

    PubMed

    Seiner, Hanuš; Sedlák, Petr; Bodnárová, Lucie; Drahokoupil, Jan; Kopecký, Vít; Kopeček, Jaromír; Landa, Michal; Heczko, Oleg

    2013-10-23

    The evolution of elastic properties with temperature and magnetic field was studied in two differently heat-treated single crystals of the Ni-Mn-Ga magnetic shape memory alloy using resonant ultrasound spectroscopy. Quenching and slow furnace cooling were used to obtain different densities of antiphase boundaries. We found that the crystals exhibited pronounced differences in the c' elastic coefficient and related shear damping in high-temperature ferromagnetic phases (austenite and premartensite). The difference can be ascribed to the formation of fine magnetic domain patterns and pinning of the magnetic domain walls on antiphase boundaries in the material with a high density of antiphase boundaries due to quenching. The fine domain pattern arising from mutual interactions between antiphase boundaries and ferromagnetic domain walls effectively reduces the magnetocrystalline anisotropy and amplifies the contribution of magnetostriction to the elastic response of the material. As a result, the anomalous elastic softening prior to martensite transformation is significantly enhanced in the quenched sample. Thus, for any comparison of experimental data and theoretical calculations the microstructural changes induced by specific heat treatment must be taken into account.

  16. Empirical mapping of Ni-Mn-Ga properties with composition and valence electron concentration

    NASA Astrophysics Data System (ADS)

    Jin, X.; Marioni, M.; Bono, D.; Allen, S. M.; O'Handley, R. C.; Hsu, T. Y.

    2002-05-01

    A range of Ni-Mn-Ga alloy compositions close to the stoichiometric Heusler composition, Ni2MnGa, has been reported to show field-induced strains of several percent. Such observations, and the magnitude of the strain observed, depend on the values of several critical material parameters, most importantly the martensitic transformation temperature (Tmart), Curie temperature (TC), saturation magnetization (Ms), strength of the magnetocrystalline anisotropy, and the details of the martensite structure. Here, data collected from a variety of sources are plotted and their variations are fit with empirical formulas to afford a better overall picture of the behavior of this system. It is found that the martensitic transformation temperature is the parameter most sensitive to the composition; saturation magnetization appears to peak sharply at 7.5 valence electrons/atom, finally the composition field over which the saturation magnetization exceeds 60 emu/g, and 300 K

  17. Pulsed laser deposition of NiMnGa thin films on silicon

    NASA Astrophysics Data System (ADS)

    Hakola, A.; Heczko, O.; Jaakkola, A.; Kajava, T.; Ullakko, K.

    Thin films of the magnetic shape-memory (MSM) material NiMnGa have been deposited on Si(100) substrates using pulsed laser deposition. The --200 300nm-thick films were prepared at substrate temperatures ranging from 450 °C to 650 °C and at different background Ar pressures. Large saturation magnetizations, up to 60% of the bulk value, were measured for the films. Only the films deposited in vacuum or at Ar pressures below 10-3 mbar and at temperatures between 500 °C and 600 °C were ferromagnetic. The films are mainly crystallized in the austenitic phase and they have a smooth surface with a low droplet density (0.01 μm-2). The magnetization and surface quality are sufficient that the films could be utilized in the realization of thin-film MSM devices.

  18. Ferromagnetic shape memory alloys for positioning with nanometric resolution

    NASA Astrophysics Data System (ADS)

    Feuchtwanger, Jorge; Asua, Estibalitz; García-Arribas, Alfredo; Etxebarria, Victor; Barandiaran, Jose M.

    2009-08-01

    Ferromagnetic shape memory alloys are promising active elements for actuators. Our work centered on achieving and maintaining an intermediate fixed deformation so that they can be used as precision positioning actuators. For this purpose, a custom actuator was built using a single crystal of NiMnGa. The results show that these alloys can be controlled within less than 5 nm for both precision and accuracy, a result comparable to piezoelectric ceramics. Interestingly, the defect structure plays a fundamental role in achieving such performance. The stochastically distributed defects determine a progressive diminution of the magnetic field strength required to achieve the control.

  19. Microstructural observation of elastic domains in ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Craciunescu, Corneliu M.; Mitelea, Ion; Sgavardea, Gheorghe

    2012-08-01

    The microstructure of ferromagnetic shape memory alloys belonging to the Co-Ni-Ga and Ni-Mn-Ga system is analyzed in the martensitic state and during the martensitic phase transition, in order to explore the influence of the composition on the occurrence of the shape memory properties. The compositional range of the Co-Ni-Ga alloys investigated is associated with a two-phase microstructure, where the matrix shows the martensitic structure and a transformation into austenite on heating. The microstructure in the Co-Ni-Ga system shows a phase transition between the B2 austenite and L10 martensite, but the γ (disordered fcc A1) and the ordered γ' (fcc L12) can also be present - depending on the composition, and state, and influence the phase transition in as-cast, quenched and aged alloys. The exploration of the microstructural aspects reveals typical elastic domains that form in the martensitic phase, but also precipitates that can influence the overall martensitic transformation, thus hindering the total output. Compared to the NiMnGa system, the CoNiGa shows significantly less brittleness when deformed in the martensitic state.

  20. NiMnGa nanostructures produced by electron beam lithography and Ar-ion etching

    NASA Astrophysics Data System (ADS)

    Auernhammer, D.; Schmitt, M.; Ohtsuka, M.; Kohl, M.

    2008-05-01

    The technologies of electron beam lithography, dry etching and systems integration are investigated to fabricate a series of Ni-Mn-Ga double-beam structures designed with decreasing critical dimensions of 10 μm, 1 μm and 400 nm. Ni-Mn-Ga thin films of 1 μm thickness are deposited by magnetron sputtering and heat-treated in free-standing condition after selective removal of the substrate. Differential scanning calorimetry and electrical resistance measurements on the films show the characteristic features of martensitic transformation above room temperature. First optical beam deflection experiments demonstrate the magnetic and thermal actuation performance of the double-beam structures.

  1. Implications of twinning kinetics on the frequency response in NiMnGa actuators

    NASA Astrophysics Data System (ADS)

    Faran, Eilon; Shilo, Doron

    2012-04-01

    The explicit kinetic relation for twin wall motion in NiMnGa is used to correlate basic material properties to magneto-mechanical actuation rates in these crystals. In particular, we identify two parameters: the Peierls energy barrier and the twin wall mobility, which directly determine the dynamic response of NiMnGa actuators at frequencies above 10 Hz. Comparison between the kinetics of type I and type II twin walls reveals a correlation between the Peierls energy barrier and the commonly used twinning stress property. However, it is shown that twinning stress dictates twin wall dynamics only at very slow frequencies, typically below 1 Hz.

  2. Intermartensitic transformation in a NiMnGa alloy

    NASA Astrophysics Data System (ADS)

    Dai, Liyang; Cullen, James; Wuttig, Manfred

    2004-06-01

    The temperature dependencies of the elastic constants of martensitic Ni0.50Mn0.284Ga0.216 were studied in the temperature range from 428 K down to 200 K. Measurements were conducted using the ultrasonic continuous-wave method in a 0.8 T magnetic field. At 220 K abrupt changes were found in the temperature dependences of the velocities of all 11 elastic wave modes, which indicates a structural phase change from the tetragonal (5M) martensite to a second, probably tetragonal, phase (nonlayered) at lower temperature.

  3. Modeling the dynamical response of ferromagnetic shape memory alloy actuators using a dissipative Euler-Lagrange equation

    NASA Astrophysics Data System (ADS)

    Weetman, Philip; Akhras, George

    2009-01-01

    A phenomenological dynamical model of ferromagnetic shape memory alloy based actuators is developed. The parameters of effective mass density, viscosity, and elasticity are defined and used in a dissipative Euler-Lagrange equation to determine the martensite variant fraction and strain as a function of time. These three parameters are determined by fitting our simulations to recent experiments on a NiMnGa based actuator. In addition to the simplicity of only three fitting parameters to model martensite variant evolution, the present model is a convenient formulation of the problem because it incorporates self-consistently all stresses and loads in the system.

  4. Magnetic and calorimetric investigations of ferromagnetic shape memory alloy Ni54Fe19Ga27

    NASA Astrophysics Data System (ADS)

    Sharma, V. K.; Chattopadhyay, M. K.; Kumar, Ravi; Ganguli, Tapas; Kaul, Rakesh; Majumdar, S.; Roy, S. B.

    2007-06-01

    We report results of magnetization and differential scanning calorimetry measurements in the ferromagnetic shape memory alloy Ni54Fe19Ga27. This alloy undergoes an austenite-martensite phase transition in its ferromagnetic state. The nature of the ferromagnetic state, both in the austenite and the martensite phase, is studied in detail. The ferromagnetic state in the martensite phase is found to have higher anisotropy energy as compared with the austenite phase. The estimated anisotropy constant is comparable to that of a well-studied ferromagnetic shape memory alloy system NiMnGa. Further, the present study highlights various interesting features accompanying the martensitic transition (MT). These features suggest the possibility of either a premartensitic transition and/or an inter-MT in this system.

  5. Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

    SciTech Connect

    Schleicher, B. Niemann, R.; Schultz, L.; Fähler, S.; Diestel, A.; Hühne, R.

    2015-08-07

    Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg{sub 1/3}Nb{sub 2/3}){sub 0.72}Ti{sub 0.28}O{sub 3} substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.

  6. Epitaxial Ni-Mn-Ga-Co thin films on PMN-PT substrates for multicaloric applications

    NASA Astrophysics Data System (ADS)

    Schleicher, B.; Niemann, R.; Diestel, A.; Hühne, R.; Schultz, L.; Fähler, S.

    2015-08-01

    Multicaloric stacks consisting of a magnetocaloric film on a piezoelectric substrate promise improved caloric properties as the transition temperature can be controlled by both magnetic and electric fields. We present epitaxially grown magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrates. Structure and microstructure of two samples, being in the austenitic and martensitic state at room temperature, are investigated by X-ray diffraction in two- and four-circle geometry and by atomic force microscopy. In addition, high temperature magnetometry was performed on the latter sample. The combination of these methods allows separating the influence of epitaxial growth and martensitic transformation. A preferential alignment of twin boundaries is observed already in the as-deposited state, which indicates the presence of prestress, without applying an electric field to the substrate. A temperature-magnetic field phase diagram is presented, which demonstrates the inverse magnetocaloric effect of the epitaxial Ni-Mn-Ga-Co film.

  7. Large magnetic field-induced work output in a NiMnGa seven-layered modulated martensite

    NASA Astrophysics Data System (ADS)

    Pagounis, E.; Szczerba, M. J.; Chulist, R.; Laufenberg, M.

    2015-10-01

    We report the performance of a Ni-Mn-Ga single crystal with a seven-layered lattice modulation (14M martensite), demonstrating large actuation work output driven by an external magnetic field. A magnetic field-induced strain of 11.2%, a twinning stress of 0.64 MPa, and a magneto-crystalline anisotropy energy of 195 kJ/m3 are measured at room temperature, which exceed the best results reported in Ni-Mn-Ga 14M martensites. The produced magnetically induced work output of about 70 kJ/m3 makes the material attractive for actuator applications. Detailed XRD investigation reveals that the studied 14M martensite is stress-induced. With increasing compression stress, the stress-induced intermartensitic transformation sequence 10M → 14M → NM was demonstrated.

  8. Coupling of metals and biominerals: characterizing the interface between ferromagnetic shape-memory alloys and hydroxyapatite.

    PubMed

    Allenstein, Uta; Selle, Susanne; Tadsen, Meike; Patzig, Christian; Höche, Thomas; Zink, Mareike; Mayr, Stefan G

    2015-07-22

    Durable, mechanically robust osseointegration of metal implants poses one of the largest challenges in contemporary orthopedics. The application of biomimetic hydroxyapatite (HAp) coatings as mediators for enhanced mechanical coupling to natural bone constitutes a promising approach. Motivated by recent advances in the field of smart metals that might open the venue for alternate therapeutic concepts, we explore their mechanical coupling to sputter-deposited HAp layers in a combined experimental-theoretical study. While experimental delamination tests and comprehensive structural characterization, including high-resolution transmission electron microscopy, are utilized to establish structure-property relationships, density functional theory based total energy calculations unravel the underlying physics and chemistry of bonding and confirm the experimental findings. Experiments and modeling indicate that sputter-deposited HAp coatings are strongly adherent to the exemplary ferromagnetic shape-memory alloys, Ni-Mn-Ga and Fe-Pd, with delamination stresses and interface bonding strength exceeding the physiological scales by orders of magnitude.

  9. Model for the magnetomechanical behavior of NiMnGa driven with collinear field and stress

    NASA Astrophysics Data System (ADS)

    Wang, Xiang; Dapino, Marcelo J.

    2006-03-01

    This paper presents a model for NiMnGa transducers driven with collinear magnetic fields and stresses. Prior work by the authors demonstrates the existence of reversible strains under the application of collinear magnetic fields and stresses oriented along the [001] crystallographic axis of a cylindrical rod of single-crystal Ni 50Mn 28.7Ga 21.3. Internal bias stresses from pinning sites in the material are believed to provide the restoring force which allows for the reversibility of the strain. A constitutive model to describe the motion of twin boundaries in the presence of energetically strong pinning sites is presented. The effective pinning strength is represented by an internal bias stress oriented transversely. Stochastic homogenization is then used to account for variability in the bias stresses throughout the material and inhomogeneity in the interaction field intensity. The internal rod dynamics are modeled through force balancing with boundary conditions dictated by the constructive details of the transducer and mechanical load. The model is formulated in variational form, resulting in a second-order temporal system with magnetic field induced strain as the driving mechanism. Model result for unloaded conditions is compared with experimental measurements.

  10. Volume magnetic domain mirroring in magnetic shape memory crystals

    NASA Astrophysics Data System (ADS)

    Lai, Yiu-Wai; Schäfer, Rudolf; Schultz, Ludwig; McCord, Jeffrey

    2010-01-01

    From the magnetic domain patterns at adjacent crystal surfaces of NiMnGa shape memory crystals the internal domain configurations across a hidden twin-boundary are derived. The results proof the existence of domains extending from the sample surfaces into the nonvisible sample volume. Moreover, the structural twin boundary inside the material acts as a mirror for the basic domains. The analysis validates the relevance of surface magnetic response analysis for the understanding of the magnetoelastic behavior of magnetic shape memory alloys and is essential for the interpretation of magnetic domain images obtained from other surface-restricted observation techniques.

  11. Computer simulations of the Ni2MnGa alloys

    NASA Astrophysics Data System (ADS)

    Breczko, Teodor M.; Nelayev, Vladislav; Dovzhik, Krishna; Najbuk, Miroslaw

    2008-07-01

    This article reports an computer simulations of physical properties of Heusler NiMnGa alloy. Computer simulation are devoted to austenite phase. The chemical composition of researched specimens causes generation martesite and austenite phases.

  12. Development of a meso-scale thermo-magneto-mechanical free energy model for NiMnGa

    NASA Astrophysics Data System (ADS)

    Morrison, Phillip; Seelecke, Stefan; Krevet, Berthold; Kohl, Manfred

    2008-03-01

    This paper motivates a one-dimensional thermo-magneto-mechanical free energy model for NiMnGa. Following a discussion of material behavior and modeling purpose, we present what might be referred to as a meso-scale model, incorporating micro-scale physics while striving for macro-scale simplicity. Development of the model begins with the construction of a free energy landscape for the material, with strain and magnetization as its order parameters. This landscape includes paraboloidal energy wells - isolated from each other by energy barriers - to represent stable states of the material. The energy well positions and barrier heights are allowed to vary as functions of stress, magnetic field, and temperature. The resulting equations are employed within the theory of thermally activated processes to find the phase-fraction evolution of a sample. Previous results demonstrating the potential of the modeling approach are included.

  13. 4D STUDY OF STRAIN GRADIENTS EVOLUTION IN TWINNED NiMnGa SINGLE CRYSTALS UNDER MAGNETIC FIELD

    SciTech Connect

    Barabash, Rozaliya; Xu, Ruqing; Barabash, Oleg M; Sozinov, Alexei

    2014-01-01

    Time-resolved 3D X-ray microscopy with a submicron beam size was used to follow the evolution of strains in off-stoichiometric NiMnGa twinned crystals near type I (hard) twin boundary under magnetic field. Laminate A/B microstructure was revealed near the twin boundaries in A variant. Large strain gradients are observed in the C variant in the immediate vicinity of the type I twin boundary: the lattice is under large tensile strains ~0.4% along the c- axes within first micron. Distinct a and b lattice parameter evolution with temperature and magnetic field is demonstrated. In an applied magnetic field the strain field was observed at larger distances from the twin boundary and becomes more complex. Stochastic twin boundary motion was observed after the magnetic field reaches a certain critical value.

  14. Ni-Mn-Ga Single Crystal Exhibiting Multiple Magnetic Shape Memory Effects

    NASA Astrophysics Data System (ADS)

    Heczko, Oleg; Veřtát, Petr; Vronka, Marek; Kopecky, Vít; Perevertov, Oleksiy

    2016-09-01

    Both magnetically induced phase transformation and magnetically induced reorientation (MIR) effects were observed in one Ni50Mn28Ga22 single crystal sample by direct measurement of the magnetic field-induced strain. We investigated various twinning microstructures ranged from single twin interface to fine twinning and crossing twins to evaluate what controls the apparent twinning stress crucial for MIR. The main challenges for the applications of these effects are outlined.

  15. Electromotive force generation using the dynamic response of Ni0Mn28.5Ga21.5 magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Bruno, N.; Ciocanel, C.; Feigenbaum, H.

    2011-04-01

    Magnetic Shape Memory Alloys (MSMAs) are materials that respond to a change in either compressive stress or magnetic field, and can be used for applications such as actuation, sensing, and power harvesting. MSMA prismatic specimens are usually loaded magneto-mechanically by a compressive stress applied along the longest side of the specimen and by a magnetic field applied normal to the direction of the compressive stress. Karaman et al. proved the viability of using MSMAs, specifically NiMnGa single crystals, for energy harvesting applications using up to 5 Hz of cyclic stress. The group proposed a simple mathematical model to predict electrical voltage output generated by the material during the shape recovery process. The voltage output predicted by the model matched well with experimental results recorded at low frequencies1. The magnetization reversal responsible for the voltage output has been approximated by Karaman et al. does not use the constitutive relations for the magneto-mechanical behavior of the material, such as that proposed by Kiefer and Lagoudas2,3. This work presents simulated and experimental results describing the electromotive force (EMF) producing capabilities of a NiMnGa magnetic shape memory alloy (MSMA) at frequencies of up to 10 Hz. Unlike previous work, the current paper uses the constitutive model developed by Kiefer and Lagoudas2-4 and the corresponding magnetization relations to theoretically predict the voltage output of the material. COMSOL Multiphysics 3.5a and Simulink were used to generate the simulated results for different constant bias magnetic fields and frequencies of excitation, partial reorientation strains and stress amplitudes. Simulated results are compared to experimental data and the reasons for data match/mismatch are discussed.

  16. Phenomenological modeling of ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Kiefer, Bjorn; Lagoudas, Dimitris C.

    2004-07-01

    A thermodynamically consistent phenomenological model is presented which captures the ferromagnetic shape memory effect, i. e. the large macroscopically observable shape change of magnetic shape memory materials under the application of external magnetic fields. In its most general form the model includes the influence of the microstructure for both the volume fraction of different martensitic variants and magnetic domains on the described macroscopic constitutive behavior. A phase diagram based approach is taken to postulate functions governing the onset and termination of the reorientation process. A numerical example is given for an experiment on a NiMnGa single crystal specimen reported in the literature, for which the model is reduced to a two-dimensional case of an assumed magnetic domain structure.

  17. Fiber laser drilling of Ni46Mn27Ga27 ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Biffi, C. A.; Tuissi, A.

    2014-11-01

    The interest in ferromagnetic shape memory alloys (SMAs), such as NiMnGa, is increasing, thanks to the functional properties of these smart and functional materials. One of the most evident properties of these systems is their brittleness, which makes attractive the study of unconventional manufacturing processes, such as laser machining. In this work the interaction of laser beam, once focalized on the surface of Ni46Mn27Ga27 [at%] alloy, has been studied. The experiments were performed with a single laser pulse, using a 1 kW continuous wave fiber laser. The morphology of the laser machined surfaces was evaluated using scanning electron microscopy, coupled with energetic dispersion spectroscopy for the measurement of the chemical composition. The results showed that the high quality of the laser beam, coupled with great irradiances available, allow for blind or through holes to be machined on 1.8 mm plates with a single pulse in the order of a few ms. Holes were produced with size in the range of 200-300 μm; despite the long pulse duration, low amount of melted material is produced around the hole periphery. No significant variation of the chemical composition has been detected on the entrance surfaces while the exit ones have been characterized by the loss of Ga content, due to its melting point being significantly lower with respect to the other alloying elements.

  18. Structural, microstructural and magnetocaloric investigations in high-energy ball milled NiMnGa powders

    NASA Astrophysics Data System (ADS)

    de Santanna, Y. V. B.; de Melo, M. A. C.; Santos, I. A.; Coelho, A. A.; Gama, S.; Cótica, L. F.

    2008-11-01

    In this paper, structural, microstrucutural and magnetocaloric properties of Ni 2.18Mn 0.82Ga alloys submitted to high-energy ball milling are reported. A 7-layered orthorhombic martensitic ( Pnnm) phase was detected in post-milling annealed samples, which reached a microstrucuture composed predominantly by nanograins. The magnetocaloric effect is strongly weakened in comparison with as-cast samples of similar composition. This effect can be attributed to the absence of the mesoscale twin-related martensitic variants in the nanostructurated powders. However, post-milled samples annealed at 1123 K for 4 h present relative cooling powers as high as those observed for manganites. Therefore, these materials can be considered as potential candidates for use as regenerators in prototypal magnetic refrigerators.

  19. Rearrangement of twin variants in ferromagnetic shape memory alloy polyurethane composites studied by stroboscopic neutron diffraction

    NASA Astrophysics Data System (ADS)

    Feuchtwanger, J.; Lázpita, P.; Vidal, N.; Barandiaran, J. M.; Gutiérrez, J.; Hansen, T.; Peel, M.; Mondelli, C.; O'Handley, R. C.; Allen, S. M.

    2008-03-01

    The use of ferromagnetic shape memory alloy (FSMA) particles as fillers in polymeric matrix composites has been proposed for vibration damping. The large pseudo-plastic recoverable deformation of the FSMA particles due to the rearrangement of twin variants can dissipate a large amount of energy, both under compression and tension. The composites studied are made by mixing particles of NiMnGa with a polyurethane matrix. A magnetic field is applied to the composite while the matrix sets, to achieve a strong [112] texture in the field direction. In situ strobed neutron diffraction measurements were carried out while the composites were subjected to a cyclic deformation. They show that the intensity of certain peaks varies during the deformation cycle. All the peaks that show this behavior can be grouped into pairs that stem from a single austenitic peak. The (020) and (112) martensite peaks correspond to the splitting of the (220) austenite peak, and the intensity of one increases as that of the other decreases. The neutron measurements show directly that there is a change in the texture of the composite during the stress cycle applied to the composite and confirm that the large mechanical loss observed in the stress-strain cycles is in good part due to the rearrangement of twin variants in the FSMA filler used in the composites.

  20. Structural and Electromagnetic Properties of Ni-Mn-Ga Thin Films Deposited on Si Substrates

    NASA Astrophysics Data System (ADS)

    Pereira, M. J.; Lourenço, A. A. C. S.; Amaral, V. S.

    2014-07-01

    Ni2MnGa thin films raise great interest due to their properties, which provide them with strong potential for technological applications. Ni2MnGa thin films were prepared by r.f. sputtering deposition on Si substrates at low temperature (400 ºC). Film thicknesses in the range 10-120 nm were obtained. A study of the structural, magnetic and electrical properties of the films is presented. We find that the deposited films show some degree of crystallinity, with coexisting cubic and tetragonal structural phases, the first one being preponderant over the latter, particularly in the thinner films. The films possess soft magnetic properties and their coercivity is thickness dependent in the range 15-200 Oe at 300K. Electrical resistivity measurements signal the structural transition and suggest the occurrence of avalanche and return-point memory effects, in temperature cycling through the magnetic/structural transition range.

  1. Compression-induced texture change in NiMnGa-polymer composites observed by synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Scheerbaum, Nils; Hinz, Dietrich; Gutfleisch, Oliver; Skrotzki, Werner; Schultz, Ludwig

    2007-05-01

    Composites consisting of magnetic shape memory (MSM) particles embedded in a polyester matrix were prepared. Single-crystalline MSM particles were obtained by mortar grinding of melt-extracted and subsequently annealed Ni50.9Mn27.1Ga22.0 (at. %) fibers. The crystal structure of the martensite is tetragonal (5M) with c

  2. In-Situ Observation of the Stress-Induced Stochastic Twin Boundary Motion in off Stoichiometric NiMnGa Single Crystal

    SciTech Connect

    Barabash, Rozaliya; Kirchlechner, Christoph; Robach, Odile; Sozinov, Alexei

    2013-01-01

    Stochastic motion of the type II twin boundary in off stoichiometric NiMnGa single crystal is confirmed by in-situ X-ray microdiffraction during external stress field loading. Assymmetry between tensile and compressive parts of the loading and large hysteresis loop is found. Formation of local strained regions is predecessing each boundary movement. The location of strained regions adjusts to the position of the twin boundary. Abrupt motion of the boundary correlates with the corresponding spikes at the load/displacement curve.

  3. In-situ observation of stress-induced stochastic twin boundary motion in off stoichiometric NiMnGa single crystals

    NASA Astrophysics Data System (ADS)

    Barabash, Rozaliya I.; Kirchlechner, Christoph; Robach, Odile; Ulrich, Olivier; Micha, Jean-Sébastien; Sozinov, Alexei; Barabash, Oleg M.

    2013-07-01

    In-situ X-ray microdiffraction is used to illuminate the physics of non-uniform stochastic motion of type II twin boundaries in NiMnGa twinned crystals during external stress field loading. Asymmetry between tensile and compressive loading and a large hysteresis loop were found. The formation of local strained regions precedes each boundary movement. The location of strained regions adjusts to the position of the twin boundary. Abrupt motion of the boundary correlates with corresponding spikes at the load/displacement curve.

  4. Cytocompatibility evaluation of NiMnSn meta-magnetic shape memory alloys for biomedical applications.

    PubMed

    Guiza-Arguello, Viviana R; Monroe, James A; Karaman, Ibrahim; Hahn, Mariah S

    2016-07-01

    Recently, magnetic shape memory alloys (MSMAs) have emerged as an interesting extension to conventional shape memory alloys (SMAs) due to their capacity to undergo reversible deformation in response to an externally applied magnetic field. Meta-magnetic SMAs (M-MSMAs) are a class of MSMAs that are able to transform magnetic energy to mechanical work by harnessing a magnetic-field induced phase transformation, and thus have the capacity to impose up to 10 times greater stress than conventional MSMAs. As such, M-MSMAs may hold substantial promise in biomedical applications requiring extracorporeal device activation. In the present study, the cytotoxicity and ion release from an Ni50 Mn36 Sn14 atomic percent composition M-MSMA were evaluated using NIH/3T3 fibroblasts. Initial studies showed that the viability of cells exposed to NiMnSn ion leachants was 60 to 67% of tissue culture polystyrene (TCP) controls over 10 to 14 days of culture. This represents a significant improvement in cytocompatibility relative to NiMnGa alloys, one of the most extensively studied MSMA systems, which have been reported to induce 80% cell death in only 48 h. Furthermore, NiMnSn M-MSMA associated cell viability was increased to 80% of TCP controls following layer-by-layer alloy coating with poly(allylamine hydrochloride)/poly(acrylic acid) [PAH/PAA]. Ion release measures revealed that the PAH/PAA coatings decreased total Sn and Mn ion release by 50% and 25%, respectively, and optical microscopy evaluation indicated that the coatings reduced NiMnSn surface oxidation. To our knowledge, this study presents the first cytotoxicity evaluation of NiMnSn M-MSMAs and lays the groundwork for their further biological evaluation. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 853-863, 2016. PMID:25953682

  5. Magnetic field-induced phase transformation and variant reorientation in nickel-manganese-gallium and nickel-manganese-cobalt-indium magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Karaca, Haluk Ersin

    The purpose of this work is to reveal the governing mechanisms responsible for the magnetic field-induced (i) martensite reorientation in Ni 2MnGa single crystals, (ii) stress-assisted phase transformation in Ni2MnGa single crystals and (iii) phase transformation in NiMnCoIn alloys. The ultimate goal of utilizing these mechanisms is to increase the actuation stress levels in magnetic shape memory alloys (MSMAs). Extensive experimental work on magneto-thermo-mechanical (MTM) characterization of these materials enabled us to (i) better understand the ways to increase the actuation stress and strain and decrease the required magnetic field for actuation in MSMAs, (ii) determine the effects of main MTM parameters on reversible magnetic field induced phase transformation, such as magnetocrystalline anisotropy energy (MAE), Zeeman energy (ZE), stress hysteresis, thermal hysteresis, critical stress for the stress induced phase transformation and crystal orientation, (iii) find out the feasibility of employing polycrystal MSMAs, and (iv) formulate a thermodynamical framework to capture the energetics of magnetic field-induced phase transformations in MSMAs. Magnetic shape memory properties of Ni2MnGa single crystals were characterized by monitoring magnetic field-induced strain (MFIS) as a function of compressive stress and stress-induced strain as a function of magnetic field. It is revealed that the selection of the operating temperature with respect to martensite start and Curie temperatures is critical in optimizing actuator performance. The actuation stress of 5 MPa and work output of 157 kJm-3 are obtained by the field-induced variant reorientation in NiMnGa alloys. Reversible and one-way stress-assisted field-induced phase transformations are observed in Ni2MnGa single crystals under low field magnitudes (<0.7T) and resulted in at least an order of magnitude higher actuation stress levels. It is very promising to provide higher work output levels and operating

  6. Field-temperature phase diagrams of freestanding and substrate-constrained epitaxial Ni-Mn-Ga-Co films for magnetocaloric applications

    NASA Astrophysics Data System (ADS)

    Diestel, A.; Niemann, R.; Schleicher, B.; Schwabe, S.; Schultz, L.; Fähler, S.

    2015-07-01

    Ferroic cooling processes that rely on field-induced first-order transformations of solid materials are a promising step towards a more energy-efficient refrigeration technology. In particular, thin films are discussed for their fast heat transfer and possible applications in microsystems. Substrate-constrained films are not useful since their substrates act as a heat sink. In this article, we examine a substrate-constrained and a freestanding epitaxial film of magnetocaloric Ni-Mn-Ga-Co. We compare phase diagrams and entropy changes obtained by magnetic field and temperature scans, which differ. We observe an asymmetry of the hysteresis between heating and cooling branch, which vanishes at high magnetic fields. These effects are discussed with respect to the vector character of a magnetic field, which acts differently on the nucleation and growth processes compared to the scalar character of the temperature.

  7. Temperature dependence of the magnetic-field-induced strain of NiMnGa in the presence of an acoustic drive

    NASA Astrophysics Data System (ADS)

    Peterson, Bradley W.; Allen, Samuel M.; O'Handley, Robert C.

    2008-08-01

    A small amplitude acoustic signal was applied to a Ni-Mn-Ga single crystal. The effect of the acoustic signal in enhancing the magnetic-field-induced strain was measured as a function of temperature over the range of 1-35°C below the austenite-start temperature. Strain output was found to decrease with decreasing temperature as a result of lowered twin-boundary mobility. The combination of a piezoelectric drive with the magnetic drive yields an improvement in strain response for all temperatures investigated; however, the piezoenhanced, field-induced strain is maximized at 12.5°C, where ∂ɛ /∂T is maximum.

  8. Characterization of the martensitic transformation in melt-spun NiMnGa ribbons by magnetoinductive effect

    NASA Astrophysics Data System (ADS)

    Pérez-Landazábal, J. I.; Gomez-Polo, C.; Recarte, V.; Seguí, C.; Cesari, E.; Ochin, P.

    2005-04-01

    The magnetoinductance effect, in particular, the temperature dependence of the AC complex impedance, Z(T), has been employed in the characterization of the martensitic transformation (MT) in a melt-spun Ni 52.5Mn 24.5Ga 23 ribbon. While the resistive component shows the characteristic decrease associated with the martensite-to-austenite transformation, the inductive component reflects the temperature dependence of the magnetic permeability of the sample. These structural and magnetic changes associated with the characteristic MT were experimentally checked by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results indicate that the AC impedance technique can be employed as a very simple and versatile characterization technique in the analysis of MT in magnetic memory shape alloys.

  9. A theoretical and experimental investigation of power harvesting using the NiMnGa martensite reorientation mechanism

    NASA Astrophysics Data System (ADS)

    Bruno, Nickolaus M.; Ciocanel, Constantin; Feigenbaum, Heidi P.; Waldauer, Alex

    2012-09-01

    Magnetic shape memory alloys (MSMAs) can exhibit the shape memory effect when there is a magnetic field in the vicinity of a material point. The microstructure of the MSMAs is comprised of tetragonal martensite variants, each with their preferred internal magnetization orientation. Starting from a random variant orientation, the application of a large enough magnetic field will cause the variants to reorient so that the internal magnetization vectors align with the external field. Then, keeping the magnetic field constant and adding a variable compressive stress in a direction normal to that of the magnetic field, some or all of the martensitic variants may rotate into a stress preferred state. As the variants reorient, the internal magnetization vectors rotate, and the material’s magnetization changes. For power harvesting and sensing applications, the change in magnetization induces a current in a pickup coil placed around the MSMA specimen, resulting in an output voltage at its terminals according to Faraday’s law of inductance. This paper focuses on the evaluation of the voltage output, both experimentally and numerically, in an attempt to assess the ability of a MSMA thermodynamic based constitutive model, used in conjunction with Faraday’s law of induction, to predict the variant reorientation induced voltage output. Assessing the accuracy of the predicted voltage is beneficial for the design of both MSMA based power harvesting devices and MSMA based displacement sensors.

  10. Investigations into the physical mechanisms that facilitate transformation hysteresis in shape memory alloys

    NASA Astrophysics Data System (ADS)

    Hamilton, Reginald F.

    Shape Memory Alloys (SMAs) undergo a reversible martensitic transformation (MT) that may be thermal- or stress-induced enabling the recovery of large deformations, up to 12% strain, can be fully recovered, albeit a hysteresis exists. Characterizing the hysteresis for classes of SMAs is essential for their practical application. It is well known that the hysteresis is due to energy dissipative mechanisms, with the primary mechanisms being frictional resistance to interfacial motion and partial plastic accommodation of shape and volume changes. In previous work, however, the origins of potential dissipative mechanisms have not been clarified, and the factors that influence these mechanisms (i.e. external stress fields, matrix strength properties, precipitate microstructure, plastic accommodation, detwinning, etc.) have not been investigated with rigorous experimentation. In this study, an experimental program is designed to address this issue. This comprehensive experimental program, including stress-free thermal cycling, constant load thermal cycling, and constant temperature stress/strain cycling, is undertaken for NiTi, CoNiAl, NiFeGa, and NiMnGa SMAs in the aged and unaged states. The NiFeGa and NiMnGa classes of SMAs undergo martensite to martensite inter-martensitic transformations. The experimental findings characterize the effect of second-phase particles and inter-martensitic transformations on the level of hysteresis. To ascertain physical mechanisms responsible for the hysteresis, in-situ transmission electron microscopy (TEM) analysis provides insight into microstructure features. The results expose the role of frictional resistance and partial plastic accommodation on the observed differential magnitudes of thermal and stress hysteresis. In particular, larger hysteresis magnitudes are mainly attributed to dislocation emissions at the austenite/martensite phase boundary, designated micro-scale plasticity, that lower coherent interface strains, and thus

  11. Shape Memory Alloy Actuator

    NASA Technical Reports Server (NTRS)

    Baumbick, Robert J. (Inventor)

    2000-01-01

    The present invention discloses and teaches a unique, remote optically controlled micro actuator particularly suitable for aerospace vehicle applications wherein hot gas, or in the alternative optical energy, is employed as the medium by which shape memory alloy elements are activated. In gas turbine powered aircraft the source of the hot gas may be the turbine engine compressor or turbine sections.

  12. Basic Properties of Magnetic Shape-Memory Materials from First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Entel, Peter; Dannenberg, Antje; Siewert, Mario; Herper, Heike C.; Gruner, Markus E.; Comtesse, Denis; Elmers, Hans-Joachim; Kallmayer, Michael

    2012-08-01

    The mutual influence of phase transformations, magnetism, and electronic properties of magnetic-shape memory Heusler materials is a basic issue of electronic structure calculations based on density functional theory. In this article, we show that these calculations can be pursued to finite temperatures, which allows to derive on a first-principles basis the temperature versus composition phase diagram of the pseudo-binary Ni-Mn-(Ga, In, Sn, Sb) system. The free energy calculations show that the phonon contribution stabilizes the body-centered-cubic (bcc)-like austenite structure at elevated temperatures, whereas magnetism favors the low-temperature martensite phase with body-centered-tetragonal (bct) or rather face-centered-tetragonal (fct) structure. The calculations also allow to make predictions of magnetostructural and magnetic field induced properties of other (new) magnetic Heusler alloys not based on NiMn such as Co-Ni-(Ga-Zn) and Fe-Co-Ni-(Ga-Zn) intermetallic compounds.

  13. Modulated interaction in double-layer shape memory-based micro-designed actuators

    NASA Astrophysics Data System (ADS)

    Crăciunescu, Corneliu; Ercuta, Aurel

    2015-12-01

    The effect of superposed transitions in actuators with layered shape memory alloy (SMA) films undergoing martensitic phase transformation is analyzed in terms of a model developed for two layers of different composition, deposited at the same temperature on a substrate. A significant difference is observed in the actuation versus temperature relationship, depending on the thermal and elastic properties of the SMA layers and their martensitic transformation temperature. The prediction of the actuation is exemplified using a multilayer model and is verified for a cantilever actuator with NiTi and NiMnGa layers deposited on a Si substrate. The model sets the ground for a smart selection of SMAs in order to achieve a modulated actuation.

  14. Shape memory alloy actuator

    DOEpatents

    Varma, Venugopal K.

    2001-01-01

    An actuator for cycling between first and second positions includes a first shaped memory alloy (SMA) leg, a second SMA leg. At least one heating/cooling device is thermally connected to at least one of the legs, each heating/cooling device capable of simultaneously heating one leg while cooling the other leg. The heating/cooling devices can include thermoelectric and/or thermoionic elements.

  15. Shape memory alloy thaw sensors

    DOEpatents

    Shahinpoor, Mohsen; Martinez, David R.

    1998-01-01

    A sensor permanently indicates that it has been exposed to temperatures exceeding a critical temperature for a predetermined time period. An element of the sensor made from shape memory alloy changes shape when exposed, even temporarily, to temperatures above the Austenitic temperature of the shape memory alloy. The shape change of the SMA element causes the sensor to change between two readily distinguishable states.

  16. Technical Seminar "Shape Memory Alloys"

    NASA Video Gallery

    Shape memory alloys are a unique group of materials that remember their original shape and return to that shape after being strained. How could the aerospace, automotive, and energy exploration ind...

  17. Shape memory alloy thaw sensors

    DOEpatents

    Shahinpoor, M.; Martinez, D.R.

    1998-04-07

    A sensor permanently indicates that it has been exposed to temperatures exceeding a critical temperature for a predetermined time period. An element of the sensor made from shape memory alloy changes shape when exposed, even temporarily, to temperatures above the austenitic temperature of the shape memory alloy. The shape change of the SMA element causes the sensor to change between two readily distinguishable states. 16 figs.

  18. A model for ferromagnetic shape memory thin film actuators

    NASA Astrophysics Data System (ADS)

    Lee, Kwok-Lun; Seelecke, Stefan

    2005-05-01

    The last decade has witnessed the discovery of materials combining shape memory behavior with ferromagnetic properties (FSMAs), see James & Wuttig1, James et al.2, Ullakko et al.3. These materials feature the so-called giant magnetostrain effect, which, in contrast to conventional magnetostriction is due motion of martensite twins. This effect has motivated the development of a new class of active materials transducers, which combine intrinsic sensing capabilities with superior actuation speed and improved efficiency when compared to conventional shape memory alloys. Currently, thin film technology is being developed intensively in order to pave the way for applications in micro- and nanotechnology. As an example, Kohl et al., recently proposed a novel actuation mechanism based on NiMnGa thin film technology, which makes use of both the ferromagnetic transition and the martensitic transformation allowing the realization of an almost perfect antagonism in a single component part. The implementation of the mechanism led to the award-winning development of an optical microscanner. Possible applications in nanotechnology arise, e.g., by combination of smart NiMnGa actuators with scanning probe technologies. The key aspect of Kohl's device is the fact that it employs electric heating for actuation, which requires a thermo-magneto-mechanical model for analysis. The research presented in this paper aims at the development of a model that simulates this particular material behavior. It is based on ideas originally developed for conventional shape memory alloy behavior, (Mueller & Achenbach, Achenbach, Seelecke, Seelecke & Mueller) and couples it with a simple expression for the nonlinear temperature- and position-dependent effective magnetic force. This early and strongly simplified version does not account for a full coupling between SMA behavior and ferromagnetism yet, and does not incorporate the hysteretic character of the magnetization phenomena either. It can however

  19. Thermoelastic behaviour of martensitic alloy in the vicinity of critical point in the stress-temperature phase diagram

    NASA Astrophysics Data System (ADS)

    L'vov, V. A.; Matsishin, N.; Glavatska, N.

    2010-04-01

    The theoretical phase diagram of the shape memory alloy, which exhibits the first-order martensitic phase transition of the cubic-tetragonal type, has been considered. The thermoelastic behaviour of the ultra-soft Ni-Mn-Ga alloy in the vicinity of the endpoint of the phase transitions line has been modelled. To this end, the strain-temperature and stress-strain dependencies have been computed with the account of the temperature dependence of the elastic modulus of the alloy. Two important features of thermoelastic behaviour of the alloy have been disclosed: (1) even in the case of complete stress-induced martensitic transformation (MT), the MT strain determined from the length of the plateaus at the stress-strain curves is smaller than the 'spontaneous' tetragonal distortion of the crystal lattice, which arises on cooling of the alloy and (2) the stress-strain loops may include the plateau-like segment even at temperatures above the critical temperature, which corresponds to the endpoint of the stress-strain phase diagram. These features render the observation of the endpoint of phase transitions line impossible with the help of the stress-strain tests and make preferable the direct structural studies of MTs in the stressed single-crystalline specimens.

  20. Influence of Mn incorporation for Ni on the magnetocaloric properties of rapidly solidified off-stoichiometric NiMnGa ribbons

    NASA Astrophysics Data System (ADS)

    Dey, Sushmita; Singh, Satnam; Roy, R. K.; Ghosh, M.; Mitra, A.; Panda, A. K.

    2016-01-01

    The present investigation addresses the magnetocaloric behaviour in a series of Ni77-xMnxGa23 (x=23, 24, 25, 27 and 29) rapidly solidified alloys prepared in the form of ribbons by melt spinning technique. The approach of the study is to identify the off-stoichiometric composition wherein room temperature magneto-structural transformation is achieved. The alloy chemistry was tailored through Mn incorporation for Ni such that the magnetic and structural transitions were at close proximity to achieve highest entropy value of ΔS equal to 8.51 J Kg-1 K-1 for #Mn24 ribbon measured at an applied field of 3 T. When such transitions are more staggered as in #Mn29 the entropy value of ribbon reduced to as low as 1.61 J Kg-1 K-1. Near room temperature transformations in #Mn24 ribbon have been observed through calorimetric and thermomagnetic evaluation. Reverse martensitic transformation (martensite→autstenite) temperature indicates not only distinct change in the saturation flux density but also an inter-martensitic phase. Microstructural analysis of #Mn24 alloy ribbon revealed structural ordering with the existence of plate morphology evidenced for martensitic phase.

  1. Shape memory alloy consortium (SMAC)

    NASA Astrophysics Data System (ADS)

    Jacot, A. Dean

    1999-07-01

    The application of smart structures to helicopter rotors has received widespread study in recent years. This is one of the major thrusts of the Shape Memory Alloy Consortium (SMAC) program. SMAC includes 3 companies and 4 Universities in a cost sharing consortium funded under DARPA Smart Materials and Structures program. This paper describes the objective of the SMAC effort, and its relationship to a previous DARPA smart structure rotorcraft program from which it originated. The SMAC program includes NiTinol fatigue/characterization studies, SMA actuator development, and ferromagnetic SMA material development. The paper summarizes the SMAC effort, and includes background and details on Boeing's development of a SMA torsional actuator for rotorcraft applications. SMA actuation is used to retwist the rotorcraft blade in flight, and result in a significant payload increase for either helicopters or tiltrotors. This paper is also augmented by several other papers in this conference with specific results from other SMAC consortium members.

  2. Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

    NASA Astrophysics Data System (ADS)

    Niemann, R.; Hahn, S.; Diestel, A.; Backen, A.; Schultz, L.; Nielsch, K.; Wagner, M. F.-X.; Fähler, S.

    2016-06-01

    Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.

  3. Hysteresis in magnetic shape memory composites: Modeling and simulation

    NASA Astrophysics Data System (ADS)

    Conti, Sergio; Lenz, Martin; Rumpf, Martin

    2016-04-01

    Magnetic shape memory alloys are characterized by the coupling between the reorientation of structural variants and the rearrangement of magnetic domains. This permits to control the shape change via an external magnetic field, at least in single crystals. Composite materials with single-crystalline particles embedded in a softer matrix have been proposed as a way to overcome the blocking of the reorientation at grain boundaries. We investigate hysteresis phenomena for small NiMnGa single crystals embedded in a polymer matrix for slowly varying magnetic fields. The evolution of the microstructure is studied within the rate-independent variational framework proposed by Mielke and Theil (1999). The underlying variational model incorporates linearized elasticity, micromagnetism, stray field and a dissipation term proportional to the volume swept by the twin boundary. The time discretization is based on an incremental minimization of the sum of energy and dissipation. A backtracking approach is employed to approximately ensure the global minimality condition. We illustrate and discuss the influence of the particle geometry (volume fraction, shape, arrangement) and the polymer elastic parameters on the observed hysteresis and compare with recent experimental results.

  4. A lightweight shape-memory magnesium alloy

    NASA Astrophysics Data System (ADS)

    Ogawa, Yukiko; Ando, Daisuke; Sutou, Yuji; Koike, Junichi

    2016-07-01

    Shape-memory alloys (SMAs), which display shape recovery upon heating, as well as superelasticity, offer many technological advantages in various applications. Those distinctive behaviors have been observed in many polycrystalline alloy systems such as nickel titantium (TiNi)–, copper-, iron-, nickel-, cobalt-, and Ti-based alloys but not in lightweight alloys such as magnesium (Mg) and aluminum alloys. Here we present a Mg SMA showing superelasticity of 4.4% at –150°C and shape recovery upon heating. The shape-memory properties are caused by reversible martensitic transformation. This Mg alloy includes lightweight scandium, and its density is about 2 grams per cubic centimeter, which is one-third less than that of practical TiNi SMAs. This finding raises the potential for development and application of lightweight SMAs across a number of industries.

  5. A lightweight shape-memory magnesium alloy.

    PubMed

    Ogawa, Yukiko; Ando, Daisuke; Sutou, Yuji; Koike, Junichi

    2016-07-22

    Shape-memory alloys (SMAs), which display shape recovery upon heating, as well as superelasticity, offer many technological advantages in various applications. Those distinctive behaviors have been observed in many polycrystalline alloy systems such as nickel titantium (TiNi)-, copper-, iron-, nickel-, cobalt-, and Ti-based alloys but not in lightweight alloys such as magnesium (Mg) and aluminum alloys. Here we present a Mg SMA showing superelasticity of 4.4% at -150°C and shape recovery upon heating. The shape-memory properties are caused by reversible martensitic transformation. This Mg alloy includes lightweight scandium, and its density is about 2 grams per cubic centimeter, which is one-third less than that of practical TiNi SMAs. This finding raises the potential for development and application of lightweight SMAs across a number of industries. PMID:27463668

  6. A lightweight shape-memory magnesium alloy

    NASA Astrophysics Data System (ADS)

    Ogawa, Yukiko; Ando, Daisuke; Sutou, Yuji; Koike, Junichi

    2016-07-01

    Shape-memory alloys (SMAs), which display shape recovery upon heating, as well as superelasticity, offer many technological advantages in various applications. Those distinctive behaviors have been observed in many polycrystalline alloy systems such as nickel titantium (TiNi)-, copper-, iron-, nickel-, cobalt-, and Ti-based alloys but not in lightweight alloys such as magnesium (Mg) and aluminum alloys. Here we present a Mg SMA showing superelasticity of 4.4% at -150°C and shape recovery upon heating. The shape-memory properties are caused by reversible martensitic transformation. This Mg alloy includes lightweight scandium, and its density is about 2 grams per cubic centimeter, which is one-third less than that of practical TiNi SMAs. This finding raises the potential for development and application of lightweight SMAs across a number of industries.

  7. A jumping shape memory alloy under heat.

    PubMed

    Yang, Shuiyuan; Omori, Toshihiro; Wang, Cuiping; Liu, Yong; Nagasako, Makoto; Ruan, Jingjing; Kainuma, Ryosuke; Ishida, Kiyohito; Liu, Xingjun

    2016-02-16

    Shape memory alloys are typical temperature-sensitive metallic functional materials due to superelasticity and shape recovery characteristics. The conventional shape memory effect involves the formation and deformation of thermally induced martensite and its reverse transformation. The shape recovery process usually takes place over a temperature range, showing relatively low temperature-sensitivity. Here we report novel Cu-Al-Fe-Mn shape memory alloys. Their stress-strain and shape recovery behaviors are clearly different from the conventional shape memory alloys. In this study, although the Cu-12.2Al-4.3Fe-6.6Mn and Cu-12.9Al-3.8Fe-5.6Mn alloys possess predominantly L2(1) parent before deformation, the 2H martensite stress-induced from L2(1) parent could be retained after unloading. Furthermore, their shape recovery response is extremely temperature-sensitive, in which a giant residual strain of about 9% recovers instantly and completely during heating. At the same time, the phenomenon of the jumping of the sample occurs. It is originated from the instantaneous completion of the reverse transformation of the stabilized 2H martensite. This novel Cu-Al-Fe-Mn shape memory alloys have great potentials as new temperature-sensitive functional materials.

  8. A jumping shape memory alloy under heat

    PubMed Central

    Yang, Shuiyuan; Omori, Toshihiro; Wang, Cuiping; Liu, Yong; Nagasako, Makoto; Ruan, Jingjing; Kainuma, Ryosuke; Ishida, Kiyohito; Liu, Xingjun

    2016-01-01

    Shape memory alloys are typical temperature-sensitive metallic functional materials due to superelasticity and shape recovery characteristics. The conventional shape memory effect involves the formation and deformation of thermally induced martensite and its reverse transformation. The shape recovery process usually takes place over a temperature range, showing relatively low temperature-sensitivity. Here we report novel Cu-Al-Fe-Mn shape memory alloys. Their stress-strain and shape recovery behaviors are clearly different from the conventional shape memory alloys. In this study, although the Cu-12.2Al-4.3Fe-6.6Mn and Cu-12.9Al-3.8Fe-5.6Mn alloys possess predominantly L21 parent before deformation, the 2H martensite stress-induced from L21 parent could be retained after unloading. Furthermore, their shape recovery response is extremely temperature-sensitive, in which a giant residual strain of about 9% recovers instantly and completely during heating. At the same time, the phenomenon of the jumping of the sample occurs. It is originated from the instantaneous completion of the reverse transformation of the stabilized 2H martensite. This novel Cu-Al-Fe-Mn shape memory alloys have great potentials as new temperature-sensitive functional materials. PMID:26880700

  9. A jumping shape memory alloy under heat

    NASA Astrophysics Data System (ADS)

    Yang, Shuiyuan; Omori, Toshihiro; Wang, Cuiping; Liu, Yong; Nagasako, Makoto; Ruan, Jingjing; Kainuma, Ryosuke; Ishida, Kiyohito; Liu, Xingjun

    2016-02-01

    Shape memory alloys are typical temperature-sensitive metallic functional materials due to superelasticity and shape recovery characteristics. The conventional shape memory effect involves the formation and deformation of thermally induced martensite and its reverse transformation. The shape recovery process usually takes place over a temperature range, showing relatively low temperature-sensitivity. Here we report novel Cu-Al-Fe-Mn shape memory alloys. Their stress-strain and shape recovery behaviors are clearly different from the conventional shape memory alloys. In this study, although the Cu-12.2Al-4.3Fe-6.6Mn and Cu-12.9Al-3.8Fe-5.6Mn alloys possess predominantly L21 parent before deformation, the 2H martensite stress-induced from L21 parent could be retained after unloading. Furthermore, their shape recovery response is extremely temperature-sensitive, in which a giant residual strain of about 9% recovers instantly and completely during heating. At the same time, the phenomenon of the jumping of the sample occurs. It is originated from the instantaneous completion of the reverse transformation of the stabilized 2H martensite. This novel Cu-Al-Fe-Mn shape memory alloys have great potentials as new temperature-sensitive functional materials.

  10. Neutron diffraction study of the martensitic transformation and chemical order in Heusler alloy Ni1.91Mn1.29Ga0.8

    DOE PAGES

    Ari-Gur, Pnina; Garlea, Vasile O.; Cao, Huibo; Ge, Y.; Aaltio, I.; Hannula, S. P.; Koledov, V.

