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Sample records for ni shape memory

  1. Shape memory effect of laser welded NiTi plates

    NASA Astrophysics Data System (ADS)

    Oliveira, J. P.; Fernandes, F. M. Braz; Schell, N.; Miranda, R. M.

    2015-07-01

    Laser welding is a suitable joining technique for shape memory alloys (SMAs). This paper reports the existence of shape memory effect (SME) on laser welded NiTi joints, subjected to bending tests, and correlates this effect with the microstructural analysis performed with X-ray diffraction (XRD). All welded samples were able to recover their initial shape after bending to 180°, which is a remarkable result for industrial applications of NiTi involving laser welding.

  2. 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.

  3. Shape memory behavior of single crystal and polycrystalline Ni-rich NiTiHf high temperature shape memory alloys

    NASA Astrophysics Data System (ADS)

    Saghaian, Sayed M.

    NiTiHf shape memory alloys have been receiving considerable attention for high temperature and high strength applications since they could have transformation temperatures above 100 °C, shape memory effect under high stress (above 500 MPa) and superelasticity at high temperatures. Moreover, their shape memory properties can be tailored by microstructural engineering. However, NiTiHf alloys have some drawbacks such as low ductility and high work hardening in stress induced martensite transformation region. In order to overcome these limitations, studies have been focused on microstructural engineering by aging, alloying and processing. Shape memory properties and microstructure of four Ni-rich NiTiHf alloys (Ni50.3Ti29.7Hf20, Ni50.7Ti 29.3Hf20, Ni51.2Ti28.8Hf20, and Ni52Ti28Hf20 (at. %)) were systematically characterized in the furnace cooled condition. H-phase precipitates were formed during furnace cooling in compositions with greater than 50.3Ni and the driving force for nucleation increased with Ni content. Alloy strength increased while recoverable strain decreased with increasing Ni content due to changes in precipitate characteristics. The effects of the heat treatments on the transformation characteristics and microstructure of the Ni-rich NiTiHf shape memory alloys have been investigated. Transformation temperatures are found to be highly annealing temperature dependent. Generation of nanosize precipitates (˜20 nm in size) after three hours aging at 450 °C and 550 °C improved the strength of the material, resulting in a near perfect dimensional stability under high stress levels (> 1500 MPa) with a work output of 20-30 J cm- 3. Superelastic behavior with 4% recoverable strain was demonstrated at low and high temperatures where stress could reach to a maximum value of more than 2 GPa after three hours aging at 450 and 550 °C for alloys with Ni great than 50.3 at. %. Shape memory properties of polycrystalline Ni50.3Ti29.7 Hf20 alloys were studied via

  4. Nondestructive Evaluation of Ni-Ti Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    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.

  5. 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.

  6. The ferromagnetic shape-memory effect in Ni Mn Ga

    NASA Astrophysics Data System (ADS)

    Marioni, M. A.; O'Handley, R. C.; Allen, S. M.; Hall, S. R.; Paul, D. I.; Richard, M. L.; Feuchtwanger, J.; Peterson, B. W.; Chambers, J. M.; Techapiesancharoenkij, R.

    2005-04-01

    Active materials have long been used in the construction of sensors and devices. Examples are piezo-electric ceramics and shape memory alloys. The more recently developed ferromagnetic shape-memory alloys (FSMAs) have received considerable attention due to their large magnetic field-induced, reversible strains (up to 10%). In this article, we review the basic physical characteristics of the FSMA Ni-Mn-Ga (crystallography, thermal, mechanical and magnetic behavior). Also, we present some of the works currently under way in the areas of pulse-field and acoustic-assisted actuation, and vibration energy absorption.

  7. Corrosion resistance tests on NiTi shape memory alloy.

    PubMed

    Rondelli, G

    1996-10-01

    The corrosion performances of NiTi shape memory alloys (SMA) in human body simulating fluids were evaluated in comparison with other implant materials. As for the passivity current in potentiostatic conditions, taken as an index of ion release, the values are about three times higher for NiTi than for Ti6Al4V and austenitic stainless steels. Regarding the localized corrosion, while plain potentiodynamic scans indicated for NiTi alloy good resistance to pitting attack similar to Ti6Al4V, tests in which the passive film is abruptly damaged (i.e. potentiostatic scratch test and modified ASTM F746) pointed out that the characteristics of the passive film formed on NiTi alloy (whose strength can be related to the alloy's biocompatibility) are not as good as those on Ti6Al4V but are comparable or inferior to those on austenitic stainless steels.

  8. Boriding of Binary Ni-Ti Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Ucar, Nazim; Dogan, Sule; Karakas, Mustafa Serdar; Calik, Adnan

    2016-11-01

    Boriding of binary Ni-Ti shape memory alloys was carried out in a solid medium at 1273 K for 2, 4, 6, and 8 h using the powder pack method with proprietary Ekabor-Ni powders. Characterization of the boride layer formed on the surface of alloys was done by optical microscopy and scanning electron microscopy. The presence of boride, silicide, and borosilicide phases in the boride layers was confirmed by X-ray diffraction analysis. The thickness and microhardness of the boride layers increased with increasing boriding time. Hardness profiles showed a rapid decrease in hardness moving from the boride layer to the main structure. The high hardness of the boride layer was attributed mainly to the formation of TiB2. A parabolic relationship was observed between layer thickness and boriding time, and the growth rate constant for the boriding treatment was calculated as 0.62×10-8 cm2 s-1.

  9. NiMnGa/Si Shape Memory Bimorph Nanoactuation

    NASA Astrophysics Data System (ADS)

    Lambrecht, Franziska; Lay, Christian; Aseguinolaza, Iván R.; Chernenko, Volodymyr; Kohl, Manfred

    2016-12-01

    The size dependences of thermal bimorph and shape memory effect of nanoscale shape memory alloy (SMA)/Si bimorph actuators are investigated in situ in a scanning electron microscope and by finite element simulations. By combining silicon nanomachining and magnetron sputtering, freestanding NiMnGa/Si bimorph cantilever structures with film/substrate thickness of 200/250 nm and decreasing lateral dimensions are fabricated. Electrical resistance and mechanical beam bending tests upon direct Joule heating demonstrate martensitic phase transformation and reversible thermal bimorph effect, respectively. Corresponding characteristics are strongly affected by the large temperature gradient in the order of 50 K/µm forming along the nano bimorph cantilever upon electro-thermal actuation, which, in addition, depends on the size-dependent heat conductivity in the Si nano layer. Furthermore, the martensitic transformation temperatures show a size-dependent decrease by about 40 K for decreasing lateral dimensions down to 200 nm. The effects of heating temperature and stress distribution on the nanoactuation performance are analyzed by finite element simulations revealing thickness ratio of SMA/Si of 90/250 nm to achieve an optimum SME. Differential thermal expansion and thermo-elastic effects are discriminated by comparative measurements and simulations on Ni/Si bimorph reference actuators.

  10. 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.

  11. Multi-stage martensitic transformation in Ni-rich NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wang, Xiebin; Verlinden, Bert; Kustov, Sergey

    Precipitation hardening is an effective way to improve the functional stability of NiTi shape memory alloys. The precipitates, mainly Ni4Ti3, could be introduced by aging treatment in Ni-rich NiTi alloys. However, the presence of Ni4Ti3 precipitates could disturb the transformation behavior, resulting in the multi-stage martensitic transformation (MMT). With the presence of MMT, it is difficult to control the transformation behavior, and thus limits the applicability of NiTi alloys. In this work, previous efforts on explaining the observed MMT are summarized. The difficulties in developing a unified explanation are discussed, and a possible way to avoid the MMT is proposed.

  12. 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.

  13. 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.

  14. 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.

  15. Reverse Shape Memory Effect Related to α → γ Transformation in a Fe-Mn-Al-Ni Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Peng, Huabei; Huang, Pan; Zhou, Tiannan; Wang, Shanling; Wen, Yuhua

    2017-02-01

    In this study, we investigated the shape memory behavior and phase transformations of solution-treated Fe43.61Mn34.74Al13.38Ni8.27 alloy between room temperature and 1173 K (900 °C). This alloy exhibits the reverse shape memory effect resulting from the phase transformation of α (bcc) → γ (fcc) between 673 K and 1073 K (400 °C and 800 °C) in addition to the shape memory effect resulting from the martensitic reverse transformation of γ' (fcc) → α (bcc) below 673 K (400 °C). There is a high density of hairpin-shaped dislocations in the α phase undergoing the martensitic reverse transformation of γ' → α. The lath γ phase, which preferentially nucleates and grows in the reversed α phase, has the same crystal orientation with the reverse-transformed γ' martensite. However, the vermiculate γ phase, which is precipitated in the α phase between lath γ phase, has different crystal orientations. The lath γ phase is beneficial to attaining better reverse shape memory effect than the vermiculate γ phase.

  16. 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.

  17. Electrochemical and corrosion behaviors of sputtered TiNi shape memory films

    NASA Astrophysics Data System (ADS)

    Li, K.; Huang, X.; Zhao, Z. S.; Li, Y.; Fu, Y. Q.

    2016-03-01

    Electrochemical and corrosion behaviors of TiNi-based shape memory thin films were explored using electrochemical impedance spectroscopy (EIS) and polarization methods in phosphate buffered saline solutions at 37 °C. Compared with those of electro-polished and passivated bulk NiTi shape memory alloys, the break-down potentials of the sputter-deposited amorphous TiNi films were much higher. After crystallization, the break-down potentials of the TiNi films were comparable with that of the bulk NiTi shape memory alloy. Additionally, variation of composition of the TiNi films showed little influence on their corrosion behavior. The EIS data were fitted using a parallel resistance-capacitance circuit associated with passive oxide layer on the tested samples. The thickness of the oxide layer for the TiNi thin films was found much thinner than that of bulk NiTi shape memory alloy. During electrochemical testing, the oxide thickness of the bulk alloy reached its maximum at a voltage of 0.6-0.8 V, whereas those of TiNi films were increased continuously up to a voltage of 1.2 V.

  18. Two-way Shape Memory Effect of NiTi under Compressive Loading Cycles

    NASA Astrophysics Data System (ADS)

    Yoo, Young Ik; Lee, Jung Ju

    In this study, the two-way shape memory effect (TWSME) of a Ni-54.5 at.% Ti alloy was investigated experimentally to develop a NiTi linear actuator. The two-way shape memory effect was induced through a compressive shape memory cycle composed of four steps: (1) loading to maximum deformation; (2) unloading; (3) heating; (4) and cooling. Six types of specimens (one solid cylindrical and five tubular) were used to obtain the twoway shape memory strain and two-way recovery stress and to evaluate the actuating capacity. The two-way actuating strain showed a convergent tendency after several training cycles for the same maximum deformation. A maximum value of the two-way strain was obtained for 7% of maximum deformation, independently of the geometry of the tubular specimens. The two-way strains obtained by the shape memory cycles and two-way recovery stress linearly increase as a function of the maximum deformation and the two-way strain, respectively, and the geometry of specimen affects the two-way recovery stress. Although the results show that sufficient recovery stress can be generated by either the two-way shape memory process or by the one-way shape memory process, the two-way shape memory process can be applied more conveniently to actuating applications.

  19. Functionally grading the shape memory response in NiTi films: Laser irradiation

    SciTech Connect

    Birnbaum, A. J.; Satoh, G.; Yao, Y. L.

    2009-08-15

    A new process and mechanism are presented for controlling the shape memory response spatially within monolithic NiTi thin film structures. This technique is shown to effectively control the martensitic phase transformation temperature and exhibits control over aspects of the mechanical and shape memory responses as well. Specifically, the martensitic phase transformation temperature decreases with incident laser energy density. Concomitant modifications are observed in both the mechanical and shape memory responses in laser processed films. Analysis and characterization are performed via temperature controlled optical microscopy, x-ray diffraction, atomic force microscopy, and nanoindentation.

  20. 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.

  1. 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.

  2. Design and development of novel antibacterial Ti-Ni-Cu shape memory alloys for biomedical application

    PubMed Central

    Li, H. F.; Qiu, K. J.; Zhou, F. Y.; Li, L.; Zheng, Y. F.

    2016-01-01

    In the case of medical implants, foreign materials are preferential sites for bacterial adhesion and microbial contamination, which can lead to the development of prosthetic infections. Commercially biomedical TiNi shape memory alloys are the most commonly used materials for permanent implants in contact with bone and dental, and the prevention of infections of TiNi biomedical shape memory alloys in clinical cases is therefore a crucial challenge for orthopaedic and dental surgeons. In the present study, copper has been chosen as the alloying element for design and development novel ternary biomedical Ti‒Ni‒Cu shape memory alloys with antibacterial properties. The effects of copper alloying element on the microstructure, mechanical properties, corrosion behaviors, cytocompatibility and antibacterial properties of biomedical Ti‒Ni‒Cu shape memory alloys have been systematically investigated. The results demonstrated that Ti‒Ni‒Cu alloys have good mechanical properties, and remain the excellent shape memory effects after adding copper alloying element. The corrosion behaviors of Ti‒Ni‒Cu alloys are better than the commercial biomedical Ti‒50.8Ni alloys. The Ti‒Ni‒Cu alloys exhibit excellent antibacterial properties while maintaining the good cytocompatibility, which would further guarantee the potential application of Ti‒Ni‒Cu alloys as future biomedical implants and devices without inducing bacterial infections. PMID:27897182

  3. Design and development of novel antibacterial Ti-Ni-Cu shape memory alloys for biomedical application.

    PubMed

    Li, H F; Qiu, K J; Zhou, F Y; Li, L; Zheng, Y F

    2016-11-29

    In the case of medical implants, foreign materials are preferential sites for bacterial adhesion and microbial contamination, which can lead to the development of prosthetic infections. Commercially biomedical TiNi shape memory alloys are the most commonly used materials for permanent implants in contact with bone and dental, and the prevention of infections of TiNi biomedical shape memory alloys in clinical cases is therefore a crucial challenge for orthopaedic and dental surgeons. In the present study, copper has been chosen as the alloying element for design and development novel ternary biomedical Ti‒Ni‒Cu shape memory alloys with antibacterial properties. The effects of copper alloying element on the microstructure, mechanical properties, corrosion behaviors, cytocompatibility and antibacterial properties of biomedical Ti‒Ni‒Cu shape memory alloys have been systematically investigated. The results demonstrated that Ti‒Ni‒Cu alloys have good mechanical properties, and remain the excellent shape memory effects after adding copper alloying element. The corrosion behaviors of Ti‒Ni‒Cu alloys are better than the commercial biomedical Ti‒50.8Ni alloys. The Ti‒Ni‒Cu alloys exhibit excellent antibacterial properties while maintaining the good cytocompatibility, which would further guarantee the potential application of Ti‒Ni‒Cu alloys as future biomedical implants and devices without inducing bacterial infections.

  4. Design and development of novel antibacterial Ti-Ni-Cu shape memory alloys for biomedical application

    NASA Astrophysics Data System (ADS)

    Li, H. F.; Qiu, K. J.; Zhou, F. Y.; Li, L.; Zheng, Y. F.

    2016-11-01

    In the case of medical implants, foreign materials are preferential sites for bacterial adhesion and microbial contamination, which can lead to the development of prosthetic infections. Commercially biomedical TiNi shape memory alloys are the most commonly used materials for permanent implants in contact with bone and dental, and the prevention of infections of TiNi biomedical shape memory alloys in clinical cases is therefore a crucial challenge for orthopaedic and dental surgeons. In the present study, copper has been chosen as the alloying element for design and development novel ternary biomedical Ti‒Ni‒Cu shape memory alloys with antibacterial properties. The effects of copper alloying element on the microstructure, mechanical properties, corrosion behaviors, cytocompatibility and antibacterial properties of biomedical Ti‒Ni‒Cu shape memory alloys have been systematically investigated. The results demonstrated that Ti‒Ni‒Cu alloys have good mechanical properties, and remain the excellent shape memory effects after adding copper alloying element. The corrosion behaviors of Ti‒Ni‒Cu alloys are better than the commercial biomedical Ti‒50.8Ni alloys. The Ti‒Ni‒Cu alloys exhibit excellent antibacterial properties while maintaining the good cytocompatibility, which would further guarantee the potential application of Ti‒Ni‒Cu alloys as future biomedical implants and devices without inducing bacterial infections.

  5. 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.

  6. Fast Response Shape Memory Effect Titanium Nickel (TiNi) Foam Torque Tubes

    NASA Technical Reports Server (NTRS)

    Jardine, Peter

    2014-01-01

    Shape Change Technologies has developed a process to manufacture net-shaped TiNi foam torque tubes that demonstrate the shape memory effect. The torque tubes dramatically reduce response time by a factor of 10. This Phase II project matured the actuator technology by rigorously characterizing the process to optimize the quality of the TiNi and developing a set of metrics to provide ISO 9002 quality assurance. A laboratory virtual instrument engineering workbench (LabVIEW'TM')-based, real-time control of the torsional actuators was developed. These actuators were developed with The Boeing Company for aerospace applications.

  7. 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.

  8. 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.

  9. Shape-memory properties in Ni-Ti sputter-deposited film

    NASA Technical Reports Server (NTRS)

    Busch, J. D.; Johnson, A. D.; Lee, C. H.; Stevenson, D. A.

    1990-01-01

    A Ni-Ti alloy, generically called nitinol, was prepared from sputtering targets of two different compositions on glass substrates using a dc magnetron source. The as-deposited films were amorphous in structure and did not exhibit a shape memory. The amorphous films were crystallized with a suitable annealing process, and the transformation properties were measured using differential scanning calorimetry. The annealed films demonstrated a strong shape-memory effect. Stress/strain measurements and physical manipulation were used to evaluate the shape recovery. These tests demonstrated sustained tensile stresses of up to 480 MPa in the high-temperature phase, and a characteristic plastic deformation in the low-temperature phase.

  10. 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.

  11. Nitride coating enhances endothelialization on biomedical NiTi shape memory alloy.

    PubMed

    Ion, Raluca; Luculescu, Catalin; Cimpean, Anisoara; Marx, Philippe; Gordin, Doina-Margareta; Gloriant, Thierry

    2016-05-01

    Surface nitriding was demonstrated to be an effective process for improving the biocompatibility of implantable devices. In this study, we investigated the benefits of nitriding the NiTi shape memory alloy for vascular stent applications. Results from cell experiments indicated that, compared to untreated NiTi, a superficial gas nitriding treatment enhanced the adhesion of human umbilical vein endothelial cells (HUVECs), cell spreading and proliferation. This investigation provides data to demonstrate the possibility of improving the rate of endothelialization on NiTi by means of nitride coating.

  12. Shape-memory NiTi with two-dimensional networks of micro-channels.

    PubMed

    Neurohr, Anselm J; Dunand, David C

    2011-04-01

    A process was developed for fabricating arrays of micro-channels in shape-memory NiTi for bone implant applications, with a tailorable internal architecture expected to improve biomechanical compatibility and osseointegration. Ni-51.4 at.% Ti with 24-34 vol.% porosity was fabricated by electrochemical dissolution of parallel layers of steel wire meshes embedded within a NiTi matrix during hot pressing of NiTi powders. The resulting NiTi structures exhibit parallel layers of orthogonally interconnected micro-channels with 350-400 μm diameters that exactly replicate the steel meshes. When low-carbon steel wires are used, iron diffuses into the surrounding NiTi during the densification step, creating a Fe-enriched zone near the wires. For high-carbon steel wires, TiC forms at the steel/NiTi interface and inhibits iron diffusion but also depletes some titanium from the adjacent NiTi. In both cases, the NiTi regions near the micro-channels exhibit altered phase transformation characteristics. These NiTi structures with replicated networks of micro-channels have excellent potential as bone implants and scaffolds given: (i) the versatility in channel size, shape, fraction and spatial arrangement; (ii) their low stiffness (15-26 GPa), close to 12-17 GPa for cortical bone; (iii) their high compressive strength (420-600 MPa at 8-9% strain); and (iv) their excellent compressive strain recovery (91-94% of an applied strain of 6%) by a combination of elasticity, superelasticity and the shape-memory effect.

  13. Assessing the biocompatibility of NiTi shape memory alloys used for medical applications.

    PubMed

    Es-Souni, Mohammed; Es-Souni, Martha; Fischer-Brandies, Helge

    2005-02-01

    The present paper reviews aspects related to the biocompatibility of NiTi shape memory alloys used for medical applications. These smart metallic materials, which are characterised by outstanding mechanical properties, have been gaining increasing importance over the last two decades in many minimal invasive surgery and diagnostic applications, as well as for other uses, such as in orthodontic appliances. Due to the presence of high amounts of Ni, the cytotoxicity of such alloys is under scrutiny. In this review paper we analyse work published on the biocompatibility of NiTi alloys, considering aspects related to: (1) corrosion properties and the different methods used to test them, as well as specimen surface states; (2) biocompatibility tests in vitro and in vivo; (3) the release of Ni ions. It is shown that NiTi shape memory alloys are generally characterised by good corrosion properties, in most cases superior to those of conventional stainless steel or Co-Cr-Mo-based biomedical materials. The majority of biocompatibility studies suggest that these alloys have low cytotoxicity (both in vitro and in vivo) as well as low genotoxicity. The release of Ni ions depends on the surface state and the surface chemistry. Smooth surfaces with well-controlled structures and chemistries of the outermost protective TiO2 layer lead to negligible release of Ni ions, with concentrations below the normal human daily intake.

  14. Complex transformation field created by geometrical gradient design of NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Bakhtiari, Reza; Shariat, Bashir S.; Motazedian, Fakhrodin; Wu, Zhigang; Zhang, Junsong; Yang, Hong; Liu, Yinong

    Owing to geometrical non-uniformity, geometrically graded shape memory alloy (SMA) structures by design have the ability to exhibit different and novel thermal and mechanical behaviors compared to geometrically uniform conventional SMAs. This paper reports a study of the pseudoelastic behavior of geometrically graded NiTi plates. This geometrical gradient creates partial stress gradient over stress-induced martensitic transformation, providing enlarged stress controlling interval for shape memory actuation. Finite element modeling framework has been established to predict the deformation behavior of such structures in tensile loading cycles, which was validated by experiments. The modeling results show that the transformation mostly propagates along the gradient direction as the loading level increases.

  15. New oxidation treatment of NiTi shape memory alloys to obtain Ni-free surfaces and to improve biocompatibility.

    PubMed

    Michiardi, A; Aparicio, C; Planell, J A; Gil, F J

    2006-05-01

    Various oxidation treatments were applied to nearly equiatomic NiTi alloys so as to form a Ni-free protective oxide on the surface. Sample surfaces were analyzed by X-ray Photoelectron Spectroscopy, and NiTi transformation temperatures were determined by differential scanning calorimetry (DSC) before and after the surface treatment. An ion release experiment was carried out up to one month of immersion in SBF for both oxidized and untreated surfaces. The results show that oxidation treatment in a low-oxygen pressure atmosphere leads to a high surface Ti/Ni ratio, a very low Ni surface concentration and a thick oxide layer. This oxidation treatment does not significantly affect the shape memory properties of the alloy. Moreover, the oxide formed significantly decreases Ni release into exterior medium comparing with untreated surfaces. As a consequence, this new oxidation treatment could be of great interest for biomedical applications, as it could minimize sensitization and allergies and improve biocompatibility and corrosion resistance of NiTi shape memory alloys.

  16. Nanoscale design of Ni-Al shape memory alloys.

    PubMed

    Subramaniyan, Arun K; Sun, C T

    2009-02-25

    Nanoscale design of Ni-Al alloys was performed to optimize the phase transformation behavior. The distribution of nickel and aluminum atoms was identified as a key parameter in the phase transformation process. A design criterion based on thermal expansion asymmetry was proposed. The effectiveness of the design criterion was validated using molecular dynamics simulations.

  17. Investigation on microstructure and martensitic transformation of neodymium-added NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Maashaa, Dovchinvanchig; Dorj, Ulzii-Orshikh; Lee, Malrey; Lee, Min Hi; Zhao, Chunwang; Dashjav, Munguntsetseg; Woo, Seon-Mi

    2016-10-01

    The effect of rare earth element neodymium (Nd) addition on the microstructure and martensitic transformation behavior of Ni50Ti50-xNdx (x = 0, 0.1, 0.3, 0.5 and 0.7 at.%) shape memory alloy was investigated by scanning electronic microscope, X-ray diffraction and differential scanning calorimetry. The results show that the microstructure of Ni-Ti-Nd ternary alloy consists of NiNd phase, NiTi2 and the NiTi matrix. A one-step martensitic transformation is observed in the alloys. The martensitic transformation temperature Ms increases sharply increasing 0.1-0.7 at.% Nd content is added.

  18. An x-ray absorption spectroscopy study of Ni-Mn-Ga shape memory alloys.

    PubMed

    Sathe, V G; Dubey, Aditi; Banik, Soma; Barman, S R; Olivi, L

    2013-01-30

    The austenite to martensite phase transition in Ni-Mn-Ga ferromagnetic shape memory alloys was studied by extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy. The spectra at all the three elements', namely, Mn, Ga and Ni, K-edges in several Ni-Mn-Ga samples (with both Ni and Mn excess) were analyzed at room temperature and low temperatures. The EXAFS analysis suggested a displacement of Mn and Ga atoms in opposite direction with respect to the Ni atoms when the compound transforms from the austenite phase to the martensite phase. The first coordination distances around the Mn and Ga atoms remained undisturbed on transition, while the second and subsequent shells showed dramatic changes indicating the presence of a modulated structure. The Mn rich compounds showed the presence of antisite disorder of Mn and Ga. The XANES results showed remarkable changes in the unoccupied partial density of states corresponding to Mn and Ni, while the electronic structure of Ga remained unperturbed across the martensite transition. The post-edge features in the Mn K-edge XANES spectra changed from a double peak like structure to a flat peak like structure upon phase transition. The study establishes strong correlation between the crystal structure and the unoccupied electronic structure in these shape memory alloys.

  19. Porous NiTi shape memory alloys produced by SHS: microstructure and biocompatibility in comparison with Ti2Ni and TiNi3.

    PubMed

    Bassani, Paola; Panseri, Silvia; Ruffini, Andrea; Montesi, Monica; Ghetti, Martina; Zanotti, Claudio; Tampieri, Anna; Tuissi, Ausonio

    2014-10-01

    Shape memory alloys based on NiTi have found their main applications in manufacturing of new biomedical devices mainly in surgery tools, stents and orthopedics. Porous NiTi can exhibit an engineering elastic modulus comparable to that of cortical bone (12-17 GPa). This condition, combined with proper pore size, allows good osteointegration. Open cells porous NiTi was produced by self propagating high temperature synthesis (SHS), starting from Ni and Ti mixed powders. The main NiTi phase is formed during SHS together with other Ni-Ti compounds. The biocompatibility of such material was investigated by single culture experiment and ionic release on small specimen. In particular, NiTi and porous NiTi were evaluated together with elemental Ti and Ni reference metals and the two intermetallic TiNi3, Ti2Ni phases. This approach permitted to clearly identify the influence of secondary phases in porous NiTi materials and relation with Ni-ion release. The results indicated, apart the well-known high toxicity of Ni, also toxicity of TiNi3, whilst phases with higher Ti content showed high biocompatibility. A slightly reduced biocompatibility of porous NiTi was ascribed to combined effect of TiNi3 presence and topography that requires higher effort for the cells to adapt to the surface.

  20. Cu-Al-Ni Shape Memory Single Crystal Wires with High Transformation Temperature

    NASA Technical Reports Server (NTRS)

    Hautcoeur, Alain; Fouché, Florian; Sicre, Jacques

    2016-01-01

    CN-250X is a new material with higher performance than Nickel-Titanium Shape Memory Alloy (SMA). For space mechanisms, the main disadvantage of Nickel-Titanium Shape Memory Alloy is the limited transformation temperature. The new CN-250X Nimesis alloy is a Cu-Al-Ni single crystal wire available in large quantity because of a new industrial process. The triggering of actuators made with this Cu-Al-Ni single crystal wire can range from ambient temperature to 200 C in cycling and even to 250 C in one-shot mode. Another advantage of CN-250X is a better shape recovery (8 to 10%) than Ni-Ti (6 to 7%). Nimesis is the first company able to produce this type of material with its new special industrial process. A characterization study is presented in this work, including the two main solicitation modes for this material: tensile and torsion. Different tests measure the shape recovery of Cu-Al-Ni single crystals wires during heating from room temperature to a temperature higher than temperature of end of martensitic transformation.

  1. Characterization of Sputtered Nickel-Titanium (NiTi) Stress and Thermally Actuated Cantilever Bimorphs Based on NiTi Shape Memory Alloy (SMA)

    DTIC Science & Technology

    2015-11-01

    Actuated Cantilever Bimorphs Based on NiTi Shape Memory Alloy (SMA) by Merric D Srour, Cory R Knick, and Christopher J Morris Sensors and...applications7 so a natural focus was to achieve large recovery stresses in films as thin as possible. By varying the sputtering parameters of NiTi...alloys. Sensors and Actuators A. 2002;99:55–58. 2. Ohta A, Bhansali S, Kishimoto I, Umeda A. Novel fabrication techique of TiNi shape memory alloy

  2. 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

  3. 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].

  4. Fabrication of porous NiTi shape memory alloy structures using laser engineered net shaping.

    PubMed

    Krishna, B Vamsi; Bose, Susmita; Bandyopadhyay, Amit

    2009-05-01

    Porous NiTi alloy samples were fabricated with 12-36% porosity from equiatomic NiTi alloy powder using laser engineered net shaping (LENS). The effects of processing parameters on density and properties of laser-processed NiTi alloy samples were investigated. It was found that the density increased rapidly with increasing the specific energy input up to 50 J/mm(3). Further increase in the energy input had small effect on density. High cooling rates associated with LENS processing resulted in higher amount of cubic B2 phase, and increased the reverse transformation temperatures of porous NiTi samples due to thermally induced stresses and defects. Transformation temperatures were found to be independent of pore volume, though higher pore volume in the samples decreased the maximum recoverable strain from 6% to 4%. Porous NiTi alloy samples with 12-36% porosity exhibited low Young's modulus between 2 and 18 GPa as well as high compressive strength and recoverable strain. Because of high open pore volume between 36% and 62% of total volume fraction porosity, these porous NiTi alloy samples can potentially accelerate the healing process and improve biological fixation when implanted in vivo. Thus porous NiTi is a promising biomaterial for hard tissue replacements.

  5. A macroscopic multi-mechanism based constitutive model for the thermo-mechanical cyclic degeneration of shape memory effect of NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Yu, Chao; Kang, Guozheng; Kan, Qianhua

    2017-01-01

    A macroscopic based multi-mechanism constitutive model is constructed in the framework of irreversible thermodynamics to describe the degeneration of shape memory effect occurring in the thermo-mechanical cyclic deformation of NiTi shape memory alloys (SMAs). Three phases, austenite A, twinned martensite Mt and detwinned martensite Md , as well as the phase transitions occurring between each pair of phases (A→ M t , Mt→ A , A→ M d , Md→ A , and Mt→ M d) are considered in the proposed model. Meanwhile, two kinds of inelastic deformation mechanisms, martensite transformation-induced plasticity and reorientation-induced plasticity, are used to explain the degeneration of shape memory effects of NiTi SMAs. The evolution equations of internal variables are proposed by attributing the degeneration of shape memory effect to the interaction between the three phases (A, Mt , and Md) and plastic deformation. Finally, the capability of the proposed model is verified by comparing the predictions with the experimental results of NiTi SMAs. It is shown that the degeneration of shape memory effect and its dependence on the loading level can be reasonably described by the proposed model.

  6. Investigation of the martensitic transformation of (Cu-Zn-Ni) shape memory alloys

    NASA Astrophysics Data System (ADS)

    Naat, N. A.; Mohammed, M. A.

    2017-02-01

    (Cu-Zn-Ni) shape memory alloy with different percent have been prepared by using high frequency induction furnace under argon atmosphere. All of the specimens obtained from this alloys were heated in furnace for (15 minutes at 865°C) for homogenization and quenched in iced-water. Comparisons has been made with data obtained via differential scanning calorimetry (DSC) and energy-dispersive X-ray spectroscopy (EDS). The metallographic analyses were carried out by using optical microscopy (OM).

  7. 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.

  8. Martensitic transformation and shape memory effect in ferromagnetic Heusler alloy Ni2FeGa

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Zhang, M.; Cui, Y. T.; Zhou, Y. Q.; Wang, W. H.; Wu, G. H.; Zhang, X. X.; Xiao, Gang

    2003-01-01

    We have synthesized ferromagnetic Heusler alloy Ni2FeGa using the melt-spinning technique. The Ni2FeGa ribbon, having a high chemical ordering L21 structure, exhibits a thermoelastic martensitic transformation from cubic to orthorhombic structure at 142 K and a premartensitic transformation. The alloy has a relatively high Curie temperature of 430 K, a magnetization of 73 Am2/kg, and a low saturated field of 0.6 T. The textured samples with preferentially oriented grains show a completely recoverable two-way shape memory effect with a strain of 0.3% upon the thermoelastic martensitic transformation.

  9. Characterization of Polylactide Layer Deposited on Ni-Ti Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Goryczka, Tomasz; Szaraniec, Barbara

    2014-07-01

    Polylactide (PLA) thin layer was deposited on the surface of the as-quenched NiTi shape memory alloy. First, NiTi alloy was quenched from the 850°C, then its surface was covered with PLA. Deposited PLA is in an amorphous state, whereas the as-quenched NiTi alloy stays in the B2 structure. PLA deposition caused smoothing of the surface and changed its hydrophilic character to hydrophobic one. In general, procedure of PLA deposition does not influence the course of the reversible martensitic transformation. After deformation of NiTi sample covered with PLA up to 4%, its surface does not reveal any cracks and still remains continuous.

  10. 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.

  11. Magnetic properties and electronic structure of Mn-Ni-Ga magnetic shape memory alloys.

    PubMed

    D'Souza, Sunil Wilfred; Roy, Tufan; Barman, Sudipta Roy; Chakrabarti, Aparna

    2014-12-17

    Influence of disorder, antisite defects, martensite transition and compositional variation on the magnetic properties and electronic structure of Mn(2)NiGa and Mn(1+x)Ni(2-x)Ga magnetic shape memory alloys have been studied by using full potential spin-polarized scalar relativistic Korringa-Kohn-Rostocker (FP-SPRKKR) method. Mn(2)NiGa is ferrimagnetic and its total spin moment increases when disorder in the occupancy of MnNi (Mn atom in Ni position) is considered. The moment further increases when Mn-Ga antisite defect [1] is included in the calculation. A reasonable estimate of TC for Mn(2)NiGa is obtained from the exchange parameters for the disordered structure. Disorder influences the electronic structure of Mn(2)NiGa through overall broadening of the density of states and a decrease in the exchange splitting. Inclusion of antisite defects marginally broaden the minority spin partial DOS (PDOS), while the majority spin PDOS is hardly affected. For Mn(1+x)Ni(2-x)Ga where 1 ⩾ x ⩾ 0, as x decreases, Mn(Mn) moment increases while Mn(Ni) moment decreases in both austenite and martensite phases. For x ⩾ 0.25, the total moment of the martensite phase is smaller compared to the austenite phase, which indicates possible occurrence of inverse magnetocaloric effect. We find that the redistribution of Ni 3d- Mn(Ni) 3d minority spin electron states close to the Fermi level is primarily responsible for the stability of the martensite phase in Mn-Ni-Ga.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. The response of macrophages to a Cu-Al-Ni shape memory alloy.

    PubMed

    Colić, Miodrag; Tomić, Sergej; Rudolf, Rebeka; Anzel, Ivan; Lojen, Gorazd

    2010-09-01

    Cu-Al-Ni shape memory alloys (SMAs) have been investigated as materials for medical devices, but little is known about their biocompatibility. The aim of this work was to study the response of rat peritoneal macrophages (PMØ) to a Cu-Al-Ni SMA in vitro, by measuring the functional activity of mitochondria, necrosis, apoptosis, and production of proinflammatory cytokines. Rapidly solidified (RS) thin ribbons were used for the tests. The control alloy was a permanent mold casting of the same composition, but without the shape memory effect. Our results showed that the control alloy was severely cytotoxic, whereas RS ribbons induced neither necrosis nor apoptosis of PMØ. These findings correlated with the data that RS ribbons are significantly more resistant to corrosion compared to the control alloy, as judged by the lesser release of Cu and Ni in the conditioning medium. However, the ribbons generated intracellular reactive oxygen species and upregulated the production of IL-6 by PMØ. These effects were almost completely abolished by conditioning the RS ribbons for 5 weeks. In conclusion, RS significantly improves the corrosion stability and biocompatibility of Cu-Al-Ni SMA. The biocompatibility of this functional material could be additionally enhanced by conditioning the ribbons in cell culture medium.

  17. Characterization of NiTi Shape Memory Damping Elements designed for Automotive Safety Systems

    NASA Astrophysics Data System (ADS)

    Strittmatter, Joachim; Clipa, Victor; Gheorghita, Viorel; Gümpel, Paul

    2014-07-01

    Actuator elements made of NiTi shape memory material are more and more known in industry because of their unique properties. Due to the martensitic phase change, they can revert to their original shape by heating when subjected to an appropriate treatment. This thermal shape memory effect (SME) can show a significant shape change combined with a considerable force. Therefore such elements can be used to solve many technical tasks in the field of actuating elements and mechatronics and will play an increasing role in the next years, especially within the automotive technology, energy management, power, and mechanical engineering as well as medical technology. Beside this thermal SME, these materials also show a mechanical SME, characterized by a superelastic plateau with reversible elongations in the range of 8%. This behavior is based on the building of stress-induced martensite of loaded austenite material at constant temperature and facilitates a lot of applications especially in the medical field. Both SMEs are attended by energy dissipation during the martensitic phase change. This paper describes the first results obtained on different actuator and superelastic NiTi wires concerning their use as damping elements in automotive safety systems. In a first step, the damping behavior of small NiTi wires up to 0.5 mm diameter was examined at testing speeds varying between 0.1 and 50 mm/s upon an adapted tensile testing machine. In order to realize higher testing speeds, a drop impact testing machine was designed, which allows testing speeds up to 4000 mm/s. After introducing this new type of testing machine, the first results of vertical-shock tests of superelastic and electrically activated actuator wires are presented. The characterization of these high dynamic phase change parameters represents the basis for new applications for shape memory damping elements, especially in automotive safety systems.

  18. Excess Ni-doping induced enhanced room temperature magneto-functionality in Ni-Mn-Sn based shape memory alloy

    SciTech Connect

    Pramanick, S.; Giri, S.; Majumdar, S.; Chatterjee, S.

    2014-09-15

    Present work reports on the observation of large magnetoresistance (∼−30% at 80 kOe) and magnetocaloric effect (∼12 J·kg{sup −1}·K{sup −1} for 0–50 kOe) near room temperature (∼290 K) on the Ni-excess ferromagnetic shape memory alloy Ni{sub 2.04}Mn{sub 1.4}Sn{sub 0.56}. The sample can be thought of being derived from the parent Ni{sub 2}Mn{sub 1.4}Sn{sub 0.6} alloy, where excess Ni was doped at the expense of Sn. Such Ni doping enhances the martensitic transition temperature and for the Ni{sub 2.04}Mn{sub 1.4}Sn{sub 0.56} it is found to be optimum (288 K). The doped alloy shows enhanced magneto-functional properties as well as reduced saturation magnetization as compared to the undoped counterpart at low temperature. A probable increment of antiferromagnetic correlation between Mn-atoms on Ni substitution can be accounted for the enhanced magneto-functional properties as well as reduction in saturation moment.

  19. Role of Si in Improving the Shape Recovery of FeMnSiCrNi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Maji, Bikas C.; Krishnan, Madangopal; Gouthama; Ray, R. K.

    2011-08-01

    The effect of Si addition on the microstructure and shape recovery of FeMnSiCrNi shape memory alloys has been studied. The microstructural observations revealed that in these alloys the microstructure remains single-phase austenite ( γ) up to 6 pct Si and, beyond that, becomes two-phase γ + δ ferrite. The Fe5Ni3Si2 type intermetallic phase starts appearing in the microstructure after 7 pct Si and makes these alloys brittle. Silicon addition does not affect the transformation temperature and mechanical properties of the γ phase until 6 pct, though the amount of shape recovery is observed to increase monotonically. Alloys having more than 6 pct Si show poor recovery due to the formation of δ-ferrite. The shape memory effect (SME) in these alloys is essentially due to the γ to stress-induced ɛ martensite transformation, and the extent of recovery is proportional to the amount of stress-induced ɛ martensite. Alloys containing less than 4 pct and more than 6 pct Si exhibit poor recovery due to the formation of stress-induced α' martensite through γ- ɛ- α' transformation and the large volume fraction of δ-ferrite, respectively. Silicon addition decreases the stacking fault energy (SFE) and the shear modulus of these alloys and results in easy nucleation of stress-induced ɛ martensite; consequently, the amount of shape recovery is enhanced. The amount of athermal ɛ martensite formed during cooling is also observed to decrease with the increase in Si.

  20. 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.

  1. 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.

  2. Martensitic and magnetic transformation in Mn50Ni50-xSnx ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ma, L.; Wang, S. Q.; Li, Y. Z.; Zhen, C. M.; Hou, D. L.; Wang, W. H.; Chen, J. L.; Wu, G. H.

    2012-10-01

    A martensitic transformation (MT) from a body-centered-cubic austenitic phase to a tetragonal martensitic phase has been found in Mn50Ni50-xSnx (0 ≤ x ≤ 11) alloys. The martensitic transformation temperature can be decreased by about 71.6 K by increasing the Sn concentration by 1 at. %. For 9 ≤ x ≤ 11, Mn50Ni50-xSnx ferromagnetic shape memory alloys are obtained. Due to the large magnetization difference (ΔM = 60 emu/g) and small thermal hysteresis (ΔT = 6 K) in the Mn50Ni40Sn10 alloy, a two-way magnetic-field-induced martensitic transformation is observed with dT/dH = 2 K/T.

  3. Effects of Ni content on the shape memory properties and microstructure of Ni-rich NiTi-20Hf alloys

    NASA Astrophysics Data System (ADS)

    Saghaian, S. M.; Karaca, H. E.; Tobe, H.; Pons, J.; Santamarta, R.; Chumlyakov, Y. I.; Noebe, R. D.

    2016-09-01

    Shape memory properties and microstructure of four Ni-rich NiTiHf alloys (Ni50.3Ti29.7Hf20, Ni50.7Ti29.3Hf20, Ni51.2Ti28.8Hf20, and Ni52Ti28Hf20 (at.%)) were systematically characterized in the furnace cooled condition. H-phase precipitates were formed during furnace cooling in compositions with greater than 50.3Ni and the driving force for nucleation increased with Ni content. Alloy strength increased while recoverable strain decreased with increasing Ni content due to changes in precipitate characteristics. When the precipitates were small (˜5-15 nm), they were readily absorbed by martensite plates, which resulted in maximum recoverable strain of 2% in Ni50.7Ti29.3Hf20. With increasing Ni content, the size (>100 nm) and volume fraction of precipitates increased and the growth of martensite plates was constrained between the precipitates when the Ni concentration was greater than 50.7 at.%. Near perfect dimensional stability with negligible irrecoverable strain was observed at stress levels as high as 2 GPa in the Ni52Ti28Hf20 alloy, though the recoverable strain was rather small. In general, strong local stress fields were created at precipitate/matrix interphases, which lead to high stored elastic energy during the martensitic transformation.

  4. 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.

  5. 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.

  6. Microscale Repeatability of the Shape-Memory Effect in Fine NiTi Wires

    NASA Astrophysics Data System (ADS)

    Gong, Joyce Yue; Daly, Samantha H.

    2016-12-01

    An experimental investigation into microscale transformation characteristics of polycrystalline NiTi wires of 500 µm diameter during shape memory cycling is discussed, with emphasis on the characterization of a pronounced heterogeneity in the strain distribution evident during detwinning of the martensite phase upon application of load and its persistence throughout the actuation cycle. Using scanning electron microscopy-digital image correlation, full-field strain maps at the microscale were obtained during shape memory cycling. It was found that the strains induced by detwinning were quite heterogeneous at the microscale, and could display a large degree of similarity with thermo-mechanical cycling that tended to increase as cycling progressed. Residual strain concentrated at locations where strain accumulation from detwinning and plasticity were significant, indicating that martensitic detwinning and the associated plasticity that occurs with it is spatially correlated to the subsequent accumulation of residual strain at the microscale.

  7. Structure Analysis of a Precipitate Phase in an Ni-Rich High Temperature NiTiHf Shape Memory Alloy

    SciTech Connect

    Yang, Fan; Coughlin, D. R.; Phillips, Patrick J.; Yang, L.; Devaraj, Arun; Kovarik, Libor; Noebe, Ronald D.; Mills, M. J.