    2015-11-05

    In this study, Heusler alloys of Ni-Mn-Ga compositions demonstrate ferromagnetic shape memory effect in the martensitic state. The transformation temperature and the chemical order depend strongly on the composition. In the current work, the structure and chemical order of the martensitic phase of Ni1.91Mn1.29Ga0.8 were studied using neutron diffraction; the diffraction pattern was refined using the FullProf software. It was determined that the structural transition occurs around 330 K. At room temperature, 300 K, which is below the martensite transformation temperature, all the Bragg reflections can be described by a monoclinic lattice with a symmetry of space group P 1more » 2/m 1 and lattice constants of a = 4.23047(7) [Å], b = 5.58333(6) [Å], c = 21.0179(2) [Å], beta = 90.328(1). The chemical order is of critical importance in these alloys, and it was previously studied at 363 K. Analysis of the neutron diffraction in the monoclinic phase shows that the chemical order is maintained during the martensitic transformation.« less

  11. Neutron diffraction study of the martensitic transformation and chemical order in Heusler alloy Ni1.91Mn1.29Ga0.8

    SciTech Connect

    Ari-Gur, Pnina; Garlea, Vasile O.; Cao, Huibo; Ge, Y.; Aaltio, I.; Hannula, S. P.; Koledov, V.

    2015-11-05

    In this study, Heusler alloys of Ni-Mn-Ga compositions demonstrate ferromagnetic shape memory effect in the martensitic state. The transformation temperature and the chemical order depend strongly on the composition. In the current work, the structure and chemical order of the martensitic phase of Ni1.91Mn1.29Ga0.8 were studied using neutron diffraction; the diffraction pattern was refined using the FullProf software. It was determined that the structural transition occurs around 330 K. At room temperature, 300 K, which is below the martensite transformation temperature, all the Bragg reflections can be described by a monoclinic lattice with a symmetry of space group P 1 2/m 1 and lattice constants of a = 4.23047(7) [Å], b = 5.58333(6) [Å], c = 21.0179(2) [Å], beta = 90.328(1). The chemical order is of critical importance in these alloys, and it was previously studied at 363 K. Analysis of the neutron diffraction in the monoclinic phase shows that the chemical order is maintained during the martensitic transformation.

  12. Shape-Memory-Alloy Actuator For Flight Controls

    NASA Technical Reports Server (NTRS)

    Barret, Chris

    1995-01-01

    Report proposes use of shape-memory-alloy actuators, instead of hydraulic actuators, for aerodynamic flight-control surfaces. Actuator made of shape-memory alloy converts thermal energy into mechanical work by changing shape as it makes transitions between martensitic and austenitic crystalline phase states of alloy. Because both hot exhaust gases and cryogenic propellant liquids available aboard launch rockets, shape-memory-alloy actuators exceptionally suited for use aboard such rockets.

  13. Precipitation Hardenable High Temperature Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald Dean (Inventor); Draper, Susan L. (Inventor); Nathal, Michael V. (Inventor); Crombie, Edwin A. (Inventor)

    2010-01-01

    A composition of the invention is a high temperature shape memory alloy having high work output, and is made from (Ni+Pt+Y),Ti(100-x) wherein x is present in a total amount of 49-55 atomic % Pt is present in a total amount of 10-30 atomic %, Y is one or more of Au, Pd. and Cu and is present in a total amount of 0 to 10 atomic %. The alloy has a matrix phase wherein the total concentration of Ni, Pt, and the one or more of Pd. Au, and Cu is greater than 50 atomic %.

  14. Experimental study of directionally solidified ferromagnetic shape memory alloy under multi-field coupling

    NASA Astrophysics Data System (ADS)

    Zhu, Yuping; Chen, Tao; Teng, Yao; Liu, Bingfei; Xue, Lijun

    2016-11-01

    Directionally solidified, polycrystalline Ni-Mn-Ga is studied in this paper. The polycrystalline Ni-Mn-Ga samples were cut at different angles to solidification direction. The magnetic field induced strain under constant stress and the temperature-induced strain under constant magnetic field during the loading-unloading cycle were measured. The experimental results show that the mechanical behavior during the loading-unloading cycle of the material is nonlinear and anisotropic. Based on the experimental results, the effects of multi-field coupling factors, such as stress, magnetic field, temperature and cutting angle on the mechanical behaviors were analyzed. Some useful conclusions were obtained, which will provide guidance for practical applications.

  15. Mechanocaloric effects in shape memory alloys.

    PubMed

    Mañosa, Lluís; Planes, Antoni

    2016-08-13

    Shape memory alloys (SMA) are a class of ferroic materials which undergo a structural (martensitic) transition where the associated ferroic property is a lattice distortion (strain). The sensitiveness of the transition to the conjugated external field (stress), together with the latent heat of the transition, gives rise to giant mechanocaloric effects. In non-magnetic SMA, the lattice distortion is mostly described by a pure shear and the martensitic transition in this family of alloys is strongly affected by uniaxial stress, whereas it is basically insensitive to hydrostatic pressure. As a result, non-magnetic alloys exhibit giant elastocaloric effects but negligible barocaloric effects. By contrast, in a number of magnetic SMA, the lattice distortion at the martensitic transition involves a volume change in addition to the shear strain. Those alloys are affected by both uniaxial stress and hydrostatic pressure and they exhibit giant elastocaloric and barocaloric effects. The paper aims at providing a critical survey of available experimental data on elastocaloric and barocaloric effects in magnetic and non-magnetic SMA.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

  16. Shape memory alloy/shape memory polymer tools

    DOEpatents

    Seward, Kirk P.; Krulevitch, Peter A.

    2005-03-29

    Micro-electromechanical tools for minimally invasive techniques including microsurgery. These tools utilize composite shape memory alloy (SMA), shape memory polymer (SMP) and combinations of SMA and SMP to produce catheter distal tips, actuators, etc., which are bistable. Applications for these structures include: 1) a method for reversible fine positioning of a catheter tip, 2) a method for reversible fine positioning of tools or therapeutic catheters by a guide catheter, 3) a method for bending articulation through the body's vasculature, 4) methods for controlled stent delivery, deployment, and repositioning, and 5) catheters with variable modulus, with vibration mode, with inchworm capability, and with articulated tips. These actuators and catheter tips are bistable and are opportune for in vivo usage because the materials are biocompatible and convenient for intravascular use as well as other minimal by invasive techniques.

  17. Fastening apparatus having shape memory alloy actuator

    NASA Astrophysics Data System (ADS)

    McKinnis, Darin N.

    1992-11-01

    A releasable fastening apparatus is presented. The device includes a connecting member and a housing. The housing supports a gripping mechanism that is adapted to engage the connecting member. A triggering member is movable within the housing between a first position in which it constrains the gripping mechanism in locked engagement with the connecting member, and a second position in which the gripping mechanism is disengaged from the connecting member. A shaped memory alloy actuator is employed for translating the triggering member from its first to its second position. The actuator is designed to expand longitudinally when transitioned from a martensitic to an austenitic state.

  18. Fastening apparatus having shape memory alloy actuator

    NASA Technical Reports Server (NTRS)

    Mckinnis, Darin N. (Inventor)

    1992-01-01

    A releasable fastening apparatus is presented. The device includes a connecting member and a housing. The housing supports a gripping mechanism that is adapted to engage the connecting member. A triggering member is movable within the housing between a first position in which it constrains the gripping mechanism in locked engagement with the connecting member, and a second position in which the gripping mechanism is disengaged from the connecting member. A shaped memory alloy actuator is employed for translating the triggering member from its first to its second position. The actuator is designed to expand longitudinally when transitioned from a martensitic to an austenitic state.

  19. Shape memory alloy seals for geothermal applications

    SciTech Connect

    Friske, Warren H.; Schwartzbart, Harry

    1982-10-08

    Rockwell International's Energy Systems Group, under contract to Brookhaven National Laboratory, has completed a 2-year program to develop a novel temperature-actuated seal concept for geothermal applications. This seal concept uses the unique properties of a shape memory alloy (Nitinol) to perform the sealing function. The several advantages of the concept are discussed in the paper. Demonstration tests of both face and shaft seals have shown that leaktight seals are feasible. Supporting materials studies have included corrosion tests in geothermal fluids, elevated temperature tensile tests, experimental electroplating and metallographic evaluations of microstructures.

  20. Constitutive Models for Shape Memory Alloy Polycrystals

    NASA Technical Reports Server (NTRS)

    Comstock, R. J., Jr.; Somerday, M.; Wert, J. A.

    1996-01-01

    Shape memory alloys (SMA) exhibiting the superelastic or one-way effects can produce large recoverable strains upon application of a stress. In single crystals this stress and resulting strain are very orientation dependent. We show experimental stress/strain curves for a Ni-Al single crystal for various loading orientations. Also shown are model predictions; the open and closed circles indicate recoverable strains obtained at various stages in the transformation process. Because of the strong orientation dependence of shape memory properties, crystallographic texture can be expected to play an important role in the mechanical behavior of polycrystalline SMA. It is desirable to formulate a constitutive model to better understand and exploit the unique properties of SMA.

  1. Shape-memory alloy micro-actuator

    NASA Technical Reports Server (NTRS)

    Busch, John D. (Inventor); Johnson, Alfred D. (Inventor)

    1991-01-01

    A method of producing an integral piece of thermo-sensitive material, which is responsive to a shift in temperature from below to above a phase transformation temperature range to alter the material's condition to a shape-memory condition and move from one position to another. The method is characterized by depositing a thin film of shape-memory material, such as Nickel titanium (Ni-Ti) onto a substrate by vacuum deposition process such that the alloy exhibits an amorphous non-crystalline structure. The coated substrate is then annealed in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cool down rate to produce an ordered, partially disordered or fully disordered BCC structure such that the alloy undergoes thermoelastic, martinsetic phase transformation in response to alteration in temperature to pass from a martinsetic phase when at a temperature below a phase transformation range and capable of a high level of recoverable strain to a parent austenitic phase in a memory shape when at a temperature above the phase transformation range. Also disclosed are actuator devices employing shape-memory material actuators that deform from a set shape toward an original shape when subjected to a critical temperature level after having been initially deformed from the original shape into the set shape while at a lower temperature. The actuators are mechanically coupled to one or more movable elements such that the temperature-induce deformation of the actuators exerts a force or generates a motion of the mechanical element(s).

  2. Method of preparing a two-way shape memory alloy

    DOEpatents

    Johnson, A.D.

    1984-03-06

    A two-way shape memory alloy, a method of training a shape memory alloy, and a heat engine employing the two-way shape memory alloy to do external work during both heating and cooling phases are disclosed. The alloy is heated under a first training stress to a temperature which is above the upper operating temperature of the alloy, then cooled to a cold temperature below the zero-force transition temperature of the alloy, then deformed while applying a second training stress which is greater in magnitude than the stress at which the alloy is to be operated, then heated back to the hot temperature, changing from the second training stress back to the first training stress. 8 figs.

  3. Method of preparing a two-way shape memory alloy

    DOEpatents

    Johnson, Alfred D.

    1984-01-01

    A two-way shape memory alloy, a method of training a shape memory alloy, and a heat engine employing the two-way shape memory alloy to do external work during both heating and cooling phases. The alloy is heated under a first training stress to a temperature which is above the upper operating temperature of the alloy, then cooled to a cold temperature below the zero-force transition temperature of the alloy, then deformed while applying a second training stress which is greater in magnitude than the stress at which the alloy is to be operated, then heated back to the hot temperature, changing from the second training stress back to the first training stress.

  4. Method for fabricating uranium alloy articles without shape memory effects

    DOEpatents

    Banker, John G.

    1985-01-01

    Uranium-rich niobium and niobium-zirconium alloys possess a characteristic known as shape memory effect wherein shaped articles of these alloys recover their original shape when heated. The present invention circumvents this memory behavior by forming the alloys into the desired configuration at elevated temperatures with "cold" matched dies and maintaining the shaped articles between the dies until the articles cool to ambient temperature.

  5. Method for fabricating uranium alloy articles without shape memory effects

    DOEpatents

    Banker, J.G.

    1980-05-21

    Uranium-rich niobium and niobium-zirconium alloys possess a characteristic known as shape memory effect wherein shaped articles of these alloys recover their original shape when heated. The present invention circumvents this memory behavior by forming the alloys into the desired configuration at elevated temperatures with cold matched dies and maintaining the shaped articles between the dies until the articles cool to ambient temperature.

  6. Nondestructive evaluation of Ni-Ti shape memory alloy

    SciTech Connect

    Meir, S.; Gordon, S.; Karsh, M.; Ayers, R.; Olson, D. L.; Wiezman, A.

    2011-06-23

    The nondestructive evaluation of nickel titanium (Ni-Ti) alloys for applications such as heat treatment for biomaterials applications (dental) and welding was investigated. Ni-Ti alloys and its ternary alloys are valued for mechanical properties in addition to the shape memory effect. Two analytical approaches were perused in this work. Assessment of the microstructure of the alloy that determines the martensitic start temperature (Ms) of Ni-Ti alloy as a function of heat treatment, and secondly, an attempt to evaluate a Friction Stir Welding, which involves thermo-mechanical processing of the alloy.

  7. Shape memory alloys: New materials for future engineering

    NASA Technical Reports Server (NTRS)

    Hornbogen, E.

    1988-01-01

    Shape memory is a new material property. An alloy which experiences relative severe plastic deformation resumes its original shape again after heating by 10 to 100 C. Besides simple shape memory, in similar alloys there is the second effect where the change in shape is caused exclusively by little temperature change. In pseudo-elasticity, the alloy exhibits a rubber-like behavior, i.e., large, reversible deformation at little change in tension. Beta Cu and beta NiTi alloys have been used in practice. The probability is that soon alloys based on Fe will become available. Recently increasing applications for this alloy were found in various areas of technology, even medical technology. A review with 24 references is given, including properties, production, applications and fundamental principles of the shape memory effect.

  8. High-Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Biffi, C. A.; Tuissi, A.

    2014-10-01

    In this paper, an experimental study of laser micro-processing on a Cu-Zr-based shape memory alloy (SMA), which is suitable for high-temperature (HT) applications, is discussed. A first evaluation of the interaction between a laser beam and Zr50Cu28Ni7Co15 HT SMA is highlighted. Single laser pulses at various levels of power and pulse duration were applied to evaluate their effect on the sample surfaces. Blind and through microholes were produced with sizes on the order of a few hundreds of microns; the results were characterized from the morphological viewpoint using a scanning electron microscope. The high beam quality allows the holes to be created with good circularity and little melted material around the hole periphery. An analysis of the chemical composition was performed using energy dispersive spectroscopy, revealing that compositional changes were limited, while important oxidation occurred on the hole surfaces. Additionally, laser micro-cutting tests were also proposed to evaluate the cut edge morphology and dimensions. The main result of this paper concerned the good behavior of the material upon interaction with the laser beam, which suggests that microfeatures can be successfully produced in this alloy.

  9. Martensite transformation and shape memory effect on NiTi-Zr high temperature shape memory alloys

    SciTech Connect

    Pu, Z.; Tseng, H.; Wu, K.

    1995-10-17

    NiTi-Zr high temperature alloys possess relatively poor shape memory properties and ductility in comparison with NiTi-Hf and NiTi-Pd alloys. During martensite transformation of the newly-developed NiTi-Zr high temperature shape memory alloys (SMAs) the temperature increases along with Zr content when the Zr content is more than 10 at%. As the Zr content increases, the fully reversible strain of the alloys decreases. However, complete strain recovery behavior is exhibited by all the alloys studied in this paper, even those with a Zr content of 20 at%. Stability of the NiTi-Zr alloys during thermal cycling was also tested and results indicate that the NiTi-Zr alloys have poor stability against thermal cycling. The reasons for the deterioration of the shape memory effect and stability have yet to be determined.

  10. Final Technical Report: Nanostructured Shape Memory ALloys

    SciTech Connect

    Wendy Crone; Walter Drugan; Arthur Ellis; John Perepezko

    2005-07-28

    With this grant we explored the properties that result from combining the effects of nanostructuring and shape memory using both experimental and theoretical approaches. We developed new methods to make nanostructured NiTi by melt-spinning and cold rolling fabrication strategies, which elicited significantly different behavior. A template synthesis method was also used to created nanoparticles. In order to characterize the particles we created, we developed a new magnetically-assisted particle manipulation technique to manipulate and position nanoscale samples for testing. Beyond characterization, this technique has broader implications for assembly of nanoscale devices and we demonstrated promising applications for optical switching through magnetically-controlled scattering and polarization capabilities. Nanoparticles of nickel-titanium (NiTi) shape memory alloy were also produced using thin film deposition technology and nanosphere lithography. Our work revealed the first direct evidence that the thermally-induced martensitic transformation of these films allows for partial indent recovery on the nanoscale. In addition to thoroughly characterizing and modeling the nanoindentation behavior in NiTi thin films, we demonstrated the feasibility of using nanoindentation on an SMA film for write-read-erase schemes for data storage.

  11. Multi-range force sensors utilizing shape memory alloys

    DOEpatents

    Varma, Venugopal K.

    2003-04-15

    The present invention provides a multi-range force sensor comprising a load cell made of a shape memory alloy, a strain sensing system, a temperature modulating system, and a temperature monitoring system. The ability of the force sensor to measure contact forces in multiple ranges is effected by the change in temperature of the shape memory alloy. The heating and cooling system functions to place the shape memory alloy of the load cell in either a low temperature, low strength phase for measuring small contact forces, or a high temperature, high strength phase for measuring large contact forces. Once the load cell is in the desired phase, the strain sensing system is utilized to obtain the applied contact force. The temperature monitoring system is utilized to ensure that the shape memory alloy is in one phase or the other.

  12. Nonhysteretic superelasticity of shape memory alloys at the nanoscale.

    PubMed

    Zhang, Zhen; Ding, Xiangdong; Sun, Jun; Suzuki, Tetsuro; Lookman, Turab; Otsuka, Kazuhiro; Ren, Xiaobing

    2013-10-01

    We perform molecular dynamics simulations to show that shape memory alloy nanoparticles below the critical size not only demonstrate superelasticity but also exhibit features such as absence of hysteresis, continuous nonlinear elastic distortion, and high blocking force. Atomic level investigations show that this nonhysteretic superelasticity results from a continuous transformation from the parent phase to martensite under external stress. This aspect of shape memory alloys is attributed to a surface effect; i.e., the surface locally retards the formation of martensite and then induces a critical-end-point-like behavior when the system is below the critical size. Our work potentially broadens the application of shape memory alloys to the nanoscale. It also suggests a method to achieve nonhysteretic superelasticity in conventional bulk shape memory alloys.

  13. Shape memory effect of the Ni-Ti-Hf high temperature shape memory alloy

    SciTech Connect

    Wu, K.H.; Pu, Z.; Tseng, H.K.; Biancaniello, F.S.

    1995-11-17

    The one-way shape memory effect of the newly-developed TiNi-Hf high temperature shape memory alloys has been investigated. The results of the study show that TiNi-Hf high temperature alloys possess a relatively high shape memory effect. All the alloys, even those with an Hf content as high as 30at%, exhibit complete strain recovery behavior. However, as the Hf content increases, the fully reversible strain of the alloys decreases. The increase of the second phase as the Hf content increases is the primary reason for the deterioration of the shape memory effect and ductility. The shape memory properties also deteriorate as the deformation temperature increases.

  14. Acoustic assisted, field-induced strain in ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Peterson, Bradley W.; Feuchtwanger, Jorge; Chambers, Joshua M.; Bono, David; Hall, Steven R.; Allen, Samuel M.; O'Handley, Robert C.

    2004-06-01

    A technique has been developed that uses acoustic energy to assist a magnetic field in driving twin boundary motion in a NiMnGa single crystal. Acoustic assisted magnetic-field-induced strain has been observed to increase the magnetic-field-induced strain response by up to one order of magnitude. This effect is most pronounced for magnetic field drives near the twin boundary threshold field. Increasing frequency of the acoustic wave input is shown to increase strain up to about 4 kHz after which there is a small decline in FSMA strain for higher frequencies.

  15. Phase Transformations in Electrically Conductive Ferromagnetic Shape-Memory Alloys, Their Thermodynamics and Analysis

    NASA Astrophysics Data System (ADS)

    Roubíček, Tomáš; Tomassetti, Giuseppe

    2013-10-01

    We derive a thermodynamically consistent general continuum-mechanical model describing mutually coupled martensitic and ferro/paramagnetic phase transformations in electrically-conductive magnetostrictive materials such as NiMnGa. We use small-strain and eddy-current approximations, yet large velocities and electric current injected through the boundary are allowed. Fully nonlinear coupling of magneto-mechanical and thermal effects is considered. The existence of energy-preserving weak solutions is proved by showing convergence of time-discrete approximations constructed by a carefully designed semi-implicit regularized scheme.

  16. A shape-memory alloy for high-temperature applications

    SciTech Connect

    Duerig, T.W.; Albrecht, J.; Gessinger, G.H.

    1982-12-01

    An alloy based on the Cu-Al-Ni ternary system has been developed at the research center of Brown, Boveri and Co., Baden, Switzerland, which provides a fully reversible (two-way) shape memory effect at significantly higher temperatures than those afforded by commercial memory alloys such as NiTi and Cu-Zn-Al. The higher temperature capability of this alloy could open new fields for the application of the shape memory effect, particularly in thermal switching and protection devices. After suitable deformation and processing, a shape change is observed while heating the alloy through the temperature interval from 175 to 190/sup 0/C. This shape change can be completely reversed during subsequent cooling from 155 to 125/sup 0/C. The magnitude of the reversible strain produced by this alloy is 1.5%; somewhat higher strains can be achieved if lower memory temperatures can be accepted, and conversely, better high temperature capabilities can be achieved by accepting smaller reversible strains. The memory effects in this alloy have been found to be unaffected by short overheatings to temperatures as high as 300/sup 0/C.

  17. Damping capacity of TiNi-based shape memory alloys

    NASA Astrophysics Data System (ADS)

    Rong, L. J.; Jiang, H. C.; Liu, S. W.; Zhao, X. Q.

    2007-07-01

    Damping capacity is another primary characteristic of shape memory alloys (SMA) besides shape memory effect and superelasticity. Damping behavior of Ti-riched TiNi SMA, porous TiNi SMA and a novel TiNi/AlSi composite have been investigated using dynamic mechanical analyzer (DMA) in this investigation. All these alloys are in martensitic state at room temperature and thus possess the high potential application value. Ti 50.2Ni 49.8 SMA has better damping capacity in pure martensitic state and phase transformation region due to the motion of martensite twin interface. As a kind of promising material for effective dampers and shock absorbing devices, porous TiNi SMA can exhibit higher damping capacity than the dense one due to the existence of the three-dimensioned connecting pore structure. It is found that the internal friction of porous TiNi SMA mainly originates from microplastic deformation and mobility of martensite interface and increases with the increase of the porosity. A novel TiNi/AlSi composite has been developed successfully by infiltrating AlSi alloy into the open pores of porous TiNi alloy with 60% porosity through compression casting. It shows the same phase transformation characteristics as the porous TiNi alloy. The damping capacity of the composite has been increased and the compressive strength has been also promoted remarkably. Suggestions for developing higher damping alloys based on TiNi shape memory alloy are proposed in this paper.

  18. Production of Cu-Al-Ni Shape Memory Alloys by Mechanical Alloy

    SciTech Connect

    Goegebakan, Musa; Soguksu, Ali Kemal; Uzun, Orhan; Dogan, Ali

    2007-04-23

    The mechanical alloying technique has been used to produce shape memory Cu83Al13Ni4 alloy. The structure and thermal properties were examined by using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The morphology of the surface suggests the presence of martensite.

  19. Thermomechanical Methodology for Stabilizing Shape Memory Alloy (SMA) Response

    NASA Technical Reports Server (NTRS)

    Padula, Santo A., II (Inventor)

    2016-01-01

    Methods and apparatuses for stabilizing the strain-temperature response for a shape memory alloy are provided. To perform stabilization of a second sample of the shape memory alloy, a first sample of the shape memory alloy is selected for isobaric treatment and the second sample is selected for isothermal treatment. When applying the isobaric treatment to the first sample, a constant stress is applied to the first sample. Temperature is also cycled from a minimum temperature to a maximum temperature until a strain on the first sample stabilizes. Once the strain on the first sample stabilizes, the isothermal treatment is performed on the second sample. During isothermal treatment, different levels of stress on the second sample are applied until a strain on the second sample matches the stabilized strain on the first sample.

  20. Thermomechanical Methodology for Stabilizing Shape Memory Alloy (SMA) Response

    NASA Technical Reports Server (NTRS)

    Padula, II, Santo A (Inventor)

    2013-01-01

    Methods and apparatuses for stabilizing the strain-temperature response for a shape memory alloy are provided. To perform stabilization of a second sample of the shape memory alloy, a first sample of the shape memory alloy is selected for isobaric treatment and the second sample is selected for isothermal treatment. When applying the isobaric treatment to the first sample, a constant stress is applied to the first sample. Temperature is also cycled from a minimum temperature to a maximum temperature until a strain on the first sample stabilizes. Once the strain on the first sample stabilizes, the isothermal treatment is performed on the second sample. During isothermal treatment, different levels of stress on the second sample are applied until a strain on the second sample matches the stabilized strain on the first sample.

  1. Periodic Cellular Structure Technology for Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Chen, Edward Y.

    2015-01-01

    Shape memory alloys are being considered for a wide variety of adaptive components for engine and airframe applications because they can undergo large amounts of strain and then revert to their original shape upon heating or unloading. Transition45 Technologies, Inc., has developed an innovative periodic cellular structure (PCS) technology for shape memory alloys that enables fabrication of complex bulk configurations, such as lattice block structures. These innovative structures are manufactured using an advanced reactive metal casting technology that offers a relatively low cost and established approach for constructing near-net shape aerospace components. Transition45 is continuing to characterize these structures to determine how best to design a PCS to better exploit the use of shape memory alloys in aerospace applications.

  2. Fatigue Resistance of Liquid-assisted Self-repairing Aluminum Alloys Reinforced with Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Wright, M. Clara; Manuel, Michele; Wallace, Terryl

    2013-01-01

    A self-repairing aluminum-based composite system has been developed using a liquid-assisted healing theory in conjunction with the shape memory effect of wire reinforcements. The metal-metal composite was thermodynamically designed to have a matrix with a relatively even dispersion of a low-melting eutectic phase, allowing for repair of cracks at a predetermined temperature. Additionally, shape memory alloy (SMA) wire reinforcements were used within the composite to provide crack closure. Investigators focused the research on fatigue cracks propagating through the matrix in order to show a proof-of-concept Shape Memory Alloy Self-Healing (SMASH) technology for aeronautical applications.

  3. A rotating arm using shape-memory alloy

    NASA Technical Reports Server (NTRS)

    Jenkins, Phillip P.; Landis, Geoffrey A.

    1995-01-01

    NASA's Mars Pathfinder mission, to be launched in 1996, reflects a new philosophy of exploiting new technologies to reduce mission cost and accelerate the pace of space exploration. One of the experiments on board Pathfinder will demonstrate the first use in space of a multi-cycle, electrically-activated, shape-memory alloy (SMA) actuator. SMA's are metal alloys which, when heated, undergo a crystalline phase change. This change in phase alters the alloy lattice-constant, resulting in a change of dimension. Upon cooling, the alloy returns to its original lattice formation. Wire drawn from an SMA contracts in length when heated. The reversible change in length is 3 percent to 5 percent. The wire used in this actuator is a nickel-titanium alloy known as nitinol.

  4. Switchable Shape Memory Alloys (SMA) Thermal Materials Project

    NASA Technical Reports Server (NTRS)

    Falker, John; Zeitlin, Nancy; Williams, Martha; Fesmire, James

    2014-01-01

    Develop 2-way switchable thermal systems for use in systems that function in cold to hot temperature ranges using different alloy designs for SMA system concepts. In this project, KSC will specifically address designs of two proof of concept SMA systems with transition temperatures in the 65-95 C range and investigate cycle fatigue and "memory loss" due to thermal cycling.

  5. Shape memory alloys: a state of art review

    NASA Astrophysics Data System (ADS)

    Naresh, C.; Bose, P. S. C.; Rao, C. S. P.

    2016-09-01

    Shape memory alloys (SMAs) are the special materials that have the ability to return to a predetermined shape when heated. When this alloy is in below transformation temperature it undergoes low yield strength and will deform easily into any new shape which it will retain, if this alloy is heated above its transformation temperature it changes its crystal lattice structure which returns to its real shape. SMAs are remarkably different from other materials are primarily due to shape memory effect (SME) and pseudoelasticity which are related with the specific way the phase transformation occurs, biocompatibility, high specific strength, high corrosion resistance, high wear resistance and high anti-fatigue property. SMA are used in many applications such as aerospace, medical, automobile, tubes, controllers for hot water valves in showers, petroleum industry, vibration dampers, ball bearings, sensors, actuators, miniature grippers, micro valves, pumps, landing gears, eye glass frames, Material for helicopter blades, sprinklers in fine alarm systems packaging devices for electronic materials, dental materials, etc. This paper focuses on introducing shape memory alloy and their applications in past, present and in future, also revealed the concept and mechanism of shape memory materials for a particular requirement. Properties of SMAs, behaviour and characteristics of SMA, summary of recent advances and new application opportunities are also discussed.

  6. Thermomechanical Modeling of Shape Memory Alloys and Applications

    NASA Astrophysics Data System (ADS)

    Lexcellent, C.; Leclercq, S.

    The aim of the present paper is a general macroscopic description of the thermomechanical behavior of shape memory alloys (SMA). We use for framework the thermodynamics of irreversible processes. This model is efficient for describing the behavior of "smart" structures as a bronchial, a tentacle element and an prosthesis hybrid structure made of Ti Ni SMA wires embedded in a resin epoxy matrix.

  7. Magnetic field-controlled two-way shape memory in CoNiGa single crystals

    NASA Astrophysics Data System (ADS)

    Li, Y. X.; Liu, H. Y.; Meng, F. B.; Yan, L. Q.; Liu, G. D.; Dai, X. F.; Zhang, M.; Liu, Z. H.; Chen, J. L.; Wu, G. H.

    2004-05-01

    A two-way magnetic field controlled shape memory effect has been observed in single crystals of CoNiGa with martensitic transformation temperature ranging from 205 to 341 K. Two-way shape memory with -2.3% strain has been obtained in free samples. By applying a bias field of up to 2 T, the shape memory strain can be continuously controlled from negative 2.3% to positive 2.2% giving it a total strain of 4.5%. The magnetic properties of CoNiGa show that it is a good shape memory material working at relatively high temperature of up to 450 K, and has a lower magnetic anisotropy than NiMnGa.

  8. Nanoscale shape-memory alloys for ultrahigh mechanical damping.

    PubMed

    San Juan, Jose; Nó, Maria L; Schuh, Christopher A

    2009-07-01

    Shape memory alloys undergo reversible transformations between two distinct phases in response to changes in temperature or applied stress. The creation and motion of the internal interfaces between these phases during such transformations dissipates energy, making these alloys effective mechanical damping materials. Although it has been shown that reversible phase transformations can occur in nanoscale volumes, it is not known whether these transformations have a sample size dependence. Here, we demonstrate that the two phases responsible for shape memory in Cu-Al-Ni alloys are more stable in nanoscale pillars than they are in the bulk. As a result, the pillars show a damping figure of merit that is substantially higher than any previously reported value for a bulk material, making them attractive for damping applications in nanoscale and microscale devices. PMID:19581892

  9. Shape memory alloys: metallurgy, biocompatibility, and biomechanics for neurosurgical applications.

    PubMed

    Hoh, Daniel J; Hoh, Brian L; Amar, Arun P; Wang, Michael Y

    2009-05-01

    SHAPE MEMORY ALLOYS possess distinct dynamic properties with particular applications in neurosurgery. Because of their unique physical characteristics, these materials are finding increasing application where resiliency, conformation, and actuation are needed. Nitinol, the most frequently manufactured shape memory alloy, responds to thermal and mechanical stimuli with remarkable mechanical properties such as shape memory effect, super-elasticity, and high damping capacity. Nitinol has found particular use in the biomedical community because of its excellent fatigue resistance and biocompatibility, with special interest in neurosurgical applications. The properties of nitinol and its diffusionless phase transformations contribute to these unique mechanical capabilities. The features of nitinol, particularly its shape memory effect, super-elasticity, damping capacity, as well as its biocompatibility and biomechanics are discussed herein. Current and future applications of nitinol and other shape memory alloys in endovascular, spinal, and minimally invasive neurosurgery are introduced. An understanding of the metallurgic properties of nitinol provides a foundation for further exploration of its use in neurosurgical implant design.

  10. Understanding the Shape-Memory Alloys Used in Orthodontics

    PubMed Central

    Fernandes, Daniel J.; Peres, Rafael V.; Mendes, Alvaro M.; Elias, Carlos N.

    2011-01-01

    Nickel-titanium (NiTi) shape-memory alloys (SMAs) have been used in the manufacture of orthodontic wires due to their shape memory properties, super-elasticity, high ductility, and resistance to corrosion. SMAs have greater strength and lower modulus of elasticity when compared with stainless steel alloys. The pseudoelastic behavior of NiTi wires means that on unloading they return to their original shape by delivering light continuous forces over a wider range of deformation which is claimed to allow dental displacements. The aim of this paper is to discuss the physical, metallurgical, and mechanical properties of NiTi used in Orthodontics in order to analyze the shape memory properties, super-elasticity, and thermomechanical characteristics of SMA. PMID:21991455

  11. High-Speed Behavior of Some Shape Memory Alloys

    SciTech Connect

    Bragov, Anatoly M.; Lomunov, Andrey K.; Sergeichev, Ivan V.

    2006-07-28

    The results of dynamic tests of shape memory alloys Ti-Ni and Cu-Al-Ni are given. Compressive tests of Ti-Ni alloy were carried out at temperatures 293-573K. Considerable influence of temperature on module of elasticity prior to the dislocation plastic flow and dislocation yield limit has been mentioned in temperature interval of reverse martensitic transformation. For Cu-Al-Ni alloy a strain rate influence on phase yield limit, module of elasticity prior to the phase unelastic flow, module of elasticity prior to the dislocation plastic flow was negligible. The method of determination of duration of reverse martensitic transformation has been realized by the example of Cu-Al-Ni alloy.

  12. Damping of High-temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Duffy, Kirsten P.; Padula, Santo A., II; Scheiman, Daniel A.

    2008-01-01

    Researchers at NASA Glenn Research Center have been investigating high temperature shape memory alloys as potential damping materials for turbomachinery rotor blades. Analysis shows that a thin layer of SMA with a loss factor of 0.04 or more would be effective at reducing the resonant response of a titanium alloy beam. Two NiTiHf shape memory alloy compositions were tested to determine their loss factors at frequencies from 0.1 to 100 Hz, at temperatures from room temperature to 300 C, and at alternating strain levels of 34-35x10(exp -6). Elevated damping was demonstrated between the M(sub s) and M(sub f) phase transformation temperatures and between the A(sub s) and A(sub f) temperatures. The highest damping occurred at the lowest frequencies, with a loss factor of 0.2-0.26 at 0.1 Hz. However, the peak damping decreased with increasing frequency, and showed significant temperature hysteresis in heating and cooling. Keywords: High-temperature, shape memory alloy, damping, aircraft engine blades, NiTiHf

  13. Development of Superelastic Effect in Ferrous Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Olson, Scott

    Shape memory alloys (SMAs) with high levels of superelasticity are used where there is a need for the application of large levels of force, or high damping. Current commercially available SMAs require expensive fabrication and lack sufficient ductility for many applications. There is a need for a superelastic material with better properties and easier processing. Y. Tanaka et al. have developed a novel iron based shape memory alloy, NCATB. This alloy still requires complex thermomechanical processing, and does not utilize lessons learned in optimizing Nitinol. To develop the properties of this alloy, it was synthesized in lab from its constituent elements, and thermomechanically processed. Samples were prepared for analysis using conventional metallographic techniques, and investigated with light optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, and mechanical testing. The recrystallization following cold rolling, as well as aging heat treatments, were determined to be critical to increasing the hardness of the NCATB. Overall, smaller grains and longer aging times increased the hardness. The as-cast microstructure exhibits significant tantalum segregation along the dendrite boundaries. Incomplete homogenization of the as-cast microstructure leads to a propensity for a Tarich phase to form along subsequent recrystallized grain boundaries. This phase lead to alloy embrittlement, preventing the NCATB as processed from having the desired superelasticity. An additional high temperature thermomechanical treatment following casting solutionized the tantalum from the dendrite boundaries, and further improved the NCATB hardenability.

  14. Shape memory alloys. (Latest citations from the INSPEC database). Published Search

    SciTech Connect

    Not Available

    1994-03-01

    The bibliography contains citations concerning theories and experiments on shape memory effects of various alloys. Alloys studied include nickel, tin, indium, lead, copper, and titanium. Citations discuss shape memory crystallography, properties, processing, alloying, and mechanisms. (Contains 250 citations and includes a subject term index and title list.)

  15. Shape memory in nanostructured metallic alloys

    NASA Astrophysics Data System (ADS)

    Guda Vishnu, Karthik

    Materials with nanoscale dimensions show mechanical and structural properties different to those at the macro scale and engineering their nanostructure opens up potential avenues for designing materials tailored for a specific application. This work is focused on shape memory materials, an important class of active materials with wide variety of applications in medical, aerospace and automobile industries, due to their two important properties of super-elasticity and shape memory. These unique properties originate from a solid-solid transformation called martensite transformation and the main objectives of this research are to i) study the atomic mechanisms of the martensite transformation, ii) study the effect of nano-structure on shape memory behavior and iii) computationally explore avenues through which their performance is optimized. A combination of density functional theory (DFT) and molecular dynamics (MD) simulations is used to achieve this. This approach gives an atomic level description and the effects of size, surfaces and interfaces are explicitly described. Detailed analysis of the atomic mechanisms of the martensite transformation in NiTi using DFT revealed a new phase transformation (B19'-B19'') that sheds light on why the theoretically predicted ground state (BCO) is not observed experimentally and that the experimentally observed martensite phase (B19') can be stabilized by internal stresses. This finding is very important as the theoretically predicted ground state does not allow for shape memory in nanoscale NiTi samples. The size effects caused by the presence of free surfaces and the role of nanostructure in martensite transformation have been investigated in thin NiTi slabs. Surface energies of B2 phase (austenite), B19 (orthorhombic), B19' (martensite) and the body centered orthorhombic phase (BCO) are calculated using DFT. (110)B2 surfaces with in-plane atomic displacements stabilize the austenite phase with respect to B19' and BCO, thus

  16. Three-Dimensional Cellular Structures Enhanced By Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Nathal, Michael V.; Krause, David L.; Wilmoth, Nathan G.; Bednarcyk, Brett A.; Baker, Eric H.

    2014-01-01

    This research effort explored lightweight structural concepts married with advanced smart materials to achieve a wide variety of benefits in airframe and engine components. Lattice block structures were cast from an aerospace structural titanium alloy Ti-6Al-4V and a NiTi shape memory alloy (SMA), and preliminary properties have been measured. A finite element-based modeling approach that can rapidly and accurately capture the deformation response of lattice architectures was developed. The Ti-6-4 and SMA material behavior was calibrated via experimental tests of ligaments machined from the lattice. Benchmark testing of complete lattice structures verified the main aspects of the model as well as demonstrated the advantages of the lattice structure. Shape memory behavior of a sample machined from a lattice block was also demonstrated.

  17. Shape Control of Solar Collectors Using Shape Memory Alloy Actuators

    NASA Technical Reports Server (NTRS)

    Lobitz, D. W.; Grossman, J. W.; Allen, J. J.; Rice, T. M.; Liang, C.; Davidson, F. M.

    1996-01-01

    Solar collectors that are focused on a central receiver are designed with a mechanism for defocusing the collector or disabling it by turning it out of the path of the sun's rays. This is required to avoid damaging the receiver during periods of inoperability. In either of these two cases a fail-safe operation is very desirable where during power outages the collector passively goes to its defocused or deactivated state. This paper is principally concerned with focusing and defocusing the collector in a fail-safe manner using shape memory alloy actuators. Shape memory alloys are well suited to this application in that once calibrated the actuators can be operated in an on/off mode using a minimal amount of electric power. Also, in contrast to other smart materials that were investigated for this application, shape memory alloys are capable of providing enough stroke at the appropriate force levels to focus the collector. Design and analysis details presented, along with comparisons to test data taken from an actual prototype, demonstrate that the collector can be repeatedly focused and defocused within accuracies required by typical solar energy systems. In this paper the design, analysis and testing of a solar collector which is deformed into its desired shape by shape memory alloy actuators is presented. Computations indicate collector shapes much closer to spherical and with smaller focal lengths can be achieved by moving the actuators inward to a radius of approximately 6 inches. This would require actuators with considerably more stroke and some alternate SMA actuators are currently under consideration. Whatever SMA actuator is finally chosen for this application, repeatability and fatigue tests will be required to investigate the long term performance of the actuator.

  18. Low Temperature Shape Memory Alloys for Adaptive, Autonomous Systems Project

    NASA Technical Reports Server (NTRS)

    Falker, John; Zeitlin, Nancy; Williams, Martha; Benafan, Othmane; Fesmire, James

    2015-01-01

    The objective of this joint activity between Kennedy Space Center (KSC) and Glenn Research Center (GRC) is to develop and evaluate the applicability of 2-way SMAs in proof-of-concept, low-temperature adaptive autonomous systems. As part of this low technology readiness (TRL) activity, we will develop and train low-temperature novel, 2-way shape memory alloys (SMAs) with actuation temperatures ranging from 0 C to 150 C. These experimental alloys will also be preliminary tested to evaluate their performance parameters and transformation (actuation) temperatures in low- temperature or cryogenic adaptive proof-of-concept systems. The challenge will be in the development, design, and training of the alloys for 2-way actuation at those temperatures.

  19. Characterization Results of a Novel Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Collado, M.; Nava, N.; Herranz, S.; Ramiro, C.; San Juan, J. M.; Patti, S.; Lautier, J.-M.

    2012-07-01

    A novel Shape Memory Alloy (SMA) has been developed as an alternative to currently available alloys. This material, called SMARQ, shows a higher working range of temperatures with respect to the SMA materials used until now, mainly NiTi based alloys. SMARQ is a fully European material technology and production processes, which allows the manufacture of high quality products, with tuneable transformation temperatures up to 200oC. A full Characterization test campaign has been completed in order to obtain the material properties and check its suitability to be used as active material in space actuators. Details of the tests and results of the characterization test campaign, focused in the material unique properties for their use in actuators, will be presented in this work. Some application examples of space mechanisms and actuators, currently under development, will be summarized as part of this work, demonstrating the technology suitability for the development of space actuators.

  20. Absence of magnetic domain wall motion during magnetic field induced twin boundary motion in bulk magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Lai, Y. W.; Scheerbaum, N.; Hinz, D.; Gutfleisch, O.; Schäfer, R.; Schultz, L.; McCord, J.

    2007-05-01

    A detailed study of twin boundary motion in NiMnGa single crystals together with in situ magnetic domain observation is presented. Optical polarization microscopy in connection with a magneto-optical indicator film technique was used to investigate the reorganization of the magnetic domains during twin boundary motion over a wide magnetic field range. Images at different field strengths demonstrate that no magnetic domain wall motion within the twins takes place, even during the structural reorientation by twin boundary movement. This absence of interaction of magnetic and structural domains is different from currently proposed models, which assume domain wall movement under an external field.

  1. Thermally activated retainer means utilizing shape memory alloy

    NASA Technical Reports Server (NTRS)

    Grimaldi, Margaret E. (Inventor); Hartz, Leslie S. (Inventor)

    1993-01-01

    A retainer member suitable for retaining a gap filler placed in gaps between adjacent tile members is presented. One edge of the retainer member may be attached to the gap filler and another edge may be provided with a plurality of tab members which in an intermediate position do not interfere with placement or removal of the gap filler between tile members. The retainer member may be fabricated from a shape memory alloy which when heated to a specified memory temperature will thermally activate the tab members to predetermined memory positions engaging the tile members to retain the gap filler in the gap. This invention has particular application to the thermal tiles on space vehicles such as the Space Shuttle Orbiter.

  2. Precipitate Phases in Several High Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Yang, Fan

    Initiated by the aerospace industry, there has been a great interest to develop high temperature shape memory alloys (HTSMAs) for actuator type of application at elevated temperatures. Several NiTi based ternary systems have been shown to be potential candidates for HTSMAs and this work focuses on one or more alloys in the TiNiPt, TiNiPd, NiTiHf, NiPdTiHf systems. The sheer scope of alloys of varying compositions across all four systems suggests that the questions raised and addressed in this work are just the tip of the iceberg. This work focuses on materials characterization and aims to investigate microstructural evolution of these alloys as a function of heat treatment. The information gained through the study can serve as guidance for future alloy processing. The emphasis of this work is to describe novel precipitate phases that are formed under aging in the ternary systems and one quaternary system. Employing conventional transmission electron microscopy (TEM), high resolution high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), 3D atom probe tomography (3D APT), as well as ab initio calculations, the complete description of the unit cell for the new precipitates was determined. The methodology is summarized in the appendix to help elucidate some basics of such a process.

  3. Crystallographic texture and the preferential orientation of a martensite in the polycrystalline Ni2.08Mn0.96Ga0.96 alloy

    NASA Astrophysics Data System (ADS)

    Musabirov, I. I.; Mulyukov, R. R.; Koledov, V. V.

    2015-04-01

    A study of the relationship of the crystallographic texture, the preferential orientation of martensite twins and the geometry changes during the martensite transformation of polycrystalline NiMnGa alloy is shown. Two states of alloy are investigated: as-cast state and the state after annealing at 923 K for 5 hours. It is shown that in the initial state the austenite phase has crystallographic axial texture <001>, while martensite has the two-component texture of the <001> and <110>. The preferential orientation of the martensitic twins in the martensitic structure is found. The crystallographic texture of the alloy after annealing is not changed, however, no preferential orientation of the martensitic twins is observed. In the martensitic phase structure martensitic twins are oriented randomly. Anisotropy of the thermal expansion during the martensitic transformation is shown, while in the annealed state such effect is not found.

  4. Solid state engine using nitinol memory alloy

    DOEpatents

    Golestaneh, Ahmad A.

    1981-01-01

    A device for converting heat energy to mechanical energy includes a reservoir of a hot fluid and a rotor assembly mounted thereabove so a portion of it dips into the hot fluid. The rotor assembly may include a shaft having four spokes extending radially outwardly therefrom at right angles to each other, a floating ring and four flexible elements composed of a thermal memory material having a critical temperature between the temperature of the hot fluid and that of the ambient atmosphere extending between the ends of the spokes and the floating ring. Preferably, the flexible elements are attached to the floating ring through curved leaf springs. Energetic shape recovery of the flexible elements in the hot fluid causes the rotor assembly to rotate.

  5. Solid state engine using nitinol memory alloy

    DOEpatents

    Golestaneh, A.A.

    1980-01-21

    A device for converting heat energy to mechanical energy includes a reservoir of a hot fluid and a rotor assembly mounted thereabove so a portion of it dips into the hot fluid. The rotor assembly may include a shaft having four spokes extending radially outwardly therefrom at right angles to each other, a floating ring and four flexible elements composed of a thermal memory material having a critical temperature between the temperature of the hot fluid and that of the ambient atmosphere extending between the ends of the spokes and the floating ring. Preferably, the flexible elements are attached to the floating ring through curved leaf springs. Energetic shape recovery of the flexible elements in the hot fluid causes the rotor assembly to rotate.

  6. Shape memory alloy seals for geothermal applications

    SciTech Connect

    Not Available

    1985-09-15

    A shape memory radial seal was fabricated with a ''U'' cross section. Upon heating the seal recovered its original ''V'' shape and produced a high pressure seal. The sealing pressure which can be developed is approximately 41 MPa (60,000 psi), well in excess of the pressure which can be produced in conventional elastomeric seals. The low modulus martensite can conform readily to the sealing surface, and upon recovery produce a seal capable of high pressure fluid or gas confinement. The corrosion resistance of nickel-titanium in a broad range of aggressive fluids has been well established and, as such, there is little doubt that, had time permitted, a geothermal pump of flange fluid tried would have been successful.

  7. Deformation and Failure Mechanisms of Shape Memory Alloys

    SciTech Connect

    Daly, Samantha Hayes

    2015-04-15

    The goal of this research was to understand the fundamental mechanics that drive the deformation and failure of shape memory alloys (SMAs). SMAs are difficult materials to characterize because of the complex phase transformations that give rise to their unique properties, including shape memory and superelasticity. These phase transformations occur across multiple length scales (one example being the martensite-austenite twinning that underlies macroscopic strain localization) and result in a large hysteresis. In order to optimize the use of this hysteretic behavior in energy storage and damping applications, we must first have a quantitative understanding of this transformation behavior. Prior results on shape memory alloys have been largely qualitative (i.e., mapping phase transformations through cracked oxide coatings or surface morphology). The PI developed and utilized new approaches to provide a quantitative, full-field characterization of phase transformation, conducting a comprehensive suite of experiments across multiple length scales and tying these results to theoretical and computational analysis. The research funded by this award utilized new combinations of scanning electron microscopy, diffraction, digital image correlation, and custom testing equipment and procedures to study phase transformation processes at a wide range of length scales, with a focus at small length scales with spatial resolution on the order of 1 nanometer. These experiments probe the basic connections between length scales during phase transformation. In addition to the insights gained on the fundamental mechanisms driving transformations in shape memory alloys, the unique experimental methodologies developed under this award are applicable to a wide range of solid-to-solid phase transformations and other strain localization mechanisms.

  8. Properties and medical applications of shape memory alloys.

    PubMed

    Tarniţă, Daniela; Tarniţă, D N; Bîzdoacă, N; Mîndrilă, I; Vasilescu, Mirela

    2009-01-01

    One of the most known intelligent material is nitinol, which offers many functional advantages over conventional implantable alloys. Applications of SMA to the biomedical field have been successful because of their functional qualities, enhancing both the possibility and the execution of less invasive surgeries. The biocompatibility of these alloys is one of their most important features. Different applications exploit the shape memory effect (one-way or two-way) and the super elasticity, so that they can be employed in orthopedic and cardiovascular applications, as well as in the manufacture of new surgical tools. Therefore, one can say that smart materials, especially SMA, are becoming noticeable in the biomedical field. Super elastic NiTi has become a material of strategic importance as it allows to overcome a wide range of technical and design issues relating to the miniaturization of medical devices and the increasing trend for less invasive and therefore less traumatic procedures. This paper will consider just why the main properties of shape memory alloys hold so many opportunities for medical devices and will review a selection of current applications. PMID:19221641

  9. Texture memory and strain-texture mapping in a NiTi shape memory alloy

    SciTech Connect

    Ye, B.; Majumdar, B. S.; Dutta, I.

    2007-08-06

    The authors report on the near-reversible strain hysteresis during thermal cycling of a polycrystalline NiTi shape memory alloy at a constant stress that is below the yield strength of the martensite. In situ neutron diffraction experiments are used to demonstrate that the strain hysteresis occurs due to a texture memory effect, where the martensite develops a texture when it is cooled under load from the austenite phase and is thereafter ''remembered.'' Further, the authors quantitatively relate the texture to the strain by developing a calculated strain-texture map or pole figure for the martensite phase, and indicate its applicability in other martensitic transformations.

  10. Novel tribological systems using shape memory alloys and thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Yijun

    Shape memory alloys and thin films are shown to have robust indentation-induced shape memory and superelastic effects. Loading conditions that are similar to indentations are very common in tribological systems. Therefore novel tribological systems that have better wear resistance and stronger coating to substrate adhesion can be engineered using indentation-induced shape memory and superelastic effects. By incorporating superelastic NiTi thin films as interlayers between chromium nitride (CrN) and diamond-like carbon (DLC) hard coatings and aluminum substrates, it is shown that the superelasticity can improve tribological performance and increase interfacial adhesion. The NiTi interlayers were sputter deposited onto 6061 T6 aluminum and M2 steel substrates. CrN and DLC coatings were deposited by unbalanced magnetron sputter deposition. Temperature scanning X-ray diffraction and nanoindentation were used to characterize NiTi interlayers. Temperature scanning wear and scratch tests showed that superelastic NiTi interlayers improved tribological performance on aluminum substrates significantly. The two-way shape memory effect under contact loading conditions is demonstrated for the first time, which could be used to make novel tribological systems. Spherical indents in NiTi shape memory alloys and thin films had reversible depth changes that were driven by temperature cycling, after thermomechanical cycling, or one-cycle slip-plasticity deformation training. Reversible surface topography was realized after the indents were planarized. Micro- and nano- scale circular surface protrusions arose from planarized spherical indents in bulk and thin film NiTi alloy; line surface protrusions appeared from planarized scratch tracks. Functional surfaces with reversible surface topography can potentially result in novel tribological systems with reversible friction coefficient. A three dimensional constitutive model was developed to describe shape memory effects with slip

  11. Shape Memory Alloy Actuator Design: CASMART Collaborative Best Practices

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane; Brown, Jeff; Calkins, F. Tad; Kumar, Parikshith; Stebner, Aaron; Turner, Travis; Vaidyanathan, Raj; Webster, John; Young, Marcus L.

    2011-01-01

    Upon examination of shape memory alloy (SMA) actuation designs, there are many considerations and methodologies that are common to them all. A goal of CASMART's design working group is to compile the collective experiences of CASMART's member organizations into a single medium that engineers can then use to make the best decisions regarding SMA system design. In this paper, a review of recent work toward this goal is presented, spanning a wide range of design aspects including evaluation, properties, testing, modeling, alloy selection, fabrication, actuator processing, design optimization, controls, and system integration. We have documented each aspect, based on our collective experiences, so that the design engineer may access the tools and information needed to successfully design and develop SMA systems. Through comparison of several case studies, it is shown that there is not an obvious single, linear route a designer can adopt to navigate the path of concept to product. SMA engineering aspects will have different priorities and emphasis for different applications.

  12. Damping capacity in shape memory alloy honeycomb structures

    NASA Astrophysics Data System (ADS)

    Boucher, M.-A.; Smith, C. W.; Scarpa, F.; Miller, W.; Hassan, M. R.

    2010-04-01

    SMA honeycombs have been recently developed by several Authors [1, 2] as innovative cellular structures with selfhealing capability following mechanical indentation, unusual deformation (negative Poisson's ratio [3]), and possible enhanced damping capacity due to the natural vibration dissipation characteristics of SMAs under pseudoelastic and superelastic regime. In this work we describe the nonlinear damping effects of novel shape memory alloy honeycomb assemblies subjected to combine mechanical sinusoidal and thermal loading. The SMA honeycomb structures made with Ni48Ti46Cu6 are designed with single and two-phase polymeric components (epoxy), to enhance the damping characteristics of the base SMA for broadband frequency vibration.

  13. Thermo-Mechanical Methodology for Stabilizing Shape Memory Alloy Response

    NASA Technical Reports Server (NTRS)

    Padula, Santo

    2013-01-01

    This innovation is capable of significantly reducing the amount of time required to stabilize the strain-temperature response of a shape memory alloy (SMA). Unlike traditional stabilization processes that take days to weeks to achieve stabilized response, this innovation accomplishes stabilization in a matter of minutes, thus making it highly useful for the successful and practical implementation of SMA-based technologies in real-world applications. The innovation can also be applied to complex geometry components, not just simple geometries like wires or rods.

  14. Shape memory alloy heat engines and energy harvesting systems

    DOEpatents

    Browne, Alan L; Johnson, Nancy L; Keefe, Andrew C; Alexander, Paul W; Sarosi, Peter Maxwell; Herrera, Guillermo A; Yates, James Ryan

    2013-12-17

    A heat engine includes a first rotatable pulley and a second rotatable pulled spaced from the first rotatable pulley. A shape memory alloy (SMA) element is disposed about respective portions of the pulleys at an SMA pulley ratio. The SMA element includes first spring coil and a first fiber core within the first spring coil. A timing cable is disposed about disposed about respective portions of the pulleys at a timing pulley ratio, which is different than the SMA pulley ratio. The SMA element converts a thermal energy gradient between the hot region and the cold region into mechanical energy.

  15. Memory alloy heat engine and method of operation

    DOEpatents

    Johnson, Alfred Davis

    1977-01-01

    A heat engine and method of operation employing an alloy having a shape memory effect. A memory alloy element such as one or more wire loops are cyclically moved through a heat source, along a path toward a heat sink, through the heat sink and then along another path in counter-flow heat exchange relationship with the wire in the first path. The portion of the wire along the first path is caused to elongate to its trained length under minimum tension as it is cooled. The portion of the wire along the second path is caused to contract under maximum tension as it is heated. The resultant tension differential between the wires in the two paths is applied as a force through a distance to produce mechanical work. In one embodiment a first set of endless memory alloy wires are reeved in non-slip engagement between a pair of pulleys which are mounted for conjoint rotation within respective hot and cold reservoirs. Another set of endless memory alloy wires are reeved in non-slip engagement about another pair of pulleys which are mounted in the respective hot and cold reservoirs. The pulleys in the cold reservoir are of a larger diameter than those in the hot reservoir and the opposite reaches of the wires between the two sets of pulleys extend in closely spaced-apart relationship in counter-flow heat regenerator zones. The pulleys are turned to move the two sets of wires in opposite directions. The wires are stretched as they are cooled upon movement through the heat regenerator toward the cold reservoirs, and the wires contract as they are heated upon movement through the regenerator zones toward the hot reservoir. This contraction of wires exerts a larger torque on the greater diameter pulleys for turning the pulleys and supplying mechanical power. Means is provided for applying a variable tension to the wires. Phase change means is provided for controlling the angular phase of the pulleys of each set for purposes of start up procedure as well as for optimizing engine

  16. Applications of the directional solidification in magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Huang, Y. J.; Liu, J.; Hu, Q. D.; Liu, Q. H.; Karaman, I.; Li, J. G.

    2016-03-01

    A zone melting liquid metal cooling (ZMLMC) method of directional solidification was applied to prepare highly-oriented Ni52Fe17Ga27Co4 magnetic shape memory alloys. At high temperature gradient and low growth velocity, the well-developed preferred orientation for coarse columnar crystals was obtained. Such a structure leads to a large complete pseudoelastic recovery of 5% at 348 K. Moreover, the pseudoelastic behaviours and the kinetics of the martensitic transformation (MT) are significantly affected by the intersection angle between the loading direction and the grain boundaries.

  17. Characterization of shape memory alloys for safety mechanisms.

    SciTech Connect

    McLaughlin, Jarred T.; Buchheit, Thomas Edward; Massad, Jordan Elias

    2008-03-01

    Shape memory alloys (SMAs) are metals that exhibit large recoverable strains and exert large forces with tremendous energy densities. The behavior of SMAs is thermomechanically coupled. Their response to temperature is sensitive to their loading condition and their response to loading is sensitive to their thermal condition. This coupled behavior is not to be circumvented, but to be confronted and understood, since it is what manifests SMA's superior clamping performance. To reasonably characterize the coupled behavior of SMA clamping rings used in safety mechanisms, we conduct a series of experiments on SMA samples. The results of the tests will allow increased fidelity in modeling and failure analysis of parts.

  18. The Possibility of Muscle Tissue Reconstruction Using Shape Memory Alloys

    PubMed Central

    Higa, Masaru; Amae, Shintaro; Yambe, Tomoyuki; Okuyama, Takeshi; Takagi, Toshiyuki; Matsuki, Hidetoshi

    2005-01-01

    Severe dysfunction of muscle tissues can be treated by transplantation but the success rate is still not high enough. One possibility instead is to replace the dysfunctional muscle with artificial muscles. This article introduces a unique approach using shape memory alloys (SMAs) to replace the anal sphincter muscle for solving the problem of fecal incontinence. The use of SMAs that exhibit a two-way shape memory effect allows the device to function like a sphincter muscle and facilitates simple design. In this article, we will give a brief introduction to the functional material—SMA—together with its medical applications, and will follow this with a description of the recent progress in research and development of an SMA-based artificial sphincter. The possibility of its commercialization will also be discussed. PMID:19521522

  19. Internal friction associated with the premartensitic transformation and twin boundary motion of Ni50+xMn25-xGa25 (x = 0-2) alloys

    NASA Astrophysics Data System (ADS)

    Liu, Junyi; Wang, Jingmin; Jiang, Chengbao; Xu, Huibin

    2013-03-01

    The internal friction (IF) during the martensitic transformation (MT) has been extensively studied in NiMnGa alloys. In this paper, temperature dependence of the IF associated with the premartensitic transformation (PMT) and twin boundary motion (TBM) was investigated in Ni50+xMn25-xGa25 (x = 0-2) alloys. Both the composition and frequency had no obvious effect on the IF peak position of the PMT and TBM. With increasing frequency from 0.1 Hz to 5 Hz, the IF peak height corresponding to the TBM was significantly decreased, but was kept constant during the PMT. The observed phenomena were discussed in terms of the different microscopic mechanisms of the TBM and PMT.

  20. Effects of magnetic field on the shape memory behavior of single and polycrystalline magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Turabi, Ali Sadi

    Shape memory alloys and polymers have been extensively researched recently because of their unique ability to recover large deformations. Shape memory polymers (SMPs) are able to recover large deformations compared to shape memory alloys (SMAs), although SMAs have higher strength and are able to generate more stress during recovery. This project focuses on procedure for fabrication and Finite Element Modeling (FEM) of a shape memory composite actuator. First, SMP was characterized to reveal its mechanical properties. Specifically, glass transition temperature, the effects of temperature and strain rate on compressive response and recovery properties of shape memory polymer were studied. Then, shape memory properties of a NiTi wire, including transformation temperatures and stress generation, were investigated. SMC actuator was fabricated by using epoxy based SMP and NiTi SMA wire. Experimental tests confirmed the reversible behavior of fabricated shape memory composites. (Abstract shortened by ProQuest.).

  1. A Shape Memory Alloy Based Cryogenic Thermal Conduction Switch

    NASA Astrophysics Data System (ADS)

    Krishnan, V. B.; Singh, J. D.; Woodruff, T. R.; Notardonato, W. U.; Vaidyanathan, R.

    2004-06-01

    Shape memory alloys (SMAs) can produce large strains when deformed (e.g., up to 8%). Heating results in a phase transformation and associated recovery of all the accumulated strain. This strain recovery can occur against large forces, resulting in their use as actuators. Thus an SMA element can integrate both sensory and actuation functions, by inherently sensing a change in temperature and actuating by undergoing a shape change as a result of a temperature-induced phase transformation. Two aspects of our work on cryogenic SMAs are addressed here. First — a shape memory alloy based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulkhead arrangement is discussed. Such a switch integrates the sensor element and the actuator element and can be used to create a variable thermal sink to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. Second — fabrication via arc-melting and subsequent materials testing of SMAs with cryogenic transformation temperatures for use in the aforementioned switch is discussed.

  2. A Shape Memory Alloy Based Cryogenic Thermal Conduction Switch

    SciTech Connect

    Krishnan, V.B.; Singh, J.D.; Woodruff, T.R.; Vaidyanathan, R.; Notardonato, W.U.

    2004-06-28

    Shape memory alloys (SMAs) can produce large strains when deformed (e.g., up to 8%). Heating results in a phase transformation and associated recovery of all the accumulated strain. This strain recovery can occur against large forces, resulting in their use as actuators. Thus an SMA element can integrate both sensory and actuation functions, by inherently sensing a change in temperature and actuating by undergoing a shape change as a result of a temperature-induced phase transformation. Two aspects of our work on cryogenic SMAs are addressed here. First - a shape memory alloy based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulkhead arrangement is discussed. Such a switch integrates the sensor element and the actuator element and can be used to create a variable thermal sink to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. Second - fabrication via arc-melting and subsequent materials testing of SMAs with cryogenic transformation temperatures for use in the aforementioned switch is discussed.

  3. Structural transformations in NiTi shape memory alloy nanowires

    NASA Astrophysics Data System (ADS)

    Mirzaeifar, Reza; Gall, Ken; Zhu, Ting; Yavari, Arash; DesRoches, Reginald

    2014-05-01

    Martensitic phase transformation in bulk Nickle-Titanium (NiTi)—the most widely used shape memory alloy—has been extensively studied in the past. However, the structures and properties of nanostructured NiTi remain poorly understood. Here, we perform molecular dynamics simulations to study structural transformations in NiTi nanowires. We find that the tendency to reduce the surface energy in NiTi nanowires can lead to a new phase transformation mechanism from the austenitic B2 to the martensitic B19 phase. We further show that the NiTi nanowires exhibit the pseudoelastic effects during thermo-mechanical cycling of loading and unloading via the B2 and B19 transformations. Our simulations also reveal the unique formation of compound twins, which are expected to dominate the patterning of the nanostructured NiTi alloys at high loads. This work provides the novel mechanistic insights into the martensitic phase transformations in nanostructured shape memory alloy systems.

  4. A Shape Memory Alloy Based Cryogenic Thermal Conduction Switch

    NASA Technical Reports Server (NTRS)

    Notardonato, W. U.; Krishnan, V. B.; Singh, J. D.; Woodruff, T. R.; Vaidyanathan, R.

    2005-01-01

    Shape memory alloys (SMAs) can produce large strains when deformed (e.g., up to 8%). Heating results in a phase transformation and associated recovery of all the accumulated strain. This strain recovery can occur against large forces, resulting in their use as actuators. Thus an SMA element can integrate both sensory and actuation functions, by inherently sensing a change in temperature and actuating by undergoing a shape change as a result of a temperature-induced phase transformation. Two aspects of our work on cryogenic SMAs are addressed here. First - a shape memory alloy based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulkhead arrangement is discussed. Such a switch integrates the sensor element and the actuator element and can be used to create a variable thermal sink to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. Second - fabrication via arc-melting and subsequent materials testing of SMAs with cryogenic transformation temperatures for use in the aforementioned switch is discussed.

  5. Strategies for Self-Repairing Shape Memory Alloy Actuators

    NASA Astrophysics Data System (ADS)

    Langbein, Sven; Czechowicz, Alexander Jaroslaw; Meier, Horst

    2011-07-01

    Shape memory alloys (SMAs) are thermally activated smart materials. Due to their ability to change into a previously imprinted actual shape by the means of thermal activation, they are suitable as actuators for microsystems and, within certain limitations, macroscopic systems. A commonly used shape memory actuator type is an alloy of nickel and titanium (NiTi), which starts to transform its inner phase from martensitic to austenitic structure at a certain austenite start temperature. Retransformation starts at martensitic start temperature after running a hysteresis cycle. Most SMA-systems use straight wire actuators because of their simple integration, the occurring cost reduction and the resulting miniaturization. Unfortunately, SMA-actuators are only seldom used by constructors and system developers. This is due to occurring functional fatigue effects which depend on boundary conditions like system loads, strains, and number of cycles. The actuating stroke does not reduce essentially during the first thousand cycles. Striking is the elongation of the wire while maintaining the stroke during cycling (walking). In order to create a system which adjusts and repairs itself, different concepts to solve this problem are presented. They vary from smart control methods to constructive solutions with calibration systems. The systems are analyzed due to their effective, life cycle, and system costs showing outstanding advantages in comparison to commonly used SMA actuators.

  6. A magnetic shape memory micropump: contact-free, and compatible with PCR and human DNA profiling

    NASA Astrophysics Data System (ADS)

    Ullakko, K.; Wendell, L.; Smith, A.; Müllner, P.; Hampikian, G.

    2012-11-01

    Magnetic shape memory (MSM) Ni-Mn-Ga elements are relatively new materials with a variety of remarkable properties. They respond to changes in magnetic fields by elongating and shortening up to 6%. We have constructed a micropump which consists principally of a single component, the MSM element. The pump can be driven by the rotation of a diametrically magnetized cylindrical magnet or by an electrical rotation of the magnetic field; it is reversible, and can be effectively operated by hand without any electrical power. The MSM element does not inhibit the polymerase chain reaction. We demonstrate that it is compatible with forensic applications and show that it does not inhibit human DNA profiling. This novel pump is suitable for lab-on-a-chip applications that require microfluidics.

  7. Thermal response of novel shape memory polymer-shape memory alloy hybrids

    NASA Astrophysics Data System (ADS)

    Rossiter, Jonathan; Takashima, Kazuto; Mukai, Toshiharu

    2014-03-01

    Shape memory polymers (SMP) and shape memory alloys (SMA) have both been proven important smart materials in their own fields. Shape memory polymers can be formed into complex three-dimensional structures and can undergo shape programming and large strain recovery. These are especially important for deployable structures including those for space applications and micro-structures such as stents. Shape memory alloys on the other hand are readily exploitable in a range of applications where simple, silent, light-weight and low-cost repeatable actuation is required. These include servos, valves and mobile robotic artificial muscles. Despite their differences, one important commonality between SMPs and SMAs is that they are both typically activated by thermal energy. Given this common characteristic it is important to consider how these two will behave when in close environmental proximity, and hence exposed to the same thermal stimulus, and when they are incorporated into a hybrid SMA-SMP structure. In this paper we propose and examine the operation of SMA-SMP hybrids. The relationship between the two temperatures Tg, the glass transition temperature of the polymer, and Ta, the nominal austenite to martensite transition temperature of the alloy is considered. We examine how the choice of these two temperatures affects the thermal response of the hybrid. Electrical stimulation of the SMA is also considered as a method not only of actuating the SMA but also of inducing heating in the surrounding polymer, with consequent effects on actuator behaviour. Likewise by varying the rate and degree of thermal stimulation of the SMA significantly different actuation and structural stiffness can be achieved. Novel SMP-SMA hybrid actuators and structures have many ready applications in deployable structures, robotics and tuneable engineering systems.

  8. Functional Characterization of a Novel Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Collado, M.; Cabás, R.; San Juan, J.; López-Ferreño, I.

    2014-07-01

    A novel shape memory alloy (SMA) has been developed as an alternative to currently available alloys. This alloy, commercially known by its proprietary brand SMARQ, shows a higher working range of temperatures with respect to the SMA materials used until now in actuators, limited to environment temperatures below 90 °C. SMARQ is a high temperature SMA (HTSMA) based on a fully European material technology and production processes, which allows the manufacture of high quality products, with tuneable transformation temperatures up to 200 °C. Both, material and production processes have been evaluated for its use in space applications. A full characterization test campaign has been completed in order to obtain the material properties and check its suitability to be used as active material in space actuators. In order to perform the functional characterization of the material, it has been considered as the key element of a basic SMA actuator, consisting in the SMA wire and the mechanical and electrical interfaces. The functional tests presented in this work have been focused on the actuator behavior when heated by means of an electrical current. Alloy composition has been adjusted in order to match a transition temperature (As) of +145 °C, which satisfies the application requirements of operating temperatures in the range of -70 and +125 °C. Details of the tests and results of the characterization test campaign, focused in the material unique properties for their use in actuators, will be presented in this work. Some application examples in the field of space mechanisms and actuators, currently under development, will be summarized as part of this work, demonstrating the technology suitability as active material for space actuators.

  9. Radioactive material package closures with the use of shape memory alloys

    SciTech Connect

    Koski, J.A.; Bronowski, D.R.

    1997-11-01

    When heated from room temperature to 165 C, some shape memory metal alloys such as titanium-nickel alloys have the ability to return to a previously defined shape or size with dimensional changes up to 7%. In contrast, the thermal expansion of most metals over this temperature range is about 0.1 to 0.2%. The dimension change of shape memory alloys, which occurs during a martensite to austenite phase transition, can generate stresses as high as 700 MPa (100 kspi). These properties can be used to create a closure for radioactive materials packages that provides for easy robotic or manual operations and results in reproducible, tamper-proof seals. This paper describes some proposed closure methods with shape memory alloys for radioactive material packages. Properties of the shape memory alloys are first summarized, then some possible alternative sealing methods discussed, and, finally, results from an initial proof-of-concept experiment described.

  10. Modeling and Characterization of the Magnetocaloric Effect in Ni2MnGa Materials

    SciTech Connect

    Nicholson, Don M; Odbadrakh, Khorgolkhuu; Rios, Orlando; Hodges, Jason P; Ludtka, Gerard Michael; Porter, Wallace D; Sefat, A. S.; Rusanu, Aurelian; Evans III, Boyd Mccutchen

    2012-01-01

    Magnetic shape memory alloys have great promise as magneto-caloric effect refrigerant materials due to their combined magnetic and structural transitions. Computational and experimental research is reported on the Ni2MnGa material system. The magnetic states of this system have been explored using the Wang-Landau statistical approach in conjunction with the Locally Self-consistent Multiple-Scattering (LSMS) method to explore the magnetic states responsible for the magnet-caloric effect in this material. The effects of alloying agents on the transition temperatures of the Ni2MnGa alloy were investigated using differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). Neutron scattering experiments were performed to observe the structural and magnetic phase transformations at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) on alloys of Ni-Mn-Ga and Ni-Mn-Ga-Cu-Fe. Data from the observations are discussed in comparison with the computational studies.

  11. Multiscale Characterization of Nickel Titanium Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Gall, Keith

    Shape memory alloys were characterized by a variety of methods to investigate the relationship between microstructural phase transformation, macroscale deformation due to mechanical loading, material geometry, and initial material state. The major portion of the work is application of digital image correlation at several length scales to SMAs under mechanical loading. In addition, the connection between electrical resistance, stress, and strain was studied in NiTi wires. Finally, a new processing method was investigated to develop porous NiTi samples, which can be examined under DIC in future work. The phase transformation temperatures of a Nickel-Titanium based shape memory alloy (SMA) were initially evaluated under stress-free conditions by the differential scanning calorimetric (DSC) technique. Results show that the phase transformation temperature is significantly higher for transition from de-twinned martensite to austenite than from twinned martensite or R phase to austenite. To further examine transformation temperatures as a function of initial state a tensile test apparatus with in-situ electrical resistance (ER) measurements was used to evaluate the transformation properties of SMAs at a variety of stress levels and initial compositions. The results show that stress has a significant influence on the transformation of detwinned martensite, but a small influence on R phase and twinned martensite transformations. Electrical resistance changes linearly with strain during the transformations from both kinds of martensite to austenite. The linearity between ER and strain during the transformation from de-twinned martensite to austenite is not affected by the stress, facilitating application to control algorithms. A revised phase diagram is drawn to express these results. To better understand the nature of the local and global strain fields that accompany phase transformation in shape memory alloys (SMAs), here we use high resolution imaging together with image

  12. Simulation of Payload Vibration Protection by Shape Memory Alloy Parts

    NASA Astrophysics Data System (ADS)

    Volkov, Aleksandr E.; Evard, Margarita E.; Red'kina, Kristina V.; Vikulenkov, Andrey V.; Makarov, Vyacheslav P.; Moisheev, Aleksandr A.; Markachev, Nikolay A.; Uspenskiy, Evgeniy S.

    2014-07-01

    A system of vibroisolation under consideration consists of a payload connected to a vibrating housing by plane shape memory alloy (SMA) slotted elements. The calculation of the mechanical behavior of the SMA is based on a microstructural theory. Simulations of harmonic and of impact excitations are carried out. The results have shown that protective properties of this system depend on the SMA state. The maximum reduction of the acceleration amplitude for harmonic excitation is reached when the SMA is in the martensitic (pseudo-plastic) state or in the two-phase state. A variation of temperature allows changing the resonance frequency and thus escaping from the resonance and controlling a mode of vibration.

  13. Shape memory alloy actuated adaptive exhaust nozzle for jet engine

    NASA Technical Reports Server (NTRS)

    Song, Gangbing (Inventor); Ma, Ning (Inventor)

    2009-01-01

    The proposed adaptive exhaust nozzle features an innovative use of the shape memory alloy (SMA) actuators for actively control of the opening area of the exhaust nozzle for jet engines. The SMA actuators remotely control the opening area of the exhaust nozzle through a set of mechanism. An important advantage of using SMA actuators is the reduction of weight of the actuator system for variable area exhaust nozzle. Another advantage is that the SMA actuator can be activated using the heat from the exhaust and eliminate the need of other energy source. A prototype has been designed and fabricated. The functionality of the proposed SMA actuated adaptive exhaust nozzle is verified in the open-loop tests.

  14. Electromagnetic heating of a shape memory alloy translator

    NASA Astrophysics Data System (ADS)

    Giroux, E.-A.; Maglione, M.; Gueldry, A.; Mantoux, J.-L.

    1996-03-01

    The active part of a linear translator is a shape memory alloy (SMA) made of nickel and titanium (NiTi) wire which is to be thermally cycled. We have achieved heating using electromagnetic radiation with a magnetic sheath and low-frequency waves at 8 kHz and without magnetic sheath and radio frequency waves at 28 MHz. The heating is equivalent for these two arrangements. In vitro experiments have been confirmed by computer simulations of the radiation distribution within the implant. We thus show that electromagnetic radiation could specifically heat a NiTi wire inside a stainless steel tube without heating the tube. An application could be a femoral prosthesis for the lengthening of the bone.

  15. Shape memory alloy heat engines and energy harvesting systems

    DOEpatents

    Browne, Alan L; Johnson, Nancy L; Shaw, John Andrew; Churchill, Christopher Burton; Keefe, Andrew C; McKnight, Geoffrey P; Alexander, Paul W; Herrera, Guillermo A; Yates, James Ryan; Brown, Jeffrey W

    2014-09-30

    A heat engine includes a first rotatable pulley and a second rotatable pulley spaced from the first rotatable pulley. A shape memory alloy (SMA) element is disposed about respective portions of the pulleys at an SMA pulley ratio. The SMA element includes a first wire, a second wire, and a matrix joining the first wire and the second wire. The first wire and the second wire are in contact with the pulleys, but the matrix is not in contact with the pulleys. A timing cable is disposed about respective portions of the pulleys at a timing pulley ratio, which is different than the SMA pulley ratio. The SMA element converts a thermal energy gradient between the hot region and the cold region into mechanical energy.

  16. Simulation of grain size effects in nanocrystalline shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ahluwalia, Rajeev; Quek, Siu Sin; Wu, David T.

    2015-06-01

    Recently, it has been demonstrated that martensitic transformation in nanocrystalline shape memory alloys can be suppressed for small grain sizes. Motivated by these results, we study the grain size dependence of martensitic transformations and stress-strain response of nanocrystalline shape memory alloys within the framework of the Ginzburg-Landau (GL) theory. A GL model for a square to rectangle transformation in polycrystals is extended to account for grain boundary effects. We propose that an inhibition of the transformation in grain boundary regions can occur, if the grain boundary energy of the martensite is higher than that of the austenite phase. We show that this inhibition of transformation in grain boundary regions has a strong influence on domain patterns inside grains. Although the transformation is inhibited only at the grain boundaries, it leads to a suppression of the transformation even inside the grains as grain size is decreased. In fact, below a critical grain size, the transformation can be completely suppressed. We explain these results in terms of the extra strain gradient cost associated with grain boundaries, when the transformation is inhibited at grain boundaries. On the other hand, no significant size effects are observed when transformation is not inhibited at grain boundaries. We also study the grain size dependence of the stress strain curve. It is found that when the transformation is inhibited at grain boundaries, a significant reduction in the hysteresis associated with stress-strain curves during the loading-unloading cycles is observed. The hysteresis for this situation reduces even further as the grain size is reduced, which is consistent with recent experiments. The simulations also demonstrate that the mechanical behavior is influenced by inter-granular interactions and the local microstructural neighbourhood of a grain has a stronger influence than the orientation of the grain itself.

  17. Shape memory alloy resetable spring lift for pedestrian protection

    NASA Astrophysics Data System (ADS)

    Barnes, Brian M.; Brei, Diann E.; Luntz, Jonathan E.; Strom, Kenneth; Browne, Alan L.; Johnson, Nancy

    2008-03-01

    Pedestrian protection has become an increasingly important aspect of automotive safety with new regulations taking effect around the world. Because it is increasingly difficult to meet these new regulations with traditional passive approaches, active lifts are being explored that increase the "crush zone" between the hood and rigid under-hood components as a means of mitigating the consequences of an impact with a non-occupant. Active lifts, however, are technically challenging because of the simultaneously high forces, stroke and quick timing resulting in most of the current devices being single use. This paper introduces the SMArt (Shape Memory Alloy ReseTable) Spring Lift, an automatically resetable and fully reusable device, which couples conventional standard compression springs to store the energy required for a hood lift, with Shape Memory Alloys actuators to achieve both an ultra high speed release of the spring and automatic reset of the system for multiple uses. Each of the four SMArt Device subsystems, lift, release, lower and reset/dissipate, are individually described. Two identical complete prototypes were fabricated and mounted at the rear corners of the hood, incorporated within a full-scale vehicle testbed at the SMARTT (Smart Material Advanced Research and Technology Transfer) lab at University of Michigan. Full operational cycle testing of a stationary vehicle in a laboratory setting confirms the ultrafast latch release, controlled lift profile, gravity lower to reposition the hood, and spring recompression via the ratchet engine successfully rearming the device for repeat cycles. While this is only a laboratory demonstration and extensive testing and development would be required for transition to a fielded product, this study does indicate that the SMArt Lift has promise as an alternative approach to pedestrian protection.

  18. Understanding Phase-Change Memory Alloys from a Chemical Perspective

    NASA Astrophysics Data System (ADS)

    Kolobov, A. V.; Fons, P.; Tominaga, J.

    2015-09-01

    Phase-change memories (PCM) are associated with reversible ultra-fast low-energy crystal-to-amorphous switching in GeTe-based alloys co-existing with the high stability of the two phases at ambient temperature, a unique property that has been recently explained by the high fragility of the glass-forming liquid phase, where the activation barrier for crystallisation drastically increases as the temperature decreases from the glass-transition to room temperature. At the same time the atomistic dynamics of the phase-change process and the associated changes in the nature of bonding have remained unknown. In this work we demonstrate that key to this behavior is the formation of transient three-center bonds in the excited state that is enabled due to the presence of lone-pair electrons. Our findings additionally reveal previously ignored fundamental similarities between the mechanisms of reversible photoinduced structural changes in chalcogenide glasses and phase-change alloys and offer new insights into the development of efficient PCM materials.

  19. High-transition-temperature shape memory alloy film

    NASA Astrophysics Data System (ADS)

    Johnson, A. David; Martynov, Valery V.; Shahoian, Erik J.

    1995-05-01

    Using conventional magnetron sputtering deposition processes three different types of shape memory alloys (FeNi based, CuAl based and TiNi based) were examined as potential candidates for the production of high temperature SMA thin film. CuAlNi and TiNiHf SMA were successfully deposited on silicon wafers and thin films of 4 - 20 micrometers were produced. After annealing at approximately equals 500 degree(s)C both CuAlNi and TiNiHf films exhibited reversible high temperature martensitic transition. For CuAlNi thin films, annealing itself was found to be inadequate for obtaining transformation intervals corresponding to that of the target. To deal with the problem it is expected that additional quenching after solid solution heat treatment will be necessary. Of the three alloys examined, the most promising candidate for high temperature thin film microactuators is TiNiHf. It was found that by changing the Hf content in the target, the transformation start temperature of thin films can be easily adjusted in a temperature range from 100 degree(s)C to 200 degree(s)C.

  20. Understanding Phase-Change Memory Alloys from a Chemical Perspective

    PubMed Central

    Kolobov, A.V.; Fons, P.; Tominaga, J.

    2015-01-01

    Phase-change memories (PCM) are associated with reversible ultra-fast low-energy crystal-to-amorphous switching in GeTe-based alloys co-existing with the high stability of the two phases at ambient temperature, a unique property that has been recently explained by the high fragility of the glass-forming liquid phase, where the activation barrier for crystallisation drastically increases as the temperature decreases from the glass-transition to room temperature. At the same time the atomistic dynamics of the phase-change process and the associated changes in the nature of bonding have remained unknown. In this work we demonstrate that key to this behavior is the formation of transient three-center bonds in the excited state that is enabled due to the presence of lone-pair electrons. Our findings additionally reveal previously ignored fundamental similarities between the mechanisms of reversible photoinduced structural changes in chalcogenide glasses and phase-change alloys and offer new insights into the development of efficient PCM materials. PMID:26323962

  1. Understanding Phase-Change Memory Alloys from a Chemical Perspective.

    PubMed

    Kolobov, A V; Fons, P; Tominaga, J

    2015-01-01

    Phase-change memories (PCM) are associated with reversible ultra-fast low-energy crystal-to-amorphous switching in GeTe-based alloys co-existing with the high stability of the two phases at ambient temperature, a unique property that has been recently explained by the high fragility of the glass-forming liquid phase, where the activation barrier for crystallisation drastically increases as the temperature decreases from the glass-transition to room temperature. At the same time the atomistic dynamics of the phase-change process and the associated changes in the nature of bonding have remained unknown. In this work we demonstrate that key to this behavior is the formation of transient three-center bonds in the excited state that is enabled due to the presence of lone-pair electrons. Our findings additionally reveal previously ignored fundamental similarities between the mechanisms of reversible photoinduced structural changes in chalcogenide glasses and phase-change alloys and offer new insights into the development of efficient PCM materials. PMID:26323962

  2. Applications of shape memory alloys for neurology and neuromuscular rehabilitation.

    PubMed

    Pittaccio, Simone; Garavaglia, Lorenzo; Ceriotti, Carlo; Passaretti, Francesca

    2015-01-01

    Shape memory alloys (SMAs) are a very promising class of metallic materials that display interesting nonlinear properties, such as pseudoelasticity (PE), shape memory effect (SME) and damping capacity, due to high mechanical hysteresis and internal friction. Our group has applied SMA in the field of neuromuscular rehabilitation, designing some new devices based on the mentioned SMA properties: in particular, a new type of orthosis for spastic limb repositioning, which allows residual voluntary movement of the impaired limb and has no predetermined final target position, but follows and supports muscular elongation in a dynamic and compliant way. Considering patients in the sub-acute phase after a neurological lesion, and possibly bedridden, the paper presents a mobiliser for the ankle joint, which is designed exploiting the SME to provide passive exercise to the paretic lower limb. Two different SMA-based applications in the field of neuroscience are then presented, a guide and a limb mobiliser specially designed to be compatible with diagnostic instrumentations that impose rigid constraints in terms of electromagnetic compatibility and noise distortion. Finally, the paper discusses possible uses of these materials in the treatment of movement disorders, such as dystonia or hyperkinesia, where their dynamic characteristics can be advantageous. PMID:26023790

  3. Applications of Shape Memory Alloys for Neurology and Neuromuscular Rehabilitation

    PubMed Central

    Pittaccio, Simone; Garavaglia, Lorenzo; Ceriotti, Carlo; Passaretti, Francesca

    2015-01-01

    Shape memory alloys (SMAs) are a very promising class of metallic materials that display interesting nonlinear properties, such as pseudoelasticity (PE), shape memory effect (SME) and damping capacity, due to high mechanical hysteresis and internal friction. Our group has applied SMA in the field of neuromuscular rehabilitation, designing some new devices based on the mentioned SMA properties: in particular, a new type of orthosis for spastic limb repositioning, which allows residual voluntary movement of the impaired limb and has no predetermined final target position, but follows and supports muscular elongation in a dynamic and compliant way. Considering patients in the sub-acute phase after a neurological lesion, and possibly bedridden, the paper presents a mobiliser for the ankle joint, which is designed exploiting the SME to provide passive exercise to the paretic lower limb. Two different SMA-based applications in the field of neuroscience are then presented, a guide and a limb mobiliser specially designed to be compatible with diagnostic instrumentations that impose rigid constraints in terms of electromagnetic compatibility and noise distortion. Finally, the paper discusses possible uses of these materials in the treatment of movement disorders, such as dystonia or hyperkinesia, where their dynamic characteristics can be advantageous. PMID:26023790

  4. Applications of shape memory alloys for neurology and neuromuscular rehabilitation.

    PubMed

    Pittaccio, Simone; Garavaglia, Lorenzo; Ceriotti, Carlo; Passaretti, Francesca

    2015-01-01

    Shape memory alloys (SMAs) are a very promising class of metallic materials that display interesting nonlinear properties, such as pseudoelasticity (PE), shape memory effect (SME) and damping capacity, due to high mechanical hysteresis and internal friction. Our group has applied SMA in the field of neuromuscular rehabilitation, designing some new devices based on the mentioned SMA properties: in particular, a new type of orthosis for spastic limb repositioning, which allows residual voluntary movement of the impaired limb and has no predetermined final target position, but follows and supports muscular elongation in a dynamic and compliant way. Considering patients in the sub-acute phase after a neurological lesion, and possibly bedridden, the paper presents a mobiliser for the ankle joint, which is designed exploiting the SME to provide passive exercise to the paretic lower limb. Two different SMA-based applications in the field of neuroscience are then presented, a guide and a limb mobiliser specially designed to be compatible with diagnostic instrumentations that impose rigid constraints in terms of electromagnetic compatibility and noise distortion. Finally, the paper discusses possible uses of these materials in the treatment of movement disorders, such as dystonia or hyperkinesia, where their dynamic characteristics can be advantageous.

  5. Investigation of residual stresses in shape memory alloy (SMA) composites

    NASA Astrophysics Data System (ADS)

    Berman, Justin Bradley

    Shape memory alloy (SMA) composites are a class of smart materials in which SMA actuators are embedded in a host matrix. The shape memory effect allows for stress induced phase transformations and large recoverable strains that make SMA composites promising candidates for structural shape/vibration control, impact absorption, aircraft deicing or in-flight airfoil shape control systems. However, the difference in thermal expansion between the SMA and the host material leads to residual stresses during processing. In addition, the SMA transformation from martensite to austenite, or the reverse, also generate stresses. These stresses acting in combination can lead to SMA/polymer interfacial debonding or microcracking of the host matrix. The present work was undertaken to study the behavior of nitinol shape memory alloys embedded in epoxy and glass/epoxy matrices and to investigate the development of residual stresses during their manufacture and actuation. A three-phase concentric cylinder micromechanics model and an SMA composite thermoelastic beam theory were developed to analyze the micromechanical and structural-level thermal and transformational stresses for nitinol composites induced by nitinol wires embedded in a host matrix. A series of warpage experiments were conducted on nitinol composite beams during heating cycles to provide experimental validation of model predictions and to assess their thermoelastic structural behavior under non-mechanical loading. Micromechanical model results indicate that excessive residual hoop stresses in nitino/graphite/epoxy composites leads to radial cracking around the embedded nitinol wires. Based on modeling results, the most important factor in reducing residual stresses (and thereby preventing radial cracking) is increasing the level of recovery strain for the nitinol wire. The SMA composite beam model agrees well with experimental data captured for the nitinol/epoxy beam series. Warpage experiments on nitinol

  6. Precipitation-Strengthened, High-Temperature, High-Force Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald D.; Draper, Susan L.; Nathal, Michael V.; Crombie, Edwin A.

    2008-01-01

    Shape memory alloys (SMAs) are an enabling component in the development of compact, lightweight, durable, high-force actuation systems particularly for use where hydraulics or electrical motors are not practical. However, commercial shape memory alloys based on NiTi are only suitable for applications near room temperature, due to their relatively low transformation temperatures, while many potential applications require higher temperature capability. Consequently, a family of (Ni,Pt)(sub 1-x)Ti(sub x) shape memory alloys with Ti concentrations ranging from about 15 to 25 at.% have been developed for applications in which there are requirements for SMA actuators to exert high forces at operating temperatures higher than those of conventional binary NiTi SMAs. These alloys can be heat treated in the range of 500 C to produce a series of fine precipitate phases that increase the strength of alloy while maintaining a high transformation temperature, even in Ti-lean compositions.

  7. High Work Output Ni-Ti-Pt High Temperature Shape Memory Alloys and Associated Processing Methods

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald D. (Inventor); Draper, Susan L. (Inventor); Nathal, Michael V. (Inventor); Garg, Anita (Inventor)

    2009-01-01

    According to the invention, compositions of Ni-Ti-Pt high temperature, high force, shape memory alloys are disclosed that have transition temperatures above 100 C.; have narrow hysteresis; and produce a high specific work output.

  8. Shape memory alloys. (Latest citations from the INSPEC: Information services for the physics and engineering communities database). Published Search

    SciTech Connect

    Not Available

    1993-08-01

    The bibliography contains citations concerning theories and experiments on shape memory effects of various alloys. Alloys studied include nickel, tin, indium, lead, copper, and titanium. Citations discuss shape memory crystallography, properties, processing, alloying, and mechanisms. (Contains 250 citations and includes a subject term index and title list.)

  9. Shape memory alloy seals for geothermal applications. Final report. Report ESG-82-14

    SciTech Connect

    Friske, Warren H.; Schwartzbart, Harry

    1982-07-30

    A novel temperature-actuated seal for geothermal applications is under development. This program uses the shape memory property of nickel-titanium (Nitinol) alloys to achieve an improved seal in geothermal downhole pumps. Nitinol flange face seals and pump shaft seals have been designed, fabricated, and tested. It has been demonstrated that the shape memory effect of Nitinol alloys can be utilized to activate and maintain a leaktight seal in geothermal environments.

  10. Large internal stress-assisted twin-boundary motion in Ni2MnGa ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Nie, Z. H.; Cong, D. Y.; Liu, D. M.; Ren, Y.; Pötschke, M.; Roth, S.; Wang, Y. D.

    2011-10-01

    The twin boundary motion driven by thermo-magnetic coupling was in-situ studied in a NiMnGa single crystal using high-energy x-ray diffraction technique. An unstable martensite with an internal stress of ˜8 MPa was obtained through a thermo-magnetic training. The triple martensite variants assisted by internal stress are distinct from the self-accommodated martensite twin variants with a stress-free state, and a single martensite-variant can be actuated only by a magnetic field of ˜0.34 T, equivalent to an actuator stress of about 1.3 MPa. The generation of so large internal stress among variants is attributed to the altered martensite nucleation sites triggered by external fields during thermo-magnetic training.

  11. Thermomechanical response of shape memory alloy hybrid composites

    NASA Astrophysics Data System (ADS)

    Turner, Travis L.

    2000-10-01

    This study examines the use of embedded shape memory alloy (SMA) actuators for adaptive control of the themomechanical response of composite structures. Control of static and dynamic responses are demonstrated including thermal buckling, thermal post-buckling, vibration, sonic fatigue, and acoustic transmission. A thermomechanical model is presented for analyzing such shape memory alloy hybrid composite (SMAHC) structures exposed to thermal and mechanical loads. Also presented are (1) fabrication procedures for SMAHC specimens, (2) characterization of the constituent materials for model quantification, (3) development of the test apparatus for conducting static and dynamic experiments on specimens with and without SMA, (4) discussion of the experimental results, and (5) validation of the analytical and numerical tools developed in the study. The constitutive model developed to describe the mechanics of a SMAHC lamina captures the material nonlinearity with temperature of the SMA and matrix material if necessary. It is in a form that is amenable to commercial finite element (FE) code implementation. The model is valid for constrained, restrained, or free recovery configurations with appropriate measurements of fundamental engineering properties. This constitutive model is used along with classical lamination theory and the FE method to formulate the equations of motion for panel-type structures subjected to steady-state thermal and dynamic mechanical loads. Mechanical loads that are considered include acoustic pressure, inertial (base acceleration), and concentrated forces. Four solution types are developed from the governing equations including thermal buckling, thermal post-buckling, dynamic response, and acoustic transmission/radiation. These solution procedures are compared with closed-form and/or other known solutions to benchmark the numerical tools developed in this study. Practical solutions for overcoming fabrication issues and obtaining repeatable

  12. Potential High-Temperature Shape-Memory Alloys Identified in the Ti(Ni,Pt) System

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald D.; Biles, Tiffany A.; Garg, Anita; Nathal, Michael V.

    2004-01-01

    "Shape memory" is a unique property of certain alloys that, when deformed (within certain strain limits) at low temperatures, will remember and recover to their original predeformed shape upon heating. It occurs when an alloy is deformed in the low-temperature martensitic phase and is then heated above its transformation temperature back to an austenitic state. As the material passes through this solid-state phase transformation on heating, it also recovers its original shape. This behavior is widely exploited, near room temperature, in commercially available NiTi alloys for connectors, couplings, valves, actuators, stents, and other medical and dental devices. In addition, there are limitless applications in the aerospace, automotive, chemical processing, and many other industries for materials that exhibit this type of shape-memory behavior at higher temperatures. But for high temperatures, there are currently no commercial shape-memory alloys. Although there are significant challenges to the development of high-temperature shape-memory alloys, at the NASA Glenn Research Center we have identified a series of alloy compositions in the Ti-Ni-Pt system that show great promise as potential high-temperature shape-memory materials.

  13. Smart structures for deformable mirrors actuated by shape memory alloy

    NASA Astrophysics Data System (ADS)

    Riva, M.; Bettini, P.; Di Landro, L.; Sala, G.; Zerbi, F. M.

    2010-07-01

    Deformable mirrors actuated by smart structures are promising devices for next generation astronomical instrumentation. Thermal activated Shape Memory Alloys are materials able to recover their original shape, after an external deformation, if heated above a characteristic temperature. If the recovery of the shape is completely or partially prevented by the presence of constraints, the material can generate recovery stress. Thanks to this feature, these materials can be positively exploited in Smart Structures if properly embedded into host materials. This paper will show the technological processes developed for an efficient use of SMA-based actuators embedded in smart structures tailored to astronomical instrumentation. In particular the analysis of the interface with the host material. Some possible modeling approaches to the actuators behavior will be addressed taking into account trade-offs between detailed analysis and overall performance prediction as a function of the computational time. We developed a combined Finite Element and Raytracing analysis devoted to a parametric performance predictions of a SMA based substrate applicable to deformable mirrors. We took in detail into account the possibility to change the focal length of the mirror keeping a satisfactory image quality. Finally a possible approach with some preliminary results for an efficient control system for the strongly non-linear SMA actuators will be presented.

  14. Interfacial stresses in shape memory alloy-reinforced composites

    NASA Astrophysics Data System (ADS)

    Hiremath, S. R.; Prajapati, Maulik; Rakesh, S.; Roy Mahapatra, D.

    2014-03-01

    Debonding of Shape Memory Alloy (SMA) wires in SMA reinforced polymer matrix composites is a complex phenomenon compared to other fabric fiber debonding in similar matrix composites. This paper focuses on experimental study and analytical correlation of stress required for debonding of thermal SMA actuator wire reinforced composites. Fiber pull-out tests are carried out on thermal SMA actuator at parent state to understand the effect of stress induced detwinned martensites. An ASTM standard is followed as benchmark method for fiber pull-out test. Debonding stress is derived with the help of non-local shear-lag theory applied to elasto-plastic interface. Furthermore, experimental investigations are carried out to study the effect of Laser shot peening on SMA surface to improve the interfacial strength. Variation in debonding stress due to length of SMA wire reinforced in epoxy are investigated for non-peened and peened SMA wires. Experimental results of interfacial strength variation due to various L/d ratio for non-peened and peened SMA actuator wires in epoxy matrix are discussed.

  15. MOSFET Switching Circuit Protects Shape Memory Alloy Actuators

    NASA Technical Reports Server (NTRS)

    Gummin, Mark A.

    2011-01-01

    A small-footprint, full surface-mount-component printed circuit board employs MOSFET (metal-oxide-semiconductor field-effect transistor) power switches to switch high currents from any input power supply from 3 to 30 V. High-force shape memory alloy (SMA) actuators generally require high current (up to 9 A at 28 V) to actuate. SMA wires (the driving element of the actuators) can be quickly overheated if power is not removed at the end of stroke, which can damage the wires. The new analog driver prevents overheating of the SMA wires in an actuator by momentarily removing power when the end limit switch is closed, thereby allowing complex control schemes to be adopted without concern for overheating. Either an integral pushbutton or microprocessor-controlled gate or control line inputs switch current to the actuator until the end switch line goes from logic high to logic low state. Power is then momentarily removed (switched off by the MOSFET). The analog driver is suited to use with nearly any SMA actuator.

  16. Shape Memory Alloy (SMA)-Based Launch Lock

    NASA Technical Reports Server (NTRS)

    Badescu, Mircea; Bao, Xiaoqi; Bar-Cohen, Yoseph

    2014-01-01

    Most NASA missions require the use of a launch lock for securing moving components during the launch or securing the payload before release. A launch lock is a device used to prevent unwanted motion and secure the controlled components. The current launch locks are based on pyrotechnic, electro mechanically or NiTi driven pin pullers and they are mostly one time use mechanisms that are usually bulky and involve a relatively high mass. Generally, the use of piezoelectric actuation provides high precession nanometer accuracy but it relies on friction to generate displacement. During launch, the generated vibrations can release the normal force between the actuator components allowing shaft's free motion which could result in damage to the actuated structures or instruments. This problem is common to other linear actuators that consist of a ball screw mechanism. The authors are exploring the development of a novel launch lock mechanism that is activated by a shape memory alloy (SMA) material ring, a rigid element and an SMA ring holding flexure. The proposed design and analytical model will be described and discussed in this paper.

  17. Modiolus-hugging intracochlear electrode array with shape memory alloy.

    PubMed

    Min, Kyou Sik; Jun, Sang Beom; Lim, Yoon Seob; Park, Se-Ik; Kim, Sung June

    2013-01-01

    In the cochlear implant system, the distance between spiral ganglia and the electrodes within the volume of the scala tympani cavity significantly affects the efficiency of the electrical stimulation in terms of the threshold current level and spatial selectivity. Because the spiral ganglia are situated inside the modiolus, the central axis of the cochlea, it is desirable that the electrode array hugs the modiolus to minimize the distance between the electrodes and the ganglia. In the present study, we propose a shape-memory-alloy-(SMA-) embedded intracochlear electrode which gives a straight electrode a curved modiolus-hugging shape using the restoration force of the SMA as triggered by resistive heating after insertion into the cochlea. An eight-channel ball-type electrode array is fabricated with an embedded titanium-nickel SMA backbone wire. It is demonstrated that the electrode array changes its shape in a transparent plastic human cochlear model. To verify the safe insertion of the electrode array into the human cochlea, the contact pressures during insertion at the electrode tip and the contact pressures over the electrode length after insertion were calculated using a 3D finite element analysis. The results indicate that the SMA-embedded electrode is functionally and mechanically feasible for clinical applications. PMID:23762181

  18. Frequency-dependent energy harvesting via magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Sayyaadi, Hassan; Askari Farsangi, Mohammad Amin

    2015-11-01

    This paper is focused on presenting an accurate framework to describe frequency-dependent energy harvesting via magnetic shape memory alloys (MSMAs). Modeling strategy incorporates the phenomenological constitutive model developed formerly together with the magnetic diffusion equation. A hyperbolic hardening function is employed to define reorientation-induced strain hardening in the material, and the diffusion equation is used to add dynamic effects to the model. The MSMA prismatic specimen is surrounded by a pickup coil, and the induced voltage during martensite-variant reorientation is investigated with the help of Faraday’s law of magnetic field induction. It has been shown that, in order to harvest the maximum RMS voltage in the MSMA-based energy harvester, an optimum value of bias magnetic field exists, which is the corresponding magnetic field for the start of pseudoelasticity behavior. In addition, to achieve a more compact energy harvester with higher energy density, a specimen with a lower aspect ratio can be chosen. As the main novelty of the paper, it is found that the dynamic effects play a major role in determining the harvested voltage and power, especially for high excitation frequency or specimen thickness.

  19. A novel inertial energy harvester using magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Askari Farsangi, Mohammad Amin; Sayyaadi, Hassan; Zakerzadeh, Mohammad Reza

    2016-10-01

    This paper studies the output voltage from a novel inertial energy harvester using magnetic shape memory alloys (MSMAs). The MSMA elements are attached to the root of a cantilever beam by means of two steps. In order to get electrical voltage, two coils are wound around the MSMAs and a shock load is applied to a tip mass at the end of the beam to have vibration in it. The beam vibration causes strain in the MSMAs along their longitudinal directions and as a result the magnetic flux alters in the coils. The change of magnetic flux in the surrounding coil produces an AC voltage. In order to predict the output voltage, the nonlinear governing equations of beam motion based on Euler-Bernoulli model and von Kármán theory are derived. A thermodynamics-based constitutive model is used to predict the nonlinear strain and magnetization response of the MSMAs. Also, the induced voltage during martensite variant reorientation in MSMAs is investigated with the help of Faraday’s law of induction. Finally, the effect of different parameters including bias magnetic field, pre-strain and number of MSMA elements are investigated in details. The results show that this novel energy harvester has the capability of using as an alternative to the current piezoelectric and magnetostrictive ones for harvesting energy from ambient vibration.

  20. Experimental characterization of shape memory alloy actuator cables

    NASA Astrophysics Data System (ADS)

    Biggs, Daniel B.; Shaw, John A.

    2016-04-01

    Wire rope (or cables) are a fundamental structural element in many engineering applications. Recently, there has been growing interest in stranding NiTi wires into cables to scale up the adaptive properties of NiTi tension elements and to make use of the desirable properties of wire rope. Exploratory experiments were performed to study the actuation behavior of two NiTi shape memory alloy cables and straight monofilament wire of the same material. The specimens were held under various dead loads ranging from 50 MPa to 400 MPa and thermally cycled 25 times from 140°C to 5°C at a rate of 12°C/min. Performance metrics of actuation stroke, residual strain, and work output were measured and compared between specimen types. The 7x7 cable exhibited similar actuation to the single straight wire, but with slightly longer stroke and marginally more shakedown, while maintaining equivalent specific work output. This leads to the conclusion that the 7x7 cable effectively scaled up the adaptive properties the straight wire. Under loads below 150 MPa, the 1x27 cable had up to double the actuation stroke and work output, but exhibited larger shakedown and poorer performance when loaded higher.

  1. Stable Crack Growth During Thermal Actuation of Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Jape, S.; Baxevanis, T.; Lagoudas, D. C.

    2016-03-01

    A finite element analysis of crack growth is carried out in shape memory alloys subjected to thermal variations under plane strain, mode I, constant applied loading. The crack is assumed to propagate at a critical level of the crack-tip energy release rate which is modeled using the virtual crack closure technique. The load level, applied at a high temperature at which the austenite phase is stable, is assumed sufficiently low so that the resulting crack-tip energy release rate is smaller than the critical value but sufficiently high so that the critical value is reached during cooling, initiating crack growth (Baxevanis and Lagoudas in Int J Fract 191:191-213, 2015). Stable crack growth is observed, mainly associated with the shielding effect of the transformed material left in the wake of the advancing crack. Results pertaining to the near-tip mechanical fields and fracture toughness are presented and their sensitivity to phase transformation metrics and bias load levels is investigated.

  2. Thermomechanical Modeling of Stress Relaxation in Shape Memory Alloy Wires

    NASA Astrophysics Data System (ADS)

    Zare, Fateme; Kadkhodaei, Mahmoud; Salafian, Iman

    2015-04-01

    When a shape memory alloy (SMA) is subjected to a mechanical load, especially at high strain rates, its temperature varies due to thermomechanical coupling in the response of these materials. Thus, if strain is kept constant during the transformation, temperature change will cause stress to decrease during loading and to increase during unloading. A decrease in stress under constant strain indicates stress relaxation, and an increase in stress indicates stress recovery, i.e., reverse stress relaxation. In this paper, a fully coupled thermomechanical model is developed in a continuum framework to study stress relaxation and stress recovery in SMA wires. Numerical simulations at different ambient temperatures, applied strain rates, wire radii, and relaxation intervals are done to show the abilities of the proposed model in predicting relaxation phenomena in various conditions where strain remains constant during loading or unloading. Relaxation experiments were also performed on NiTi wires, and the numerical and empirical results are shown to be in a good agreement.

  3. Shape memory alloy-based active chiral composite cells

    NASA Astrophysics Data System (ADS)

    Prajapati, Maulik; Roy Mahapatra, D.

    2014-04-01

    Wing morphing is one of the emerging methodology towards improving aerodynamic efficiency of flight vehicle structures. In this paper a morphing structural element is designed and studied which has its origin in the well known chiral structures. The new aspect of design and functionality explored in this paper is that the chiral cell is actuated using thermal Shape Memory Alloy (SMA) actuator wires to provide directional motion. Such structure utilizes the potential of different actuations concepts based on actuator embedded in the chiral structure skin. This paper describes a new class of chiral cell structure with integrated SMA wire for actuation. Chiral topological constructs are obtained by considering passive and active load path decoupling and sub-optimal shape changes. Single cell of chiral honeycomb with actuators are analyzed using finite element simulation results and experiments. To this end, a multi-cell plan-form is characterized showing interesting possibilities in structural morphing applications. The applicability of the developed chiral cell to flexible wing skin, variable stiffness based design and controlling longitudinal-to-transverse stiffness ratio are discussed.