    2013-03-22

    Thermal aging of the high temperature shape memory alloy 50.3Ni-29.7Ti-20Hf (at.%) introduces a novel precipitate phase, which plays an important role in improving shape memory properties. The precipitate phase was investigated by conventional electron diffraction, high resolution scanning transmission electron microscopy (STEM) and three dimensional atom probe tomography. An unrelaxed orthorhombic atomic structural model is proposed based on these observations. This model was subsequently relaxed by ab initio calculations. As a result of the relaxation, atom shuffle displacements occur, which in turn yields improved agreement with the STEM images. The relaxed structure, which is termed the “H-phase”, has also been verified to be thermodymanically stable at 0 K.

  8. 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.

  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. Microstructure, Phase Transformations, and Properties of Hot-Extruded Ni-Rich NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Lekston, Z.; Zubko, M.; Prusik, K.; Stróż, D.

    2014-07-01

    Processing of NiTi shape memory alloys strongly influences their microstructure, phase transformations, mechanical, and shape memory properties. Hot forging, hot swaging, or hot rolling are efficient techniques for obtaining the desired shape, but during multiple operations the material must be heated and worked in the temperature range from 700 to 900 °C. During these processes, intense oxidation takes place. In order to reduce it, the hot-pack working is applied. The hot extrusion is more effective for reduction of ingot, billet, and rod diameters than hot forging, hot swaging, or hot rolling. Also, during hot extrusion the material surface undergoes considerably less oxidation. In the present work, results of the characterization by differential scanning calorimetry, low-temperature x-ray powder diffraction, and three-point bending and free recovery ASTM F2082-06 tests of the samples after hot direct extrusion and heat treatment are presented. The obtained alloy after hot direct extrusion exhibits desired shape memory effect. The phase transformations during cooling and heating cycle occur with the presence of the R phase. The range of the characteristic temperatures for the obtained material gives possibility for further medical applications. After annealing at 400 and 500 °C, the characteristic temperatures shift to higher values.

  11. Relationship between microstructure, cytotoxicity and corrosion properties of a Cu-Al-Ni shape memory alloy.

    PubMed

    Colić, Miodrag; Rudolf, Rebeka; Stamenković, Dragoslav; Anzel, Ivan; Vucević, Dragana; Jenko, Monika; Lazić, Vojkan; Lojen, Gorazd

    2010-01-01

    Cu-Al-Ni shape memory alloys (SMAs) have been investigated as materials for medical devices, but their biomedical application is still limited. The aim of this work was to compare the microstructure, corrosion and cytotoxicity in vitro of a Cu-Al-Ni SMA. Rapidly solidified (RS) thin ribbons, manufactured via melt spinning, were used for the tests. The control alloy was a permanent mould casting of the same composition, but without shape memory effect. The results show that RS ribbons are significantly more resistant to corrosion compared with the control alloy, as judged by the lesser release of Cu and Ni into the conditioning medium. These results correlate with the finding that RS ribbons were not cytotoxic to L929 mouse fibroblasts and rat thymocytes. In addition, the RS ribbon conditioning medium inhibited cellular proliferation and IL-2 production by activated rat splenocytes to a much lesser extent. The inhibitory effects were almost completely abolished by conditioning the RS ribbons in culture medium for 4 weeks. Microstructural analysis showed that RS ribbons are martensitic, with boron particles as a minor phase. In contrast, the control Cu-Al-Ni alloy had a complex multiphase microstructure. Examination of the alloy surfaces after conditioning by energy dispersive X-ray and Auger electron spectroscopy showed the formation of Cu and Al oxide layers and confirmed that the metals in RS ribbons are less susceptible to oxidation and corrosion compared with the control alloy. In conclusion, these results suggest that rapid solidification significantly improves the corrosion stability and biocompatibility in vitro of Cu-Al-Ni SMA ribbons.

  12. Work production using the two-way shape memory effect in NiTi and a Ni-rich NiTiHf high-temperature shape memory alloy

    NASA Astrophysics Data System (ADS)

    Atli, K. C.; Karaman, I.; Noebe, R. D.; Bigelow, G.; Gaydosh, D.

    2015-12-01

    The work output capacity of the two-way shape memory effect (TWSME) in a Ni50.3Ti29.7Hf20 (at%) high-temperature shape memory alloy (HTSMA) was investigated and compared to that of binary Ni49.9Ti50.1 (at%). TWSME was induced through a training procedure of 100 thermomechanical cycles under different tensile stresses. It was observed that TWSME in as-extruded and trained Ni50.3Ti29.7Hf20 could produce 0.7% strain against a compressive stress of 100 MPa, corresponding to a maximum work output of 0.08 J g-1, compared to a maximum value of 0.06 J g-1 for binary NiTi. A peak aging heat treatment of 3 h at 550 °C, which previously has been shown to result in near-perfect functional stability in Ni50.3Ti29.7Hf20 during isobaric thermal cycling, did not improve the TWSME and actually resulted in a decrease in the magnitude and stability of the TWSME and its work output capacity. Nevertheless, the magnitude of TWSM behavior of Ni50.3Ti29.7Hf20, in the absence of an aging heat treatment, renders it an attractive candidate for high-temperature TWSM actuation.

  13. 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.

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

    DOE PAGES

    Barabash, Rozaliya I.; Barabash, Oleg M.; Popov, Dmitry; ...

    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.

  15. In Situ Neutron Diffraction Study of NiTi-21Pt High-Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Benafan, O.; Gaydosh, D. J.; Noebe, R. D.; Qiu, S.; Vaidyanathan, R.

    2016-12-01

    In situ neutron diffraction was used to investigate the microstructural features of stoichiometric and Ti-rich NiTiPt high-temperature shape memory alloys with target compositions of Ni29Ti50Pt21 and Ni28.5Ti50.5Pt21 (in atomic percent), respectively. The alloys' isothermal and thermomechanical properties (i.e., moduli, thermal expansion, transformation strains, and dimensional stability) were correlated to the lattice strains, volume-averaged elastic moduli, and textures as determined by neutron diffraction. In addition, the unique aspects of this technique when applied to martensitic transformations in shape memory alloys are highlighted throughout the paper.

  16. 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.

  17. Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane

    2012-01-01

    The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.

  18. Effect of cold rolling on fatigue crack propagation of TiNi/Al6061 shape memory composite

    NASA Astrophysics Data System (ADS)

    Park, Young Chul; Kang, Jung Ho; Lee, Jin Kyung; Lee, Gyu Chang; Furuya, Yasybumi

    2007-08-01

    A TiNi alloy fiber was used to recover the original shape of materials using its shape memory effect. The shape memory alloy plays an important role within the metal matrix composite. The shape memory alloy can control the crack propagation in the metal matrix composite, and improve the tensile strength of the composite. In this study, TiNi/Al6061 shape memory alloy (SMA) composite was fabricated by the hot press method, and pressed by a roller for its strength improvement. The four kinds of specimens were fabricated with 0%, 3.2%, 5.2% and 7% volume fraction of TiNi alloy fiber, respectively. A fatigue test has been performed to evaluate the crack initiation and propagation for the TiNi/Al6061 SMA composite fabricated by this method. In order to study the shape memory effect of the TiNi alloy fiber, the test has also been done under both room temperature and high temperature conditions. The relationship between the crack growth rate and the stress intensity factor was clarified for the composite, and the cold rolling effect was also studied.

  19. An experimental study of the two-way shape memory effect in a NiTi tubular actuator

    NASA Astrophysics Data System (ADS)

    Yoo, Young Ik; Lee, Jung Ju; Lee, Chang Ho; Lim, Jae Hyuk

    2010-12-01

    In this paper, the two-way shape memory effect (TWSME) in a Ti-54.5 Ni(wt%) alloy was investigated experimentally to develop a NiTi linear actuator. The two-way shape memory effect was induced through a compressive shape memory cycle comprising four steps: (1) loading to maximum deformation; (2) unloading (3) heating and (4) cooling. Six types of specimen (one solid cylindrical and five tubular) were used to obtain the two-way shape memory strain and two-way recovery stress and to evaluate the actuating capacity. The two-way actuating strain showed a saturated tendency after several training cycles for the same maximum deformation. A maximum value of the two-way strain was obtained for 7% of maximum deformation, independently of the geometry of the tubular specimens. The two-way strains obtained by the shape memory cycles and two-way recovery stress linearly increase as a function of the maximum deformation and the two-way strain, respectively, and the geometry of specimen affects the two-way recovery stress. Although the results show that sufficient recovery stress can be generated by either the two-way shape memory process or by the one-way shape memory process, the two-way shape memory process can be applied more conveniently to actuating applications.

  20. Optimizing Ni-Ti-based shape memory alloys for ferroic cooling

    NASA Astrophysics Data System (ADS)

    Wieczorek, A.; Frenzel, J.; Schmidt, M.; Maaß, B.; Seelecke, S.; Schütze, A.; Eggeler, G.

    Due to their large latent heats, pseudoelastic Ni-Ti-based shape memory alloys (SMAs) are attractive candidate materials for ferroic cooling, where elementary solid-state processes like martensitic transformations yield the required heat effects. The present work aims for a chemical and microstructural optimization of Ni-Ti for ferroic cooling. A large number of Ni-Ti-based alloy compositions were evaluated in terms of phase transformation temperatures, latent heats, mechanical hysteresis widths and functional stability. The aim was to identify material states with superior properties for ferroic cooling. Different material states were prepared by arc melting, various heat treatments and thermo-mechanical processing. The cooling performance of selected materials was assessed by differential scanning calorimetry, uniaxial tensile loading/unloading, and by using a specially designed ferroic cooling demonstrator setup. A Ni45Ti47.25Cu5V2.75 SMA was identified as a potential candidate material for ferroic cooling. This material combines extremely stable pseudoelasticity at room temperature and a very low hysteresis width. The ferroic cooling efficiency of this material is four times higher than in the case of binary Ni-Ti.

  1. 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.

  2. 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.

  3. High Strain Rate Compression of Martensitic NiTi Shape Memory Alloy at Different Temperatures

    NASA Astrophysics Data System (ADS)

    Qiu, Ying; Young, Marcus L.; Nie, Xu

    2017-02-01

    The compressive response of martensitic NiTi shape memory alloy (SMA) rods has been investigated using a modified Kolsky compression bar at various strain rates (400, 800, and 1200 s-1) and temperatures [room temperature and 373 K (100 °C)], i.e., in the martensitic state and in the austenitic state. SEM, DSC, and XRD were performed on NiTi SMA rod samples after high strain rate compression in order to reveal the influence of strain rate and temperature on the microstructural evolution, phase transformation, and crystal structure. It is found that at room temperature, the critical stress increases slightly as strain rate increases, whereas the strain-hardening rate decreases. However, the critical stress under high strain rate compression at 373 K (100 °C) increase first and then decrease due to competing strain hardening and thermal softening effects. After high rate compression, the microstructure of both martensitic and austenitic NiTi SMAs changes as a function of increasing strain rate, while the phase transformation after deformation is independent of the strain rate at room temperature and 373 K (100 °C). The preferred crystal plane of the martensitic NiTi SMA changes from ( 1bar{1}1 )M before compression to (111)M after compression, while the preferred plane remains the same for austenitic NiTi SMA before and after compression. Additionally, dynamic recovery and recrystallization are also observed to occur after deformation of the austenitic NiTi SMA at 373 K (100 °C). The findings presented here extend the basic understanding of the deformation behavior of NiTi SMAs and its relation to microstructure, phase transformation, and crystal structure, especially at high strain rates.

  4. Characterisation of melt spun Ni-Ti shape memory Ribbons' microstructure

    NASA Astrophysics Data System (ADS)

    Mehrabi, Kambiz; Brunčko, Mihael; Kneissl, Albert C.; Čolič, Miodrag; Stamenković, Dragoslav; Ferčec, Janko; Anžel, Ivan; Rudolf, Rebeka

    2012-06-01

    NiTi alloys are the most technologically important medical Shape Memory Alloys in a wide range of applications used in Orthopaedics, Neurology, Cardiology and interventional Radiology as guide-wires, self-expandable stents, stent grafts, inferior vena cava filters and clinical instruments. This paper discusses the use of rapid solidification by the melt spinning method for the preparation of thin NiTi ribbons for medical uses. Generally, the application of rapid solidification via melt-spinning can change the microstructure drastically, which improves ductility and shape memory characteristics and leads to samples with small dimensions. As the increase in the wheel speed led to a reduced ribbon thickness, the cooling rate increased and, therefore, the martensitic substructure became finer. Furthermore, no transition from the crystalline phase to the amorphous phase was obtained by increasing the cooling rate, even at a wheel speed of 30 m/s. Specimens for our metallographic investigation were cut from the longitudinal cross sections of melt-spun ribbons. Conventional TEM studies were carried out with an acceleration voltage of 120 kV. Additionally, the chemical composition of the samples was examined with a TEM equipped with an EDX analyser. The crystallographic structure was determined using Bragg-Brentano x-ray diffraction with Cu-Kα radiation at room temperature.

  5. 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.

  6. 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.

  7. 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.

  8. Polymer (PTFE) and shape memory alloy (NiTi) intercalated nano-biocomposites

    NASA Astrophysics Data System (ADS)

    Anjum, S. S.; Rao, J.; Nicholls, J. R.

    2012-09-01

    Engineering on a nano-scale has been undertaken to mimic a biomaterial by forming an intercalated nano-composite structure by PVD sputtering of a polymer with a nickel-titanium (NiTi) shape memory alloy (SMA). A PTFE polymer has been selected due to its elastic properties, low interactions with water, optimum surface energies, stability and chemical resistance. NiTi SMAs allow the coatings to be energy absorbent and thus suitable in load bearing situations. The coatings are aimed to constantly withstand variable adverse biological environments whilst maintaining their characteristics. The nano-intercalated structures have been characterised for their wettability, friction coefficients, chemical composition, and morphology. Intercalation of a polymer with energy-absorbing alloys uncovers a set of material systems that will offer characteristics such as self-healing of hierarchal tissue in the body. The reformation of PTFE following sputter deposition was confirmed by FTIR spectra. According to SEM analysis PTFE shows a promising surface interaction with NiTi, forming stable coatings. Surface interactions are evident by the hydrophobic behaviour of films as the composite's water contact angle is around 86° which lies in-between that of PTFE and NiTi. The nano composite films are lubricious and have a measured CoF below 0.2 which does not vary with layer thickness.

  9. 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.

  10. 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.

  11. Shape-memory transformations of NiTi: Minimum-energy pathways between austenite, martensites, and kinetically limited intermediate states

    DOE PAGES

    Zarkevich, N. A.; Johnson, D. D.

    2014-12-24

    NiTi is the most used shape-memory alloy, nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudge elastic band (GSSNEB) method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between body-centered orthorhombic (BCO) groundstate and a newly identified stable austenite (“glassy” B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited R-phase), and between martensite variants (BCO orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed, butmore » unstable B2. Furthermore, these high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.« less

  12. Shape-memory transformations of NiTi: Minimum-energy pathways between austenite, martensites, and kinetically limited intermediate states

    SciTech Connect

    Zarkevich, N. A.; Johnson, D. D.

    2014-12-24

    NiTi is the most used shape-memory alloy, nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudge elastic band (GSSNEB) method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between body-centered orthorhombic (BCO) groundstate and a newly identified stable austenite (“glassy” B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited R-phase), and between martensite variants (BCO orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed, but unstable B2. Furthermore, these high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.

  13. Shape-memory transformations of NiTi: minimum-energy pathways between austenite, martensites, and kinetically limited intermediate states.

    PubMed

    Zarkevich, N A; Johnson, D D

    2014-12-31

    NiTi is the most used shape-memory alloy; nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudged elastic band method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between a body-centered orthorhombic (bco) ground state and a newly identified stable austenite ("glassy" B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited R phase), and between martensite variants (bco orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed, but unstable B2. These high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.

  14. Recent breakthrough development of the magnetic shape memory effect in Ni Mn Ga alloys

    NASA Astrophysics Data System (ADS)

    Söderberg, O.; Ge, Y.; Sozinov, A.; Hannula, S.-P.; Lindroos, V. K.

    2005-10-01

    Magnetic shape memory (MSM) alloys or ferromagnetic shape memory alloy (FSMA) materials discovered by Ullakko et al (1996 Appl. Phys. Lett. 69 1966-8) have received increasing interest, since they can produce a large strain with rather high frequencies without a change in the external temperature. These materials have potential for actuator and sensor applications. MSM materials exhibit giant magnetic field induced strain (MFIS) based on the rearrangements of the crystallographic domains (twin variants). The magnetization energy of the material is lowered when such twin variants that have the easy axis of magnetization along the field start to grow due to twin boundary motion. Currently, the best working MSM materials are the near-stoichiometric Ni2MnGa Heusler alloys in which the properties are highly composition dependent. Their modulated martensitic structures, 5M and 7M, show 6% or 10% response respectively in a magnetic field less than 800 kA m-1. The MSM service temperature of the 5M alloys is between 150 and 333 K, and the optimal frequency region is up to 500 Hz. The fatigue life of the MSM elements has been shown to be at least 50 × 106 shape change cycles. This paper reviews the research work carried out at Helsinki University of Technology on MSM materials since 1998.

  15. Effect of Pre-straining on the Shape Recovery of Fe-Mn-Si-Cr-Ni Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Maji, Bikas C.; Krishnan, Madangopal; Verma, Amit; Basu, R.; Samajdar, I.; Ray, Ranjit K.

    2015-02-01

    The effect of pre-straining on the shape recovery behavior of Fe-14Mn-6Si-9Cr-5Ni (wt pct) shape memory alloy (SMA) has been studied. The shape recovery associated with the reverse ɛ martensitic transformation, i.e., ɛ → γ, was characterized by dilatometry using specimens which were pre-strained to different extent (0 to 14 pct). Dilatometric studies revealed that in Fe-Mn-Si-Cr-Ni SMA, the shape recovery takes place in two stages: (i) in the first stage, the unpinned fraction of stress-induced ɛ martensite reverts back to parent phase γ in the temperature regime of 353 K to 653 K (80 °C to 380 °C) and (ii) in the second stage the remaining "pinned" ɛ martensite is unpinned by the decomposition of deformation-induced α' martensite in the temperature range of 743 K to 893 K (470 °C to 620 °C). The amount of recovery in the first stage decreases with pre-strain, whereas it increases in the second stage. The ɛ → γ transformation finish temperature, A f, increases with increase in pre-strain amount, though the reverse transformation start temperature, A S, remains unaffected. Microstructural characterization revealed that the amount of deformation-induced α' martensite depends on the mode of straining and the crystallographic texture of the starting material. The reversion of α' martensite is seen to occur by the precipitation of Fe5Ni3Si2-type intermetallic π-phase within these plates.

  16. 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.

  17. 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.

  18. New system for manipulation of nanoobjects based on composite Ti2NiCu/Pt nanotweezers with shape memory effect

    NASA Astrophysics Data System (ADS)

    Zhikharev, A. M.; Irzhak, A. V.; Beresin, M. Y.; Lega, P. V.; Koledov, V. V.; Kasyanov, N. N.; Martynov, G. S.

    2016-08-01

    We report the new system for manipulation of nanoobjects based on composite Ti2NiCu/Pt nanotweezers with shape memory effect. The design consists of the bimetallic Ti2NiCu/Pt shape memory nanotweezers placed on a tip of electrochemically etched tungsten needle. The semiconductor diode placed on the tip of the needle plays both role of resistive element of the heater and temperature sensor for feedback control loop closing. The device is compatible with existing positioning systems like OmniProbe®, Kleindiek®, etc. and may find numerous practical applications in various tasks of nanotechnology connected with 3D manipulation.

  19. 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.

  20. 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.

  1. 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.

  2. Room temperature magnetocaloric effect in Ni-Mn-In-Cr ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Akkera, Harish Sharma; Singh, Inderdeep; Kaur, Davinder

    2017-02-01

    The influence of Cr substitution for In on the martensitic phase transformation and magnetocaloric effect (MCE) has been investigated in Ni-Mn-Cr-In ferromagnetic shape memory alloy (FSMA) thin films fabricated by magnetron sputtering. Temperature dependent magnetization (M-T) measurements demonstrated that the martensitic transformation temperatures (TM) monotonously increase with the increase of Cr content due to change in valence electron concentration (e/a) and cell volume. From the study of isothermal magnetization curves (M-H), magnetocaloric effect around the martensitic transformation has been investigated in these FSMA thin films. The magnetic entropy change ∆SM of 7.0 mJ/cm3-K was observed in Ni51.1Mn34.9In9.5Cr4.5 film at 302 K in an applied field of 2 T. Further, the refrigerant capacity (RC) was also calculated for all the films in an applied field of 2 T. These findings indicate that the Cr doped Ni-Mn-In FSMA thin films are potential candidates for room temperature micro-length-scale magnetic refrigeration applications.

  3. Dissimilar laser welding of NiTi shape memory alloy and copper

    NASA Astrophysics Data System (ADS)

    Zeng, Z.; Panton, B.; Oliveira, J. P.; Han, A.; Zhou, Y. N.

    2015-12-01

    This work is the first investigation of joining NiTi and copper. The successful Nd:YAG laser welding of NiTi to copper achieved in this work enables new methods of connecting shape memory alloys to electro-mechanical systems. Joints made with an optimum peak power of 2.2 kW accommodated pseudoelastic deformation of NiTi, proving their use with high strength actuators. Fracture occurred through the cross section of these defect-free joints. A lower peak power of 1.8 kW created weak joints with limited weld penetration of the copper sheet. This lack of bonding resulted in fracture occurring across the small disconnected joint areas. Joints made with a higher peak power of 2.6 kW had significant cracking in the fusion zone. Two regions of distinct Cu composition were found in the fusion zone, and cracking occurred at the interface between these regions because of their different physical properties. Failure initiated at this cracking and propagated through the fusion zone that had been embrittled by mixing with over 20 at.% Cu.

  4. 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.

  5. Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires

    NASA Astrophysics Data System (ADS)

    Carl, Matthew; Zhang, Baozhuo; Young, Marcus L.

    2016-09-01

    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.

  6. Mechanical and functional behavior of high-temperature Ni-Ti-Pt shape memory alloys

    DOE PAGES

    Buchheit, Thomas E.; Susan, Donald F.; Massad, Jordan E.; ...

    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

  7. Mechanical and functional behavior of high-temperature Ni-Ti-Pt shape memory alloys

    SciTech Connect

    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 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. 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.

  8. Laser and Surface Processes of NiTi Shape Memory Elements for Micro-actuation

    NASA Astrophysics Data System (ADS)

    Nespoli, Adelaide; Biffi, Carlo Alberto; Previtali, Barbara; Villa, Elena; Tuissi, Ausonio

    2014-04-01

    In the current microtechnology for actuation field, shape memory alloys (SMA) are considered one of the best candidates for the production of mini/micro devices thanks to their high power-to-weight ratio as function of the actuator weight and hence for their capability of generating high mechanical performance in very limited spaces. In the microscale the most suitable conformation of a SMA actuator is given by a planar wavy formed arrangement, i.e., the snake-like shape, which allows high strokes, considerable forces, and devices with very low sizes. This uncommon and complex geometry becomes more difficult to be realized when the actuator dimensions are scaled down to micrometric values. In this work, micro-snake-like actuators are laser machined using a nanosecond pulsed fiber laser, starting from a 120- μm-thick NiTi sheet. Chemical and electrochemical surface polishes are also investigated for the removal of the thermal damages of the laser process. Calorimetric and thermo-mechanical tests are accomplished to assess the NiTi microdevice performance after each step of the working process. It is shown that laser machining has to be followed by some post-processes in order to obtain a micro-actuator with good thermo-mechanical properties.

  9. Characterization of Stoichiometric and Aging Effects on NiTiHf High Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Coughlin, Daniel Robert

    NiTiHf ternary alloys exhibit attractive high temperature shape memory alloy (HTSMA) properties. Material properties include moderate transformation strain, relatively high transformation temperature, stable pseudoelastic (PE) behavior, and very small irrecoverable strain during load biased tests. The addition of Hf is more attractive than Pt and Pd due to the fact that Hf has a lower cost. Four NiTiHf alloys with different chemical compositions spanning stoichiometry were used to analyze microstructure and mechanical behavior. Research will mainly be focused on the Ni-rich alloys based on that the Ni-lean alloys do not exhibit the previously mentioned HTSMA material properties. The alloys analyzed all had 20(at.)% Hf with varying Ti concentrations (29(at.)%, 29.7(at.)%, 30(at.)%, and 30.5(at.)%). All of the alloys were formed by induction melting, homogenized at 1050C for 72hrs, and then hot extruded with a diameter reduction of 7:1 at a temperature of 900C. In addition to the homogenized and extruded condition, several short-term aging cycles above 400C were completed on each of the alloys. Certain microstructure and mechanical properties are obtained when Hf is added to NiTi and a proper aging cycle is used. Results from isothermal compression tests that were executed above the austenite finish temperature determined that the Ni-rich NiTiHf alloys exhibited all the necessary properties to be considered for HTSMA applications. The test temperature range of the isothermal compression tests were chosen to characterize the transition from PE behavior to austenite plasticity and to examine the deformation behavior of the B2 phase at high temperatures. Results from compression tests showed a strengthening effect when the test temperature was increased through the PE test region. The strengthening effect is due to the yield stress and plasticity being related to the stress induced martensite that is created during the compression test executed above the austenite

  10. 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.

  11. First-principles prediction of shape memory behavior and ferrimagnetism in Mn2NiSn.

    PubMed

    Paul, Souvik; Ghosh, Subhradip

    2011-05-25

    Using first-principles density functional theory, we show that, in Mn(2)NiSn, an energy lowering phase transition from the cubic to tetragonal phase occurs which indicates a martensitic phase transition. This structural phase transition is nearly volume-conserving, implying that this alloy can exhibit shape memory behavior. The magnetic ground state is a ferrimagnetic one with antiparallel Mn spin moments. The calculated moments with different electronic structure methods in the cubic phase compare well with each other but differ from the experimental values by more than 1 μ(B). The reason behind this discrepancy is explored by considering antisite disorder in our calculations, which indicates that the site ordering in this alloy can be quite complex.

  12. Elastocaloric and magnetocaloric effects in Ni-Mn-Sn(Cu) shape-memory alloy

    NASA Astrophysics Data System (ADS)

    Castillo-Villa, Pedro O.; Mañosa, Lluís; Planes, Antoni; Soto-Parra, Daniel E.; Sánchez-Llamazares, J. L.; Flores-Zúñiga, H.; Frontera, Carlos

    2013-02-01

    We have studied magnetocaloric and elastocaloric properties of a Ni-Mn-Sn(Cu) metamagnetic shape-memory alloy undergoing a magneto-structural transition (martensitic type) close to room temperature. Changes of entropy have been induced by isothermally applying both mechanical (uniaxial stress) and magnetic fields. These entropy changes have been, respectively, estimated from dilatometric measurements giving the length of the sample as a function of temperature at selected applied forces and magnetic fields and from magnetization measurements as a function of temperature at selected applied magnetic fields. Our results indicate that the elastocaloric effect is conventional and occurs in two steps which reflect the interplay between the martensitic and the incipient magnetic transitions. By contrast, the magnetocaloric effect is inverse and occurs in a single step that encompasses the effect arising from both transitions.

  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. Avalanches in compressed Ti-Ni shape-memory porous alloys: An acoustic emission study

    NASA Astrophysics Data System (ADS)

    Soto-Parra, Daniel; Zhang, Xiaoxin; Cao, Shanshan; Vives, Eduard; Salje, Ekhard K. H.; Planes, Antoni

    2015-06-01

    Mechanical avalanches during compression of martensitic porous Ti-Ni have been characterized by high-frequency acoustic emission (AE). Two sequences of AE signals were found in the same sample. The first sequence is mainly generated by detwinning at the early stages of compression while fracture dominates the later stages. Fracture also determines the catastrophic failure (big crash). For high-porosity samples, the AE energies of both sequences display power-law distributions with exponents ɛ ≃2 (twinning) and 1.7 (fracture). The two power laws confirm that twinning and fracture both lead to avalanche criticality during compression. As twinning precedes fracture, the observation of twinning allows us to predict incipient fracture of the porous shape memory material as an early warning sign (i.e., in bone implants) before the fracture collapse actually happens.

  15. Avalanches in compressed Ti-Ni shape-memory porous alloys: An acoustic emission study.

    PubMed

    Soto-Parra, Daniel; Zhang, Xiaoxin; Cao, Shanshan; Vives, Eduard; Salje, Ekhard K H; Planes, Antoni

    2015-06-01

    Mechanical avalanches during compression of martensitic porous Ti-Ni have been characterized by high-frequency acoustic emission (AE). Two sequences of AE signals were found in the same sample. The first sequence is mainly generated by detwinning at the early stages of compression while fracture dominates the later stages. Fracture also determines the catastrophic failure (big crash). For high-porosity samples, the AE energies of both sequences display power-law distributions with exponents ɛ≃2 (twinning) and 1.7 (fracture). The two power laws confirm that twinning and fracture both lead to avalanche criticality during compression. As twinning precedes fracture, the observation of twinning allows us to predict incipient fracture of the porous shape memory material as an early warning sign (i.e., in bone implants) before the fracture collapse actually happens.

  16. 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.

  17. Neutron diffraction studies of magnetic-shape memory Ni-Mn-Ga single crystal

    NASA Astrophysics Data System (ADS)

    Heczko, Oleg; Prokes, Karel; Hannula, Simo-Pekka

    2007-09-01

    Neutron diffraction of single crystal of the typical example of magnetic-shape memory (MSM) alloy Ni 49.7Mn 29.3Ga 21 was carried out with a 2D position sensitive detector. The quality and inhomogeneity of the single crystal and martensite variant distribution was studied using ω-scan of selected nuclear Bragg reflections. The neutron diffraction reveals split of the (2 0 0) reflection of major martensite variant and large structural inhomogeneities in martensite phase. Using measurement in reciprocal space, we recorded a set of reflections that appear due to structural modulation (5 M) of the martensite, however, the set seems to be incomplete with missing or very weak reflections of second order compared with X-ray diffraction. The line of the magnetic reflection arising from the supposed antiferromagnetic ordering of the excess Mn atoms was very weak and it is difficult to discern from the background.

  18. [Study of blood compatibility on TiO2 coated biomedical Ni-Ti shape memory alloy].

    PubMed

    Gao, Shuchun; Zhai, Yuchun; Hu, Jinling

    2011-10-01

    We coated a thin TiO2 film on the surface of Ni-Ti shape memory alloy by activated sputter method in the present work. The blood platelet adherence and antithrombogenicity of the TiO2-coated Ni-Ti alloy were evaluated. The results showed that the platelets on the TiO2-coated Ni-Ti alloy were fewer than those on 316L stainless steel, and no agglomeration or distortion for the platelets on the coated alloy was found, which means less probability of blood coagulation for the alloy. The coagulation time on the coated Ni-Ti shape memory alloy was longer than that on the 316L. Compared with that on the 316L stainless steel, the TiO2 coated Ni-Ti shape memory alloy showed better blood compatibility, indicating that the Ni-Ti alloy with TiO2 coating is a kind of ideal biomedical materials with high clinical value.

  19. Comparative study on microstructure and martensitic transformation of aged Ni-rich NiTi and NiTiCo shape memory alloys

    NASA Astrophysics Data System (ADS)

    El-Bagoury, Nader

    2016-05-01

    In this article the influence of aging heat treatment conditions of 250, 350, 450 and 550 °C for 3 h on the microstructure, martensitic transformation temperatures and mechanical properties of Ni51Ti49Co0 and Ni47 Ti49Co4 shape memory alloys was investigated. This comparative study was carried out using X-ray diffraction analysis, scanning electron microscope, energy dispersive spectrometer, differential scanning calorimeter and Vickers hardness tester. The results show that the microstructure of both aged alloys contains martensite phase and Ti2Ni in addition to some other precipitates. The martensitic transformation temperature was increased steadily by increasing the ageing temperature and lowering the value of valence electron number (ev/a) and concentration. Moreover, the hardness measurements were gradually increased at first by increasing the aging temperature from 250 to 350 °C. Further elevating in aging temperature to 450 and 550 °C decreases the hardness value.

  20. Structure and properties of Ti-Ni-Au shape memory alloys

    NASA Astrophysics Data System (ADS)

    Butler, Todd

    Ternary Ti-Ni-X based alloys, where X = Pt, Pd, Hf, Au or Zr, show promise as high temperature shape memory alloys (HTSMAs). In comparison to binary Ni-Ti alloys, some hypo-stoichiometric versions of these ternary compositions exhibit higher transformation temperatures and better mechanical stability due to the formation of nano-scale precipitates. In this study, a Ti 49Ni26Au25 (at.%) alloy was solution annealed at 1050°C for 3 hours and isothermally aged at 400°C and 550°C. A specimen was also annealed at 1050°C for 3 hours and furnace cooled. Ageing resulted in a very high peak micro-hardness for both temperatures. The structures and chemistries of the phases formed during ageing were characterized by wavelength dispersive x-ray spectroscopy (WDS), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), transmission electron microscopy (TEM), three-dimensional atom probe tomography (3DAP), x-ray diffraction (XRD), and differential scanning calorimetry (DSC). It was found that ageing at both 400°C and 550°C resulted in the formation of two different precipitates. First, two variants of a (Au,Ni)4Ti3 type phase form with SADPs similar to tetragonal D1a. The proposed orientation relationships with the matrix are the following: [001]D1a || [100] B2 with (011)B2 // (310)D1a and [001¯ ]D1a || [100]B2 with {011}B2 || (310) D1a. It is then postulated that the (Au,Ni)-rich phase creates local Ti-rich regions that promote the precipitation of two Ti2(Ni,Au) variants with tetragonal (I4/mmm) type symmetry. Their proposed orientation relationships with the matrix are the following: [100]Ti2(Ni,Au) || [100]B2 with (001)B2 || (001)Ti2(Ni.Au) and (001)B2 || (100)Ti2(Ni,Au). The combination of both phases appears to inhibit martensitic transformation by stabilizing the high temperature austenite phase, as evident by no transformation peaks in the aged specimens via DSC. However, it is interesting to note that the as-cast and 1050°C furnace cooled

  1. 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.

  2. 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.

  3. Mechanical and Microstructural Characterization of Porous NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Scalzo, O.; Turenne, S.; Gauthier, M.; Brailovski, V.

    2009-09-01

    This article presents the mechanical behavior of porous NiTi in the context of biomedical applications related to bone prostheses. To produce the porous metallic material, a novel technique consisting of mixing prealloyed NiTi powder with a polymer powder and a foaming agent has been used. This method permits control of the size of pores and the porosity level. For the present study, pores similar to those found in bones (400 to 500 μm) were obtained with a total porosity of the specimens varying from 50 to 70 pct. The compression mechanical testing carried out on small cylindrical specimens revealed shape memory deformation recovery up to 6.4 pct, while the superelastic behavior resulted in a reversible deformation up to 7.7 pct. By varying the amount of porosity, it was possible to obtain Young’s moduli in the range of 2.6 to 4.6 GPa, which is similar to the modulus of cancellous (spongy) human bone.

  4. Pulsed field actuation of Ni-Mn-Ga ferromagnetic shape memory alloy single crystal

    NASA Astrophysics Data System (ADS)

    Marioni, M.; Bono, D.; Banful, A. B.; del Rosario, M.; Rodriguez, E.; Peterson, B. W.; Allen, S. M.; O'Handley, R. C.

    2003-10-01

    Ferromagnetic Shape Memory Alloy Ni-Mn-Ga has twin boundaries in the martensitic phase that move when a suitable magnetic field is applied. In this fashion strains of up to 6% have been observed for static fields in single crystals [1]. Recently 2.5% strain has been demonstrated [2] in Ni-Mn-Ga single crystals for oscillating fields up to frequencies of 75 Hz (150 Hz actuation). This work studies the actuation of single crystals when pulsed fields are applied. Fields in the 0.4-1.5MA/m-range were generated in an air coil with rise times of the order of 1ms and below. The elongation of the samples is measured with a light beam reflected off the tip of the crystal. Single twin boundaries have been observed to advance 0.16 mm during 600 μsec-ong pulses. Actuation has been shown to be possible at least up to frequencies of 1700 Hz.

  5. Magnetic glass in shape memory alloy: Ni45Co5Mn38Sn12.

    PubMed

    Lakhani, Archana; Banerjee, A; Chaddah, P; Chen, X; Ramanujan, R V

    2012-09-26

    The first order martensitic transition in the ferromagnetic shape memory alloy Ni(45)Co(5)Mn(38)Sn(12) is also a magnetic transition and has a large field induced effect. While cooling in the presence of a field this first order magnetic martensite transition is kinetically arrested. Depending on the cooling field, a fraction of the arrested ferromagnetic austenite phase persists down to the lowest temperature as a magnetic glassy state, similar to the one observed in various intermetallic alloys and in half doped manganites. A detailed investigation of this first order ferromagnetic austenite (FM-A) to low magnetization martensite (LM-M) state transition as a function of temperature and field has been carried out by magnetization measurements. Extensive cooling and heating in unequal field (CHUF) measurements and a novel field cooled protocol for isothermal MH measurements (FC-MH) are utilized to investigate the glass like arrested states and show a reverse martensite transition. Finally, we determine a field-temperature (HT) phase diagram of Ni(45)Co(5)Mn(38)Sn(12) from various magnetization measurements which brings out the regions where thermodynamic and metastable states coexist in the HT space, clearly depicting this system as a 'magnetic glass'.

  6. 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.

  7. Mechanical and shape memory properties of porous Ni50.1Ti49.9 alloys manufactured by selective laser melting.

    PubMed

    Taheri Andani, Mohsen; Saedi, Soheil; Turabi, Ali Sadi; Karamooz, M R; Haberland, Christoph; Karaca, Haluk Ersin; Elahinia, Mohammad

    2017-04-01

    Near equiatomic NiTi shape memory alloys were fabricated in dense and designed porous forms by Selective Laser Melting (SLM) and their mechanical and shape memory properties were systematically characterized. Particularly, the effects of pore morphology on their mechanical responses were investigated. Dense and porous NiTi alloys exhibited good shape memory effect with a recoverable strain of about 5% and functional stability after eight cycles of compression. The stiffness and residual plastic strain of porous NiTi were found to depend highly on the pore shape and the level of porosity. Since porous NiTi structures have lower elastic modulus and density than dense NiTi with still good shape memory properties, they are promising materials for lightweight structures, energy absorbers, and biomedical implants.

  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. Deformation induced martensite in NiTi and its shape memory effects generated by low temperature laser shock peening

    NASA Astrophysics Data System (ADS)

    Liao, Yiliang; Ye, Chang; Lin, Dong; Suslov, Sergey; Cheng, Gary J.

    2012-08-01

    In this study, laser shock peening (LSP) was utilized to generate localized deformation induced martensite (DIM) in NiTi shape memory alloy. The DIM was investigated by x-ray diffraction and transmission electron microscopy. The effects of temperature and laser intensity on DIM transformation were investigated. It has been found that higher laser intensity and lower processing temperature leads to higher volume fraction of DIM. This is attributed to the increase of the chemical driving force and the increase in the density of potential martensite variant for martensite nucleation at low temperatures. The localized shape memory effect in micrometer scale after low temperature LSP has been evaluated.

  10. Stress-induced martensite variant reorientation in magnetic shape memory Ni Mn Ga single crystal studied by neutron diffraction

    NASA Astrophysics Data System (ADS)

    Molnar, P.; Sittner, P.; Lukas, P.; Hannula, S.-P.; Heczko, O.

    2008-06-01

    Stress-induced martensite variant reorientation in magnetic shape memory Ni-Mn-Ga single crystal was studied in situ by the neutron diffraction technique. Principles of determination of individual tetragonal martensitic variants in shape memory alloys are explained. Using neutron diffraction we show that the macroscopic strain originates solely from the martensite structure reorientation or variant redistribution. Neutron diffraction also reveals that the reorientation of martensite is not fully completed even at a stress value of 25 MPa, which is about 20 times larger than the mean stress needed for reorientation. Only one twinning system is active during the reorientation process.

  11. Metamagnetic shape memory effect in a Heusler-type Ni43Co7Mn39Sn11 polycrystalline alloy

    NASA Astrophysics Data System (ADS)

    Kainuma, R.; Imano, Y.; Ito, W.; Morito, H.; Sutou, Y.; Oikawa, K.; Fujita, A.; Ishida, K.; Okamoto, S.; Kitakami, O.; Kanomata, T.

    2006-05-01

    Shape memory and magnetic properties of a Ni43Co7Mn39Sn11 Heusler polycrystalline alloy were investigated by differential scanning calorimetry, the sample extraction method, and the three-terminal capacitance method. A unique martensitic transformation from the ferromagnetic parent phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced "reverse" transition was confirmed in a high magnetic field. In addition, a large magnetic-field-induced shape recovery strain of about 1.0% was observed to accompany reverse martensitic transformation, and the metamagnetic shape memory effect, which was firstly reported in a Ni45Co5Mn36.7In13.3 Heusler single crystal, was confirmed in a polycrystalline specimen.

  12. Prediction of precipitate evolution and martensite transformation in Ti-Ni-Cu shape memory alloys by computational thermodynamics

    NASA Astrophysics Data System (ADS)

    Povoden-Karadeniz, A.; Cirstea, D. C.; Kozeschnik, E.

    2016-04-01

    Ti-50Ni to Ti-55Ni (at.%) can be termed as the pioneer of shape memory alloys (SMA). Intermetallic precipitates play an important role for strengthening. Their influence on the start temperature of the martensitic transformation is a crucial property for the shape memory effect. Efforts for increasing the martensite start temperature include replacement of a part of Ni atoms by Cu. The influence of Cu-addition to Ti-Ni SMA on T0- temperatures and the character of the austenite-martensite transformation is evaluated using a new thermodynamic database for the Ti-Ni-system extended by Cu. Trends of precipitation of intermetallic phases are simulated by combining the assessed thermodynamics of the Ti-Ni-Cu system with assessed diffusion mobility data and kinetic models, as implemented in the solid-state transformation software MatCalc and are presented in the form of time-temperature-precipitation diagrams. Thermodynamic equilibrium considerations, complemented by predictive thermo-kinetic precipitation simulation, facilitates SMA alloy design and definition of optimized aging conditions.

  13. A novel active fire protection approach for structural steel members using NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Sadiq, H.; Wong, M. B.; Al-Mahaidi, R.; Zhao, X. L.

    2013-02-01

    A novel active fire protection approach, based on integrating a shape memory alloy, NiTi, with a steel structure, was proposed to satisfy the fire resistance requirements in structural design. To demonstrate the principles of this approach, a simple structure in the form of a simply supported steel beam was used. The internal action of the beam due to a transverse applied load was reduced by utilizing the shape memory effect in the NiTi alloy at rising temperatures. As a result, the net internal action from the load design was kept below the deteriorated load capacity of the beam during the fire scenario for period of time that was longer than that of the original beam without the NiTi alloy. By integrating the NiTi alloy into the beam system, the structure remained stable even though the steel temperature exceeded the critical temperature which may have caused the original beam structure to collapse. Prior to testing the composite NiTi-steel beam under simulated fire conditions, the NiTi alloy specimens were characterized at high temperatures. At 300 °C, the stiffness of the specimens increased by three times and its strength by four times over that at room temperature. The results obtained from the high-temperature characterization highlighted the great potential of the alloy being used in fire engineering applications.

  14. Damping characteristics of R-phase NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Wu, Kuang-Hsi; Dalip, S. K.; Liu, Y. Q.; Pu, Zhongjie J.

    1995-05-01

    This paper focuses on the study of damping behavior associated with the R-phase in NiTi shape memory alloy. The variation of the tan((delta) ) and Young's modulus as a function of temperature, ramp rate, frequency, and applied amplitude are systematically studied using a dynamic mechanical analyzer (DMA). It was found that the tan((delta) ) versus the temperature curve exhibits four peaks during the thermal cycle, two peaks each in the heating and in the cooling process. These peaks correspond to the martensite to R-phase, R-phase to austenite, austenite to R-phase, and R-phase to martensite transformations. The value of the tan((delta) ) at each peak is in proportion to the ramp rate and in reverse proportion to frequency. The vibration amplitude tends to have a minor effect on the tan((delta) ). The variation of these peaks with ramp rate, frequency, and amplitude are discussed based on the Delorme and De Jonghe damping model. In addition, the experimental results show that an isotropic softening occurs in the Young's modulus during martensite to R-phase, R-phase to austenite, austenite to R-phase, and R-phase to martensite transformations.