  4. Improvement of needle type applicator made of shape memory alloy.

    PubMed

    Kanazawa, Y; Kato, K; Yabuhara, T; Uzuka, T; Takahashi, H; Fujii, Y

    2008-01-01

    This paper discusses radio frequency (RF) interstitial hyperthermia for brain tumors with a developed needle type applicator made of a shape memory alloy (SMA). The problem with the heating method of interstitial hyperthermia is the small heating area. So, we proposed a new heating method using a needle type electrode made of SMA which consists of nickel (Ni), copper (Cu) and titanium (Ti) for expanding the heating area. Here, we proposed the heating method that the leading end of needle type electrode was divided into four parts and the leading end spreads in four directions with a temperature rise. First, the proposed RF interstitial hyperthermia system with the SMA needle was presented. Second, the results obtained by the experimental heating of the agar phantom by using the developed SMA needle type applicator were presented. Third, comparing experimental results, we discussed the heating properties of the developed system. Finally, from these results, it is confirmed that the developed needle type applicator made of SMA is useful for wide heating by invasive hyperthermia.

  5. Tailored processing of epoxy with embedded shape memory alloy wires

    NASA Astrophysics Data System (ADS)

    Kirkby, E. L.; O'Keane, J.; de Oliveira, R.; Michaud, V. J.; Månson, J.-A. E.

    2009-09-01

    We present the development of a low-temperature liquid composite moulding cure schedule that is compatible with the fabrication of shape memory alloy (SMA)-epoxy composite materials. With this process, the SMA wires do not need to be maintained in place with an external frame, even though the peak post-cure temperature exceeds the activation temperature of the SMA wires. The intrinsic interfacial shear strength of the final material is experimentally determined from single wire pull-out tests, and is compared with the shear stress exerted at the interface by an activated SMA wire. These measurements show that the interface is strong enough to withstand the maximum activation stress. This is confirmed through tests involving the cyclic activation of SMA wires embedded in epoxy samples. The paper successfully demonstrates that, by careful tailoring of the processing schedule, an SMA-epoxy composite that maintains a strong interfacial bond during both processing and subsequent activation of the embedded wires can be fabricated using standard composite processing methods.

  6. Shape-Memory-Alloy-Based Deicing System Developed

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Ice buildup on aircraft leading edge surfaces has historically been a problem. Most conventional deicing systems rely either on surface heating to melt the accreted ice or pneumatic surface inflation to mechanically debond the ice. Deicers that rely solely on surface heating require large amounts of power. Pneumatic deicers usually cannot remove thin layers of ice and lack durability. Thus, there is a need for an advanced, low-power ice protection system. As part of the NASA Small Business and Innovation Research (SBIR) program, Innovative Dynamics, Inc., developed an aircraft deicing system that utilizes the properties of Shape Memory Alloys (SMA). The SMA-based system has achieved promising improvements in energy efficiency and durability over more conventional deicers. When they are thermally activated, SMA materials change shape; this is analogous to a conventional thermal expansion. The thermal input is currently applied via conventional technology, but there are plans to implement a passive thermal input that is supplied from the energy transfer due to the formation of the ice itself. The actively powered deicer was tested in the NASA Lewis Icing Research Tunnel on a powered rotating rig in early 1995. The system showed promise, deicing both rime and glaze ice shapes as thin as 1/8 in. The first prototype SMA deicer reduced power usage by 45 percent over existing electrothermal systems. This prototype system was targeted for rotorcraft system development. However, there are current plans underway to develop a fixed-wing version of the deicer.

  7. On the Potentials of Shape Memory Alloy Valves

    NASA Astrophysics Data System (ADS)

    Czechowicz, A.; Lygin, K.; Langbein, S.

    2014-07-01

    Shape memory alloys (SMA) can be utilized as thermal and electrical-activated drives for valve applications. By using the high actuation forces and medium strokes in combination with SMA intrinsic sensor functions, smart and versatile valve elements for multi-purpose applications can be designed. The sensoric functions, based on the change of the electrical characteristics of the SMA drive, allow to detect the system's condition as well as the system's fatigue. The paper systematizes the usability of the intrinsic sensor function with particular emphasis on service potentials. A methodical overview over the design-options of different applications is presented in the first part of the publications. This is followed by a methodical analysis of the potentials of SMA in service applications. Since the product development process is not only a mechanical engineering matter, the production and the service options according to such valves have to be regarded. Besides this publication presents an innovative production process based on a fused deposition production process (FDPP) of valves which contains the installation of SMA actuators during production. The publications present several demonstrator systems which have been produced with FDPP and analyzed in applications.

  8. Flutter of buckled shape memory alloy reinforced laminates

    NASA Astrophysics Data System (ADS)

    Kuo, Shih-Yao; Shiau, Le-Chung; Lai, Chin-Hsin

    2012-03-01

    The effect of shape memory alloys (SMA) on the linear and nonlinear flutter behaviors of buckled cross-ply and angle-ply laminates was investigated in the frequency and time domains using the finite element method. In particular, this study takes the first move toward examining the effect of varying the SMA fiber spacing. Von Karman large deformation assumptions and quasi-steady aerodynamic theory were employed. The flutter boundary, stability boundary, time history response, and phase plane plots of SMA reinforced cross-ply and angle-ply laminates are presented. The numerical results show that increase in the SMA fiber volume fraction and prestrain may generate more recovery stress, and increase the stiffness of the SMA reinforced laminates. Therefore, the flutter boundary and critical load of the plate may be increased significantly. All five types of panel behavior, namely flat, buckled, limit-cycle, periodic, and chaotic motion, are clearly displayed and successively identified. This study sheds light on improving the flutter boundary efficiently by increasing the SMA fiber volume fraction to reinforce the center of the plate.

  9. Shape Memory Alloy (SMA)-based launch lock

    NASA Astrophysics Data System (ADS)

    Badescu, Mircea; Bao, Xiaoqi; Bar-Cohen, Yoseph

    2014-04-01

    Most NASA missions require the use of a launch lock for securing moving components during the launch or securing the payload before release. A launch lock is a device used to prevent unwanted motion and secure the controlled components. The current launch locks are based on pyrotechnic, electro mechanically or NiTi driven pin pullers and they are mostly one time use mechanisms that are usually bulky and involve a relatively high mass. Generally, the use of piezoelectric actuation provides high precession nanometer accuracy but it relies on friction to generate displacement. During launch, the generated vibrations can release the normal force between the actuator components allowing free motion of the shaft, which could result in damage to the actuated structures or instruments. This problem is common to other linear actuators that consist of a ball screw mechanism. The authors are exploring the development of a novel launch lock mechanism that is activated by a shape memory alloy (SMA) material ring, a rigid element and an SMA ring holding flexure. The proposed design and analytical model will be described and discussed in this paper.

  10. Directions for High-Temperature Shape Memory Alloys' Improvement: Straight Way to High-Entropy Materials?

    NASA Astrophysics Data System (ADS)

    Firstov, G. S.; Kosorukova, T. A.; Koval, Yu N.; Verhovlyuk, P. A.

    2015-10-01

    Nowadays, all thermo-mechanical effects, associated with the martensitic structural phase transitions, are still in the focus of scientists and engineers, especially once these phenomena are taking place at elevated temperatures. The list of the materials, undergoing high-temperature martensitic transformation, is constantly widening. Still, industrial application of these materials, called high-temperature shape memory alloys, is far enough due to the lack of understanding of the peculiarities of the high-temperature martensitic transformation and shape memory effect. The present work attempts to show how the development of the proper directions for high-temperature shape memory alloys' improvement might lead to the creation of essentially new functional materials.

  11. Potential High-Temperature Shape-Memory-Alloy Actuator Material Identified

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald D.; Gaydosh, Darrell J.; Biles, Tiffany A.; Garg, Anita

    2005-01-01

    Shape-memory alloys are unique "smart materials" that can be used in a wide variety of adaptive or "intelligent" components. Because of a martensitic solid-state phase transformation in these materials, they can display rather unusual mechanical properties including shape-memory behavior. This phenomenon occurs when the material is deformed at low temperatures (below the martensite finish temperature, Mf) and then heated through the martensite-to-austenite phase transformation. As the material is heated to the austenite finish temperature Af, it is able to recover its predeformed shape. If a bias is applied to the material as it tries to recover its original shape, work can be extracted from the shape-memory alloy as it transforms. Therefore, shape-memory alloys are being considered for compact solid-state actuation devices to replace hydraulic, pneumatic, or motor-driven systems.

  12. A Review of TiNiPdCu Alloy System for High Temperature Shape Memory Applications

    NASA Astrophysics Data System (ADS)

    Khan, M. Imran; Kim, Hee Young; Miyazaki, Shuichi

    2015-06-01

    High temperature shape memory alloys (HTSMAs) are important smart materials and possess a significant potential to improve many engineering systems. Many TiNi-based high temperature ternary alloy systems have been reported in literature including TiNiPd, TiNiPt, TiNiZr, TiNiAu, TiNiHf, etc. Some quaternary additions of certain elements in the above systems have been successful to further improve many important shape memory and mechanical properties. The success criteria for an HTSMA become strict in terms of its cyclic stability, maximum recoverable strain, creep resistance, and corrosion resistance at high temperatures. TiNiPdCu alloy system has been recently proposed as a promising HTSMA. Unique nanoscaled precipitates formed in TiNiPdCu-based HTSMAs are found to be stable at temperatures above 773 K, while keeping the benefits of ease of fabrication. It is expected that this alloy system possesses significant potential especially for the high temperature shape memory applications. Till now many research reports have been published on this alloy system. In the present work, a comprehensive review of the TiNiPdCu system is presented in terms of thermomechanical behavior, nanoscale precipitation mechanism, microstructural features, high temperature shape memory and mechanical properties, and the important parameters to control the high temperature performance of these alloys.

  13. Shape memory alloy actuation for a variable area fan nozzle

    NASA Astrophysics Data System (ADS)

    Rey, Nancy; Tillman, Gregory; Miller, Robin M.; Wynosky, Thomas; Larkin, Michael J.; Flamm, Jeffrey D.; Bangert, Linda S.

    2001-06-01

    The ability to control fan nozzle exit area is an enabling technology for next generation high-bypass-ratio turbofan engines. Performance benefits for such designs are estimated at up to 9% in thrust specific fuel consumption (TSFC) relative to current fixed-geometry engines. Conventionally actuated variable area fan nozzle (VAN) concepts tend to be heavy and complicated, with significant aircraft integration, reliability and packaging issues. The goal of this effort was to eliminate these undesirable features and formulate a design that meets or exceeds leakage, durability, reliability, maintenance and manufacturing cost goals. A Shape Memory Alloy (SMA) bundled cable actuator acting to move an array of flaps around the fan nozzle annulus is a concept that meets these requirements. The SMA bundled cable actuator developed by the United Technologies Corporation (Patents Pending) provides significant work output (greater than 2200 in-lb per flap, through the range of motion) in a compact package and minimizes system complexity. Results of a detailed design study indicate substantial engine performance, weight, and range benefits. The SMA- based actuation system is roughly two times lighter than a conventional mechanical system, with significant aircraft direct operating cost savings (2-3%) and range improvements (5-6%) relative to a fixed-geometry nozzle geared turbofan. A full-scale sector model of this VAN system was built and then tested at the Jet Exit Test Facility at NASA Langley to demonstrate the system's ability to achieve 20% area variation of the nozzle under full scale aerodynamic loads. The actuator exceeded requirements, achieving repeated actuation against full-scale loads representative of typical cruise as well as greater than worst-case (ultimate) aerodynamic conditions. Based on these encouraging results, work is continuing with the goal of a flight test on a C-17 transport aircraft.

  14. Cyclic response of shape memory alloy smart composite beams

    NASA Astrophysics Data System (ADS)

    Friend, Clifford M.; Morgan, Neil B.

    1994-09-01

    'Smart' structure are an emerging technology which will provide the possibility of engineering structures with enhanced functionality for a wide range of applications. In most current Smart Structural Concepts a mechatronic or 'Frankenstein' approach is adopted where separate sensors, signal processing and actuators are 'bolted-together' to produce a 'Smart' system response. In the majority of these concepts the sensors and actuators are integrated within the host structure itself, and many of the sensor and actuator materials are familiar from other more conventional sensing/actuation applications. Amongst the materials used/proposed for actuators are Shape- Memory Alloys (SMAs) since these materials offer a range of attractive properties, including the possibility of high strain/stress actuation. The literature-base on the integration of SMA actuators into composite structures is not extensive. However, their use has been investigated for vibration [1], acoustic radiation [1,2], damage [3], buckling [1,2], and shape [1] control. An interesting feature of this work has been a heavy bias towards modelling, with only limited attempts to experimentally verify the calculated results. Previous work has also failed to produce a systematic database on one other key issue. This is the durability of SPA hybrid composites. The present work was therefore undertaken to provide a preliminary appraisal of the durability issues associated with the use of SMA hybrid composites. This work addressed a number of issues including (i) the effect of actuator fraction on strain outputs, (ii) the effect of actuator fraction and maximum strain on the cyclic stability of shape changes, and (iii) the effect of these variables on damage accumulation within the hybrid structures.

  15. Improved Damage Resistant Composite Materials Incorporating Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Paine, Jeffrey S. N.; Rogers, Craig A.

    1996-01-01

    Metallic shape memory alloys (SMA) such as nitinol have unique shape recovery behavior and mechanical properties associated with a material phase change that have been used in a variety of sensing and actuation applications. Recent studies have shown that integrating nitinol-SMA actuators into composite materials increases the composite material's functionality. Hybrid composites of conventional graphite/epoxy or glass/epoxy and nitinol-SMA elements can perform functions in applications where monolithic composites perform inadequately. One such application is the use of hybrid composites to function both in load bearing and armor capacities. While monolithic composites with high strength-to-weight ratios function efficiently as loadbearing structures, because of their brittle nature, impact loading can cause significant catastrophic damage. Initial composite failure modes such as delamination and matrix cracking dissipate some impact energy, but when stress exceeds the composite's ultimate strength, fiber fracture and material perforation become dominant. One of the few methods that has been developed to reduce material perforation is hybridizing polymer matrix composites with tough kevlar or high modulus polyethynylene plies. The tough fibers increase the impact resistance and the stiffer and stronger graphite fibers carry the majority of the load. Similarly, by adding nitinol-SMA elements that absorb impact energy through the stress-induced martensitic phase transformation, the composites' impact perforation resistance can be greatly enhanced. The results of drop-weight and high velocity gas-gun impact testing of various composite materials will be presented. The results demonstrate that hybridizing composites with nitinol-SMA elements significantly increases perforation resistance compared to other traditional toughening elements. Inspection of the composite specimens at various stages of perforation by optical microscope illustrates the mechanisms by which

  16. Studies on the effect of grain refinement and thermal processing on shape memory characteristics of Cu Al Ni alloys

    NASA Astrophysics Data System (ADS)

    Sampath, V.

    2005-10-01

    Though Ni-Ti shape memory alloys are used extensively in a variety of engineering and medical applications because of their attractive shape memory characteristics, they still suffer from certain drawbacks, such as low transformation temperatures, difficulty in production and processing and high cost of raw materials. Copper-based alloys have, therefore, come as an alternative to Ni-Ti shape memory alloys. They are easier to produce and process and are also less expensive. They are used where Ni-Ti alloys cannot be used. But Cu-Al-Ni shape memory alloys also pose problems since they are brittle and possess lower shape recovery strains and stresses. With a view to increasing the shape memory characteristics and ductility of Cu-Al-Ni shape memory alloys, they were subjected to grain refinement and thermomechanical processing. The present study establishes that grain-refining additions result in considerable reduction in the grain size of the alloys. In addition, grain refinement and alloying cause an increase in the transformation temperatures. The results are analysed in the light of the explanations/theories put forth in recent papers related to Cu-Al-Ni shape memory alloys, and an attempt has been made to compare the results.

  17. LACBED characterization of dislocations in Cu-Al-Ni shape memory alloys processed by powder metallurgy

    NASA Astrophysics Data System (ADS)

    Rodriguez, P. P.; Ibarra, A.; San Jean, J.; Morniro, J. P.; No, M. L.

    2003-10-01

    Powder metallurgy Cu-AI-Ni shape memory alloys show excellent thermomechanical properties, being the fracture behavior close to the one observed in single crystals. However, the microstructural mechanisms responsible of such behavior are still under study. In this paper we present the characterization of the dislocations present in these alloys by Large Angle Convergent Beam Electron Diffraction (LACBED) in two different stages of the elaboration process: after HIP compaction and after hot rolling.

  18. Optimal Performance of Buildings Isolated By Shape-Memory-Alloy-Rubber-Bearing (SMARB) Under Random Earthquakes

    NASA Astrophysics Data System (ADS)

    Das, Sumanta; Mishra, Sudib K.

    2014-05-01

    Shape Memory Alloy (SMA)-based bearing has been proposed recently for improved base isolation by optimal choice of its transformation strength. Presently, superior performances of the Shape-Memory-Alloy-Rubber-Bearing (SMARB) over the elastomeric bearing are established in mitigating seismic vibration under constraint on maximum isolator displacement. The optimal transformation strengths are proposed through constrained optimization based on stochastic responses. Numerical simulation reveals that Lead Rubber Bearings (LRB) either fails to provide feasible parameters or leads to large floor acceleration, compromising the isolation efficiency. Contrarily, optimal SMARB can efficiently enforce such constraint without greatly affecting the isolation efficiency. Evidence of robustness of SMARB over LRB is also established.

  19. Ion beam sputter deposition of TiNi shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Davies, Sam T.; Tsuchiya, Kazuyoshi

    1999-08-01

    The development of functional or smart materials for integration into microsystem is of increasing interest. An example is the shape memory effect exhibited by certain metal alloys which, in principle, can be exploited in the fabrication of micro-scale manipulators or actuators, thereby providing on-chip micromechanical functionality. We have investigated an ion beam sputter deposition process for the growth of TiNi shape memory alloy thin films and demonstrated the required control to produce equiatomic composition, uniform coverage and atomic layer-by-layer growth rates on engineering surfaces. The process uses argon ions at intermediate energy produced by a Kaufman-type ion source to sputter non-alloyed targets of high purity titanium and nickel. Precise measurements of deposition rates allows compositional control during thin film growth. As the sputtering targets and substrates are remote from the discharge plasma, deposition occurs under good vacuum of approximately 10-6 mtorr thus promoting high quality films. Furthermore, the ion beam energetics allow deposition at relatively low substrate temperatures of < 150 degrees C with as-deposited films exhibiting shape memory properties without post-process high temperature annealing. Thermal imagin is used to monitor changes which are characteristic of the shape memory effect and is indicative of changes in specific heat capacity and thermal conductivity as the TiNi shape memory alloy undergoes martensitic to austenitic phase transformations.

  20. Hot Workability of CuZr-Based Shape Memory Alloys for Potential High-Temperature Applications

    NASA Astrophysics Data System (ADS)

    Biffi, Carlo Alberto; Tuissi, Ausonio

    2014-07-01

    The research on high-temperature shape memory alloys has been growing because of the interest of several potential industrial fields, such as automotive, aerospace, mechanical, and control systems. One suitable candidate is given by the CuZr system, because of its relative low price in comparison with others, like the NiTi-based one. In this context, the goal of this work is the study of hot workability of some CuZr-based shape memory alloys. In particular, this study addresses on the effect of hot rolling process on the metallurgical and calorimetric properties of the CuZr system. The addition of some alloying elements (Cr, Co, Ni, and Ti) is taken into account and their effect is also put in comparison with each other. The alloys were produced by means of an arc melting furnace in inert atmosphere under the shape of cigars. Due to the high reactivity of these alloys at high temperature, the cigars were sealed in a stainless steel can before the processing and two different procedures of hot rolling were tested. The characterization of the rolled alloys is performed using discrete scanning calorimetry in terms of evolution of the martensitic transformation and scanning electron microscopy for the microstructural investigations. Additionally, preliminary tests of laser interaction has been also proposed on the alloy more interesting for potential applications, characterized by high transformation temperatures and its good thermal stability.

  1. Airfoil-based piezoelectric energy harvesting by exploiting the pseudoelastic hysteresis of shape memory alloy springs

    NASA Astrophysics Data System (ADS)

    de Sousa, Vagner Candido; De Marqui Junior, Carlos

    2015-12-01

    The modeling and analysis of an electromechanically coupled typical aeroelastic section with shape memory alloy springs for wind energy harvesting is addressed in this paper. An airfoil with two-degrees-of-freedom, namely pitch and plunge, is considered and piezoelectric coupling is added to the plunge degree-of-freedom. A load resistance is assumed in the electrical domain of the problem in order to estimate the electrical power output. Shape memory alloy coil springs are modeled in the pitch degree-of-freedom of the typical section. A nickel-titanium alloy that exhibits pseudoelasticity at room temperature is assumed. The constitutive model for the shape memory alloy is based on classical phenomenological models. The unsteady aerodynamic loads are obtained by Jones’ approximation to Wagner’s indicial function. The resulting nonlinear electroaeroelastic model is cast into a state-space representation and solved with a Runge-Kutta method. The effects of preload values of the shape memory springs and resistive power generation on the aeroelastic behavior of the wind energy harvester are investigated at the flutter boundary and in a post-flutter regime. The nonlinear kinetics of the austenite-to-martensite phase transformation changes the typical linear flutter behavior to stable limit-cycle oscillations over a range of airflow speeds. Such nonlinear aeroelastic behavior introduced by the hysteretic behavior of the SMA springs provides an important source of persistent electrical power.

  2. Review of properties of magnetic shape memory (MSM) alloys and MSM actuator designs

    NASA Astrophysics Data System (ADS)

    Gabdullin, N.; Khan, S. H.

    2015-02-01

    Magnetic shape memory alloys are a new group of "smart" materials that exhibit large strain of 6-12% when subjected to magnetic fields. This indicates their enormous potential to be used in different electromagnetic (EM) devices such as actuators, sensors, energy harvesters and dampers. Shape change in MSM materials is controlled by magnetic field and doesn't involve phase transformation, allowing it to overcome a number of disadvantages of conventional shape memory alloys (SMAs). MSM devices are capable of producing large force and stroke output in considerably small dimensions. At the same time they can have fast response and potentially very long lifetime. This paper discusses different modern designs and approaches to MSM actuator design with their advantages and disadvantages. An overview on characteristics of MSM alloys is also presented in order to highlight how different properties of the material influence the total output of a device.

  3. Apparatus and method for low-temperature training of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Swanger, A. M.; Fesmire, J. E.; Trigwell, S.; Gibson, T. L.; Williams, M. K.; Benafan, O.

    2015-12-01

    An apparatus and method for the low-temperature thermo-mechanical training of shape memory alloys (SMA) has been developed. The experimental SMA materials are being evaluated as prototypes for applicability in novel thermal management systems for future cryogenic applications. Alloys providing two-way actuation at cryogenic temperatures are the chief target. The mechanical training regimen was focused on the controlled movement of rectangular strips, with S-bend configurations, at temperatures as low as 30 K. The custom holding fixture included temperature sensors and a low heat-leak linear actuator with a magnetic coupling. The fixture was mounted to a Gifford-McMahon cryocooler providing up to 25 W of cooling power at 20 K and housed within a custom vacuum chamber. Operations included both training cycles and verification of shape memory movement. The system design and operation are discussed. Results of the training for select prototype alloys are presented.

  4. Apparatus and Method for Low-Temperature Training of Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Swanger, A. M.; Fesmire, J. E.; Trigwell, S.; Gibson, T. L.; Williams, M. K.; Benafan, O.

    2015-01-01

    An apparatus and method for the low-temperature thermo-mechanical training of shape memory alloys (SMA) has been developed. The experimental SMA materials are being evaluated as prototypes for applicability in novel thermal management systems for future cryogenic applications. Alloys providing two-way actuation at cryogenic temperatures are the chief target. The mechanical training regimen was focused on the controlled movement of rectangular strips, with S-bend configurations, at temperatures as low as 30 K. The custom holding fixture included temperature sensors and a low heat-leak linear actuator with a magnetic coupling. The fixture was mounted to a Gifford-McMahon cryocooler providing up to 25 W of cooling power at 20 K and housed within a custom vacuum chamber. Operations included both training cycles and verification of shape memory movement. The system design and operation are discussed. Results of the training for select prototype alloys are presented.

  5. Spray Forming of NiTi and NiTiPd Shape-Memory Alloys

    NASA Technical Reports Server (NTRS)

    Mabe, James; Ruggeri, Robert; Noebe, Ronald

    2008-01-01

    In the work to be presented, vacuum plasma spray forming has been used as a process to deposit and consolidate prealloyed NiTi and NiTiPd powders into near net shape actuators. Testing showed that excellent shape memory behavior could be developed in the deposited materials and the investigation proved that VPS forming could be a means to directly form a wide range of shape memory alloy components. The results of DSC characterization and actual actuation test results will be presented demonstrating the behavior of a Nitinol 55 alloy and a higher transition temperature NiTiPd alloy in the form of torque tube actuators that could be used in aircraft and aerospace controls.

  6. The Investigation of a Shape Memory Alloy Micro-Damper for MEMS Applications

    PubMed Central

    Pan, Qiang; Cho, Chongdu

    2007-01-01

    Some shape memory alloys like NiTi show noticeable high damping property in pseudoelastic range. Due to its unique characteristics, a NiTi alloy is commonly used for passive damping applications, in which the energy may be dissipated by the conversion from mechanical to thermal energy. This study presents a shape memory alloy based micro-damper, which exploits the pseudoelasticity of NiTi wires for energy dissipation. The mechanical model and functional principle of the micro-damper are explained in detail. Moreover, the mechanical behavior of NiTi wires subjected to various temperatures, strain rates and strain amplitudes is observed. Resulting from those experimental results, the damping properties of the micro-damper involving secant stiffness, energy dissipation and loss factor are analyzed. The result indicates the proposed NiTi based micro-damper exhibits good energy dissipation ability, compared with conventional materials damper.

  7. Surface corrosion enhancement of passive films on NiTi shape memory alloy in different solutions.

    PubMed

    Jinlong, Lv; Tongxiang, Liang; Chen, Wang; Limin, Dong

    2016-06-01

    The corrosion behaviors of NiTi shape memory alloy in NaCl solution, H2SO4 solution and borate buffer solution were investigated. It was found that TiO2 in passive film improved the corrosion resistance of NiTi shape memory. However, low corrosion resistance of passive film was observed in low pH value acidic solution due to TiO2 dissolution. Moreover, the corrosion resistance of NiTi shape memory alloy decreased with the increasing of passivated potential in the three solutions. The donor density in passive film increased with the increasing of passivated potential. Different solutions affect the semiconductor characteristics of the passive film. The reducing in the corrosion resistance was attributed to the more donor concentrations in passive film and thinner thickness of the passive film.

  8. A Low Hysteresis NiTiFe Shape Memory Alloy Based Thermal Conduction Switch

    SciTech Connect

    Lemanski, J. L.; Krishnan, V. B.; Manjeri, R. Mahadevan; Vaidyanathan, R.; Notardonato, W. U.

    2006-03-31

    Shape memory alloys possess the ability to return to a preset shape by undergoing a solid state phase transformation at a particular temperature. This work reports on the development and testing of a low temperature thermal conduction switch that incorporates a NiTiFe shape memory element for actuation. The switch was developed to provide a variable conductive pathway between liquid methane and liquid oxygen dewars in order to passively regulate the temperature of methane. The shape memory element in the switch undergoes a rhombohedral or R-phase transformation that is associated with a small hysteresis (typically 1-2 deg. C) and offers the advantage of precision control over a set temperature range. For the NiTiFe alloy used, its thermomechanical processing, subsequent characterization using dilatometry, differential scanning calorimetry and implementation in the conduction switch configuration are addressed.

  9. Identification of epsilon martensite in a Fe-based shape memory alloy by means of EBSD.

    PubMed

    Verbeken, K; Van Caenegem, N; Raabe, D

    2009-01-01

    Ferrous shape memory alloys (SMAs) are often thought to become a new, important group of SMAs. The shape memory effect in these alloys is based on the reversible, stress-induced martensitic transformation of austenite to epsilon martensite. The identification and quantification of epsilon martensite is crucial when evaluating the shape memory behaviour of this material. Previous work displayed that promising results were obtained when studying the evolution of the amount of epsilon martensite after different processing steps with Electron BackScatter Diffraction (EBSD). The present work will discuss in detail, on the one hand, the challenges and opportunities arising during the identification of epsilon martensite by means of EBSD and, on the other hand, the possible interpretations that might be given to these findings. It will be illustrated that although the specific nature of the austenite to epsilon martensite transformation can still cause some points of discussion, EBSD has a high potential for identifying epsilon martensite.

  10. Characterization of Ternary NiTiPt High-Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Rios, Orlando; Noebe, Ronald; Biles, Tiffany; Garg, Anita; Palczer, Anna; Scheiman, Daniel; Seifert, Hans Jurgen; Kaufman, Michael

    2005-01-01

    Pt additions substituted for Ni in NiTi alloys are known to increase the transformation temperature of the alloy but only at fairly high Pt levels. However, until now only ternary compositions with a very specific stoichiometry, Ni50-xPtxTi50, have been investigated and then only to very limited extent. In order to learn about this potential high-temperature shape memory alloy system, a series of over twenty alloys along and on either side of a line of constant stoichiometry between NiTi and TiPt were arc melted, homogenized, and characterized in terms of their microstructure, transformation temperatures, and hardness. The resulting microstructures were examined by scanning electron microscopy and the phase compositions quantified by energy dispersive spectroscopy."Stoichiometric" compositions along a line of constant stoichiometry between NiTi to TiPt were essentially single phase but by any deviations from a stoichiometry of (Ni,Pt)50Ti50 resulted in the presence of at least two different intermetallic phases, depending on the overall composition of the alloy. Essentially all alloys, whether single or two-phase, still under went a martensitic transformation. It was found that the transformation temperatures were depressed with initial Pt additions but at levels greater than 10 at.% the transformation temperature increased linearly with Pt content. Also, the transformation temperatures were relatively insensitive to alloy stoichiometry within the range of alloys examined. Finally, the dependence of hardness on Pt content for a series of Ni50-xPtxTi50 alloys showed solution softening at low Pt levels, while hardening was observed in ternary alloys containing more than about 10 at.% Pt. On either side of these "stoichiometric" compositions, hardness was also found to increase significantly.

  11. Relationship among grain size, annealing twins and shape memory effect in Fe–Mn–Si based shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wang, Gaixia; Peng, Huabei; Zhang, Chengyan; Wang, Shanling; Wen, Yuhua

    2016-07-01

    In order to clarify the relationship among grain size, annealing twins and the shape memory effect in Fe–Mn–Si based shape memory alloys, the Fe–21.63Mn–5.60Si–9.32Cr–5.38Ni (weight %) alloy with a grain size ranging from 48.9 μm–253.6 μm was obtained by adjusting the heating temperature or heating time after 20% cold-rolling. The densities of grain boundaries and annealing twins increase with a decrease in grain size, whereas the volume fraction and width of stress-induced ε martensite after 9% deformation at Ms + 10 K decrease. This result indicates that grain refinement raises the constraint effects of grain boundaries and annealing twins upon martensitic transformation. In this case, the ability to suppress the plastic deformation and facilitate the stress-induced ε martensite transformation deteriorates after grain refinement owing to the enhancement of the constraint effects. It is demonstrated by the result that the difference at Ms + 10 K between the critical stress for plastic yielding and that for inducing martensitic transformation is smaller for the specimen with a grain size of 48.9 μm than for the specimen with a grain size of 253.6 μm. Therefore, the shape memory effect declined by decreasing the grain size.

  12. Relationship among grain size, annealing twins and shape memory effect in Fe-Mn-Si based shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wang, Gaixia; Peng, Huabei; Zhang, Chengyan; Wang, Shanling; Wen, Yuhua

    2016-07-01

    In order to clarify the relationship among grain size, annealing twins and the shape memory effect in Fe-Mn-Si based shape memory alloys, the Fe-21.63Mn-5.60Si-9.32Cr-5.38Ni (weight %) alloy with a grain size ranging from 48.9 μm-253.6 μm was obtained by adjusting the heating temperature or heating time after 20% cold-rolling. The densities of grain boundaries and annealing twins increase with a decrease in grain size, whereas the volume fraction and width of stress-induced ɛ martensite after 9% deformation at Ms + 10 K decrease. This result indicates that grain refinement raises the constraint effects of grain boundaries and annealing twins upon martensitic transformation. In this case, the ability to suppress the plastic deformation and facilitate the stress-induced ɛ martensite transformation deteriorates after grain refinement owing to the enhancement of the constraint effects. It is demonstrated by the result that the difference at Ms + 10 K between the critical stress for plastic yielding and that for inducing martensitic transformation is smaller for the specimen with a grain size of 48.9 μm than for the specimen with a grain size of 253.6 μm. Therefore, the shape memory effect declined by decreasing the grain size.

  13. An Implicit Algorithm for the Numerical Simulation of Shape-Memory Alloys

    SciTech Connect

    Becker, R; Stolken, J; Jannetti, C; Bassani, J

    2003-10-16

    Shape-memory alloys (SMA) have the potential to be used in a variety of interesting applications due to their unique properties of pseudoelasticity and the shape-memory effect. However, in order to design SMA devices efficiently, a physics-based constitutive model is required to accurately simulate the behavior of shape-memory alloys. The scope of this work is to extend the numerical capabilities of the SMA constitutive model developed by Jannetti et. al. (2003), to handle large-scale polycrystalline simulations. The constitutive model is implemented within the finite-element software ABAQUS/Standard using a user defined material subroutine, or UMAT. To improve the efficiency of the numerical simulations, so that polycrystalline specimens of shape-memory alloys can be modeled, a fully implicit algorithm has been implemented to integrate the constitutive equations. Using an implicit integration scheme increases the efficiency of the UMAT over the previously implemented explicit integration method by a factor of more than 100 for single crystal simulations.

  14. Static critical phenomena in Co-Ni-Ga ferromagnetic shape memory alloy

    SciTech Connect

    Sethi, Brahmananda Sarma, S. Srinivasan, A. Santra, S. B.

    2014-04-24

    Ferromagnetic shape memory alloys are smart materials because they exhibit temperature driven shape memory effect and magnetic field induced strain. Thus two types of energy, i.e. thermal and magnetic, are used to control their shape memory behaviour. Study of critical phenomenon in such materials has received increased experimental and theoretical attention for better understanding of the magnetic phase transition behavior as well as further development of ferromagnetic shape memory materials. In the present study we report the preparation and characterization of bulk Co{sub 45}Ni{sub 25}Ga{sub 30} alloy, prepared by a sequence of arc melting technique followed by homogenization at 1150 °C for 24 hours and ice-water quenching. Structural and magnetic properties of the alloys were studied by means of X-ray diffraction and vibrating sample magnetometer in an applied field range of ±18 kOe equipped with a high temperature oven. We have determined the critical temperature T{sub C} (∼375.5 K) and the critical exponents viz; β=0.40, γ=1.68 and δ=5.2. Asymptotic critical exponents β, γ, and δ obey Widom scaling relation, γ+β=βδ, and the magnetization data satisfy the scaling equation of state for second-order phase transition in the asymptotic critical region.

  15. Shape Memory Effect in Cast Versus Deformation-Processed NiTiNb Alloys

    NASA Astrophysics Data System (ADS)

    Hamilton, Reginald F.; Lanba, Asheesh; Ozbulut, Osman E.; Tittmann, Bernhard R.

    2015-06-01

    The shape memory effect (SME) response of a deformation-processed NiTiNb shape memory alloy is benchmarked against the response of a cast alloy. The insoluble Nb element ternary addition is known to widen the hysteresis with respect to the binary NiTi alloy. Cast microstructures naturally consist of a cellular arrangement of characteristic eutectic microconstituents surrounding primary matrix regions. Deformation processing typically aligns the microconstituents such that the microstructure resembles discontinuous fiber-reinforced composites. Processed alloys are typically characterized for heat-to-recover applications and thus deformed at constant temperature and subsequently heated for SME recovery, and the critical stress levels are expected to facilitate plastic deformation of the microconstituents. The current work employs thermal cycling under constant bias stresses below those critical levels. This comparative study of cast versus deformation-processed NiTiNb alloys contrasts the strain-temperature responses in terms of forward Δ T F = M s - M f and reverse Δ T R = A f - A s temperature intervals, the thermal hysteresis, and the recovery ratio. The results underscore that the deformation-processed microstructure inherently promotes irreversibility and differential forward and reverse transformation pathways.

  16. Thermomechanical behavior of NiTiPdPt high temperature shape memory alloy springs

    NASA Astrophysics Data System (ADS)

    Nicholson, D. E.; Padula, S. A., II; Noebe, R. D.; Benafan, O.; Vaidyanathan, R.

    2014-12-01

    Transformation strains in high temperature shape memory alloys (HTSMAs) are generally smaller than for conventional NiTi alloys and can be purposefully limited in cases where stability and repeatability at elevated temperatures are desired. Yet such alloys can still be used in actuator applications that require large strokes when used in the form of springs. Thus there is a need to understand the thermomechanical behavior of shape memory alloy spring actuators, particularly those consisting of alternative alloys. In this work, a modular test setup was assembled with the objective of acquiring stroke, stress, temperature, and moment data in real time during joule heating and forced convective cooling of Ni19.5Ti50.5Pd25Pt5 HTSMA springs. The spring actuators were subjected to both monotonic axial loading and thermomechanical cycling. The role of rotational constraints (i.e., by restricting rotation or allowing for free rotation at the ends of the springs) on stroke performance was also assessed. Finally, recognizing that evolution in the material microstructure can result in changes in HTSMA spring geometry, the effect of material microstructural evolution on spring performance was examined. This was done by taking into consideration the changes in geometry that occurred during thermomechanical cycling. This work thus provides insight into designing with HTSMA springs and predicting their thermomechanical performance.

  17. Corrosion Behavior of Ti-55Ni-1.2Co High Stiffness Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Huang, Xu; Norwich, Dennis W.; Ehrlinspiel, Michael

    2014-07-01

    The corrosion behavior of high stiffness nominal Ti-55Ni-1.2Co (wt.%) shape memory alloys (SMAs) was systematically investigated in the present study including straight wires, wire-formed stents, and laser-cut stents. It was found that the corrosion behavior of Ti-55Ni-1.2Co alloys is comparable with those of binary NiTiNol counterparts, which is attributed to the small alloying amount of cobalt. Additionally, the corrosion resistance of high stiffness Ti-55Ni-1.2Co SMAs is independent of the stent-forming method. To explore the galvanic corrosion susceptibility between Ti-55Ni-1.2Co and binary NiTiNol alloys, a NiTiNol sleeve was laser welded to the Ti-55Ni-1.2Co stent. Interestingly, there is no galvanic corrosion observed in this NiTiCo-NiTiNol component, even after immersion of the component in phosphate-buffered saline solution at 37 °C for three months. This study will shed some light on the industrial applications of high stiffness Ti-55Ni-1.2Co shape memory alloys.

  18. Properties of Porous TiNbZr Shape Memory Alloy Fabricated by Mechanical Alloying and Hot Isostatic Pressing

    NASA Astrophysics Data System (ADS)

    Ma, L. W.; Chung, C. Y.; Tong, Y. X.; Zheng, Y. F.

    2011-07-01

    In the past decades, systematic researches have been focused on studying Ti-Nb-based SMAs by adding ternary elements, such as Mo, Sn, Zr, etc. However, only arc melting or induction melting methods, with subsequent hot or cold rolling, were used to fabricate these Ni-free SMAs. There is no work related to powder metallurgy and porous structures. This study focuses on the fabrication and characterization of porous Ti-22Nb-6Zr (at.%) shape memory alloys produced using elemental powders by means of mechanical alloying and hot isostatic pressing. It is found that the porous Ti-22Nb-6Zr alloys prepared by the HIP process exhibit a homogenous pore distribution with spherical pores, while the pores have irregular shape in the specimen prepared by conventional sintering. X-ray diffraction analysis showed that the solid solution-treated Ti-22Nb-6Zr alloy consists of both β phase and α″ martensite phase. Morphologies of martensite were observed. Finally, the porous Ti-22Nb-6Zr SMAs produced by both MA and HIP exhibit good mechanical properties, such as superior superelasticity, with maximum recoverable strain of ~3% and high compressive strength.

  19. Elevated Temperature, In Situ Micromechanical Characterization of a High Temperature Ternary Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Wheeler, J. M.; Niederberger, C.; Raghavan, R.; Thompson, G.; Weaver, M.; Michler, J.

    2015-12-01

    The microthermomechanical behavior of a precipitation-hardenable Ni-48Ti-25Pd (at.%) shape memory alloy has been investigated as a function of temperature. Micropillars were fabricated within a large <145>-oriented grain and compressed in situ in the SEM at elevated temperatures corresponding to the martensite and austenite phase transformation temperatures. The precipitation-strengthened alloys exhibited stable pseudoelastic behavior with little or no residual strains when near the transformation temperatures. In the plastic regime, slip was observed to occur via pencil glide, circumventing the fine scale precipitates along multiple slip planes.

  20. Improvement in the Shape Memory Response of Ti50.5Ni24.5Pd25 High-Temperature Shape Memory Alloy with Scandium Microalloying

    NASA Technical Reports Server (NTRS)

    Atli, K. C.; Karaman, I; Noebe, R. D.; Garg, A.; Chumlyakov, Y. I.; Kireeva, I. V.

    2010-01-01

    A Ti(50.5)Ni(24.5)Pd25 high-temperature shape memory alloy (HTSMA) is microalloyed with 0.5 at. pct scandium (Sc) to enhance its shape-memory characteristics, in particular, dimensional stability under repeated thermomechanical cycles. For both Ti(50.5)Ni(24.5)Pd25 and the Sc-alloyed material, differential scanning calorimetry is conducted for multiple cycles to characterize cyclic stability of the transformation temperatures. The microstructure is evaluated using electron microscopy, X-ray diffractometry, and wavelength dispersive spectroscopy. Isobaric thermal cycling experiments are used to determine transformation temperatures, dimensional stability, and work output as a function of stress. The Sc-doped alloy displays more stable shape memory response with smaller irrecoverable strain and narrower thermal hysteresis than the baseline ternary alloy. This improvement in performance is attributed to the solid solution hardening effect of Sc.

  1. The influence of ageing on martensite ordering and stabilization in shape memory Cu-Al-Ni alloys

    SciTech Connect

    Aydogdu, A.; Aydogdu, Y.; Adiguzel, O.

    1997-05-01

    The martensitic transformation and the associated mechanical shape reversibility in copper-based shape memory alloys is strongly influenced by quenching and ageing treatments. Ageing of martensite in as-quenched Cu-Al-Ni alloys can result in loss of memory behavior. Structural studies have been carried out to measure the changes in the degree of order that develop during martensitic ageing of two Cu-Al-Ni alloys. Stabilization is directly related to disordering in martensitic state and the spacing differences ({Delta}d) between selected pairs of diffraction planes reflect the degree of ordering in martensite. The changes in degree of order are shown to be similar in as-quenched and post-quenched {beta}-phase annealed alloys, thereby leading to the conclusion that loss of memory in as-quenched alloys is not solely attributable to any extra changes in degree of order brought about by excess vacancies during martensitic ageing.

  2. Martensite aging effect in a Ti{sub 50}Pd{sub 50} high temperature shape memory alloy

    SciTech Connect

    Cai, W.; Otsuka, Kazuhiro

    1999-11-19

    Ti-Pd alloy system is one of the potential high temperature shape memory alloys due to its high martensitic transformation temperatures. Thus, many researches including shape memory characteristics, martensitic transformations and mechanical behavior of the alloys have been done in recent yeas. However, martensite aging effect in the alloy, which is an important issue as to the stability of martensite at high temperature, has not been reported yet. Ti{sub 50}Pd{sub 50} transforms from B2 parent phase to B19 martensite upon cooling, and M{sub s} is 823 K (25) and T{sub m} is 1,673 K (26). Thus M{sub s}/T{sub m} ratio of the alloy is about 0.49, and the alloy may show strong martensite aging effect according to the above proposal. It is now of interest to examine whether the Ti{sub 50}Pd{sub 50} alloy show martensite aging effect. As will be shown, the Ti{sub 50}Pd{sub 50} alloy indeed shows the aging effect, as expected; however, the aging effect of this alloy exhibits a unique feature, which is not found in other shape memory alloys.

  3. Shape memory alloys. December 1986-December 1987 (citations from the INSPEC: Information Services for the Physics and Engineering Communities data base). Report for December 1986-December 1987

    SciTech Connect

    Not Available

    1987-12-01

    This bibliography contains citations concerning experiments on shape-memory effects of various alloys. Alloys studied include nickel, tin, indium, lead, copper, and titanium. Studies include crystallography, properties, processing, alloying, and mechanisms that result in shape memory effects. (This updated bibliography contains 79 citations, all of which are new entries to the previous edition.)

  4. Shape-memory alloys. January 1975-November 1986 (citations from the INSPEC: Information Services for the Physics and Engineering Communities data base). Report for January 1975-November 1986

    SciTech Connect

    Not Available

    1987-12-01

    This bibliography contains citations concerning experiments on shape-memory effects of various alloys. Alloys studied include nickel, tin, indium, lead, copper, and titanium. Studies include crystallography, properties, processing, alloying, and mechanisms that result in shape-memory effects. (This updated bibliography contains 327 citations, none of which are new entries to the previous edition.)

  5. The kinetic relation for twin wall motion in NiMnGa—part 2

    NASA Astrophysics Data System (ADS)

    Faran, Eilon; Shilo, Doron

    2013-03-01

    A combined theoretical and experimental investigation of twin wall motion in ferromagnetic shape memory alloy (FSMA) NiMnGa is presented. A general analysis of twinning dynamics in ferroelastic and ferroelectric crystals reveals that different kinetic relations for sidewise twin wall motion appear under different ranges of the driving force. All these relations are shown to be governed by several nano-scale properties of the twin wall. For high values of the driving force with respect to a crystal's Peierls barrier, uniform viscous motion is obtained. Recently (Faran and Shilo, 2011), we reported on a pioneering experimental demonstration of this important kinetic relation through magnetically induced twin wall motion in NiMnGa. In the lower driving force range, twin wall propagates through thermally activated nucleation and growth of twin wall steps. Here, we present a model for step nucleation that leads to an exponential-type kinetic relation that is governed by the values of the step's physical properties. Comparison of experimental results for type I and type II twin walls with model predictions allow for the extraction of all the fundamental material properties that govern twinning dynamics in NiMnGa. In addition, the effect of demagnetization energy on twin wall motion and local variations in viscosity values are presented and discussed.

  6. Thermomechanical testing of FeNiCoTi shape memory alloy for active confinement of concrete

    NASA Astrophysics Data System (ADS)

    Chen, Qiwen; Andrawes, Bassem; Sehitoglu, Huseyin

    2014-05-01

    The thermomechanical properties of a new type of shape memory alloy (SMA), FeNiCoTi, are explored in this paper with the aim of examining the feasibility of using this new material as transverse reinforcement for concrete structures subjected to earthquake loading. One advantage of using FeNiCoTi alloy is its cost effectiveness compared to commonly studied NiTi alloy. Differential scanning calorimetry (DSC) tests are conducted to investigate the transformation temperatures of FeNiCoTi alloy under different heat treatment methods and prestrain schemes. First, a heat treatment method is established to produce FeNiCoTi alloy with wide thermal hysteresis that is pertinent to civil structural applications. Next, recovery stress tests are conducted to explore the effect of parameters including heating method, heating temperature, heating rate, heating protocol and prestrain level on the recovery stress. An optimum prestrain level is determined based on the recovery stress results. Moreover, cyclic tests are carried out to examine the cyclic response of FeNiCoTi alloy after stress recovery. Thermal cyclic tests are also carried out on the FeNiCoTi alloy to better understand the effect of temperature variation on the recovery stress. In addition, reheating of the FeNiCoTi alloy after deformation is conducted to examine the reusability of the material after being subjected to excessive deformation. Test results of the FeNiCoTi alloy indicate that this cost-effective SMA can potentially be a promising new material for civil structural applications.

  7. Effects of twin boundary mobility on domain microstructure evolution in magnetic shape memory alloys: Phase field simulation

    SciTech Connect

    Jin, Yongmei M.

    2009-02-09

    Effects of twin boundary mobility on domain microstructure evolution during magnetic field-induced deformation in magnetic shape memory alloys are studied by phase field micromagnetic microelastic modeling. The simulations show that different twin boundary mobilities lead to drastically different domain microstructures and evolution pathways, yielding very different magnetization and strain responses, even with opposite signs. The study also reveals complex domain phenomena in magnetic shape memory alloys.

  8. Shape Memory Alloys and their Applications in Power Generation and Refrigeration

    SciTech Connect

    Cui, Jun

    2013-07-01

    The shape memory effect is closely related to the reversible martensitic phase transformation, which is diffusionless and involves shear deformation. The recoverable transformation between the two phases with different crystalline symmetry results in reversible changes in physical properties such as electrical conductivity, magnetization, and elasticity. Accompanying the transformation is a change of entropy. Fascinating applications are developed based on these changes. In this paper, the history, fundamentals and technical challenges of both thermoelastic and ferromagnetic shape memory alloys are briefly reviewed; applications related to energy conversion such as power generation and refrigeration as well as recent developments will be discussed.

  9. Shape Memory Alloys and Their Applications in Power Generation and Refrigeration

    SciTech Connect

    Cui, Jun

    2013-03-27

    The shape memory effect is closely related to the reversible martensitic phase transformation, which is diffusionless and involves shear deformation. The recoverable transformation between the two phases with different crystalline symmetry results in reversible changes in physical properties such as electrical conductivity, magnetization, and elasticity. Accompanying the transformation is a change of entropy. Fascinating applications are developed based on these changes. In this paper, the history, fundamentals and technical challenges of both thermoelastic and ferromagnetic shape memory alloys are briefly reviewed; applications related to energy conversion such as power generation and refrigeration as well as recent developments will be discussed.

  10. Load carrying capacity of RCC beams by replacing steel reinforcement bars with shape memory alloy bars

    NASA Astrophysics Data System (ADS)

    Bajoria, Kamal M.; Kaduskar, Shreya S.

    2016-04-01

    In this paper the structural behavior of reinforced concrete (RC) beams with smart rebars under two point loading system has been numerically studied, using Finite Element Method. The material used in this study is Super-elastic Shape Memory Alloys (SE SMAs) which contains nickel and titanium. In this study, different quantities of steel and SMA rebars have been used for reinforcement and the behavior of these models under two point bending loading system is studied. A comparison of load carrying capacity for the model between steel reinforced concrete beam and the beam reinforced with S.M.A and steel are performed. The results show that RC beams reinforced with combination of shape memory alloy and steel show better performance.

  11. Development of a shape memory alloy actuator for a robotic eye prosthesis

    NASA Astrophysics Data System (ADS)

    Bunton, T. B. Wolfe; Faulkner, M. G.; Wolfaardt, J.

    2005-08-01

    The quality of life of patients who wear an orbital prosthesis would be vastly improved if their prostheses were also able to execute vertical and horizontal motion. This requires appropriate actuation and control systems to create an intelligent prosthesis. A method of actuation that meets the demanding design criteria is currently not available. The present work considers an activation system that follows a design philosophy of biomimicry, simplicity and space optimization. While several methods of actuation were considered, shape memory alloys were chosen for their high power density, high actuation forces and high displacements. The behaviour of specific shape memory alloys as an actuator was investigated to determine the force obtained, the transformation temperatures and details of the material processing. In addition, a large-scale prototype was constructed to validate the response of the proposed system.

  12. Performance of Integrated Fiber Optic, Piezoelectric, and Shape Memory Alloy Actuators/Sensors in Thermoset Composites

    NASA Technical Reports Server (NTRS)

    Trottier, C. Michael

    1996-01-01

    Recently, scientists and engineers have investigated the advantages of smart materials and structures by including actuators in material systems for controlling and altering the response of structural environments. Applications of these materials systems include vibration suppression/isolation, precision positioning, damage detection and tunable devices. Some of the embedded materials being investigated for accomplishing these tasks include piezoelectric ceramics, shape memory alloys, and fiber optics. These materials have some benefits and some shortcomings; each is being studied for use in active material design in the SPICES (Synthesis and Processing of Intelligent Cost Effective Structures) Consortium. The focus of this paper concerns the manufacturing aspects of smart structures by incorporating piezoelectric ceramics, shape memory alloys and fiber optics in a reinforced thermoset matrix via resin transfer molding (RTM).

  13. The alloy with a memory, 55-Nitinol: Its physical metallurgy, properties, and applications

    NASA Technical Reports Server (NTRS)

    Jackson, C. M.; Wagner, H. J.; Wasilewski, R. J.

    1972-01-01

    A series of nickel titanium alloys (55-Nitinol), which are unique in that they possess a shape memory, are described. Components made of these materials that are altered in their shapes by deformation under proper conditions return to predetermined shapes when they are heated to the proper temperature range. The shape memory, together with the force exerted and the ability of the material to do mechanical work as it returns to its predetermined shape, suggest a wide variety of industrial applications for the alloy. Also included are discussions of the physical metallurgy and the mechanical, physical, and chemical properties of 55-Nitinol; procedures for melting and processing the material into useful shapes; and a summary of applications.

  14. Investigation of the Thermomechanical Response of Shape Memory Alloy Hybrid Composite Beams

    NASA Technical Reports Server (NTRS)

    Davis, Brian A.