  15. 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.

  16. Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2016-01-18

    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.

  17. Production of Ni100-x-yMnxGay magnetic shape memory alloys by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Hatchard, T. D.; Thorne, J. S.; Farrell, S. P.; Dunlap, R. A.

    2008-11-01

    Powdered samples of a variety of compositions of the off-stoichiometric magnetic shape memory alloy Ni2MnGa have been prepared by mechanical alloying from elemental precursors. As-milled powders are highly disordered and show very weak ferromagnetic order. Annealing produces a well-ordered L21 Heusler phase with high saturation magnetization. Annealing results in a consistent loss of Ga of about 1-4 at.% (of total sample composition). Structural and magnetic properties of a range of compositions have been measured and are reported in the present work. A magnetically oriented metal-polymer composite has been prepared by mixing the powdered sample in epoxy and curing under an externally applied magnetic field. The magnetic anisotropy energy of the composite sample has been measured and found to be about 20% of the value expected for a single crystal of similar composition. Possibilities for increasing the magnetic anisotropy of metal-polymer composites are discussed. Results are discussed in terms of the effects of structural and chemical order on the resulting magnetic properties in the context of a model based on indirect exchange interactions.

  18. 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.

  19. Treatment of Clavicular Nonunions with Shape Memory Ni-Ti Alloy Swan-Like Bone Connector

    NASA Astrophysics Data System (ADS)

    Liu, Xin-Wei; Xu, Shuo-Gui; Wang, Pan-Feng; Zhang, Chun-Cai

    2011-07-01

    Disability caused by nonunited fracture of the clavicle is a rare condition that is expressed by local pain. This condition is usually treated by reduction of the fracture and stable fixation with augmentation by autogenous bone graft. This is a retrospective study to assess outcome of the treatment of clavicular nonunion with a novel shape memory Ni-Ti alloy swan-like bone connector (SMC). August, 2003 to December, 2006, 5 consecutive patients with clavicular nonunion were treated using SMC in our hospital. The SMC device was cooled with ice before implantation and then warmed to 40-50 °C after implantation, to produce balanced axial and compression forces that would stabilize the fracture. We have used cancellous bone grafting in all our cases to obtain solid healing. Average follow-up was 37 months (range 25-58). In all patients, satisfactory osseous union was achieved. There was no complication from the hardware. The average Constant score which is for evaluating function of injured shoulder after operation was 86 points (average Constant score for the unaffected shoulder was 95). All patients were very satisfied with the treatment and outcome. The SMC provides a new effective method for fracture fixation and treatment of bone nonunion for clavicle.

  20. Composition-structure-function diagrams of Ti-Ni-Au thin film shape memory alloys.

    PubMed

    Buenconsejo, Pio John S; Ludwig, Alfred

    2014-12-08

    Ti-Ni-Au thin film materials libraries were prepared from multilayer precursors by combinatorial sputtering. The materials libraries were annealed at 500, 600, and 700 °C for 1 h and then characterized by high-throughput methods to investigate the relations between composition, structure and functional properties. The identified relations were visualized in functional phase diagrams. The goal is to identify composition regions that are suitable as high temperature shape memory alloys. Phase transforming compositions were identified by electrical resistance measured during thermal cycles in the range of -20 and 250 °C. Three phase transformation paths were confirmed: (1) B2-R, (2) B2-R-B19', and (3) B2-B19. For the materials library annealed at 500 °C only the B2-R transformation was observed. For the materials libraries annealed at 600 and 700 °C, all transformation paths were observed. High transformation temperatures (M(s) ≈ 100 °C) were only obtained by annealing at 600 or 700 °C, and with compositions of Ti ≈ 50 at. % and Au > 20 at. %. This is the composition range that undergoes B2-B19 transformation. The phase transformation behaviors were explained according to the compositional and annealing temperature dependence of phase/structure formation, as revealed by X-ray diffraction analysis of the materials libraries.

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

    Ćakιr, Aslι; Righi, Lara; Albertini, Franca; Acet, Mehmet; Farle, Michael; Aktürk, Selçuk

    2013-11-01

    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 Ni50Mn50-xGax 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→L10, 5M →7M, and 5M→7M→L10 with decreasing temperature. The L10 non-modulated structure is most stable at low temperature.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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 Ni50.0Mn28.5Ga21.5 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.

  5. Long-term superelastic cycling at nano-scale in Cu-Al-Ni shape memory alloy micropillars

    SciTech Connect

    San Juan, J. Gómez-Cortés, J. F.

    2014-01-06

    Superelastic behavior at nano-scale has been studied along cycling in Cu-Al-Ni shape memory alloy micropillars. Arrays of square micropillars were produced by focused ion beam milling, on slides of [001] oriented Cu-Al-Ni single crystals. Superelastic behavior of micropillars, due to the stress-induced martensitic transformation, has been studied by nano-compression tests during thousand cycles, and its evolution has been followed along cycling. Each pillar has undergone more than thousand cycles without any detrimental evolution. Moreover, we demonstrate that after thousand cycles they exhibit a perfectly reproducible and completely recoverable superelastic behavior.

  6. Fabrication and static characterization of carbon-fiber-reinforced polymers with embedded NiTi shape memory wire actuators

    NASA Astrophysics Data System (ADS)

    de Araújo, C. J.; Rodrigues, L. F. A.; Coutinho Neto, J. F.; Reis, R. P. B.

    2008-12-01

    In this work, unidirectional carbon-fiber-reinforced polymers (CFRP) with embedded NiTi shape memory alloy (SMA) wire actuators were manufactured using a universal testing machine equipped with a thermally controlled chamber. Beam specimens containing cold-worked, annealed and trained NiTi SMA wires distributed along their neutral plane were fabricated. Several tests in a three-point bending mode at different constant temperatures were performed. To verify thermal buckling effects, electrical activation of the specimens was realized in a cantilevered beam mode and the influence of the SMA wire actuators on the tip deflection of the composite is demonstrated.

  7. Laser welding of NiTi shape memory alloy wires and tubes for multi-functional design applications

    NASA Astrophysics Data System (ADS)

    Zeng, Zhi; Yang, Mao; Oliveira, João Pedro; Song, Di; Peng, Bei

    2016-08-01

    Welding and joining of NiTi shape memory alloys is essential for their integration into an increasing variety of applications. Almost all manufacturers and a significant number of researchers focus their investigation on welding NiTi, which can present both pseudoelasticity (PE) and shape memory effect. Integration of these materials would provide increased flexibility in terms of smart design, in particular for multi-functional systems. The current work investigates the mechanical, physical and phase transformation properties of similar (base materials (BMs) with the same composition) and dissimilar (BMs with different compositions) NiTi welded shape memory wires. The similar and dissimilar welded joints were successfully achieved by laser welding, which can reach up to 88.4% and 67.5% of the wire BM ductility. The joint break force of the similar and dissimilar joints were of 77.2% and 71.4% of the wire BM, respectively. Moreover, laser welding was found to effectively preserve the PE on the similar welded structures. The residual plastic strain variation of the dissimilar welded specimens at different temperatures during the cycling test may be helpful for design of multi-functional or flexible monolithic structures.

  8. 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.

  9. 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).

  10. Nature of hardness evolution in nanocrystalline NiTi shape memory alloys during solid-state phase transition.

    PubMed

    Amini, Abbas; Cheng, Chun

    2013-01-01

    Due to a distinct nature of thermomechanical smart materials' reaction to applied loads, a revolutionary approach is needed to measure the hardness and to understand its size effect for pseudoelastic NiTi shape memory alloys (SMAs) during the solid-state phase transition. Spherical hardness is increased with depths during the phase transition in NiTi SMAs. This behaviour is contrary to the decrease in the hardness of NiTi SMAs with depths using sharp tips and the depth-insensitive hardness of traditional metallic alloys using spherical tips. In contrast with the common dislocation theory for the hardness measurement, the nature of NiTi SMAs' hardness is explained by the balance between the interface and the bulk energy of phase transformed SMAs. Contrary to the energy balance in the indentation zone using sharp tips, the interface energy was numerically shown to be less dominant than the bulk energy of the phase transition zone using spherical tips.

  11. Magnetron sputtered Cu3N/NiTiCu shape memory thin film heterostructures for MEMS applications

    NASA Astrophysics Data System (ADS)

    Kaur, Navjot; Choudhary, Nitin; Goyal, Rajendra N.; Viladkar, S.; Matai, I.; Gopinath, P.; Chockalingam, S.; Kaur, Davinder

    2013-03-01

    In the present study, for the first time, Cu3N/NiTiCu/Si heterostructures were successfully grown using magnetron sputtering technique. Nanocrystalline copper nitride (Cu3N with thickness 200 nm) thin films and copper nanodots were subsequently deposited on the surface of 2-μm-thick NiTiCu shape memory thin films in order to improve the surface corrosion and nickel release properties of NiTiCu thin films. Interestingly, the phase transformation from martensite phase to austenite phase has been observed in Cu3N/NiTiCu heterostructures with corresponding change in texture and surface morphology of top Cu3N films. Field emission scanning electron microscopy and atomic force microscope images of the heterostructures reveals the formation of 20-nm-sized copper nanodots on NiTiCu surface at higher deposition temperature (450 °C) of Cu3N. Cu3N passivated NiTiCu films possess low corrosion current density with higher corrosion potential and, therefore, better corrosion resistance as compared to pure NiTiCu films. The concentration of Ni released from the Cu3N/NiTiCu samples was observed to be much less than that of pure NiTiCu film. It can be reduced to the factor of about one-ninth after the surface passivation resulting in smooth, homogeneous and highly corrosion resistant surface. The antibacterial and cytotoxicity of pure and Cu3N coated NiTiCu thin films were investigated through green fluorescent protein expressing E. coli bacteria and human embryonic kidney cells. The results show the strong antibacterial property and non cytotoxicity of Cu3N/NiTiCu heterostructure. This work is of immense technological importance due to variety of BioMEMS applications.

  12. Understanding the Shape-Memory Behavior in Ti-(~49 At. Pct) Ni Alloy by Nanoindentation Measurement

    NASA Astrophysics Data System (ADS)

    Sinha, A.; Datta, S.; Chakraborti, P. C.; Chattopadhyay, P. P.

    2013-04-01

    The influence of aging treatment on the work-hardening behavior of near-equiatomic NiTi alloy has been studied at the microstructural scale by conducting the instrumented indentation measurement. The maximum shape recovery is achieved at the peak aged condition. The improvement in shape recovery has been attributed to the delayed onset of plasticity. A comparison has been made between the recoverable strain obtained from the tensile experiments and the recovery index parameter determined from the nanoindentation measurements.

  13. Design of automatic rotor blades folding system using NiTi shape memory alloy actuator

    NASA Astrophysics Data System (ADS)

    Ali, M. I. F.; Abdullah, E. J.

    2016-10-01

    This present paper will study the requirements for development of a new Automatic Rotor Blades Folding (ARBF) system that could possibly solve the availability, compatibility and complexity issue of upgrading a manual to a fully automatic rotor blades folding system of a helicopter. As a subject matter, the Royal Malaysian Navy Super Lynx Mk 100 was chosen as the baseline model. The aim of the study was to propose a design of SMART ARBF's Shape Memory Alloy (SMA) actuator and proof of operating concept using a developed scale down prototype model. The performance target for the full folding sequence is less than ten minutes. Further analysis on design requirements was carried out, which consisted of three main phases. Phase 1 was studying the SMA behavior on the Nickel Titanium (NiTi) SMA wire and spring (extension type). Technical values like activation requirement, contraction length, and stroke- power and stroke-temperature relationship were gathered. Phase 2 was the development of the prototype where the proposed design of stepped-retractable SMA actuator was introduced. A complete model of the SMART ARBF system that consisted of a base, a main rotor hub, four main rotor blades, four SMA actuators and also electrical wiring connections was fabricated and assembled. Phase 3 was test and analysis whereby a PINENG-PN968s-10000mAh Power Bank's 5 volts, which was reduced to 2.5 volts using LM2596 Step-Down Converter, powered and activated the NiTi spring inside each actuator. The bias spring (compression type), which functions to protract and push the blades to spread position, will compress together with the retraction of actuators and pull the blades to the folding position. Once the power was removed and SMA spring deactivated, the bias spring stiffness will extend the SMA spring and casing and push the blades back to spread position. The timing for the whole revolution was recorded. Based on the experimental analysis, the recorded timing for folding sequence is

  14. Effects of Stoichiometry on Transformation Temperatures and Actuator-Type Performance of NiTiPd and NiTiPdX High-Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Bigelow, Glen S.; Gaydosh, Darrell; Garg, Anita; Padula, Santo A., II; Noebe, Ronald D.

    2007-01-01

    High-temperature shape memory NiTiPd and NiTiPdX (X=Au, Pt, Hf) alloys were produced with titanium equivalent (Ti+Hf) compositions of 50.5, 50.0, 49.5, and 49.0 at.%. Thermo-mechanical testing in compression was used to evaluate the transformation temperatures, transformation strain, work output, and permanent deformation behavior of each alloy to study the effects of quaternary alloying and stoichiometry on high-temperature shape memory alloy behavior. Microstructural evaluation showed the presence of second phases for all alloy compositions. No load transformation temperatures in the stoichiometric alloys were relatively unchanged by Au and Pt substitutions, while the substitution of Hf for Ti causes a drop in transformation temperatures. The NiTiPd, NiTiPdAu and NiTiPdHf alloys exhibited transformation temperatures that were highest in the Ti-rich compositions, slightly lower at stoichiometry, and significantly reduced when the Ti equivalent composition was less than 50 at.%. For the NiTiPdPt alloy, transformation temperatures were highest for the Ti-rich compositions, lowest at stoichiometry, and slightly higher in the Ni-rich composition. When thermally cycled under constant stresses of up to 300 MPa, all of the alloys had transformation strains, and therefore work outputs, which increased with increasing stress. In each series of alloys, the transformation strain and thus work output was highest for stoichiometric or Ti-rich compositions while permanent strain associated with the constant-load thermal cycling was lowest for alloys with Ni-equivalent-rich compositions. Based on these results, basic rules for optimizing the composition of NiTiPd alloys for actuator performance will be discussed.

  15. Surface structure and corrosion resistance of short-time heat-treated NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Vojtěch, D.; Voděrová, M.; Fojt, J.; Novák, P.; Kubásek, T.

    2010-12-01

    NiTi alloys are attractive materials that are used for medicine, however, Ni-release may cause allergic reactions in an organism. The Ni-release rate is strongly affected by the surface state of the NiTi alloy that is mainly determined by its processing route. In this study, a NiTi shape memory alloy (50.9 at.% Ni) was heat-treated by several regimes simulating the shape setting procedure, the last step in the manufacture of implants. Heating temperatures were between 500 and 550 °C and durations from 5 to 10 min. Heat treatments were performed in air at normal and low pressure and in a salt bath. The purpose of the treatments was to obtain and compare different surface states of the Ni-Ti alloy. The surface state and chemistry of heat-treated samples were investigated by electron microscopy, X-ray photoelectron spectroscopy and Raman spectrometry. The amount of nickel released into a model physiological solution of pH 2 and into concentrated HCl was taken as a measure of the corrosion rate. It was found that the heat treatments produced surface TiO 2 layers measuring 15-50 nm in thickness that were depleted in nickel. The sample covered by the 15-nm thick oxide that was treated at 500 °C/5 min in a low pressure air showed the best corrosion performance in terms of Ni-release. As the oxide thickness increased, due to either temperature or oxygen activity change, Ni-release into the physiological solution accelerated. This finding is discussed in relation to the internal structure of the oxide layers.

  16. 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.

  17. Unoccupied electronic structure of Ni2MnGa ferromagnetic shape memory alloy

    SciTech Connect

    Maniraj, M.; D׳Souza, S. W.; Rai, Abhishek; Schlagel, D. L.; Lograsso, T. A.; Chakrabarti, Aparna; Barman, S. R.

    2015-08-20

    Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni2MnGa is significant in the austenite phase. Furthermore, in the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Finally, based on the first principle calculations of the electronic structure of Ni–Mn–Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band.

  18. Unoccupied electronic structure of Ni2MnGa ferromagnetic shape memory alloy

    DOE PAGES

    Maniraj, M.; D׳Souza, S. W.; Rai, Abhishek; ...

    2015-08-20

    Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni2MnGa is significant in the austenite phase. Furthermore, in the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Finally, based on the first principle calculations of the electronic structure of Ni–Mn–Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band.

  19. Intrinsic Micromechanism of Multi-step Structural Transformation in MnNi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Cui, Shushan; Wan, Jianfeng; Rong, Yonghua; Zhang, Jihua

    2017-03-01

    Simulation of the multi-step transformation of cubic matrix → multi-variant tetragonal domain → orthorhombic domain was realized by phase-field method. The intrinsic micromechanism of the second-step transformation in MnNi alloys was studied. It was found that the orthorhombic variant originated from the tetragonal variant with similar orientation, and bar-shaped orthorhombic phase firstly occurred around the interface of twinning bands. The second-step transformation resulted in localized variation of internal stress.

  20. Design and development of NiTi-based precipitation-strengthened high-temperature shape memory alloys for actuator applications

    NASA Astrophysics Data System (ADS)

    Hsu, Derek Hsen Dai

    As a vital constituent in the field of smart materials and structures, shape memory alloys (SMAs) are becoming ever-more important due to their wide range of commercial and industrial applications such as aircraft couplings, orthodontic wires, and eyeglasses frames. However, two major obstacles preventing SMAs from fulfilling their potential as excellent actuator materials are: 1) the lack of commercially-viable SMAs that operate at elevated temperatures, and 2) the degradation of mechanical properties and shape memory behavior due to thermal cyclic fatigue. This research utilized a thermodynamically-driven systems design approach to optimize the desired properties by controlling the microstructure and processing of high-temperature SMAs (HTSMAs). To tackle the two aforementioned problems with HTSMAs, the introduction of Ni2TiAl coherent nanoprecipitates in a Ni-Ti-Zr/Hf HTSMA matrix is hypothesized to strengthen the martensite phase while simultaneously increasing the transformation temperature. Differential scanning calorimetry (DSC) was used to determine the transformation temperatures and thermal cyclic stability of each alloy. Also, microstructural characterization was performed using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). Lastly, compression testing was used to assess the mechanical behavior of the alloys. From the investigation of the first set of Ni48.5Ti31.5-X Zr20AlX (X = 0, 1, 2, 3) prototype alloys, Al addition was found to decrease the transformation temperatures, decrease the thermal cyclic stability, but also increase the strength due to the nucleation and growth of embrittling NiTi2 and NiTiZr Laves phases. However, the anticipated Heusler phase precipitation did not occur. The next study focused on Ni50Ti30-XHf20Al X (X = 0, 1, 2, 3, 4, 5) prototype alloys which replaced Zr with Hf to avoid the formation of brittle Laves phases

  1. Nonlocal superelastic model of size-dependent hardening and dissipation in single crystal Cu-Al-Ni shape memory alloys.

    PubMed

    Qiao, Lei; Rimoli, Julian J; Chen, Ying; Schuh, Christopher A; Radovitzky, Raul

    2011-02-25

    We propose a nonlocal continuum model to describe the size-dependent superelastic effect observed in recent experiments of single crystal Cu-Al-Ni shape memory alloys. The model introduces two length scales, one in the free energy and one in the dissipation, which account for the size-dependent hardening and dissipation in the loading and unloading response of micro- and nanopillars subject to compression tests. The information provided by the model suggests that the size dependence observed in the dissipation is likely to be associated with a nonuniform evolution of the distribution of the austenitic and martensitic phases during the loading cycle.

  2. Growth and characterization of ferromagnetic shape memory alloy Co 50Ni 20FeGa 29 single crystals

    NASA Astrophysics Data System (ADS)

    Dai, X. F.; Wang, H. Y.; Chen, L. J.; Duan, X. F.; Chen, J. L.; Wu, G. H.; Zhu, Hao; Xiao, John Q.

    2006-05-01

    Single crystals of Co 50Ni 20FeGa 29 with B2 phase have been obtained in a deep supercooling condition. The interface-facets and the segregation effect lead to the formation of ordered defects that store a directional internal stress. These defects give to a large energy barrier that leads to a very sharp martensitic transformation within a temperature window of only 2 K. The single crystals show good shape memory effect and superelasticity, which are anisotropic between the growth direction [0 0 1] and its equivalent direction [0 1 0]. The anisotropic behaviors are attributed to the directional internal stress caused by the ordered defects.

  3. Exploration of TiNi shape memory alloy for potential application in a new area: tribological engineering

    NASA Astrophysics Data System (ADS)

    Li, D. Y.

    2000-10-01

    TiNi alloy is a well known shape memory alloy and has been widely used for bio-medical, mechanical and electrical applications. Recent research has demonstrated that TiNi alloy exhibits high resistance to wear and can be a superior tribo-material. Performance of this alloy benefits from its pseudoelasticity, resulting from a reversible martensitic transformation. Extensive research has been conducted at the University of Alberta to investigate wear behavior of TiNi alloy during various wear processes, including erosion, corrosive erosion, sliding wear and microscopic wear. The mechanism responsible for high wear resistance of TiNi alloy has been clarified to some degree and new phenomena are being continuously discovered. In particular, efforts have been made to develop tribo-composites using TiNi alloy as the matrix, reinforced by hard ceramic particles, including nano-structured particles. The composites obtained possess considerably enhanced wear resistance. This paper briefly reports progress in our studies on the development of this novel tribo-material.

  4. Treatment of Nonunion of Scaphoid Waist with Ni-Ti Shape-Memory Alloy Connector and Iliac Bone Graft

    NASA Astrophysics Data System (ADS)

    Cao, Lie-Hu; Xu, Shuo-Gui; Wu, Ya-Le; Zhang, Chun-Cai

    2011-07-01

    After fracture, the unique anatomy and blood supply of the scaphoid itself predisposes to nonunion. Scaphoid nonunion presents a formidable challenge to surgeons because of the difficulties for fixation, and the high failure rate after treatment. The Ni-Ti shape-memory alloy can provide compressive stress at the nonunion site, which is the key point for bone healing. Hence, we designed a shape-memory bone connector named arched shape-memory connector (ASC). We conducted a retrospective study looking at the union rate and complications and correlating the outcome of treatment with this device. The study reviewed a cohort of six consecutive patients presenting with scaphoid waist nonunion, who were treated with ASC and iliac cancellous bone grafting at our center from August 2002 to December 2007. The patients with nonunion achieved a 100% union rate. All the patients who achieved union had good pain relief and improved function. Our study demonstrates that scaphoid waist nonunions can be successfully treated by ASC and iliac bone grafting.

  5. Effect of the surface state of the Ti-Ni alloy products on the shape memory effect parameters

    NASA Astrophysics Data System (ADS)

    Prokoshkin, S. D.; Ryklina, E. P.; Chernavina, A. A.; Abramov, V. Ya.; Krestnikov, N. S.

    2009-12-01

    The depth profiles of the structure, composition, and properties of the oxide layer that forms on the surface of Ti-Ni alloy products during postdeformation annealing (PDA) are studied. These parameters depend substantially on the holding temperature and time during PDA. The application of low-temperature thermomechanical treatment improves the state of surface as compared to quenching due to a decrease in the oxide-layer depth by more than an order of magnitude. The state of the surface of Ti-Ni alloy products significantly affects the characteristic martensite transformation temperatures and the shape memory effect parameters. This effect is more pronounced as the sample thickness (diameter) decreases. It is impossible to predict this effect on the entire set of the functional properties of the alloy products because of its ambiguity. Therefore, the oxide layer should be removed by etching to obtain reliable and reproducible results.

  6. Undercooling growth and magnetic characterization of ferromagnetic shape memory alloy Ni2FeGa single crystals

    NASA Astrophysics Data System (ADS)

    Qian, J. F.; Zhang, H. G.; Chen, J. L.; Wang, W. H.; Wu, G. H.

    2014-02-01

    Ni2FeGa single crystals have been grown in undercooling conditions provided by a glass-purification method. It has been found that trace amounts of γ phase embededin the single crystalline matrix preferentially orients in the <1 0 0> orientation along the growth direction. This γ phase generates directional residual stress and results in an anisotropic two-way shape memory effect. Large strains of -2.5% in the [0 0 1] and 1.5% in the [0 1 0] directions have been observed. This trace γ phase also improves the ductility of the material, thus the crystals could be plastically deformed at room temperature in the parent phase. The <1 1 0> and <1 1 1> orientations in Ni2FeGa alloy were identified as the easy and hard magnetization directions, respectively, in the parent phase by using low field M-T measurements.

  7. Breakdown of Shape Memory Effect in Bent Cu-Al-Ni Nanopillars: When Twin Boundaries Become Stacking Faults.

    PubMed

    Liu, Lifeng; Ding, Xiangdong; Sun, Jun; Li, Suzhi; Salje, Ekhard K H

    2016-01-13

    Bent Cu-Al-Ni nanopillars (diameters 90-750 nm) show a shape memory effect, SME, for diameters D > 300 nm. The SME and the associated twinning are located in a small deformed section of the nanopillar. Thick nanopillars (D > 300 nm) transform to austenite under heating, including the deformed region. Thin nanopillars (D < 130 nm) do not twin but generate highly disordered sequences of stacking faults in the deformed region. No SME occurs and heating converts only the undeformed regions into austenite. The defect-rich, deformed region remains in the martensite phase even after prolonged heating in the stability field of austenite. A complex mixture of twins and stacking faults was found for diameters 130 nm < D < 300 nm. The size effect of the SME in Cu-Al-Ni nanopillars consists of an approximately linear reduction of the SME between 300 and 130 nm when the SME completely vanishes for smaller diameters.

  8. Effect of warm rolling on the martensite transformation temperatures, shape memory effect, and superelasticity in Ti49.2Ni50.8 alloy

    NASA Astrophysics Data System (ADS)

    Lotkov, Aleksander; Zhapova, Dorzhima; Grishkov, Victor; Cherniavsky, Alexander; Timkin, Victor

    2016-11-01

    The paper presents research data demonstrating the effect of warm caliber rolling on the martensite transformation temperatures, shape memory effect, and superelasticity in Ti49.2Ni50.8 (at %). The experimental values of inelastic strain in coarse-grained and microcrystalline Ti49.2Ni50.8 (at %) specimens exceed the theoretical limit of recoverable strain or maximum lattice strain for TiNi-based alloys.

  9. Shape memory polymers

    DOEpatents

    Wilson, Thomas S.; Bearinger, Jane P.

    2015-06-09

    New shape memory polymer compositions, methods for synthesizing new shape memory polymers, and apparatus comprising an actuator and a shape memory polymer wherein the shape memory polymer comprises at least a portion of the actuator. A shape memory polymer comprising a polymer composition which physically forms a network structure wherein the polymer composition has shape-memory behavior and can be formed into a permanent primary shape, re-formed into a stable secondary shape, and controllably actuated to recover the permanent primary shape. Polymers have optimal aliphatic network structures due to minimization of dangling chains by using monomers that are symmetrical and that have matching amine and hydroxyl groups providing polymers and polymer foams with clarity, tight (narrow temperature range) single transitions, and high shape recovery and recovery force that are especially useful for implanting in the human body.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

    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.

  12. Characterization of Ternary NiTiPd High-Temperature Shape-Memory Alloys under Load-Biased Thermal Cycling

    NASA Technical Reports Server (NTRS)

    Bigelow, Glen S.; Padula, Santo A.; Noebe, Ronald D.; Garg, Anita; Gaydosh, Darrell

    2010-01-01

    While NiTiPd alloys have been extensively studied for proposed use in high-temperature shape-memory applications, little is known about the shape-memory response of these materials under stress. Consequently, the isobaric thermal cyclic responses of five (Ni,Pd)49.5Ti50.5 alloys with constant stoichiometry and Pd contents ranging from 15 to 46 at. pct were investigated. From these tests, transformation temperatures, transformation strain (which is proportional to work output), and unrecovered strain per cycle (a measure of dimensional instability) were determined as a function of stress for each alloy. It was found that increasing the Pd content over this range resulted in a linear increase in transformation temperature, as expected. At a given stress level, work output decreased while the amount of unrecovered strain produced during each load-biased thermal cycle increased with increasing Pd content, during the initial thermal cycles. However, continued thermal cycling at constant stress resulted in a saturation of the work output and nearly eliminated further unrecovered strain under certain conditions, resulting in stable behavior amenable to many actuator applications.

  13. The effect of martensite plasticity on the cyclic deformation of super-elastic NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2014-01-01

    Based on stress-controlled cyclic tension-unloading experiments with different peak stresses, the effect of martensite plasticity on the cyclic deformation of super-elastic NiTi shape memory alloy micro-tubes is investigated and discussed. The experimental results show that the reverse transformation from the induced martensite phase to the austenite phase is gradually restricted by the plastic deformation of the induced martensite phase caused by an applied peak stress that is sufficiently high (higher than 900 MPa), and the extent of such restriction increases with further increasing the peak stress. The residual and peak strains of super-elastic NiTi shape memory alloy accumulate progressively, i.e., transformation ratchetting occurs during the cyclic tension-unloading with peak stresses from 600 to 900 MPa, and the transformation ratchetting strain increases with the increase of the peak stress. When the peak stress is higher than 900 MPa, the peak strain becomes almost unchanged, but the residual strain accumulates and the dissipation energy per cycle decreases very quickly with the increasing number of cycles due to the restricted reverse transformation by the martensite plasticity. Furthermore, a quantitative relationship between the applied stress and the stabilized residual strain is obtained to reasonably predict the evolution of the peak strain and the residual strain.

  14. Development of a self-stressing NiTiNb shape memory alloy (SMA)/fiber reinforced polymer (FRP) patch

    NASA Astrophysics Data System (ADS)

    El-Tahan, M.; Dawood, M.; Song, G.

    2015-06-01

    The objective of this research is to develop a self-stressing patch using a combination of shape memory alloys (SMAs) and fiber reinforced polymer (FRP) composites. Prestressed carbon FRP patches are emerging as a promising alternative to traditional methods to repair cracked steel structures and civil infrastructure. However, prestressing these patches typically requires heavy and complex fixtures, which is impractical in many applications. This paper presents a new approach in which the prestressing force is applied by restraining the shape memory effect of NiTiNb SMA wires. The wires are subsequently embedded in an FRP overlay patch. This method overcomes the practical challenges associated with conventional prestressing. This paper presents the conceptual development of the self-stressing patch with the support of experimental observations. The bond between the SMA wires and the FRP is evaluated using pull-out tests. The paper concludes with an experimental study that evaluates the patch response during activation subsequent monotonic tensile loading. The results demonstrate that the self-stressing patch with NiTiNb SMA is capable of generating a significant prestressing force with minimal tool and labor requirements.

  15. Influence of test procedures on the thermomechanical properties of a 55NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Padula, Santo A., II; Gaydosh, Darrell J.; Noebe, Ronald D.; Bigelow, Glen S.; Garg, Anita; Lagoudas, Dimitris; Karaman, Ibrahim; Atli, Kadri C.

    2008-03-01

    Over the past few decades, binary NiTi shape memory alloys have received attention due to their unique mechanical characteristics, leading to their potential use in low-temperature, solid-state actuator applications. However, prior to using these materials for such applications, the physical response of these systems to mechanical and thermal stimuli must be thoroughly understood and modeled to aid designers in developing SMA-enabled systems. Even though shape memory alloys have been around for almost five decades, very little effort has been made to standardize testing procedures. Although some standards for measuring the transformation temperatures of SMA's are available, no real standards exist for determining the various mechanical and thermomechanical properties that govern the usefulness of these unique materials. Consequently, this study involved testing a 55NiTi alloy using a variety of different test methodologies. All samples tested were taken from the same heat and batch to remove the influence of sample pedigree on the observed results. When the material was tested under constant-stress, thermal-cycle conditions, variations in the characteristic material responses were observed, depending on test methodology. The transformation strain and irreversible strain were impacted more than the transformation temperatures, which only showed an affect with regard to applied external stress. In some cases, test methodology altered the transformation strain by 0.005-0.01mm/mm, which translates into a difference in work output capability of approximately 2 J/cm 3 (290 in•lbf/in 3). These results indicate the need for the development of testing standards so that meaningful data can be generated and successfully incorporated into viable models and hardware. The use of consistent testing procedures is also important when comparing results from one research organization to another. To this end, differences in the observed responses will be presented, contrasted and

  16. Influence of Test Procedures on the Thermomechanical Properties of a 55NiTi Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Padula, Santo A., II; Gaydosh, Darrell J.; Noebe, Ronald D.; Bigelow, Glen S.; Garg, Anita; Lagoudas, Dimitris; Karaman, Ibrahim; Atli, Kadri C.

    2008-01-01

    Over the past few decades, binary NiTi shape memory alloys have received attention due to their unique mechanical characteristics, leading to their potential use in low-temperature, solid-state actuator applications. However, prior to using these materials for such applications, the physical response of these systems to mechanical and thermal stimuli must be thoroughly understood and modeled to aid designers in developing SMA-enabled systems. Even though shape memory alloys have been around for almost five decades, very little effort has been made to standardize testing procedures. Although some standards for measuring the transformation temperatures of SMA s are available, no real standards exist for determining the various mechanical and thermomechanical properties that govern the usefulness of these unique materials. Consequently, this study involved testing a 55NiTi alloy using a variety of different test methodologies. All samples tested were taken from the same heat and batch to remove the influence of sample pedigree on the observed results. When the material was tested under constant-stress, thermal-cycle conditions, variations in the characteristic material responses were observed, depending on test methodology. The transformation strain and irreversible strain were impacted more than the transformation temperatures, which only showed an affect with regard to applied external stress. In some cases, test methodology altered the transformation strain by 0.005-0.01mm/mm, which translates into a difference in work output capability of approximately 2 J/cu cm (290 in!lbf/cu in). These results indicate the need for the development of testing standards so that meaningful data can be generated and successfully incorporated into viable models and hardware. The use of consistent testing procedures is also important when comparing results from one research organization to another. To this end, differences in the observed responses will be presented, contrasted and

  17. Microwave sintering effects on the microstructure and mechanical properties of Ti-51at%Ni shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ibrahim, Mustafa K.; Hamzah, E.; Saud, Safaa N.; Abu Bakar, E. N. E.; Bahador, A.

    2017-03-01

    Ti-51at%Ni shape memory alloys (SMAs) were successfully produced via a powder metallurgy and microwave sintering technique. The influence of sintering parameters on porosity reduction, microstructure, phase transformation temperatures, and mechanical properties were investigated by optical microscopy, field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), compression tests, and microhardness tests. Varying the microwave temperature and holding time was found to strongly affect the density of porosity, presence of precipitates, transformation temperatures, and mechanical properties. The lowest density and smallest pore size were observed in the Ti-51at%Ni samples sintered at 900°C for 5 min or at 900°C for 30 min. The predominant martensite phases of β2 and β19' were observed in the microstructure of Ti-51at%Ni, and their existence varied in accordance with the sintering temperature and the holding time. In the DSC thermograms, multi-transformation peaks were observed during heating, whereas a single peak was observed during cooling; these peaks correspond to the presence of the β2, R, and β19' phases. The maximum strength and strain among the Ti-51at%Ni SMAs were 1376 MPa and 29%, respectively, for the sample sintered at 900°C for 30 min because of this sample's minimal porosity.

  18. Stress-Induced Martensite in Front of Crack Tips in NiTi Shape Memory Alloys: Modeling Versus Experiments

    NASA Astrophysics Data System (ADS)

    Maletta, C.; Young, M. L.

    2011-07-01

    NiTi-based shape memory alloys (SMAs) exhibit an unusual stress distribution at the crack tip as compared to common engineering materials, due to a stress-induced martensitic transformation resulting from highly localized stresses. Understanding the fracture mechanics of NiTi-based SMAs is critical to many of their applications. Here, we develop an analytical model, which predicts the boundaries of the transformation region in the crack tip vicinity of NiTi-based SMAs. The proposed model is based on a recent analytical approach which uses modified linear elastic fracture mechanics concepts to predict the crack tip stress distribution and transformation region in SMAs but, unfortunately, it applies only to the plane stress condition. To overcome this limitation, the proposed model accounts for stress triaxiality, which plays an important role in restricting crack tip plastic deformations in common ductile metals as well as the stress-induced martensite in NiTi SMAs. The effects of triaxial stress at the crack tip are taken into account by including a new parameter, the transformation constraint factor, which is based on the plastic constraint factor of elasto-plastic materials. The predictions of the model are compared with synchrotron x-ray micro-diffraction observations and satisfactory agreement is observed between the two results. Finally, the evolution of crack tip transformation boundaries during fracture tests of miniature compact tension specimens is predicted and the effects of applied load and crack length are discussed.

  19. Experimental observations on mechanical response of three-phase NiTi shape memory alloy under uniaxial tension

    NASA Astrophysics Data System (ADS)

    Xiao, Yao; Zeng, Pan; Lei, Liping

    2016-10-01

    In this paper, the mechanical behavior of three-phase NiTi shape memory alloy (SMA) is examined in a wide temperature range using in situ digital image correlation. By varying the temperature and the cooling/heating history, we get the specimens with initial austenite (A), initial R-phase (R), initial martensite (M), initial mixture of A and R, initial mixture of R and M and initial mixture of A and M. It is observed in the experiments that NiTi SMA exhibits localized A → M transformation and R → M transformation while homogenous R-reorientation and martensitic reorientation. Moreover, the influence of the initial mixed states, i.e. mixture of A and M, mixture of R and M and mixture of A and R, on the mechanical response of NiTi SMA is discussed. Interestingly, we find that the specimens with initial mixture of R and M demonstrate homogenous deformation manner and the emergence of R in M facilitates the transformation of NiTi SMA greatly. The three-phase phase diagram is also established. The thermal dependences of the critical transformation stresses associated with various transformation processes are calculated for further theoretical investigation and simulation.

  20. Correlation between Mechanical Behavior and Actuator-type Performance of Ni-Ti-Pd High-temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Bigelow, Glen S.; Padula, Santo A., II; Garg, Anita; Noebe, Ronald D.

    2007-01-01

    High-temperature shape memory alloys in the NiTiPd system are being investigated as lower cost alternatives to NiTiPt alloys for use in compact solid-state actuators for the aerospace, automotive, and power generation industries. A range of ternary NiTiPd alloys containing 15 to 46 at.% Pd has been processed and actuator mimicking tests (thermal cycling under load) were used to measure transformation temperatures, work behavior, and dimensional stability. With increasing Pd content, the work output of the material decreased, while the amount of permanent strain resulting from each load-biased thermal cycle increased. Monotonic isothermal tension testing of the high-temperature austenite and low temperature martensite phases was used to partially explain these behaviors, where a mismatch in yield strength between the austenite and martensite phases was observed at high Pd levels. Moreover, to further understand the source of the permanent strain at lower Pd levels, strain recovery tests were conducted to determine the onset of plastic deformation in the martensite phase. Consequently, the work behavior and dimensional stability during thermal cycling under load of the various NiTiPd alloys is discussed in relation to the deformation behavior of the materials as revealed by the strain recovery and monotonic tension tests.

  1. Role of B19' martensite deformation in stabilizing two-way shape memory behavior in NiTi

    DOE PAGES

    Benafan, O.; Padula, S. A.; Noebe, R. D.; ...

    2012-11-01

    Deformation of a B19' martensitic, polycrystallineNi49.9Ti50.1 (at. %) shape memoryalloy and its influence on the magnitude and stability of the ensuing two-way shape memory effect (TWSME) was investigated by combined ex situ mechanical experimentation and in situneutron diffraction measurements at stress and temperature. The microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were captured and compared to the bulk macroscopic response of the alloy. With increasing uniaxial strain, it was observed that B19' martensite deformed by reorientation and detwinning with preferred selection of the (1¯50)M and (010)M variants, (201¯)B19' deformation twinning, and dislocationmore » activity. These mechanisms were indicated by changes in bulk texture from the neutron diffraction measurements. Partial reversibility of the reoriented variants and deformation twins was also captured upon load removal and thermal cycling, which after isothermal deformation to strains between 6% and 22% resulted in a strong TWSME. Consequently, TWSME functional parameters including TWSME strain, strain reduction, and transformation temperatures were characterized and it was found that prior martensite deformation to 14% strain provided the optimum condition for the TWSME, resulting in a stable two-way shape memory strain of 2.2%. Thus, isothermal deformation of martensite was found to be a quick and efficient method for creating a strong and stable TWSME in Ni₄₉.₉Ti₅₀.₁.« less

  2. 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.

  3. Thermomechanical behavior and microstructural evolution of a Ni(Pd)-rich Ni24.3Ti49.7Pd26 high temperature shape memory alloy

    DOE PAGES

    Benafan, O.; Garg, A.; Noebe, R. D.; ...

    2015-04-20

    We investigated the effect of thermomechanical cycling on a slightly Ni(Pd)-rich Ni24.3Ti49.7Pd26 (near stochiometric Ni–Ti basis with Pd replacing Ni) high temperature shape memory alloy. Furthermore, aged tensile specimens (400 °C/24 h/furnace cooled) were subjected to constant-stress thermal cycling in conjunction with microstructural assessment via in situ neutron diffraction and transmission electron microscopy (TEM), before and after testing. It was shown that in spite of the slightly Ni(Pd)-rich composition and heat treatment used to precipitation harden the alloy, the material exhibited dimensional instabilities with residual strain accumulation reaching 1.5% over 10 thermomechanical cycles. This was attributed to insufficient strengthening ofmore » the material (insufficient volume fraction of precipitate phase) to prevent plasticity from occurring concomitant with the martensitic transformation. In situ neutron diffraction revealed the presence of retained martensite while cycling under 300 MPa stress, which was also confirmed by transmission electron microscopy of post-cycled samples. Neutron diffraction analysis of the post-thermally-cycled samples under no-load revealed residual lattice strains in the martensite and austenite phases, remnant texture in the martensite phase, and peak broadening of the austenite phase. The texture we developed in the martensite phase was composed mainly of those martensitic tensile variants observed during thermomechanical cycling. Presence of a high density of dislocations, deformation twins, and retained martensite was revealed in the austenite state via in-situ TEM in the post-cycled material, providing an explanation for the observed peak broadening in the neutron diffraction spectra. Despite the dimensional instabilities, this alloy exhibited a biased transformation strain on the order of 3% and a two-way shape memory effect (TWSME) strain of ~2%, at relatively high actuation temperatures.« less

  4. Shape Memory Characteristics of Ti(sub 49.5)Ni(sub 25)Pd(sub 25)Sc(sub 0.5) High-Temperature Shape Memory Alloy After Severe Plastic Deformation

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    A Ti(49.5)Ni25Pd25Sc(0.5) high-temperature shape memory alloy is thermomechanically processed to obtain enhanced shape-memory characteristics: in particular, dimensional stability upon repeated thermal cycles under constant loads. This is accomplished using severe plastic deformation via equal channel angular extrusion (ECAE) and post-processing annealing heat treatments. The results of the thermomechanical experiments reveal that the processed materials display enhanced shape memory response, exhibiting higher recoverable transformation and reduced irrecoverable strain levels upon thermal cycling compared with the unprocessed material. This improvement is attributed to the increased strength and resistance of the material against defect generation upon phase transformation as a result of the microstructural refinement due to the ECAE process, as supported by the electron microscopy observations.

  5. Structural and magnetic properties of magnetron sputtered Ni-Mn-Sn ferromagnetic shape memory alloy thin films

    SciTech Connect

    Vishnoi, Ritu; Kaur, Davinder

    2010-05-15

    In the present study, structural and magnetic properties of Mn-rich, off-stoichiometric, nanocrystalline Ni-Mn-Sn ferromagnetic shape memory alloy thin films, grown on Si (100) substrates at 550 deg. C by dc magnetron sputtering have been systematically investigated. The crystallization, surface morphology, and structural features were studied using x-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy. The structural transition from austenite to martensite was observed with an increase of Mn content. Austenitic phase with mixed L2{sub 1}/A2+B2 structure has been observed at room temperature in Ni{sub 52.6}Mn{sub 23.7}Sn{sub 23.6} (S{sub 1}) and Ni{sub 51.5}Mn{sub 26.1}Sn{sub 22.2} (S{sub 2}) films, while those with composition of Ni{sub 58.9}Mn{sub 28.0}Sn{sub 13.0} (S{sub 3}) and Ni{sub 58.3}Mn{sub 29.0}Sn{sub 12.6} (S{sub 4}) show martensitic phase with 14M modulated monoclinic structures. Field induced martensite-austenite transformation has been observed in magnetization studies using superconducting quantum interference device magnetometer. Temperature dependent magnetization measurements demonstrate the influence of magnetic field on the structural phase transition temperature. The investigations reveal an increase of martensitic transformation temperature (T{sub M}) with corresponding increase in substitution of Mn. The films exhibit ferromagnetic behavior at low temperatures below Curie temperature (T{sub C}). The decrease in saturation moment with increasing Mn content, indicates the existence of antiferromagnetic correlations within ferromagnetic matrix.

  6. Stress transfer during different deformation stages in a nano-precipitate-strenthened Ni-Ti shape memory alloy

    DOE PAGES

    Dong, Y. H.; Cong, D. Y.; Nie, Z. H.; ...

    2015-11-16

    Understanding the role of fine coherent precipitates in the micromechanical behavior of precipitate-strengthened shape memory alloys (SMAs), which still remains a mystery heretofore, is of crucial importance to the design of advanced SMAs with optimal functional and mechanical properties. Here, we investigate the lattice strain evolution of, and the stress partition between the nanoscale Ni4Ti3 precipitates and the matrix in a precipitate-strengthened Ni-Ti SMA during different deformation stages by in-situ synchrotron high-energy X-ray diffraction technique. We found that, during R-phase reorientation and stress-induced martensitic transformation, which both involve the shear deformation process, the lattice strain of the nanoscale precipitates drasticallymore » increases by a magnitude of 0.5%, which corresponds to an abrupt increase of ~520 MPa in internal stress. This indicates that stress repartition occurs and most of the stress is transferred to the precipitates during the shear deformation of the matrix. Lastly, it is further revealed that the nanoscale precipitates which only have a low volume fraction bear a considerable amount of applied stress during all deformation stages investigated, implying that the nanoscale precipitates play an important role in the deformation behavior of the precipitate-strengthened Ni-Ti SMAs.« less

  7. Uniaxial-stress tuned large magnetic-shape-memory effect in Ni-Co-Mn-Sb Heusler alloys

    NASA Astrophysics Data System (ADS)

    Salazar Mejía, C.; Küchler, R.; Nayak, A. K.; Felser, C.; Nicklas, M.

    2017-02-01

    Combined strain and magnetization measurements on the Heusler shape-memory alloys Ni45Co5Mn38Sb12 and Ni44Co6Mn38Sb12 give evidence for strong magneto-structural coupling. The sample length changes up to 1% at the martensitic transformation, between a ferromagnetic, austenitic phase at high temperatures and a weakly magnetic, low-symmetry martensitic phase at lower temperatures. Under moderate uniaxial stress, the change in the sample length increases to and saturates at about 3%, pointing to stabilization of a single martensitic variant. A reverse martensitic transformation can also be induced by applying magnetic field: we find that within the temperature range of thermal hysteresis of the martensitic transformation, applying a field can induce a metastable expansion of the sample, while at slightly lower temperatures, the field response is reversible. These findings provide key information for future use of Ni(Co)-Mn-Sb-based Heusler compounds in, e.g., actuators and mechanical switches.

  8. Effects of Quenching Media on Phase Transformation Characteristics and Hardness of Cu-Al-Ni-Co Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Saud, Safaa N.; Hamzah, E.; Abubakar, T.; Farahany, S.; Bakhsheshi-Rad, H. R.

    2015-04-01

    This paper presents the investigation on the effects of various thermal treatments and quenching media on the phase transformation behaviour of Cu-Al-Ni-Co shape memory alloys (SMAs). The transformation temperatures were determined using a differential scanning calorimeter. The variation of cooling rates had a consequential effect on the phase transformation characteristics of the Cu-Al-Ni-Co SMAs. Nevertheless, the transformation temperature peaks were varied in terms of location as well as heat flow. The results indicated that there was an improvement in transformation temperatures whenever ice water was used as quenching medium. It was also observed that the forward transformation temperatures were higher than the reverse transformation. It was verified that the required heat for the transformation of martensite into austenite was more than the transformation of austenite into martensite. Moreover, thermodynamic parameters, such as enthalpy and entropy, tended to decrease and increase as a result of the changes in the cooling rates of each medium. To clarify the variations of the structures and properties of Cu-Al-Ni-Co SMA quenched samples, x-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, and Vickers hardness were used.

  9. Stress transfer during different deformation stages in a nano-precipitate-strengthened Ni-Ti shape memory alloy

    SciTech Connect

    Dong, Y. H.; Cong, D. Y. He, Z. B.; Li, L. F.; Wang, Y. D.; Nie, Z. H.; Wang, Z. L.; Ren, Y.

    2015-11-16

    Understanding the role of fine coherent precipitates in the micromechanical behavior of precipitate-strengthened shape memory alloys (SMAs), which still remains a mystery heretofore, is of crucial importance to the design of advanced SMAs with optimal functional and mechanical properties. Here, we investigate the lattice strain evolution of, and the stress partition between the nanoscale Ni{sub 4}Ti{sub 3} precipitates and the matrix in a precipitate-strengthened Ni-Ti SMA during different deformation stages by in-situ synchrotron high-energy X-ray diffraction technique. We found that, during R-phase reorientation and stress-induced martensitic transformation, which both involve the shear deformation process, the lattice strain of the nanoscale precipitates drastically increases by a magnitude of 0.5%, which corresponds to an abrupt increase of ∼520 MPa in internal stress. This indicates that stress repartition occurs and most of the stress is transferred to the precipitates during the shear deformation of the matrix. It is further revealed that the nanoscale precipitates which only have a low volume fraction bear a considerable amount of applied stress during all deformation stages investigated, implying that the nanoscale precipitates play an important role in the deformation behavior of the precipitate-strengthened Ni-Ti SMAs.

  10. Stress transfer during different deformation stages in a nano-precipitate-strenthened Ni-Ti shape memory alloy

    SciTech Connect

    Dong, Y. H.; Cong, D. Y.; Nie, Z. H.; He, Z. B.; Wang, Z. L.; Ren, Yang; Wang, Y. D.; Li, L. F.

    2015-11-16

    Understanding the role of fine coherent precipitates in the micromechanical behavior of precipitate-strengthened shape memory alloys (SMAs), which still remains a mystery heretofore, is of crucial importance to the design of advanced SMAs with optimal functional and mechanical properties. Here, we investigate the lattice strain evolution of, and the stress partition between the nanoscale Ni4Ti3 precipitates and the matrix in a precipitate-strengthened Ni-Ti SMA during different deformation stages by in-situ synchrotron high-energy X-ray diffraction technique. We found that, during R-phase reorientation and stress-induced martensitic transformation, which both involve the shear deformation process, the lattice strain of the nanoscale precipitates drastically increases by a magnitude of 0.5%, which corresponds to an abrupt increase of ~520 MPa in internal stress. This indicates that stress repartition occurs and most of the stress is transferred to the precipitates during the shear deformation of the matrix. Lastly, it is further revealed that the nanoscale precipitates which only have a low volume fraction bear a considerable amount of applied stress during all deformation stages investigated, implying that the nanoscale precipitates play an important role in the deformation behavior of the precipitate-strengthened Ni-Ti SMAs.

  11. In-Situ Fracture Observation and Fracture Toughness Analysis of Ni-Mn-Ga-Fe Ferromagnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Euh, Kwangjun; Lee, Jung-Moo; Nam, Duk-Hyun; Lee, Sunghak

    2011-12-01

    The fracture property improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile γ particles was explained by direct observation of microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable amount of γ particles in β grains after the homogenization treatment at 1073 K to 1373 K (800 °C to 1100 °C). With increasing homogenization temperature, γ particles were coarsened and distributed homogeneously along β grain boundaries as well as inside β grains. According to the in-situ microfracture observation, γ particles effectively acted as blocking sites of crack propagation and provided the stable crack growth, which could be confirmed by the R-curve analysis. The increase in fracture resistance with increasing crack length improved overall fracture properties of the Ni-Mn-Ga-Fe alloys. This improvement could be explained by mechanisms of blocking of crack propagation and crack blunting and bridging.

  12. Study on hemocompatibility and corrosion behavior of ion implanted TiNi shape memory alloy and Co-based alloys.

    PubMed

    Liang, Chenghao; Huang, Naibao

    2007-10-01

    Biomedical TiNi shape memory alloy and Co-based alloys were ion implanted, and corrosion resistance and hemocompatibility of these had been investigated with electrochemical method, dynamic clotting time, and hemolysis rate tests. The results indicated that the electrochemical stability and anodic polarization behavior of the materials were improved significantly after ion implantation. When TiNi, Co-based alloys were implanted Mo + C and Ti + C, respectively, the corrosion potentials were enhanced more than 200 mV, passive current densities decreased, and passive ranges were broadened. Dynamic clotting time of the ion implanted substances was prolonged and hemolysis rate decreased. All the results pointed out that corrosion resistance and hemocompatibility of the alloys were improved by ion implantation, and effects of dual implantation was better than that of C single implantation. X-ray diffraction analysis of the alloys after dual implantation revealed that TiC, Mo(2)C, Mo(9)Ti(4), and Mo appeared on the surface of TiNi alloy, and CoC(x), Co(3)Ti, TiC, and TiO on the surface of Co-based alloys. These phases dispersing on the alloy surface formed amorphous film, prevented dissolving of alloy elements and improved the corrosion resistance and hemocompatibility of the alloys.

  13. Magnetic shape memory fatigue

    NASA Astrophysics Data System (ADS)

    Heczko, Oleg; Straka, Ladislav; Soderberg, Outi; Hannula, Simo-Pekka

    2005-05-01

    Single crystal specimens of having compositions close to Ni2MnGa and exhibiting magnetic shape memory effect (MSME) were tested in a rotating magnetic field at a frequency of 5.7 Hz. The applied magnetic field, about 0.7 T was strong enough to induce the MSME. Test of one specimen was discontinued because of the structural failure of the specimens after 0.5 million cycles. Second specimen was tested up to 37 millions cycles. The evolution of the martensitic morphology and crack propagation were observed by optical microscopy. To characterize the magnetic shape memory behavior the simultaneous measurements of the field-induced strain and magnetization as a function of the magnetic field and external load was used. The full MSM effect, about 6% obtained prior the test, decreased to about 3% during the first million cycles. This value stayed then approximately constant up to 37 millions cycles of rotating magnetic field. The magnetic field needed to initiate the MSME increased. The observed behavior is discussed within the framework of observed martensitic band structure in the specimens and the existence of initial cracks and other obstacles for martensitic twin boundary motion.

  14. High-cycle fatigue of 10M Ni-Mn-Ga magnetic shape memory alloy in reversed mechanical loading

    NASA Astrophysics Data System (ADS)

    Aaltio, I.; Soroka, A.; Ge, Y.; Söderberg, O.; Hannula, S.-P.

    2010-07-01

    Application of Ni-Mn-Ga magnetic shape memory alloys in magnetic-field-induced actuation relies on their performance in long-term high-cycle fatigue. In this paper the performance and changes in the microstructure of a Ni-Mn-Ga 10M martensite single crystal material are reported in a long-term mechanically induced shape change cycling. The longest test was run for 2 × 109 cycles at a frequency of 250 Hz and a strain amplitude of ± 1%. After the test a clear increase of the dynamic stiffness of the material was detected. Three specimens out of ten were cycled until fracture occurred and their fracture mechanism was studied. It was observed that the macroscopic crack growth took place roughly at a 45° angle with respect to the loading direction that was along the lang100rang crystallographic direction of the sample. The macroscopic fracture plane seemed to correspond roughly to the {111} crystal planes. On a microscopic scale the fracture propagated in a step-like manner at least partly along crystallographic planes. The steps at the fracture plane correspond to the {101} twin planes, with the height of steps along the lang101rang direction. The final fracture of the samples occurred in a brittle manner after the critical stress was exceeded.

  15. Macroscopic and Microstructural Aspects of the Transformation Behavior in a Polycrystalline NiTi Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane; Noebe, Ronald D.; Padula, Santo A., II; Lerch, Bradley A.; Bigelow, Glen S.; Gaydosh, Darrell J.; Garg, Anita; An, Ke; Vaidyanathan, Raj

    2013-01-01

    The mechanical and microstructural behavior of a polycrystalline Ni(49.9)Ti(50.1) (at.%) shape memory alloy was investigated as a function of temperature around the transformation regime. The bulk macroscopic responses, measured using ex situ tensile deformation and impulse excitation tests, were compared to the microstructural evolution captured using in situ neutron diffraction. The onset stress for inelastic deformation and dynamic Young's modulus were found to decrease with temperature, in the martensite regime, reaching a significant minimum at approximately 80 C followed by an increase in both properties, attributed to the martensite to austenite transformation. The initial decrease in material compliance during heating affected the ease with which martensite reorientation and detwinning could occur, ultimately impacting the stress for inelastic deformation prior to the start of the reverse transformation.

  16. Structure-Property Relationship of Cu-Al-Ni-Fe Shape Memory Alloys in Different Quenching Media

    NASA Astrophysics Data System (ADS)

    Saud, Safaa N.; Hamzah, E.; Abubakar, T.; Farahany, S.

    2014-01-01

    This paper presents the effects of heat treatments using various quenching media on the phase transformation parameters and microstructure parameters. The effects of different quenching methods, step-quenched and up-quenched, in various media were evaluated by using differential scanning calorimetry, field emission electron microscopy, energy-dispersive spectrometry, atomic force microscopy, x-ray diffraction, and Vicker's hardness. The variations of the structure and properties of Cu-Al-Ni-Fe shape memory alloys were linked to the variations of morphology, type, and stabilization of the obtained phase. From the DSC results, the use of ice water as a quenching medium produced the highest transformation temperatures, while a brine solution-quenching medium resulted in the highest change of the entropy and enthalpy. Additionally, it was found that the best grain refinement was observed through the use of an oil-quenching medium, due to its high cooling rate.

  17. Structure and thermomechanical behavior of NiTiPt shape memory alloy wires.

    PubMed

    Lin, Brian; Gall, Ken; Maier, Hans J; Waldron, Robbie

    2009-01-01

    The objective of this work is to understand the structure-property relationships in polycrystalline NiTiPt (Ti 42.7 at.% Ni 7.5 at %Pt) with a composition showing pseudoelasticity at ambient temperatures. Structural characterization of the alloy includes grain size determination and texture analysis while the thermomechanical properties are explored using tensile testing. Variation in heat treatment is used as a vehicle to modify microstructure. The results are compared to experiments on Ni-rich NiTi alloy wires (Ti-51.0 at.% Ni), which are in commercial use in various biomedical applications. With regards to microstructure, both alloys exhibit a <111> fiber texture along the wire drawing axis; however, the NiTiPt alloy grain size is smaller than that of the Ni-rich NiTi wires, while the latter materials contain second-phase precipitates. Given the nanometer-scale grain size in NiTiPt and the dispersed, nanometer-scale precipitate size in NiTi, the overall strength and ductility of the alloys are essentially identical when given appropriate heat treatments. Property differences include a much smaller stress hysteresis and smaller temperature dependence of the transformation stress for NiTiPt alloys compared to NiTi alloys. Potential benefits and implications for use in vascular stent applications are discussed.

  18. Effect of aging on the phase transformation and mechanical behavior of Ti{sub 36}Ni{sub 49}Hf{sub 15} high temperature shape memory alloy

    SciTech Connect

    Meng, X.L.; Zheng, Y.F.; Wang, Z.; Zhao, L.C.

    2000-01-31

    The TiNiHf alloys are newly developed as high temperature shape memory alloys with the high transformation temperatures and with lower cost in comparison with TiNiX (X = Pd, Pt) alloys. Until now, no results about the effects of aging at high temperature (above 953K) in the TiNiHf alloys are reported. The purpose of the present work is to investigate the microstructure, transformation temperature, mechanical properties and shape memory effects (SMEs) for Ti{sub 36}Ni{sub 49}Hf{sub 15} alloy aged at 973K for different hours by transmission electron microscopy (TEM), X-ray diffraction (XRD) techniques, electrical resistance-temperature measurement, bending and tensile tests.

  19. X-ray Diffraction Investigations of Shape Memory NiTi Wire

    NASA Astrophysics Data System (ADS)

    Honarvar, Mohammad; Konh, Bardia; Podder, Tarun K.; Dicker, Adam P.; Yu, Yan; Hutapea, Parsaoran

    2015-08-01

    Outstanding properties of nitinol, known as shape memory and superelasticity, make them suitable alternatives in several biomedical, aerospace, and civil applications. For instance, nitinol wires have been used as the actuator components in many innovative medical devices aiming to make surgical tasks less invasive and more efficient. In most of these applications, it is desired to have a consistent strain response of nitinol wires; therefore, it is necessary to investigate the internal phase transformations from microstructural point of view. In this study, the effect of influencing factors such as biased stress during thermal cycle, the maximum temperature wires experienced during heating part of thermal cycle, and also wire diameters on the amount of unrecovered strain occurred between the first and the second thermal cycles has been investigated. The generation of different phase compositions in the same thermomechanical condition for different wire diameters has been discussed using x-ray diffraction (XRD) method. The location and intensity of characteristic peaks were studied prior and after the loading cycles. It was observed that nitinol wires of diameters less than 0.19 mm exhibit unrecovered strain while heated to the range of 70-80 °C in a thermal cycle, whereas no unrecovered strain was found in wires with larger diameter. The observation was supported by the XRD patterns where the formation of R-phase instead of martensite was shown in wire diameters of less than 0.19 mm after cooling back to room temperature.

  20. A new mechanical characterization method for thin film microactuators and its application to NiTiCi shape memory alloy

    SciTech Connect

    Seward, Kirk P.

    1999-06-01

    In an effort to develop a more full characterization tool of shape memory alloys, a new technique is presented for the mechanical characterization of microactuators and applied to SMA thin films. A test instrument was designed to utilize a spring-loaded transducer in measuring displacements with resolution of 1.5 pm and forces with resolution of 0.2 mN. Employing an out-of-plane loading method for freestanding SMA thin films, strain resolution of 30με and stress resolution of 2.5 MPa were achieved. This new testing method is presented against previous SMA characterization methods for purposes of comparison. Four mm long, 2 μm thick NiTiCu ligaments suspended across open windows were bulk micromachined for use in the out-of-plane stress and strain measurements. The fabrication process used to micromachine the ligaments is presented step-by-step, alongside methods of fabrication that failed to produce testable ligaments. Static analysis showed that 63% of the applied strain was recovered while ligaments were subjected to tensile stresses of 870 MPa. In terms of recoverable stress and recoverable strain, the ligaments achieved maximum recovery of 700 MPa and 3.0% strain. No permanent deformations were seen in any ligament during deflection measurements. Maximum actuation forces and displacements produced by the 4 mm ligaments situated on 1 cm square test chips were 56 mN and 300 μm, respectively. Fatigue analysis of the ligaments showed degradation in recoverable strain from 0.33% to 0.24% with 200,000 cycles, corresponding to deflections of 90 μm and forces of 25 mN. Cycling also produced a wavering shape memory effect late in ligament life, leading to broad inconsistencies of as much as 35% deviation from average. Unexpected phenomena like stress-induced martensitic twinning that leads to less recoverable stress and the shape memory behavior of long life devices are addressed. Finally, a model for design of microactuators using shape memory alloys is presented

  1. Shape Memory Effect and Superelasticity in [001] Single Crystals of Fe-Ni-Co-Al-Nb(B) Ferromagnetic Alloy

    NASA Astrophysics Data System (ADS)

    Chumlyakov, Yu. I.; Kireeva, I. V.; Kuts, O. A.; Panchenko, M. Yu.; Karaka, É.; Maier, H. J.

    2015-11-01

    Shape memory effect (SME) and superelasticity (SE) during thermoelastic martensitic transformation (MT) from the FCC high-temperature γ-phase to the BCT α'-martensite are investigated in Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% Nb (Nb) and Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% Nb - 0.05% B (NbB) (at.%) single crystals oriented for tension along the [001] direction after aging at 973 K for 10 h. Non-equiaxial (NiAl) β-phase particles with thickness d and length l equal to 60-80 and 340-500 nm, respectively, and volume fraction f ≥ 3-5% are precipitated in Nb crystals during aging simultaneously with the (FeNiCo)3(AlNb) γ´-phase with sizes d = 12.5-16.5 nm. It is shown that precipitation of the β-phase with f ≤ 3-5% in the crystal volume does not reduce the crystal plasticity, and SME of 4.2% and SE up to 6.5% under loading are observed during thermoelastic γ-α' MT in single crystals in a wide range of temperatures from 77 to 293 K. The β-phase is not detected in NbB crystals during aging. It is established that boron in NbB crystals slows down the aging processes: the γ'-phase particles have sizes 6.5-8 nm. The SME of 4.2% and SE up to 4.0% are observed in NbB crystals at temperatures from 77 to 243 K.

  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. Strain and texture evolution during mechanical loading of a crack tip in martensitic shape-memory NiTi.

    SciTech Connect

    Daymond, M. R.; Young, M. L.; Almer, J. D.; Dunand, D. C.; Queen's Univ.; Northwestern Univ.

    2007-06-01

    In situ synchrotron X-ray diffraction measurements are used to create two-dimensional maps of elastic strain and texture, averaged over a compact-tension specimen thickness, near a crack tip in a martensitic NiTi alloy. After fatigue crack propagation, the material ahead of the crack and in its wake exhibits a strong texture, which is eliminated by subsequent shape-memory heat treatment, indicating that this texture is due to detwinning, the main deformation mechanism of NiTi. Upon subsequent application of a static tensile stresses, the highly textured zone reappears and grows around the crack tip as the applied stress is increased. At the highest applied stress intensity of 35MPam1/2, large tensile strains are measured ahead of the crack tip and considerable elastic anisotropy is observed. This detwinning zone is similar to the plastic zone produced by dislocation slip present around cracks in other metals. The texture in this zone is not significantly altered after mechanical unloading, despite the development of substantial triaxial compressive residual strains in this zone.

  4. Large magnetic entropy change and magnetoresistance in a Ni41Co9Mn40Sn10 magnetic shape memory alloy

    DOE PAGES

    Huang, L.; Cong, D. Y.; Ma, L.; ...

    2015-07-02

    A polycrystalline Ni41Co9Mn40Sn10 (at. %) magnetic shape memory alloy was prepared by arc melting and characterized mainly by magnetic measurements, in-situ high-energy X-ray diffraction (HEXRD), and mechanical testing. A large magnetoresistance of 53.8% (under 5 T) and a large magnetic entropy change of 31.9 J/(kg K) (under 5 T) were simultaneously achieved. Both of these values are among the highest values reported so far in Ni-Mn-Sn-based Heusler alloys. The large magnetic entropy change, closely related to the structural entropy change, is attributed to the large unit cell volume change across martensitic transformation as revealed by our in-situ HEXRD experiment. Furthermore,more » good compressive properties were also obtained. Lastly, the combination of large magnetoresistance, large magnetic entropy change, and good compressive properties, as well as low cost makes this alloy a promising candidate for multifunctional applications.« less

  5. Stress analysis, structure and magnetic properties of sputter deposited Ni-Mn-Ga ferromagnetic shape memory thin films

    NASA Astrophysics Data System (ADS)

    Annadurai, A.; Manivel Raja, M.; Prabahar, K.; Kumar, Atul; Kannan, M. D.; Jayakumar, S.

    2011-11-01

    The residual stress instituted in Ni-Mn-Ga thin films during deposition is a key parameter influencing their shape memory applications by affecting its structural and magnetic properties. A series of Ni-Mn-Ga thin films were prepared by dc magnetron sputtering on Si(1 0 0) and glass substrates at four different sputtering powers of 25, 45, 75 and 100 W for systematic investigation of the residual stress and its effect on structure and magnetic properties. The residual stresses in thin films were characterized by a laser scanning technique. The as-deposited films were annealed at 600 °C for 1 h in vacuum for structural and magnetic ordering. The compressive stresses observed in as-deposited films transformed into tensile stresses upon annealing. The annealed films were found to be crystalline and possess mixed phases of both austenite and martensite, exhibiting good soft magnetic properties. It was found that the increase of sputtering power induced coarsening in thin films. Typical saturation magnetization and coercivity values were found to be 330 emu/cm 3 and 215 Oe, respectively. The films deposited at 75 and 100 W display both structural and magnetic transitions above room temperature.

  6. Effects of Ni addition on the magnetostriction and microstructures of Fe70-xPd30Nix high-temperature ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Lin, Yin-Chih; Lin, Chien-Feng

    2012-04-01

    This study investigated the effects of adding a third alloying element, Ni, to create Fe70-xPd30Nix (x = 2, 4, 6, and 8 at. % Ni) ferromagnetic shape memory alloys. The Ni replaced a portion of the Fe. The magnetostriction and microstructures of Fe70-xPd30Nix high-temperature ferromagnetic shape memory alloys were studied in detail. Investigation of the magnetostriction and microstructures indicated that the greater Ni amount in the Fe70-xPd30Nix alloys caused the less saturation magnetostriction at room temperature (RT); it was also observed that it was more difficult to generate an annealed recrystallization. However, greater Ni addition into the Fe70-xPd30Nix (x = 6 and 8 at. % Ni) alloys, the L10 + L1m twin phase decomposition into stoichiometric L10 + L1m + αbct structures could be suppressed when the alloys were aged at 500 °C for 100 h. The result was that the Fe70-xPd30Nix (x = 6 and 8 at. % Ni) alloys maintained a high magnetostriction and magnetostrictive susceptibility (Δλ‖s/ΔH) after the 500 °C/100 h aged treatment. This magnetic property of the Fe70-xPd30Nix (x = 6 and 8 at. % Ni) alloys is suitable for application in a high temperature (T > 500 °C) and high frequency environment.

  7. Radiopaque Shape Memory Alloys: NiTi-Er with Stable Superelasticity

    NASA Astrophysics Data System (ADS)

    Tuissi, Ausonio; Carr, Shane; Butler, James; Gandhi, Abbasi A.; O'Donoghue, Lisa; McNamara, Karrina; Carlson, James M.; Lavelle, Shay; Tiernan, Peter; Biffi, Carlo A.; Bassani, Paola; Tofail, Syed A. M.

    2016-06-01

    Binary NiTi alloy is one of the most important biomaterials currently used in minimally invasive procedures and indwelling devices. The poor visibility of intermetallic NiTi under X-ray could be an unsatisfactory feature especially for developing low-dimensional implantable devices for the body. It is a matter of fact that the alloying of a third radiopaque element, such as noble or heavy metals, in NiTi can significantly enhance the alloy's radiopacity. Recently, it was demonstrated that the addition of a rare earth element such as Erbium has led to an equivalent radiopacity at a much lower cost than the equivalent addition of noble metals. This work reviews the main physical aspects related to the radiopacity of NiTi alloys and compares the radiopacity of NiTi-Er compositions with other NiTi-based alloys containing Pd, Pt, W and Cr. Furthermore, a NiTi-6Er alloy is produced by spark plasma sintering, and successfully processed by conventional hot and cold working procedures to a continuous wire showing stable superelastic behaviour (up to 4 % in strain), suitable for developing biomedical devices.

  8. Preferred site occupation and magnetic properties of Ni-Fe-Ga-Co ferromagnetic shape memory alloys by first-principles calculations

    NASA Astrophysics Data System (ADS)

    Bai, Jing; Chen, Yue; Li, Ze; Jiang, Pan; Wei, Pu; Zhao, Xiang

    2016-12-01

    First-principles calculations have been used to investigate the effects of Co addition on the preferred site occupation and magnetic properties of Ni-Fe-Ga-Co ferromagnetic shape memory alloys. The formation energy results indicate that the excess Ni constituent preferentially occupies the Fe sites in the off-stoichiometric Ni-Fe-Ga ternary alloy. The added Co tends to take the normal-Ni sites in the Ni-Fe-Ga-Co quaternary alloy during composition adjustment process. The total magnetic moment increases with Co content of the Ni36-xFe12Ga16Cox (x=0, 1, 2, 3 and 4) alloys. The difference between the up and down electronic density of states at the Fermi level gives rise to the increased magnetic property.

  9. Crystallographic, magnetic, and electronic structures of ferromagnetic shape memory alloys Ni2XGa (X=Mn,Fe,Co) from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Bai, J.; Raulot, J. M.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.

    2011-01-01

    The crystallographic, magnetic and electronic structures of the ferromagnetic shape memory alloys Ni2XGa (X=Mn, Fe, and Co), are systematically investigated by means of the first-principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The lattice parameters of both austenitic and martensitic phases in Ni2MnGa have been calculated. The formation energies of the cubic phase of Ni2XGa are estimated, and show a destabilization tendency if Mn atom is substituted by Fe or Co. From Ni2MnGa to Ni2CoGa, the down spin total density of states (DOS) at Fermi level is gradually increasing, whereas that of the up spin part remains almost unchanged. This is the main origin of the difference of the magnetic moment in these alloys. The partial DOS is dominated by the Ni and Mn 3d states in the bonding region below EF. There are two bond types existing in Ni2XGa: one is between neighboring Ni atoms in Ni2MnGa; the other is between Ni and X atoms in Ni2FeGa and Ni2CoGa alloys.

  10. Plasma Arc Melting (PAM) and Corrosion Resistance of Pure NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Tuissi, A.; Rondelli, G.; Bassani, P.

    2015-03-01

    Plasma arc melting (PAM) as a suitable non-contaminating melting route for manufacturing high-quality NiTi alloy was successfully examined. The corrosion resistance of PAM Nitinol was evaluated by both potentiodynamic and potentiostatic tests and compared with lower purity NiTi produced by vacuum induction melting (VIM). For the electro-polished surfaces, excellent corrosion resistance of NiTi comparable with the Ti alloys was found with no pitting up to 800 mV versus saturated calomel electrode in simulated body fluid at 37 °C. Potentiostatic results of PAM Nitinol indicate slightly better corrosion resistance than the lower quality VIM alloy.

  11. The influence of the substrate on the adhesive strength of the micro-arc oxidation coating developed on TiNi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Hsieh, Shy-Feng; Ou, Shih-Fu; Chou, Chia-Kai

    2017-01-01

    TiNi shape memory alloys (SMAs), used as long-term implant materials, have a disadvantage. Ni-ion release from the alloys may trigger allergies in the human body. Micro-arc oxidation has been utilized to modify the surface of the TiNi SMA for improving its corrosion resistance and biocompatibility. However, there are very few reports investigating the essential adhesive strength between the micro-arc oxidized film and TiNi SMA. Two primary goals were attained by this study. First, Ti50Ni48.5Mo1.5 SMA having a phase transformation temperature (Af) less than body temperature and good shape recovery were prepared. Next, the Ti50Ni50 and Ti50Ni48.5Mo1.5 SMA surfaces were modified by micro-arc oxidation in phosphoric acid by applying relatively low voltages to maintain the adhesive strength. The results indicated that the pore size, film thickness, and P content increased with applied voltage. The micro-arc oxidized film, comprising Ti oxides, Ni oxide, and phosphate compounds, exhibited a glassy amorphous structure. The outmost surface of the micro-arc oxidized film contained a large amount of P (>12 at%) but only a trace of Ni (<5 at%). The adhesive strengths of all the micro-arc oxidized films exceeded the requirements of ISO 13779. Furthermore, Mo addition into TiNi SMAs was found to be favorable for improving the adhesive strength of the micro-arc oxidized film.

  12. Processing and Characterization of NiTi Shape Memory Alloy Particle Reinforced Sn-In Solders

    DTIC Science & Technology

    2006-12-01

    behavior of different phases of NiTi at constant temperature............................ 16 Figure 8. DSC curves of NiTi wire . Note that upon...cooling the wire transforms to R-phase prior to the martensitic transformation. Upon heating, the As and Af temperatures are similar, as the monoclinic...Copper Rod Interface .......................................... 40 Figure 19. Typical Micro-structure of the monolithic solder

  13. Empirical Study of the Multiaxial, Thermomechanical Behavior of NiTiHf Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Shukla, Dhwanil; Noebe, Ronald D.; Stebner Aaron P.

    2013-01-01

    An empirical study was conducted to characterize the multiaxial, thermomechanical responses of new high temperature NiTiHf alloys. The experimentation included loading thin walled tube Ni(sub 50.3)Ti(sub 29.7)Hf(sub 20) alloy samples along both proportional and nonproportional axial-torsion paths at different temperatures while measuring surface strains using stereo digital image correlation. A Ni(sub 50.3)Ti(sub 33.7)Hf(sub 16) alloy was also studied in tension and compression to document the effect of slightly depleting the Hf content on the constitutive responses of NiTiHf alloys. Samples of both alloys were made from nearly texture free polycrystalline material processed by hot extrusion. Analysis of the data shows that very small changes in composition significantly alter NiTiHf alloy properties, as the austenite finish (Af) temperature of the 16-at Hf alloy was found to be approximately 60 C less than the 20-at Hf alloy (approximately 120 C vs. 180 C). In addition, the 16-at Hf alloy exhibited smaller compressive transformation strains (2 vs. 2.5 percent). Multi-axial characterization of the 20-at % Hf alloy showed that while the random polycrystal transformation strains in tension (4 percent) and compression (2.5 percent) are modest in comparison with binary NiTi (6 percent, 4 percent), the torsion performance is superior (7 vs. 4 shear strain width to the pseudoelastic plateau).

  14. Fiber laser micromachining of thin NiTi tubes for shape memory vascular stents

    NASA Astrophysics Data System (ADS)

    Liu, Lei; Li, Dong Bo; Tong, Yi Fei; Zhu, Yu Fu

    2016-07-01

    Nickel titanium (NiTi) alloy has widely been used in the vascular stent manufacturing due to its excellent properties. Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser is commonly used for the preparation of metal vascular stents. Recently, fiber lasers have been used for stent profiling for better cutting quality. To investigate the cutting-kerf characters of NiTi vascular stents fabricated by fiber laser cutting, laser cutting experiments with thin NiTi tubes were conducted in this study, while NiTi sheets were used in other fiber laser cutting studies. Different with striation topography, new topographies such as layer topography and topography mixed with layers and striations were observed, and the underlying reason for new topographies was also discussed. Comparative research on different topographies was conducted through analyzing the surface roughness, kerf width, heat-affected zone (HAZ) and dross formation. Laser cutting process parameters have a comprehensive influence on the cutting quality; in this study, the process parameters' influences on the cutting quality were studied from the view of power density along the cutting direction. The present research provides a guideline for improving the cutting quality of NiTi vascular stents.

  15. A Novel Training-Free Processed Fe-Mn-Si-Cr-Ni Shape Memory Alloy Undergoing δ → γ Phase Transformation

    NASA Astrophysics Data System (ADS)

    Peng, Huabei; Wang, Gaixia; Du, Yangyang; Wang, Shanling; Chen, Jie; Wen, Yuhua

    2016-07-01

    We not only suppress the formation of twin boundaries but also introduce a high density of stacking faults by taking advantage of δ → γ phase transformation in a processed Fe-19.38Mn-5.29Si-8.98Cr-4.83Ni shape memory alloy. As a result, its shape memory effect is remarkably improved after heating at 1533 K (1260 °C) (single-phase region of δ ferrite) and air cooling due to δ → γ phase transformation.

  16. Machining and Phase Transformation Response of Room-Temperature Austenitic NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Kaynak, Yusuf

    2014-09-01

    This experimental work reports the results of a study addressing tool wear, surface topography, and x-ray diffraction analysis for the finish cutting process of room-temperature austenitic NiTi alloy. Turning operation of NiTi alloy was conducted under dry, minimum quantity lubrication (MQL) and cryogenic cooling conditions at various cutting speeds. Findings revealed that cryogenic machining substantially reduced tool wear and improved surface topography and quality of the finished parts in comparison with the other two approaches. Phase transformation on the surface of work material was not observed after dry and MQL machining, but B19' martensite phase was found on the surface of cryogenically machined samples.

  17. Constitutive model for the dynamic response of a NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Shi, Xiaohong; Zeng, Xiangguo; Chen, Huayan

    2016-07-01

    In this paper, based on irreversible thermodynamic theory, the Helmholtz free energy function, was selected to deduce both the master equations and evolution equations of the constitutive model of a NiTi alloy under high strain. The Helmholtz free energy function contains the parameters of the reflecting phase transition and plastic property. The constitutive model for a NiTi alloy was implemented using a semi-implicit stress integration algorithm. Four successive stages can be differentiated and simulated: parent phase elasticity, martensitic phase transition, martensitic elasticity, and dislocation yield. The simulation results are in good agreement with the experimental results.

  18. Shape memory alloys. Ultralow-fatigue shape memory alloy films.

    PubMed

    Chluba, Christoph; Ge, Wenwei; Lima de Miranda, Rodrigo; Strobel, Julian; Kienle, Lorenz; Quandt, Eckhard; Wuttig, Manfred

    2015-05-29

    Functional shape memory alloys need to operate reversibly and repeatedly. Quantitative measures of reversibility include the relative volume change of the participating phases and compatibility matrices for twinning. But no similar argument is known for repeatability. This is especially crucial for many future applications, such as artificial heart valves or elastocaloric cooling, in which more than 10 million transformation cycles will be required. We report on the discovery of an ultralow-fatigue shape memory alloy film system based on TiNiCu that allows at least 10 million transformation cycles. We found that these films contain Ti2Cu precipitates embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle.

  19. Effect of morphology on exchange bias in NiMnSn and NiCoMnIn magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Lapa, Pavel N.; Monroe, James A.; Franco, Brian E.; Karaman, Ibrahim; Roshchin, Igor V.

    2014-03-01

    Exchange bias (EB) is one of puzzling magnetic properties of magnetic shape memory alloys (MSMA). Despite a few attempts to explain the mechanism, there is no comprehensive model describing it. The main obstacle is the lack of information about the magnetic structure of martensitic and austenite phases. In contrast to classical EB systems where the exchange coupling happens at the interface between ferromagnetic and antiferromagnetic layers, the EB in MSMA is attributed to coexistence of ferromagnetic and antiferromagnetic regions. We report the results of structural analysis obtained using wavelength-dispersive X-ray spectroscopy (WDS) and magnetic characterization of these samples. We observe a correlation of EB with the secondary heat treatment for NiCoMnIn alloys. Comparative first order reversal curve (FORC) analysis for NiMnSn samples with different heat treatment suggests a correlation between morphology and distribution of exchange bias values. Additionally, exchange bias in these alloys can be induced even after zero-field cooling by applying a constant field for 2 hours before measuring the magnetization curve. This behavior is consistent with magnetic glassiness observed in these alloys at low temperatures. The work is funded by TAMU and US NSF-DMR MMN program/MWN initiative grant 1108396.

  20. High Temperature Magnetic Shape Memory Ni-Mn-Ga Alloys for a New Class of Actuators and Sensor

    DTIC Science & Technology

    2005-01-01

    sensors. Specifics of the project are: (i) the complex theoretical and experimental study of a correlation between electronic, magnetic, and crystalline ... structure and the phase transformation temperatures with occurrence of magnetic shape memory effect (MSME) using various experimental techniques and

  1. Shape memory and transformation behavior of high strength 60NiTi in compression

    NASA Astrophysics Data System (ADS)

    Kaya, I.

    2016-12-01

    This study investigates the transformation behavior of highly Ni-rich 60NiTi alloys after aging at 600 °C for 3 h. After 600 °C-3h aging, R-phase disappeared and alloy transformed in one step. The latent heats of austenite to martensite and martensite to austenite transformations were 13 Jg-1 and 16.4 Jg-1, respectively, for 600 °C-3h aged alloy. The elastic strain energy of 0.75 Jg-1 was obtained in aged alloy. The maximum recoverable transformation strain of 1.7% is obtained under 500 MPa in compression. The superelastic behavior was observed accompanied with a recoverable strain of 1.4%, even high stress level of 1000 MPa is applied.

  2. Deformation behavior of Nb nanowires in TiNiCu shape memory alloy matrix

    DOE PAGES

    Jiang, Daqiang; Liu, Yinong; Yu, Cun; ...

    2015-08-18

    An in-situ nanowire Nb/TiNiCu composite is fabricated based on the concept of strain under-matching between a phase transforming matrix and high strength nanomaterials. The deformation behavior of the Nb nanowire was investigated by means of in-situ synchrotron X-ray diffraction when the TiNiCu matrix underwent different deformation modes. The maximum lattice strain of the Nb nanowires was about 5% when the matrix deformed via martensitic transformation or 1% when deforming plastically by dislocation slip. As a result, the Nb nanowires showed a lattice strain of 3.5% when the matrix deformed in the mixed mode of plastic deformation and martensitic transformation, whichmore » means that the occurrence of plastic deformation does not impede load transfer from the matrix to the nanowires.« less

  3. Deformation behavior of Nb nanowires in TiNiCu shape memory alloy matrix

    SciTech Connect

    Jiang, Daqiang; Liu, Yinong; Yu, Cun; Liu, Weilong; Yang, Hong; Jiang, Xiaohua; Ren, Yang; Cui, Lishan

    2015-08-18

    An in-situ nanowire Nb/TiNiCu composite is fabricated based on the concept of strain under-matching between a phase transforming matrix and high strength nanomaterials. The deformation behavior of the Nb nanowire was investigated by means of in-situ synchrotron X-ray diffraction when the TiNiCu matrix underwent different deformation modes. The maximum lattice strain of the Nb nanowires was about 5% when the matrix deformed via martensitic transformation or 1% when deforming plastically by dislocation slip. As a result, the Nb nanowires showed a lattice strain of 3.5% when the matrix deformed in the mixed mode of plastic deformation and martensitic transformation, which means that the occurrence of plastic deformation does not impede load transfer from the matrix to the nanowires.

  4. 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.

  5. Modeling of hydrogen effect on the superelastic behavior of Ni-Ti shape memory alloy wires

    NASA Astrophysics Data System (ADS)

    Lachiguer, Amani; Bouby, Céline; Gamaoun, Fehmi; Bouraoui, Tarak; Ben Zineb, Tarak

    2016-11-01

    Superelastic NiTi wires are widely used in orthodontic treatments, but sometimes fracture can be observed after few months of use in buccal cavity and attributed to the degradation of NiTi mechanical properties due to hydrogen absorption. In this paper, a modeling approach is proposed in order to describe the effect of hydrogen diffusion on the transformation properties of NiTi SMAs. In order to experimentally predict such effects, cathodic hydrogen charging was performed at a current density of 10 A/{m}2 for 6h, 24h, 48h and 72h in 0.9% NaCl aqueous solution at room temperature. Tensile tests were carried out shortly after hydrogen charging. The obtained stress-strain curves showed an increase of yield transformation stresses for forward and reverse martensitic transformations and a decrease of maximum transformation strain. Using Fick’s second law, the transformation temperatures variation can be expressed as a function of the mean concentration of absorbed hydrogen and then taked into account in the SMA constitutive model developed by Chemisky et al (2011). The numerical results are compared to the experimental ones to calibrate the proposed method. Simulations showed that hydrogen diffusion induces a shifting of transfomation temperatures, a decreasing of maximum transformation strain and an increasing of yield transfomation stresses.

  6. Use of a Ni60Ti shape memory alloy for active jet engine chevron application: II. Experimentally validated numerical analysis

    NASA Astrophysics Data System (ADS)

    Hartl, D. J.; Mooney, J. T.; Lagoudas, D. C.; Calkins, F. T.; Mabe, J. H.

    2010-01-01

    A shape memory alloy (SMA) composition of Ni60Ti40 (wt%) was chosen for the fabrication of active beam components used as cyclic actuators and incorporated into morphing aerospace structures. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich NiTi composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization. The second part of this two-part work focuses on the numerical modeling of the jet engine chevron application, where the end goal is the accurate prediction of the VGC actuation response. A three-dimensional (3D) thermomechanical constitutive model is used for the analysis and is calibrated using the axial testing results from part I. To best capture the material response, features of several SMA constitutive models proposed in the literature are combined to form a new model that accounts for two material behaviors not previously addressed simultaneously. These are the variation in the generated maximum actuation strain with applied stress level and a smooth strain-temperature constitutive response at the beginning and end of transformation. The accuracy of the modeling effort is assessed by comparing the analysis deflection predictions for a given loading path imposed on the VGC or its subcomponents to independently obtained experimental results consisting of photogrammetric data. For the case of full actuation of the assembled VGC, the average error in predicted centerline deflection is less than 6%.