    2005-01-01

    Previous work at NASA Langley Research Center (LaRC) involved fabrication and testing of composite beams with embedded, pre-strained shape memory alloy (SMA) ribbons. That study also provided comparison of experimental results with numerical predictions from a research code making use of a new thermoelastic model for shape memory alloy hybrid composite (SMAHC) structures. The previous work showed qualitative validation of the numerical model. However, deficiencies in the experimental-numerical correlation were noted and hypotheses for the discrepancies were given for further investigation. The goal of this work is to refine the experimental measurement and numerical modeling approaches in order to better understand the discrepancies, improve the correlation between prediction and measurement, and provide rigorous quantitative validation of the numerical model. Thermal buckling, post-buckling, and random responses to thermal and inertial (base acceleration) loads are studied. Excellent agreement is achieved between the predicted and measured results, thereby quantitatively validating the numerical tool.

  15. Assessment of Shape Memory Alloys - From Atoms To Actuators - Via In Situ Neutron Diffraction

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane

    2014-01-01

    As shape memory alloys (SMAs) become an established actuator technology, it is important to identify the fundamental mechanisms responsible for their performance by understanding microstructure performance relationships from processing to final form. Yet, microstructural examination of SMAs at stress and temperature is often a challenge since structural changes occur with stress and temperature and microstructures cannot be preserved through quenching or after stress removal, as would be the case for conventional materials. One solution to this dilemma is in situ neutron diffraction, which has been applied to the investigation of SMAs and has offered a unique approach to reveal the fundamental micromechanics and microstructural aspects of bulk SMAs in a non-destructive setting. Through this technique, it is possible to directly correlate the micromechanical responses (e.g., internal residual stresses, lattice strains), microstructural evolutions (e.g., texture, defects) and phase transformation properties (e.g., phase fractions, kinetics) to the macroscopic actuator behavior. In this work, in situ neutron diffraction was systematically employed to evaluate the deformation and transformation behavior of SMAs under typical actuator conditions. Austenite and martensite phases, yield behavior, variant selection and transformation temperatures were characterized for a polycrystalline NiTi (49.9 at. Ni). As the alloy transforms under thermomechanical loading, the measured textures and lattice plane-level variations were directly related to the cyclic actuation-strain characteristics and the dimensional instability (strain ratcheting) commonly observed in this alloy. The effect of training on the shape memory characteristics of the alloy and the development of two-way shape memory effect (TWSME) were also assessed. The final conversion from a material to a useful actuator, typically termed shape setting, was also investigated in situ during constrained heatingcooling and

  16. Constitutive modelling of magnetic shape memory alloys with discrete and continuous symmetries

    PubMed Central

    Haldar, K.; Lagoudas, D. C.

    2014-01-01

    A free energy-based constitutive formulation is considered for magnetic shape memory alloys. Internal state variables are introduced whose evolution describes the transition from reference state to the deformed and transformed one. We impose material symmetry restrictions on the Gibbs free energy and on the evolution equations of the internal state variables. Discrete symmetry is considered for single crystals, whereas continuous symmetry is considered for polycrystalline materials. PMID:25197247

  17. Wireless and passive temperature indicator utilizing the large hysteresis of magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Bergmair, Bernhard; Liu, Jian; Huber, Thomas; Gutfleisch, Oliver; Suess, Dieter

    2012-07-01

    An ultra-low cost, wireless magnetoelastic temperature indicator is presented. It comprises a magnetostrictive amorphous ribbon, a Ni-Mn-Sn-Co magnetic shape memory alloy with a highly tunable transformation temperature, and a bias magnet. It allows to remotely detect irreversible changes due to transgressions of upper or lower temperature thresholds. Therefore, the proposed temperature indicator is particularly suitable for monitoring the temperature-controlled supply chain of, e.g., deep frozen and chilled food or pharmaceuticals.

  18. Experimental evaluation of shape memory alloy actuation technique in adaptive antenna design concepts

    NASA Technical Reports Server (NTRS)

    Kefauver, W. Neill; Carpenter, Bernie F.

    1994-01-01

    Creation of an antenna system that could autonomously adapt contours of reflecting surfaces to compensate for structural loads induced by a variable environment would maximize performance of space-based communication systems. Design of such a system requires the comprehensive development and integration of advanced actuator, sensor, and control technologies. As an initial step in this process, a test has been performed to assess the use of a shape memory alloy as a potential actuation technique. For this test, an existing, offset, cassegrain antenna system was retrofit with a subreflector equipped with shape memory alloy actuators for surface contour control. The impacts that the actuators had on both the subreflector contour and the antenna system patterns were measured. The results of this study indicate the potential for using shape memory alloy actuation techniques to adaptively control antenna performance; both variations in gain and beam steering capabilities were demonstrated. Future development effort is required to evolve this potential into a useful technology for satellite applications.

  19. Dynamic mechanical analyze of superelastic CuMnAl shape memory alloy

    NASA Astrophysics Data System (ADS)

    (Dragoș Ursanu, A. I.; Stanciu, S.; Pricop, B.; Săndulache, F.; Cimpoeșu, N.

    2016-08-01

    A new shape memory alloy was obtain from high purity Cu, Mn and Al elements using a induce furnace. The intelligent material present negative transformation temperatures and an austenite like state at room temperature. The austenite state of CuMnAl shape memory alloy present superelasticity property. Five kilograms ingot was obtain of Cu10Mn10Al alloy. From the base material (melted state) were cut samples with 6 mm thickness using a mechanical saw. After an homogenization heat treatment the samples were hot rolled through four passes with a reduction coefficient of 20%. Experimental lamellas were obtained with 1.5 mm thickness and 90x10 mm length and width. After the hot rolled treatment the materials were heat treated at 800°C for 20 minutes and chilled in water. Four samples, one just laminated and three heat treated by aging, were analyzed with a Netzsch DMA equipment to establish the elastic modulus and the internal friction values of the materials. Metallic materials microstructure was analyzed using a scanning electron microscope Vega Tescan LMH II type. After the aging heat treatment a decrease of internal friction is observed on the entire analyze range which is assigned to formation of Al-based precipitates that block the internal movement of the alloy characteristic phases.

  20. Ferromagnetic shape memory flapper for remotely actuated propulsion systems

    NASA Astrophysics Data System (ADS)

    Kanner, Oren Y.; Shilo, Doron; Sheng, Jian; James, Richard D.; Ganor, Yaniv

    2013-08-01

    Generating propulsion with small-scale devices is a major challenge due to both the domination of viscous forces at low Reynolds numbers as well as the small relative stroke length of traditional actuators. Ferromagnetic shape memory materials are good candidates for such devices as they exhibit a unique combination of large strains and fast responses, and can be remotely activated by magnetic fields. This paper presents the design, analysis, and realization of a novel NiMnGa shear actuation method, which is especially suitable for small-scale fluid propulsion. A fluid mechanics analysis shows that the two key parameters for powerful propulsion are the engineering shear strain and twin boundary velocity. Using high-speed photography, we directly measure both parameters under an alternating magnetic field. Reynolds numbers in the inertial flow regime (>700) are evaluated. Measurements of the transient thrust show values up to 40 mN, significantly higher than biological equivalents. This work paves the way for new remotely activated and controlled propulsion for untethered micro-scale robots.

  1. Thermal Behavior of Mechanically Alloyed Powders Used for Producing an Fe-Mn-Si-Cr-Ni Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Pricop, B.; Söyler, U.; Lohan, N. M.; Özkal, B.; Bujoreanu, L. G.; Chicet, D.; Munteanu, C.

    2012-11-01

    In order to produce shape memory rings for constrained-recovery pipe couplings, from Fe-14 Mn-6 Si-9 Cr-5 Ni (mass%) powders, the main technological steps were (i) mechanical alloying, (ii) sintering, (iii) hot rolling, (iv) hot-shape setting, and (v) thermomechanical training. The article generally describes, within its experimental-procedure section, the last four technological steps of this process the primary purpose of which has been to accurately control both chemical composition and the grain size of shape memory rings. Details of the results obtained in the first technological step, on raw powders employed both in an initial commercial state and in a mixture state of commercial and mechanically alloyed (MA) powders, which were subjected to several heating-cooling cycles have been reported and discussed. By means of differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and X-ray diffraction (XRD), the thermal behaviors of the two sample powders have been analyzed. The effects of the heating-cooling cycles, on raw commercial powders and on 50% MA powders, respectively, were argued from the point of view of specific temperatures and heat variations, of elemental diffusion after thermal cycling and of crystallographic parameters, determined by DSC, SEM, and XRD, respectively.

  2. Comparative In Vitro Study of Ti-12V-9Sn Shape Memory Alloy with C.P. Ti and Ti-12V Alloy for Potential Biomedical Application

    NASA Astrophysics Data System (ADS)

    Qiu, K. J.; Wang, B. L.; Zhou, F. Y.; Lin, W. J.; Li, L.; Lin, J. P.; Zheng, Y. F.

    2012-12-01

    The microstructure, mechanical properties, and electrochemical behavior of Ti-12V-9Sn shape memory alloy were investigated, with commercial pure titanium (C.P. Ti) and Ti-12V alloy as controls. The metastable β phase was partially retained and α″ martensite phase was obtained in Ti-12V-9Sn alloy, whereas only martensitic phases (α' and α″) existed in Ti-12V alloy at room temperature. Ti-12V-9Sn alloy exhibited a good combination of strength and elongation, which showed a "double yield" feature, along with a complete shape recovery strain of 4%. The electrochemical measurements indicated that all of the experimental samples exhibited excellent corrosion resistance in the artificial saliva with and without 0.2% NaF, among which Ti-12V-9Sn alloy possessed the lowest corrosion current density in both kinds of simulated body fluids.

  3. The martensitic transformation and magnetic properties in Ni50- x Fe x Mn32Al18 ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Xuan, H. C.; Zhang, Y. Q.; Li, H.; Han, P. D.; Wang, D. H.; Du, Y. W.

    2015-05-01

    The martensitic transformation (MT) and magnetic properties have been investigated in a series of Ni50- x Fe x Mn32Al18 ferromagnetic shape memory alloys. The substitution of Fe for Ni reduces the MT temperature of Ni-Fe-Mn-Al alloys effectively, and the magnetization of the austenite was significantly enhanced in these high-doped alloys. The Fe introduction converts antiferromagnetic austenite to ferrimagnetic state, and therefore, the unique MT occurs between ferrimagnetic and antiferromagnetic state in these alloys. The MT temperatures decreased by about 15 K under the magnetic field of 30 kOe for x = 8 alloy. The positive value of magnetic entropy change was determined to 3.35 J/kg K around the MT in the field change of 30 kOe for x = 6 alloy. These results suggest that Ni50- x Fe x Mn32Al18 alloys would be the promising candidates for magnetic multifunctional materials.

  4. A review of modeling techniques for advanced effects in shape memory alloy behavior

    NASA Astrophysics Data System (ADS)

    Cisse, Cheikh; Zaki, Wael; Ben Zineb, Tarak

    2016-10-01

    micro, micro-macro and macro scales focusing pseudoelastic and shape memory effects. The paper reviews and discusses various techniques used in the literature for modeling complex behaviors observed in shape memory alloys (SMAs) that go beyond the core pseudoelastic and shape memory effects. These behaviors, which will be collectively referred to herein as ‘secondary effects’, include mismatch between austenite and martensite moduli, martensite reorientation under nonproportional multiaxial loading, slip and transformation-induced plasticity and their influence on martensite transformation, strong thermomechanical coupling and the influence of loading rate, tensile-compressive asymmetry, and the formation of internal loops due to incomplete phase transformation. In addition, because of their importance for practical design considerations, the paper discusses functional and structural fatigue, and fracture mechanics of SMAs.

  5. Lowering the power consumption of Ni-Ti shape memory alloy

    NASA Astrophysics Data System (ADS)

    Villanueva, Alex; Gupta, Shashaak; Priya, Shashank

    2012-04-01

    Shape memory alloy (SMA) wires are capable of providing contractile strain mimicking the functionality of muscle fibers. They are promising for the development of biomimetic robots due to their high power density and desired form factor. However, they suffer from significantly high power consumption. The focus of this paper was to address this drawback associated with SMAs. Two different parameters were investigated in this study: i) lowering of the martensite to austentite phase transition temperatures and ii) the reduction of the thermal hysteresis. For an equiatomic Ni-Ti alloy, replacing nickel with 10 at% copper reduces the thermal hysteresis by 50% or more. For Ni- Ti alloys with nickel content greater than 50 at%, transition temperature decreases linearly at a rate of 100 °C/Ni at%. Given these two power reducing factors, an alloy with composition of Ni40+xTi50-xCu10 was synthesized with x = 0, +/-1, +/-2, +/-3, +/-4, +/-5. Metal powders were melted in an argon atmosphere using an RF induction furnace to produce ingots. All the synthesized samples were characterized by differential scanning calorimetric (DSC) analysis to reveal martensite to austenite and austenite to martensite transition temperatures during heating and cooling cycles respectively. Scanning electron microscopy (SEM) was conducted to identify the density and microstructure of the fractured samples. The alloy composition and synthesis method presented in this preliminary work shows the possibility of achieving low power consuming, high performance SMAs.

  6. Mechanical behavior and phase stability of NiAl-based shape memory alloys

    SciTech Connect

    George, E.P.; Liu, C.T.; Horton, J.A.; Kunsmann, H.; King, T.; Kao, M.

    1993-12-31

    NiAl-based shape memory alloys (SMAs) can be made ductile by alloying with 100--300 wppm B and 14--20 at.% Fe. The addition of Fe has the undesirable effect that it lowers the temperature (A{sub p}) of the martensite {yields} austenite phase transformation. Fortunately, however, A can be raised by lowering the ``equivalent`` amount of Al in the alloy. In this way a high A{sub p} temperature of {approximately}190 C has been obtained without sacrificing ductility. Furthermore, a recoverable strain of 0.7% has been obtained in a Ni-Al-Fe alloy with A{sub p} temperature of {approximately}140 C. Iron additions do not suppress the aging-induced embrittlement that occurs in NiAl alloys at 300--500 C as a result of Ni{sub 5}Al{sub 3} precipitation. Manganese additions (up to 10 at.%) have the effect of lowering A{sub p}, degrading hot workability, and decreasing room-temperature ductility.

  7. Ferromagnetic interactions and martensitic transformation in Fe doped Ni-Mn-In shape memory alloys

    SciTech Connect

    Lobo, D. N.; Priolkar, K. R.; Emura, S.; Nigam, A. K.

    2014-11-14

    The structure, magnetic, and martensitic properties of Fe doped Ni-Mn-In magnetic shape memory alloys have been studied by differential scanning calorimetry, magnetization, resistivity, X-ray diffraction (XRD), and EXAFS. While Ni{sub 2}MnIn{sub 1−x}Fe{sub x} (0 ≤ x ≤ 0.6) alloys are ferromagnetic and non martensitic, the martensitic transformation temperature in Ni{sub 2}Mn{sub 1.5}In{sub 1−y}Fe{sub y} and Ni{sub 2}Mn{sub 1.6}In{sub 1−y}Fe{sub y} increases for lower Fe concentrations (y ≤ 0.05) before decreasing sharply for higher Fe concentrations. XRD analysis reveals presence of cubic and tetragonal structural phases in Ni{sub 2}MnIn{sub 1−x}Fe{sub x} at room temperature with tetragonal phase content increasing with Fe doping. Even though the local structure around Mn and Ni in these Fe doped alloys is similar to martensitic Mn rich Ni-Mn-In alloys, presence of ferromagnetic interactions and structural disorder induced by Fe affect Mn-Ni-Mn antiferromagnetic interactions resulting in suppression of martensitic transformation in these Fe doped alloys.

  8. In vitro investigation of NiTiW shape memory alloy as potential biomaterial with enhanced radiopacity.

    PubMed

    Li, Huafang; Cong, Ying; Zheng, Yufeng; Cui, Lishan

    2016-03-01

    In the present study, a novel kind of NiTiW shape memory alloy with chemical composition of Ni43.5Ti45.5W11 (at.%) has been successfully developed with excellent X-ray radiopacity by the introduction of pure W precipitates into the NiTi matrix phase. Its microstructure, X-ray radiopacity, mechanical properties, corrosion resistance in simulated body fluid, hemocompatibility and in vitro cytocompatibility were systematically investigated. The typical microstructural feature of NiTiW alloy at room temperature was tiny pure W particles randomly distributing in the NiTi matrix phase. The presence of W precipitates was found to result in enhanced radiopacity and microhardness of NiTiW alloy in comparison to that of NiTi binary alloy. NiTiW alloy exhibits excellent shape memory effect, and a maximum shape recovery ratio of about 30% was obtained with a total prestrain of 8% for the NiTiW alloy sample. In the electrochemical test, NiTiW alloy presented an excellent corrosion resistance in simulated body fluid, comparable to that of NiTi alloy. Hemocompatibility tests indicated that the NiTiW alloy has quite low hemolysis (lower than 0.5%) and the adherent platelet showed round shape without pseudopod. Besides, in vitro cell viability tests demonstrated that the cell viability is all above 90%, and the cells spread well on the NiTiW alloy, having polygon or spindle healthy morphology. The hemocompatibility tests, in vitro cell viability tests and morphology observation indicated that the NiTiW shape memory alloys have excellent biocompatibility. The excellent X-ray radiopacity makes the NiTiW alloys show obvious advantages in orthopedic, stomatological, neurological and cardiovascular domains where radiopacity is quite important factor in order to guarantee successful implantation. PMID:26706563

  9. In vitro investigation of NiTiW shape memory alloy as potential biomaterial with enhanced radiopacity.

    PubMed

    Li, Huafang; Cong, Ying; Zheng, Yufeng; Cui, Lishan

    2016-03-01

    In the present study, a novel kind of NiTiW shape memory alloy with chemical composition of Ni43.5Ti45.5W11 (at.%) has been successfully developed with excellent X-ray radiopacity by the introduction of pure W precipitates into the NiTi matrix phase. Its microstructure, X-ray radiopacity, mechanical properties, corrosion resistance in simulated body fluid, hemocompatibility and in vitro cytocompatibility were systematically investigated. The typical microstructural feature of NiTiW alloy at room temperature was tiny pure W particles randomly distributing in the NiTi matrix phase. The presence of W precipitates was found to result in enhanced radiopacity and microhardness of NiTiW alloy in comparison to that of NiTi binary alloy. NiTiW alloy exhibits excellent shape memory effect, and a maximum shape recovery ratio of about 30% was obtained with a total prestrain of 8% for the NiTiW alloy sample. In the electrochemical test, NiTiW alloy presented an excellent corrosion resistance in simulated body fluid, comparable to that of NiTi alloy. Hemocompatibility tests indicated that the NiTiW alloy has quite low hemolysis (lower than 0.5%) and the adherent platelet showed round shape without pseudopod. Besides, in vitro cell viability tests demonstrated that the cell viability is all above 90%, and the cells spread well on the NiTiW alloy, having polygon or spindle healthy morphology. The hemocompatibility tests, in vitro cell viability tests and morphology observation indicated that the NiTiW shape memory alloys have excellent biocompatibility. The excellent X-ray radiopacity makes the NiTiW alloys show obvious advantages in orthopedic, stomatological, neurological and cardiovascular domains where radiopacity is quite important factor in order to guarantee successful implantation.

  10. Experimental Studies on Dynamic Vibration Absorber using Shape Memory Alloy (NiTi) Springs

    SciTech Connect

    Kumar, V. Raj; Kumar, M. B. Bharathi Raj; Kumar, M. Senthil

    2011-10-20

    Shape memory alloy (SMA) springs have been used as actuators in many applications although their use in the vibration control area is very recent. Since shape memory alloys differ from conventional alloy materials in many ways, the traditional design approach for springs is not completely suitable for designing SMA springs. Some vibration control concepts utilizing unique characteristics of SMA's will be presented in this paper.A dynamic vibration absorber (DVA) using shape memory alloy (SMA) actuator is developed for attenuation of vibration in a cantilever beam. The design procedure of the DVA is presented. The system consists of a cantilever beam which is considered to generate the real-time vibration using shaker. A SMA spring is used with a mass attached to its end. The stiffness of the SMA spring is dynamically varied in such a way to attenuate the vibration. Both simulation and experimentation are carried out using PID controller. The experiments were carried out by interfacing the experimental setup with a computer using LabVIEW software, Data acquisition and control are implemented using a PCI data acquisition card. Standard PID controllers have been used to control the vibration of the beam. Experimental results are used to demonstrate the effectiveness of the controllers designed and the usefulness of the proposed test platform by exciting the structure at resonance. In experimental setup, an accelerometer is used to measure the vibration which is fed to computer and correspondingly the SMA spring is actuated to change its stiffness to control the vibration. The results obtained illustrate that the developed DVA using SMA actuator is very effective in reducing structural response and have great potential to be an active vibration control medium.

  11. Internal stress induced texture in Ni-Mn-Ga based glass-covered microwires

    NASA Astrophysics Data System (ADS)

    Rodionova, V.; Ilyn, M.; Granovsky, A.; Perov, N.; Zhukova, V.; Abrosimova, G.; Aronin, A.; Kiselev, A.; Zhukov, A.

    2013-09-01

    We have studied magnetic and structural properties of the composite microwires consisted of the metallic core and the outer glass shell. Nominal chemical composition of the core was Ni49.5Mn25.4Ga25.1, its diameter was 13.2 μm, and the total diameter of the glass-covered microwires was 26.4 μm. We have found out that at room temperature the core of the as-cast microwires was composed by two phases with tetragonal I4/mmm and cubic Fm3m crystal structures, but annealing rendered it single phase. Measurements of the magnetic properties have demonstrated substantial growth of the magnetic anisotropy with cooling, which we have attributed to the phase transition from the room-temperature austenitic to the low-temperature martensitic state. Magnetic easy axis was found to be perpendicular to the axis of the microwires at low temperatures. We believe that it is a result of the crystallographic texture induced in the martensite by high internal stress characteristic of the glass-covered magnetic microwires. Though rearrangement of the martensitic microstructure under external pressure was previously observed in the single crystal Ni2MnGa samples, in composite materials this effect is new and can be potentially useful for the applications.

  12. Strain characteristics and superelastic response of NiMnGa single crystals

    NASA Astrophysics Data System (ADS)

    Cui, Yuting; Wu, Liang; You, Suqin; Zhang, Jian; Wu, Zhenxing; Kong, Chunyang; Chen, Jinglan; Wu, Guangheng

    2009-10-01

    The intermartensitic transformation, in a two-step complete thermoelastic martensitic transformation in Ni 53.2Mn 22.6Ga 24.2 single crystals, provides a much larger strain than that of the martensitic transformation. With a biasing magnetic field, the intermartensitic transformation strain is inhibited and the martensitic transformation strain is enhanced. Compressive stress-strain characteristics can be affected greatly by a static magnetic field. At low deformation temperature, the irreversible transformation strain induced by the stress becomes reversible, when a static magnetic field is applied. Further, the magnitude of the stress necessary for rearrangement of martensitic variants is dependent on the direction of the biasing magnetic field. Moreover, a well-defined character of the twin-boundary motion, similar to the soliton motion, has been observed upon loading or unloading.

  13. Modelling of magneto-mechanical behaviour of Ni?Mn?Ga single crytals

    NASA Astrophysics Data System (ADS)

    Kiang, Jademond; Tong, Liyong

    2005-04-01

    Reviews on the various models to describe the quasi-static magnetic-field-induced strains available in the literature are summarised. Two constitutive models, namely the Three-Segment model and Single Segment Model, are formulated aimed at predicting the quasi-static cyclic magnetic-field-induced strain under zero and non-zero stress bias. These two models provide reasonable correlation with experiments available in the literature. Some of the advantages of these two models are that they are in constitutive format, with low-order terms (second order) and hence are readily usable in the modelling of magneto-mechanical coupling effects such as in Finite Element formulations. The parameters of these two models are derived from the magnetisation and mechanical stress-strain behaviour of the material, and hence are readily obtainable from simple magnetisation and mechanical stress-strain tests. The magnetic-field-induced strain is then transformed into different orientations in three-dimensional space using strain tensors, based on certain assumptions, in order to apprehend the theoretical possibilities of magnetic-field-induced strain combinations in this material. It was shown that by varying the orientation of the twin-boundaries of the material, vast combinations of axial and shear magnetic-field-induced strains can be realised. The potential applications of this material are thus broadened dramatically.

  14. Superelasticity by reversible variant reorientation in a Ni-Mn-Ga microwire with bamboo grains

    DOE PAGES

    Wang, Z. L.; Zheng, P.; Nie, Z. H.; Ren, Y.; Wang, Y. D.; Mullner, P.; Dunand, D. C.

    2015-08-26

    The link between microstructure and mechanical properties is investigated for a superelastic Ni–Mn–Ga microwire with 226 μm diameter, created by solidification via the Taylor method. The wire, which consists of bamboo grains with tetragonal martensite matrix and coarse γ precipitates, exhibits fully reversible superelastic behavior up to 4% tensile strain. Upon multiple tensile load–unload cycles, reproducible stress fluctuations of ~3 MPa are measured on the loading superelastic stress plateau of ~50 MPa. During cycles at various temperatures spanning -70 to 55 °C, the plateau stress decreases from 58 to 48 MPa near linearly with increasing temperature. Based on in situmore » synchrotron X-ray diffraction measurements, we conclude that this superelastic behavior is due to reversible martensite variants reorientation (i.e., reversible twinning) with lattice rotation of ~13°. The reproducible stress plateau fluctuations are assigned to reversible twinning at well-defined locations along the wire. The strain recovery during unloading is attributed to reverse twinning, driven by the internal stress generated on loading between the elastic γ precipitates and the twinning martensite matrix. Lastly, the temperature dependence of the twining stress on loading is related to the change in tetragonality of the martensite, as measured by X-ray diffraction.« less

  15. Superelasticity by reversible variant reorientation in a Ni-Mn-Ga microwire with bamboo grains

    SciTech Connect

    Wang, Z. L.; Zheng, P.; Nie, Z. H.; Ren, Y.; Wang, Y. D.; Mullner, P.; Dunand, D. C.

    2015-08-26

    The link between microstructure and mechanical properties is investigated for a superelastic Ni–Mn–Ga microwire with 226 μm diameter, created by solidification via the Taylor method. The wire, which consists of bamboo grains with tetragonal martensite matrix and coarse γ precipitates, exhibits fully reversible superelastic behavior up to 4% tensile strain. Upon multiple tensile load–unload cycles, reproducible stress fluctuations of ~3 MPa are measured on the loading superelastic stress plateau of ~50 MPa. During cycles at various temperatures spanning -70 to 55 °C, the plateau stress decreases from 58 to 48 MPa near linearly with increasing temperature. Based on in situ synchrotron X-ray diffraction measurements, we conclude that this superelastic behavior is due to reversible martensite variants reorientation (i.e., reversible twinning) with lattice rotation of ~13°. The reproducible stress plateau fluctuations are assigned to reversible twinning at well-defined locations along the wire. The strain recovery during unloading is attributed to reverse twinning, driven by the internal stress generated on loading between the elastic γ precipitates and the twinning martensite matrix. Lastly, the temperature dependence of the twining stress on loading is related to the change in tetragonality of the martensite, as measured by X-ray diffraction.

  16. Reversible surface morphology in shape-memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Wu, M. J.; Huang, W. M.; Fu, Y. Q.; Chollet, F.; Hu, Y. Y.; Cai, M.

    2009-02-01

    Reversible surface morphology can be used for significantly changing many surface properties such as roughness, friction, reflection, surface tension, etc. However, it is not easy to realize atop metals at micron scale around ambient temperature. In this paper, we demonstrate that TiNi and TiNi based (e.g., TiNiCu) shape-memory thin films, which are sputter-deposited atop a silicon wafer, may have different types of thermally-induced reversible surface morphologies. Apart from the well-known surface relief phenomenon, irregular surface trenches may appear in the fully crystallized thin films, but disappear upon heating. On the other hand, in partially crystallized thin films, the crystalline structures (islands) appear in chrysanthemum-shape at high temperature; while at room temperature, the surface morphology within the islands changes to standard martensite striations. Both phenomena are fully repeatable upon thermal cycling. The mechanisms behind these phenomena are investigated.

  17. Smart wing shape memory alloy actuator design and performance

    NASA Astrophysics Data System (ADS)

    Jardine, A. Peter; Flanagan, John S.; Martin, Christopher A.; Carpenter, Bernie F.

    1997-05-01

    Shape Memory Effect TiNi torque tubes were fabricated, tested and installed to supply 2500 in.lbs and 500 in.lbs of torque for inboard and outboard sections, respectively, of the DARPA smart wing wind tunnel model. Structural connections to the tubes were designed so that the entire assembly would fit within the interior of the wing, whose maximum dimensions of depth ranged from 1.125' to 0.375', depending on the position along the wing span. The torque tubes themselves were made by the gun drilling a TiNi ingot and ElectroSpark Discharge Machining to the required dimensions, which were calculated from a simple model described in a previous paper. The torque tubes were placed into the wing and twist deflections were measured. Deflections on the wing were measured at 1.3 degree(s), which provided a significant increase (approximately 8%) in the wing rolling moment.

  18. Degradation of the shape memory effect in copper-base alloys

    SciTech Connect

    Stalmans, R.; Van Humbeeck, J.; Delaey, L. . Dept. of Metallurgy and Materials Science)

    1994-12-01

    The reversible transformation of the parent phase (austenite) to the product phase (martensite) is the basis of several shape memory properties in specific Cu-base alloys. In this respect, the two-way memory effect (TWME) refers the reversible, spontaneous shape change from a hot austenitic shape to a cold martensitic shape during cooling and heating without the application of external stresses. It is known that the magnitude of the TWME decrease during thermal or thermomechanical cycling, in particular in Cu-base shape memory alloys. It is however important to remark that this decrease, indicated as degradation of the TWME, can be caused as well by a decrease of the spontaneous martensitic strain, i.e. a degradation of the cold shape, as by an increase of the residual austenitic strain, i.e. a degradation of the hot shape, or by a combination of both. The degradation of the TWME, and of the hot and cold shape is influenced by a number of factors including the alloy composition, the processing, the heat treatment, the training procedure and the parameters of the thermal or thermomechanical cycling. The knowledge of the degradation phenomena is still limited. In a subsequent study of the relationships between training and the two-way memory behavior, the authors have shown that the degradation of the hot shape already starts during training. It was found that the residual austenitic strain [gamma][sub a] increases gradually during training cycling; [gamma][sub a] is also in the case of training composed of a recoverable residual strain [gamma][sub ar] and a non-recoverable residual strain [gamma][sub anr]. The present paper reports the results of the specific experiments which were designed based upon the results described above. The evolutions during thermal cycling of the TWME, of the martensitic strain and austenitic strain, and of the recoverable and non-recoverable austenitic strain are presented and discussed.

  19. Stability and optimization of P-phase precipitates in nickel-titanium-palladium shape memory alloys

    NASA Astrophysics Data System (ADS)

    Coppa, Anne Catherine

    The motivation for this research is the understanding of phase transformations that lead to an increase in the shape memory effect (SME) transformation temperature in a Ni-Ti-Pd shape memory alloy (SMA). The research addressed three major parts of this transformation---(1) The phase stability of the P-phase precipitate previously discovered with an emphasis on its stoichiometric limits by changing the Ni and Pd content with the Ti11(Ni,Pd)13 ratio; (2) The effects of P-phase precipitation on the martensitic transformation temperature in near-equiatomic Ti(Ni,Pd) alloys; and (3) The effects of dilute additions of Hf (0.1-1 at.%) to the precipitation and shape memory transformation temperature in Ni-Ti-Pd. P-phase stabilization: The compositional limits of the P-phase have been systematically studied by varying the Pd and Ni content in the P-phase's Ti11(Ni+Pd)13 stoichiometry. Each alloy was solutionized at 1050°C followed by water quenching, and aging at 400°C for 100 hours. Four distinct phases were identified---Ti 2Pd3, B2 Ni-Ti, P- and P1-phases dependent on alloy composition---by electron and x-ray diffraction. The latter precipitate phases become more stable with increasing Ni at the expense of Pd content. Atom probe tomography revealed the P-phase composition to be 45.8Ti-29.2Ni-25Pd (at.%) or Ti 11(Ni7Pd6) as compared to the P1-phase 44.7Ti- 45.8Ni-9.4Pd (at.%) or Ti5Ni5Pd. Optimization of P-phase precipitation: The effect of aging time and temperature on precipitation and subsequent martensitic transformation temperatures for a series of Ni-(50.5-49.2)Ti-32Pd (at.%) shape memory alloys has been studied. Structure-property relationships were developed through detailed microstructural characterization involving transmission electron microscopy, diffraction analysis, and atom probe tomography with links to microhardness measurements and transformation temperatures established by differential scanning calorimetry. The Ti-rich alloy contained relatively coarse

  20. A candidate Zr-doped Sb2Te alloy for phase change memory application

    NASA Astrophysics Data System (ADS)

    Zheng, Yonghui; Cheng, Yan; Zhu, Min; Ji, Xinglong; Wang, Qing; Song, Sannian; Song, Zhitang; Liu, Weili; Feng, Songlin

    2016-02-01

    Here, Zr-doped Sb2Te alloy is proposed for phase change memory (PCM). Zr-doping enhances the crystallization temperature and thermal stability of Sb2Te alloy effectively. Crystalline Zr2(Sb2Te)98 film is manifested as a single phase without phase separation and the growth of crystal grain is dramatically suppressed. The density change of Zr2(Sb2Te)98 material between amorphous and crystalline is ˜2.65 ± 0.03%, which is much smaller than that of Ge2Sb2Te5 (6.5%). Phase change memory cells based on Zr2(Sb2Te)98 material can be reversibly switched by applying 40-400 ns width voltage pulses, and the reset current is relatively small when comparing with the prototypical Ge2Sb2Sb5 material. The resistance ON-OFF ratio of about 1.3 orders of magnitude is enough for figuring "0" and "1" out. Besides, endurance up to 4.1 × 104 cycles makes Zr-doped Sb2Te alloy a potential candidate for PCM.

  1. Thermodynamic constitutive model for load-biased thermal cycling test of shape memory alloy

    SciTech Connect

    Young, Sung; Nam, Tae-Hyun

    2013-12-15

    Graphical abstract: - Highlights: • Thermodynamic calculation model for martensitic transformation of shape memory alloy was proposed. • Evolution of the self-accommodation was considered independently by a rate-dependent kinetic equation. • Finite element calculation was conducted for B2–B19′ transformation of Ti–44.5Ni–5Cu–0.5 V (at.%). • Three-dimensional numerical results predict the macroscopic strain under bias loading accurately. - Abstract: This paper presents a three-dimensional calculation model for martensitic phase transformation of shape memory alloy. Constitutive model based on thermodynamic theory was provided. The average behavior was accounted for by considering the volume fraction of each martensitic variant in the material. Evolution of the volume fraction of each variant was determined by a rate-dependent kinetic equation. We assumed that nucleation rate is faster for the self-accommodation than for the stress-induced variants. Three-dimensional finite element analysis was conducted and the results were compared with the experimental data of Ti–44.5Ni–5Cu–0.5 V (at.%) alloy under bias loading.

  2. Smart Material Demonstrators Based on Shape Memory Alloys and Electroceramics

    NASA Technical Reports Server (NTRS)

    Cooke, Arther V.

    1996-01-01

    This paper describes the development and characterization of two technology demonstrators that were produced under the auspices of an ARPA sponsored smart materials synthesis and processing effort. The ARPA Smart Materials and Synthesis (SMS) Program was a 2 year, $10M partnership led by Martin Marietta Laboratories - Baltimore and included Lockheed Missiles & Space Co., NRL, AVX Corp., Martin Marietta Astronautics Groups, BDM Federal, Inc., Virginia Tech, Clemson, University of Maryland, Denver University, and The Johns Hopkins University. In order to demonstrate the usefulness of magnetron sputtered shape memory foil and the manufacturability of reliable, reproducible electrostrictive actuators, the team designed a broadband active vibration cancellation device for suppressing the vibration load on delicate instruments and precision pointing devices mounted on orbiting satellites and spacecraft. The results of extensive device characterization and bench testing are discussed. Initial simulation results show excellent control authority and amplitude attenuation over the range of anticipated disturbance frequencies. The SMS Team has also developed an active 1-3 composite comprising micro-electrostrictive actuators embedded in a polymeric matrix suitable for underwater applications such as sonar quieting and listening arrays, and for medical imaging. Follow-on programs employing these technologies are also described.

  3. Parametric analysis of a shape memory alloy actuated arm

    NASA Astrophysics Data System (ADS)

    Wright, Cody; Bilgen, Onur

    2016-04-01

    Using a pair of antagonistic Shape Memory Allow (SMA) wires, it may be possible to produce a mechanism that replicates human musculoskeletal movement. The movement of interest is the articulation of the elbow joint actuated by the biceps brachii muscle. In an effort to understand the bio-mechanics of the arm, a single degree of freedom crankslider mechanism is used to model the movement of the arm induced by the biceps brachii muscle. First, a purely kinematical analysis is performed on a rigid body crank-slider. Force analysis is also done modeling the muscle as a simple linear spring. Torque, rocking angle, and energy are calculated for a range of crank-slider geometries. The SMA wire characteristics are experimentally determined for the martensite detwinned and full austenite phases. Using the experimental data, an idealized actuator characteristic curve is produced for the SMA wire. Kinematic and force analyses are performed on the nonlinear wire characteristic curve and a linearized wire curve; both cases are applied to the crankslider mechanism. Performance metrics for both cases are compared, followed by discussion.

  4. Influence of Tin Additions on the Phase-Transformation Characteristics of Mechanical Alloyed Cu-Al-Ni Shape-Memory Alloy

    NASA Astrophysics Data System (ADS)

    Saud, Safaa N.; Hamzah, E.; Abubakar, T.; Bakhsheshi-Rad, H. R.; Mohammed, M. N.

    2016-07-01

    The influence of the addition of Sn to Cu-Al-Ni alloy as a fourth element with different percentages of 0.5, 1.0, and 1.5 wt pct on the microstructure, phase-transformation temperatures, mechanical properties, and corrosion behaviors was investigated. The modified and unmodified alloys were fabricated by mechanical alloying followed by microwave sintering. The sintered and homogenized alloys of Cu-Al-Ni-xSn shape-memory alloys had a refined particle structure with an average particle size of 40 to 50 µm associated with an improvement in the mechanical properties and corrosion resistance. With the addition of Sn, the porosity density tends to decrease, which can also lead to improvements in the properties of the modified alloys. The minimum porosity percentage was observed in the Cu-Al-Ni-1.0 wt pct Sn alloy, which resulted in enhancing the ductility, strain recovery, and corrosion resistance. Further increasing the Sn addition to 1.5 wt pct, the strength of the alloy increased because the highest volume fraction of precipitates was formed. Regarding the corrosion behavior, addition of Sn up to 1 wt pct increased the corrosion resistance of the base SMA from 2.97 to 19.20 kΩ cm2 because of formation of a protective film that contains hydrated tin oxyhydroxide, aluminum dihydroxychloride, and copper chloride on the alloy. However, further addition of Sn reduced the corrosion resistance.

  5. Influence of Tin Additions on the Phase-Transformation Characteristics of Mechanical Alloyed Cu-Al-Ni Shape-Memory Alloy

    NASA Astrophysics Data System (ADS)

    Saud, Safaa N.; Hamzah, E.; Abubakar, T.; Bakhsheshi-Rad, H. R.; Mohammed, M. N.

    2016-10-01

    The influence of the addition of Sn to Cu-Al-Ni alloy as a fourth element with different percentages of 0.5, 1.0, and 1.5 wt pct on the microstructure, phase-transformation temperatures, mechanical properties, and corrosion behaviors was investigated. The modified and unmodified alloys were fabricated by mechanical alloying followed by microwave sintering. The sintered and homogenized alloys of Cu-Al-Ni- xSn shape-memory alloys had a refined particle structure with an average particle size of 40 to 50 µm associated with an improvement in the mechanical properties and corrosion resistance. With the addition of Sn, the porosity density tends to decrease, which can also lead to improvements in the properties of the modified alloys. The minimum porosity percentage was observed in the Cu-Al-Ni-1.0 wt pct Sn alloy, which resulted in enhancing the ductility, strain recovery, and corrosion resistance. Further increasing the Sn addition to 1.5 wt pct, the strength of the alloy increased because the highest volume fraction of precipitates was formed. Regarding the corrosion behavior, addition of Sn up to 1 wt pct increased the corrosion resistance of the base SMA from 2.97 to 19.20 kΩ cm2 because of formation of a protective film that contains hydrated tin oxyhydroxide, aluminum dihydroxychloride, and copper chloride on the alloy. However, further addition of Sn reduced the corrosion resistance.

  6. Effect of Quarterly Element Addition of Cobalt on Phase Transformation Characteristics of Cu-Al-Ni Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Saud, Safaa Najah; Abu Bakar, Tuty Asma; Hamzah, Esah; Ibrahim, Mustafa Khaleel; Bahador, Abollah

    2015-08-01

    In the current study, a new type of Cu-based shape memory alloys with the function of shape memory effect was successfully produced with the introduction of high-purity Co precipitates between the phases of Cu-Al-Ni shape memory alloy. The microstructure, transformation characteristics, and mechanical properties were systematically investigated by means of differential scanning calorimetry, field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy, X-ray diffraction (XRD), a tensile test, a hardness test, and a shape memory effect test. The typical microstructures show that a new phase was formed, known as the γ 2 phase, and the volume friction and the size of this phase were gradually increased with the increasing Co content. According to the results of the XRD and EDS, it was confirmed that the γ 2 phase represents a compound of Al75Co22Ni3. However, the presence of γ 2 phase in the modified alloys was found to result in an increase of the transformation temperatures in comparison with the unmodified alloy. Nevertheless, it was found that with 1 wt pct of Co addition, a maximum ductility of 7 pct was achieved, corresponding to an increase in the strain recovery by the shape memory effect to 95 pct with respect to the unmodified alloy of 50 pct.

  7. NiTiCu Shape Memory Alloy Characterization Through Microhardness Tests

    NASA Astrophysics Data System (ADS)

    Fabregat-Sanjuan, Albert; Ferrando, Francesc; De la Flor, Silvia

    2014-07-01

    NiTiCu alloys are one of the most investigated shape memory alloys (SMAs) because of their better performance as SMA actuators in a variety of industrial and engineering applications. However, NiTiCu alloys are strongly influenced by thermomechanical cycling (TMC), which causes degradation depending on the stress and strain level applied. Since heat treatment (HT) and TMC are essential for NiTiCu alloys, understanding how hardness evolves at different levels of TMC and different HT temperatures is a useful tool for characterizing the material. The aim of this paper is to investigate the relationship between hardness and different HT temperatures and different TMCs. All the microhardness tests were done below martensite finish temperature (Mf) because the apparent material hardness measured below Mf fairly reflects the relative strengthening of SMAs without involving martensitic transformation artifacts. Resistivity and break tensile tests were carried out as a first step in order to understand the effect of different HT temperatures. Microstructure was also examined to provide a basis for a mechanistic understanding of the effect of different HT temperatures. Next, the degradation of mechanical properties (functional fatigue) at different levels of TMC was evaluated to assess their relationship to the evolution of hardness. Finally, an attempt was made to establish a link between the increase in hardness and different HT temperatures with different levels of TMC.

  8. Magnetocaloric effect and its relation to shape-memory properties in ferromagnetic Heusler alloys.

    PubMed

    Planes, Antoni; Mañosa, Lluís; Acet, Mehmet

    2009-06-10

    Magnetic Heusler alloys which undergo a martensitic transition display interesting functional properties. In the present review, we survey the magnetocaloric effects of Ni-Mn-based Heusler alloys and discuss their relation with the magnetic shape-memory and magnetic superelasticity reported in these materials. We show that all these effects are a consequence of a strong coupling between structure and magnetism which enables a magnetic field to rearrange martensitic variants as well as to provide the possibility to induce the martensitic transition. These two features are respectively controlled by the magnetic anisotropy of the martensitic phase and by the difference in magnetic moments between the structural phases. The relevance of each of these contributions to the magnetocaloric properties is analysed.

  9. Improving the bioactivity of NiTi shape memory alloy by heat and alkali treatment

    NASA Astrophysics Data System (ADS)

    Qiang, Wei; Zhen-duo, Cui; Xian-jin, Yang; Jie, Shi

    2008-11-01

    TiO 2 films were formed on an NiTi alloy surface by heat treatment in air at 600 °C. Heat treated NiTi shape memory alloys were subsequently alkali treated with 1 M, 3 M and 5 M NaOH solutions respectively, to improve their bioactivity. Then treated NiTi samples were soaked in 1.5SBF to evaluate their in vitro performance. The results showed that the 3 M NaOH treatment is the most appropriate method. A large amount of apatite formed within 1 day's soaking in 1.5SBF, after 7 day's soaking TiO 2/HA composite layer formed on the NiTi surface. SEM, XRD, FT-IR and TEM results showed that the morphology and microstructure are similar to the human bone apatite.

  10. Combinatorial search of thermoelastic shape-memory alloys with extremely small hysteresis width.

    PubMed

    Cui, Jun; Chu, Yong S; Famodu, Olugbenga O; Furuya, Yasubumi; Hattrick-Simpers, Jae; James, Richard D; Ludwig, Alfred; Thienhaus, Sigurd; Wuttig, Manfred; Zhang, Zhiyong; Takeuchi, Ichiro

    2006-04-01

    Reversibility of structural phase transformations has profound technological implications in a wide range of applications from fatigue life in shape-memory alloys (SMAs) to magnetism in multiferroic oxides. The geometric nonlinear theory of martensite universally applicable to all structural transitions has been developed. It predicts the reversibility of the transitions as manifested in the hysteresis behaviour based solely on crystal symmetry and geometric compatibilities between phases. In this article, we report on the verification of the theory using the high-throughput approach. The thin-film composition-spread technique was devised to rapidly map the lattice parameters and the thermal hysteresis of ternary alloy systems. A clear relationship between the hysteresis and the middle eigenvalue of the transformation stretch tensor as predicted by the theory was observed for the first time. We have also identified a new composition region of titanium-rich SMAs with potential for improved control of SMA properties.

  11. Sign reversal of transformation entropy change in Co2Cr(Ga,Si) shape memory alloys

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Omori, Toshihiro; Nagasako, Makoto; Kanomata, Takeshi; Kainuma, Ryosuke

    2015-11-01

    In situ X-ray diffraction (XRD) measurements and compression tests were performed on Co2Cr(Ga,Si) shape memory alloys. The reentrant martensitic transformation behavior was directly observed during the in situ XRD measurements. The high-temperature parent phase and low-temperature reentrant parent phase were found to have a continuous temperature dependence of lattice parameter, therefore suggesting that they are the same phase in nature. Moreover, compression tests were performed on a parent-phase single crystal sample; an evolution from normal to inverse temperature dependence of critical stress for martensitic transformation was directly observed. Based on the Clausius-Clapeyron analysis, a sign reversal of entropy change can be expected on the same alloy.

  12. Histomorphometric analysis of the response of rat tibiae to shape memory alloy (nitinol).

    PubMed

    Takeshita, F; Takata, H; Ayukawa, Y; Suetsugu, T

    1997-01-01

    The bone reaction to nitinol (Ni-Ti), a metal with shape memory, and other materials inserted transcortically and extending into the medullary canal of rat tibiae was quantitatively assessed using an image processing system. The materials examined were implants, all of the same shape and size, composed of nitinol, pure titanium (Ti), anodic oxidized Ti (AO-Ti), a titanium alloy (Ti-6Al-4V) and pure nickel (Ni). While the other four implant materials were progressively encapsulated with bone tissues, Ni was encapsulated with connective tissues through the 168-day experimental period, and the Ni implants showed no bone contact at any time during the experimental period. Histometric analysis revealed no significant difference among the tissue reactions to Ti, AO-Ti and Ti-6Al-4V, but Ni-Ti implants showed significantly (P < 0.01) lower percentage bone contact and bone contact area than any of the other titanium or titanium alloy materials.

  13. Temperature dependence of magnetic susceptibility in the vicinity of martensitic transformation in ferromagnetic shape memory alloys.

    PubMed

    Zablotskii, V; Pérez-Landazábal, J I; Recarte, V; Gómez-Polo, C

    2010-08-11

    Temperature dependences of low-field quasistatic magnetic susceptibility in the vicinity of martensitic transitions in an NiFeGa alloy are studied both by experiment and analytically. Pronounced reversible jumps of the magnetic susceptibility were observed near the martensitic transition temperature. A general description of the temperature dependences of the susceptibility in ferromagnetic austenite and martensite phases and the susceptibility jump at the transition is suggested. As a result, the main factors governing the temperature dependences of the magnetic susceptibility in the magnetic shape memory alloys are revealed. The magnetic susceptibility jump value is found to be related to changes of: (i) magnetic anisotropy; (ii) magnetic domain wall geometrical constraints (those determined by the alignment and size of twin variants) and (iii) mean magnetic domain spacing.

  14. Magnetic ordering in magnetic shape memory alloy Ni-Mn-In-Co

    NASA Astrophysics Data System (ADS)

    Ollefs, K.; Schöppner, Ch.; Titov, I.; Meckenstock, R.; Wilhelm, F.; Rogalev, A.; Liu, J.; Gutfleisch, O.; Farle, M.; Wende, H.; Acet, M.

    2015-12-01

    Structural and magnetic properties across the martensite-austenite phase transitions in the shape memory alloy Ni-Mn-In-Co are studied using complementary experimental techniques: ferromagnetic resonance, macroscopic magnetization measurements, and x-ray magnetic circular dichroism in the temperature range from 5 to 450 K. Ferromagnetic resonance experiments show coexisting antiferromagnetic and ferromagnetic correlations for the martensite phase and ferromagnetic and paramagnetic correlations in the austenite phase. Magnetization measurements reveal spin-glass-like behavior for T <30 K and Ni and Co K -edge x-ray magnetic circular dichroism measurements confirm an assignment of a ferromagnetic resonance line purely to Ni (and Co) for a wide temperature range from 125 to 225 K. Hence a combined analysis of ferromagnetic resonance and x-ray magnetic circular dichroism allows us to attribute particular magnetic resonance signals to individual elemental species in the alloy.

  15. Magnetic-field-induced strain in Ni2MnGa shape-memory alloy (abstract)

    NASA Astrophysics Data System (ADS)

    Ullakko, K.; Huang, J. K.; Kanter, C.; Kokorin, V. V.; O'Handley, R. C.

    1997-04-01

    Rare-earth/transition-metal alloys can exhibit magnetostrictive strains of order 0.17% in modest fields. Larger strains are of interest for many actuator applications. Certain alloys that undergo martensitic transformations exhibit a shape-memory effect that can yield strains up to 20% upon heating the deformed martensitic phase and they can show superelasticity upon application of a small stress. These methods of activation can be a disadvantage for many applications; magnetic activation of a shape-memory effect is desired. Several magnetic shape-memory alloys exist, among them intermetallics based on Ni2MnGa, which are the subject of this work. These materials experience a 6.6% c-axis contraction on cooling through the martensitic transition temperature, which is near 273 K; this strain is accommodated by formation of an ensemble of strained twin crystals separated by twin boundaries. Strains of several percent could be produced magnetically if the twin boundaries could be moved under application of a magnetic field. We report observations of strains of nearly 0.2% induced along [001] in unstressed crystals of Ni2MnGa with magnetic fields of 8 kOe applied at 265 K (Fig. 1). (This strain is an order of magnitude larger than the magnetostrictive strain we measure in the parent Heusler phase at 283 K.) Our data suggest that these giant strains are associated with the superelastic motion of twin boundaries in the martensitic phase, which is stable below about 274 K; the strength of the measured anisotropy energy density, MSHa/2 is comparable to the elastic energy density, eσ/2, needed for superelastic twin boundary motion.1 The strains we observe are equivalent to those achieved in terfenol-D and represent only a small fraction of the strain available if the twin variants of the martensitic phase can be oriented prior to application of a field.

  16. Shape memory properties and microstructural evolution of rapidly solidified CuAlBe alloys

    SciTech Connect

    Ergen, Semra; Uzun, Orhan; Yilmaz, Fikret; Kiliçaslan, M. Fatih

    2013-06-15

    In this work, the effects of Be addition on the microstructure and phase transformation temperatures of Cu–12Al–xBe (x = 0.4, 0.5 and 0.6 wt.%) shape memory alloys fabricated by using the arc-melting and melt-spinning techniques have been investigated. X-ray diffraction analysis revealed that the arc-melted alloys consisted of austenitic β{sub 1}, martensitic β{sub 1}′ and γ{sub 2} precipitate phases, whereas melt-spun ribbons were composed of a fully martensitic phase. The average grain size of martensitic phases in melt-spun ribbons was determined by electron microscopy images, showing a decrease with increasing Beryllium (Be) amount. Moreover, it was found that the Be addition in the arc-melted alloys had a distinct effect on the morphology of the γ{sub 2} precipitate phase. Transmission electron microscopy analysis showed that the thickness of martensitic plates in the melt-spun ribbons reduced with increasing Be addition. In a differential scanning calorimeter analysis, no martensitic transformation (M{sub s}) peak was observed in arc-melted alloys, but it was clearly detected in melt-spun ribbons, in which M{sub s} decreased dramatically with increasing Be addition. The improvement in the shape memory ability of melt-spun ribbons was explained in terms of the refinement in grain size and martensitic plates. - Highlights: • The CuAlBe SMAs were produced by means of arc-melter and melt-spinner techniques. • MT was directly obtained in melt-spuns without any intermediate process. • The transformation temperatures decreased with increasing Be amount. • The thickness of martensitic plates in the ribbons reduced with increasing Be. • SMP of CuAl was improved by the addition of Be together with rapid solidification.

  17. Effects of interface treatment on the fatigue behaviour of shape memory alloy reinforced polymer composites

    NASA Astrophysics Data System (ADS)

    Hiremath, S. R.; Harish, K.; Vasireddi, Ramakrishna; Benal, M. M.; Mahapatra, D. R.