  7. Shape memory characteristics and mechanical properties of powder metallurgy processed Ti50Ni40Cu10 alloy.

    PubMed

    Kim, Yeon-Wook

    2014-10-01

    Ti-Ni-Cu alloy powders were prepared by gas atomization and porous bulk specimens were fabricated by spark plasma sintering (SPS). The microstructure of as-solidified powders exhibited a cellular structure and they contained a high density of nano-sized porosities which were located in the intercellular regions. XRD analysis showed that one-step martensitic transformation of B2-B19 occurred in all alloy powders and SPS specimens. When the martensitic transformation start temperature (M(s)) and austenite transformation finish temperature (A(f)) were determined in order to analyze the dependence of powder size on transformation temperatures, the M(s) increased slightly from -17.5 degrees C to - 14.6 degrees C as increasing the powder size ranging from between 25 and 50 μm to ranging between 100 and 150 μm. However, the M(s) and A(f) of the as-atomized powders is much smaller than those of SPS specimens and the M(s) of porous specimen was about 10.9 degrees C. Loading-unloading compressive tests were carried out to investigate the mechanical properties of porous Ti-Ni-Cu specimen. The specimen was compressed to the strain of 6% at a temperature higher than A,. After unloading, the residual strain was 2.1%. After the compressed specimen was heated to 60 degrees C and held for 30 minutes and then cooled to room temperature, the changes in the length of the specimens were measured. Then it was found that the recovered strain ascribed to shape memory effect was 1.5%.

  8. Composition, Compatibility, and the Functional Performances of Ternary NiTiX High-Temperature Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Bucsek, Ashley N.; Hudish, Grant A.; Bigelow, Glen S.; Noebe, Ronald D.; Stebner, Aaron P.

    2016-03-01

    A general procedure to optimize shape memory alloys (SMAs) for specific engineering performance metrics is outlined and demonstrated through a study of ternary, NiTiX high-temperature SMAs, where X = Pd, Hf, Zr. Transformation strains are calculated using the crystallographic theory of martensite and compared to the cofactor conditions, both requiring only lattice parameters as inputs. Measurements of transformation temperatures and hysteresis provide additional comparisons between microstructural-based and transformation properties. The relationships between microstructural-based properties and engineering performance metrics are then thoroughly explored. Use of this procedure demonstrates that SMAs can be tuned for specific applications using relatively simple, fast, and inexpensive measurements and theoretical calculations. The results also indicate an overall trade-off between compatibility and strains, suggesting that alloys may be optimized for either minimal hysteresis or large transformation strains and work output. However, further analysis of the effects of aging shows that better combinations of uncompromised properties are possible through solid solution strengthening.

  9. Phase Transformation and Creep Behavior in Ti50Pd30Ni20 High Temperature Shape Memory Alloy in Compression

    NASA Technical Reports Server (NTRS)

    Kumar, Parikshith K.; Desai, Uri; Monroe, James; Lagoudas, Dimitris C.; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glenn

    2010-01-01

    The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

  10. Experimental Study of the Biaxial Cyclic Behavior of Thin-Wall Tubes of NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Wang, X. M.; Zhou, Q. T.; Liu, H.; Deng, C. H.; Yue, Z. F.

    2012-11-01

    Combined torsion-tension cycling experiments were performed on thin-wall tubes (with thickness/radius ratio of 1:20, similar to that found for stents) of nearly equiatomic NiTi shape memory alloys (SMAs). Experiments were controlled by axial displacement and torsional angle with step loading involving torsional loading to a maximum strain, followed by tensile loading, and reverse-order unloading. The superelasticity of the material is confirmed by pure torsion and tension experiments at the test temperature. The evolution of equivalent stress-strain curves as well as the separated tensile and torsional stress-strain curves during cycling is analyzed. Results show that the equivalent stress increases greatly with a small amount of applied axial strain, and the equivalent stress-strain curves have negative slopes in the phase transformation region. The shear stress drops when the torsional strain is maintained at its maximum value and the tensile strain is increased. The shear stress increases with decreasing tensile strain, but it cannot recover to the original value after the complete unloading of the tensile strain. Attention is also paid to dissipated energy density and characteristic stress evolutions during cycling.

  11. Ellipsometry applied to phase transitions and relaxation phenomena in Ni2MnGa ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Dejneka, A.; Zablotskii, V.; Tyunina, M.; Jastrabik, L.; Pérez-Landazábal, J. I.; Recarte, V.; Sánchez-Alarcos, V.; Chernenko, V. A.

    2012-10-01

    The temperature dependences of the refractive index, n(T), calculated from ellipsometric data during the premartensitic and martensite transitions in a Ni2MnGa ferromagnetic shape memory alloy allow to detect all critical temperatures of the sample. The performed measurements reveal the behavior of a surface layer of a few tens nanometers depth due to the light absorption. Optical measurements reveal the earlier onset of premartensitic transition at the sample surface and shows unknown new features like time and temperature dependent effects related to the crystal surface. The underlying mechanisms of the observed temperature changes of the equilibrium n0 may be related to temperature dependent interactions between free electrons and phonons as well as between electrons and defects. A giant isothermal creep (up to 20%) of the refractive index was found for temperatures below T0 = 315 K. Below T0 the creep amplitude grows with the temperature difference T0-T. The creep disappears and the relaxation time becomes zero at temperatures above T0.

  12. Effect of atomic order on the martensitic and magnetic transformations in Ni-Mn-Ga ferromagnetic shape memory alloys.

    PubMed

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

    2010-04-28

    The influence of long-range L2(1) atomic order on the martensitic and magnetic transformations of Ni-Mn-Ga shape memory alloys has been investigated. In order to correlate the structural and magnetic transformation temperatures with the atomic order, calorimetric, magnetic and neutron diffraction measurements have been performed on polycrystalline and single-crystalline alloys subjected to different thermal treatments. It is found that both transformation temperatures increase with increasing atomic order, showing exactly the same linear dependence on the degree of L2(1) atomic order. A quantitative correlation between atomic order and transformation temperatures has been established, from which the effect of atomic order on the relative stability between the structural phases has been quantified. On the other hand, the kinetics of the post-quench ordering process taking place in these alloys has been studied. It is shown that the activation energy of the ordering process agrees quite well with the activation energy of the Mn self-diffusion process.

  13. Large field-induced irreversibility in Ni-Mn based Heusler shape-memory alloys: A pulsed magnetic field study

    NASA Astrophysics Data System (ADS)

    Nayak, A. K.; Mejia, C. Salazar; D'Souza, S. W.; Chadov, S.; Skourski, Y.; Felser, C.; Nicklas, M.

    2014-12-01

    We present a pulsed magnetic field study on the magnetic and magnetostriction properties of Ni-Mn-Z (Z =In , Sn, and Sb) based Heusler shape-memory alloys. These materials generally display a field-induced magnetostructural transition that could lead to an irreversible phase transition, when measured near the martensitic transition temperature. Here, we show that independently of the transition temperature, the critical field for the phase transition sensitively depends on the main-group element in the sample. Irrespective of their compositions, all samples display a magnetization of around 2 μB/f .u . in the martensite phase and about 6 μB/f .u . in the cubic austenite phase. Our magnetic and magnetostriction measurements at low temperatures exhibit a partial or complete arrest of the high-field austenite phase below the reverse martensitic transition. This results in a large irreversibility with a hysteresis width as high as 24 T. We introduce a theoretical model to discuss the experimental results.

  14. Constitutive modeling of tension-torsion coupling and tension-compression asymmetry in NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Mehrabi, Reza; Kadkhodaei, Mahmoud; Elahinia, Mohammad

    2014-07-01

    A three-dimensional phenomenological model based on microplane theory is extended to capture the coupling effects between tension and torsion in complex multiaxial loadings. Inelastic strain in a microplane approach is a component of transformation strain and anisotropic strain. Since the anisotropy effect is induced during martensitic transformation, anisotropic strain is defined as a function of transformation strain. Out-of-plane strain is induced in simple tension and pure torsion in free-end conditions. Anisotropy tensor is experimentally extracted and is used in the proposed model to predict the behavior in multiaxial loading. The ability of this extended microplane model to predict the tension-torsion coupling effects as well as the induced transformation anisotropic behavior of NiTi shape memory alloys is demonstrated. In addition, the microplane model is modified to capture the asymmetric behavior in tension and compression during uniaxial and multiaxial loadings. To this end, numerical correlations between the results of the modified microplane model are compared with experimental results to demonstrate the validity of the extended model.

  15. Superelasticity of Cu-Ni-Al shape-memory fibers prepared by melt extraction technique

    NASA Astrophysics Data System (ADS)

    Li, Dong-yue; Zhang, Shu-ling; Liao, Wei-bing; Geng, Gui-hong; Zhang, Yong

    2016-08-01

    In the paper, a melt extraction method was used to fabricate Cu-4Ni-14Al (wt%) fiber materials with diameters between 50 and 200 μm. The fibers exhibited superelasticity and temperature-induced martensitic transformation. The microstructures and superelasticity behavior of the fibers were studied via scanning electron microscopy (SEM) and a dynamic mechanical analyzer (DMA), respectively. Appropriate heat treatment further improves the plasticity of Cu-based alloys. The serration behavior observed during the loading process is due to the multiple martensite phase transformation.

  16. Strain rate response of a Ni-Ti shape memory alloy after hydrogen charging

    NASA Astrophysics Data System (ADS)

    Gamaoun, Fehmi; Hassine, Tarak; Bouraoui, Tarak

    2014-01-01

    In this work, we investigate the susceptibility of Ni-Ti superelastic wires to the strain rates during tensile testing after hydrogen charging. Cathodic hydrogen charging is performed at a current density of 10 A/m² during 2-12 h in 0.9% NaCl solution and aged for 24 h at room temperature. Specimens underwent one cycle of loading-unloading reaching a stress value of 700 MPa. During loading, strain rates from 10-6 to 5 × 10-2 s-1 have been achieved. After 8 h of hydrogen charging, an embrittlement has been detected in the tensile strain rate range of 10-6 to 10-4 s-1. In contrast, no embrittlement has been detected for strain rates of 10-3 s-1 and higher. However, after 12 h of hydrogen charging and 24 h of annealing at room temperature, the embrittlement occurs in the beginning of the austenite-martensite transformation for all the studied strain rate values. These results show that for a range of critical amounts of diffused hydrogen, the embrittlement of the Ni-Ti superelastic alloy strongly depends on the strain rate during the tensile test. Moreover, it has been shown that this embrittlement occurs for low values of strain rates rather than the higher ones. This behaviour is attributed to the interaction between the diffused hydrogen and growth of the martensitic domain.

  17. Fundamental Development on Utilizing the R-phase Transformation in NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Wang, Xiebin; Kustov, Sergey; Verlinden, Bert; Van Humbeeck, Jan

    2015-06-01

    In near equiatomic NiTi alloys, the reversible thermoelastic transformation between B2-structured austenite phase and the R-phase is attracting increasing interest for practical applications. However, the following two issues limit the widespread utilization of the R-phase transformation: (1) there is no effective approach to control the R-phase transformation temperatures; (2) it is not easy to largely separate the temperature domain of the R-phase and the B19' martensite phase transformation, especially in the presence of an external force. This article reviews concisely the work of the present authors on solving the above two problems. The effect of grain size on the aging microstructure and related transformation behavior is first discussed. Inspired by these findings, an approach to solve the above two problems has been developed by introducing nanoscaled Ni4Ti3 precipitates in the samples with micron-sized grains. The performance of alloys associated with the R-phase transformation, which shows controllable transformation temperatures, is summarized.

  18. EBSD studies of microstructure and texture in Ni-Ti-Co shape memory strip and ribbon.

    PubMed

    Goryczka, T

    2010-03-01

    The electron back scattered diffraction method was applied for carrying out detailed surface studies of the ternary Ni-Ti-Co alloy produced using melt-spinning and twin roll casting techniques. The samples were studied in the as-cast state without grinding or polishing. It was found that in the melt-spun ribbon apart from fine narrow columnar grains, that extended along the ribbon thickness, wider columnar grains parallel to the ribbon surface were also observed. These grains were textured along the {100}011 orientation. The twin roll cast strip revealed more complex and inhomogeneous morphology of its surface. Mainly, the axes of the grains were oriented along two textural components: 100 for the fine grains and {100}011 for the columnar grains parallel to the surface. In addition to the results obtained from the X-ray diffraction, the electron back scattered diffraction technique revealed the 111 fibre texture in the sample.

  19. Initial oxidation of pure and K doped NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Tollefsen, H.; Raaen, S.

    2009-06-01

    Initial oxidation of pure and K doped nitinol has been studied by photoelectron spectroscopy. The composition of the TiOx layer that forms on the surface is found to depend on the temperature during oxidation. The oxidation at high temperatures results in enhanced formation of lower oxides, whereas TiO2 predominates for oxidation at lower temperatures, e.g., 70 °C. Submonolayer coverage of K on NiTi enhances the formation of TiO2 on the expense of lower oxides, which is of consequence for formation of a protective oxide layer and biocompatibility. Oxidation in the martensitic phase was found to be independent of temperature for temperatures between -40 and 10 °C, whereas in the austenitic phase the oxide growth is thermally activated.

  20. In vitro response of preosteoblastic MG63 cells on Ni-free Ti shape memory substrates.

    PubMed

    Arciniegas, M; Peña, J; Gil, F J; Manero, J M

    2013-07-01

    Ni-free Ti alloys are a potential strategy to overcome the risk of Ni-adverse reactions and rigidity mismatch for implant materials. Here, we report the biological behavior induced for two promising candidate alloys--Ti19.1Nb8.8Zr (M(S) temperature of 46°C and elastic modulus of 74 GPa) and Ti41.2Nb6.1Zr (elastic modulus of 67 GPa)--on cultured MG63 cells, as well as their physical and chemical properties. Contact angle results revealed the hydrophobic character of the former alloy (59.02° ± 2.35°) attributed to the presence of the martensitic phase, while the latter one presented a hydrophilic response (67.77° ± 2.78°). Results showed also that the cell adhesion response (after 4 and 8 h of incubation) in both substrates was not statistically different to that obtained in the cp Ti as control material. These surfaces induced well spread cell morphology with cytoplasmic extension like filopodia of up to 100 μm even at short culture times and presented an uninterrupted proliferation after longer incubation times (9 days). A decrement in the proliferation rate was appreciated from the Ti19.1Nb8.8Zr surface at that time, which was attributed to an earlier activation of the cell differentiation stage, as confirmed by the twofold increment of alkaline phosphatase activity. The results also evidenced that the presence of a 2 nm thick layer of amorphous Nb₂O₅, which was detected on both alloys, has a significant effect on cell behavior favoring the cell adhesion and morphology response of the new alloys studied.

  1. The martensitic transformation, magnetocaloric effect, and magnetoresistance in high-Mn content Mn47+xNi43-xSn10 ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Xuan, H. C.; Zheng, Y. X.; Ma, S. C.; Cao, Q. Q.; Wang, D. H.; Du, Y. W.

    2010-11-01

    A series of high-Mn content Mn47+xNi43-xSn10 (x=0, 1, 2, 3, 4, and 5) ferromagnetic shape memory alloys were prepared by arc melting method. The martensitic transformation were observed in these alloys, even the content of Mn is higher than 50 at. %. The phase transition temperature of these alloys can be adjusted by tuning the compositions of Ni and Mn. Large positive magnetic entropy change and negative magnetoresistance which originate from the magnetic-field-induced martensitic transformation are obtained in these alloys.

  2. On the Transformation Behavior of NiTi Shape-Memory Alloy Produced by SLM

    NASA Astrophysics Data System (ADS)

    Speirs, Mathew; Wang, X.; Van Baelen, S.; Ahadi, A.; Dadbakhsh, S.; Kruth, J.-P.; Van Humbeeck, J.

    2016-12-01

    Selective laser melting has been applied as a production technique of nickel titanium (NiTi) parts. In this study, the scanning parameters and atmosphere control used during production were varied to assess the effects on the final component transformation criteria. Two production runs were completed: one in a high ( 1800 ppm O2) and one in a low-oxygen ( 220 ppm O2) environment. Further solution treatment was applied to analyze precipitation effects. It was found that the transformation temperature varies greatly even at identical energy densities highlighting the need for further in-depth investigations. In this respect, it was observed that oxidation was the dominating factor, increased with higher laser power adapted to higher scanning velocity. Once the atmospheric oxygen content was lowered from 1800 to about 220 ppm, a much smaller variation of transformation temperatures was obtained. In addition to oxidation, other contributing factors, such as nickel depletion (via evaporation during processing) as well as thermal stresses and textures, are further discussed and/or postulated. These results demonstrated the importance of processing and material conditions such as O2 content, powder composition, and laser scanning parameters. These parameters should be precisely controlled to reach desired transformation criteria for functional components made by SLM.

  3. Challenges and Progress in the Development of High-Temperature Shape Memory Alloys Based on NiTiX Compositions for High-Force Actuator Applications

    NASA Technical Reports Server (NTRS)

    Padula, Santo, II; Bigelow, Glen; Noebe, Ronald; Gaydosh, Darrell; Garg, Anita

    2006-01-01

    Interest in high-temperature shape memory alloys (HTSMA) has been growing in the aerospace, automotive, process control, and energy industries. However, actual materials development has seriously lagged component design, with current commercial NiTi alloys severely limited in their temperature capability. Additions of Pd, Pt, Au, Hf, and Zr at levels greater than 10 at.% have been shown to increase the transformation temperature of NiTi alloys, but with few exceptions, the shape memory behavior (strain recovery) of these NiTiX systems has been determined only under stress free conditions. Given the limited amount of basic mechanical test data and general lack of information regarding the work attributes of these materials, a program to investigate the mechanical behavior of potential HTSMAs, with transformation temperatures between 100 and 500 C, was initiated. This paper summarizes the results of studies, focusing on both the practical temperature limitations for ternary TiNiPd and TiNiPt systems based on the work output of these alloys and the ability of these alloys to undergo repeated thermal cycling under load without significant permanent deformation or "walking". These issues are ultimately controlled by the detwinning stress of the martensite and resistance to dislocation slip of the individual martensite and austenite phases. Finally, general rules that govern the development of useful, high work output, next-generation HTSMA materials, based on the lessons learned in this work, will be provided

  4. Precipitation Behavior of Thermo-Mechanically Treated Ti50Ni20Au20Cu10 High-Temperature Shape-Memory Alloy

    NASA Astrophysics Data System (ADS)

    Kayani, Saif Haider; Imran Khan, M.; Khalid, Fazal Ahmad; Kim, Hee Young; Miyazaki, Shuichi

    2016-03-01

    In the present work, precipitation behavior of TiNiAuCu-based high-temperature shape-memory alloys is studied. Two alloys with compositions Ti50Ni30Au20 and Ti50Ni20Au20Cu10 were prepared. After 30 % cold rolling, both alloys were then annealed at different temperatures. Formation of Cu-rich TiAuCu and Ti-rich Ti3Au precipitates was observed in Ti50Ni20Au20Cu10 alloy when annealed at different temperatures after cold deformation. It was noticed that prior cold deformation has significant effect on the precipitation behavior. A similar kind of precipitation behavior has been previously reported in TiNiPdCu alloys. Both TiAuCu and Ti3Au type precipitates were found to be deficient in Ni content which causes an increase in Ni content of the matrix and a small decrease in transformation temperatures of the Ti50Ni20Au20Cu10 alloy.

  5. Shape memory polymer medical device

    DOEpatents

    Maitland, Duncan; Benett, William J.; Bearinger, Jane P.; Wilson, Thomas S.; Small, IV, Ward; Schumann, Daniel L.; Jensen, Wayne A.; Ortega, Jason M.; Marion, III, John E.; Loge, Jeffrey M.

    2010-06-29

    A system for removing matter from a conduit. The system includes the steps of passing a transport vehicle and a shape memory polymer material through the conduit, transmitting energy to the shape memory polymer material for moving the shape memory polymer material from a first shape to a second and different shape, and withdrawing the transport vehicle and the shape memory polymer material through the conduit carrying the matter.

  6. Effects of deformation on microstructure and mechanical properties of a Cu-Al-Ni shape memory alloy

    SciTech Connect

    Sari, U. Kirindi, T.

    2008-07-15

    In Cu-11.92 wt.%Al-3.78 wt.%Ni shape memory alloy, the influence of deformation and thermal treatments on the microstructure and mechanical properties under the compression test were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). Experiments show that the mechanical properties of the alloy can be enhanced by convenient heat treatments. The alloy exhibits good mechanical properties with high ultimate compression strength and ductility after annealing at high temperature. However, it exhibits brittle fracture and dramatic strain hardening, with linear stress-strain behavior after annealing at low temperature. The changes in the mechanical properties have been linked to the evolution of the degree of order, occurrence of precipitation, and variation of the grain size. From microstructural observations, it is seen that the {beta}{sub 1}' (18R) and {gamma}{sub 1}' (2H) martensite phases coexist at different fractions in the undeformed and deformed states. Deformation induces the changes between the {beta}{sub 1}' and {gamma}{sub 1}' martensites and deformation-induced martensites form at preferred orientations as mechanical twins. The {beta}{sub 1}' martensite variants are twin-related with respect to the (1-bar 2-bar 8){sub 18R} mirror plane and a new orientation relationship for these twin variants is derived as (1-bar 2-bar 8){sub A}-parallel (1-bar 2-bar 8){sub C}: [4-bar 61] {sub A}-parallel [4-bar 61]{sub C}. Additionally, an increase in the amount of deformation causes martensite reorientation, de-twinning, and dislocation generation; also, the martensite plates are seen to have rearranged in the same orientation to be parallel with each other.

  7. Use of a Ni60Ti shape memory alloy for active jet engine chevron application: I. Thermomechanical characterization

    NASA Astrophysics Data System (ADS)

    Hartl, D. J.; Lagoudas, D. C.; Calkins, F. T.; Mabe, J. H.

    2010-01-01

    A shape memory alloy (SMA) with a composition of Ni60Ti40 (wt%) was chosen for the fabrication of active beam elements intended for use as cyclic actuators and incorporated into a morphing aerospace structure. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization. The characterization performed in part I of this work was intended to provide quantitative information used to predict the response of SMA beam actuators of the same composition and with the same heat treatment history. Material in the form of plates was received and ASTM standard tensile testing coupons were fabricated and tested. To fully characterize the material response as an actuator, various thermomechanical experiments were performed. Properties such as actuation strain and transformation temperatures as a function of applied stress were of primary interest. Results from differential scanning calorimetry, monotonic tensile loading and constant stress thermal loading for the as-received, untrained material are first presented. These show lower transformation temperatures, higher elastic stiffnesses (60-90 GPa) and lower recoverable transformation strains (≈1.5%) when compared to equiatomic NiTi (Nitinol). Stabilization (training) cycles were applied to the tensile specimens and characterization tests were repeated for the stable (trained) material. The effects of specimen training included the saturation of cyclically generated irrecoverable plastic strains and a broadening of the thermal transformation hysteresis. A set of final derived material properties for this

  8. Shape Memory Alloy Actuator

    NASA Technical Reports Server (NTRS)

    Baumbick, Robert J. (Inventor)

    2002-01-01

    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.

  9. 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.

  10. Surface XPS characterization of NiTi shape memory alloy after advanced oxidation processes in UV/H 2O 2 photocatalytic system

    NASA Astrophysics Data System (ADS)

    Wang, R. M.; Chu, C. L.; Hu, T.; Dong, Y. S.; Guo, C.; Sheng, X. B.; Lin, P. H.; Chung, C. Y.; Chu, P. K.

    2007-08-01

    Surface structure of NiTi shape memory alloy (SMA) was modified by advanced oxidation processes (AOP) in an ultraviolet (UV)/H 2O 2 photocatalytic system, and then systematically characterized with x-ray photoelectron spectroscopy (XPS). It is found that the AOP in UV/H 2O 2 photocatalytic system leads to formation of titanium oxides film on NiTi substrate. Depth profiles of O, Ni and Ti show such a film possesses a graded interface structure to NiTi substrate and there is no intermediate Ni-rich layer like that produced in conventional high temperature oxidation. Except TiO 2 phase, some titanium suboxides (TiO, Ti 2O 3) may also exist in the titanium oxides film. Oxygen mainly presents in metal oxides and some chemisorbed water and OH - are found in titanium oxides film. Ni nearly reaches zero on the upper surface and relatively depleted in the whole titanium oxides film. The work indicates the AOP in UV/H 2O 2 photocatalytic system is a promising way to favor the widespread application of biomedical NiTi SMA by improving its biocompatibility.

  11. Effect of thermal oxidation on the surface characteristics and corrosion behavior of a Ta-implanted Ti-50.6Ni shape memory alloy

    NASA Astrophysics Data System (ADS)

    Wang, Sheng-nan; Li, Yan; Zhao, Ting-ting

    2012-12-01

    A NiTi shape memory alloy (SMA) modified by Ta ion implantation was subjected to oxidation treatment in air at 723 and 873 K. Atomic force microscopy (AFM), Auger electron spectroscopy (AES), and grazing incidence X-ray diffraction (GIXRD) measurements were conducted to investigate the surface characteristics, including surface topography, elemental depth profiles, and surface phase structures. The surface roughness of the Ta-implanted NiTi increases after oxidation, and the higher the oxidation temperature is, the larger the value is. The surface of the Ta-implanted NiTi oxidized at 723 K is a nanolayer mainly composed of TiO2/Ta2O5 and TiO with depressed Ni content. The Ta-implanted NiTi oxidized at 873 K is mainly covered by rutile TiO2 in several micrometers of thickness. Potentiodynamic polarization tests indicated that the corrosion resistance of the Ta-implanted NiTi was improved after thermal oxidation at 723 K, but a negative impact was found for the Ta-implanted NiTi oxidized at 873 K.

  12. Anomalous transport and thermal properties of NiTi and with Cu and Fe-doped shape memory alloys near the martensitic transition

    NASA Astrophysics Data System (ADS)

    Ingale, B. D.; Wei, W. C.; Chang, P. C.; Kuo, Y. K.; Wu, S. K.

    2011-12-01

    The temperature dependent electrical and thermal properties including electrical resistivity (ρ), specific heat (CP), Seebeck coefficient (S) and thermal conductivity (κ) have been studied for the polycrystalline NiTi, Ti50Ni40Cu10 and Ti50Ni48.5Fe1.5 shape memory alloys from 10-400 K. It was found that the electrical resistivity and Seebeck coefficient exhibit a typical metallic behavior throughout the temperature range investigated. A significant thermal hysteresis between warming and cooling was observed in all the three alloys which is a manifestation of the first-order nature of martensitic transitions. Our results indicate the presence of two stage martnesite transformations, i.e. B2 → B19 → B19' for Ti50Ni40Cu10 while B2 → R → B19' for NiTi and Ti50Ni48.5Fe1.5 alloys. An analysis on the measured thermal conductivity reveals that the anomalous feature in κ at the B19 ↔ B19' transformation for Ti50Ni40Cu10 is essentially attributed to the electronic contribution, while an enormously large peak in warming run observed at the B19 → B2 transformation is due to the change in lattice thermal conductivity.

  13. 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.

  14. PIIID-formed (Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti coatings on NiTi shape memory alloy for medical applications.

    PubMed

    Sun, Tao; Wang, Lang-Ping; Wang, Min; Tong, Ho-Wang; Lu, William W

    2012-08-01

    (Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti composite coatings were fabricated on NiTi shape memory alloy via plasma immersion ion implantation and deposition (PIIID). Surface morphology of samples was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross-sectional morphology indicated that the PIIID-formed coatings were dense and uniform. X-ray diffraction (XRD) was used to characterize the phase composition of samples. X-ray photoelectron spectroscopy (XPS) results showed that the surface of coated NiTi SMA samples was Ni-free. Nanoindentation measurements and pin-on-disc tests were carried out to evaluate mechanical properties and wear resistance of coated NiTi SMA, respectively. For the in vitro biological assessment of the composite coatings in terms of cell morphology and cell viability, osteoblast-like SaOS-2 cells and breast cancer MCF-7 cells were cultured on NiTi SMA samples, respectively. SaOS-2 cells attached and spread better on coated NiTi SMA. Viability of MCF-7 cells showed that the PIIID-formed composite coatings were noncytotoxic and coated samples were more biocompatible than uncoated samples.

  15. Effect of surface modification by nitrogen ion implantation on the electrochemical and cellular behaviors of super-elastic NiTi shape memory alloy.

    PubMed

    Maleki-Ghaleh, H; Khalil-Allafi, J; Sadeghpour-Motlagh, M; Shakeri, M S; Masoudfar, S; Farrokhi, A; Beygi Khosrowshahi, Y; Nadernezhad, A; Siadati, M H; Javidi, M; Shakiba, M; Aghaie, E

    2014-12-01

    The aim of this investigation was to enhance the biological behavior of NiTi shape memory alloy while preserving its super-elastic behavior in order to facilitate its compatibility for application in human body. The surfaces of NiTi samples were bombarded by three different nitrogen doses. Small-angle X-ray diffraction was employed for evaluating the generated phases on the bombarded surfaces. The electrochemical behaviors of the bare and surface-modified NiTi samples were studied in simulated body fluid (SBF) using electrochemical impedance and potentio-dynamic polarization tests. Ni ion release during a 2-month period of service in the SBF environment was evaluated using atomic absorption spectrometry. The cellular behavior of nitrogen-modified samples was studied using fibroblast cells. Furthermore, the effect of surface modification on super-elasticity was investigated by tensile test. The results showed the improvement of both corrosion and biological behaviors of the modified NiTi samples. However, no significant change in the super-elasticity was observed. Samples modified at 1.4E18 ion cm(-2) showed the highest corrosion resistance and the lowest Ni ion release.

  16. Investigations on the influence of composition in the development of Ni-Ti shape memory alloy using laser based additive manufacturing

    NASA Astrophysics Data System (ADS)

    Shiva, S.; Palani, I. A.; Mishra, S. K.; Paul, C. P.; Kukreja, L. M.

    2015-06-01

    Among the various shaped memory alloys (SMA), nitinol (Ni-Ti alloy) finds applications in automotive, aerospace, biomedical and robotics. The conventional route of fabrication of SMA has several limitations, like formation of stable secondary phases, fabrication of simple geometries, etc. This paper reports a novel method of fabricating SMA using a laser based additive manufacturing technique. Three different compositions of Ni and Ti powders (Ni-45% Ti-55%; Ni-50% Ti-50%; Ni-55% Ti45%) were pre-mixed using ball-milling and laser based additive manufacturing system was employed to fabricate circular rings. The material properties of fabricated rings were evaluated using Scanning Electron Microscopy (SEM), Differential scanning calorimeter (DSC), X-ray diffraction (XRD) system and micro-hardness test. All the characterized results showed that SMA could be manufactured using the laser based additive manufacturing process. The properties of laser additive manufactured SMA (Ni-50% Ti-50%) were found to be close to that of conventionally processed SMA.

  17. Influence of Ti additions on martensitic transformation and magnetic properties of cast Ni51Fe22-xGa27Tix shape memory alloys

    NASA Astrophysics Data System (ADS)

    El-Bagoury, Nader; Mohsen, Q.; Kaseem, M. A.; Hessien, M. M.

    2013-09-01

    The effect of Ti addition on the microstructure, martensitic transformation, magnetic and mechanical properties of polycrystalline Ni51Fe22- x Ga27Ti x ( x=0, 2 and 4) ferromagnetic shape memory alloy was investigated by scanning electron microscope, differential scanning calorimetry and X-ray diffraction. The results showed that the martensitic transformation temperature increases monotonously with the increase of fraction of Ti substitution for Fe. The increase in the martensite transformation temperatures should be related to the change of the electron concentration after the addition of Ti to Ni51Fe22- x Ga27Ti x alloys. According to the results of X-ray diffraction and magnetic properties, Ti has significant effect the structure of Ni51Fe22- x Ga27Ti x . Adding of 4 at% Ti altered the structure of the matrix from five-layered tetragonal martensite of Ni51Fe22Ga27 and Ni51Fe20Ga27Ti2 alloys to non-modulated tetragonal martensite. Magnetic properties proved that the alloy transits from ferromagnetic, five-layered tetragonal martensite, to paramagnetic, non-modulated martensite structure, with increasing Ti content to 4 at.%. Saturation magnetization, remnant magnetization and coercivity of the alloy were significantly influenced by Ti additions. Hardness values of Ni51Fe22Ga27 increased by the addition of Ti.

  18. Effect of Cr addition on the structural, magnetic and mechanical properties of magnetron sputtered Ni-Mn-In ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Akkera, Harish Sharma; Kaur, Davinder

    2016-12-01

    The effect of Cr substitution for In on the structural, martensitic phase transformation and mechanical properties of Ni-Mn-In ferromagnetic shape memory alloy (FSMA) thin films was systematically investigated. X-ray diffraction results revealed that the Ni-Mn-In-Cr thin films possessed purely austenitic cubic L21 structure at lower content of Cr, whereas higher Cr content, the Ni-Mn-In-Cr thin films exhibited martensitic structure at room temperature. The temperature-dependent magnetization ( M- T) and resistance ( R- T) results confirmed that the monotonous increase in martensitic transformation temperatures ( T M) with the addition of Cr content. Further, the room temperature nanoindentation studies revealed the mechanical properties such as hardness ( H), elastic modulus ( E), plasticity index ( H/ E) and resistance to plastic deformation ( H 3/ E 2) of all the samples. The addition of Cr content significantly enhanced the hardness (28.2 ± 2.4 GPa) and resistance to plastic deformation H 3/ E 2 (0.261) of Ni50.4Mn34.96In13.56Cr1.08 film as compared with pure Ni-Mn-In film. As a result, the appropriate addition of Cr significantly improved the mechanical properties with a decrease in grain size, which could be further attributed to the grain boundary strengthening mechanism. These findings indicate that the Cr-doped Ni-Mn-In FSMA thin films are potential candidates for microelectromechanical systems applications.

  19. 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.

  20. Shape Memory Actuator System

    DTIC Science & Technology

    1998-07-31

    The advantage in utilizing 15 shape-memory cables made of Nitinol for size reduction of the remote control actuator system is 1 Fi well suited for...a submarine environment because of its non-magnetic and corrosion resistance 17 properties. Use of thermoelastic Nitinol introduces other...problems because of the cooling and 18 resetting properties of Nitinol cables. It is therefore an important object of the present invention 19 on to

  1. NiTi Alloy Negator Springs for Long-Stroke Constant-Force Shape Memory Actuators: Modeling, Simulation and Testing

    NASA Astrophysics Data System (ADS)

    Spaggiari, Andrea; Dragoni, Eugenio; Tuissi, Ausonio

    2014-07-01

    This work aims at the experimental characterization and modeling validation of shape memory alloy (SMA) Negator springs. According to the classic engineering books on springs, a Negator spring is a spiral spring made of strip of metal wound on the flat with an inherent curvature such that, in repose, each coil wraps tightly on its inner neighbor. The main feature of a Negator springs is the nearly constant force displacement behavior in the unwinding of the strip. Moreover the stroke is very long, theoretically infinite, as it depends only on the length of the initial strip. A Negator spring made in SMA is built and experimentally tested to demonstrate the feasibility of this actuator. The shape memory Negator spring behavior can be modeled with an analytical procedure, which is in good agreement with the experimental test and can be used for design purposes. In both cases, the material is modeled as elastic in austenitic range, while an exponential continuum law is used to describe the martensitic behavior. The experimental results confirms the applicability of this kind of geometry to the shape memory alloy actuators, and the analytical model is confirmed to be a powerful design tool to dimension and predict the spring behavior both in martensitic and austenitic range.

  2. Determining Recoverable and Irrecoverable Contributions to Accumulated Strain in a NiTiPd High-Temperature Shape Memory Alloy During Thermomechanical Cycling

    NASA Technical Reports Server (NTRS)

    Monroe, J. A.; Karaman, I.; Lagoudas, D. C.; Bigelow, G.; Noebe, R. D.; Padula, S., II

    2011-01-01

    When Ni(29.5)Ti(50.5)Pd30 shape memory alloy is thermally cycled under stress, significant strain can accumulate due to elasticity, remnant oriented martensite and plasticity. The strain due to remnant martensite can be recovered by further thermal cycling under 0 MPa until the original transformation-induced volume change and martensite coefficient of thermal expansion are obtained. Using this technique, it was determined that the 8.15% total accumulated strain after cycling under 200 MPa consisted of 0.38%, 3.97% and 3.87% for elasticity, remnant oriented martensite and creep/plasticity, respectively.

  3. Energy-dispersive neutron imaging and diffraction of magnetically driven twins in a Ni2MnGa single crystal magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Kabra, Saurabh; Kelleher, Joe; Kockelmann, Winfried; Gutmann, Matthias; Tremsin, Anton

    2016-09-01

    Single crystals of a partially twinned magnetic shape memory alloy, Ni2MnGa, were imaged using neutron diffraction and energy-resolved imaging techniques at the ISIS spallation neutron source. Single crystal neutron diffraction showed that the crystal produces two twin variants with a specific crystallographic relationship. Transmission images were captured using a time of flight MCP/Timepix neutron counting detector. The twinned and untwinned regions were clearly distinguishable in images corresponding to narrow-energy transmission images. Further, the spatially-resolved transmission spectra were used to elucidate the orientations of the crystallites in the different volumes of the crystal.

  4. Magnetic Properties and Phase Diagram of Ni50Mn_{50-x}Ga_{x/2}In_{x/2} Magnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Yoshida, Yasuki; Omori, Toshihiro; Kanomata, Takeshi; Kainuma, Ryosuke

    2016-12-01

    Ni50Mn50- x Ga x/2In x/2 magnetic shape memory alloys were systematically prepared, and the magnetic properties as well as the phase diagram, including atomic ordering, martensitic and magnetic transitions, were investigated. The B2- L21 order-disorder transformation showed a parabolic-like curve against the Ga+In composition. The martensitic transformation temperature was found to decrease with increasing Ga+In composition and to slightly bend downwards below the Curie temperature of the parent phase. Spontaneous magnetization was investigated for both parent and martensite alloys. The magnetism of martensite phase was found to show glassy magnetic behaviors by thermomagnetization and AC susceptibility measurements.

  5. Structural and phase transformations, mechanical properties, and shape-memory effects in quasibinary Ni50Ti38Hf12 alloy obtained by quenching from the melt

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Kuranova, N. N.; Pushin, A. V.; Uksusnikov, A. N.; Kourov, N. I.; Kuntsevich, T. E.

    2016-12-01

    Methods of transmission and scanning electron microscopy and chemical microanalysis, electron diffraction, and X-ray diffraction were used to systematically study the structure and the chemical and phase composition of the Ni50Ti38Hf12 alloy synthesized by rapid quenching from the melt and subjected to various heat treatments. The critical temperatures of the devitrification of the initially amorphous rapidly quenched alloy and the B2 ↔ B19' thermoelastic martensitic transformations have been determined. The lattice parameters of the B2 austenite and thermoelastic B19' martensite have been measured. The main features of the formation of an ultrafine-grained structure in the alloy and the subsequent phase transformations (martensitic transformation and the decomposition with the formation of an intermetallic phase of the (Ti,Hf)2Ni type) have been studied depending on the regimes of heat treatment. Based on the results of measurements of mechanical properties upon tension (σM, σu, and δ) and the shape-memory effects (degree of shape recovery depending on the deformation by bending; and magnitude of the reversible strain ɛrev), regimes for obtaining high-strength and plastic states of the alloy with a shape-memory effect have been established.

  6. Inverse magnetocaloric effect in Mn{sub 2}NiGa and Mn{sub 1.75}Ni{sub 1.25}Ga magnetic shape memory alloys

    SciTech Connect

    Singh, Sanjay Barman, S. R.; Esakki Muthu, S.; Arumugam, S.; Senyshyn, A.; Rajput, P.; Suard, E.

    2014-02-03

    Inverse magnetocaloric effect is demonstrated in Mn{sub 2}NiGa and Mn{sub 1.75}Ni{sub 1.25}Ga magnetic shape memory alloys. The entropy change at the martensite transition is larger in Mn{sub 1.75}Ni{sub 1.25}Ga, and it increases linearly with magnetic field in both the specimens. Existence of inverse magnetocaloric effect is consistent with the observation that magnetization in the martensite phase is smaller than the austenite phase. Although the Mn content is smaller in Mn{sub 1.75}Ni{sub 1.25}Ga, from neutron diffraction, we show that the origin of inverse magnetocaloric effect is the antiferromagnetic interaction between the Mn atoms occupying inequivalent sites.

  7. 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.

  8. Evaluation of passive oxide layer formation-biocompatibility relationship in NiTi shape memory alloys: geometry and body location dependency.

    PubMed

    Toker, S M; Canadinc, D; Maier, H J; Birer, O

    2014-03-01

    A systematic set of ex-situ experiments were carried out on Nickel-Titanium (NiTi) shape memory alloy (SMA) in order to identify the dependence of its biocompatibility on sample geometry and body location. NiTi samples with three different geometries were immersed into three different fluids simulating different body parts. The changes observed in alloy surface and chemical content of fluids upon immersion experiments designed for four different time periods were analyzed in terms of ion release, oxide layer formation, and chemical composition of the surface layer. The results indicate that both sample geometry and immersion fluid significantly affect the alloy biocompatibility, as evidenced by the passive oxide layer formation on the alloy surface and ion release from the samples. Upon a 30 day immersion period, all three types of NiTi samples exhibited lower ion release than the critical value for clinic applications. However; a significant amount of ion release was detected in the case of gastric fluid, warranting a thorough investigation prior to utility of NiTi in gastrointestinal treatments involving long-time contact with tissue. Furthermore, certain geometries appear to be safer than the others for each fluid, providing a new set of guidelines to follow while designing implants making use of NiTi SMAs to be employed in treatments targeting specific body parts.

  9. (Ti, O)/Ti and (Ti, O, N)/Ti composite coatings fabricated via PIIID for the medical application of NiTi shape memory alloy.

    PubMed

    Sun, Tao; Wang, Lang-Ping; Wang, Min

    2011-02-01

    In this investigation, the plasma immersion ion implantation and deposition (PIIID) technique was used to fabricate (Ti, O)/Ti or (Ti, O, N)/Ti coatings on a NiTi shape memory alloy (SMA, 50.8 at.% Ni) to improve its corrosion, wear resistance, and bioactivity. After coating fabrication, the structure and properties of composite coatings were studied, and the coated and uncoated NiTi SMA samples were compared with each other. Scanning electron microscopic (SEM) examination of coating surfaces and cross-sections showed that (Ti, O)/Ti and (Ti, O, N)/Ti composite coatings were dense and uniform, having thickness values of 1.16 ± 0.08 μm and 0.95 ± 0.06 μm, respectively. X-ray diffraction (XRD) results revealed that there were no diffraction peaks corresponding to TiO(2) or TiN for (Ti, O)/Ti and (Ti, O, N)/Ti composite coatings, suggesting that after the PIIID treatment, TiO(2) and TiN were amorphous or nanosized in the coatings. Energy dispersive X-ray (EDX) analysis indicated that the interface between the coating and NiTi SMA substrate was gradual rather than sharp. In addition, EDX elemental mapping of coating cross-sections showed that Ni was depleted from the surface. Differential scanning calorimetry (DSC) curves revealed that the shape memory ability of NiTi SMA was not degraded by the PIIID treatment. The width of wear tracks on (Ti, O, N)/Ti coated NiTi SMA samples was reduced 6.5-fold, in comparison with that on uncoated samples. The corrosion potential (E(corr) ) was improved from -466.20 ± 37.82 mV for uncoated samples to 125.50 ± 21.49 mV and -185.40 ± 37.05 mV for (Ti, O)/Ti coated and (Ti, O, N)/Ti coated samples, respectively. Both types of coatings facilitated bone-like apatite formation on the surface of NiTi SMA in simulated body fluid (SBF), indicating their in vitro bioactivity.

  10. 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...

  11. The formation of the two-way shape memory effect in rapidly quenched TiNiCu alloy under laser radiation

    NASA Astrophysics Data System (ADS)

    Shelyakov, A. V.; Sitnikov, N. N.; Sheyfer, D. V.; Borodako, K. A.; Menushenkov, A. P.; Fominski, V. Yu

    2015-11-01

    The effect of pulsed laser radiation (λ = 248 nm, τ = 20 ns) on structural properties and shape memory behavior of the rapidly quenched Ti50Ni25Cu25 alloy ribbon was studied. The radiation energy density was varied from 2 to 20 mJ mm-2. The samples were characterized by means of scanning electron microscopy, x-ray diffraction, microhardness measurements and shape memory bending tests. It was ascertained that the action of the laser radiation leads to the formation of a structural composite material due to amorphization or martensite modification in the surface layer of the ribbon. Two methods are proposed which allow one to generate the pronounced two-way shape memory effect (TWSME) in a local area of the ribbon by using only a single pulse of the laser radiation. With increasing energy density of laser treatment, the magnitude of the reversible angular displacement with realization of the TWSME increases. The developed techniques can be used for the creation of various micromechanical devices.

  12. Thermoelastic martensitic transformations, mechanical properties, and shape-memory effects in rapidly quenched Ni45Ti32Hf18Cu5 alloy in the ultrafine-grained state

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Pushin, A. V.; Kuranova, N. N.; Kuntsevich, T. E.; Uksusnikov, A. N.; Dyakina, V. P.; Kourov, N. I.

    2016-12-01

    Methods of transmission and scanning electron microscopy and chemical microanalysis, electron diffraction, and X-ray diffraction were used to study the structure and the chemical and phase composition of ribbons of the four-component quasi-binary alloy Ni45Ti32Hf18Cu5. The influence of the synthesis regimes and subsequent heat treatment of the alloy on the formation of the amorphized state and ultrafine-grained structure has been determined. The critical temperatures of the devitrification and of the B2 ↔ B19' thermoelastic martensitic transformation have been established based on the data of the temperature dependences of the electrical resistivity. The lattice parameters of the B2 and B19' phases and the (Ti,Hf)2Ni phase have been determined by X-ray diffraction. The mechanical properties of the alloy were determined in tensile tests, and the shape-memory effects in the ribbons of the alloy were measured using bending tests.

  13. Shape Memory effect and Superelasticity in the [001] Single crystals of a FeNiCoAlTa Alloy with γ-α'-Thermoelastic Martensitic Transformations

    NASA Astrophysics Data System (ADS)

    Chumlyakov, Yu. I.; Kireeva, I. V.; Kretinina, I. V.; Keinikh, K. S.; Kuts, O. A.; Kirillov, V. A.; Karaman, I.; Maier, H.

    2013-12-01

    Using single crystals of a Fe - 28% Ni - 17% Co - 11.5% Al - 25% Ta (аt.%) alloy, oriented for tensile loading along the [001] direction, the shape-memory (SME) and superelasticity (SE) effects caused by reversible thermoelastic martensitic transformations (MTs) from a high-temperature fcc-phase into a bctmartensite are investigated. It is demonstrated that the conditions necessary for the thermoelastic MTs to occur are achieved by aging at 973 K within the time interval (t) from 0.5 to 7.0 hours, which is accompanied by precipitation of the γ'-phase particles, (FeNiCo)3(AlTa), whose d < 8-12 nm. When the size of the γ'-precipitates becomes as large as d ≥ 8-12 nm, the MT becomes partially reversible. The physical causes underlying the kinetics of thermoelstic reversible fcc-bct MTs are discussed.

  14. Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-07-01

    In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 μm is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life.

  15. Porous Shape Memory Polymers.

    PubMed

    Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C; Wilson, Thomas S; Maitland, Duncan J

    2013-02-04

    Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use.

  16. Porous Shape Memory Polymers

    PubMed Central

    Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C.; Wilson, Thomas S.; Maitland, Duncan J.

    2013-01-01

    Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use. PMID:23646038

  17. Influence of Hydrogen and Number of Particle Variants on Ordinary and Two-Way Shape Memory Effects in Ti-Ni Single Crystals

    NASA Astrophysics Data System (ADS)

    Kireeva, I. V.; Platonova, Yu. N.; Chumlyakov, Yu. I.

    2017-02-01

    The ordinary and two-way shape memory effects (SMEs) are investigated for [ overline{1} 12] single crystals of Ti-51.3Ni (at.%) alloy aged at 823 K for 1.5 h in free state and under tensile stress of 150 MPa without hydrogen and after saturation by hydrogen. It is established that without hydrogen in [ overline{1} 12] single crystals with one and four variants of Ti3Ni4 particles the maximum magnitude of the ordinary SME is 1.9-2.6% under the external stress σext = 250 MPa. Under σext > 250 MPa, crystals are destroyed. The magnitude of the two-way SME caused by the B2- R- B19' MT equal to 1.1% at σext = 0 is observed in [ overline{1} 12] single crystals with one variant of Ti3Ni4 particles. The physical reason for the observed two-way SME is the internal compressive stresses oriented along the [ overline{1} 12] directions arising from one variant of Ti3Ni4 particles as a result of aging under tensile stress of 150 MPa. It is established that hydrogen does not influence the TR temperature, reduces the plasticity, and suppresses the two-way SME. The suppression of two-way SME in the [ overline{1} 12] single crystals of the Ti-51.3Ni (at.%) alloy with one variant of Ti3Ni4 particles is caused by shielding of stress fields from one variant of Ti3Ni4 particles and multiple nucleation of R- and B19' martensite variants under loading with saturation by hydrogen.

  18. 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.

  19. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  20. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    PubMed Central

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-01-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques. PMID:27138030

  1. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy.

    PubMed

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-03

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  2. Characterization of Ni19.5Ti50.5Pd25Pt5 High-Temperature Shape Memory Alloy Springs and their Potential Application in Aeronautics

    NASA Technical Reports Server (NTRS)

    Stebner, Aaron; Padula, Santo A.; Noebe, Ronald D.

    2008-01-01

    Shape memory alloys (SMAs) have been used as actuators in many different industries since the discovery of the shape memory effect, but the use of SMAs as actuation devices in aeronautics has been limited due to the temperature constraints of commercially available materials. Consequently, work is being done at NASA's Glenn Research Center to develop new SMAs capable of being used in high temperature environments. One of the more promising high-temperature shape memory alloys (HTSMAs) is Ni19.5Ti50.5Pd25Pt5. Recent work has shown that this material is capable of being used in operating environments of up to 250 C. This material has been shown to have very useful actuation capabilities, demonstrating repeatable strain recoveries up to 2.5% in the presence of an externally applied load. Based on these findings, further work has been initiated to explore potential applications and alternative forms of this alloy, such as springs. Thus, characterization of Ni19.5Ti50.5Pd25Pt5 springs, including their mechanical response and how variations in this response correlate to changes in geometric parameters, are discussed. The effects of loading history, or training, on spring behavior were also investigated. A comparison of the springs with wire actuators is made and the benefits of using one actuator form as opposed to the other discussed. These findings are used to discuss design considerations for a surge-control mechanism that could be used in the centrifugal compressor of a T-700 helicopter engine.

  3. Comparative Analysis of the Effects of Severe Plastic Deformation and Thermomechanical Training on the Functional Stability of Ti50.5Ni24.5Pd25 High-Temperature Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Atli, K. C.; Karaman, I.; Noebe, R. D.; Maier, H. J.

    2010-01-01

    We compare the effectiveness of a conventional thermomechanical training procedure and severe plastic deformation via equal channel angular extrusion to achieve improved functional stability in a Ti50.5Ni24.5Pd25 high-temperature shape memory alloy. Thermomechanical testing indicates that both methods result in enhanced shape memory characteristics, such as reduced irrecoverable strain and thermal hysteresis. The mechanisms responsible for the improvements are discussed in light of microstructural findings from transmission electron microscopy.

  4. 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.).

  5. Influence of partial shape memory deformation on the burst character of its recovery in heated Ni-Fe-Ga-Co alloy crystals

    NASA Astrophysics Data System (ADS)

    Nikolaev, V. I.; Yakushev, P. N.; Malygin, G. A.; Averkin, A. I.; Pulnev, S. A.; Zograf, G. P.; Kustov, S. B.; Chumlyakov, Yu. I.

    2016-04-01

    Room-temperature stress-strain curves of Ni49Fe18Ga27Co6 alloy single crystals possessing shape memory (SM) have been studied. Specific features of these diagrams are revealed upon compressive loading of these single crystals in the [110] A direction. The influence of preliminary SM deformation on the process of its recovery during the reverse martensite transformation has been studied. It is established that SM deformation above 4.2% leads to a sharp increase in the shape recovery on heating and the process exhibits a burst character, involving motion of the entire crystal. The experimental data are analyzed and stress-strain curves are simulated in the framework of the theory of diffuse martensitic transitions.

  6. Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

    SciTech Connect

    Emre, Baris; Bruno, Nickolaus M.; Yuce Emre, Suheyla; Karaman, Ibrahim

    2014-12-08

    The effect of Nb substitution for Ni in Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloys potential candidates for solid state refrigeration near room temperature.

  7. First-principles investigation of the composition dependent properties of Ni2+xMn1-xGa shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Li, Chun-Mei; Luo, Hu-Bin; Hu, Qing-Miao; Yang, Rui; Johansson, Börje; Vitos, Levente

    2010-07-01

    The composition dependent lattice parameter, phase stability, elastic moduli, and magnetic transition temperature of the Ni2+xMn1-xGa shape-memory alloys are studied by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. The lattice parameter and tetragonal shear modulus of the cubic L21 austenite phase decreases linearly with increasing concentration x of excess Ni atoms. The heats of formation of both cubic L21 and tetragonal β‴ phases and their difference increase with x , indicating decreasing stability of the cubic and tetragonal phases and increasing driving force for the L21 to β‴ martensitic transition. Investigating the electronic density of states, we find that the Ni-induced decreasing phase stability can mainly be ascribed to the weakening of the covalent bonding between minority spin states of Ni and Ga. Using the computed parameters, the composition dependence of the martensitic transition temperature is discussed. The theoretical Curie temperature, estimated from the Heisenberg model in combination with the mean-field approximation, is larger for the β‴ phase than for the L21 phase. For both phases, the Curie temperature decreases nearly linearly with increasing x .

  8. Martensitic transformation and phase stability of In-doped Ni-Mn-Sn shape memory alloys from first-principles calculations

    SciTech Connect

    Xiao, H. B.; Yang, C. P. Wang, R. L.; Luo, X.; Marchenkov, V. V.

    2014-05-28

    The effect of the alloying element Indium (In) on the martensitic transition, magnetic properties, and phase stabilities of Ni{sub 8}Mn{sub 6}Sn{sub 2−x}In{sub x} shape memory alloys has been investigated using the first-principles pseudopotential plane-wave method based on density functional theory. The energy difference between the austenitic and martensitic phases was found to increase with increasing In content, which implies an enhancement of the martensitic phase transition temperature (T{sub M}). Moreover, the formation energy results indicate that In-doping increases the relative stability of Ni{sub 8}Mn{sub 6}Sn{sub 2−x}In{sub x} both in austenite and martensite. This results from a reduction in density of states near the Fermi level regions caused by Ni-3d–In-5p hybridization when Sn is replaced by In. The equilibrium equation of state results show that the alloys Ni{sub 8}Mn{sub 6}Sn{sub 2−x}In{sub x} exhibit an energetically degenerated effect for an In content of x = ∼1.5. This implies the coexistence of antiparallel and parallel configurations in the austenite.

  9. Martensitic transition, inverse magnetocaloric effect and shape memory characteristics in Mn48-xCuxNi42Sn10 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Liu, Changqin; Li, Zhe; Zhang, Yuanlei; Liu, Yang; Sun, Junkun; Huang, Yinsheng; Kang, Baojuan; Xu, Kun; Deng, Dongmei; Jing, Chao

    2017-03-01

    In this paper, we have systematically prepared a serials of polycrystalline Mn48-xCuxNi42Sn10 alloys (x=0, 1, 3, 5, 6, 8, 10 and 12) and investigated the influence of the Cu doping on martensitic transition (MT) as well as magnetic properties. Experimental results indicate that the MT temperature and the martensite Curie temperature (TcM) shift to high temperature with increasing the substitution of Cu (from Mn rich alloy to Ni rich alloy), while the austenite Curie temperature (TcA) is almost unchanged. It was found that the structures undergo L21 and 4O with the increasing of Cu concentration near room temperature. Therefore, the magnetostructural transition can be tuned by appropriate Cu doping in these alloys. Moreover, we mainly studied the multiple functional properties for inverse magnetocaloric effect and shape memory characteristics associated with the martensitic transition. A large positive isothermal entropy change of Mn48Ni42Sn10 was obtained, and the maximum transition entropy change achieves about 48 J/kg K as x=8. In addition, a considerable temperature-induced spontaneous strain with the value of 0.16% was obtained for Mn48Ni42Sn10 alloys.

  10. 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.

  11. Shape memory thermal conduction switch

    NASA Technical Reports Server (NTRS)

    Vaidyanathan, Rajan (Inventor); Krishnan, Vinu (Inventor); Notardonato, William U. (Inventor)

    2010-01-01

    A thermal conduction switch includes a thermally-conductive first member having a first thermal contacting structure for securing the first member as a stationary member to a thermally regulated body or a body requiring thermal regulation. A movable thermally-conductive second member has a second thermal contacting surface. A thermally conductive coupler is interposed between the first member and the second member for thermally coupling the first member to the second member. At least one control spring is coupled between the first member and the second member. The control spring includes a NiTiFe comprising shape memory (SM) material that provides a phase change temperature <273 K, a transformation range <40 K, and a hysteresis of <10 K. A bias spring is between the first member and the second member. At the phase change the switch provides a distance change (displacement) between first and second member by at least 1 mm, such as 2 to 4 mm.

  12. 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.

  13. 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

  14. Fluctuations of chemical composition of austenite and their consequence on shape memory effect in Fe-Mn-(Si, Cr, Ni, C, N) alloys

    SciTech Connect

    Bliznuk, V.V.; Gavriljuk, V.G. . E-mail: gavr@imp.kiev.ua; Kopitsa, G.P.; Grigoriev, S.V.; Runov, V.V.

    2004-09-20

    Polycrystalline samples of shape memory iron-based alloys containing 17, and 30 mass% Mn and alloyed with Si, Cr, Ni, C, N were studied by means of small angle scattering of polarized neutrons (SAPNS). A direct correlation between chemical homogeneity of the Fe-Mn, Fe-Mn-Si, Fe-Mn-Si-Cr, Fe-Mn-Si-Cr-Ni solid solutions and the values of reversible strain caused by the {gamma} {yields} {epsilon} {yields} {gamma} martensitic transformation was found. The addition of silicon to the Fe-Mn alloys significantly improves chemical homogeneity of the fcc solid solution on the scale of larger than several nm, which correlates with the essential increase of reversible strain. A similar to silicon but weaker effect was observed in the case of nitrogen addition to the Fe-Mn-Si-Cr, Fe-Mn-Si-Cr-Ni alloys. Based on the obtained experimental data and in consistency with the previously expressed idea by Sade et al., the positive effect of silicon and nitrogen on chemical homogeneity and SME in Fe-Mn alloys is attributed to the short-range atomic ordering induced by these elements.

  15. Effect of the M(s) transformation temperature on the wear behaviour of NiTi shape memory alloys for articular prosthesis.

    PubMed

    Peña, J; Solano, E; Mendoza, A; Casals, J; Planell, J A; Gil, F J

    2005-01-01

    The main objective of this work has been the characterisation and correlation of the wear behaviour of the NiTi shape memory alloys in their different phases. The weight losses for the different alloys in function of the present phase, and of the M(s) transformation temperature are studied. Adhesive wear tests, Pin-on-Disk, according to the ASTM-G99 standard have been carried out. The thermoelastic martensitic transformations that cause the super-elastic effect, the reorientation and coalescence of martensitic plates and the damping effect promotes a high ability to accommodate large deformations without generating permanent damages that causes the wear. The resulting plastic deformation may be accumulated during wear process without generating fracture. The results show that the wear resistance is mainly dependent of the M(s) transformation temperature for both alloys. For the NiTi alloys also the Ni atomic percentage and the hardness of the alloys are important parameters in the wear behavior.

  16. 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.

  17. First-principles investigations of the electronic structure and properties related to shape-memory behavior in Mn2NiX (X = Al,Ga,In,Sn) alloys

    NASA Astrophysics Data System (ADS)

    Paul, Souvik; Ghosh, Subhradip

    2011-09-01

    Using first-principles density functional theory based method we have performed a systematic investigations of the electronic structures, the structural and magnetic properties related to shape memory applications for Mn2NiAl,Mn2NiGa,Mn2NiSn and Mn2NiIn alloys. Our results confirm that all the alloys undergo a volume conserving martensitic transformation at low temperatures and that the low temperature stable phase is a non-modulated tetragonal one. The relative stabilities of the martensitic phases and the magnetic properties differ considerably for Mn2NiAl, Mn2NiGa and Mn2NiIn and Mn2NiSn. Details of the electronic structures suggest that the differences in hybridizations between the magnetic components are responsible for these trends. Quantitative estimates of the energetics and the magnetizations indicate that Mn2NiGa and Mn2NiAl are more promising candidates for shape memory applications.

  18. Electronic structure and elastic properties of single crystal of shape memory alloys TiNi(1-x)Cux: An ab initio study

    NASA Astrophysics Data System (ADS)

    Fathi, M. B.; Kanjouri, F.; Farhadi, G.

    2015-07-01

    Nitinol as a superelastic shape memory alloy (SMA) has been the focus of physical-chemical studies in recent decades in respect to functionality of biocompatibility in the body. Superelastic properties of nitinol are the direct results of the electronic structure of this material while dealing with the ab initio behavior of microstructure. In the present work, the elastic properties and electronic structure of B2-phase binary TiNi(1-x)Cux (x = 0, 0.25 and 0.75) shape memory alloys are discussed aiming at understanding of the physical properties underlying superelastic behavior. The calculations have been performed with the program package WIEN2K, in the framework of first-principle, all-electron density functional theory (DFT) within the scheme of the generalized gradient approximation (GGA). The optimized lattice parameters and independent elastic constants are obtained for use in the calculation of the bulk and shear moduli, Young modulus, Poisson ratio and Zener anisotropy parameter. For different alloying fractions x, the tetragonal (C‧) and trigonal (C44) shear constants are calculated and brittle/ductile behavior of these compounds is discussed. Finally, a qualitative discussion of dependence of elastic behavior of these compounds upon the electronic density of states (DOS) is presented.

  19. Vibrational and magnetic contributions to the entropy change associated with the martensitic transformation of Ni-Fe-Ga ferromagnetic shape memory alloys.

    PubMed

    Recarte, V; Pérez-Landazábal, J I; Gómez-Polo, C; Sánchez-Alarcos, V; Cesari, E; Pons, J

    2010-10-20

    Ferromagnetic shape memory alloys undergo a martensitic transformation accompanied by a change in the magnetic and vibrational properties. However, these property changes are not independent. In this paper, the interplay between magnetic and vibrational properties in the martensitic transformation entropy change has been analyzed for Ni-Fe-Ga ferromagnetic shape memory alloys. The martensitic transformation entropy change has a magnetic and a vibrational contribution, ΔS(p−>m)=ΔS(vib)(p−>m) + ΔS(mag)(p−>m). Using a mean field approximation for the magnetic entropy, the full entropy ΔS(p−>m) has been decomposed and the magnetic contribution ΔS(mag)(p−>m) calculated. Upon removing the magnetic term, the vibrational entropy ΔS(vib)(p−>m) does not change substantially in the composition range where T(M) is below T(C). This latter contribution to the martensitic transformation entropy change has been analyzed using a Debye distribution for the density of states and a proportion of Einstein modes that account for the anomalous phonon mode of the austenite.

  20. Large and reversible elastocaloric effect near room temperature in a Ga-doped Ni-Mn-In metamagnetic shape-memory alloy

    NASA Astrophysics Data System (ADS)

    Camarillo, Juan-Pablo; Aguilar-Ortiz, Christian-Omar; Flores-Zúñiga, Horacio; Ríos-Jara, David; Soto-Parra, Daniel-Enrique; Stern-Taulats, Enric; Mañosa, Lluís; Planes, Antoni

    We report a giant elastocaloric effect near room temperature in a polycrystalline Ga-doped Ni-Mn-In ferromagnetic shape-memory alloy. The elastocaloric effect has been quantified by measuring both isothermal stress-induced entropy changes and adiabatic stress-induced temperature changes. A reproducible maximum entropy change, ΔSrev≃ 25 JṡK‑1ṡkg‑1, upon cycling across the martensitic transition was obtained by application of a compressive stress of 100MPa. The corresponding maximum amount of cooling, ΔTadi≃‑4.9K, was measured when this stress was rapidly removed. These values are comparable with those reported for giant magnetocaloric materials, which are induced by application and release of a high magnetic field. Therefore, the studied material is a good candidate to be used in solid-state refrigeration devices based on the elastocaloric effect.

  1. Deployment shock attenuation of a solar array tape hinge by means of the Martensite detwinning of NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Ho; Jeong, Ju-Won; Kim, Young-Jin; Lee, Jung-Ju

    2016-03-01

    This paper presents a new tape hinge for attenuating the deployment shock of a satellite solar array. This hinge uses the Martensite detwinning of Shape Memory Alloy (SMA). To attenuate the deployment shock, a NiTi SMA strip is assembled between two curved steel strips. The attenuation performance of the hinge is analyzed using a SMA detwinning constitutive equation. A prototype of the hinge is manufactured and its characteristics are measured in a bending test and in a deployment test. Finally, the deployment performance of the prototype hinge is investigated on a satellite model. It is shown that the new SMA damped tape hinge can effectively minimize the deployment shock and dynamic perturbation while also maintaining suitable deployment performance.

  2. Two internal-friction peaks related to thermoelastic martensitic transformations in CuAlNiMnTi shape-memory alloy

    SciTech Connect

    Gong, C.L.; Han, F.S.; Li, Z.; Wang, M.P.

    2004-09-01

    A partial phase transition method was used in internal friction measurements to study the motion of phase interface in martensitic transition of CuAlNiMnTi polycrystalline shape memory alloy. It is found that the IF peak arisen from the reversible martensitic transition is in fact composed of two independent IF peaks that relate to different motion modes of the interface. The low-temperature peak corresponds to the minimum of relative dynamic modulus and is attributed to an elastic modulus softening effect caused by the viscous motion of the phase interface. The high-temperature peak corresponds to the inflection point of the relative dynamic modulus and the volume change produced by the normal motion of the phase interface is responsible for the peak.

  3. First-principles study of the lattice instabilities in Mn2NiX (X = Al, Ga, In, Sn) magnetic shape memory alloys.

    PubMed

    Paul, Souvik; Sanyal, Biplab; Ghosh, Subhradip

    2015-01-28

    Using first-principles based density functional theory, we have investigated the structural instabilities in the austenite phases of Mn(2)NiX (X = Al, Ga, In, Sn) magnetic shape memory alloys. A complete softening is observed in the acoustic TA(2) branches for all the materials along [ξξ0] directions leading to instability in the austenite structure which effectively stabilizes into martensitic structure. The reasons behind this softening are traced back to the repulsion from the optical T(2g) branches and to the nesting features in the Fermi surfaces. The vibrational density of states, the force constants and the elastic moduli are also computed and analyzed, which reconfirm the underlying mechanism behind the instabilities. The results indicate that the phonon anomalies are related to the occurrence of possible pre-martensitic phases which can be quite complex.

  4. Effect of yttrium on martensite-austenite phase transformation temperatures and high temperature oxidation kinetics of Ti-Ni-Hf high-temperature shape memory alloys

    NASA Astrophysics Data System (ADS)

    Kim, Jeoung Han; Kim, Kyong Min; Yeom, Jong Taek; Young, Sung

    2016-03-01

    The effect of yttrium (< 5.5 at%) on the martensite-austenite phase transformation temperatures, microstructural evolution, and hot workability of Ti-Ni-Hf high-temperature shape memory alloys is investigated. For these purposes, differential scanning calorimetry, hot compression, and thermo-gravimetric tests are conducted. The phase transformation temperatures are not noticeably influenced by the addition of yttrium up to 4.5 at%. Furthermore, the hot workability is not significantly affected by the yttrium addition up to 1.0 at%. However, when the amount of yttrium addition exceeds 1.0 at%, the hot workability deteriorates significantly. In contrast, remarkable improvement in the high temperature oxidation resistance due to the yttrium addition is demonstrated. The total thickness of the oxide layers is substantially thinner in the Y-added specimen. In particular, the thickness of (Ti,Hf) oxide layer is reduced from 200 µm to 120 µm by the addition of 0.3 at% Y.

  5. Properties of a Ni 19.5Pd 30Ti 50.5 high-temperature shape memory alloy in tension and compression

    NASA Astrophysics Data System (ADS)

    Noebe, Ronald; Padula, Santo, II; Bigelow, Glen; Rios, Orlando; Garg, Anita; Lerch, Brad

    2006-03-01

    Potential applications involving high-temperature shape memory alloys have been growing in recent years. Even in those cases where promising new alloys have been identified, the knowledge base for such materials contains gaps crucial to their maturation and implementation in actuator and other applications. We begin to address this issue by characterizing the mechanical behavior of a Ni 19.5Pd 30Ti 50.5 high-temperature shape memory alloy in both uniaxial tension and compression at various temperatures. Differences in the isothermal uniaxial deformation behavior were most notable at test temperatures below the martensite finish temperature. The elastic modulus of the material was very dependent on strain level; therefore, dynamic Young's Modulus was determined as a function of temperature by an impulse excitation technique. More importantly, the performance of a thermally activated actuator material is dependent on the work output of the alloy. Consequently, the strain-temperature response of the Ni 19.5Pd 30Ti 50.5 alloy under various loads was determined in both tension and compression and the specific work output calculated and compared in both loading conditions. It was found that the transformation strain and thus, the specific work output were similar regardless of the loading condition. Also, in both tension and compression, the strain-temperature loops determined under constant load conditions did not close due to the fact that the transformation strain during cooling was always larger than the transformation strain during heating. This was apparently the result of permanent plastic deformation of the martensite phase with each cycle. Consequently, before this alloy can be used under cyclic actuation conditions, modification of the microstructure or composition would be required to increase the resistance of the alloy to plastic deformation by slip.

  6. Giant solid-state barocaloric effect in the Ni-Mn-In magnetic shape-memory alloy.

    PubMed

    Mañosa, Lluís; González-Alonso, David; Planes, Antoni; Bonnot, Erell; Barrio, Maria; Tamarit, Josep-Lluís; Aksoy, Seda; Acet, Mehmet

    2010-06-01

    The search for materials showing large caloric effects close to room temperature has become a challenge in modern materials physics and it is expected that such a class of materials will provide a way to renew present cooling devices that are based on the vapour compression of hazardous gases. Up to now, the most promising materials are giant magnetocaloric materials. The discovery of materials showing a giant magnetocaloric effect at temperatures close to ambient has opened up the possibility of using them for refrigeration. As caloric effects refer to the isothermal entropy change achieved by application of an external field, several caloric effects can take place on tuning different external parameters such as pressure and electric field. Indeed the occurrence of large electrocaloric and elastocaloric effects has recently been reported. Here we show that the application of a moderate hydrostatic pressure to a magnetic shape-memory alloy gives rise to a caloric effect with a magnitude that is comparable to the giant magnetocaloric effect reported in this class of materials. We anticipate that similar barocaloric effects will occur in many giant-magnetocaloric materials undergoing magnetostructural transitions involving a volume change.

  7. Effects of Loading and Constraining Conditions on the Thermomechanical Fatigue Life of NiTi Shape Memory Wires

    NASA Astrophysics Data System (ADS)

    Scirè Mammano, G.; Dragoni, E.

    2014-07-01

    The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermal activation (thermomechanical fatigue) is central to the rational design of smart actuators based on these materials. Test results on SMAs under thermomechanical fatigue are scarce in the technical literature, and even the few data that are available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by antagonist SMA elements, their stress states are far from being constant in operation. The mismatch between actual working conditions and laboratory settings leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality by completing an experimental campaign involving four fatigue test conditions, which cover most of the typical situations occurring in practice: constant stress, constant-strain, constant stress with limited maximum strain, and linear stress-strain variation with limited maximum strain. The results from the first three test settings, recovered from the previously published works, are critically reviewed and compared with the outcome of the newly performed tests under the fourth arrangement (linear stress-strain variation). General design recommendations emerging from the experimental data are put forward for engineering use.

  8. Hybrid Shape Memory Alloy Composites for Extreme Environments

    DTIC Science & Technology

    2011-10-01

    Shape Memory Alloys in Oil Well Applications,” Sintef Petroleum Research, 1999, Trondheim, Norway. 5. Hartl, D. J., Lagoudas, D., Mabe, J., Calkins ...Materials and Structures, Vol. 19, No. 1., 2009. 6. Hartl, D. J., Lagoudas, D., Mabe, J., Calkins , F., and Mooney, J., “Use of Ni60Ti Shape Memory

  9. Effect of shock-wave loading on mechanical and thermomechanical characteristics of shape-memory alloys 45Ti-45Ni-10Nb and 43Ti-46Ni-8Nb-3Zr

    NASA Astrophysics Data System (ADS)

    Popov, N. N.; Lar'kin, V. F.; Ogorodnikov, V. A.; Presnyakov, D. V.; Lar'kina, Yu. A.; Aushev, A. A.; Sysoyeva, T. I.; Suvorova, E. B.; Kostyleva, A. A.

    2016-09-01

    This work was performed to study the behavior of 45Ti-45Ni-10Nb and 43Ti-46Ni-8Nb-3Zr (at %) shape-memory alloys (SMAs) under the effect of severe dynamic deformation to use the obtained results to develop technologies based on SMAs. Cast alloys were used for the tests. The elemental and phase compositions of the alloys in the initial state, as well as the phase composition, kinetics, and temperatures of phase transformations after heat treatment (annealing in a vacuum at 850°C for 4 h, furnace cooling) have been determined. The mechanical and thermomechanical characteristics of these alloys before and after shock-wave loading have been determined.

  10. Thermomechanical behavior and microstructural evolution of a Ni(Pd)-rich Ni24.3Ti49.7Pd26 high temperature shape memory alloy

    SciTech Connect

    Benafan, O.; Garg, A.; Noebe, R. D.; Bigelow, G. S.; Padula, S. A.; Gaydosh, D. J.; Vaidyanathan, R.; Clausen, B.; Vogel, S. C.

    2015-04-20

    We investigated the effect of thermomechanical cycling on a slightly Ni(Pd)-rich Ni24.3Ti49.7Pd26 (near stochiometric Ni–Ti basis with Pd replacing Ni) high temperature shape memory alloy. Furthermore, aged tensile specimens (400 °C/24 h/furnace cooled) were subjected to constant-stress thermal cycling in conjunction with microstructural assessment via in situ neutron diffraction and transmission electron microscopy (TEM), before and after testing. It was shown that in spite of the slightly Ni(Pd)-rich composition and heat treatment used to precipitation harden the alloy, the material exhibited dimensional instabilities with residual strain accumulation reaching 1.5% over 10 thermomechanical cycles. This was attributed to insufficient strengthening of the material (insufficient volume fraction of precipitate phase) to prevent plasticity from occurring concomitant with the martensitic transformation. In situ neutron diffraction revealed the presence of retained martensite while cycling under 300 MPa stress, which was also confirmed by transmission electron microscopy of post-cycled samples. Neutron diffraction analysis of the post-thermally-cycled samples under no-load revealed residual lattice strains in the martensite and austenite phases, remnant texture in the martensite phase, and peak broadening of the austenite phase. The texture we developed in the martensite phase was composed mainly of those martensitic tensile variants observed during thermomechanical cycling. Presence of a high density of dislocations, deformation twins, and retained martensite was revealed in the austenite state via in-situ TEM in the post-cycled material, providing an explanation for the observed peak broadening in the neutron diffraction spectra. Despite the dimensional instabilities, this alloy exhibited a biased transformation strain on the order of 3% and a two-way shape memory effect (TWSME) strain of ~2%, at relatively high actuation

  11. 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

  12. Shape memory metals. Final report

    SciTech Connect

    Dworak, T.D.

    1993-09-01

    The ability to define a manufacturing process to form, heat-treat, and join parts made of nickel-titanium and/or copper-zinc-aluminum shape memory alloys was investigated. The specific emphasis was to define a process that would produce shape memory alloy parts in the configuration of helical coils emulating the appearance of compression springs. In addition, the mechanical strength of the finished parts along with the development of a electrical lead attachment method using shape memory alloy wire was investigated.

  13. Development and Verification of Sputtered Thin-Film Nickel-Titanium (NiTi) Shape Memory Alloy (SMA)

    DTIC Science & Technology

    2015-08-01

    the films were sputtered onto a sacrificial 2 photoresist layer, released in acetone , and then rinsed with deionized water (DI) and dried...prepared by sputtering onto photoresist and lifting off the NiTi in acetone . Fig. 2 shows a DSC scan for the equiatomic Ni50Ti50. Of the compositions

  14. Effects of the interplay between atomic and magnetic order on the properties of metamagnetic Ni-Co-Mn-Ga shape memory alloys

    NASA Astrophysics Data System (ADS)

    Seguí, C.

    2014-03-01

    Ni-Co-Mn-Ga ferromagnetic shape memory alloys show metamagnetic behavior for a range of Co contents. The temperatures of the structural and magnetic transitions depend strongly on composition and atomic order degree, in such a way that combined composition and thermal treatment allows obtaining martensitic transformation between any magnetic state of austenite and martensite. This work presents a detailed analysis of the effect of atomic order on Ni-Co-Mn-Ga alloys through the evolution of structural and magnetic transitions after quench from high temperatures and during post-quest ageing. It is found that the way in which the atomic order affects the martensitic transformation temperatures and entropy depends on the magnetic order of austenite and martensite. The results can be explained assuming that improvement of atomic order decreases the free energy of the structural phases according to their magnetic order. However, it is assumed in this work that changes in the slope—that is, the entropy—of the Gibbs free energy curves are also decisive to the stability of the two-phase system. The experimental transformation entropy values have been compared with a phenomenological model, based on a Bragg-Williams approximation, accounting for the magnetic contribution. The excellent agreement obtained corroborates the magnetic origin of changes in transformation entropy brought about by atomic ordering.

  15. Observation on the transformation domains of super-elastic NiTi shape memory alloy and their evolutions during cyclic loading

    NASA Astrophysics Data System (ADS)

    Xie, Xi; Kan, Qianhua; Kang, Guozheng; Li, Jian; Qiu, Bo; Yu, Chao

    2016-04-01

    The strain field of a super-elastic NiTi shape memory alloy (SMA) and its variation during uniaxial cyclic tension-unloading were observed by a non-contact digital image correlation method, and then the transformation domains and their evolutions were indirectly investigated and discussed. It is seen that the super-elastic NiTi (SMA) exhibits a remarkable localized deformation and the transformation domains evolve periodically with the repeated cyclic tension-unloading within the first several cycles. However, the evolutions of transformation domains at the stage of stable cyclic transformation depend on applied peak stress: when the peak stress is low, no obvious transformation band is observed and the strain field is nearly uniform; when the peak stress is large enough, obvious transformation bands occur due to the residual martensite caused by the prevention of enriched dislocations to the reverse transformation from induced martensite to austenite. Temperature variations measured by an infrared thermal imaging method further verifies the formation and evolution of transformation domains.

  16. THE EFFECT OF REPEATED COMPRESSIVE DYNAMIC LOADING ON THE STRESS-INDUCED MARTENSITIC TRANSFORMATION IN NiTi SHAPE MEMORY ALLOYS

    SciTech Connect

    D. MILLER; W. THISSELL; ET AL

    2000-08-01

    It has been shown that quasi-static, cyclic, isothermal mechanical loading influences the mechanical response of the stress-induced martensitic transformation in fully annealed NiTi Shape Memory Alloys (SMAs). As the cycle number increases, hardening of the stress-strain response during the martensitic phase transformation is seen along with a decrease in the threshold stress for initiation of stress-induced martensite. Also, the amount of plastic strain and detwinned martensitic strain decreases as the cycle number increases. However, NiTi SMAs have not been experimentally explored under high compressive strain rates. This research explores the cyclic near-adiabatic stress-induced martensitic loading using a Split Hopkinskin Pressure Bar (SHPB). The results of the dynamic loading tests are presented with emphasis on the loading rate, stress-strain response, specimen temperature and post-test microstructural evaluation. The results from the high strain rate tests show similarities with the quasi-static results in the hardening of the stress-strain response and shifting of the threshold stress for initiation of stress-induced martensite.

  17. Design and fabrication of a bending rotation fatigue test rig for in situ electrochemical analysis during fatigue testing of NiTi shape memory alloy wires.

    PubMed

    Neelakantan, Lakshman; Zglinski, Jenni Kristin; Frotscher, Matthias; Eggeler, Gunther

    2013-03-01

    The current investigation proposes a novel method for simultaneous assessment of the electrochemical and structural fatigue properties of nickel-titanium shape memory alloy (NiTi SMA) wires. The design and layout of an in situ electrochemical cell in a custom-made bending rotation fatigue (BRF) test rig is presented. This newly designed test rig allows performing a wide spectrum of experiments for studying the influence of fatigue on corrosion and vice versa. This can be achieved by performing ex situ and∕or in situ measurements. The versatility of the combined electrochemical∕mechanical test rig is demonstrated by studying the electrochemical behavior of NiTi SMA wires in 0.9% NaCl electrolyte under load. The ex situ measurements allow addressing various issues, for example, the influence of pre-fatigue on the localized corrosion resistance, or the influence of hydrogen on fatigue life. Ex situ experiments showed that a pre-fatigued wire is more susceptible to localized corrosion. The synergetic effect can be concluded from the polarization studies and specifically from an in situ study of the open circuit potential (OCP) transients, which sensitively react to the elementary repassivation events related to the local failure of the oxide layer. It can also be used as an indicator for identifying the onset of the fatigue failure.

  18. The relation between lattice parameters and very low twinning stress in Ni50Mn25+x Ga25-x magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Straka, L.; Drahokoupil, J.; Pacherová, O.; Fabiánová, K.; Kopecký, V.; Seiner, H.; Hänninen, H.; Heczko, O.

    2016-02-01

    In search of the origins of the extraordinary low twinning stress of Ni-Mn-Ga 10M martensite, we studied the temperature induced changes in lattice parameters of Ni50Mn25+x Ga25-x (x = 2.7-3.9) single crystal samples and compared them with twinning stress dependences. The alloys exhibited transformation to five-layered (10M) martensite structure (cubic to monoclinic) between 297 to 328 K and exhibited the magnetic shape memory effect in martensite. The structural changes were monitored using x-ray diffraction in the temperature range 200-343 K. The 10M structure was approximated by monoclinic lattice, a = b > c, γ > 90° with the coordinates derived from the cubic unit cell of the parent L21 phase. The lattice parameters γ and c/a correlate well with the universal linear increase of twinning stress of type 1 twins with decreasing temperature. On the contrary, the twinning stress is not affected by differences between a and b and thus a/b twins seem to play no role in a - c twin boundary motion resulting in magnetically induced reorientation.

  19. Effects of the interplay between atomic and magnetic order on the properties of metamagnetic Ni-Co-Mn-Ga shape memory alloys

    SciTech Connect

    Seguí, C.

    2014-03-21

    Ni-Co-Mn-Ga ferromagnetic shape memory alloys show metamagnetic behavior for a range of Co contents. The temperatures of the structural and magnetic transitions depend strongly on composition and atomic order degree, in such a way that combined composition and thermal treatment allows obtaining martensitic transformation between any magnetic state of austenite and martensite. This work presents a detailed analysis of the effect of atomic order on Ni-Co-Mn-Ga alloys through the evolution of structural and magnetic transitions after quench from high temperatures and during post-quest ageing. It is found that the way in which the atomic order affects the martensitic transformation temperatures and entropy depends on the magnetic order of austenite and martensite. The results can be explained assuming that improvement of atomic order decreases the free energy of the structural phases according to their magnetic order. However, it is assumed in this work that changes in the slope—that is, the entropy—of the Gibbs free energy curves are also decisive to the stability of the two-phase system. The experimental transformation entropy values have been compared with a phenomenological model, based on a Bragg–Williams approximation, accounting for the magnetic contribution. The excellent agreement obtained corroborates the magnetic origin of changes in transformation entropy brought about by atomic ordering.

  20. Temperature variations at nano-scale level in phase transformed nanocrystalline NiTi shape memory alloys adjacent to graphene layers.

    PubMed

    Amini, Abbas; Cheng, Chun; Naebe, Minoo; Church, Jeffrey S; Hameed, Nishar; Asgari, Alireza; Will, Frank

    2013-07-21

    The detection and control of the temperature variation at the nano-scale level of thermo-mechanical materials during a compression process have been challenging issues. In this paper, an empirical method is proposed to predict the temperature at the nano-scale level during the solid-state phase transition phenomenon in NiTi shape memory alloys. Isothermal data was used as a reference to determine the temperature change at different loading rates. The temperature of the phase transformed zone underneath the tip increased by ∼3 to 40 °C as the loading rate increased. The temperature approached a constant with further increase in indentation depth. A few layers of graphene were used to enhance the cooling process at different loading rates. Due to the presence of graphene layers the temperature beneath the tip decreased by a further ∼3 to 10 °C depending on the loading rate. Compared with highly polished NiTi, deeper indentation depths were also observed during the solid-state phase transition, especially at the rate dependent zones. Larger superelastic deformations confirmed that the latent heat transfer through the deposited graphene layers allowed a larger phase transition volume and, therefore, more stress relaxation and penetration depth.

  1. The Influence of Hydrogen on Shape Memory Effect and Superelasticity in [001]-Oriented FeNiCoAlTi Single Crystals

    NASA Astrophysics Data System (ADS)

    Chumlyakov, Yu. I.; Kireeva, I. V.; Platonova, Yu. N.

    2016-04-01

    Using [001]-oriented single crystals of an iron-based alloy (Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% Ti at.%), which were aged at 973 K for 7 h, the influence of hydrogen on the axial-stress temperature response σ0.1(T), the values of shape-memory effect (SME) and superelasticity (SE) is investigated during thermoelastic γ-α'-martensitic transformation (MT) (γ-FCC - face centered lattice, α'-BCT - body centered tetragonal lattice) under tensile conditions. It is found that saturation of [001]-oriented single crystals of the Fe - 28% Ni - 17% Co - 11.5% Al - 2.5% Ti alloy with hydrogen within 2 h at T = 300 K and current density j = 50 mA/cm2 results in lower starting temperature, Ms, of a forward MT during cooling and Md temperature, increased strength properties of the high-temperature phase at Md temperature and wider temperature range of SE observation compared to hydrogen-free crystals. It is shown that hydrogen affects but only slightly the SME and SE values, the temperature and stress hysteresis under the above saturation mode. In [001]-oriented crystals aged at 973 K for 7 h, which are saturated with hydrogen and hydrogen-free, the SME and SE values are found to be equal to 7.8-8 and 6.5-6.9%, respectively.

  2. Design and fabrication of a bending rotation fatigue test rig for in situ electrochemical analysis during fatigue testing of NiTi shape memory alloy wires

    SciTech Connect

    Neelakantan, Lakshman; Zglinski, Jenni Kristin; Eggeler, Gunther; Frotscher, Matthias

    2013-03-15

    The current investigation proposes a novel method for simultaneous assessment of the electrochemical and structural fatigue properties of nickel-titanium shape memory alloy (NiTi SMA) wires. The design and layout of an in situ electrochemical cell in a custom-made bending rotation fatigue (BRF) test rig is presented. This newly designed test rig allows performing a wide spectrum of experiments for studying the influence of fatigue on corrosion and vice versa. This can be achieved by performing ex situ and/or in situ measurements. The versatility of the combined electrochemical/mechanical test rig is demonstrated by studying the electrochemical behavior of NiTi SMA wires in 0.9% NaCl electrolyte under load. The ex situ measurements allow addressing various issues, for example, the influence of pre-fatigue on the localized corrosion resistance, or the influence of hydrogen on fatigue life. Ex situ experiments showed that a pre-fatigued wire is more susceptible to localized corrosion. The synergetic effect can be concluded from the polarization studies and specifically from an in situ study of the open circuit potential (OCP) transients, which sensitively react to the elementary repassivation events related to the local failure of the oxide layer. It can also be used as an indicator for identifying the onset of the fatigue failure.

  3. 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 %.

  4. The Effect of Active Phase of the Work Material on Machining Performance of a NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Kaynak, Yusuf; Karaca, Haluk E.; Noebe, Ronald D.; Jawahir, I. S.

    2015-06-01

    Poor machinability with conventional machining processes is a major shortcoming that limits the manufacture of NiTi components. To better understand the effects of phase state on the machining performance of NiTi alloys, cutting temperature, tool-wear behavior, cutting force components, tool-chip contact length, chip thickness, and machined surface quality data were generated from a NiTi alloy using precooled cryogenic, dry, minimum quantity lubrication (MQL), and preheated machining conditions. Findings reveal that machining NiTi in the martensite phase, which was achieved through precooled cryogenic machining, profoundly improved the machining performance by reducing cutting force components, notch wear, and surface roughness. Machining in the austenite state, achieved through preheating, did not provide any benefit over dry and MQL machining, and these processes were, in general, inferior to cryogenic machining in terms of machining performance, particularly at higher cutting speeds.