    2015-04-01

    Interfacial properties of Shape Memory Alloy (SMA) reinforced polymer matrix composites can be enhanced by improving the interfacial bonding. This paper focuses on studying the interfacial stresses developed in the SMAepoxy interface due to various laser shot penning conditions. Fiber-pull test-setup is designed to understand the role of mechanical bias stress cycling and thermal actuation cycling. Phase transformation is tracked over mechanical and thermal fatigue cycles. A micromechanics based model developed earlier based on shear lag in SMA and energy based consistent homogenization is extended here to incorporate the stress-temperature phase diagram parameters for modeling fatigue.

  18. A condensed variational model for thermo-mechanically coupled phase transformations in polycrystalline shape memory alloys

    NASA Astrophysics Data System (ADS)

    Junker, Philipp; Hackl, Klaus

    2013-11-01

    We derive an energy-based material model for thermomechanically coupled phase transformations in polycrystalline shape memory alloys. For the variational formulation of the model, we use the principle of the minimum of the dissipation potential for nonisothermal processes for which only a minimal number of constitutive assumptions has to be made. By introducing a condensed formulation for the representative orientation distribution function, the resulting material model is numerically highly efficient. For a first analysis, we present the results of material point calculations, where the evolution of temperature as well as its influence on the mechanical material response is investigated.

  19. Variable area nozzle for gas turbine engines driven by shape memory alloy actuators

    NASA Technical Reports Server (NTRS)

    Rey, Nancy M. (Inventor); Miller, Robin M. (Inventor); Tillman, Thomas G. (Inventor); Rukus, Robert M. (Inventor); Kettle, John L. (Inventor); Dunphy, James R. (Inventor); Chaudhry, Zaffir A. (Inventor); Pearson, David D. (Inventor); Dreitlein, Kenneth C. (Inventor); Loffredo, Constantino V. (Inventor)

    2001-01-01

    A gas turbine engine includes a variable area nozzle having a plurality of flaps. The flaps are actuated by a plurality of actuating mechanisms driven by shape memory alloy (SMA) actuators to vary fan exist nozzle area. The SMA actuator has a deformed shape in its martensitic state and a parent shape in its austenitic state. The SMA actuator is heated to transform from martensitic state to austenitic state generating a force output to actuate the flaps. The variable area nozzle also includes a plurality of return mechanisms deforming the SMA actuator when the SMA actuator is in its martensitic state.

  20. Development of a shape memory alloy actuator for transanal endoscopic microsurgery.

    PubMed

    Wang, Zhigang; Hewit, Jim; Abel, Eric; Slade, Alan; Steele, Bob

    2005-01-01

    This paper describes problems in traditional transanal endoscopic microsurgery (TEM), and proposes a mechatronics approach in new design. As one of several actuation mechanisms to expose rectal cavity, a compression coil spring made of shape memory alloy (SMA) has been studied. A custom SMA spring actuator was designed to displace 12 mm with 45 N driving force. This actuator was embedded with our new TEM tubular structure and can be used to expose a rectal site up to 60 mm wide and 80 mm long. This exposure is considered to be sufficient for treating many tumors.

  1. Mobile Interfacial Microstructures in Single Crystals of Cu-Al-Ni Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Seiner, Hanuš

    2015-06-01

    This paper summarizes the main properties of the microstructures formed during reverse (austenite → martensite) transitions in single crystals of the Cu-Al-Ni shape memory alloy, and discusses the relation between these properties and the mechanical stabilization effect. It is shown that all experimentally observed interfacial microstructures ( X- and λ-interfaces and their non-classical equivalents) are not local minimizers of the quasi-static energy, and their formation is probably governed by requirements on mobility and dissipation. This conclusion is supported by finite elements models, and acoustic emission measurements.

  2. Thermodynamics of shape memory alloy wire: Modeling, experimental calibration, and simulation

    NASA Astrophysics Data System (ADS)

    Chang, Bi-Chiau

    A thermomechanical model for a shape memory alloy (SMA) wire under uniaxial loading is implemented in a finite element framework, and simulation results are compared with mechanical and infrared experimental data. The constitutive model is a one-dimensional strain-gradient continuum model of an SMA wire element, including two internal field variables, possible unstable mechanical behavior, and the relevant thermomechanical couplings resulting from latent heat effects. The model is calibrated to recent and new experiments of typical commercially available polycrystalline NiTi wire. The shape memory effect and pseudoelastic behaviors are demonstrated numerically as a function of applied displacement rate and environmental parameters, and the results compare favorably to experimental data. The model is then used to simulate a simple SMA actuator device, and its performance is assessed for different thermal boundary conditions.

  3. Low-cycle fatigue of TiNi shape memory alloy and formulation of fatigue life

    SciTech Connect

    Tobushi, Hisaaki; Nakahara, Takafumi; Shimeno, Yoshirou; Hashimoto, Takahiro

    2000-04-01

    The low-cycle fatigue of a TiNi shape memory alloy was investigated by the rotating-bending fatigue tests in air, in water and in silicone oil. (1) The influence of corrosion fatigue in water does not appear in the region of low-cycle fatigue. (2) The temperature rise measured through an infrared thermograph during the fatigue test in air is four times as large as that measured through a thermocouple. (3) The fatigue life at an elevated temperature in air coincides with the fatigue life at the same elevated temperature in water. (4) The shape memory processing temperature does not affect the fatigue life. (5) The fatigue equation is proposed to describe the fatigue life depending on strain amplitude, temperature and frequency. The fatigue life is estimated well by the proposed equation.

  4. Thermomechanical characterization of nickel-titanium-copper shape memory alloy films

    SciTech Connect

    Seward, K P; Ramsey, P B; Krulevitch, P

    2000-10-31

    In an effort to develop a more extensive model for the thermomechanical behavior of shape memory alloy (SMA) films, a novel characterization method has been developed. This automated test has been tailored to characterize films for use in micro-electromechanical system (MEMS) actuators. The shape memory effect in NiTiCu is seen in the solid-state phase transformation from an easily deformable low-temperature state to a 'shape remembering' high-temperature state. The accurate determination of engineering properties for these films necessitates measurements of both stress and strain in microfabricated test structures over the full range of desired deformation. Our various experimental methods (uniaxial tensile tests, bimorph curvature tests and diaphragm bulge tests) provide recoverable stress and strain data and the stress-strain relations for these films. Tests were performed over a range of temperatures by resistive heating or ambient heating. These measurements provide the results necessary for developing active SMA structural film design models.

  5. Effects of Palladium Content, Quaternary Alloying, and Thermomechanical Processing on the Behavior of Ni-Ti-Pd Shape Memory Alloys for Actuator Applications

    NASA Technical Reports Server (NTRS)

    Bigelow, Glen

    2008-01-01

    The need for compact, solid-state actuation systems for use in the aerospace, automotive, and other transportation industries is currently driving research in high-temperature shape memory alloys (HTSMA) having transformation temperatures above 100 C. One of the basic high temperature systems under investigation to fill this need is NiTiPd. Prior work on this alloy system has focused on phase transformations and respective temperatures, no-load shape memory behavior (strain recovery), and tensile behavior for selected alloys. In addition, a few tests have been done to determine the effect of boron additions and thermomechanical treatment on the aforementioned properties. The main properties that affect the performance of a solid state actuator, namely work output, transformation strain, and permanent deformation during thermal cycling under load have mainly been neglected. There is also no consistent data representing the mechanical behavior of this alloy system over a broad range of compositions. For this thesis, ternary NiTiPd alloys containing 15 to 46 at.% palladium were processed and the transformation temperatures, basic tensile properties, and work characteristics determined. However, testing reveals that at higher levels of alloying addition, the benefit of increased transformation temperature begins to be offset by lowered work output and permanent deformation or "walking" of the alloy during thermal cycling under load. In response to this dilemma, NiTiPd alloys have been further alloyed with gold, platinum, and hafnium additions to solid solution strengthen the martensite and parent austenite phases in order to improve the thermomechanical behavior of these materials. The tensile properties, work behavior, and dimensional stability during repeated thermal cycling under load for the ternary and quaternary alloys were compared and discussed. In addition, the benefits of more advanced thermomechanical processing or training on the dimensional stability of

  6. Aging effects in a Cu-12Al-5Ni-2Mn-1Ti shape memory alloy

    SciTech Connect

    Wei, Z.G.; Peng, H.Y.; Yang, D.Z.; Zou, W.H.

    1997-04-01

    The isothermal aging effects in an as-quenched Cu-11.88Al-5.06Ni-1.65Mn-0.96Ti (wt pct) shape memory alloy at temperatures in the range 250 C to 400 C were investigated. The changes in the state of atomic order and microstructural evolutions were traced by means of in situ X-ray diffraction and electrical resistivity measurements, as well as transmission electron microscopy (TEM) and optical observations. The kinetics of the aging process, i.e., the temperature and time dependence of the properties including hardness, resistivity, martensitic transformation temperatures, and shape memory capacity were characterized, and at least three temperature-dependent aging stages were distinguished: (1) D0{sub 3} or L2{sub 1} atomic reordering, which causes the martensic transformation temperatures to shift upward and leads the M18R martensite to tend to be a N18R type structure; (2) formation of solute-depleted bainite which results in a drastic depression in martensitic transformation temperatures and loss of the shape memory capacity, accompanied by the atomic disordering in both the remaining parent phase and bainite; and (3) precipitation of the equilibrium {alpha} and {gamma}{sub 2} phases and destruction of the shape memory capacity.

  7. Narrowing of hysteresis of cubic-tetragonal martensitic transformation by weak axial stressing of ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Kosogor, Anna

    2016-06-01

    An influence of axial mechanical stress on the hysteresis of martensitic transformation and ordinary magnetostriction of ferromagnetic shape memory alloy has been described in the framework of a Landau-type theory of phase transitions. It has been shown that weak stress can noticeably reduce the hysteresis of martensitic transformation. Moreover, the anhysteretic deformation can be observed when the applied mechanical stress exceeds a critical stress value. The main theoretical results were compared with recent experimental data. It is argued that shape memory alloys with extremely low values of shear elastic modulus are the candidates for the experimental observation of large anhysteretic deformations.

  8. Microstructural Evolution and Functional Properties of Fe-Mn-Al-Ni Shape Memory Alloy Processed by Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Niendorf, Thomas; Brenne, Florian; Krooß, Philipp; Vollmer, Malte; Günther, Johannes; Schwarze, Dieter; Biermann, Horst

    2016-06-01

    In the current study, a Fe-Mn-Al-Ni shape memory alloy is processed by additive manufacturing for the first time. Microstructural evolution upon processing is strongly affected by thermal gradients and solidification velocity and, thus, by processing parameters and the actual specimen geometry. By single-step solutionizing heat treatment pronounced grain growth is initiated leading to microstructures showing good reversibility. The compressive stress-strain response revealed maximum reversible pseudo-elastic strain of about 7.5 pct. Critical steps toward further optimization of additively manufactured Fe-Mn-Al-Ni shape memory alloys are discussed.

  9. Transformation-induced plasticity in high-temperature shape memory alloys: a one-dimensional continuum model

    NASA Astrophysics Data System (ADS)

    Sakhaei, Amir Hosein; Lim, Kian-Meng

    2016-07-01

    A constitutive model based on isotropic plasticity consideration is presented in this work to model the thermo-mechanical behavior of high-temperature shape memory alloys. In high-temperature shape memory alloys (HTSMAs), both martensitic transformation and rate-dependent plasticity (creep) occur simultaneously at high temperatures. Furthermore, transformation-induced plasticity is another deformation mechanism during martensitic transformation. All these phenomena are considered as dissipative processes to model the mechanical behavior of HTSMAs in this study. The constitutive model was implemented for one-dimensional cases, and the results have been compared with experimental data from thermal cycling test for actuator applications.

  10. Experimental Analysis and Numerical Simulation of Tensile Behaviour of TiNi Shape Memory Alloy Fibres Reinforced Epoxy Matrix Composite at High Temperatures

    SciTech Connect

    Sahli, M. L.; Necib, B.

    2011-05-04

    The shape memory alloys (SMA) possess both sensing and actuating functions due to their shape memory effect, pseudo-elasticity, high damping capability and other remarkable properties. Combining the SMA with other materials can create intelligent or smart composites. The epoxy resin composites filled with TiNi alloys fibres were fabricated and their mechanical properties have been investigated. In this study, stress/strain relationships for a composite with embedded shape memory materials (SMA) fibres are presented. The paper illustrates influence of the SMA fibres upon changes in mechanical behaviour of a composite plate with the SMA components, firstly and secondly, the actuating ability and reliability of shape memory alloy hybrid composites.

  11. Twinning-Induced Elasticity in NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Birk, Thorsten; Biswas, Somjeet; Frenzel, Jan; Eggeler, Gunther

    2016-06-01

    Pseudoelasticity (PE) in shape memory alloys relies on the formation of stress-induced martensite during loading and on the reverse transformation during unloading. PE yields reversible strains of up to 8 % and is applied in applications such as medical implants, flexible eye glass frames, damping elements, and others. Unfortunately, PE shows a strong temperature dependence and thus can only be exploited within a relatively narrow temperature window. The present work focuses on a related process, which we refer to as twinning-induced elasticity (TIE). It involves the growth and shrinkage of martensite variants which are stabilized by dislocations, which are introduced by appropriate cold work. TIE yields reversible strains of the order of 3 %. The TIE effect does not suffer from the strong temperature dependence of PE. The weak temperature dependence of mechanical TIE properties makes TIE attractive for applications where temperature fluctuations are large. In the present work, we study the TIE effect focusing on Ni50Ti50 shape memory alloy wires. The degree of plastic pre-deformation of the initial material represents a key parameter of the ingot metallurgy processing route. It governs the exploitable recoverable strain, the apparent Young's modulus, and the widths of the mechanical hysteresis. Dynamic mechanical analysis is used to study the effects of pre-deformation on elementary microstructural processes which govern TIE.

  12. Shape memory alloys for astronomical instrumentation: space and ground-based applications

    NASA Astrophysics Data System (ADS)

    Riva, M.; Rigamonti, D.; Zanetti, F.; Passaretti, F.; Villa, E.; Zerbi, F. M.

    2012-09-01

    This paper wants to illustrate possible applications of Shape Memory Alloy (SMA) as functional devices for space and ground based application in Instrumentations for Astronomy. Thermal activated Shape Memory Alloys are materials able to recover their original shape, after an external deformation, if heated above a characteristic temperature. If the recovery of the shape is completely or partially prevented by the presence of constraints, the material can generate recovery stress. Thanks to this feature, these materials can be positively exploited in Smart Structures if properly embedded into host materials. Some technological processes developed for an ecient use of SMA-based actuators embedded in smart structures tailored to astronomical instrumentation will be presented here. Some possible modeling approaches of the actuators behavior will be addressed taking into account trade- offs between detailed analysis and overall performance prediction as a function of the computational time. The Material characterization procedure adopted for the constitutive laws implementation will be described as well. Deformable composite mirrors,1 opto-mechanical mounting with superelastic kinematic behavior and damping of launch loads onto optical element2 are feasible applications that will be deeply investigated in this paper.

  13. Force-displacement characteristics of simply supported beam laminated with shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wu, Zhi-Qiang; Zhang, Zhen-Hua

    2011-12-01

    As a preliminary step in the nonlinear design of shape memory alloy (SMA) composite structures, the force-displacement characteristics of the SMA layer are studied. The bilinear hysteretic model is adopted to describe the constitutive relationship of SMA material. Under the assumption that there is no point of SMA layer finishing martensitic phase transformation during the loading and unloading process, the generalized restoring force generated by SMA layer is deduced for the case that the simply supported beam vibrates in its first mode. The generalized force is expressed as piecewise-nonlinear hysteretic function of the beam transverse displacement. Furthermore the energy dissipated by SMA layer during one period is obtained by integration, then its dependencies are discussed on the vibration amplitude and the SMA's strain (Ms-Strain) value at the beginning of martensitic phase transformation. It is shown that SMA's energy dissipating capacity is proportional to the stiffness difference of bilinear model and nonlinearly dependent on Ms-Strain. The increasing rate of the dissipating capacity gradually reduces with the amplitude increasing. The condition corresponding to the maximum dissipating capacity is deduced for given value of the vibration amplitude. The obtained results are helpful for designing beams laminated with shape memory alloys.

  14. Static rock splitters based on high temperature shape memory alloys for planetary explorations

    NASA Astrophysics Data System (ADS)

    Benafan, O.; Noebe, R. D.; Halsmer, T. J.

    2016-01-01

    A static rock splitter device based on high-force, high-temperature shape memory alloys (HTSMAs) was developed for space related applications requiring controlled geologic excavation in planetary bodies such as the moon, Mars, and near-Earth asteroids. The device, hereafter referred to as the shape memory alloy rock splitter (SMARS), consisted of active (expanding) elements made of Ni50.3Ti29.7Hf20 (at%) that generate extremely large forces in response to thermal input. The pre-shaping (training) of these elements was accomplished using isothermal, isobaric and cyclic training methods, which resulted in active components capable of generating stresses in excess of 1.5 GPa. The corresponding strains (or displacements) were also evaluated and were found to be 2-3%, essential to rock fracturing and/or splitting when placed in a borehole. SMARS performance was evaluated using a testbed consisting of a temperature controller, custom heaters and heater holders, and an enclosure for rock placement and breakage. The SMARS system was evaluated using various rock types including igneous rocks (e.g., basalt, quartz, granite) and sedimentary rocks (e.g., sandstone, limestone).

  15. Sensorless control for a sophisticated artificial myocardial contraction by using shape memory alloy fibre.

    PubMed

    Shiraishi, Y; Yambe, T; Saijo, Y; Sato, F; Tanaka, A; Yoshizawa, M; Sugai, T K; Sakata, R; Luo, Y; Park, Y; Uematsu, M; Umezu, M; Fujimoto, T; Masumoto, N; Liu, H; Baba, A; Konno, S; Nitta, S; Imachi, K; Tabayashi, K; Sasada, H; Homma, D

    2008-01-01

    The authors have been developing an artificial myocardium, which is capable of supporting natural contractile function from the outside of the ventricle. The system was originally designed by using sophisticated covalent shape memory alloy fibres, and the surface did not implicate blood compatibility. The purpose of our study on the development of artificial myocardium was to achieve the assistance of myocardial functional reproduction by the integrative small mechanical elements without sensors, so that the effective circulatory support could be accomplished. In this study, the authors fabricated the prototype artificial myocardial assist unit composed of the sophisticated shape memory alloy fibre (Biometal), the diameter of which was 100 microns, and examined the mechanical response by using pulse width modulation (PWM) control method in each unit. Prior to the evaluation of dynamic characteristics, the relationship between strain and electric resistance and also the initial response of each unit were obtained. The component for the PWM control was designed in order to regulate the myocardial contractile function, which consisted of an originally-designed RISC microcomputer with the input of displacement, and its output signal was controlled by pulse wave modulation method. As a result, the optimal PWM parameters were confirmed and the fibrous displacement was successfully regulated under the different heat transfer conditions simulating internal body temperature as well as bias tensile loading. Then it was indicated that this control theory might be applied for more sophisticated ventricular passive or active restraint by the artificial myocardium on physiological demand.

  16. Measurement and Prediction of the Thermomechanical Response of Shape Memory Alloy Hybrid Composite Beams

    NASA Technical Reports Server (NTRS)

    Davis, Brian; Turner, Travis L.; Seelecke, Stefan

    2005-01-01

    Previous work at NASA Langley Research Center (LaRC) involved fabrication and testing of composite beams with embedded, pre-strained shape memory alloy (SMA) ribbons within the beam structures. That study also provided comparison of experimental results with numerical predictions from a research code making use of a new thermoelastic model for shape memory alloy hybrid composite (SMAHC) structures. The previous work showed qualitative validation of the numerical model. However, deficiencies in the experimental-numerical correlation were noted and hypotheses for the discrepancies were given for further investigation. The goal of this work is to refine the experimental measurement and numerical modeling approaches in order to better understand the discrepancies, improve the correlation between prediction and measurement, and provide rigorous quantitative validation of the numerical analysis/design tool. The experimental investigation is refined by a more thorough test procedure and incorporation of higher fidelity measurements such as infrared thermography and projection moire interferometry. The numerical results are produced by a recently commercialized version of the constitutive model as implemented in ABAQUS and are refined by incorporation of additional measured parameters such as geometric imperfection. Thermal buckling, post-buckling, and random responses to thermal and inertial (base acceleration) loads are studied. The results demonstrate the effectiveness of SMAHC structures in controlling static and dynamic responses by adaptive stiffening. Excellent agreement is achieved between the predicted and measured results of the static and dynamic thermomechanical response, thereby providing quantitative validation of the numerical tool.

  17. Micromechanics of composites with shape memory alloy fibers in uniform thermal fields

    NASA Technical Reports Server (NTRS)

    Birman, Victor; Saravanos, Dimitris A.; Hopkins, Dale A.

    1995-01-01

    Analytical procedures are developed for a composite system consisting of shape memory alloy fibers within an elastic matrix subject to uniform temperature fluctuations. Micromechanics for the calculation of the equivalent properties of the composite are presented by extending the multi-cell model to incorporate shape memory alloy fibers. A three phase concentric cylinder model is developed for the analysis of local stresses which includes the fiber, the matrix, and the surrounding homogenized composite. The solution addresses the complexities induced by the nonlinear dependence of the in-situ martensite fraction of the fibers to the local stresses and temperature, and the local stresses developed from interactions between the fibers and matrix during the martensitic and reverse phase transformations. Results are presented for a nitinol/epoxy composite. The applications illustrate the response of the composite in isothermal longitudinal loading and unloading, and in temperature induced actuation. The local stresses developed in the composite under various stages of the martensitic and reverse phase transformation are also shown.

  18. Mathematical Modeling and Control of Nonlinear Oscillators with Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Bendame, Mohamed

    Shape memory alloys (SMAs) belong to an interesting type of materials that have attracted the attention of scientists and engineers over the last few decades. They have some interesting properties that made them the subject of extensive research to find the best ways to utilize them in different engineering, biomedical, and scientific applications. In this thesis, we develop a mathematical model and analyze the behavior of SMAs by considering a one degree of freedom nonlinear oscillator consisting of a mass connected to a fixed frame through a viscous damping and a shape memory alloy device. Due to the nonlinear and dissipative nature of shape memory alloys, optimal control and Lyapunov stability theories are used to design a controller to stabilize the response of the one degree of freedom nonlinear oscillator. Since SMAs exist in two phases, martensite and austenite, and their phase transformations are dependent on stress and temperature, this work is presented in two parts. The first part deals with the nonlinear oscillator system in its two separate phases by considering a temperature where the SMA exists in only one of the phases. A model for each phase is developed based on Landau-Ginzburg-Devonshire theory that defines the free energy in a polynomial form enabling us to describe the SMAs shape memory effect and pseudoelasticity. However, due to the phenomenon of hysteresis in SMAs, the response of the nonlinear oscillator with a SMA element, in either phase, is chaotic and unstable. In order to stabilize the chaotic behavior, an optimal linear quadratic regulator controller is designed around a stable equilibrium for the martensitic and the austenitic phases. The closed-loop response for each phase is then simulated and computational results are presented. The second part of the thesis deals with the entire system in its dynamics by combining the two phases and taking into account the effect of temperature on the response of the system. Governing equations

  19. Mechanical and functional behavior of high-temperature Ni-Ti-Pt shape memory alloys

    DOE PAGES

    Buchheit, Thomas E.; Susan, Donald F.; Massad, Jordan E.; McElhanon, James R.; Noebe, Ronald D.

    2016-01-22

    A series of Ti-rich Ni-Ti-Pt ternary alloys with 13 to 18 at. pct Pt were processed by vacuum arc melting and characterized for their transformation behavior to identify shape memory alloys (SMA) that undergo transformation between 448 K and 498 K (175 °C and 225 °C) and achieve recoverable strain exceeding 2 pct. From this broader set of compositions, three alloys containing 15.5 to 16.5 at. pct Pt exhibited transformation temperatures in the vicinity of 473 K (200 °C), thus were targeted for more detailed characterization. Preliminary microstructural evaluation of these three compositions revealed a martensitic microstructure with small amountsmore » of Ti2(Ni,Pt) particles. Room temperature mechanical testing gave a response characteristic of martensitic de-twinning followed by a typical work-hardening behavior to failure. Elevated mechanical testing, performed while the materials were in the austenitic state, revealed yield stresses of approximately 500 MPa and 3.5 pct elongation to failure. Thermal strain recovery characteristics were more carefully investigated with unbiased incremental strain-temperature tests across the 1 to 5 pct strain range, as well as cyclic strain-temperature tests at 3 pct strain. As a result, the unbiased shape recovery results indicated a complicated strain recovery path, dependent on prestrain level, but overall acceptable SMA behavior within the targeted temperature and recoverable strain range.« less

  20. Mechanical and Functional Behavior of High-Temperature Ni-Ti-Pt Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Buchheit, Thomas E.; Susan, Donald F.; Massad, Jordan E.; McElhanon, James R.; Noebe, Ronald D.

    2016-04-01

    A series of Ti-rich Ni-Ti-Pt ternary alloys with 13 to 18 at. pct Pt were processed by vacuum arc melting and characterized for their transformation behavior to identify shape memory alloys (SMA) that undergo transformation between 448 K and 498 K (175 °C and 225 °C) and achieve recoverable strain exceeding 2 pct. From this broader set of compositions, three alloys containing 15.5 to 16.5 at. pct Pt exhibited transformation temperatures in the vicinity of 473 K (200 °C), thus were targeted for more detailed characterization. Preliminary microstructural evaluation of these three compositions revealed a martensitic microstructure with small amounts of Ti2(Ni,Pt) particles. Room temperature mechanical testing gave a response characteristic of martensitic de-twinning followed by a typical work-hardening behavior to failure. Elevated mechanical testing, performed while the materials were in the austenitic state, revealed yield stresses of approximately 500 MPa and 3.5 pct elongation to failure. Thermal strain recovery characteristics were more carefully investigated with unbiased incremental strain-temperature tests across the 1 to 5 pct strain range, as well as cyclic strain-temperature tests at 3 pct strain. The unbiased shape recovery results indicated a complicated strain recovery path, dependent on prestrain level, but overall acceptable SMA behavior within the targeted temperature and recoverable strain range.

  1. Oxidation Kinetics of a NiPtTi High Temperature Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Humphrey, Donald L.; Noebe, Ronald D.

    2007-01-01

    A high temperature shape memory alloy (HTSMA), Ni30Pt50Ti, with an M(sub s) near 600 C, was isothermally oxidized in air for 100 hr over the temperature range of 500 to 900 C. Parabolic kinetics were confirmed by log-log and parabolic plots and showed no indication of fast transient oxidation. The overall behavior could be best described by the Arrhenius relationship: k(sub p) = 1.64 x 10(exp 12)[(-250 kJ/mole)/RT] mg(sup 2)/cm(sup 4)hr. This is about a factor of 4 reduction compared to values measured here for a binary Ni47Ti commercial SMA. The activation energy agreed with most literature values for TiO2 scale growth measured for elemental Ti and other NiTi alloys. Assuming uniform alloy depletion of a 20 mil (0.5 mm) dia. HTSMA wire, approx. 1 percent Ti reduction is predicted after 20,000 hr oxidation at 500 C, but becomes much more serious at higher temperatures.

  2. Modeling and design of a vibration energy harvester using the magnetic shape memory effect

    NASA Astrophysics Data System (ADS)

    Saren, A.; Musiienko, D.; Smith, A. R.; Tellinen, J.; Ullakko, K.

    2015-09-01

    In this study, a vibration energy harvester is investigated which uses a Ni-Mn-Ga sample that is mechanically strained between 130 and 300 Hz while in a constant biasing magnetic field. The crystallographic reorientation of the sample during mechanical actuation changes its magnetic properties due to the magnetic shape memory (MSM) effect. This leads to an oscillation of the magnetic flux in the yoke which generates electrical energy by inducing an alternating current within the pick-up coils. A power of 69.5 mW (with a corresponding power density of 1.37 mW mm-3 compared to the active volume of the MSM element) at 195 Hz was obtained by optimizing the biasing magnetic field, electrical resistance and electrical resonance. The optimization of the electrical resonance increased the energy generated by nearly a factor of four when compared to a circuit with no resonance. These results are strongly supported by a theoretical model and simulation which gives corresponding values with an error of approximately 20% of the experimental data. This model will be used in the design of future MSM energy harvesters and their optimization for specific frequencies and power outputs.

  3. A Study of Thermo-mechanically Processed High Stiffness NiTiCo Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Manjeri, R. M.; Norwich, D.; Sczerzenie, F.; Huang, X.; Long, M.; Ehrlinspiel, M.

    2016-03-01

    This work investigates a vacuum induction melted-vacuum arc re-melted (VIM-VAR) and thermo-mechanically processed ternary NiTiCo shape memory alloy. The NiTiCo ingot was hot processed to 6.35-mm-diameter coiled wire. The coiled wire was subsequently cold drawn to a final wire diameter of 0.53 mm, with interpass anneals. The wires were shape set at 450 °C for 3.5 min. After electropolishing, the wires were subjected to microstructural, thermal, and mechanical characterization studies. Microstructural analysis was performed by transmission electron microscope (TEM), thermal analyses by differential scanning calorimeter (DSC), and bend-free recovery and mechanical testing by uniaxial tensile testing. TEM did not reveal Ni-rich precipitates—either at the grain boundary or in the grain interior. Energy dispersive x-ray spectroscopy showed a uniform distribution of Ni, Ti, and Co in the sample. The DSC results on the shape set wire showed a single-step transformation between the austenite and the R-phase, in the forward and reverse directions. Cyclic tensile tests of the shape set wire, processed under optimum conditions, showed minimum residual strain and a stable upper plateau stress. Further, the fatigue behavior of NiTi and NiTiCo alloys was studied by rotating beam testing. The results showed that the fatigue properties of NiTiCo, under zero mean strain, are equivalent to that of binary NiTi in the high-cycle and medium-cycle regimes, taking into account the higher stiffness of NiTiCo. The above analyses helped in establishing the processing-structure-property correlation in a VIM-VAR-melted NiTiCo shape memory alloy.

  4. Oxide Scales Formed on NiTi and NiPtTi Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Garg, Anita; Rogers, Richard B.; Noebe, Ronald D.

    2011-01-01

    Ni-49Ti and Ni-30Pt-50Ti (at.%) shape memory alloys were oxidized isothermally in air over the temperature range of 500 to 900 C. The microstructure, composition, and phase content of the scales were studied by SEM, EDS, XRD, and metallography. Extensive plan view SEM/EDS identified various features of intact or spalled scale surfaces. The outer surface of the scale was a relatively pure TiO2 rutile structure, typified by a distinct highly striated and faceted crystal morphology. Crystal size increased significantly with temperature. Spalled regions exhibited some porosity and less distinct features. More detailed information was obtained by correlation of SEM/EDS studies of 700 C/100 hr cross-sections with XRD analyses of serial or taper-polishing of plan surfaces. Overall, multiple layers exhibited graded mixtures of NiO, TiO2, NiTiO3, Ni(Ti) or Pt(Ni,Ti) metal dispersoids, Ni3Ti or Pt3Ti depletion zones, and substrate, in that order. The NiTi alloy contained a 3 at.% Fe impurity that appeared in embedded localized Fe-Ti-rich oxides, while the NiPtTi alloy contained a 2 v/o dispersion of TiC that appeared in lower layers. The oxidation kinetics of both alloys (in a previous report) indicated parabolic growth and an activation energy (250 kJ/mole) near those reported in other Ti and NiTi studies. This is generally consistent with TiO2 existing as the primary scale constituent, as described here.

  5. Microstructure of cryogenically treated martensitic shape memory nickel-titanium alloy

    PubMed Central

    Vinothkumar, Thilla Sekar; Kandaswamy, Deivanayagam; Prabhakaran, Gopalakrishnan; Rajadurai, Arunachalam

    2015-01-01

    Context: Recent introduction of shape memory (SM) nickel-titanium (NiTi) alloy into endodontics is a major breakthrough. Although the flexibility of these instruments was enhanced, fracture of rotary endodontic instruments during instrumentation is an important challenge for the operator. Implementation of supplementary manufacturing methods that would improve the fatigue life of the instrument is desirable. Aim: The purpose of this study was to investigate the role of dry cryogenic treatment (CT) conditions on the microstructure of martensitic SM NiTi alloy. Materials and Methods: Experiments were conducted on Ni-51 wt% Ti-49 wt% SM alloy. Five cylindrical specimens and five sheet specimens were subjected to different CT conditions: Deep CT (DCT) 24 group: −185°C; 24 h, DCT 6 group: −185°C; 6 h, shallow CT (SCT) 24 group: −80°C, 24 h, SCT 6 group: −80°C, 6 h and control group. Microstructure of surface was observed on cylindrical specimens with an optical microscope and scanning electron microscope at different magnifications. Subsurface structure was analyzed on sheet specimens using X-ray diffraction (XRD). Results: Microstructures of all SM NiTi specimens had equiaxed grains (approximately 25 μm) with well-defined boundaries and precipitates. XRD patterns of cryogenically treated specimens revealed accentuation of austenite and martensite peaks. The volume of martensite and its crystallite size was relatively more in DCT 24 specimen. Conclusions: DCT with 24 h soaking period increases the martensite content of the SM NiTi alloy without altering the grain size. PMID:26180413

  6. Fast Preisach modeling method for shape memory alloy actuators using major hysteresis loops

    NASA Astrophysics Data System (ADS)

    Choi, Byung-Jun; Lee, Yun-Jung; Choi, Bong-Yeol

    2004-10-01

    The control accuracy of smart actuators, such as a shape memory alloy (SMA) or piezoceramic actuator, is limited due to their inherent hysteresis nonlinearities with a local memory, resulting from the influence of a previous input on subsequent behavior. In addition, the existence of minor loops in the major loop because of a local memory also makes the mathematical modeling and design of a controller difficult for SMA actuators. Therefore, to enhance the controllability of a smart actuator, the Preisach hysteresis model has emerged as an appropriate behavioral model, yet the modeling is difficult and the model equation complex. Accordingly, to resolve these difficulties, the current paper proposes a simple method based on applying the proportional relationship between the major loop and the FOD curves of an SMA actuator to the Preisach model. As such, using only data for the major hysteresis loop, the proposed method enables the FOD curves to be easily approximated and the output length rapidly computed. The efficacy of the proposed Preisach modeling method is confirmed based on comparative experiments with the classical Preisach model.

  7. A 3-D constitutive model for pressure-dependent phase transformation of porous shape memory alloys.

    PubMed

    Ashrafi, M J; Arghavani, J; Naghdabadi, R; Sohrabpour, S

    2015-02-01

    Porous shape memory alloys (SMAs) exhibit the interesting characteristics of porous metals together with shape memory effect and pseudo-elasticity of SMAs that make them appropriate for biomedical applications. In this paper, a 3-D phenomenological constitutive model for the pseudo-elastic behavior and shape memory effect of porous SMAs is developed within the framework of irreversible thermodynamics. Comparing to micromechanical and computational models, the proposed model is computationally cost effective and predicts the behavior of porous SMAs under proportional and non-proportional multiaxial loadings. Considering the pressure dependency of phase transformation in porous SMAs, proper internal variables, free energy and limit functions are introduced. With the aim of numerical implementation, time discretization and solution algorithm for the proposed model are also presented. Due to lack of enough experimental data on multiaxial loadings of porous SMAs, we employ a computational simulation method (CSM) together with available experimental data to validate the proposed constitutive model. The method is based on a 3-D finite element model of a representative volume element (RVE) with random pores pattern. Good agreement between the numerical predictions of the model and CSM results is observed for elastic and phase transformation behaviors in various thermomechanical loadings.

  8. Use of shape memory alloys in the robust control of smart structures. Final report, February 1990-June 1993

    SciTech Connect

    Rao, V.S.; O'Keefe, T.J.; Koval, L.R.

    1993-08-01

    This report details an integrated interdisciplinary approach for designing and implementing robust controllers on smart structures. The application of shape memory alloy materials as actuators and sensors in the active control of smart structures has been investigated. A process was developed for the electrodeposition of In-Tl alloys in a composition range where this system exhibits the shape memory effect. Cu-Zn, Au-Ca, and In-Cd alloy films were produced using the electrolytic techniques and their shape memory properties evaluated. To demonstrate some of the capabilities of smart structures and to determine the limitations imposed by hardware realizations, we have designed and fabricated experimental test articles incorporating flexible structures with SMA actuators, strain gauge sensors, signal processing circuits and digital controllers. Structural identification techniques have been employed in determining mathematical models of test articles from experimental data. A modified robust control design methodology was developed to accommodate the limited control force provided by the SMA actuators. The robustness properties of closed loop structural systems were verified experimentally. Adaptive control methods were implemented. Neural network based identification and control algorithms were developed. Smart structures, Shape memory alloys, Electrodeposition process, Robust control, Control using neural networks.

  9. Processing of Ni30Pt20Ti50 High-Temperature Shape-Memory Alloy Into Thin Rod Demonstrated

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald D.; Draper, Susan L.; Biles, Tiffany A.; Leonhardt, Todd

    2005-01-01

    High-temperature shape-memory alloys (HTSMAs) based on nickel-titanium (NiTi) with significant ternary additions of palladium (Pd), platinum (Pt), gold (Au), or hafnium (Hf) have been identified as potential high-temperature actuator materials for use up to 500 C. These materials provide an enabling technology for the development of "smart structures" used to control the noise, emissions, or efficiency of gas turbine engines. The demand for these high-temperature versions of conventional shape-memory alloys also has been growing in the automotive, process control, and energy industries. However these materials, including the NiPtTi alloys being developed at the NASA Glenn Research Center, will never find widespread acceptance unless they can be readily processed into useable forms.

  10. Long-Time Stability of Ni-Ti-Shape Memory Alloys for Automotive Safety Systems

    NASA Astrophysics Data System (ADS)

    Strittmatter, Joachim; Gümpel, Paul

    2011-07-01

    In automotive a lot of electromagnetically, pyrotechnically or mechanically driven actuators are integrated to run comfort systems and to control safety systems in modern passenger cars. Using shape memory alloys (SMA) the existing systems could be simplified, performing the same function through new mechanisms with reduced size, weight, and costs. A drawback for the use of SMA in safety systems is the lack of materials knowledge concerning the durability of the switching function (long-time stability of the shape memory effect). Pedestrian safety systems play a significant role to reduce injuries and fatal casualties caused by accidents. One automotive safety system for pedestrian protection is the bonnet lifting system. Based on such an application, this article gives an introduction to existing bonnet lifting systems for pedestrian protection, describes the use of quick changing shape memory actuators and the results of the study concerning the long-time stability of the tested NiTi-wires. These wires were trained, exposed up to 4 years at elevated temperatures (up to 140 °C) and tested regarding their phase change temperatures, times, and strokes. For example, it was found that A P-temperature is shifted toward higher temperatures with longer exposing periods and higher temperatures. However, in the functional testing plant a delay in the switching time could not be detected. This article gives some answers concerning the long-time stability of NiTi-wires that were missing till now. With this knowledge, the number of future automotive applications using SMA can be increased. It can be concluded, that the use of quick changing shape memory actuators in safety systems could simplify the mechanism, reduce maintenance and manufacturing costs and should be insertable also for other automotive applications.

  11. In Situ Photoelectron Emission Microscopy of a Thermally Induced Martensitic Transformation in a CuZnAI Shape Memory Alloy

    SciTech Connect

    Xiong, Gang; Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.; Cai, Mingdong; Langford, Stephen C.; Dickinson, J T.

    2006-02-27

    Photoemission electron microscopy, in conjunction with photoemission spectroscopy, reflectivity, and surface roughness measurements, is used to study the thermally-induced martensitic transformation in a CuZnAI shape memory alloy. Real-time phase transformation is observed as a nearly instantaneous change of photoelectron intensity, accompanied by microstructural deformation and displacement due to the shape memory effect. The difference in the photoelectron intensity before and after the phase transformation is attributed to the concomitant change of work function as measured by photoelectron spectroscopy. Photoemission electron microscopy is shown to be a valuable new technique facilitating the study of phase transformations in shape memory alloys, and provides real-time information on microstructural changes and phase-dependent electronic properties.

  12. Embedded Shape Memory Alloy Particles for the Self-Sensing of Fatigue Crack Growth in an Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Leser, William Paul

    Future aerospace vehicles will be built using novel materials for mission conditions that are difficult to replicate in a laboratory. Structural health monitoring and condition-based maintenance will be critical to ensure the reliability of such vehicles. A multi-functional aluminum alloy containing embedded shape memory alloy (SMA) particles to detect fatigue crack growth is proposed. The regions of intensified strain near the tip of a growing fatigue crack cause the SMA particles to undergo a solid-to-solid phase transformation from austenite to martensite, releasing a detectable and identifiable acoustic emission (AE) signal that can be used to locate the crack in the affected component. This study investigates the AE response of two SMA systems, Ni-Ti, and Co-Ni-Al. Tensile (Ni-Ti) and compressive (Co-Ni-Al) tests were conducted to study the strain-induced transformation response in both of the alloy systems. It was found that the critical stress for transformation in both SMA systems was easily identified by a burst of AE activity during both transformation and reverse transformation. AE signals from these experiments were collected for use as training data for a Bayesian classifier to be used to identify transformation signals in a Al7050 matrix with embedded SMA particles. The Al/SMA composite was made by vacuum hot pressing SMA powder between aluminum plates. The effect of hot pressing temperature and subsequent heat treatments (solutionizing and peak aging) on the SMA particles was studied. It was found that, at the temperatures required, Co-Ni-Al developed a second phase that restricted the transformation from austenite to martensite, thus rendering it ineffective as a candidate for the embedded particles. Conversely, Ni-Ti did survive the embedding process and it was found that the solutionizing heat treatment applied after hot pressing was the main driver in determining the final transformation temperatures for the Ni-Ti particles. The effect of hot

  13. Shape memory effect associated with a deformation at a temperature just below A[sub S] in a Fe-Mn-Cr-Si-Ni shape memory alloy

    SciTech Connect

    Federzoni, L.; Guenin, G. )

    1994-07-01

    The shape memory effect of Fe-Mn based shape memory alloys is due to the formation of stress-induced [var epsilon]-martensite by deformation and to its reversion by heating over A[sub f], which permit it to recover a part of the original shape. The shape memory effect is directly associated with the [gamma][yields][var epsilon] transformation. For this reason, the authors have established the best conditions to induce the [var epsilon]-martensite inside an austenitic matrix: the deformation must take place at a temperature close to the M[sub s]. It has been established that a deformation made at a higher temperature degrades the shape memory effect. The purpose of this paper is to evaluate the shape memory effect in the case of a deformation applied at a relatively high temperature (just below A[sub s]) on samples containing a high volume fraction of [var epsilon]-martensite before the deformation. It is shown that an other mechanism of shape memory effect occurs in these conditions and allows to reach an interesting shape memory effect ([approximately]2%).

  14. Shape memory alloy nanostructures with coupled dynamic thermo-mechanical effects

    NASA Astrophysics Data System (ADS)

    Dhote, R. P.; Gomez, H.; Melnik, R. N. V.; Zu, J.

    2015-07-01

    Employing the Ginzburg-Landau phase-field theory, a new coupled dynamic thermo-mechanical 3D model has been proposed for modeling the cubic-to-tetragonal martensitic transformations in shape memory alloy (SMA) nanostructures. The stress-induced phase transformations and thermo-mechanical behavior of nanostructured SMAs have been investigated. The mechanical and thermal hysteresis phenomena, local non-uniform phase transformations and corresponding non-uniform temperatures and deformations' distributions are captured successfully using the developed model. The predicted microstructure evolution qualitatively matches with the experimental observations. The developed coupled dynamic model has provided a better understanding of underlying martensitic transformation mechanisms in SMAs, as well as their effect on the thermo-mechanical behavior of nanostructures.

  15. PATH OPTIMIZATION AND CONTROL OF A SHAPE MEMORY ALLOY ACTUATED CATHETER FOR ENDOCARDIAL RADIOFREQUENCY ABLATION

    PubMed Central

    Wiest, Jennifer H.; Buckner, Gregory D.

    2014-01-01

    This paper introduces a real-time path optimization and control strategy for shape memory alloy (SMA) actuated cardiac ablation catheters, potentially enabling the creation of more precise lesions with reduced procedure times and improved patient outcomes. Catheter tip locations and orientations are optimized using parallel genetic algorithms to produce continuous ablation paths with near normal tissue contact through physician-specified points. A nonlinear multivariable control strategy is presented to compensate for SMA hysteresis, bandwidth limitations, and coupling between system inputs. Simulated and experimental results demonstrate efficient generation of ablation paths and optimal reference trajectories. Closed-loop control of the SMA-actuated catheter along optimized ablation paths is validated experimentally. PMID:25684857

  16. Calibration and Finite Element Implementation of an Energy-Based Material Model for Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Junker, Philipp; Hackl, Klaus

    2016-06-01

    Numerical simulations are a powerful tool to analyze the complex thermo-mechanically coupled material behavior of shape memory alloys during product engineering. The benefit of the simulations strongly depends on the quality of the underlying material model. In this contribution, we discuss a variational approach which is based solely on energetic considerations and demonstrate that unique calibration of such a model is sufficient to predict the material behavior at varying ambient temperature. In the beginning, we recall the necessary equations of the material model and explain the fundamental idea. Afterwards, we focus on the numerical implementation and provide all information that is needed for programing. Then, we show two different ways to calibrate the model and discuss the results. Furthermore, we show how this model is used during real-life industrial product engineering.

  17. A Shape-Memory Alloy Thermal Conduction Switch for Use at Cryogenic Temperatures

    NASA Technical Reports Server (NTRS)

    Vaidyanathan, Raj

    2004-01-01

    The following summarizes the activities performed under NASA grant NAG10-323 from September 1, 2002 through September 30, 2004 at the. Univ ersity of Central Florida. A version of this has already been submitt ed for publication in the international journal Swart Materials and S tructures in December 2004. Additionally, a version of this has alrea dy appeared in print in Advances in Cryogenic Engineering, American Institute of Physics, (2004) 50A 26-3; in an article entitled "A Shape Memory Alloy Based Cryogenic Thermal Conduction Switch" by V.B. Krish nan. J.D. Singh. T.R. Woodruff. W.U. Notardonato and R. Vaidyanathan (article is attached at the end of this report).

  18. Issues Concerning the Oxidation of Ni(Pt)Ti Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Smialek, James

    2011-01-01

    The oxidation behavior of the Ni-30Pt-50Ti high temperature shape memory alloy is compared to that of conventional NiTi nitinol SMAs. The oxidation rates were 1/4 those of NiTi under identical conditions. Ni-Ti-X SMAs are dominated by TiO2 scales, but, in some cases, the activation energy diverges for unexplained reasons. Typically, islands of metallic Ni or Pt(Ni) particles are embedded in lower scale layers due to rapid selective growth of TiO2 and low oxygen potential within the scale. The blocking effect of Pt-rich particles and lower diffusivity of Pt-rich depletion zones are proposed to account for the reduction in oxidation rates.

  19. Shape Memory Alloy Research and Development at NASA Glenn - Current and Future Progress

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane

    2015-01-01

    Shape memory alloys (SMAs) are a unique class of multifunctional materials that have the ability to recover large deformations or generate high stresses in response to thermal, mechanical and or electromagnetic stimuli. These abilities have made them a viable option for actuation systems in aerospace, medical, and automotive applications, amongst others. However, despite many advantages and the fact that SMA actuators have been developed and used for many years, so far they have only found service in a limited range of applications. In order to expand their applications, further developments are needed to increase their reliability and stability and to address processing, testing and qualification needed for large-scale commercial application of SMA actuators.

  20. Fatigue properties of NiTi shape-memory alloy thin plates

    NASA Astrophysics Data System (ADS)

    Yamamoto, Hiroshi; Taya, Minoru; Liang, Yuanchang; Namli, Onur C.; Saito, Makoto

    2013-04-01

    The mechanical and fatigue characteristics of superelastic NiTi thin plates in the large strain area were obtained by tensile and pulsating 4-point bending tests to establish the design guidelines for the ferromagnetic shape memory alloy (FSMA) composite actuator and its fatigue life. The stress-strain curves of NiTi thin plates were found to be strain rate dependent. The finite element analysis (FEA) result using the stress-strain curve measured by tensile test is in good agreement with the experimental results of the 4-point bending tests. The relationship between the maximum bending strain and the number of cycles to failure in pulsating 4-point bending fatigue tests was obtained as well as an analysis of the fatigue fracture surfaces of NiTi thin plates.

  1. Fiber-optic nonlinear endomicroscopy with focus scanning by using shape memory alloy actuation

    PubMed Central

    Wu, Yicong; Zhang, Yuying; Xi, Jiefeng; Li, Ming-Jun; Li, Xingde

    2010-01-01

    A miniature fiber optic endomicroscope with built-in dynamic focus scanning capability is developed for the first time for 3-D two-photon fluorescence (TPF) imaging of biological samples. Fast 2-D lateral beam scanning is realized by resonantly vibrating a double-clad fiber cantilever with a tubular piezoactuator. Slow axial scanning is achieved by moving the distal end of the imaging probe with an extremely compact electrically driven shape memory alloy (SMA). The 10-mm-long SMA allows 150-μm contractions with a driving voltage varying only from 50 to 100 mV. The response of the SMA contraction with the applied voltage is nonlinear, but repeatable and can be accurately calibrated. Depth-resolved imaging of acriflavine-stained biological tissues and unstained white paper with the endomicroscope is performed, and the results demonstrate the feasibility of 3-D nonlinear optical imaging with the SMA-based scanning fiber-optic endomicroscope. PMID:21198147

  2. Structural Acoustic Response of a Shape Memory Alloy Hybrid Composite Panel (Lessons Learned)

    NASA Technical Reports Server (NTRS)

    Turner, Travis L.

    2002-01-01

    This study presents results from an effort to fabricate a shape memory alloy hybrid composite (SMAHC) panel specimen and test the structure for dynamic response and noise transmission characteristics under the action of thermal and random acoustic loads. A method for fabricating a SMAHC laminate with bi-directional SMA reinforcement is described. Glass-epoxy unidirectional prepreg tape and Nitinol ribbon comprise the material system. Thermal activation of the Nitinol actuators was achieved through resistive heating. The experimental hardware required for mechanical support of the panel/actuators and for establishing convenient electrical connectivity to the actuators is presented. Other experimental apparatus necessary for controlling the panel temperature and acquiring structural acoustic data are also described. Deficiency in the thermal control system was discovered in the process of performing the elevated temperature tests. Discussion of the experimental results focuses on determining the causes for the deficiency and establishing means for rectifying the problem.

  3. Computational modeling of size-dependent superelasticity of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Qiao, Lei; Radovitzky, Raul

    2016-08-01

    We propose a nonlocal continuum model to describe the size-dependent superelastic responses observed in recent experiments of shape memory alloys. The modeling approach extends a superelasticity formulation based on the martensitic volume fraction, and combines it with gradient plasticity theories. Size effects are incorporated through two internal length scales, an energetic length scale and a dissipative length scale, which correspond to the gradient terms in the free energy and the dissipation, respectively. We also propose a computational framework based on a variational formulation to solve the coupled governing equations resulting from the nonlocal superelastic model. Within this framework, a robust and scalable algorithm is implemented for large scale three-dimensional problems. A numerical study of the grain boundary constraint effect shows that the model is able to capture the size-dependent stress hysteresis and strain hardening during the loading and unloading cycles in polycrystalline SMAs.

  4. Development of shape memory alloy (SMA)-based actuator for remotely piloted vehicles (RPVs)

    NASA Astrophysics Data System (ADS)

    Prasad, M. Hari

    2003-10-01

    While the experimental use of shape memory alloys (SMAs) is widespread in aerospace integrated actuation systems, much of the practical value of SMA technology is realized in linear and rotary actuators. This report will introduce an attempt to develop a full-scaled SMA based actuator to replace electro-mechanical actuator for flap actuation of a Remotely Piloted Vehicle (RPV). At the heart of this actuator there is thermally sensitive wire that, when heated, contracts and provides useable mechanical energy. This linear actuation is converted into rotary, for the required actuation of flap. The actuator configurations were sized to fit inside the wing of the RPV where presently the electro-mechanical actuator is housed. The torque supplied to the flap is similarly calculated from full-scale requirements. Using common engineering principles, this design will demonstrate how to design a typical SMA actuator. Test of the actuator performance (stroke, force movement) is done on special test fixture.

  5. Vibration suppression by modulation of elastic modulus using shape memory alloy

    SciTech Connect

    Segalman, D.J.; Parker, G.G.; Inman, D.J.

    1993-03-01

    The first portion of this paper proposes a method of fabricating a material whose modulus can be changed substantially through the application of a specified stimulus. The particular implementation presented here indirectly exploits the large deformation associated with shape memory alloys to achieve the desired modulation of stiffness. The next portion of this paper discusses a class of vibration problems for which such materials have a serious potential for vibration suppression. These are problems, such as the spinning up of rotating machinery, in which the excitation at any time lies within a narrow frequency band, and that band moves through the frequency spectrum in a predictable manner. Finally, an example problem is examined and the utility of this approach is discussed.

  6. High thermal stable and fast switching Ni-Ge-Te alloy for phase change memory applications

    NASA Astrophysics Data System (ADS)

    Cao, Liangliang; Wu, Liangcai; Zhu, Wenqing; Ji, Xinglong; Zheng, Yonghui; Song, Zhitang; Rao, Feng; Song, Sannian; Ma, Zhongyuan; Xu, Ling

    2015-12-01

    Ni-Ge-Te phase change material is proposed and investigated for phase change memory (PCM) applications. With Ni addition, the crystallization temperature, the data retention ability, and the crystallization speed are remarkably improved. The Ni-Ge-Te material has a high crystallization temperature (250 °C) and good data retention ability (149 °C). A reversible switching between SET and RESET state can be achieved by an electrical pulse as short as 6 ns. Up to ˜3 × 104 SET/RESET cycles are obtained with a resistance ratio of about two orders of magnitude. All of these demonstrate that Ni-Ge-Te alloy is a promising material for high speed and high temperature PCM applications.