  5. Understanding the phase transitions of the Ni2MnGa magnetic shape memory system from first principles.

    PubMed

    Uijttewaal, M A; Hickel, T; Neugebauer, J; Gruner, M E; Entel, P

    2009-01-23

    The free energies of the austenite, the (modulated) premartensite and the unmodulated martensite of Ni2MnGa are determined using density functional theory and including quasiharmonic phonons and fixed-spin-moment magnons. This approach very well reproduces the complete phase sequence (martensite<-->premartensite<-->austenite) of stoichiometric Ni2MnGa as a function of temperature. By analyzing the relevant free energy contributions, we also understand the delicate interplay of phonons and magnons driving both phase transitions.

  6. Shape Memory Response of Polycrystalline NiTi12.5Hf Alloy: Transformation at Small Scales

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Patriarca, L.; Li, G.; Sehitoglu, H.; Soejima, Y.; Ito, T.; Nishida, M.

    2015-09-01

    The transformation behavior of NiTiHf alloys is intriguing. In NiTiHf alloys, the experimental transformation strains have been reported to be considerably lower than theoretical transformation strains. In this study, the transformation strain is established with very careful strain measurements at small scales in isobaric and isothermal experiments. Because of the heterogeneity of strain distributions, the results depend on the sub-region considered. The measured local transformation strain can be as high as 6.0 % in compression which is in very good agreement with theoretical calculations for NiTi12.5Hf. The comprehension of NiTi12.5Hf alloy was furthered upon extensive microstructural characterization including high-resolution electron microscopy, establishing the volume fractions of precipitates and twin type. The volume fraction of precipitates is similar to that of Ni-rich binary NiTi alloys. Meanwhile, the twinning modes in the martensite are compound and Type I twins which were used in the theoretical calculations of transformation strains. This material also generates a high work output and represents a foundation for understanding higher Hf compositions.

  7. On the Recovery Stress of a Ni50.3Ti29.7Hf20 High Temperature Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Benafan, O.; Noebe, R. D.; Padula, S. A., II; Bigelow, G. S.; Gaydosh, D. J.; Garg, A.; Halsmer, T. J.

    2015-01-01

    Recovery stress in shape memory alloys (SMAs), also known as blocking stress, is an important property generally obtained during heating under a dimensional constraint as the material undergoes the martensitic phase transformation. This property has been instinctively utilized in most SMA shape-setting procedures, and has been used in numerous applications such as fastening and joining, rock splitting, safety release mechanisms, reinforced composites, medical devices, and many other applications. The stress generation is also relevant to actuator applications where jamming loads (e.g., in case the actuator gets stuck and is impeded from moving) need to be determined for proper hardware sizing. Recovery stresses in many SMA systems have been shown to reach stresses in the order of 800 MPa, achieved via thermo-mechanical training such as pre-straining, heat treatments or other factors. With the advent of high strength, high temperature SMAs, recovery stress data has been rarely probed, and there is no information pertinent to the magnitudes of these stresses. Thus, the purpose of this work is to investigate the recovery stress capability of a precipitation strengthened, Ni50.3Ti29.7Hf20 (at.) high temperature SMA in uniaxial tension and compression. This material has been shown to exhibit outstanding strength and stability during constant-stress, thermal cycling, but no data exists on constant-strain thermal cycling. Several training routines were implemented as part of this work including isothermal pre-straining, isobaric thermal cycling, and isothermal cyclic training routines. Regardless of the training method used, the recovery stress was characterized using constant-strain (strain-controlled condition) thermal cycling between the upper and lower cycle temperatures. Preliminary results indicate recovery stresses in excess of 1.5 GPa were obtained after a specific training routine. This stress magnitude is significantly higher than conventional NiTi stress

  8. Magnetic Compton scattering study of Ni2+xMn1-xGa ferromagnetic shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Ahuja, B. L.; Sharma, B. K.; Mathur, S.; Heda, N. L.; Itou, M.; Andrejczuk, A.; Sakurai, Y.; Chakrabarti, Aparna; Banik, S.; Awasthi, A. M.; Barman, S. R.

    2007-04-01

    In this paper, we report the spin-polarized momentum densities of Ni2+xMn1-xGa ( x=0.03 , 0.26, and 0.35) Heusler alloys at various temperatures and magnetic fields using magnetic Compton scattering technique. Magnetization studies are also performed for comparison. It is seen that the variation of magnetic effect (ratio of magnetic to charge intensities) is consistent with the martensitic transition, as shown by the differential scanning calorimetry data. The magnetic Compton profiles have been analyzed mainly in terms of the contributions from the 3d electrons of Mn to determine their role in the formation of total spin moment. The full potential linearized augmented plane-wave method has been used to calculate the spin-polarized energy bands and the spin moments of Ni2MnGa and Ni2.25Mn0.75Ga . Ni2MnGa exhibits half metallicity along certain high-symmetry directions of the Brillouin zone. For Ni2MnGa , the total and Mn local moments obtained from Compton scattering are in excellent agreement with theory.

  9. Fretting behavior of NiTi shape memory alloy against long bone in the imitated human physiological solution

    NASA Astrophysics Data System (ADS)

    Yin, Y.; Xu, Y. T.; Xia, T. D.; Da, G. Z.

    2007-07-01

    The environment of orthopaedic implants sometimes induces vibrations at the contact of the modular prostheses components. In this paper the fretting behavior of NiTi SMAs against human bones in the imitated human physiological solution was studied at various displacement amplitudes and Ph value. Surface micrograph after fretting was observed by MEF3 microscope. Appearance of fretting scar was measured by 2206 roughness tester. The result shows that the friction coefficient between the bone and NiTi SMAs pairs declined due to the lubrication effect of Hank's solution, and which increased when Ph value of fluid was not 7.2 due to the corrosion. So the friction coefficient at acid and alkali Hank's solution is higher than those at the neutral solution and ambient air condition. Generally speaking, the friction coefficient between the bone and NiTi SMAs tend to be stable with the increasing amplitude at all test conditions. It is because that the surface was oxidized to restrain the forming of wear debris and the further development of fretting scars. Although the length and width of the wear scars in simulation body fluid are smaller than that at ambient air condition, the surface of NiTi SMAs damaged is characterized by deep scratches with debris particles within the contact area. Fretting regime of NiTi/bones pairs exhibits the mixed regime at ambient air condition and the slip regime in the Hank's solution.

  10. Magnetic and magnetocaloric properties of ferromagnetic shape memory alloy Mn50Ni40In10-xSbx

    NASA Astrophysics Data System (ADS)

    Liu, Hongyan; Liu, Zhuhong; Li, Getian; Ma, Xingqiao

    2016-10-01

    Magnetic properties of Mn50Ni40In10-xSbx alloys and thermal history effect on the magnetization behavior and magnetic entropy change of Mn50Ni40In9Sb1 have been systematically studied. It indicates that the martensitic transformation temperature gradually increases with the increase of Sb content. Meanwhile, the overall magnetization of austenite decreases and that of martensite increases. The magnetization behavior, the critical magnetic field for martensite-to-austenite transformation and the magnetic entropy are very sensitive to the thermal history effect. The maximum magnetic entropy change is up to 27.1 J kg-1 K-1 in Mn50Ni40In9Sb1 alloy under a magnetic field of 30 kOe with continuous heating method.

  11. Effect of Isothermal Aging on the Physical Properties of Mn53Ni23Ga22 Ferromagnetic Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Dong, G. F.; Gao, Z. Y.

    2016-09-01

    The effect of isothermal aging on the physical properties of Mn53Ni25Ga22 alloy has been systematically investigated. The results showed that the (Mn,Ni)4Ga-type precipitates are observed in all isothermal aged samples. However, second phases tended to align into grains and had two preferred orientations. The martensitic transformation temperatures decreased remarkably with the increase of aging time, while structure of the alloy gradually changed from five-layer tetragonal martensite to austenite. Additionally, we found that the appropriate aging-treated alloys can significantly enhance the saturation magnetization of Mn53Ni25Ga22 alloy. However, the Curie temperatures decreased remarkably with increased aging time due to the variation of the composition of the alloy.

  12. Three-dimensional deformation response of a NiTi shape memory helical-coil actuator during thermomechanical cycling: experimentally validated numerical model

    NASA Astrophysics Data System (ADS)

    Dhakal, B.; Nicholson, D. E.; Saleeb, A. F.; Padula, S. A., II; Vaidyanathan, R.

    2016-09-01

    Shape memory alloy (SMA) actuators often operate under a complex state of stress for an extended number of thermomechanical cycles in many aerospace and engineering applications. Hence, it becomes important to account for multi-axial stress states and deformation characteristics (which evolve with thermomechanical cycling) when calibrating any SMA model for implementation in large-scale simulation of actuators. To this end, the present work is focused on the experimental validation of an SMA model calibrated for the transient and cyclic evolutionary behavior of shape memory Ni49.9Ti50.1, for the actuation of axially loaded helical-coil springs. The approach requires both experimental and computational aspects to appropriately assess the thermomechanical response of these multi-dimensional structures. As such, an instrumented and controlled experimental setup was assembled to obtain temperature, torque, degree of twist and extension, while controlling end constraints during heating and cooling of an SMA spring under a constant externally applied axial load. The computational component assesses the capabilities of a general, multi-axial, SMA material-modeling framework, calibrated for Ni49.9Ti50.1 with regard to its usefulness in the simulation of SMA helical-coil spring actuators. Axial extension, being the primary response, was examined on an axially-loaded spring with multiple active coils. Two different conditions of end boundary constraint were investigated in both the numerical simulations as well as the validation experiments: Case (1) where the loading end is restrained against twist (and the resulting torque measured as the secondary response) and Case (2) where the loading end is free to twist (and the degree of twist measured as the secondary response). The present study focuses on the transient and evolutionary response associated with the initial isothermal loading and the subsequent thermal cycles under applied constant axial load. The experimental

  13. Structure and thermoelastic martensitic transformations in ternary Ni-Ti-Hf alloys with a high-temperature shape memory effect

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Kuranova, N. N.; Pushin, A. V.; Uksusnikov, A. N.; Kourov, N. I.

    2016-07-01

    The effect of alloying by 12-20 at % Hf on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary alloys of the quasi-binary NiTi-NiHf section is studied by transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction. The electrical resistivity is measured at various temperatures to determine the critical transformation temperatures. The data on phase composition are used to plot a full diagram for the high-temperature thermoelastic B2 ↔ B19' martensitic transformations, which occur in the temperature range 320-600 K when the hafnium content increases from 12 to 20 at %. The lattice parameters of the B2 and B19' phases are measured, and the microstructure of the B19' martensite is analyzed.

  14. Nickel release behavior and surface characteristics of porous NiTi shape memory alloy modified by different chemical processes.

    PubMed

    Wu, Shuilin; Liu, Xiangmei; Chan, Y L; Chu, Paul K; Chung, C Y; Chu, Chenglin; Yeung, Kelvin W K; Lu, W W; Cheung, Kenneth M C; Luk, K D K

    2009-05-01

    As a non-line-of-sight surface modification technique, chemical treatment is an effective method to treat porous NiTi with complex surface morphologies and large exposed areas due to its liquidity and low temperature. In the work described here, three different chemical processes are used to treat porous NiTi alloys. Our results show that H(2)O(2) treatment, NaOH treatment, and H(2)O(2) pre-treatment plus subsequent NaOH treatment can mitigate leaching of nickel from the alloy. The porous NiTi samples modified by the two latter processes favor deposition of a layer composed of Ca and P due to the formation of bioactive Na(2)TiO(3) on the surface. Among the three processes, H(2)O(2) pre-treatment plus subsequent NaOH modification is the most effective in suppressing nickel release. Small area X-ray photoelectron spectroscopy reveals that the surfaces treated by different chemical processes have different structures and compositions. The sample modified by the H(2)O(2) treatment is composed of rough TiO(2) on the outer surface and an oxide transition layer underneath whereas the sample treated by NaOH comprises a surface layer of titanium oxide and Na(2)TiO(3) together with a transition layer. The sample processed by the H(2)O(2) and NaOH treatment has a pure Na(2)TiO(3) layer on the surface and a transition layer underneath. These results help to elucidate the different nickel release behavior and bioactivity of porous NiTi alloys processed by different methods.

  15. 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).

  16. Residual stress induced stabilization of martensite phase and its effect on the magnetostructural transition in Mn-rich Ni-Mn-In/Ga magnetic shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Singh, Sanjay; Kushwaha, Pallavi; Scheibel, F.; Liermann, Hanns-Peter; Barman, S. R.; Acet, M.; Felser, C.; Pandey, Dhananjai

    2015-07-01

    The irreversibility of the martensite transition in magnetic shape memory alloys (MSMAs) with respect to the external magnetic field is one of the biggest challenges that limits their application as giant caloric materials. This transition is a magnetostructural transition that is accompanied with a steep drop in magnetization (i.e.,Δ M ) around the martensite start temperature (Ms) due to the lower magnetization of the martensite phase. In this Rapid Communication, we show that Δ M around Ms in Mn-rich Ni-Mn-based MSMAs gets suppressed by two orders of magnitude in crushed powders due to the stabilization of the martensite phase at temperatures well above Ms and the austenite finish (Af) temperatures due to residual stresses. Analysis of the intensities and the FWHM of the x-ray powder-diffraction patterns reveals stabilized martensite phase fractions as 97 % , 75 % , and 90 % with corresponding residual microstrains as 5.4 % , 5.6 % , and 3 % in crushed powders of the three different Mn-rich Ni-Mn alloys, namely, M n1.8N i1.8I n0.4 , M n1.75N i1.25Ga , and M n1.9N i1.1Ga , respectively. Even after annealing at 773 K, the residual stress stabilized martensite phase does not fully revert to the equilibrium cubic austenite phase as the magnetostructural transition is only partially restored with a reduced value of Δ M . Our results have a very significant bearing on the application of such alloys as inverse magnetocaloric and barocaloric materials.

  17. Development and Characterization of Improved NiTiPd High-Temperature Shape-Memory Alloys by Solid-Solution Strengthening and Thermomechanical Processing

    NASA Technical Reports Server (NTRS)

    Bigelow, Glen; Noebe, Ronald; Padula, Santo, II; Garg, Anita; Olson, David

    2006-01-01

    The need for compact, solid-state actuation systems for use in the aerospace, automotive, and other transportation industries is currently motivating research in high-temperature shape-memory alloys (HTSMA) with transformation temperatures greater than 100 C. One of the basic high-temperature alloys investigated to fill this need is Ni(19.5)Ti(50.5)Pd30. Initial testing has indicated that this alloy, while having acceptable work characteristics, suffers from significant permanent deformation (or ratcheting) during thermal cycling under load. In an effort to overcome this deficiency, various solid-solution alloying and thermomechanical processing schemes were investigated. Solid-solution strengthening was achieved by substituting 5at% gold or platinum for palladium in Ni(19.5)Ti(50.5)Pd30, the so-called baseline alloy, to strengthen the martensite and austenite phases against slip processes and improve thermomechanical behavior. Tensile properties, work behavior, and dimensional stability during repeated thermal cycling under load for the ternary and quaternary alloys were compared. The relative difference in yield strength between the martensite and austenite phases and the dimensional stability of the alloy were improved by the quaternary additions, while work output was only minimally impacted. The three alloys were also thermomechanically processed by cycling repeatedly through the transformation range under a constant stress. This so-called training process dramatically improved the dimensional stability in these samples and also recovered the slight decrease in work output caused by quaternary alloying. An added benefit of the solid-solution strengthening was maintenance of enhanced dimensional stability of the trained material to higher temperatures compared to the baseline alloy, providing a greater measure of over-temperature capability.

  18. Shape memory polymer foams for endovascular therapies

    DOEpatents

    Wilson, Thomas S.; Maitland, Duncan J.

    2015-05-26

    A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

  19. Shape memory polymer foams for endovascular therapies

    DOEpatents

    Wilson, Thomas S.; Maitland, Duncan J.

    2017-03-21

    A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

  20. Shape memory polymer foams for endovascular therapies

    DOEpatents

    Wilson, Thomas S [Castro Valley, CA; Maitland, Duncan J [Pleasant Hill, CA

    2012-03-13

    A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

  1. Effect of Nano CeO2 Addition on the Microstructure and Properties of a Cu-Al-Ni Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Pandey, Abhishek; Jain, Ashish Kumar; Hussain, Shahadat; Sampath, V.; Dasgupta, Rupa

    2016-08-01

    This article deals with the effect of adding nano CeO2 to act as a grain pinner/refiner to a known Cu-Al-Ni shape memory alloy. Elements were taken in a predefined ratio to prepare 300 g alloy per batch and melted in an induction furnace. Casting was followed by homogenization at 1173 K (900 °C) and rolling to make sheets of 0.5-mm thickness. Further, samples were characterized for microstructure using optical and electron microscope, hardness, and different phase studies by X-ray and transformation temperatures by differential scanning calorimetry. X-ray peak broadenings and changes were investigated to estimate the crystallite size, lattice strain, and phase changes due to different processing steps. A nearly uniform distribution of CeO2 and better martensitic structure were observed with increasing CeO2. The addition of CeO2 also shows a visible effect on the transformation temperature and phase formation.

  2. In-situ TOF neutron diffraction studies of cyclic softening in superelasticity of a NiFeGaCo shape memory alloy

    DOE PAGES

    Yang, Hui; Yu, Dunji; Chen, Yan; ...

    2016-10-24

    Real-time in-situ neutron diffraction was conducted during uniaxial cycling compression of a Ni49.3Fe18Ga27Co5.7 shape memory alloy to explore the mechanism on its superelasticity at room temperature, which was manifested by the almost recoverable large strains and the apparent cyclic softening. Based on the Rietveld refinements, the real-time evolution of volume fraction of martensite was in-situ monitored, indicating the incremental amount of residual martensite with increasing load cycles. Real-time changes in intensities and lattice strains of {hkl} reflections for individual phase were obtained through fitting individual peaks, which reveal the quantitative information on phase transformation kinetics as a function ofmore » grain orientation and stress/strain partitioning. Moreover, a large compressive residual stress was evidenced in the parent phase, which should be balanced by the residual martensite after the second unloading cycle. As a result, the large compressive residual stress found in the parent austenite phase may account for the cyclic effect on critical stress required for triggering the martensitic transformation in the subsequent loading.« less

  3. Simulations of Self-Expanding Braided Stent Using Macroscopic Model of NiTi Shape Memory Alloys Covering R-Phase

    NASA Astrophysics Data System (ADS)

    Frost, M.; Sedlák, P.; Kruisová, A.; Landa, M.

    2014-07-01

    Self-expanding stents or stentgrafts made from Nitinol superelastic alloy are widely used for a less invasive treatment of disease-induced localized flow constriction in the cardiovascular system. The therapy is based on insertion of a stent into a blood vessel to maintain the inner diameter of the vessel; it provides highly effective results at minimal cost and with reduced hospital stays. However, since stent is an external mechanical healing tool implemented into human body for quite a long time, information on the mechanical performance of it is of fundamental importance with respect to patient's safety and comfort. Advantageously, computational structural analysis can provide valuable information on the response of the product in an environment where in vivo experimentation is extremely expensive or impossible. With this motivation, a numerical model of a particular braided self-expanding stent was developed. As a reasonable approximation substantially reducing computational demands, the stent was considered to be composed of a set of helical springs with specific constrains reflecting geometry of the structure. An advanced constitutive model for NiTi-based shape memory alloys including R-phase transition was employed in analysis. Comparison to measurements shows a very good match between the numerical solution and experimental results. Relation between diameter of the stent and uniform radial pressure on its surface is estimated. Information about internal phase and stress state of the material during compression loading provided by the model is used to estimate fatigue properties of the stent during cyclic loading.

  4. Crystal lattice of martensite and the reserve of recoverable strain of thermally and thermomechanically treated Ti-Ni shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Prokoshkin, S. D.; Korotitskiy, A. V.; Brailovski, V.; Inaekyan, K. E.; Dubinskiy, S. M.

    2011-08-01

    X-ray diffraction has been used to study shape-memory alloys of composition Ti-(49.73-51.05 at %) Ni subjected to quenching and thermomechanical treatment (TMT) by the scheme "cold deformation ( e = 0.3-1.9) + postdeformation annealing (200-500°C) to provide different defectness of the parent B2 austenite. For the quenched alloys, the concentration dependences of the lattice parameters of the B19' martensite, maximum lattice strain upon martensitic transformation, the crystallographic orientation of the lattice in single crystals, and the reserve of recoverable strain in polycrystals have been determined. The lattice parameters of martensite formed from polygonized, i.e., nanosubgranular, or from nanocrystalline austenite differ from the corresponding parameters of quenched martensite formed from recrystallized austenite, and their difference increases with increasing defectness of the parent-austenite lattice. An increase in the defectness of the austenite lattice is accompanied by a decrease in the reserve of recoverable strain. The deformation of the existing martensite or the formation of stress-assisted martensite under the anisotropic action of external stresses changes the interplanar spacing and the thermal expansion coefficient in different crystallographic directions but does not affect the averaged lattice parameters near the M s- M f interval and the reserve of recoverable strain.

  5. In-situ TOF neutron diffraction studies of cyclic softening in superelasticity of a NiFeGaCo shape memory alloy

    SciTech Connect

    Yang, Hui; Yu, Dunji; Chen, Yan; Mu, Juan; Wang, Y. D.; An, Ke

    2016-10-24

    Real-time in-situ neutron diffraction was conducted during uniaxial cycling compression of a Ni49.3Fe18Ga27Co5.7 shape memory alloy to explore the mechanism on its superelasticity at room temperature, which was manifested by the almost recoverable large strains and the apparent cyclic softening. Based on the Rietveld refinements, the real-time evolution of volume fraction of martensite was in-situ monitored, indicating the incremental amount of residual martensite with increasing load cycles. Real-time changes in intensities and lattice strains of {hkl} reflections for individual phase were obtained through fitting individual peaks, which reveal the quantitative information on phase transformation kinetics as a function of grain orientation and stress/strain partitioning. Moreover, a large compressive residual stress was evidenced in the parent phase, which should be balanced by the residual martensite after the second unloading cycle. As a result, the large compressive residual stress found in the parent austenite phase may account for the cyclic effect on critical stress required for triggering the martensitic transformation in the subsequent loading.

  6. Fabrication of a helical coil shape memory alloy actuator

    NASA Astrophysics Data System (ADS)

    Odonnell, R. E.

    1992-02-01

    A fabrication process was developed to form, heat treat, and join NiTi shape memory alloy helical coils for use as mechanical actuators. Tooling and procedures were developed to wind both extension and compression-type coils on a manual lathe. Heat treating fixtures and techniques were used to set the 'memory' of the NiTi alloy to the desired configuration. A swaging process was devised to fasten shape memory alloy extension coils to end fittings for use in actuator testing and for potential attachment to mechanical devices. The strength of this mechanical joint was evaluated.

  7. Fabrication of a helical coil shape memory alloy actuator

    SciTech Connect

    O'Donnell, R.E.

    1992-02-01

    A fabrication process was developed to form, heat treat, and join NiTi shape memory alloy helical coils for use as mechanical actuators. Tooling and procedures were developed to wind both extension and compression-type coils on a manual lathe. Heat treating fixtures and techniques were used to set the memory'' of the NiTi alloy to the desired configuration. A swaging process was devised to fasten shape memory alloy extension coils to end fittings for use in actuator testing and for potential attachment to mechanical devices. The strength of this mechanical joint was evaluated.

  8. Fabrication of a helical coil shape memory alloy actuator

    SciTech Connect

    O`Donnell, R.E.

    1992-02-01

    A fabrication process was developed to form, heat treat, and join NiTi shape memory alloy helical coils for use as mechanical actuators. Tooling and procedures were developed to wind both extension and compression-type coils on a manual lathe. Heat treating fixtures and techniques were used to set the ``memory`` of the NiTi alloy to the desired configuration. A swaging process was devised to fasten shape memory alloy extension coils to end fittings for use in actuator testing and for potential attachment to mechanical devices. The strength of this mechanical joint was evaluated.

  9. Multifunctional shape-memory polymers.

    PubMed

    Behl, Marc; Razzaq, Muhammad Yasar; Lendlein, Andreas

    2010-08-17

    The thermally-induced shape-memory effect (SME) is the capability of a material to change its shape in a predefined way in response to heat. In shape-memory polymers (SMP) this shape change is the entropy-driven recovery of a mechanical deformation, which was obtained before by application of external stress and was temporarily fixed by formation of physical crosslinks. The high technological significance of SMP becomes apparent in many established products (e.g., packaging materials, assembling devices, textiles, and membranes) and the broad SMP development activities in the field of biomedical as well as aerospace applications (e.g., medical devices or morphing structures for aerospace vehicles). Inspired by the complex and diverse requirements of these applications fundamental research is aiming at multifunctional SMP, in which SME is combined with additional functions and is proceeding rapidly. In this review different concepts for the creation of multifunctionality are derived from the various polymer network architectures of thermally-induced SMP. Multimaterial systems, such as nanocomposites, are described as well as one-component polymer systems, in which independent functions are integrated. Future challenges will be to transfer the concept of multifunctionality to other emerging shape-memory technologies like light-sensitive SMP, reversible shape changing effects or triple-shape polymers.

  10. Theoretical investigation of the magnetic and structural transitions of Ni-Co-Mn-Sn metamagnetic shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Li, Chun-Mei; Hu, Qing-Miao; Yang, Rui; Johansson, Börje; Vitos, Levente

    2015-07-01

    The composition-dependent crystal structure, elastic modulus, phase stability, and magnetic property of Ni2 -xCoxMn1.60Sn0.40 (0 ≤x ≤0.50 ) are studied by using first-principles calculations in combination with atomistic spin dynamics method. It is shown that the present lattice parameters and Curie temperature (TC) are in agreement with the available experimental data. The martensitic phase transformation (MPT) occurs for x <0.43 , where the austenite is in the ferromagnetic (FM) state whereas the martensite is in the antiferromagnetic (AFM) one at 0 K. The x dependence of the lattice parameter, elastic modulus, and energy difference between the FM austenite and the AFM martensite well accounts for the decrease of the MPT temperature (TM) with the Co addition. With increasing x , the increase of the magnetic excitation energy between the paramagnetic and FM austenite of these alloys is in line with the TC˜x . The Ni 3 d as well as the Co 3 d electronic states near the Fermi level are confirmed mainly dominating the phase stability of the studied alloys.

  11. Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Noebe, R. D.

    2013-01-01

    This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

  12. Thermomechanical model for evaluation of the superelastic response of NiTi shape memory alloys under dynamic conditions

    NASA Astrophysics Data System (ADS)

    Soul, H.; Yawny, A.

    2013-03-01

    The development of a 1D thermomechanical model for simulating the response of uniaxial superelastic NiTi elements is described. The formulation of the model includes consideration of the dependence of the critical stresses for forward and reverse transformation on the temperature, the occurrence of strain rate effects due to self-heating/cooling associated with the latent heat of the stress induced martensitic transformation, the localized character of the stress induced transformation in superelastic NiTi wires and ribbons, the possibility of nucleation events during both the forward and reverse transformations and the occurrence of non-recoverable residual strains. Numerical simulations allowed rationalization of different features commonly observed in experiments and their dependence on strain rate and environment conditions. Comparisons of numerical results with experimental cycles obtained in the present work and also with data published in the literature indicate the potentiality of the developed model as a design tool for simulating the response of superelastic materials subjected to realistic service conditions.

  13. 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.

  14. Magnetic structure and phase transition of Ni2Mn1.48Sb0.52 magnetic shape memory compound

    DOE PAGES

    Yang, Y. B.; Liu, S. Q.; Zhao, H.; ...

    2016-02-06

    Here, a comprehensive study of the structural and magnetic properties of the Ni2Mn1.48Sb0.52 compound is presente using neutron diffraction and magnetic measurements. It is found that Mn atoms on 4a and 4 sites are ferrimagnetic coupled in the austenitic phase. At 300 K, the magnetic moments of Mn (4a) an Mn (4b) are determined to be 2.72(3) μB and -2.67(5) μB, respectively. From 260 K to 4 K, the compound is in martensite phase and the magnetic moments of Mn (2a), Mn (2f), Mn (2b), Mn (2e) at 4 K ar 2.2(5) μB, 2.3(5) μB, -2.1(5) μB, and -2.6(5) μB,more » respectively.« less

  15. 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

  16. Understanding the shape-memory alloys used in orthodontics.

    PubMed

    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.

  17. 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.

  18. Structural and phase transformations in quasi-binary TiNi-TiCu alloys with thermomechanical shape-memory effects

    NASA Astrophysics Data System (ADS)

    Pushin, V. G.; Kuranova, N. N.; Makarov, V. V.; Pushin, A. V.; Korolev, A. V.; Kourov, N. I.

    2015-12-01

    The structure, thermoelastic martensitic transformations, and physical properties of the usual microcrystalline and rapidly quenched submicrocrystalline ternary alloys of the quasi-binary TiNi-TiCu section with a copper content to 35 at % have been studied in a wide temperature range. The fine structure of the alloys has been investigated by the methods of the analytical transmission and scanning electron microscopy, and selected-area electron diffraction, including the in situ heating and cooling in the column of the microscope. The main specific features of the premartensitic state of the B2 austenite, the morphology, and the fine structure of the B19 and B19' martensitic phases have been established, and their evolution upon the alloying with copper and upon grain refinement and cooling and heating in situ have been studied. According to the data of the temperature measurements of electrical resistance, magnetic susceptibility, and XRD analysis, generalized complete diagrams of the B2 ↔ B19', B2 ↔ B19 ↔ B19' and B2↔ B19 martensitic transformations that occur upon cooling in these alloys with an increase in the copper concentration in the limits of 0-8, 8-15, and 15-35 at %, respectively, have been constructed.

  19. FOREWORD: Shape Memory and Related Technologies

    NASA Astrophysics Data System (ADS)

    Liu, Yong

    2005-10-01

    The International Symposium on Shape Memory and Related Technologies (SMART2004) successfully took place in Singapore from November 24 to 26, 2004. SMART2004 aimed to provide a forum for presenting and discussing recent developments in the processing, characterization, application and performance prediction of shape memory materials, particularly shape memory alloys and magnetic shape memory materials. In recent years, we have seen a surge in the research and application of shape memory materials. This is due on the one hand to the successful applications of shape memory alloys (SMAs), particularly NiTi (nitinol), in medical practices and, on the other hand, to the discovery of magnetic shape memory (MSM) materials (or, ferromagnetic shape memory alloys, FSMAs). In recent years, applications of SMAs in various engineering practices have flourished owing to the unique combination of novel properties including high power density related to shape recovery, superelasticity with tunable hysteresis, high damping capacity combined with good fatigue resistance, excellent wear resistance due to unconventional deformation mechanisms (stress-induced phase transformation and martensite reorientation), and excellent biocompatibility and anticorrosion resistance, etc. In~the case of MSMs (or FSMAs), their giant shape change in a relatively low magnetic field has great potential to supplement the traditional actuation mechanisms and to have a great impact on the world of modern technology. Common mechanisms existing in both types of materials, namely thermoelastic phase transformation, martensite domain switching and their controlling factors, are of particular interest to the scientific community. Despite some successful applications, some fundamental issues remain unsatisfactorily understood. This conference hoped to link the fundamental research to engineering practices, and to further identify remaining problems in order to further promote the applications of shape memory

  20. Magnetic shape memory effect in thin foils

    NASA Astrophysics Data System (ADS)

    Heczko, Oleg; Soroka, Aleksandr; Hannula, Simo-Pekka

    2008-07-01

    The magnetic shape memory (MSM) effect was observed in Ni-Mn-Ga freestanding thin foils down to 90μm in thickness using top-down approach. The foils were prepared by thinning the bulk crystals exhibiting MSM effect. The effect was evaluated from the magnetization curves. The significant decrease in magnetic field needed to initiate the MSM effect (magnetic field induced strain or martensite structure reorientation) was observed for the studied foils down to μ0H=0.088T or H =70kA/m. Observation suggests that the pinning of twin boundaries on the internal obstacles rather than pinning on surface lowers twin boundaries' mobility.

  1. 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.

  2. a Study on Fatigue Damage of Shape Memory Alloy Composite Using Nde Technique

    NASA Astrophysics Data System (ADS)

    Park, Young-Chul; Lee, Jin-Kyung; Lee, Sang-Pill; Lee, Gyu-Chang; Lee, Joon-Hyun; Cho, Youn-Ho; Lee, Jong-Back

    TiNi shape memory alloy was used to recover the shape of transformed objects using its shape memory effect. This shape memory effect plays an important role inside metal matrix composite. A composite using shape memory alloy has a large advantage that can control crack initiation and propagation, when compared with other composites due to the shape memory effect of shape memory alloy under high temperature. In this study, TiNi/Al6061 and TiNi/2024 shape memory composites were fabricated by the hot press method, and a fatigue test was performed to evaluate the fatigue damage for the shape memory composites under room temperature and high temperature. The relationship of the crack growth rate and the stress intensity factor for these shape memory composites were clarified at both temperature conditions. The delay effect of crack propagation due to shape memory alloy was also evaluated under high temperature. In addition, an acoustic emission technique was used to evaluate the crack initiation and the control of crack propagation by shape memory effect under fatigue test nondestructively. The relationship between AE parameter and the degree of fatigue damage of the shape memory composites was discussed.

  3. Modeling and Bayesian Parameter Estimation for Shape Memory Alloy Bending Actuators

    DTIC Science & Technology

    2012-02-01

    prosthetic hand,” Technology and Health Care 10, 91–106 (2002). 4. Hartl, D., Lagoudas, D., Calkins , F., and Mabe, J., “Use of a ni60ti shape memory...Lagoudas, D., Calkins , F., and Mabe, J., “Use of a ni60ti shape memory alloy for active jet engine chevron application: II. experimentally validated

  4. A nanoscale shape memory oxide

    NASA Astrophysics Data System (ADS)

    Zhang, Jinxing; Ke, Xiaoxing; Gou, Gaoyang; Seidel, Jan; Xiang, Bin; Yu, Pu; Liang, Wen-I.; Minor, Andrew M.; Chu, Ying-Hao; van Tendeloo, Gustaaf; Ren, Xiaobing; Ramesh, Ramamoorthy

    2013-11-01

    Stimulus-responsive shape-memory materials have attracted tremendous research interests recently, with much effort focused on improving their mechanical actuation. Driven by the needs of nanoelectromechanical devices, materials with large mechanical strain, particularly at nanoscale level, are therefore desired. Here we report on the discovery of a large shape-memory effect in bismuth ferrite at the nanoscale. A maximum strain of up to ~14% and a large volumetric work density of ~600±90 J cm-3 can be achieved in association with a martensitic-like phase transformation. With a single step, control of the phase transformation by thermal activation or electric field has been reversibly achieved without the assistance of external recovery stress. Although aspects such as hysteresis, microcracking and so on have to be taken into consideration for real devices, the large shape-memory effect in this oxide surpasses most alloys and, therefore, demonstrates itself as an extraordinary material for potential use in state-of-art nanosystems.

  5. Shape memory polymer actuator and catheter

    DOEpatents

    Maitland, Duncan J.; Lee, Abraham P.; Schumann, Daniel L.; Matthews, Dennis L.; Decker, Derek E.; Jungreis, Charles A.

    2004-05-25

    An actuator system is provided for acting upon a material in a vessel. The system includes an optical fiber and a shape memory polymer material operatively connected to the optical fiber. The shape memory polymer material is adapted to move from a first shape for moving through said vessel to a second shape where it can act upon said material.

  6. Shape memory polymer actuator and catheter

    DOEpatents

    Maitland, Duncan J.; Lee, Abraham P.; Schumann, Daniel L.; Matthews, Dennis L.; Decker, Derek E.; Jungreis, Charles A.

    2007-11-06

    An actuator system is provided for acting upon a material in a vessel. The system includes an optical fiber and a shape memory polymer material operatively connected to the optical fiber. The shape memory polymer material is adapted to move from a first shape for moving through said vessel to a second shape where it can act upon said material.

  7. Porous shape memory alloy scaffolds for biomedical applications: a review

    NASA Astrophysics Data System (ADS)

    Wen, C. E.; Xiong, J. Y.; Li, Y. C.; Hodgson, P. D.

    2010-05-01

    The interest in using porous shape memory alloy (SMA) scaffolds as implant materials has been growing in recent years due to the combination of their unique mechanical and functional properties, i.e. shape memory effect and superelasticity, low elastic modulus combined with new bone tissue ingrowth ability and vascularization. These attractive properties are of great benefit to the healing process for implant applications. This paper reviews current state-of-the art on the processing, porous characteristics and mechanical properties of porous SMAs for biomedical applications, with special focus on the most widely used SMA nickel-titanium (NiTi), including (i) microstructural features, mechanical and functional properties of NiTi SMAs; (ii) main processing methods for the fabrication of porous NiTi SMAs and their mechanical properties and (iii) new-generation Ni-free, biocompatible porous SMA scaffolds.

  8. Effect of Thermomechanical Processing on the Microstructure, Properties, and Work Behavior of a Ti50.5 Ni29.5 Pt20 High-Temperature Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald; Draper, Susan; Gaydosh, Darrell; Garga, Anita; Lerch, Brad; Penney, Nicholas; Begelow, Glen; Padula, Santo, II; Brown, Jeff

    2006-01-01

    TiNiPt shape memory alloys are particularly promising for use as solid state actuators in environments up to 300 C, due to a reasonable balance of properties, including acceptable work output. However, one of the challenges to commercializing a viable high-temperature shape memory alloy (HTSMA) is to establish the appropriate primary and secondary processing techniques for fabrication of the material in a required product form such as rod and wire. Consequently, a Ti(50.5)Ni(29.5)Pt20 alloy was processed using several techniques including single-pass high-temperature extrusion, multiple-pass high-temperature extrusion, and cold drawing to produce bar stock, thin rod, and fine wire, respectively. The effects of heat treatment on the hardness, grain size, room temperature tensile properties, and transformation temperatures of hot- and cold-worked material were examined. Basic tensile properties as a function of temperature and the strain-temperature response of the alloy under constant load, for the determination of work output, were also investigated for various forms of the Ti(50.5)Ni(29.5)Pt20 alloy, including fine wire.

  9. Finite element modeling and fabrication of an SMA-SMP shape memory composite actuator

    NASA Astrophysics Data System (ADS)

    Souri, Mohammad

    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.).

  10. Testing system for ferromagnetic shape memory microactuators.

    PubMed

    Ganor, Y; Shilo, D; Messier, J; Shield, T W; James, R D

    2007-07-01

    Ferromagnetic shape memory alloys are a class of smart materials that exhibit a unique combination of large strains and fast response when exposed to magnetic field. Accordingly, these materials have significant potential in motion generation applications such as microactuators and sensors. This article presents a novel experimental system that measures the dynamic magnetomechanical behavior of microscale ferromagnetic shape memory specimens. The system is comprised of an alternating magnetic field generator (AMFG) and a mechanical loading and sensing system. The AMFG generates a dynamic magnetic field that periodically alternates between two orthogonal directions to facilitate martensitic variant switching and to remotely achieve a full magnetic actuation cycle, without the need of mechanical resetting mechanisms. Moreover, the AMFG is designed to produce a magnetic field that inhibits 180 degrees magnetization domain switching, which causes energy loss without strain generation. The mechanical loading and sensing system maintains a constant mechanical load on the measured specimen by means of a cantilever beam, while the displacement is optically monitored with a resolution of approximately 0.1 microm. Preliminary measurements using Ni(2)MnGa single crystal specimens, with a cross section of 100x100 microm(2), verified their large actuation strains and established their potential to become a material of great importance in microactuation technology.

  11. Bioperformance of shape memory alloy single crystals.

    PubMed

    Yahia, L'h; Manceur, A; Chaffraix, P

    2006-01-01

    Shape memory alloys (SMA) represent a large family of alloys that show unique characteristics. They have been exploited in several fields for diverse applications. For the last 20 years, these alloys and more particularly Ni-Ti alloys have revolutionized the field of metallic biomaterials. Applications in the biomedical area are multiple and these materials improve significantly the quality of the diagnostics, treatments and surgeries. To our knowledge, most devices are made of SMAs in the polycrystalline form. Nevertheless, the single crystal form shows several promising advantages especially concerning its mechanical performances. In this paper we describe the advantages, advances and limits of using different SMA single crystals for biomedical applications, including biocompatibility and corrosion resistance. We also discuss the low response time of classical thermal SMAs as well as the new advances in research on magnetic SMA single crystals.

  12. Self-accommodation of B19' martensite in Ti-Ni shape memory alloys - Part I. Morphological and crystallographic studies of the variant selection rule

    NASA Astrophysics Data System (ADS)

    Nishida, M.; Nishiura, T.; Kawano, H.; Inamura, T.

    2012-06-01

    The self-accommodation morphologies of B19‧ martensite in Ti-Ni alloys have been investigated by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Twelve pairs of minimum units consisting of two habit plane variants (HPVs) with V-shaped morphology connected to a ? B19‧ type I variant accommodation twin were observed. Three types of self-accommodation morphologies, based on the V-shaped minimum unit, developed around one of the {111}B2 traces, which were triangular, rhombic and hexangular and consisted of three, four and six HPVs, respectively. In addition, the variant selection rule and the number of possible HPV combinations in each of these self-accommodation morphologies are discussed.

  13. Microstructure and transformation behavior of Ni{sub 24.7}Ti{sub 50.3}Pd{sub 25} high temperature shape-memory alloy with Sc micro-addition

    SciTech Connect

    Ramaiah, K.V.; Saikrishna, C.N.; Gouthama; Bhaumik, S.K.

    2015-08-15

    NiTiPd shape-memory alloys (SMAs) are potential functional materials for use as solid-state actuators in the temperature range 100–250 °C. The present study investigates the effect of 1.0 at.% Sc micro-addition to Ni{sub 24.7}Ti{sub 50.3}Pd{sub 25} alloy, Sc replacing either Ti or Ni. Results show that all the three alloys studied have stable transformation behavior on stress-free thermal cycling and hence, are suitable for cyclic actuation applications. However, the addition of Sc to NiTiPd alloy leads to decrease of transformation temperatures, the magnitude of decrease being greater for the alloy with Sc replacing Ni. The martensite finish (M{sub f}) temperature of 181 °C for the NiTiPd alloy decreased to 139 °C for Sc replacing Ti and 83 °C for Sc replacing Ni. Also, the indentation modulus of NiTiPdSc (Sc replacing Ni) alloy is found to be significantly low compared to the other alloys. Analysis indicates that the observed differences in the alloy properties are related to the solubility of Sc in the NiTiPd matrix. While the quaternary NiTiPdSc alloy, Sc replacing Ti, has a single phase microstructure, the alloy with Sc replacing Ni shows the presence of Sc-rich and TiPd-type second phases in the microstructure. TEM examination revealed that the TiPd-type phase has a distinct rod-like morphology (30–50 nm) arranged in a grid-like structure. The transformation and indentation behavior of the alloys is elucidated using thermodynamic calculations of frictional energy and an electronic structure based analysis. - Highlights: • TEM of Ni{sub 23.7}Ti{sub 50.3}Pd{sub 25}Sc{sub 1} showed distinct grid of TiPd-type phase nanorods < 50 nm. • Stress-free thermal cycling of all the three alloys showed stable transformation behavior. • Ni{sub 24.7}Ti{sub 49.3}Pd{sub 25}Sc{sub 1} and Ni{sub 23.7}Ti{sub 50.3}Pd{sub 25}Sc{sub 1} showed single and multiphase structures. • Sc micro-addition (1 at.%) to Ni{sub 24.7}Ti{sub 50.3}Pd{sub 25} alloy decreased TTs

  14. Design and fabrication of a novel XYθz monolithic micro-positioning stage driven by NiTi shape-memory-alloy actuators

    NASA Astrophysics Data System (ADS)

    AbuZaiter, Alaa; Faris Hikmat, Omer; Nafea, Marwan; Ali, Mohamed Sultan Mohamed

    2016-10-01

    This paper reports a new shape-memory-alloy (SMA) micro-positioning stage. The device has been monolithically micro-machined with a single fabrication step. The design comprises a moving stage that is manipulated by six SMA planar springs actuators to generate movements with three degrees of freedom. The overall design is square in shape and has dimensions of 12 mm × 12 mm × 0.25 mm. Localized thermomechanical training for shape setting of SMA planar springs was performed using electrical current induced heating at restrained condition to individually train each of the six actuators to memorize a predetermined shape. For actuation, each SMA actuator is individually driven using Joule heating induced by an electrical current. The current flow is controlled by an external pulse-width modulation signal. The thermal response and heat distribution were simulated and experimentally verified using infrared imaging. The micro-positioning results indicated maximum stage movements of 1.2 and 1.6 mm along the x- and y-directions, respectively. Rotational movements were also demonstrated with a total range of 20°. The developed micro-positioning device has been successfully used to move a small object for microscopic scanning applications.