  7. Measurement and Prediction of the Thermomechanical Response of Shape Memory Alloy Hybrid Composite Beams

    NASA Technical Reports Server (NTRS)

    Davis, Brian; Turner, Travis L.; Seelecke, Stefan

    2008-01-01

    An experimental and numerical investigation into the static and dynamic responses of shape memory alloy hybrid composite (SMAHC) beams is performed to provide quantitative validation of a recently commercialized numerical analysis/design tool for SMAHC structures. The SMAHC beam specimens consist of a composite matrix with embedded pre-strained SMA actuators, which act against the mechanical boundaries of the structure when thermally activated to adaptively stiffen the structure. Numerical results are produced from the numerical model as implemented into the commercial finite element code ABAQUS. A rigorous experimental investigation is undertaken to acquire high fidelity measurements including infrared thermography and projection moire interferometry for full-field temperature and displacement measurements, respectively. High fidelity numerical results are also obtained from the numerical model and include measured parameters, such as geometric imperfection and thermal load. Excellent agreement is achieved between the predicted and measured results of the static and dynamic thermomechanical response, thereby providing quantitative validation of the numerical tool.

  8. Lattice dynamics of the high-temperature shape-memory alloy Nb-Ru

    SciTech Connect

    Shapiro, S. M.; Xu, G.; Gu, G.; Fonda, R. W.

    2006-06-01

    Nb-Ru is a high-temperature shape-memory alloy that undergoes a martensitic transformation from a parent cubic {beta}-phase into a tetragonal {beta}{sup '} phase at T{sub M}{approx}900 deg. C. Measurements of the phonon dispersion curves on a single crystal show that the [110]-TA{sub 2} phonon branch, corresponding in the q=0 limit to the elastic constant C{sup '}=1/2(C{sub 11}-C{sub 12}) has an anomalous temperature dependence. Nearly the entire branch softens with decreasing temperature as T{sub M} is approached. The temperature dependence of the low-q phonon energies suggests that the elastic constants would approach 0 as T approaches T{sub M}, indicating a second-order transition. No additional lattice modulation is observed in the cubic phase.

  9. Shape recovery of shape memory alloy fiber embedded resin matrix smart composite after crack repair.

    PubMed

    Hamada, Kenichi; Kawano, Fumiaki; Asaoka, Kenzo

    2003-06-01

    Ni-Ti shape memory alloy fiber embedded resin matrix composites were produced for evaluation of "smart denture", a newly developing denture with the function to close its own crack. Their bending strength and shape recovery after instant crack repair was estimated. The embedded fibers did not decrease the bending strength of the composite after repair. The crack closure of the composites was performed well simply by heating at 80 degrees C. Nevertheless, they showed apparent deflection after crack repair. The following two phenomena were supposed to be the main cause of it: the polymerization shrinkage of matrix resin with heating, and the coefficient of the thermal expansion mismatch between the fiber and the matrix. The embedded fibers could close the crack of the matrix with enough high accuracy for specimen repair, but they turned out to change the specimen shape after repair.

  10. Tuning the vibration of a rotor with shape memory alloy metal rubber supports

    NASA Astrophysics Data System (ADS)

    Ma, Yanhong; Zhang, Qicheng; Zhang, Dayi; Scarpa, Fabrizio; Liu, Baolong; Hong, Jie

    2015-09-01

    The paper describes a novel smart rotor support damper with variable stiffness made with a new multifunctional material - the shape memory alloy metal rubber (SMA-MR). SMA-MR gives high load bearing capability (yield limit up to 100 MPa and stiffness exceeding 1e8 N/m), high damping (loss factor between 0.15 and 0.3) and variable stiffness (variation of 2.6 times between martensite and austenite phases). The SMA-MR has been used to replace a squeeze film damper and combined with an elastic support. The mechanical performance of the smart support damper has been investigated at room and high temperatures on a rotor test rig. The vibration tuning capabilities of the SMA-MR damper have been evaluated through FEM simulations and experimental tests. The study shows the feasibility of using the SMA-MR material for potential applications of active vibration control at different temperatures in rotordynamics systems.

  11. Photofabrication of the third dimension of NiTi shape memory alloy microactuators

    NASA Astrophysics Data System (ADS)

    Allen, David M.; Leong, Tony; Lim, Siang H.; Kohl, Manfred

    1997-09-01

    This paper describes experimental results of using various microlithography techniques to fabricate a range of microactuator devices from NiTi shape memory alloys. The range of products includes: planar double-beams form rolled foils etched form both sides; tapered double-beams; planar double beams from sputter-deposited films etched rom one side; a tubular test piece. Such photofabrication in not easily achieved and problems discussed in this paper include: achieving acceptable edge profiles through the thickness of the materials while maintaining high etch factors; tapering foil microactuators by means of chemical micro milling; coating NiTi tubes with electrophoretic photoresist; imaging a curved surface with a small radius of curvature; control of etching parameters for a constant rate of etch; the influence of NiTi oxide coatings on etching and; technical comparisons with other potential manufacturing processes.

  12. Direct observation of hierarchical nucleation of martensite and size-dependent superelasticity in shape memory alloys.

    PubMed

    Liu, Lifeng; Ding, Xiangdong; Li, Ju; Lookman, Turab; Sun, Jun

    2014-02-21

    Martensitic transformation usually creates hierarchical internal structures beyond mere change of the atomic crystal structure. Multi-stage nucleation is thus required, where nucleation (level-1) of the underlying atomic crystal lattice does not have to be immediately followed by the nucleation of higher-order superstructures (level-2 and above), such as polysynthetic laths. Using in situ transmission electron microscopy (TEM), we directly observe the nucleation of the level-2 superstructure in a Cu-Al-Ni single crystal under compression, with critical super-nuclei size L2c around 500 nm. When the sample size D decreases below L2c, the superelasticity behavior changes from a flat stress plateau to a continuously rising stress-strain curve. Such size dependence definitely would impact the application of shape memory alloys in miniaturized MEMS/NEMS devices.

  13. A novel shape memory alloy microactuator for large in-plane strokes and forces

    NASA Astrophysics Data System (ADS)

    Kabla, M.; Ben-David, E.; Shilo, D.

    2016-07-01

    This paper describes a novel concept for in-plane actuators based on a thin free-standing shape memory alloy (SMA) film. The presented guidelines can be used to design a variety of actuators that can provide a combination of large strokes and forces for linear and rotary motions. A prototype actuator demonstrated a displacement of 45 μm related to 4.5% of the SMA film length, and a force of up to 115 mN related to a stress of 230 MPa in the SMA film without plastic deformations. These capabilities allow the actuator to work against the stiff springs that are essential for the devices’ ability to sustain vibrations, impacts, and accelerations.

  14. On the driving force for crack growth during thermal actuation of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Baxevanis, T.; Parrinello, A. F.; Lagoudas, D. C.

    2016-04-01

    The effect of thermomechanically induced phase transformation on the driving force for crack growth in polycrystalline shape memory alloys is analyzed in an infinite center-cracked plate subjected to a thermal actuation cycle under mechanical load in plain strain. Finite element calculations are carried out to determine the mechanical fields near the static crack and the crack-tip energy release rate using the virtual crack closure technique. A substantial increase of the energy release rate - an order of magnitude for some material systems - is observed during the thermal cycle due to the stress redistribution induced by large scale phase transformation. Thus, phase transformation occurring due to thermal variations under mechanical load may result in crack growth if the crack-tip energy release rate reaches a material specific critical value.

  15. Design of a shape adaptive airfoil actuated by a Shape Memory Alloy strip for airplane tail

    NASA Astrophysics Data System (ADS)

    Shirzadeh, R.; Raissi Charmacani, K.; Tabesh, M.

    2011-04-01

    Of the factors that mainly affect the efficiency of the wing during a special flow regime, the shape of its airfoil cross section is the most significant. Airfoils are generally designed for a specific flight condition and, therefore, are not fully optimized in all flight conditions. It is very desirable to have an airfoil with the ability to change its shape based on the current regime. Shape memory alloy (SMA) actuators activate in response to changes in the temperature and can recover their original configuration after being deformed. This study presents the development of a method to control the shape of an airfoil using SMA actuators. To predict the thermomechanical behaviors of an SMA thin strip, 3D incremental formulation of the SMA constitutive model is implemented in FEA software package ABAQUS. The interactions between the airfoil structure and SMA thin strip actuator are investigated. Also, the aerodynamic performance of a standard airfoil with a plain flap is compared with an adaptive airfoil.

  16. Active control of sound radiation from panels using embedded shape memory alloy fibers

    NASA Astrophysics Data System (ADS)

    Rogers, C. A.; Fuller, C. R.; Liang, C.

    1990-01-01

    The fundamental relations and techniques demonstrating active structural-acoustic control using shape memory alloy (SMA) reinforced composites are discussed. A symmetric SMA reinforced laminate is described by the governing equation, then the Rayleigh-Ritz method is used to obtain an approximate solution to the governing equation, and the assumed solution is employed for the necessary energy expression. Transmission of sound through the composite plates is analyzed, the calculated natural frequencies for the first ten natural frequencies of the inactivated and fully activated plate are presented, and the transmission loss for the SMA reinforced composite plates is calculated for both the activated and inactivated cases. It is shown that acoustically excited SMA reinforced composite plates have the ability to adaptively change radiation efficiency, transmission loss, and directivity patterns of transmitted sound.

  17. Modeling the dynamic behavior of a shape memory alloy actuated catheter

    NASA Astrophysics Data System (ADS)

    Veeramani, Arun S.; Buckner, Gregory D.; Owen, Stephen B.; Cook, Richard C.; Bolotin, Gil

    2008-02-01

    In this paper we investigate the transient behavior of a simple active catheter: a central tube actuated by a single nitinol tendon enclosed by an outer sleeve. Dynamic models are developed to characterize the transient behavior and optimize the design of an experimental prototype. The bending mechanics are derived using a circular arc model and are experimentally validated. Nitinol actuation is described using the Seelecke-Muller-Achenbach model for single-crystal shape memory alloys using experimentally determined parameters. The dynamic characteristics of this active catheter system are simulated and compared with experimental results. Joule heating is used to generate tip deflections, which are computed in real time using a dual-camera imaging system. The effects of outer sleeve thickness on heat transfer and transient response characteristics are studied.

  18. Modeling and Bayesian parameter estimation for shape memory alloy bending actuators

    NASA Astrophysics Data System (ADS)

    Crews, John H.; Smith, Ralph C.

    2012-04-01

    In this paper, we employ a homogenized energy model (HEM) for shape memory alloy (SMA) bending actuators. Additionally, we utilize a Bayesian method for quantifying parameter uncertainty. The system consists of a SMA wire attached to a flexible beam. As the actuator is heated, the beam bends, providing endoscopic motion. The model parameters are fit to experimental data using an ordinary least-squares approach. The uncertainty in the fit model parameters is then quantified using Markov Chain Monte Carlo (MCMC) methods. The MCMC algorithm provides bounds on the parameters, which will ultimately be used in robust control algorithms. One purpose of the paper is to test the feasibility of the Random Walk Metropolis algorithm, the MCMC method used here.

  19. Actuator lifetime predictions for Ni60Ti40 shape memory alloy plate actuators

    NASA Astrophysics Data System (ADS)

    Wheeler, Robert; Ottmers, Cade; Hewling, Brett; Lagoudas, Dimitris

    2016-04-01

    Shape memory alloys (SMAs), due to their ability to repeatedly recover substantial deformations under applied mechanical loading, have the potential to impact the aerospace, automotive, biomedical, and energy industries as weight and volume saving replacements for conventional actuators. While numerous applications of SMA actuators have been flight tested and can be found in industrial applications, these actuators are generally limited to non-critical components, are not widely implemented and frequently one-off designs, and are generally overdesigned due to a lack of understanding of the effect of the loading path on the fatigue life and the lack of an accurate method of predicting actuator lifetimes. Previous efforts have been effective at predicting actuator lifetimes for isobaric dogbone test specimens. This study builds on previous work and investigates the actuation fatigue response of plate actuators with various stress concentrations through the use of digital image correlation and finite element simulations.

  20. Experimental Investigation on the Mechanical Instability of Superelastic NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Xiao, Yao; Zeng, Pan; Lei, Liping

    2016-09-01

    In this paper, primary attention is paid to the mechanical instability of superelastic NiTi shape memory alloy (SMA) during localized forward transformation at different temperatures. By inhibiting the localized phase transformation, we can obtain the up-down-up mechanical response of NiTi SMA, which is closely related to the intrinsic material softening during localized martensitic transformation. Furthermore, the material parameters of the up-down-up stress-strain curve are extracted, in such a way that this database can be utilized for simulation and validation of the theoretical analysis. It is found that during forward transformation, the upper yield stress, lower yield stress, Maxwell stress, and nucleation stress of NiTi SMA exhibit linear dependence on temperature. The relation between nucleation stress and temperature can be explained by the famous Clausius-Clapeyron equation, while the relation between upper/lower yield stress and temperature lacks theoretical study, which needs further investigation.

  1. Fracture toughness of shape memory alloy actuators: effect of transformation-induced plasticity

    NASA Astrophysics Data System (ADS)

    Jape, Sameer; Solomou, Alexandros; Baxevanis, Theocharis; Lagoudas, Dimitris C.

    2016-04-01

    Numerical analysis of static cracks in a plane strain center-cracked infinite medium shape memory alloy (SMA) panel subjected to cyclic thermal variations and a constant mechanical load is conducted using the finite element method. In solid-state SMA actuators, permanent changes in the material's microstructure in the form of dislocations are caused during cyclic thermomechanical loading, leading to macroscopic irreversible strains, known as transformation induced plastic (TRIP) strains. The influence of these accumulated TRIP strains on mechanical fields close to the crack tip is investigated in the present paper. Virtual crack growth technique (VCCT) in ABAQUS FEA suite is employed to calculate the crack tip energy release rate and crack is assumed to be stationary (or static) so that the crack tip energy release rate never reaches the material specific critical value. Increase in the crack tip energy release rate is observed during cooling and its relationship with accumulation of TRIP due to cyclic transformation is studied.

  2. Wear Properties of Porous NiTi Orthopedic Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Wu, Shuilin; Liu, Xiangmei; Yeung, K. W. K.; Xu, Z. S.; Chung, C. Y.; Chu, Paul K.

    2012-12-01

    Porous NiTi shape memory alloy (SMA) scaffolds have great potential to be used as orthopedic implants because of their porous structure and superior physical properties. Its metallic nature provides it with better mechanical properties and Young's modulus close to that of natural bones. Besides allowing tissue ingrowth and transfer of nutrients, porous SMA possesses unique pseudoelastic properties compatible to natural hard tissues like bones and tendons, thus expediting in vivo osseointegration. However, the nickel release from debris and the metal surface may cause osteocytic osteolysis at the interface between the artificial implants and bone tissues. Subsequent mobilization may finally lead to implant failure. In this study, the wear properties of porous NiTi with different porosities processed at different treatment temperatures are determined. The results of the study show that the porosity, phase transformation temperature, and annealing temperature are major factors influencing the wear characteristics of porous NiTi SMA.

  3. A thermomechanical model accounting for the behavior of shape memory alloys in finite deformations

    NASA Astrophysics Data System (ADS)

    Haller, Laviniu; Nedjar, Boumedienne; Moumni, Ziad; Vedinaş, Ioan; Trană, Eugen

    2016-07-01

    Shape memory alloys (SMA) comport an interesting behavior. They can undertake large strains and then recover their undeformed shape by heating. In this context, one of the aspects that challenged many researchers was the development of a mathematical model to predict the behavior of a known SMA under real-life conditions, or finite strain. This paper is aimed at working out a finite strain mathematical model for a Ni-Ti SMA, under the superelastic experiment conditions and under uniaxial mechanical loading, based on the Zaki-Moumni 3D mathematical model developed under the small perturbations assumption. Within the current article, a comparison between experimental findings and calculated results is also investigated. The proposed finite strain mathematical model shows good agreement with experimental data.

  4. Energy-based fatigue model for shape memory alloys including thermomechanical coupling

    NASA Astrophysics Data System (ADS)

    Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

    2016-03-01

    This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

  5. Direct observation of hierarchical nucleation of martensite and size-dependent superelasticity in shape memory alloys.

    PubMed

    Liu, Lifeng; Ding, Xiangdong; Li, Ju; Lookman, Turab; Sun, Jun

    2014-02-21

    Martensitic transformation usually creates hierarchical internal structures beyond mere change of the atomic crystal structure. Multi-stage nucleation is thus required, where nucleation (level-1) of the underlying atomic crystal lattice does not have to be immediately followed by the nucleation of higher-order superstructures (level-2 and above), such as polysynthetic laths. Using in situ transmission electron microscopy (TEM), we directly observe the nucleation of the level-2 superstructure in a Cu-Al-Ni single crystal under compression, with critical super-nuclei size L2c around 500 nm. When the sample size D decreases below L2c, the superelasticity behavior changes from a flat stress plateau to a continuously rising stress-strain curve. Such size dependence definitely would impact the application of shape memory alloys in miniaturized MEMS/NEMS devices. PMID:24384687

  6. Design and analysis of variable-twist tiltrotor blades using shape memory alloy hybrid composites

    NASA Astrophysics Data System (ADS)

    Park, Jae-Sang; Kim, Seong-Hwan; Jung, Sung Nam; Lee, Myeong-Kyu

    2011-01-01

    The tiltrotor blade, or proprotor, acts as a rotor in the helicopter mode and as a propeller in the airplane mode. For a better performance, the proprotor should have different built-in twist distributions along the blade span, suitable for each operational mode. This paper proposes a new variable-twist proprotor concept that can adjust the built-in twist distribution for given flight modes. For a variable-twist control, the present proprotor adopts shape memory alloy hybrid composites (SMAHC) containing shape memory alloy (SMA) wires embedded in the composite matrix. The proprotor of the Korea Aerospace Research Institute (KARI) Smart Unmanned Aerial Vehicle (SUAV), which is based on the tiltrotor concept, is used as a baseline proprotor model. The cross-sectional properties of the variable-twist proprotor are designed to maintain the cross-sectional properties of the original proprotor as closely as possible. However, the torsion stiffness is significantly reduced to accommodate the variable-twist control. A nonlinear flexible multibody dynamic analysis is employed to investigate the dynamic characteristics of the proprotor such as natural frequency and damping in the whirl flutter mode, the blade structural loads in a transition flight and the rotor performance in hover. The numerical results show that the present proprotor is designed to have a strong similarity to the baseline proprotor in dynamic and load characteristics. It is demonstrated that the present proprotor concept could be used to improve the hover performance adaptively when the variable-twist control using the SMAHC is applied appropriately.

  7. Thermal control of shape memory alloy artificial anal sphincters for complete implantation

    NASA Astrophysics Data System (ADS)

    Luo, Yun; Okuyama, Takeshi; Takagi, Toshiyuki; Kamiyama, Takamichi; Nishi, Kotaro; Yambe, Tomoyuki

    2005-02-01

    This paper presents an approach for the thermal control of an artificial anal sphincter using shape memory alloys. An artificial anal sphincter has been proposed by the authors to resolve problems of severe fecal incontinence in patients. The basic design of the artificial sphincter consists of two all-round shape memory alloy plates as the main functional parts, and heaters that are attached to the SMA plates for generating the thermal cycles required for the phase transformation accompanied shape changes of the plates. The SMA artificial sphincter could be fitted around intestines, performing an occlusion function at body temperature and a release function upon heating. Thermal compatibility of such prostheses is most important and is critical for practical use. Since a temperature rise of approximately 20 °C from body temperature is needed to activate a complete transformation of SMA plates, an earlier model of ours allowed only a short period of heating, resulting in incomplete evacuation. In this work, a thermal control approach using a temperature-responsive reed switch has been incorporated into the device to prevent the SMA plates from overheating. Then, with thermal insulation the artificial anal sphincter is expected to allow a long enough opening period for fecal continence; without any thermal impact to the surrounding tissues that would be in contact with the artificial sphincter. Thermal control was confirmed in both in vitro and in vivo experiments, suggesting the effectiveness of the present approach. The modified SMA artificial anal sphincter has been implanted into animal models for chronic experiments of up to 4 weeks, and has exhibited good performance by maintaining occlusion and release functions. At autopsy, no anomaly due to thermal impact was found on the surfaces of intestines that had been in contact with the artificial anal sphincter.

  8. Closed-loop control of a shape memory alloy actuation system for variable area fan nozzle

    NASA Astrophysics Data System (ADS)

    Barooah, Prabir; Rey, Nancy

    2002-07-01

    Shape Memory Alloys have been used in a wide variety of actuation applications. A bundled shape memory alloy cable actuator, capable of providing large force and displacement has been developed by United Technologies Corporation (patents pending) for actuating a Variable Area fan Nozzle (VAN). The ability to control fan nozzle exit area is an enabling technology for the next generation turbofan engines. Performance benefits for VAN engines are estimated to be up to 9% in Thrust Specific Fuel Consumption (TSFC) compared to traditional fixed geometry designs. The advantage of SMA actuated VAN design is light weight and low complexity compared to conventionally actuated designs. To achieve the maximum efficiency from a VAN engine, the nozzle exit area has to be continuously varied for a certain period of time during climb, since the optimum nozzle exit area is a function of several flight variables (flight Mach number, altitude etc). Hence, the actuator had to be controlled to provide the time varying desired nozzle area. A new control algorithm was developed for this purpose, which produced the desired flap area by metering the resistive heating of the SMA actuator. Since no active cooling was used, reducing overshoot was a significant challenge of the controller. A full scale, 2 flap model of the VAN system was built, which was capable of simulating a 20% nozzle area variation, and tested under full scale aerodynamic load in NASA Langley Jet Exit Test facility. The controller met all the requirements of the actuation system and was able to drive the flap position to the desired position with less than 2% overshoot in step input tests. The controller is based on a adaptive algorithm formulation with logical switches that reduces its overshoot error. Although the effectiveness of the controller was demonstrated in full scale model tests, no theoretical results as to its stability and robustness has been derived. Stability of the controller will have to be investigated

  9. Nano-hardness, wear resistance and pseudoelasticity of hafnium implanted NiTi shape memory alloy.

    PubMed

    Zhao, Tingting; Li, Yan; Liu, Yong; Zhao, Xinqing

    2012-09-01

    NiTi shape memory alloy was modified by Hf ion implantation to improve its wear resistance and surface integrity against deformation. 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 nano-hardness measured by nano-indentation was decreased even at the depth larger than the maximum reach of the implanted Hf ion. The lower coefficient of friction with much longer fretting time indicated the remarkable improvement of wear resistance of Hf implanted NiTi, especially for the sample with a moderate incident dose. The formation of TiO₂/HfO₂ nanofilm with larger thickness and decrease of the nano-hardness played important roles in the improvement of wear resistance. Moreover, Hf implanted NiTi exhibited larger pseudoelastic recovery strain and retained better surface integrity even after being strained to 10% as demonstrated by in situ scanning electron microscope observation.

  10. Shakedown based model for high-cycle fatigue of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Gu, Xiaojun; Moumni, Ziad; Zaki, Wael; Zhang, Weihong

    2016-11-01

    The paper presents a high-cycle fatigue criterion for shape memory alloys (SMAs) based on shakedown analysis. The analysis accounts for phase transformation as well as reorientation of martensite variants as possible sources of fatigue damage. In the case of high-cycle fatigue, once the structure has reached an asymptotic state, damage is assumed to become confined at the mesoscopic scale, or the scale of the grain, with no discernable inelasticity at the macroscopic scale. Using a multiscale approach, a high-cycle fatigue criterion analogous to the Dang Van model (Dang Van 1973) for elastoplastic metals is derived for SMAs obeying the Zaki–Moumni model for SMAs (Zaki and Moumni 2007a). For these alloys, a safe domain is established in stress deviator space, consisting of a hypercylinder with axis parallel to the direction of martensite orientation at the mesoscopic scale. Safety with regard to high-cycle fatigue, upon elastic shakedown, is conditioned by the persistence of the macroscopic stress path at every material point within the hypercylinder, whose size depends on the volume fraction of martensite. The proposed criterion computes a fatigue factor at each material point, indicating its degree of safeness with respect to high cycle fatigue.

  11. Gradation of Nanostructures in Cold-Rolled and Annealed Ti-Ni Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Prokoshkin, S.; Brailovski, V.; Dubinskiy, S.; Inaekyan, K.; Kreitcberg, A.

    2016-03-01

    Nanostructures formed in Ti-50.26 at.%Ni shape memory alloy as a result of post-deformation annealing (PDA) at 400 °C (1 h) after cold rolling (CR) in the e = 0.3-1.9 true strain range are classified and quantitatively studied. The statistical quantitative transmission electron microscopy analysis of bright and dark field images and selected area diffraction patterns reveal the following regularities. Two types of nanostructure form in B2-austenite as a result of PDA after CR: (a) a nanosubgrained structure, which consists of subgrains formed as a result of polygonization of the initially highly dislocated substructure; (b) a nanocrystalline structure, which represents a combination of the deformation-induced nano-grains grown during PDA and new nano-grains formed during crystallization of the amorphous phase. After moderate CR (e = 0.3), mainly nanosubgrained structure forms as a result of PDA. After CR of moderate-to-high intensity (e = 0.5-1.0) followed by PDA, the structure is mixed (nanosubgrained+nanocrystalline). After high-intensity CR (e = 1.2-1.9) and PDA, the structure is mainly nanocrystalline. This nanostructure identification allows adequate analysis of the nature of the parent phase boundaries in the thermomechanically processed Ti-Ni alloys and of their effect on the transformation and mechanical behaviors.

  12. Determination of strain fields in porous shape memory alloys using micro-computed tomography

    NASA Astrophysics Data System (ADS)

    Bormann, Therese; Friess, Sebastian; de Wild, Michael; Schumacher, Ralf; Schulz, Georg; Müller, Bert

    2010-09-01

    Shape memory alloys (SMAs) belong to 'intelligent' materials since the metal alloy can change its macroscopic shape as the result of the temperature-induced, reversible martensite-austenite phase transition. SMAs are often applied for medical applications such as stents, hinge-less instruments, artificial muscles, and dental braces. Rapid prototyping techniques, including selective laser melting (SLM), allow fabricating complex porous SMA microstructures. In the present study, the macroscopic shape changes of the SMA test structures fabricated by SLM have been investigated by means of micro computed tomography (μCT). For this purpose, the SMA structures are placed into the heating stage of the μCT system SkyScan 1172™ (SkyScan, Kontich, Belgium) to acquire three-dimensional datasets above and below the transition temperature, i.e. at room temperature and at about 80°C, respectively. The two datasets were registered on the basis of an affine registration algorithm with nine independent parameters - three for the translation, three for the rotation and three for the scaling in orthogonal directions. Essentially, the scaling parameters characterize the macroscopic deformation of the SMA structure of interest. Furthermore, applying the non-rigid registration algorithm, the three-dimensional strain field of the SMA structure on the micrometer scale comes to light. The strain fields obtained will serve for the optimization of the SLM-process and, more important, of the design of the complex shaped SMA structures for tissue engineering and medical implants.

  13. Critical Stresses for Twinning, Slip, and Transformation in Ti-Based Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Ojha, A.; Sehitoglu, H.

    2016-06-01

    We investigate the effect of Nb and Ta contents on the (i) critical resolved shear stress (CRSS) for the β - α″ transformation, (ii) the CRSS for austenite slip, and (iii) the CRSS for twin nucleation in martensite ( α″ phase) that govern shape memory and superelasticity in Ti-based alloys. The critical stresses for slip and twinning are achieved with a modified Peierls Nabarro formalism utilizing generalized stacking fault energy and the generalized planar fault energy (GPFE), respectively, obtained from first-principles density functional theory (DFT) calculations. During the calculation of the twinning stress, we show the importance of the shuffling process in stabilizing and lowering the GPFE curve. Similarly, the transformation stress is obtained with heterogeneous martensite nucleation mechanism incorporating the energy barriers associated with the transformation process. Here, we point to the role of dislocations in the shuffling process during the early stage of transformation. We show that the increase of Ta content raises the CRSS more effectively for the case of slip compared to twinning or transformation. The slip stress and twin stress magnitudes increase with an increase in the unstable fault energy ( {γ_{{us}} } ) and unstable twinning fault energy ( {γ_{{ut}} } ), respectively. In summary, as the Ta composition increases, the difference between martensite/austenite slip resistance and the transformation/twinning stress widens showing the efficacy of Ta alloying additions.

  14. Development of a Numerical Model for High-Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    DeCastro, Jonathan A.; Melcher, Kevin J.; Noebe, Ronald D.; Gaydosh, Darrell J.

    2006-01-01

    A thermomechanical hysteresis model for a high-temperature shape memory alloy (HTSMA) actuator material is presented. The model is capable of predicting strain output of a tensile-loaded HTSMA when excited by arbitrary temperature-stress inputs for the purpose of actuator and controls design. Common quasi-static generalized Preisach hysteresis models available in the literature require large sets of experimental data for model identification at a particular operating point, and substantially more data for multiple operating points. The novel algorithm introduced here proposes an alternate approach to Preisach methods that is better suited for research-stage alloys, such as recently-developed HTSMAs, for which a complete database is not yet available. A detailed description of the minor loop hysteresis model is presented in this paper, as well as a methodology for determination of model parameters. The model is then qualitatively evaluated with respect to well-established Preisach properties and against a set of low-temperature cycled loading data using a modified form of the one-dimensional Brinson constitutive equation. The computationally efficient algorithm demonstrates adherence to Preisach properties and excellent agreement to the validation data set.

  15. Control of Thermal Deflection, Panel Flutter and Acoustic Fatigue at Elevated Temperatures Using Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Mei, Chuh; Huang, Jen-Kuang

    1996-01-01

    The High Speed Civil Transport (HSCT) will have to be designed to withstand high aerodynamic load at supersonic speeds (panel flutter) and high acoustic load (acoustic or sonic fatigue) due to fluctuating boundary layer or jet engine acoustic pressure. The thermal deflection of the skin panels will also alter the vehicle's configuration, thus it may affect the aerodynamic characteristics of the vehicle and lead to poor performance. Shape memory alloys (SMA) have an unique ability to recover large strains completely when the alloy is heated above the characteristic transformation (austenite finish T(sub f)) temperature. The recovery stress and elastic modulus are both temperature dependent, and the recovery stress also depends on the initial strain. An innovative concept is to utilize the recovery stress by embedding the initially strained SMA wire in a graphite/epoxy composite laminated panel. The SMA wires are thus restrained and large inplane forces are induced in the panel at elevated temeperatures. By embedding SMA in composite panel, the panel becomes much stiffer at elevated temperatures. That is because the large tensile inplane forces induced in the panel from the SMA recovery stress. A stiffer panel would certainly yield smaller dynamic responses.

  16. Thermal Stabilization of NiTiCuV Shape Memory Alloys: Observations During Elastocaloric Training

    NASA Astrophysics Data System (ADS)

    Schmidt, Marvin; Ullrich, Johannes; Wieczorek, André; Frenzel, Jan; Schütze, Andreas; Eggeler, Gunther; Seelecke, Stefan

    2015-06-01

    The paper presents novel findings observed during the training process of superelastic, elastocalorically optimized Ni-Ti-based shape memory alloys (SMA). NiTiCuV alloys exhibit large latent heats and a small mechanical hysteresis, which may potentially lead to the development of efficient solid-state-based cooling processes. The paper starts with a brief introduction to the underlying principles of elastocaloric cooling, illustrating the effect by means of a typical thermodynamic cycle. It proceeds with the description of a custom-built testing platform that allows observation of temperature profiles and heat transfer between SMA and heat source/sink during high-loading-rate tensile tests. Similar to other SMA applications, a training process is necessary in order to guarantee stable performance. This well-known mechanical stabilization affects the stress-strain hysteresis and the cycle-dependent evolution of differential scanning calorimetry results. In addition, it can be shown here that the training is also accompanied by a cycle-dependent evolution of temperature profiles on the surface of an SMA ribbon. The applied training leads to local temperature peaks with intensity, number, and distribution of the temperature fronts showing a cycle dependency. The homogeneity of the elastocaloric effect has a significant influence on the efficiency of elastocaloric cooling process and is a key aspect of the specific material characterization.

  17. Effect of Pore Structure Regulation on the Properties of Porous TiNbZr Shape Memory Alloys for Biomedical Application

    NASA Astrophysics Data System (ADS)

    Lai, Ming; Gao, Yan; Yuan, Bin; Zhu, Min

    2015-01-01

    Recently, porous Ti-Nb-based shape memory alloys have been considered as promising implants for biomedical application, because of their non-toxic elements, low elastic modulus, and stable superelasticity. However, the inverse relationship between pore characteristics and superelasticity of porous SMAs will strongly affect their clinical application. Until now, there have been few works specifically focusing on the effect of pore structure on the mechanical properties and superelasticity of porous Ti-Nb-based SMAs. In this study, the pore structure, including porosity and pore size, of porous Ti-22Nb-6Zr alloys was successfully regulated by adjusting the amount and size of space-holder particles. XRD and SEM investigation showed that all these porous alloys had homogeneous composition. Compression tests indicated that porosity played an important role in the mechanical properties and superelasticity of these porous alloys. Those alloys with porosity in the range of 38.5%-49.7% exhibited mechanical properties approaching to cortical bones, with elastic modulus, compressive strength, and recoverable strain in the range of 7.2-11.4 GPa, 188-422 MPa, and 2.4%-2.6%, respectively. Under the same porosity, the alloys with larger pores exhibited lower elastic modulus, while the alloys with smaller pores presented higher compressive strength.

  18. Structure and properties of nitrided surface layer produced on NiTi shape memory alloy by low temperature plasma nitriding

    NASA Astrophysics Data System (ADS)

    Czarnowska, Elżbieta; Borowski, Tomasz; Sowińska, Agnieszka; Lelątko, Józef; Oleksiak, Justyna; Kamiński, Janusz; Tarnowski, Michał; Wierzchoń, Tadeusz

    2015-04-01

    NiTi shape memory alloys are used for bone and cardiological implants. However, on account of the metallosis effect, i.e. the release of the alloy elements into surrounding tissues, they are subjected to various surface treatment processes in order to improve their corrosion resistance and biocompatibility without influencing the required shape memory properties. In this paper, the microstructure, topography and morphology of TiN surface layer on NiTi alloy, and corrosion resistance, both before and after nitriding in low-temperature plasma at 290 °C, are presented. Examinations with the use of the potentiodynamic and electrochemical impedance spectroscopy methods were carried out and show an increase of corrosion resistance in Ringer's solution after glow-discharge nitriding. This surface titanium nitride layer also improved the adhesion of platelets and the proliferation of osteoblasts, which was investigated in in vitro experiments with human cells. Experimental data revealed that nitriding NiTi shape memory alloy under low-temperature plasma improves its properties for bone implant applications.

  19. A Biomechanical Research of Growth Control of Spine by Shape Memory Alloy Staples

    PubMed Central

    Zhang, Wei; Zheng, Guoquan; Zhang, Ruyi; Wang, Yan

    2013-01-01

    Shape memory alloy (SMA) staples in nickel titanium with shape memory effect are effective for spinal growth control. This study was designed to evaluate the biomechanical properties of the staples and observe the stability of the fixed segments spine after the staples were implanted. According to the vertical distance of the vertebrae, SMA staples of 5, 6.5, and 8 mm were designed. The recovery stress of 24 SMA staples in three groups was measured. The pullout strength of SMA staples and stainless steel staples in each functional spinal unit was measured. Each of the six fresh specimens was divided into three conditions: normal, single staple, and double staples. Under each condition, the angle and torque of spinal movements in six directions were tested. Results show that the differences in recovery stress and maximum pullout strength between groups were statistically significant. In left and right bending, flextion, and extention, the stability of spine was decreased in conditions of single staple and double staples. Biomechanical function of SMA staples was superior to stainless steel staple. SMA staples have the function of hemiepiphyseal compression and kyphosis and scoliosis model of thoracic vertebrae in goat could be successfully created by the fusionless technique. PMID:24350265

  20. Electro-bending characterization of adaptive 3D fiber reinforced plastics based on shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ashir, Moniruddoza; Hahn, Lars; Kluge, Axel; Nocke, Andreas; Cherif, Chokri

    2016-03-01

    The industrial importance of fiber reinforced plastics (FRPs) is growing steadily in recent years, which are mostly used in different niche products, has been growing steadily in recent years. The integration of sensors and actuators in FRP is potentially valuable for creating innovative applications and therefore the market acceptance of adaptive FRP is increasing. In particular, in the field of highly stressed FRP, structural integrated systems for continuous component parts monitoring play an important role. This presented work focuses on the electro-mechanical characterization of adaptive three-dimensional (3D)FRP with integrated textile-based actuators. Here, the friction spun hybrid yarn, consisting of shape memory alloy (SMA) in wire form as core, serves as an actuator. Because of the shape memory effect, the SMA-hybrid yarn returns to its original shape upon heating that also causes the deformation of adaptive 3D FRP. In order to investigate the influences of the deformation behavior of the adaptive 3D FRP, investigations in this research are varied according to the structural parameters such as radius of curvature of the adaptive 3D FRP, fabric types and number of layers of the fabric in the composite. Results show that reproducible deformations can be realized with adaptive 3D FRP and that structural parameters have a significant impact on the deformation capability.

  1. Smart composite shell structures with shape memory alloy wires and thin foils

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Taek; Kim, Cheol; Lee, Sang-Ryong

    2005-02-01

    Shape memory alloys (SMAs) find many applications in smart composite structural systems as the active components. Their ability to provide a high force and large displacement makes them an excellent candidate for an actuator for controlling the shape of smart structures. In this paper, using a macroscopic model that captures the thermo-mechanical behaviors and the two-way shape memory effect (TWSME) of SMAs smart morphing polymeric composite shell structures like shape-changeable UAV wings is demonstrated and analyzed numerically and experimentally when subjected to various kinds of pressure loads. The controllable shapes of the morphing shells to that thin SMA strip actuator are attached are investigated depending on various phase transformation temperatures. SMA strips start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the shell structures to deform three dimensionally. The behaviors of composite shells attached with SMA strip actuators are analyzed using the finite element methods and 3-D constitutive equations of SMAs. Several morphing composite shell structures are fabricated and their experimental shape changes depending on temperatures are compared to the numerical results. That two results show good correlations indicates the finite element analysis and 3-D constitutive equations are accurate enough to utilize them for the design of smart composite shell structures for various applications.

  2. Shape memory alloy actuated accumulator for ultra-deepwater oil and gas exploration

    NASA Astrophysics Data System (ADS)

    Patil, Devendra; Song, Gangbing

    2016-04-01

    As offshore oil and gas exploration moves further offshore and into deeper waters to reach hydrocarbon reserves, it is becoming essential for the industry to develop more reliable and efficient hydraulic accumulators to supply pressured hydraulic fluid for various control and actuation operations, such as closing rams of blowout preventers and controlling subsea valves on the seafloor. By utilizing the shape memory effect property of nitinol, which is a type of shape memory alloy (SMA), an innovative SMA actuated hydraulic accumulator prototype has been developed and successfully tested at Smart Materials and Structure Laboratory at the University of Houston. Absence of gas in the developed SMA accumulator prototype makes it immune to hydrostatic head loss caused by water depth and thus reduces the number of accumulators required in deep water operations. Experiments with a feedback control have demonstrated that the proposed SMA actuated accumulator can provide precisely regulated pressurized fluids. Furthermore the potential use of ultracapacitors along with an embedded system to control the electric power supplied to SMA allows this accumulator to be an autonomous device for deployment. The developed SMA accumulator will make deepwater oil extraction systems more compact and cost effective.

  3. Precipitation Effects on the Martensitic Transformation in a Cu-Al-Ni Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Suru, Marius-Gabriel; Lohan, Nicoleta-Monica; Pricop, Bogdan; Mihalache, Elena; Mocanu, Mihai; Bujoreanu, Leandru-Gheorghe

    2016-04-01

    This paper describes the effects of precipitation of α-phase on a Cu-Al-Ni shape memory alloy (SMA) with chemical composition bordering on β region. By differential scanning calorimetry, a series of reproducible heat flow fluctuations was determined on heating a hot-rolled martensitic Cu-Al-Ni SMA, which was associated with the precipitation of α-phase. Two heat treatments were given to the SMA so as to "freeze" its states before and after the thermal range for precipitation, respectively. The corresponding microstructures of the two heat-treated states were observed by optical and scanning electron microscopy and were compared with the initial martensitic state. Energy dispersive spectroscopy experiments were carried out to determine the chemical compositions of the different phases formed in heat-treated specimens. The initial as well as the heat-treated specimens with a lamellar shape were further comparatively investigated by dynamic mechanical analysis and two-way shape memory effect (TWSME) tests comprising heating-cooling cycles under a bending load. Temperature scans were applied to the three types of specimens (initial and heat-treated states), so as to bring out the effects of heat treatment. The storage modulus increased, corresponding to the reversion of thermoelastic martensite and disappeared with the formation of precipitates. These features are finally discussed in association with TWSME under bending.

  4. Comparing magnetostructural transitions in Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Dubenko, Igor; Granovsky, Alexander; Lahderanta, Erkki; Kashirin, Maxim; Makagonov, Vladimir; Aryal, Anil; Quetz, Abdiel; Pandey, Sudip; Rodionov, Igor; Samanta, Tapas; Stadler, Shane; Mazumdar, Dipanjan; Ali, Naushad

    2016-03-01

    The crystal structure, magnetic and transport properties, including resistivity and thermopower, of Ni50Mn18.75Cu6.25Ga25 and Ni49.80Mn34.66In15.54 Heusler alloys were studied in the (10-400) K temperature interval. We show that their physical properties are remarkably different, thereby pointing to different origin of their magnetostructural transition (MST). A Seebeck coefficient (S) was found to pass minimum of about -20 μV/K in respect of temperature for both compounds. It was shown that MST observed for both compounds results in jump-like changes in S for Ga-based compound and jump in resistivity of about 20 and 200 μΩ cm for Ga and In -based compounds, respectively. The combined analyzes of the present results with that from literature show that the density of states at the Fermi level does not change strongly at the MST in the case of Ni-Mn-In alloys as compared to that of Ni-Mn-Ga.

  5. Effect of micro-arc oxidation surface modification on the properties of the NiTi shape memory alloy.

    PubMed

    Xu, J L; Zhong, Z C; Yu, D Z; Liu, F; Luo, J M

    2012-12-01

    In this paper, the effects of micro-arc oxidation (MAO) surface modification (alumina coatings) on the phase transformation behavior, shape memory characteristics, in vitro haemocopatibility and cytocompatibility of the biomedical NiTi alloy were investigated respectively by differential scanning calorimetry, bending test, hemolysis ratio test, dynamic blood clotting test, platelet adhesion test and cytotoxicity testing by human osteoblasts (Hobs). The results showed that there were no obvious changes of the phase transformation temperatures and shape memory characteristics of the NiTi alloy after the MAO surface modification and the coating could withstand the thermal shock and volume change caused by martensite-austenite phase transformation. Compared to the uncoated NiTi alloys, the MAO surface modification could effectively improve the haemocopatibility of the coated NiTi alloys by the reduced hemolysis ratio, the prolonged dynamic clotting time and the decreased number of platelet adhesion; and the rough and porous alumina coatings could obviously promote the adherence, spread and proliferation of the Hobs with the significant increase of proliferation number of Hobs adhered on the surface of the coated NiTi alloys (P < 0.05).

  6. Formation of the thermodeformational properties of Mn-Cu-based alloys having the two-way shape memory effect

    NASA Astrophysics Data System (ADS)

    Nosova, G. I.

    2008-08-01

    The specific features of the thermodeformational behavior of Mn-Cu-based alloys with the two-way shape memory effect are revealed, and their connection with the diffusionless fcc → fct phase transition and the forming structure is discussed. The mechanism of the reversible thermal deformation caused by directed internal stresses is considered. The factors that affect the temperature interval of the highest thermal sensitivity and the value of reversible and specific thermal deformation are found, and the possibilities of their change by additional alloying and heat treatment are studied.

  7. Effects of microstructure and deformation conditions on the hot formability of Ni-Ti-Hf shape memory alloys.

    PubMed

    Kim, Jeoung Han; Park, Chan Hee; Kim, Seong Woong; Hong, Jae Keun; Oh, Chang-Seok; Jeon, Yeong Min; Kim, Kyong Min; Yeom, Jong Taek

    2014-12-01

    Ingots of Ni-Ti-Hf shape memory alloys were prepared by vacuum arc re-melting. Isothermal hot compression tests were conducted at temperatures ranging from 700 to 1000 degrees C and at strain rates from 10(-2) s(-1) to 1.0 s(-1). A decrease in the Ni content below 50.2 at.% significantly deteriorated the hot workability due to the formation of a brittle second phase. Also, the low Ni content alloy showed poor workability when the temperature exceeded 900 degrees C. Additional compression tests were conducted under various conditions to clarify the effects of the chemical composition, solidification anisotropy, and the strain rate.

  8. Design and thermo-mechanical analysis of a new NiTi shape memory alloy fixing clip.

    PubMed

    Nespoli, Adelaide; Dallolio, Villiam; Stortiero, Francesco; Besseghini, Stefano; Passaretti, Francesca; Villa, Elena

    2014-04-01

    In this work, a new NiTi shape memory alloy (SMA) bone fixator is proposed. Thanks to the shape memory effect, this device does not need any external tool for the fixation, as the anchorage is obtained only by the self-accommodation of the clip during the parent transformation. Calorimetry and thermo-mechanical tests were used to evaluate the phase transformation temperatures and to estimate the forces generated both during the fixing surgical procedure and after the surgical operation. An application on animal anatomical sample was also performed; an appropriate mechanical tightness as well as a good handiness has been found.

  9. Influence of aging and thermomechanical cycling on the magnetostriction and magnetic shape memory effect in martensitic alloy

    NASA Astrophysics Data System (ADS)

    L'vov, Victor A.; Kosogor, Anna; Barandiaran, Jose M.; Chernenko, Volodymyr A.

    2015-10-01

    An influence of internal stress created by the crystal defects on the magnetically induced reorientation (MIR) of martensite variants in the ferromagnetic shape memory alloy (FSMA) has been analyzed. Using the internal stress conception, a noticeable influence of the spatial reconfiguration of crystal defects on the ordinary magnetostriction of FSMA and magnetic shape memory (MSM) effect has been predicted. It has been shown that the defect reconfiguration, which stabilizes the martensitic phase during martensite aging, increases the shear elastic modulus. The increase of shear modulus reduces the magnetostriction value and in this way suppresses the MSM effect. The magneto-thermo-mechanical training of aged alloys destabilizes the martensitic phase, restores the initial magnetostriction value, and promotes the MSM effect.

  10. Study of Martensitic Phase transformation in a NiTiCu Thin Film Shape Memory Alloy Using Photoelectron Emission Microscopy

    SciTech Connect

    Cai, Mingdong; Langford, Stephen C.; Wu, Maggie J.; Huang, W. M.; Xiong, Gang; Droubay, Timothy C.; Joly, Alan G.; Beck, Kenneth; Hess, Wayne P.; Dickinson, J. T.

    2007-01-01

    The thermally-induced martensitic phase transformation in a polycrystalline NiTiCu thin film shape memory alloy was probed by photoelectron emission microscopy (PEEM). In situ PEEM images reveal distinct changes in microstructure and photoemission intensity at the phase transition temperatures. In particular, images of the low temperature, martensite phase are brighter than that of the high temperature, austenite phase, due to the relatively lower work function of the martensite. Ultra-violet photoelectron spectroscopy shows that the effective work function changes by about 0.16 eV during thermal cycling. In situ PEEM images also show that the network of trenches observed on the room temperature film disappear suddenly during heating and reappear suddenly during subsequent cooling. These trenches are also characterized by atomic force microscopy at selected temperatures. We describe implications of these observations with respect to the spatial distribution of phases during thermal cycling in this thin film shape memory alloy.

  11. Improvement of the shape memory characteristics of a Cu-Zn-Al alloy with manganese and zirconium addition

    SciTech Connect

    Zou, W.H.; Lam, C.W.H.; Chung, C.Y.; Lai, J.K.L.

    1997-04-15

    Cu-based shape memory alloys (SMAs) possess good shape memory effect (SME) and have the advantage of lower price than Ti-Ni SMA. However, there are still some problems which should be solved before they can be used widely. Addition of suitable alloying elements can improve the mechanical properties, stabilization of martensitic transformations and also the SME of Cu-based SMAs significantly. Cu-Zn-Al is an important Cu-based SMA that suffers from the martensite stabilization and intergranular cracking in the processing procedures and service. As a modification of Cu-Zn-Al SMAs, the effects of Mn and Zr addition on the structure and martensite transformation behavior of different heat treated Cu-21Zn-6Al-1Mn-0.5Zr (wt%) SMA have been studied and compared to that of Cu-21Zn-6Al (wt%) SMA in the present paper.

  12. Infrared thermography videos of the elastocaloric effect for shape memory alloys NiTi and Ni2FeGa

    PubMed Central

    Pataky, Garrett J.; Ertekin, Elif; Sehitoglu, Huseyin

    2015-01-01

    Infrared thermogrpahy was utilized to record the temperature change during tensile loading cycles of two shape memory alloy single crystals with pseudoelastic behavior. During unloading, a giant temperature drop was measured in the gage section due to the elastocaloric effect. This data article provides a video of a [001] oriented Ni2FeGa single crystal, including the corresponding stress–strain curve, shows the temperature drop over one cycle. The second video of a [148] oriented NiTi single crystal depicts the repeatability of the elastocaloric effect by showing two consecutive cycles. The videos are supplied in this paper. For further analysis and enhanced discussion of large temperature change in shape memory alloys, see Pataky et al. [1] PMID:26380838

  13. Infrared thermography videos of the elastocaloric effect for shape memory alloys NiTi and Ni2FeGa.

    PubMed

    Pataky, Garrett J; Ertekin, Elif; Sehitoglu, Huseyin

    2015-12-01

    Infrared thermogrpahy was utilized to record the temperature change during tensile loading cycles of two shape memory alloy single crystals with pseudoelastic behavior. During unloading, a giant temperature drop was measured in the gage section due to the elastocaloric effect. This data article provides a video of a [001] oriented Ni2FeGa single crystal, including the corresponding stress-strain curve, shows the temperature drop over one cycle. The second video of a [148] oriented NiTi single crystal depicts the repeatability of the elastocaloric effect by showing two consecutive cycles. The videos are supplied in this paper. For further analysis and enhanced discussion of large temperature change in shape memory alloys, see Pataky et al. [1].

  14. Closed chamber pupilloplasty with an injectable shape memory alloy clip in enucleated porcine eyes in the laboratory setting.

    PubMed

    Erlanger, Michael S; Olson, Jeffrey L

    2012-01-01

    A novel surgical technique and novel surgical instrumentation for closing a pupil defect in a closed chamber eye is described. The technique was performed in a laboratory setting using ex-vivo porcine eyes using a 30-gauge deployment system to repair iris defects. Given the difficulty of suturing in a closed chamber eye, the use of an injectable, shape memory alloy clip offers the advantages of rapid, easy deployment and increased strength over conventional suture techniques. PMID:22767338

  15. Modelling and control of an adaptive tuned mass damper based on shape memory alloys and eddy currents

    NASA Astrophysics Data System (ADS)

    Berardengo, M.; Cigada, A.; Guanziroli, F.; Manzoni, S.

    2015-08-01

    Tuned mass dampers have long since been used to attenuate vibrations. The need to make them adaptive in order to function even after changes of the dynamic characteristics of the system to be controlled has led to using many different technologies with the aim of improving adaptation performances. Shape memory alloys have already been proven to have properties suitable for creating adaptive tuned mass dampers for light structures. However, the literature has evidenced a number of issues concerning tuned mass dampers based on shape memory alloys, for instance the limited range of adaptation for the eigenfrequency of the damper. The present paper proposes a new layout for adaptive tuned mass dampers based on shape memory alloys, which allows to overcome many of the limitations and to reach a wide range of adaptation for the eigenfrequency. This layout relies on the use of shape memory alloy wires, so that the change of eigenfrequency is achieved by changing the axial load acting on these wires. The new tuned mass damper is then made fully adaptive by including a device that uses the principle of eddy currents, which allows also to change the damping of the tuned mass damper. Indeed, this new kind of damper is designed to dampen vibrations in systems excited by a random disturbance. The paper illustrates the layout and the model of the whole damper and validates it. This model moreover evidences all the advantages allowed by the new layout proposed. Finally, two different strategies to control the dynamic characteristics of the new adaptive tuned mass damper are presented and compared, both numerically as well as experimentally, so to illustrate strengths and drawbacks of each. The experiments and the simulations show that this new damper is fully capable of functioning when random excitation acts as disturbance on the system to control.

  16. Design and development of a shape memory alloy activated heat pipe-based thermal switch

    NASA Astrophysics Data System (ADS)

    Benafan, O.; Notardonato, W. U.; Meneghelli, B. J.; Vaidyanathan, R.

    2013-10-01

    This work reports on the design, fabrication and testing of a thermal switch wherein the open and closed states were actuated by shape memory alloy (SMA) elements while heat was transferred by a two-phase heat pipe. The motivation for such a switch comes from NASA’s need for thermal management in advanced spaceport applications associated with future lunar and Mars missions. As the temperature can approximately vary between -233 and 127 ° C during lunar day/night cycles, the switch was designed to reject heat from a cryogen tank into space during the night cycle while providing thermal isolation during the day cycle. A Ni47.1Ti49.6Fe3.3 (at.%) alloy that exhibited a reversible phase transformation between a trigonal R-phase and a cubic austenite phase was used as the sensing and actuating elements. Thermomechanical actuation, accomplished through an antagonistic spring system, resulted in strokes up to 7 mm against bias forces of up to 45 N. The actuation system was tested for more than thirty cycles, equivalent to one year of operation. The thermal performance, accomplished via a variable length, closed two-phase heat pipe, was evaluated, resulting in heat transfer rates of 13 W using pentane and 10 W using R-134a as working fluids. Experimental data were also compared to theoretical predictions where possible. Direct comparisons between different design approaches of SMA helical actuators, highlighting the effects of the helix angle, were carried out to give a layout of more accurate design methodologies.

  17. Utilization of nickel-titanium shape memory alloy for stapes prosthesis.

    PubMed

    Kasano, F; Morimitsu, T

    1997-04-01

    A new type of stapes prosthesis made of nickel-titanium shape memory alloy wire was developed and its biocompatibility was examined in 24 ears of 12 cats. The prosthesis was implanted at the long crus of the incus. The incus was examined 27-355 days after operation. In 23 ears, the prosthesis was found macroscopically well implanted at the aimed position. In one ear the prosthesis was found to be dislocated and in another the prosthesis was slightly loosened. The incudes were removed and five specimens were prepared for scanning electron microscopy and the other specimens were observed under light microscopy. Histological studies revealed severe bone resorption of the long crus in the dislocated case and moderate bone resorption in the slightly loosened case. These bone resorptions were found to be caused by the inadvertent removal of the mucosal membrane during the implant operations. In seven ears under a light microscope and in one ear under a scanning electron microscope, slight bone resorption as bone erosion was seen at the contact area of the prosthesis. This bone resorption was induced by the mechanical pressure of the prosthesis and was not progressive due to fading of the pressure of the prosthesis. With the exception of pressure induced bone erosions, there was no progressive bone resorption which was prosthesis induced. The biocompatibility of the nickel-titanium alloy stapes prosthesis with the long crus of the incus was proved. The prosthesis should be implanted loosely at the long crus of the incus without removal of the mucosal membrane. PMID:9134135

  18. Simulating Solid-Solid Phase Transition in Shape-Memory Alloy Microstructure by Face-Offsetting Method

    SciTech Connect

    Bellur Ramaswamy, Ravi S.; Tortorelli, Daniel A.; Fried, Eliot; Jiao Xiangmin

    2008-02-15

    Advances in the understanding of martensitic transformations (diffusionless, solid-solid phase transformations) have been instrumental to the recent discovery of new low hysteresis alloys. However, some key fundamental issues must be better understood to design still better alloys. Restricting attention to antiplane shear, we use finite element analysis to model the shape-memory alloy microstructure within the Abeyaratne-Knowles continuum thermomechanical framework and use an interface kinetic relation of the kind proposed by Rosakis and Tsai. Geometric singularities and topological changes associated with microstructural evolution pose significant numerical challenges. We address such challenges with a recently developed front-tracking scheme called the face-offsetting method (FOM) to explicitly model phase interfaces. Initial results demonstrate the effectiveness of FOM in resolving needle-like twinned microstructures.

  19. Effect of CO2 laser welding on the shape-memory and corrosion characteristics of TiNi alloys

    NASA Astrophysics Data System (ADS)

    Hsu, Y. T.; Wang, Y. R.; Wu, S. K.; Chen, C.

    2001-03-01

    A CO2 laser has been employed to join binary Ti50Ni50 and Ti49.5Ni50.5 shape-memory alloys (SMAs), with an emphasis on the shape-memory and corrosion characteristics. Experimental results showed that a slightly lowered martensite start ( M S) temperature and no deterioration in shape-memory character of both alloys were found after laser welding. The welded Ti50Ni50, with an increased amount of B2 phase in the weld metal (WM), had higher strength and considerably lower elongation than the base metal (BM). Potentiodynamic tests revealed the satisfactory performance of laser-welded Ti50Ni50 in 1.5 M H2SO4 and 1.5 M HNO3 solutions. However, the WM exhibited a significantly higher corrosion rate and a less stable passivity than the BM in artificial saliva. On the other hand, the pseudoelastic behavior of the laser weld was investigated only for the Ti49.5Ni50.5 alloy, to facilitate tension cycling at room temperature. The cyclic deformation of Ti49.5Ni50.5 indicated that the stress required to form stress-induced martensite ( σ m) and the permanent residual strain ( ɛ p) were higher after welding at a given number of cycles ( N), which were certainly related to the more inhomogeneous nature of the WM.

  20. Effect of Cold Rolling on Phase Transformation Temperatures of NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Pattabi, Manjunatha; Murari, M. S.

    2015-02-01

    The effect of cold rolling and heat treatment on the phase transformation behavior of NiTi shape memory alloy (SMA) heat treated at 660 °C has been investigated. Four sets of samples were cold rolled after heat treatment. The austenite-to-martensite and martensite-to-austenite transformation temperatures for samples without any cold rolling are determined through differential scanning calorimetry (DSC). The austenitic start temperature gets shifted to the higher temperature side with increase in the percentage of the cold rolling up to 12.5%. Austenitic finish temperature could not be detected in cold-rolled samples. Martensitic start temperature increases slightly with increased cold rolling while martensitc finish temperature slightly decreases. Beyond 12.5% cold work, the shape memory effect (SME) is completely lost. The evolution of austenitic phase in SMA subjected to cold rolling was studied through powder x-ray diffraction (XRD) at different temperatures in the range 25 to 160 °C at intervals of 10 °C, during heating and cooling. The XRD results agree with those of DSC. Two sets of cold-rolled samples were again heat treated to 300 and 500 °C and the transformation behavior was studied using DSC. Heat treatment at 300 °C brings back the SME, but with the presence of an intermediate R-Phase due to the additional dislocations present. Even with a heat treatment at 500 °C, the effect of cold work is not completely removed and a single-step transformation is not observed. Another set of samples subjected to cold work were heat treated at 660 °C and the transformation is studied. The effect of cold work even up to 25% is completely removed with this heat treatment as indicated by DSC. The complete regaining of the SME is further confirmed by electrical resistivity measurements also.

  1. Influence of roll and solution treatment processing on shape memory effect of Fe-14Mn-5Si-9Cr-5Ni alloy

    SciTech Connect

    Li, C.L.; Jin, Z.H.

    1998-10-01

    The shape memory effect was studied in an Fe-14Mn-5Si-9Cr-5Ni alloy rerolled at 1123 K after hot rolling at 1423 K, followed by solution treatment at different temperatures. It was found that the alloy exhibits a maximum degree of shape recovery in a bending test and a complete recovery tensile strain of 2.2% in samples that were solution heated at 973 K for 600 s and then quenched in water. The rerolled processing at 1123 K after hot rolling at 1423 K and the microstructure under solution treatment state are important for obtaining a good shape memory effect in the alloy.

  2. Surface structure and properties of biomedical NiTi shape memory alloy after Fenton's oxidation.

    PubMed

    Chu, C L; Hu, T; Wu, S L; Dong, Y S; Yin, L H; Pu, Y P; Lin, P H; Chung, C Y; Yeung, K W K; Chu, Paul K

    2007-09-01

    Fenton's oxidation is traditionally used to remove inorganic and organic pollutants from water in waster water treatment. It is an advanced oxidation process in which H2O2 is catalytically decomposed by ferrous irons into hydroxyl radicals (*OH) which have a higher oxidation potential (2.8V) than H2O2. In the work reported here, we for the first time use Fenton's oxidation to modify the surface of biomedical NiTi shape memory alloy (SMA). The influences of Fenton's oxidation on the surface microstructure, blood compatibility, leaching of harmful Ni ions and corrosion resistance in simulated body fluids is assessed using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma mass spectrometry, electrochemical tests, hemolysis analysis and the blood platelet adhesion test. The mechanical stability of the surface titania film produced by Fenton's oxidation as well as their effects on the shape memory behavior of the SMA are studied by bending tests. Our results show that Fenton's oxidation produces a novel nanostructured titania gel film with a graded structure on the NiTi substrate without an intermediate Ni-rich layer that is typical of high-temperature oxidation. Moreover, there is a clear Ni-free zone near the top surface of the titania film. The surface structural changes introduced by Fenton's oxidation improve the electrochemical corrosion resistance and mitigate Ni release. The latter effects are comparable to those observed after oxygen plasma immersion ion implantation reported previously and better than those of high-temperature oxidation. Aging in boiling water improves the crystallinity of the titania film and further reduces Ni leaching. Blood platelet adhesion is remarkably reduced after Fenton's oxidation, suggesting that the treated SMA has improved thrombo resistance. Enhancement of blood compatibility is believed to stem from the improved hemolysis resistance, the surface wettability and the

  3. A comparison of methods for the training of NiTi two-way shape memory alloy

    NASA Astrophysics Data System (ADS)

    Luo, H. Y.; Abel, E. W.

    2007-12-01

    The creation of an effective two-way shape memory alloy (TWSMA) requires appropriate heat treatment and optimal training considerations. In particular, the training method used plays a key role. This work investigates different training methods for producing NiTi TWSMA wires with the hot shape of an arc and the cold shape of a straight line. These methods are shape memory cycling, constrained cycling of deformed martensite, pseudoelastic cycling and combined shape memory and pseudoelastic cycling. In order to give a meaningful evaluation of their performance that is relevant to training TWSMA for practical applications, these training methods are assessed in terms of maximum two-way strain, changes in the original hot shape together with the transformation temperatures after the training process, and the effective production of the cold shape. It was found that only the combined shape memory and pseudoelastic cycling provides an effective training method for creating NiTi TWSMA with a non-uniaxial two-way shape change. The undesirable side effects of training are that the NiTi TWSMA wire loses partial memory of the original hot shape and its transformation temperatures shift to lower values. There also exists an optimal number of training cycles, and possibly an optimal training load for obtaining the best cold shape memory and the greatest two-way recoverable strain. These findings give future directions to advance the training technology for TWSMA.

  4. A two-degrees-of-freedom miniature manipulator actuated by antagonistic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Lai, Chih-Ming; Chu, Cheng-Yu; Lan, Chao-Chieh

    2013-08-01

    This paper presents a miniature manipulator that can provide rotations around two perpendicularly intersecting axes. Each axis is actuated by a pair of shape memory alloy (SMA) wires. SMA wire actuators are known for their large energy density and ease of actuation. These advantages make them ideal for applications that have stringent size and weight constraints. SMA actuators can be temperature-controlled to contract and relax like muscles. When correctly designed, antagonistic SMA actuators have a faster response and larger range of motion than bias-type SMA actuators. This paper proposes an antagonistic actuation model to determine the manipulator parameters that are required to generate sufficient workspace. Effects of SMA prestrain and spring stiffness on the manipulator are investigated. Taking advantage of proper prestrain, the actuator size can be made much smaller while maintaining the same motion. The use of springs in series with SMA can effectively reduce actuator stress. A controller and an anti-slack algorithm are developed to ensure fast and accurate motion. Speed, stress, and loading experiments are conducted to demonstrate the performance of the manipulator.

  5. Effect of Deformation Mode on the Wear Behavior of NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Yan, Lina; Liu, Yong

    2016-06-01

    Owing to good biocompatibility, good fatigue resistance, and excellent superelasticity, various types of bio-medical devices based on NiTi shape memory alloy (SMA) have been developed. Due to the complexity in deformation mode in service, for example NiTi implants, accurate assessment/prediction of the surface wear process is difficult. This study aims at providing a further insight into the effect of deformation mode on the wear behavior of NiTi SMA. In the present study, two types of wear testing modes were used, namely sliding wear mode and reciprocating wear mode, to investigate the effect of deformation mode on the wear behavior of NiTi SMA in both martensitic and austenitic states. It was found that, when in martensitic state and under high applied loads, sliding wear mode resulted in more surface damage as compared to that under reciprocating wear mode. When in austenitic state, although similar trends in the coefficient of friction were observed, the coefficient of friction and surface damage in general is less under reciprocating mode than under sliding mode. These observations were further discussed in terms of different deformation mechanisms involved in the wear tests, in particular, the reversibility of martensite variant reorientation and stress-induced phase transformation, respectively.

  6. Shape memory alloy-based moment connections with superior self-centering properties

    NASA Astrophysics Data System (ADS)

    Farmani, Mohammad Amin; Ghassemieh, Mehdi

    2016-07-01

    Superelastic shape memory alloys (SMAs) have the potential to create a spontaneous recentering mechanism on the connections of a structural system under seismic actions, which results in mitigation of the damage in the main structural members. In this article, innovative types of steel beam-to-column moment connections incorporating SMA bolts and plates are introduced and studied through a numerical approach. First, SMA bolted end-plate connection model is produced and analyzed by means of the finite element method to validate the numerical analysis against the prior experimental results. Then, the performance of eleven different end-plate moment connection models subjected to cyclic loading is investigated. By selecting the lower values for the moment capacity based on bolts strength in comparison to the flexural resistance of the beam, the plastic hinge is transferred from the beam section to the beam–column interface. Hence, employing superelastic materials at the connection interface could be potentially effective in providing the desired self-centering effect in the connection. To this end, the impact of utilizing superelastic SMA bolts and end-plates instead of using the conventional structural steel on the overall cyclic response of the connections is evaluated in this study. Results show that extended end-plate connections equipped with SMA bolts and end-plates, if properly proportioned and detailed, not only exhibit a clear reduction in the residual drifts after a seismic event, but also can meet the ductility requirements with good energy dissipation and sufficient stiffness.

  7. A validated model for induction heating of shape memory alloy actuators

    NASA Astrophysics Data System (ADS)

    Saunders, Robert N.; Boyd, James G.; Hartl, Darren J.; Brown, Jonathan K.; Calkins, Frederick T.; Lagoudas, Dimitris C.

    2016-04-01

    Shape memory alloy (SMA) actuators deliver high forces while being compact and reliable, making them ideal for consideration in aerospace applications. One disadvantage of these thermally driven actuators is their slow cyclic time response compared to conventional actuators. Induction heating has recently been proposed to quickly heat SMA components. However efforts to date have been purely empirical. The present work approachs this problem in a computational manner by developing a finite element model of induction heating in which the time-harmonic electromagnetic equations are solved for the Joule heat power field, the energy equation is solved for the temperature field, and the linear momentum equations are solved to find the stress, displacement, and internal state variable fields. The combined model was implemented in Abaqus using a Python script approach and applied to SMA torque tube and beam actuators. The model has also been used to examine magnetic flux concentrators to improve the induction systems performance. Induction heating experiments were performed using the SMA torque tube, and the model agreed well with the experiments.

  8. Shape memory alloy-based moment connections with superior self-centering properties

    NASA Astrophysics Data System (ADS)

    Farmani, Mohammad Amin; Ghassemieh, Mehdi

    2016-07-01

    Superelastic shape memory alloys (SMAs) have the potential to create a spontaneous recentering mechanism on the connections of a structural system under seismic actions, which results in mitigation of the damage in the main structural members. In this article, innovative types of steel beam-to-column moment connections incorporating SMA bolts and plates are introduced and studied through a numerical approach. First, SMA bolted end-plate connection model is produced and analyzed by means of the finite element method to validate the numerical analysis against the prior experimental results. Then, the performance of eleven different end-plate moment connection models subjected to cyclic loading is investigated. By selecting the lower values for the moment capacity based on bolts strength in comparison to the flexural resistance of the beam, the plastic hinge is transferred from the beam section to the beam-column interface. Hence, employing superelastic materials at the connection interface could be potentially effective in providing the desired self-centering effect in the connection. To this end, the impact of utilizing superelastic SMA bolts and end-plates instead of using the conventional structural steel on the overall cyclic response of the connections is evaluated in this study. Results show that extended end-plate connections equipped with SMA bolts and end-plates, if properly proportioned and detailed, not only exhibit a clear reduction in the residual drifts after a seismic event, but also can meet the ductility requirements with good energy dissipation and sufficient stiffness.

  9. Design of a shape-memory alloy actuated macro-scale morphing aircraft mechanism

    NASA Astrophysics Data System (ADS)

    Manzo, Justin; Garcia, Ephrahim; Wickenheiser, Adam; Horner, Garnett C.

    2005-05-01

    As more alternative, lightweight actuators have become available, the conventional fixed-wing configuration seen on modern aircraft is under investigation for efficiency on a broad scale. If an aircraft could be designed with multiple functional equilibria of drastically varying aerodynamic parameters, one craft capable of 'morphing' its shape could be used to replace two or three designed with particular intentions. One proposed shape for large-scale (geometry change on the same order of magnitude as wingspan) morphing is the Hyper-Elliptical Cambered Span (HECS) wing, designed at NASA Langley to be implemented on an unmanned aerial vehicle (UAV). Proposed mechanisms to accomplish the spanwise curvature (in the y-z plane of the craft) that allow near-continuous bending of the wing are narrowed to a tendon-based DC motor actuated system, and a shape memory alloy-based (SMA) mechanism. At Cornell, simulations and wind tunnel experiments assess the validity of the HECS wing as a potential shape for a blended-wing body craft with the potential to effectively serve the needs of two conventional UAVs, and analyze the energetics of actuation associated with a morphing maneuver accomplished with both a DC motor and SMA wire.

  10. Analysis of interfacial debonding in shape memory alloy wire-reinforced composites

    NASA Astrophysics Data System (ADS)

    Miramini, A.; Kadkhodaei, M.; Alipour, A.; Mashayekhi, M.

    2016-01-01

    One of the common types of failure in shape memory alloy (SMA) wire-reinforced composites is interfacial debonding between the fiber and the matrix. In this paper, a three dimensional finite element model for an SMA wire-reinforced composite is developed based on cohesive zone modeling to predict interfacial debonding between the SMA wire and the surrounding matrix. The interfacial debonding is also experimentally investigated by conducting a number of pull-out tests on steel as well as Nitinol wires embedded in an epoxy matrix. To evaluate the presented method, the developed finite element analysis is employed to simulate a single wire pull-out test for ordinary (e.g. steel) wires. In order to simulate SMA wire pull-out, a 3D SMA constitutive model is implemented into the commercial finite element software ABAQUS using a user material subroutine (UMAT). An acceptable agreement is shown to exist between the theoretical results and the experimental data, indicating the efficiency of the proposed approach to model interfacial debonding in SMA wire-reinforced composites.

  11. TiNi shape memory alloy coated with tungsten: a novel approach for biomedical applications.

    PubMed

    Li, Huafang; Zheng, Yufeng; Pei, Y T; De Hosson, J Th M

    2014-05-01

    This study explores the use of DC magnetron sputtering tungsten thin films for surface modification of TiNi shape memory alloy (SMA) targeting for biomedical applications. SEM, AFM and automatic contact angle meter instrument were used to determine the surface characteristics of the tungsten thin films. The hardness of the TiNi SMA with and without tungsten thin films was measured by nanoindentation tests. It is demonstrated that the tungsten thin films deposited at different magnetron sputtering conditions are characterized by a columnar microstructure and exhibit different surface morphology and roughness. The hardness of the TiNi SMA was improved significantly by tungsten thin films. The ion release, hemolysis rate, cell adhesion and cell proliferation have been investigated by inductively coupled plasma atomic emission spectrometry, CCK-8 assay and alkaline phosphatase activity test. The experimental findings indicate that TiNi SMA coated with tungsten thin film shows a substantial reduction in the release of nickel. Therefore, it has a better in vitro biocompatibility, in particular, reduced hemolysis rate, enhanced cell adhesion and differentiation due to the hydrophilic properties of the tungsten films. PMID:24481534

  12. Design and implementation of shape memory alloy-actuated nanotweezers for nanoassembly

    NASA Astrophysics Data System (ADS)

    Zhao, Hao; Chang, Ming; Liu, Xiaojun; Gabayno, Jacque Lynn; Chen, Hsieh Tsun

    2014-09-01

    Reliable and accurate tools for nanoscale manipulation are constantly sought to complement new breakthroughs in nanomaterials and nanotechnology. In this study, a new design of electrically actuated nanotweezers was developed for manipulation of individual nanowires. The design featured two chemically etched tungsten tips attached to a carbon fiber-reinforced polymer and two shape memory alloy actuators. The shape recovery effect of the spring actuators was exploited as a control mechanism for the bending and relaxation modes of the nanotweezers. This was activated by driving a potential difference of less than 1 V across the coils, which was considerably lower than for electromechanical micro/nanotweezers previously developed. To demonstrate the pick-and-place capability of the system, experiments were implemented inside the vacuum chamber of a JEOL-JSM 6300 SEM. Individual Au nanowires averaging 5-10 µm in length and 200 nm in diameter were assembled on silicon substrates using the tungsten tips to draw initials out of various nanowire shapes such as curls, loops, crosses, and zigzags. With such capability, the nanotweezers may find applications in the manufacturing of complex nanostructures or modification of surface properties of materials.

  13. Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires

    NASA Astrophysics Data System (ADS)

    Carl, Matthew; Zhang, Baozhuo; Young, Marcus L.

    2016-07-01

    Shape memory alloys (SMAs) are a new generation of materials that exhibit unique nonlinear deformations due to a phase transformation which allows the material to return to its original shape after removal of stress or a change in temperature. These unique properties are the result of a martensitic/austenitic phase transformation through the application of temperature changes or applied stress. Many technological applications of austenitic SMAs involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity, but are limited due to poor fatigue life. In this paper, commercial pseudoelastic NiTi SMA wires (50.7 at.% Ni) were placed under different bending strains and examined using scanning electron microscopy and high-energy synchrotron radiation X-ray diffraction (SR-XRD). By observing the microstructure, phase transformation temperatures, surface texture and diffraction patterns along the wire, it is shown that the wire exhibits a strong anisotropic behavior whether on the tensile or compressive side of the bending axis and that the initiation of micro-cracks in the wires is localized on the compression side, but that crack propagation will still happen if the wire is reloaded in the opposite direction. In addition, lattice strains are examined for both the austenite and martensite phases.

  14. Wear mechanism and tribological characteristics of porous NiTi shape memory alloy for bone scaffold.

    PubMed

    Wu, Shuilin; Liu, Xiangmei; Wu, Guosong; Yeung, Kelvin W K; Zheng, Dong; Chung, C Y; Xu, Z S; Chu, Paul K

    2013-09-01

    The abraded debris might cause osteocytic osteolysis on the interface between implants and bone tissues, thus inducing the subsequent mobilization of implants gradually and finally resulting in the failure of bone implants, which imposes restrictions on the applications of porous NiTi shape memory alloys (SMAs) scaffolds for bone tissue engineering. In this work, the effects of the annealing temperature, applied load, and porosity on the tribological behavior and wear resistance of three-dimensional porous NiTi SMA are investigated systematically. The porous structure and phase transformation during the exothermic process affect the tribological properties and wear mechanism significantly. In general, a larger porosity leads to better tribological resistance but sometimes, SMAs with small porosity possess better wear resistance than ones with higher porosity during the initial sliding stage. It can be ascribed to the better superelasticity of the former at the test temperature. The porous NiTi phase during the exothermic reaction also plays an important role in the wear resistance. Generally, porous NiTi has smaller friction coefficients under high loads due to stress-induced superelasticity. The wear mechanism is discussed based on plastic deformation and microcrack propagation.

  15. Pulsed-mode operation and performance of a ferromagnetic shape memory alloy actuator

    NASA Astrophysics Data System (ADS)

    Asua, E.; García-Arribas, A.; Etxebarria, V.; Feuchtwanger, J.

    2014-02-01

    The actuation capabilities and positioning performance of a single crystal ferromagnetic shape memory alloy (FSMA) operated in pulsed mode are evaluated in a prototype device. It consists of two orthogonal coil pairs that produce the magnetic fields necessary for the non-contact deformation of the material. The position of the top of the crystal after actuation is measured by a capacitive sensor. A specifically designed power module drives the discharge of a set of capacitors through the coils, producing fast current pulses of large amplitudes (about 250 A), the coil pairs are driven independently to control the direction of actuation. Open-loop experiments demonstrate that successive pulses of increasing magnitude successfully produced the desired expansion and contraction of the crystal, depending on the pair of coils that is activated. The deformation achieved is maintained after the pulses, highlighting the advantageous set-and-forget operation of the device. Closed-loop experiments are performed using a double proportional-integral-derivative controller, designed to take advantage of the energy-saving quality of the set-and-forget operation. Despite the nonlinear response and hysteric response of FSMA materials, a reference position can be reached and maintained with a maximum error of 0.5 μm.

  16. Applicability of Shape Memory Alloy Wire for an Active, Soft Orthotic

    NASA Astrophysics Data System (ADS)

    Stirling, Leia; Yu, Chih-Han; Miller, Jason; Hawkes, Elliot; Wood, Robert; Goldfield, Eugene; Nagpal, Radhika

    2011-07-01

    Current treatments for gait pathologies associated with neuromuscular disorders may employ a passive, rigid brace. While these provide certain benefits, they can also cause muscle atrophy. In this study, we examined NiTi shape memory alloy (SMA) wires that were annealed into springs to develop an active, soft orthotic (ASO) for the knee. Actively controlled SMA springs may provide variable assistances depending on factors such as when, during the gait cycle, the springs are activated; ongoing muscle activity level; and needs of the wearer. Unlike a passive brace, an active orthotic may provide individualized control, assisting the muscles so that they may be used more appropriately, and possibly leading to a re-education of the neuro-motor system and eventual independence from the orthotic system. A prototype was tested on a suspended, robotic leg to simulate the swing phase of a typical gait. The total deflection generated by the orthotic depended on the knee angle and the total number of actuators triggered, with a max deflection of 35°. While SMA wires have a high energy density, they require a significant amount of power. Furthermore, the loaded SMA spring response times were much longer than the natural frequency of an average gait for the power conditions tested. While the SMA wires are not appropriate for correction of gait pathologies as currently implemented, the ability to have a soft, actuated material could be appropriate for slower timescale applications.

  17. Mechanical properties identification and design optimization of nitinol shape memory alloy microactuators

    NASA Astrophysics Data System (ADS)

    Salehi, M.; Hamedi, M.; Salmani Nohouji, H.; Arghavani, J.

    2014-02-01

    Microactuators are essential elements of MEMS and are widely used in these devices. Microgrippers, micropositioners, microfixtures, micropumps and microvalves are well-known applications of microstructures. In this paper, the design optimization of shape memory alloy microactuators is discussed. Four different configurations of microactuator with variable geometrical parameters, generating different levels of displacement and force, are designed and analysed. In order to determine the optimum values of parameters for each microactuator, statistical design of experiments (DOE) is used. For this purpose, the Souza et al constitutive model (1988 Eur. J. Mech. A 17 789-806) is adapted for use in finite element analysis software. Mechanical properties of the SMA are identified by performing experimental tests on Ti-49.8%Ni. Finally, the specific energy of each microactuator is determined using the calibrated model and regression analysis. Moreover, the characteristic curve of each microactuator is obtained and with this virtual tool one can choose a microactuator with the desired force and displacement. The methodology discussed in this paper can be used as a reference to design appropriate microactuators for different MEMS applications producing various ranges of displacement and force.

  18. A biomimetic robotic jellyfish (Robojelly) actuated by shape memory alloy composite actuators.

    PubMed

    Villanueva, Alex; Smith, Colin; Priya, Shashank

    2011-09-01

    An analysis is conducted on the design, fabrication and performance of an underwater vehicle mimicking the propulsion mechanism and physical appearance of a medusa (jellyfish). The robotic jellyfish called Robojelly mimics the morphology and kinematics of the Aurelia aurita species. Robojelly actuates using bio-inspired shape memory alloy composite actuators. A systematic fabrication technique was developed to replicate the essential structural features of A. aurita. Robojelly's body was fabricated from RTV silicone having a total mass of 242 g and bell diameter of 164 mm. Robojelly was able to generate enough thrust in static water conditions to propel itself and achieve a proficiency of 0.19 s(-1) while the A. aurita achieves a proficiency of around 0.25 s(-1). A thrust analysis based on empirical measurements for a natural jellyfish was used to compare the performance of the different robotic configurations. The configuration with best performance was a Robojelly with segmented bell and a passive flap structure. Robojelly was found to consume an average power on the order of 17 W with the actuators not having fully reached a thermal steady state. PMID:21852714

  19. Experimental characterization and modeling of a three-variant magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Feigenbaum, Heidi P.; Ciocanel, Constantin; Eberle, J. Lance; Dikes, Jason L.

    2016-10-01

    Researchers have attempted to characterize and predict the magneto-mechanical behavior of magnetic shape memory alloys (MSMAs) for over a decade. However, all prior experimental investigations on MSMA have been performed on samples accommodating two martensite variants and generally the MSMA is only exposed to two-dimensional magneto-mechanical loading. As efforts have been underway to develop models able to predict the most general (i.e. 3D) loading conditions for MSMAs with three-varints, there is also a need for experimental data to support the calibration and validation of these models. This paper presents magneto-mechanical data from experiments where MSMA specimens, whose microstructure accommodates three martensite variants, is subjected to three-dimensional magneto-mechanical loading, along with model predictions of these experimental results. The 3D magneto-mechanical model deployed here is a modified version of the model developed by our group (LaMaster et al 2015 J. Intell. Mater. Syst. Struct. 26 663-79), and assumes that three martensite variants coexist in the material. The LaMaster et al model captures some of the general trends seen in the experimental data, but does not predict the data with a high degree of accuracy. Possible reasons for the mismatch between experimental data and model predictions are discussed.

  20. Energy-efficient miniature-scale heat pumping based on shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ossmer, Hinnerk; Wendler, Frank; Gueltig, Marcel; Lambrecht, Franziska; Miyazaki, Shuichi; Kohl, Manfred

    2016-08-01

    Cooling and thermal management comprise a major part of global energy consumption. The by far most widespread cooling technology today is vapor compression, reaching rather high efficiencies, but promoting global warming due to the use of environmentally harmful refrigerants. For widespread emerging applications using microelectronics and micro-electro-mechanical systems, thermoelectrics is the most advanced technology, which however hardly reaches coefficients of performance (COP) above 2.0. Here, we introduce a new approach for energy-efficient heat pumping using the elastocaloric effect in shape memory alloys. This development is mainly targeted at applications on miniature scales, while larger scales are envisioned by massive parallelization. Base materials are cold-rolled textured Ti49.1Ni50.5Fe0.4 foils of 30 μm thickness showing an adiabatic temperature change of +20/-16 K upon superelastic loading/unloading. Different demonstrator layouts consisting of mechanically coupled bridge structures with large surface-to-volume ratios are developed allowing for control by a single actuator as well as work recovery. Heat transfer times are in the order of 1 s, being orders of magnitude faster than for bulk geometries. Thus, first demonstrators achieve values of specific heating and cooling power of 4.5 and 2.9 W g-1, respectively. A maximum temperature difference of 9.4 K between heat source and sink is reached within 2 min. Corresponding COP on the device level are 4.9 (heating) and 3.1 (cooling).

  1. Laser-Machined Shape Memory Alloy Sensors for Position Feedback in Active Catheters

    PubMed Central

    Tung, Alexander T.; Park, Byong-Ho; Liang, David H.; Niemeyer, Günter

    2008-01-01

    Catheter-based interventions are a form of minimally invasive surgery that can decrease hospitalization time and greatly lower patient morbidity compared to traditional methods. However, percutaneous catheter procedures are hindered by a lack of precise tip manipulation when actuation forces are transmitted over the length of the catheter. Active catheters with local shape-memory-alloy (SMA) actuation can potentially provide the desired manipulation of a catheter tip, but hysteresis makes it difficult to control the actuators. A method to integrate small-volume, compliant sensors on an active catheter to provide position feedback for control would greatly improve the viability of SMA-based active catheters. In this work, we describe the design, fabrication, and performance of resistance-based position sensors that are laser-machined from superelastic SMA tubing. Combining simple material models and rapid prototyping, we can develop sensors of appropriate stiffness and sensitivity with simple modifications in sensor geometry. The sensors exhibit excellent linearity over the operating range and are designed to be easily integrated onto an active catheter substrate. PMID:19759806

  2. Shape memory alloy film for deployment and control of membrane apertures

    NASA Astrophysics Data System (ADS)

    Hill, Lisa R.; Carman, Greg; Lee, Dong-Gun; Patrick, Brian

    2004-02-01

    Nickel Titanium (NiTi) film shape memory alloy (SMA) is integrated with space-qualified polymer and mesh materials for potential use as deployment mechanisms and actuation of flexible space apertures. SMA thin film is successfully applied to Astromesh metal mesh, Kapton, Upilex, and CP-1 polymer films. Sputter deposition of NiTi onto the substrate is used to validate the material system process and demonstrate the NiTi deployment capability. Although successful, the relatively high processing temperatures required to crystallize NiTi onto the substrates requires care. A second approach is demonstrated that deposits NiTi onto a silicon substrate, followed by coating the NiTi with the desired polymer, e.g. CP-1. Micro-electro-mechanical (MEMS) processing steps are then used to remove the silicon substrate beneath the NiTi, thus freeing up the composite membrane (i.e. NiTi + CP-1). Using MEMS fabrication techniques, a hot-shaped small dome shape structure is shaped into the NiTi before deposition of the CP-1 polymer. Activation of the integrated SMA/CP-1 produces deformation of this composite structure without damage. The test articles demonstrate the feasibility to both grossly deploy and locally actuate space-qualified polymer materials.

  3. GA-based optimum design of a shape memory alloy device for seismic response mitigation

    NASA Astrophysics Data System (ADS)

    Ozbulut, O. E.; Roschke, P. N.; Y Lin, P.; Loh, C. H.

    2010-06-01

    Damping systems discussed in this work are optimized so that a three-story steel frame structure and its shape memory alloy (SMA) bracing system minimize response metrics due to a custom-tailored earthquake excitation. Multiple-objective numerical optimization that simultaneously minimizes displacements and accelerations of the structure is carried out with a genetic algorithm (GA) in order to optimize SMA bracing elements within the structure. After design of an optimal SMA damping system is complete, full-scale experimental shake table tests are conducted on a large-scale steel frame that is equipped with the optimal SMA devices. A fuzzy inference system is developed from data collected during the testing to simulate the dynamic material response of the SMA bracing subcomponents. Finally, nonlinear analyses of a three-story braced frame are carried out to evaluate the performance of comparable SMA and commonly used steel braces under dynamic loading conditions and to assess the effectiveness of GA-optimized SMA bracing design as compared to alternative designs of SMA braces. It is shown that peak displacement of a structure can be reduced without causing significant acceleration response amplification through a judicious selection of physical characteristics of the SMA devices. Also, SMA devices provide a recentering mechanism for the structure to return to its original position after a seismic event.

  4. Study on CO2 laser weldability of Fe-Mn-Si shape memory alloy

    NASA Astrophysics Data System (ADS)

    Zhou, Chaoyu; Lin, Chengxin; Liu, Linlin

    2012-04-01

    In this study, a cross-flow laser with maximum out power of 5kW was applied to the welding of Fe-Mn-Si shape memory alloys (SMA). The optimal welding processing parameters of 1mm thick Fe-Mn-Si SMA were established by orthogonal experiment. With the optimal processing parameters, power 1600W, welding speed 2.2m/min, defocusing distance 0.6mm, the tensile strength of the welded joint can achieve 93.5% of the base material, and the weld undercut and reinforcement transfer smoothly on the surface of the welding seam and the cross-section of the welding seam morphology presents "X" shape. The fracture appears in the weld fusion zone, so this area is weak during the laser welding. By the metallographic observation, the weld center structure is small equated, and the region of fusion zone is thick cellular crystal that decreases the strength of the welded joint, and the X-ray diffraction (XRD) test proves that the laser welding promotes the grain refinement. The micro-hardness analysis shows that the hardness of the fusion zone is lower than the other area clearly which is also associated to the weld structure. By the fracture scanning electron microscope (SEM) analysis, it is found that the fracture of Fe-Mn-Si SMA shows many small dimples with the optimal parameters, and the result is accorded with the base material which belongs to plastic fracture.

  5. Study on CO2 laser weldability of Fe-Mn-Si shape memory alloy

    NASA Astrophysics Data System (ADS)

    Zhou, Chaoyu; Lin, Chengxin; Liu, Linlin

    2011-11-01

    In this study, a cross-flow laser with maximum out power of 5kW was applied to the welding of Fe-Mn-Si shape memory alloys (SMA). The optimal welding processing parameters of 1mm thick Fe-Mn-Si SMA were established by orthogonal experiment. With the optimal processing parameters, power 1600W, welding speed 2.2m/min, defocusing distance 0.6mm, the tensile strength of the welded joint can achieve 93.5% of the base material, and the weld undercut and reinforcement transfer smoothly on the surface of the welding seam and the cross-section of the welding seam morphology presents "X" shape. The fracture appears in the weld fusion zone, so this area is weak during the laser welding. By the metallographic observation, the weld center structure is small equated, and the region of fusion zone is thick cellular crystal that decreases the strength of the welded joint, and the X-ray diffraction (XRD) test proves that the laser welding promotes the grain refinement. The micro-hardness analysis shows that the hardness of the fusion zone is lower than the other area clearly which is also associated to the weld structure. By the fracture scanning electron microscope (SEM) analysis, it is found that the fracture of Fe-Mn-Si SMA shows many small dimples with the optimal parameters, and the result is accorded with the base material which belongs to plastic fracture.

  6. Hysteresis phenomena in shape memory alloys by non-isothermal Ginzburg-Landau models

    NASA Astrophysics Data System (ADS)

    Dhote, R. P.; Fabrizio, M.; Melnik, R. N. V.; Zu, J.

    2013-09-01

    In this paper, we propose the new one- and three- dimensional models for the description of hysteretic phenomena in shape memory alloys (SMAs). These thermodynamic models are non-isothermal and allow to account for the thermo-mechanical material properties of both austenite and martensite phases based on the local phase value of the order parameter. They are based on the Ginzburg-Landau free energy and the phase field theory. The core of the models is a phase evolution governed by the time dependent Ginzburg-Landau (TDGL) equation and the conservation balance laws with nonlinear coupling between stress, strain and the phase order parameter. The models account for the gradient energy and have been tested in the study of material properties evolution under harmonic stress loading for all important practical cases. The representative numerical simulations have been carried out here without the gradient energy term. The developed models account for the phase dependent properties based on the compliance tensor as a function of the order parameter and stress. We also compared the results obtained with these models and observed differences in homogeneous and inhomogeneous situations due to the change in compliance. In this way, the description of quasiplastic and pseudoelastic behaviors in SMA specimens is improved and becomes in an agreement with existing experiments.

  7. Design, modelling and control of a micro-positioning actuator based on magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Minorowicz, Bartosz; Leonetti, Giuseppe; Stefanski, Frederik; Binetti, Giulio; Naso, David

    2016-07-01

    This paper presents an actuator based on magnetic shape memory alloys (MSMAs) suitable for precise positioning in a wide range (up to 1 mm). The actuator is based on the spring returned operating mode and uses a Smalley wave spring to maintain the same operating parameters of a classical coil spring, while being characterized by a smaller dimension. The MSMA element inside the actuator provides a deformation when excited by an external magnetic field, but its behavior is characterized by an asymmetric and saturated hysteresis. Thus, two models are exploited in this work to represent such a non-linear behavior, i.e., the modified and generalized Prandtl–Ishlinskii models. These models are particularly suitable for control purposes due to the existence of their analytical inversion that can be easily exploited in real time control systems. To this aim, this paper investigates three closed-loop control strategies, namely a classical PID regulator, a PID regulator with direct hysteresis compensation, and a combined PID and feedforward compensation strategy. The effectiveness of both modelling and control strategies applied to the designed MSMA-based actuator is illustrated by means of experimental results.

  8. Analysis of shape memory alloy sensory particles for damage detection via substructure and continuum damage modeling

    NASA Astrophysics Data System (ADS)

    Bielefeldt, Brent R.; Benzerga, A. Amine; Hartl, Darren J.

    2016-04-01

    The ability to monitor and predict the structural health of an aircraft is of growing importance to the aerospace industry. Currently, structural inspections and maintenance are based upon experiences with similar aircraft operating in similar conditions. While effective, these methods are time-intensive and unnecessary if the aircraft is not in danger of structural failure. It is imagined that future aircraft will utilize non-destructive evaluation methods, allowing for the near real-time monitoring of structural health. A particularly interesting method involves utilizing the unique transformation response of shape memory alloy (SMA) particles embedded in an aircraft structure. By detecting changes in the mechanical and/or electromagnetic responses of embedded particles, operators could detect the formation or propagation of fatigue cracks in the vicinity of these particles. This work focuses on a finite element model of SMA particles embedded in an aircraft wing using a substructure modeling approach in which degrees of freedom are retained only at specified points of connection to other parts or the application of boundary conditions, greatly reducing computational cost. Previous work evaluated isolated particle response to a static crack to numerically demonstrate and validate this damage detection method. This paper presents the implementation of a damage model to account for crack propagation and examine for the first time the effect of particle configuration and/or relative placement with respect to the ability to detect damage.

  9. Nanoscale compositional analysis of NiTi shape memory alloy films deposited by DC magnetron sputtering

    SciTech Connect

    Sharma, S. K.; Mohan, S.; Bysakh, S.; Kumar, A.; Kamat, S. V.

    2013-11-15

    The formation of surface oxide layer as well as compositional changes along the thickness for NiTi shape memory alloy thin films deposited by direct current magnetron sputtering at substrate temperature of 300 °C in the as-deposited condition as well as in the postannealed (at 600 °C) condition have been thoroughly studied by using secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, and scanning transmission electron microscopy-energy dispersive x-ray spectroscopy techniques. Formation of titanium oxide (predominantly titanium dioxide) layer was observed in both as-deposited and postannealed NiTi films, although the oxide layer was much thinner (8 nm) in as-deposited condition. The depletion of Ti and enrichment of Ni below the oxide layer in postannealed films also resulted in the formation of a graded microstructure consisting of titanium oxide, Ni{sub 3}Ti, and B2 NiTi. A uniform composition of B2 NiTi was obtained in the postannealed film only below a depth of 200–250 nm from the surface. Postannealed film also exhibited formation of a ternary silicide (Ni{sub x}Ti{sub y}Si) at the film–substrate interface, whereas no silicide was seen in the as-deposited film. The formation of silicide also caused a depletion of Ni in the film in a region ∼250–300 nm just above the film substrate interface.

  10. TiNi shape memory alloy coated with tungsten: a novel approach for biomedical applications.

    PubMed

    Li, Huafang; Zheng, Yufeng; Pei, Y T; De Hosson, J Th M

    2014-05-01

    This study explores the use of DC magnetron sputtering tungsten thin films for surface modification of TiNi shape memory alloy (SMA) targeting for biomedical applications. SEM, AFM and automatic contact angle meter instrument were used to determine the surface characteristics of the tungsten thin films. The hardness of the TiNi SMA with and without tungsten thin films was measured by nanoindentation tests. It is demonstrated that the tungsten thin films deposited at different magnetron sputtering conditions are characterized by a columnar microstructure and exhibit different surface morphology and roughness. The hardness of the TiNi SMA was improved significantly by tungsten thin films. The ion release, hemolysis rate, cell adhesion and cell proliferation have been investigated by inductively coupled plasma atomic emission spectrometry, CCK-8 assay and alkaline phosphatase activity test. The experimental findings indicate that TiNi SMA coated with tungsten thin film shows a substantial reduction in the release of nickel. Therefore, it has a better in vitro biocompatibility, in particular, reduced hemolysis rate, enhanced cell adhesion and differentiation due to the hydrophilic properties of the tungsten films.

  11. Energy-efficient miniature-scale heat pumping based on shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ossmer, Hinnerk; Wendler, Frank; Gueltig, Marcel; Lambrecht, Franziska; Miyazaki, Shuichi; Kohl, Manfred

    2016-08-01

    Cooling and thermal management comprise a major part of global energy consumption. The by far most widespread cooling technology today is vapor compression, reaching rather high efficiencies, but promoting global warming due to the use of environmentally harmful refrigerants. For widespread emerging applications using microelectronics and micro-electro-mechanical systems, thermoelectrics is the most advanced technology, which however hardly reaches coefficients of performance (COP) above 2.0. Here, we introduce a new approach for energy-efficient heat pumping using the elastocaloric effect in shape memory alloys. This development is mainly targeted at applications on miniature scales, while larger scales are envisioned by massive parallelization. Base materials are cold-rolled textured Ti49.1Ni50.5Fe0.4 foils of 30 μm thickness showing an adiabatic temperature change of +20/‑16 K upon superelastic loading/unloading. Different demonstrator layouts consisting of mechanically coupled bridge structures with large surface-to-volume ratios are developed allowing for control by a single actuator as well as work recovery. Heat transfer times are in the order of 1 s, being orders of magnitude faster than for bulk geometries. Thus, first demonstrators achieve values of specific heating and cooling power of 4.5 and 2.9 W g‑1, respectively. A maximum temperature difference of 9.4 K between heat source and sink is reached within 2 min. Corresponding COP on the device level are 4.9 (heating) and 3.1 (cooling).

  12. Surface characterizations of laser modified biomedical grade NiTi shape memory alloys.

    PubMed

    Pequegnat, A; Michael, A; Wang, J; Lian, K; Zhou, Y; Khan, M I

    2015-05-01

    Laser processing of shape memory alloys (SMAs) promises to enable the multifunctional capabilities needed for medical device applications. Prior to clinical implementation, the surface characterisation of laser processed SMA is essential in order to understand any adverse biological interaction that may occur. The current study systematically investigated two Ni-49.8 at.% Ti SMA laser processed surface finishes, including as-processed and polished, while comparing them to a chemically etched parent material. Spectrographic characterisation of the surface included; X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), and Raman spectroscopy. Corrosion performance and Ni ion release were also assessed using potentiodynamic cyclic polarization testing and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. Results showed that surface defects, including increased roughness, crystallinity and presence of volatile oxide species, overshadowed any possible performance improvements from an increased Ti/Ni ratio or inclusion dissolution imparted by laser processing. However, post-laser process mechanical polishing was shown to remove these defects and restore the performance, making it comparable to chemically etched NiTi material.

  13. Design of High Temperature Ti-Pd-Cr Shape Memory Alloys with Small Thermal Hysteresis

    PubMed Central

    Xue, Deqing; Yuan, Ruihao; Zhou, Yumei; Xue, Dezhen; Lookman, Turab; Zhang, Guojun; Ding, Xiangdong; Sun, Jun

    2016-01-01

    The large thermal hysteresis (ΔT) during the temperature induced martensitic transformation is a major obstacle to the functional stability of shape memory alloys (SMAs), especially for high temperature applications. We propose a design strategy for finding SMAs with small thermal hysteresis. That is, a small ΔT can be achieved in the compositional crossover region between two different martensitic transformations with opposite positive and negative changes in electrical resistance at the transformation temperature. We demonstrate this for a high temperature ternary Ti-Pd-Cr SMA by achieving both a small ΔT and high transformation temperature. We propose two possible underlying physics governing the reduction in ΔT. One is that the interfacial strain is accommodated at the austenite/martensite interface via coexistence of B19 and 9R martensites. The other is that one of transformation eigenvalues equal to 1, i.e., λ2 = 1, indicating a perfect coherent interface between austenite and martensite. Our results are not limited to Ti-Pd-Cr SMAs but potentially provide a strategy for searching for SMAs with small thermal hysteresis. PMID:27328764

  14. Computational Thermodynamics and Kinetics-Based ICME Framework for High-Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Arróyave, Raymundo; Talapatra, Anjana; Johnson, Luke; Singh, Navdeep; Ma, Ji; Karaman, Ibrahim

    2015-11-01

    Over the last decade, considerable interest in the development of High-Temperature Shape Memory Alloys (HTSMAs) for solid-state actuation has increased dramatically as key applications in the aerospace and automotive industry demand actuation temperatures well above those of conventional SMAs. Most of the research to date has focused on establishing the (forward) connections between chemistry, processing, (micro)structure, properties, and performance. Much less work has been dedicated to the development of frameworks capable of addressing the inverse problem of establishing necessary chemistry and processing schedules to achieve specific performance goals. Integrated Computational Materials Engineering (ICME) has emerged as a powerful framework to address this problem, although it has yet to be applied to the development of HTSMAs. In this paper, the contributions of computational thermodynamics and kinetics to ICME of HTSMAs are described. Some representative examples of the use of computational thermodynamics and kinetics to understand the phase stability and microstructural evolution in HTSMAs are discussed. Some very recent efforts at combining both to assist in the design of HTSMAs and limitations to the full implementation of ICME frameworks for HTSMA development are presented.

  15. Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2016-01-01

    Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (˜8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

  16. Preparing TiNiNb shape memory alloy powders by hydriding-dehydriding process

    NASA Astrophysics Data System (ADS)

    Shao, Yang; Cui, Lishan; Jiang, Xiaohua; Guo, Fangmin; Liu, Yinong; Hao, Shijie

    2016-07-01

    High-quality TiNiNb shape memory alloy (SMA) powders were prepared by hydrogenation of cold-worked TiNiNb SMA wire composed of amorphous and nancrystalline microstructure, by mechanical pulverization and vacuum dehydrogenation. It is revealed that abundant structural defects introduced by cold-work greatly promoted hydrogen diffusion, which significantly decreased hydriding temperature and shortened hydriding time. After hydrogenation, the hydrogenated sample composed of TiNiH and NbH with high brittleness can be easily ground into ultra-fine powers. The TiNiNb powers obtained by following vacuum dehydrogenation exhibit almost the same reversible phase transformation behavior as that of the original TiNiNb SMA before cold-work. Moreover, a TiNiNb part was obtained by hot-pressure sintering the hydrogenated powders, where sintering and dehydrogenation are carried out in one single step. The sintered TiNiNb part shows most the same reversible phase transformation behaviors as that of the original TiNiNb SMA and there is no visible additional brittle phase appearance.

  17. Design of High Temperature Ti-Pd-Cr Shape Memory Alloys with Small Thermal Hysteresis

    NASA Astrophysics Data System (ADS)

    Xue, Deqing; Yuan, Ruihao; Zhou, Yumei; Xue, Dezhen; Lookman, Turab; Zhang, Guojun; Ding, Xiangdong; Sun, Jun

    2016-06-01

    The large thermal hysteresis (ΔT) during the temperature induced martensitic transformation is a major obstacle to the functional stability of shape memory alloys (SMAs), especially for high temperature applications. We propose a design strategy for finding SMAs with small thermal hysteresis. That is, a small ΔT can be achieved in the compositional crossover region between two different martensitic transformations with opposite positive and negative changes in electrical resistance at the transformation temperature. We demonstrate this for a high temperature ternary Ti-Pd-Cr SMA by achieving both a small ΔT and high transformation temperature. We propose two possible underlying physics governing the reduction in ΔT. One is that the interfacial strain is accommodated at the austenite/martensite interface via coexistence of B19 and 9R martensites. The other is that one of transformation eigenvalues equal to 1, i.e., λ2 = 1, indicating a perfect coherent interface between austenite and martensite. Our results are not limited to Ti-Pd-Cr SMAs but potentially provide a strategy for searching for SMAs with small thermal hysteresis.

  18. Design and testing of a shape memory alloy buoyancy engine for unmanned underwater vehicles

    NASA Astrophysics Data System (ADS)

    Angilella, Alex J.; Gandhi, Farhan S.; Miller, Timothy F.

    2015-11-01

    The US Navy’s 2004 Unmanned Underwater Vehicle (UUV) Master Plan outlines the Navy’s aim to expand the role of UUVs, and one of the key areas of interest is the increase in UUV range and endurance. A class of UUVs known as underwater gliders achieves this objective by cyclically modifying its buoyancy and covering horizontal distance with a climb/dive pattern. The present study proposes the use of shape memory alloys (SMAs) in a buoyancy heat engine where the oceanic thermocline would be exploited to produce martensite-austenite phase transformations that in turn change the buoyancy of a piston-cylinder prototype. The working principle of the device involves transitioning between the following two states. At low temperature (at depth) the SMA wires are tensioned into a detwinned martensitic state by a parallel compressed spring. This moves the piston within the cylinder to increase the chamber dry volume and device buoyancy. At higher temperatures (near the surface) the SMA wires undergo a martensite-to-austenite phase transformation, recover part of the applied strain, and reduce the volume and buoyancy of the piston-cylinder. This paper presents the analysis, design, fabrication, and testing of a prototype device. The prototype was immersed in a water bath, and it was demonstrated that its volume would change, as expected, with change in temperature of the water bath. Simulation results showed good correlation with test data.

  19. High Strain Rate Compression of Martensitic NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Qiu, Ying; Young, Marcus L.; Nie, Xu

    2015-09-01

    The compressive response of martensitic NiTi shape memory alloys (SMAs) under high strain rate (1200 s-1) was investigated on a modified Kolsky (Split Hopkinson) compression bar. The single-loading momentum trapping system ensures precise deformation control (1.4, 1.8, 3.0, 4.8, and 9.6 % strain) and single loading during dynamic compression. With increasing strain, the phase transformation peaks shift toward lower temperatures, while the intensities of these peaks decrease and eventually disappear completely at strains above 7 %, where the onset of plastic deformation of reoriented martensite occurs. All transformation peaks are recoverable after deformation simply by annealing at 873 K (600 °C) for 30 min, except those peaks corresponding to strains above 7 % (e.g., 9.6 %) which return upon annealing, but at a lower temperature. XRD results showed the variation of the strongest diffraction peak from (1bar{1}1) to (111) crystal plane before and after high strain rate compression.

  20. Influence of Ni on Martensitic Phase Transformations in NiTi Shape Memory Alloys

    SciTech Connect

    Frenzel, J.; George, Easo P; Dlouhy, A.; Somsen, Ch.; Wagner, M. F.-X; Eggeler, G.

    2010-01-01

    High-precision data on phase transformation temperatures in NiTi, including numerical expressions for the effect of Ni on M{sub S}, M{sub F}, A{sub S}, A{sub F} and T{sub 0}, are obtained, and the reasons for the large experimental scatter observed in previous studies are discussed. Clear experimental evidence is provided confirming the predictions of Tang et al. 1999 regarding deviations from a linear relation between the thermodynamic equilibrium temperature and Ni concentration. In addition to affecting the phase transition temperatures, increasing Ni contents are found to decrease the width of thermal hysteresis and the heat of transformation. These findings are rationalized on the basis of the crystallographic data of Prokoshkin et al. 2004 and the theory of Ball and James. The results show that it is important to document carefully the details of the arc-melting procedure used to make shape memory alloys and that, if the effects of processing are properly accounted for, precise values for the Ni concentration of the NiTi matrix can be obtained.