  15. Shape-Memory-Alloy Release Mechanism

    NASA Technical Reports Server (NTRS)

    Mckinnis, Darin

    1993-01-01

    Release-nut mechanism activated by electric current applied to shape-memory alloy. Separates attached objects quickly by remote control. Does not create hazard or cause damage. Shape-memory release-nut mechanism unaffected by moisture or vacuum. Requires sustained current lasting 5 seconds or longer, and insensitive to electromagnetic interference. Mechanism can be reused.

  16. 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.

  17. Shape Memory Composite Hybrid Hinge

    NASA Technical Reports Server (NTRS)

    Fang, Houfei; Im, Eastwood; Lin, John; Scarborough, Stephen

    2012-01-01

    There are two conventional types of hinges for in-space deployment applications. The first type is mechanically deploying hinges. A typical mechanically deploying hinge is usually composed of several tens of components. It is complicated, heavy, and bulky. More components imply higher deployment failure probability. Due to the existence of relatively moving components among a mechanically deploying hinge, it unavoidably has microdynamic problems. The second type of conventional hinge relies on strain energy for deployment. A tape-spring hinge is a typical strain energy hinge. A fundamental problem of a strain energy hinge is that its deployment dynamic is uncontrollable. Usually, its deployment is associated with a large impact, which is unacceptable for many space applications. Some damping technologies have been experimented with to reduce the impact, but they increased the risks of an unsuccessful deployment. Coalescing strain energy components with shape memory composite (SMC) components to form a hybrid hinge is the solution. SMCs are well suited for deployable structures. A SMC is created from a high-performance fiber and a shape memory polymer resin. When the resin is heated to above its glass transition temperature, the composite becomes flexible and can be folded or packed. Once cooled to below the glass transition temperature, the composite remains in the packed state. When the structure is ready to be deployed, the SMC component is reheated to above the glass transition temperature, and it returns to its as-fabricated shape. A hybrid hinge is composed of two strain energy flanges (also called tape-springs) and one SMC tube. Two folding lines are placed on the SMC tube to avoid excessive strain on the SMC during folding. Two adapters are used to connect the hybrid hinge to its adjacent structural components. While the SMC tube is heated to above its glass transition temperature, a hybrid hinge can be folded and stays at folded status after the temperature

  18. Shape memory behavior of single and polycrystalline nickel rich nickel titanium alloys

    NASA Astrophysics Data System (ADS)

    Kaya, Irfan

    NiTi is the most commonly used shape memory alloy (SMA) and has been widely used for bio-medical, electrical and mechanical applications. Nickel rich NiTi shape memory alloys are coming into prominence due to their distinct superelasticity and shape memory properties as compared to near equi-atomic NiTi shape memory alloys. Besides, their lower density and higher work output than steels makes these alloys an excellent candidate for aerospace and automotive industry. Shape memory properties and phase transformation behavior of high Ni-rich Ni54Ti46 (at.%) polycrystals and Ni-rich Ni 51Ti49 (at.%) single-crystals are determined. Their properties are sensitive to heat treatments that affect the phase transformation behavior of these alloys. Phase transformation properties and microstructure were investigated in aged Ni54Ti46 alloys with differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) to reveal the precipitation characteristics and R-phase formation. It was found that Ni54Ti46 has the ability to exhibit perfect superelasticity under high stress levels (~2 GPa) with 4% total strain after 550°C-3h aging. Stress independent R-phase transformation was found to be responsible for the change in shape memory behavior with stress. The shape memory responses of [001], [011] and [111] oriented Ni 51Ti49 single-crystals alloy were reported under compression to reveal the orientation dependence of their shape memory behavior. It has been found that transformation strain, temperatures and hysteresis, Classius-Clapeyron slopes, critical stress for plastic deformation are highly orientation dependent. The effects of precipitation formation and compressive loading at selected temperatures on the two-way shape memory effect (TWSME) properties of a [111]- oriented Ni51Ti49 shape memory alloy were revealed. Additionally, aligned Ni4Ti3 precipitates were formed in a single crystal of Ni51Ti49 alloy by aging under applied compression stress along the

  19. Post polymerization cure shape memory polymers

    DOEpatents

    Wilson, Thomas S; Hearon, Michael Keith; Bearinger, Jane P

    2014-11-11

    This invention relates to chemical polymer compositions, methods of synthesis, and fabrication methods for devices regarding polymers capable of displaying shape memory behavior (SMPs) and which can first be polymerized to a linear or branched polymeric structure, having thermoplastic properties, subsequently processed into a device through processes typical of polymer melts, solutions, and dispersions and then crossed linked to a shape memory thermoset polymer retaining the processed shape.

  20. Post polymerization cure shape memory polymers

    DOEpatents

    Wilson, Thomas S.; Hearon, II, Michael Keith; Bearinger, Jane P.

    2017-01-10

    This invention relates to chemical polymer compositions, methods of synthesis, and fabrication methods for devices regarding polymers capable of displaying shape memory behavior (SMPs) and which can first be polymerized to a linear or branched polymeric structure, having thermoplastic properties, subsequently processed into a device through processes typical of polymer melts, solutions, and dispersions and then crossed linked to a shape memory thermoset polymer retaining the processed shape.

  1. Resistively heated shape memory polymer device

    DOEpatents

    Marion, III, John E.; Bearinger, Jane P.; Wilson, Thomas S.; Maitland, Duncan J.

    2016-10-25

    A resistively heated shape memory polymer device is made by providing a rod, sheet or substrate that includes a resistive medium. The rod, sheet or substrate is coated with a first shape memory polymer providing a coated intermediate unit. The coated intermediate unit is in turn coated with a conductive material providing a second intermediate unit. The second coated intermediate unit is in turn coated with an outer shape memory polymer. The rod, sheet or substrate is exposed and an electrical lead is attached to the rod, sheet or substrate. The conductive material is exposed and an electrical lead is attached to the conductive material.

  2. Medical applications of shape memory polymers

    NASA Technical Reports Server (NTRS)

    Sokolowski, Witold M.

    2005-01-01

    Shape memory polymers are described here and major advantages in some applications are identified over other medical materials such as shape memory alloys (SMA). A number of medical applications are anticipated for shape memory polymers. Some simple applications are already utilized in medical world, others are in examination process. Lately, several important applications are being considered for CHEM foams for self-deployable vascular and coronary devices. One of these potential applications, the endovascular treatment of aneurysm was experimentally investigated with encouraging results and is described in this paper as well.

  3. Data-driven Techniques to Estimate Parameters in the Homogenized Energy Model for Shape Memory Alloys

    DTIC Science & Technology

    2011-11-01

    sensor. volume 79781K. Proceedings of the SPIE 7978, 2011. [9] D.J. Hartl, D.C. Lagoudas, F.T. Calkins , and J.H. Mabe. Use of a ni60ti shape memory...D.C. Lagoudas, F.T. Calkins , and J.H. Mabe. Use of a ni60ti shape memory alloy for active jet engine chevron application: II. experimentally validated

  4. 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.

  5. 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

  6. 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.

  7. Two-dimensional shape memory graphene oxide

    PubMed Central

    Chang, Zhenyue; Deng, Junkai; Chandrakumara, Ganaka G.; Yan, Wenyi; Liu, Jefferson Zhe

    2016-01-01

    Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices. PMID:27325441

  8. Influence of annealing on martensitic transformation and magnetic entropy change in Ni37.7Co12.7Mn40.8Sn8.8 magnetic shape memory alloy ribbon

    NASA Astrophysics Data System (ADS)

    Chen, F.; Liu, W. L.; Shi, Y. G.; Müllner, P.

    2015-03-01

    The microstructure, martensitic transformation and magnetic properties of Ni37.7Co12.7Mn40.8Sn8.8 high temperature magnetic shape memory ribbon subjected to different annealing temperature were investigated. Annealing up to 1073 K slightly raised the transformation temperatures and the transformation interval, while annealing at 1173 K considerably decreased the transformation temperature and strongly widened the transformation interval due to the formation of a second phase. The as-spun and annealed ribbon at 973 K exhibited giant magnetic entropy changes of around 15 J/kg K under 15 kOe magnetic field above 400 K. Further increasing annealing temperature caused a decrease of the magnetic entropy change. To achieve a large magnetocaloric effect while keeping an elevated transformation temperature, an appropriate annealing parameter should be carefully considered.

  9. Determination of the vibrational contribution to the entropy change at the martensitic transformation in Ni-Mn-Sn metamagnetic shape memory alloys: a combined approach of time-of-flight neutron spectroscopy and ab initio calculations.

    PubMed

    Recarte, V; Zbiri, M; Jiménez-Ruiz, M; Sánchez-Alarcos, V; Pérez-Landazábal, J I

    2016-05-25

    The different contributions to the entropy change linked to the austenite-martensitic transition in a Ni-Mn-Sn metamagnetic shape memory alloy have been determined by combining different experimental techniques. The vibrational contribution has been inferred from the vibrational density of states of both the martensitic and austenite phases. This has been accomplished by combining time-of-flight neutron scattering measurements and ab initio calculations. Further, the electronic part of the entropy change has also been calculated. Since the martensitic transformation takes place between two paramagnetic phases, the magnetic contribution can be neglected and the entropy change can be reduced to the sum of two terms: vibrational and electronic. The obtained value of the vibrational contribution ([Formula: see text]) nearly provides the total entropy change measured by calorimetry ([Formula: see text]), the difference being the electronic contribution within the experimental error.

  10. Properties of a Ni(sub 19.5)Pd(sub 30)Ti(sub 50.5) high-temperature shape memory alloy in tension and compression

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald; Padula, Santo, II; Bigelow, Glen; Rios, Orlando; Garg, Anita; Lerch, Brad

    2006-01-01

    Potential applications involving high-temperature shape memory alloys have been growing in recent years. Even in those cases where promising new alloys have been identified, the knowledge base for such materials contains gaps crucial to their maturation and implementation in actuator and other applications. We begin to address this issue by characterizing the mechanical behavior of a Ni19.5Pd30Ti50.5 high-temperature shape memory alloy in both uniaxial tension and compression at various temperatures. Differences in the isothermal uniaxial deformation behavior were most notable at test temperatures below the martensite finish temperature. The elastic modulus of the material was very dependent on strain level; therefore, dynamic Young#s Modulus was determined as a function of temperature by an impulse excitation technique. More importantly, the performance of a thermally activated actuator material is dependent on the work output of the alloy. Consequently, the strain-temperature response of the Ni19.5Pd30Ti50.5 alloy under various loads was determined in both tension and compression and the specific work output calculated and compared in both loading conditions. It was found that the transformation strain and thus, the specific work output were similar regardless of the loading condition. Also, in both tension and compression, the strain-temperature loops determined under constant load conditions did not close due to the fact that the transformation strain during cooling was always larger than the transformation strain during heating. This was apparently the result of permanent plastic deformation of the martensite phase with each cycle. Consequently, before this alloy can be used under cyclic actuation conditions, modification of the microstructure or composition would be required to increase the resistance of the alloy to plastic deformation by slip.

  11. Repeated Instant Self-healing Shape Memory Composites

    NASA Astrophysics Data System (ADS)

    Wang, C. C.; Ding, Z.; Purnawali, H.; Huang, W. M.; Fan, H.; Sun, L.

    2012-12-01

    We present a shape memory composite which is made of two types of shape memory materials, namely shape memory alloy (SMA) and shape memory hybrid. This composite has repeated instant self-healing function by means of not only shape recovery but also strength recovery (over 80%). The activation of the self-healing function is triggered by joule heating the embedded SMA.

  12. Polyolefin Thermoplastics for Multiple Shape and Reversible Shape Memory.

    PubMed

    Gao, Yuan; Liu, Weifeng; Zhu, Shiping

    2017-02-08

    This work reports the first pure hydrocarbon thermoplastic polyolefin material with reversible shape memory effect under stress-free or very small external loading condition. A thermoplastic ethylene/1-octene diblock copolymer with designed chain microstructure was synthesized. The polyolefin material performed not only the conventional one-way multishape memory effects, but also a two-way reversible shape memory effect (RSME). The elongation and contraction induced by oriented crystallization with heating was confirmed as the mechanism of RSME without chemical cross-linking. This work demonstrated that the thermoplastic reversible shape memory could be achieved through careful design of chain microstructure, based on sole hydrocarbon materials such as ethylene-1-octene copolymer.

  13. Shape memory effect and superelasticity of titanium nickelide alloys implanted with high ion doses

    NASA Astrophysics Data System (ADS)

    Pogrebnjak, A. D.; Bratushka, S. N.; Beresnev, V. M.; Levintant-Zayonts, N.

    2013-12-01

    The state of the art in ion implantation of superelastic NiTi shape memory alloys is analyzed. Various technological applications of the shape memory effect are outlined. The principles and techiques of ion implantation are described. Specific features of its application for modification of surface layers in surface engineering are considered. Key properties of shape memory alloys and problems in utilization of ion implantation to improve the surface properties of shape memory alloys, such as corrosion resistance, friction coefficient, wear resistance, etc. are discussed. The bibliography includes 162 references.

  14. Simultaneous probing of phase transformations in Ni-Ti thin film shape memory alloy by synchrotron radiation-based X-ray diffraction and electrical resistivity

    SciTech Connect

    Braz Fernandes, F.M.; Silva, R.J.C.

    2013-02-15

    Nickel–Titanium (Ni–Ti) thin film shape memory alloys (SMAs) have been widely projected as novel materials which can be utilized in microdevices. Characterization of their physical properties and its correlation with phase transformations has been a challenging issue. In the present study, X-ray beam diffraction has been utilized to obtain the structural information at different temperatures while cooling. Simultaneously, electrical resistivity (ER) was measured in the phase transformation temperature range. The variation of ER and integral area of the individual diffraction peaks of the different phases as a function of temperature have been compared. A mismatch between the conventional interpretation of ER variation and the results of the XRD data has been clearly identified. - Highlights: ► Phase transformation characterization of Ni–Ti thin film SMA has been carried out. ► Simultaneous monitoring of the XRD and ER with temperature is performed. ► The variation of ER and integral area of the diffraction peaks have been compared. ► A shift of the transformation temperatures obtained by two techniques is discussed.

  15. Thermomechanical fatigue of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Lagoudas, D. C.; Miller, D. A.; Rong, L.; Kumar, P. K.

    2009-08-01

    As shape memory alloys (SMAs) gain popularity as high energy density actuators, one characteristic that becomes particularly important is the thermomechanical transformation fatigue life, in addition to maximum transformation strain and stability of actuation cycles. In this paper, a novel test frame design and testing protocol are discussed, for investigating the thermally activated transformation fatigue characteristics of SMAs under various applied loads for both complete and partial phase transformation. A Ni50Ti40Cu10 (at.%) SMA was chosen for this investigation and the effects of various heat treatments on the transformation temperatures and the transformation fatigue lives of actuators were studied. For selected heat treatments, the evolution of recoverable and irrecoverable strains up to failure under different applied stress levels was studied in detail. The influence of complete and partial transformation on the fatigue life is also presented. The irrecoverable strain accumulation as a function of the number of cycles to failure for different stress levels is presented by a relationship similar to the Manson-Coffin law for both partial and complete transformations.

  16. Infrared Brazing of Ti50Ni50 Shape Memory Alloy and Inconel 600 Alloy with Two Ag-Cu-Ti Active Braze Alloys

    NASA Astrophysics Data System (ADS)

    Shiue, Ren-Kae; Wu, Shyi-Kaan; Yang, Sheng-Hao

    2017-02-01

    Infrared brazing of Ti50Ni50 SMA and Inconel 600 alloy using Cusil-ABA and Ticusil filler metals has been investigated. The joints were dominated by Ag-Cu eutectic with proeutectic Cu in the Cusil-ABA brazed joint and with proeutectic Ag in the Ticusil one. A continuous curved belt composed of a Ni3Ti layer and a (Cu x Ni1- x )2Ti layer formed in the brazed Ti50Ni50/Ticusil/Inconel 600 joint. On the Ti50Ni50 SMA side, an intermetallic layer of (Cu x Ni1- x )2Ti formed in all joints, with x values around 0.81 and 0.47. Layers of (Cu x Ni1- x )2Ti, Ni3Ti, and mixed Ni3Ti and Ni2Cr intermetallics were observed next to the Inconel 600 substrate in the brazed Ti50Ni50/Cusil-ABA/Inconel 600 joint. The maximum shear strengths of the joints using the Cusil-ABA filler metal and the Ticusil filler metal were 324 and 300 MPa, respectively. In the Cusil-ABA brazed joint, cracks with cleavage-dominated fracture propagated along the (Cu x Ni1- x )2Ti interfacial layer next to the Ti50Ni50 SMA substrate. In the Ticusil brazed joint, ductile dimple fracture occurred in the Ag-rich matrix near the Inconel 600 alloy substrate. The absence of a detrimental Ti-Fe-(Cu) layer on the Inconel 600 substrate side can effectively improve the shear strength of the joint.

  17. Defect formation energy and magnetic structure of shape memory alloys Ni-X-Ga (X=Mn, Fe, Co) by first principle calculation

    NASA Astrophysics Data System (ADS)

    Bai, J.; Raulot, J. M.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.

    2010-09-01

    The crystallographic and magnetic structures of the Ni2XGa (X=Mn, Fe, Co), are systematically investigated by means of the first-principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The formation energies of several kinds of defects (atomic exchange, antisite, vacancy) are estimated. The Ga atoms stabilize the cubic structure, and the effect of X atoms on the structural stability is opposite. For most cases of the site occupation, the excess atoms of the rich component directly occupy the site(s) of the deficient one(s), except for Ga-rich Ni-deficient type. The magnitude of the variation in Ni moments is much larger than that of Mn in defective Ni2XGa. The value of Ni magnetic moment sensitively depends on the distance between Ni and X. Excess Mn could be ferromagnetic or antiferromagnetic, depending on the distance between the neighboring Mn atoms.

  18. Shape memory system with integrated actuation using embedded particles

    DOEpatents

    Buckley, Patrick R [New York, NY; Maitland, Duncan J [Pleasant Hill, CA

    2012-05-29

    A shape memory material with integrated actuation using embedded particles. One embodiment provides a shape memory material apparatus comprising a shape memory material body and magnetic pieces in the shape memory material body. Another embodiment provides a method of actuating a device to perform an activity on a subject comprising the steps of positioning a shape memory material body in a desired position with regard to the subject, the shape memory material body capable of being formed in a specific primary shape, reformed into a secondary stable shape, and controllably actuated to recover the specific primary shape; including pieces in the shape memory material body; and actuating the shape memory material body using the pieces causing the shape memory material body to be controllably actuated to recover the specific primary shape and perform the activity on the subject.

  19. Shape memory system with integrated actuation using embedded particles

    DOEpatents

    Buckley, Patrick R; Maitland, Duncan J

    2014-04-01

    A shape memory material with integrated actuation using embedded particles. One embodiment provides a shape memory material apparatus comprising a shape memory material body and magnetic pieces in the shape memory material body. Another embodiment provides a method of actuating a device to perform an activity on a subject comprising the steps of positioning a shape memory material body in a desired position with regard to the subject, the shape memory material body capable of being formed in a specific primary shape, reformed into a secondary stable shape, and controllably actuated to recover the specific primary shape; including pieces in the shape memory material body; and actuating the shape memory material body using the pieces causing the shape memory material body to be controllably actuated to recover the specific primary shape and perform the activity on the subject.

  20. Shape memory system with integrated actuation using embedded particles

    DOEpatents

    Buckley, Patrick R.; Maitland, Duncan J.

    2009-09-22

    A shape memory material with integrated actuation using embedded particles. One embodiment provides a shape memory material apparatus comprising a shape memory material body and magnetic pieces in the shape memory material body. Another embodiment provides a method of actuating a device to perform an activity on a subject comprising the steps of positioning a shape memory material body in a desired position with regard to the subject, the shape memory material body capable of being formed in a specific primary shape, reformed into a secondary stable shape, and controllably actuated to recover the specific primary shape; including pieces in the shape memory material body; and actuating the shape memory material body using the pieces causing the shape memory material body to be controllably actuated to recover the specific primary shape and perform the activity on the subject.

  1. Medical applications of shape memory alloys.

    PubMed

    Machado, L G; Savi, M A

    2003-06-01

    Shape memory alloys (SMA) are materials that have the ability to return to a former shape when subjected to an appropriate thermomechanical procedure. Pseudoelastic and shape memory effects are some of the behaviors presented by these alloys. The unique properties concerning these alloys have encouraged many investigators to look for applications of SMA in different fields of human knowledge. The purpose of this review article is to present a brief discussion of the thermomechanical behavior of SMA and to describe their most promising applications in the biomedical area. These include cardiovascular and orthopedic uses, and surgical instruments.

  2. Shape memory composite antennas for space applications

    NASA Astrophysics Data System (ADS)

    Santo, Loredana; Quadrini, Fabrizio; Bellisario, Denise

    2016-11-01

    Future space missions will require large space infrastructures in order to achieve scientific and technological objectives characterized by an intrinsic complexity. In this study, the development of shape memory composite structures for aerospace applications is described. In particular, the structure of a small-scale self-deployable mast has been prototyped as a proof of concept for its feasibility. The mast structure is made by interlocking two shape memory polymer composite (SMPC) strips, each one made of two layers of carbon fiber fabric with a shape memory (SM) epoxy resin interlayer. A complete deployment of the SMC structure was achieved. The versatility of this technology has been also demonstrated in previous studies, in which small scale deploying solar panels were fabricated. Obtained results are very promising in terms of manufacturing technology, and shape recovery of manufactured parts.

  3. Large magnetic entropy change and magnetoresistance in a Ni41Co9Mn40Sn10 magnetic shape memory alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, M. G.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2015-07-02

    A polycrystalline Ni41Co9Mn40Sn10 (at. %) magnetic shape memory alloy was prepared by arc melting and characterized mainly by magnetic measurements, in-situ high-energy X-ray diffraction (HEXRD), and mechanical testing. A large magnetoresistance of 53.8% (under 5 T) and a large magnetic entropy change of 31.9 J/(kg K) (under 5 T) were simultaneously achieved. Both of these values are among the highest values reported so far in Ni-Mn-Sn-based Heusler alloys. The large magnetic entropy change, closely related to the structural entropy change, is attributed to the large unit cell volume change across martensitic transformation as revealed by our in-situ HEXRD experiment. Furthermore, good compressive properties were also obtained. Lastly, the combination of large magnetoresistance, large magnetic entropy change, and good compressive properties, as well as low cost makes this alloy a promising candidate for multifunctional applications.

  4. Effect of Temperature on the Deformation Behavior of B2 Austenite in a Polycrystalline Ni49.9Ti50.1 (at.Percent) Shape Memory Alloy

    NASA Technical Reports Server (NTRS)

    Garg, A.; Benafan, O.; Noebe, R. D.; Padula, S. A., II; Clausen, B.; Vogel, S.; Vaidyanathan, R.

    2013-01-01

    Superelasticity in austenitic B2-NiTi is of great technical interest and has been studied in the past by several researchers [1]. However, investigation of temperature dependent deformation in B2-NiTi is equally important since competing mechanisms of stress-induced martensite (SIM), retained martensite, plastic and deformation twinning can lead to unusual mechanical behaviors. Identification of the role of various mechanisms contributing to the overall deformation response of B2-NiTi is imperative to understanding and maturing SMA-enabled technologies. Thus, the objective of this work was to study the deformation of polycrystalline Ni49.9Ti50.1 (at. %) above A(sub f) (105 C) in the B2 state at temperatures between 165-440 C, and generate a B2 deformation map showing active deformation mechanisms in different temperature-stress regimes.

  5. 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

  6. Shape-memory surfaces for cell mechanobiology

    PubMed Central

    Ebara, Mitsuhiro

    2015-01-01

    Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape ‘A’ to a memorized permanent shape ‘B’ upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology. PMID:27877747

  7. Development of multifunctional shape memory polymer foams

    NASA Astrophysics Data System (ADS)

    Song, Janice J.; Srivastava, Ijya; Naguib, Hani E.

    2015-05-01

    Shape memory polymers (SMP) are a class of stimuli-responsive materials which are able to respond to external stimulus such as temperature and deformation by changing their shape, and return to their original shape upon reversal or removal of the external stimulus. Although SMP materials have been studied extensively and have been used in a wide range of applications such as medicine, aerospace, and robotics, only few studies have looked at the potential of designing multifunctional SMP foams and blends. In this study, we investigate the feasibility of a design of SMP foam materials and blends. The actuator construct will contain a core SMP epoxy and blend of polylactic acid and polyurethane. The effects of the processing parameters of shape memory polymer (SMP) foams on the shape memory effect (SME) were investigated. The solid state foaming technique was employed to obtain the desired foamed cellular structure. One particular point of interest is to understand how the processing parameters affect the SMP and its glass transition temperature (Tg). By correctly tailoring these parameters it is possible to modify the SMP to have an improved shape memory effect SME.

  8. Shape-memory surfaces for cell mechanobiology

    NASA Astrophysics Data System (ADS)

    Ebara, Mitsuhiro

    2015-02-01

    Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape ‘A’ to a memorized permanent shape ‘B’ upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology.

  9. Shape-memory surfaces for cell mechanobiology.

    PubMed

    Ebara, Mitsuhiro

    2015-02-01

    Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape 'A' to a memorized permanent shape 'B' upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology.

  10. A bidirectional shape memory alloy folding actuator

    NASA Astrophysics Data System (ADS)

    Paik, Jamie K.; Wood, Robert J.

    2012-06-01

    This paper presents a low-profile bidirectional folding actuator based on annealed shape memory alloy sheets applicable for meso- and microscale systems. Despite the advantages of shape memory alloys—high strain, silent operation, and mechanical simplicity—their application is often limited to unidirectional operation. We present a bidirectional folding actuator that produces two opposing 180° motions. A laser-patterned nickel alloy (Inconel 600) heater localizes actuation to the folding sections. The actuator has a thin ( < 1 mm) profile, making it appropriate for use in robotic origami. Various design parameters and fabrication variants are described and experimentally explored in the actuator prototype.

  11. Effect of Ti addition on the structural, mechanical and damping properties of magnetron sputtered Ni-Mn-Sn ferromagnetic shape memory alloy thin films

    NASA Astrophysics Data System (ADS)

    Choudhary, Nitin; Kaur, Davinder

    2012-12-01

    Titanium (Ti) co-sputtered Ni50.4Mn34.7Sn14.9 films deposited by magnetron sputtering onto Si(1 0 0) substrates at 823 K were investigated. X-ray diffraction profiles revealed the formation of highly (2 2 0)-oriented Ni-Mn-Sn-Ti austenite phase with significant decrease in grain size with increasing Ti power. Hardness (H), elastic modulus (Er), damping (tan δ), figure of merit (FOM) and coefficient of restitution (e) of the films were evaluated using nanoindentation tests. A significant improvement in the hardness (10.5 GPa) and toughness H^3/E_r^2 (0.040) was observed in the Ni51.0Mn28.2Sn11.0Ti9.7 nanocomposite film as compared with pure Ni50.4Mn34.7Sn14.9films. An impact model, which incorporates material behaviour, is presented that predicts the experimentally observed material quantities, including energy dissipation metrics such as the coefficient of restitution e with high accuracy. The highest damping factor (tan δ = 0.061), high FOM (0.79) with low coefficient of restitution (e = 0.28) quantifies excellent energy dissipation capacity in the Ni51.0Mn28.2Sn11.0Ti9.7 nanocomposite. Temperature dependence of magnetization (M-T) curves showed an increase in martensitic transformation temperatures with increasing Ti content. The Ni-Mn-Sn-Ti composite films exhibit ferromagnetic behaviour at room temperature.

  12. The impact of substrate stimulated functional interface on magnetic and magneto-transport signature of martensitic transformation in NiMnIn shape memory alloy

    NASA Astrophysics Data System (ADS)

    Sabirianov, R.; Sokolov, A.; Kirianov, E.; Zlenko, A.; Quetz, A.; Aryal, A.; Pandey, S.; Dubenko, I.; Ali, N.; Stadler, S.; Al-Aqtash, N.

    We study the impact of the substrate on the martensite transformation of Ni-Mn-In thin films by Hall resistance measurements and discuss it using density functional theory calculations. Similarly to the bulk systems, thin films grown on MgO exhibit the martensitic transformation accompanied by large magnetoresistance and a sign reversal of the ordinary as well as anomalous Hall coefficient. Martensite transition temperature of films grown on (100) surface of MgO is near 170K, while the films grown on (111) surface of MgO show the change of Hall coefficient at 110K. The calculated total energy difference between FM austenite and FiM martensite states in Ni2Mn1.5In0.5 film on MgO (001) substrate (with Ni/MgO interface) is 0.20eV per NiMnIn f.u, compared to 0.24eV in the bulk at the same equilibrium lattice parameters, i.e. when film is ``unstrained''. When lattice parameters of Ni2Mn1.5In0.5/MgO are of those of MgO substrate, i.e. when the film experiences strong bi-axial tensile strain Δa / a = 2.4%, the energy difference is 0.08eV per NiMnIn f.u. These results clearly indicate strong interplay between lattice strain/stress and the relative stability martensite and austenite phase The work is supported by NSF.

  13. 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.

  14. 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.

  15. 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.

  16. Shape Memory Polymer Therapeutic Devices for Stroke

    SciTech Connect

    Wilson, T S; Small IV, W; Benett, W J; Bearinger, J P; Maitland, D J

    2005-10-11

    Shape memory polymers (SMPs) are attracting a great deal of interest in the scientific community for their use in applications ranging from light weight structures in space to micro-actuators in MEMS devices. These relatively new materials can be formed into a primary shape, reformed into a stable secondary shape, and then controllably actuated to recover their primary shape. The first part of this presentation will be a brief review of the types of polymeric structures which give rise to shape memory behavior in the context of new shape memory polymers with highly regular network structures recently developed at LLNL for biomedical devices. These new urethane SMPs have improved optical and physical properties relative to commercial SMPs, including improved clarity, high actuation force, and sharper actuation transition. In the second part of the presentation we discuss the development of SMP based devices for mechanically removing neurovascular occlusions which result in ischemic stroke. These devices are delivered to the site of the occlusion in compressed form, are pushed through the occlusion, actuated (usually optically) to take on an expanded conformation, and then used to dislodge and grip the thrombus while it is withdrawn through the catheter.

  17. Shape memory polymer therapeutic devices for stroke

    NASA Astrophysics Data System (ADS)

    Wilson, Thomas S.; Small, Ward, IV; Benett, William J.; Bearinger, Jane P.; Maitland, Duncan J.

    2005-11-01

    Shape memory polymers (SMPs) are attracting a great deal of interest in the scientific community for their use in applications ranging from light weight structures in space to micro-actuators in MEMS devices. These relatively new materials can be formed into a primary shape, reformed into a stable secondary shape, and then controllably actuated to recover their primary shape. The first part of this presentation will be a brief review of the types of polymeric structures which give rise to shape memory behavior in the context of new shape memory polymers with highly regular network structures recently developed at LLNL for biomedical devices. These new urethane SMPs have improved optical and physical properties relative to commercial SMPs, including improved clarity, high actuation force, and sharper actuation transition. In the second part of the presentation we discuss the development of SMP based devices for mechanically removing neurovascular occlusions which result in ischemic stroke. These devices are delivered to the site of the occlusion in compressed form, are pushed through the occlusion, actuated (usually optically) to take on an expanded conformation, and then used to dislodge and grip the thrombus while it is withdrawn through the catheter.

  18. Fatigue Crack Growth Fundamentals in Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Ojha, A.; Patriarca, L.; Sehitoglu, H.

    2015-03-01

    In this study, based on a regression of the crack tip displacements, the stress intensity range in fatigue is quantitatively determined for the shape memory alloy Ni2FeGa. The results are compared to the calculated stress intensity ranges with a micro-mechanical analysis accounting for the transformation-induced tractions. The effective stress intensity ranges obtained with both methods are in close agreement. Also, the fatigue crack closure levels were measured as 30 % of the maximum load using virtual extensometers along the crack flanks. This result is also in close agreement with the regression and micro-mechanical modeling findings. The current work pointed to the importance of elastic moduli changes and the residual transformation strains playing a role in the fatigue crack growth behavior. Additional simulations are conducted for two other important shape memory alloys, NiTi and CuZnAl, where the reductions in stress intensity range were found to be lower than Ni2FeGa.

  19. Thermo-Mechanical Response of Monolithic and NiTi Shape Memory Alloy Fiber Reinforced Sn-3.8Ag-0.7Cu Solder

    DTIC Science & Technology

    2005-09-01

    still exist from this high thermal mismatch deformation , resulting in large solder-joint stresses and strains and causing fatigue failure. The...life, but have not shown the needed improvements in thermo-mechanical fatigue life under strain - controlled conditions, which is a primary deformation ...A NiTi fiber will deform until it consists only of the correspondence variant (crystallographic orientation) that produces maximum strain . However

  20. Effect of laser treatment on the attachment and viability of mesenchymal stem cell responses on shape memory NiTi alloy.

    PubMed

    Chan, C W; Hussain, I; Waugh, D G; Lawrence, J; Man, H C

    2014-09-01

    The objectives of this study were to investigate the effect of laser-induced surface features on the morphology, attachment and viability of mesenchymal stem cells (MSCs) at different periods of time, and to evaluate the biocompatibility of different zones: laser-melted zone (MZ), heat-affected zone (HAZ) and base metal (BM) in laser-treated NiTi alloy. The surface morphology and composition were studied by scanning electron microscope (SEM) and X-ray photoemission spectroscopy (XPS), respectively. The cell morphology was examined by SEM while the cell counting and viability measurements were done by hemocytometer and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. The results indicated that the laser-induced surface features, such as surface roughening, presence of anisotropic dendritic pattern and complete surface Ni oxidation were beneficial to improve the biocompatibility of NiTi as evidenced by the highest cell attachment (4 days of culture) and viability (7 days of culture) found in the MZ. The biocompatibility of the MZ was the best, followed by the BM with the HAZ being the worst. The defective and porous oxide layer as well as the coarse grained structure might attribute to the inferior cell attachment (4 days of culture) and viability (7 days of culture) on the HAZ compared with the BM which has similar surface morphology.

  1. Formation of microcraters and hierarchically-organized surface structures in TiNi shape memory alloy irradiated with a low-energy, high-current electron beam

    SciTech Connect

    Meisner, L. L. Meisner, S. N.; Markov, A. B. Ozur, G. E. Yakovlev, E. V.; Rotshtein, V. P.; Gudimova, E. Yu.

    2015-10-27

    The regularities of surface cratering in TiNi alloy irradiated with a low-energy, high-current electron beam (LEHCEB) in dependence on energy density and number of pulses are studied. LEHCEB processing of TiNi samples was carried out using RITM-SP facility. Energy density E{sub s} was varied from 1 to 5 J/cm{sup 2}, pulse duration was 2.5–3.0 μs, the number of pulses n = 1–128. The dominant role of non-metallic inclusions [mainly, TiC(O)] in the nucleation of microcraters was found. It was revealed that at small number of pulses (n = 2), an increase in energy density leads both to increasing average diameter and density of microcraters. An increase in the number of pulses leads to a monotonic decrease in density of microcraters, and, therefore, that of the proportion of the area occupied by microcraters, as well as a decrease in the surface roughness. The multiple LEHCEB melting of TiNi alloy in crater-free modes enables to form quasi-periodical, hierarchically-organized microsized surface structures.

  2. Martensitic transformation of Ni2FeGa ferromagnetic shape-memory alloy studied via transmission electron microscopy and electron energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, H. R.; Ma, C.; Tian, H. F.; Wu, G. H.; Li, J. Q.

    2008-06-01

    The structural properties of Ni2FeGa Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the Ni2FeGa alloy was annealed into a well-defined L21 structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the ⟨110⟩ or ⟨100⟩ directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature (Ms,˜142K) , the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the ⟨100⟩ direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a 5M modulation structure along the ⟨110⟩ directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to spd orbital hybridization among the Ni-Fe-Ga atoms.

  3. Shape memory polyurethane nanocomposites with functionalized graphene

    NASA Astrophysics Data System (ADS)

    Choi, Jin Taek; Dung Dao, Trung; Oh, Kyung Min; Lee, Hyung-il; Jeong, Han Mo; Kim, Byung Kyu

    2012-07-01

    The roles of graphene in shape memory polyurethane nanocomposite (SMPUN) as a reinforcing filler, as a fixed structure for memorizing a specified original shape, and as a conductive filler to actuate shape recovery by resistive heating, were examined. The effectiveness of each role was modulated by functionalizing graphene with a hydroxyl group through oxidation with H2O2. The reinforcing effect of graphene and its role as a fixed structure were enhanced by the hydroxyl groups due to the increased grafting of polyurethane chains on graphene during the in situ preparation of SMPUN. However, the oxidation reduced the conductivity of SMPUN, resulting in deterioration of the resistive heating.

  4. Fabrication of shape memory nanofibers by electrospinning method

    NASA Astrophysics Data System (ADS)

    Zhang, Fenghua; Zhang, Zhichun; Liu, Yanju; Leng, Jinsong

    2013-04-01

    Shape memory nanofibers are capable of fixing a temporary shape and recovering a permanent shape in response to stimulus. Nafion nanofibers with shape memory effect are achieved via electrospinning technology. The resulting nanofibres exhibit the smooth, continuous, uniform fibrous structure. The diameter of nanofibers increases after annealing progress at different temperatures. The shape memory effect is evaluated in a fixed force controlled tensile test. Electrospun Nafion nanofibers show excellent shape memory properties upon heat. The shape fixity rates and shape recovery rates are about 95-96% and 87-89% after consecutive three shape memory cycles, respectively. The structure of electrospun nanofibers is stable and reversible for at least three cycles of shape memory tests. These results indicate that shape memory Nafion nanofibers can be used in a wide potential application fields such as smart materials and structures in the future.

  5. Medical applications of shape memory polymers.

    PubMed

    Sokolowski, Witold; Metcalfe, Annick; Hayashi, Shunichi; Yahia, L'Hocine; Raymond, Jean

    2007-03-01

    Shape memory polymers (SMP) are lightweight, have a high strain/shape recovery ability, are easy to process, and required properties can be tailored for variety of applications. Recently a number of medical applications have been considered and investigated, especially for polyurethane-based SMP. SMP materials were found to be biocompatible, non-toxic and non-mutagenic. The glass transition temperature (T(g)) can be tailored for shape restoration/self-deployment of clinical devices when inserted in the human body. Newly developed SMP foams, together with cold hibernated elastic memory (CHEM) processing, further broaden their potential biomedical applications. Polyurethane-based SMP are described here and major advantages are identified over other medical materials. Some SMP applications are already used in a clinical setting, whereas others are still in development. Lately, several important applications are being considered for CHEM foams as self-deployable vascular and coronary devices. One example is the endovascular treatment of aneurysms.

  6. Investigation of interfacial shear stresses, shape fixity, and actuation strain in composites incorporating shape memory polymers and shape memory alloys

    NASA Astrophysics Data System (ADS)

    Park, Jungkyu; Headings, Leon; Dapino, Marcelo; Baur, Jeffery; Tandon, Gyaneshwar

    2015-03-01

    Shape memory composites (SMCs) based on shape memory alloys (SMAs) and shape memory polymers (SMPs) allow many design possibilities due to their controllable temperature-dependent mechanical properties. The complementary characteristics of SMAs and SMPs can be utilized in systems with shape recovery created by the SMA and shape fixity provided by the SMP. In this research, three SMC operating regimes are identified and the behavior of SMC structures is analyzed by focusing on composite shape fixity and interfacial stresses. Analytical models show that SMPs can be used to adequately fix the shape of SMA actuators and springs. COMSOL finite element simulations are in agreement with analytical expressions for shape fixity and interfacial stresses. Analytical models are developed for an end-coupled linear SMP-SMA two-way actuator and the predicted strain is shown to be in good agreement with experimental test results.

  7. 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.

  8. Magnetic shape memory effect at 1.7 K

    NASA Astrophysics Data System (ADS)

    Heczko, Oleg; Kopecký, Vít; Sozinov, Alexei; Straka, Ladislav

    2013-08-01

    Magnetic shape memory effect or magnetically induced structure reorientation (MIR) occurred down to 1.7 K in 10 M martensite with composition of Ni50.0Mn27.5Ga22.5 exhibiting no intermartensite transformation. The reorientation of the martensite microstructure was mediated by the motion of single Type II twin boundary. In contrast with weak thermal dependence of Type II boundary, MIR with Type I boundary in the same alloy showed strong thermal dependence resembling normal thermal activation process and the effect disappeared below 220 K. Thus the type of the boundary is decisive for MIR at low temperatures.

  9. On phase transformation behavior of porous Shape Memory Alloys.

    PubMed

    Liu, Bingfei; Dui, Guansuo; Zhu, Yuping

    2012-01-01

    This paper is concerned on the phase transformation mechanism of porous Shape Memory Alloys (SMAs). A unit-cell model is adopted to establish the constitutive relation for porous SMAs, the stress distributions, the phase distributions and the martensitic volume fractions for the model are then derived under both pure hydrostatic stress and uniaxial compression. Further, an example for the uniaxial response under compression for a porous Ni-Ti SMA material considering hydrostatic stress is supplied. Good agreement between the theoretical prediction of the proposed model and published experimental data is observed.

  10. Fabrication and modeling of shape memory alloy springs

    NASA Astrophysics Data System (ADS)

    Heidari, B.; Kadkhodaei, M.; Barati, M.; Karimzadeh, F.

    2016-12-01

    In this paper, shape memory alloy (SMA) helical springs are produced by shape setting two sets of NiTi (Ti-55.87 at% Ni) wires, one of which showing shape memory effect and another one showing pseudoelasticity at the ambient temperature. Different pitches as well as annealing temperatures are tried to investigate the effect of such parameters on the thermomechanical characteristics of the fabricated springs. Phase transformation temperatures of the products are measured by differential scanning calorimetry and are compared with those of the original wires. Compression tests are also carried out, and stiffness of each spring is determined. The desired pitches are so that a group of springs experiences phase transition during loading while the other does not. The former shows a varying stiffness upon the application of compression, but the latter acts as passive springs with a predetermined stiffness. Based on the von-Mises effective stress and strain, an enhanced one-dimensional constitutive model is further proposed to describe the shear stress-strain response within the coils of an SMA spring. The theoretically predicted force-displacement responses of the produced springs are shown to be in a reasonable agreement with the experimental results. Finally, effects of variations in geometric parameters on the axial force-displacement response of an SMA spring are investigated.

  11. Characterization of a New Phase and Its Effect on the Work Characteristics of a Near-Stoichiometric Ni30Pt20Ti50 High-Temperature Shape Memory Alloy (HTSMA)

    NASA Technical Reports Server (NTRS)

    Garg, A.; Gaydosh, D.; Noebe, R.D.; Padula II, Santo; Bigelow, G.S.; Kaufman, M.; Kovarik, L.; Mills, M.J.; Diercks, D.; McMurray, S.

    2008-01-01

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

  12. Infrared Brazing of Ti50Ni50 Shape Memory Alloy and 316L Stainless Steel with Two Sliver-Based Fillers

    NASA Astrophysics Data System (ADS)

    Shiue, Ren-Kae; Chen, Chia-Pin; Wu, Shyi-Kaan

    2015-06-01

    Dissimilar infrared brazing Ti50Ni50 and AISI 316L stainless steel using two silver-based fillers, Cusil-ABA and Ticusil, was evaluated. The shear strength of the Ticusil brazed joint is higher than that of the Cusil-ABA brazed one due to the formation of better fillet. The maximum shear strength of 237 MPa is obtained for the Ticusil joint brazed at 1223 K (950 °C) for 60 seconds. The presence of interfacial Ti-Fe-(Cu) layer is detrimental to the shear strength of all joints.

  13. Thermomechanical behavior of shape memory elastomeric composites

    NASA Astrophysics Data System (ADS)

    Ge, Qi; Luo, Xiaofan; Rodriguez, Erika D.; Zhang, Xiao; Mather, Patrick T.; Dunn, Martin L.; Qi, H. Jerry

    2012-01-01

    Shape memory polymers (SMPs) can fix a temporary shape and recover their permanent shape in response to environmental stimuli such as heat, electricity, or irradiation. Most thermally activated SMPs use the macromolecular chain mobility change around the glass transition temperature ( Tg) to achieve the shape memory (SM) effects. During this process, the stiffness of the material typically changes by three orders of magnitude. Recently, a composite materials approach was developed to achieve thermally activated shape memory effect where the material exhibits elastomeric response in both the temporary and the recovered configurations. These shape memory elastomeric composites (SMECs) consist of an elastomeric matrix reinforced by a semicrystalline polymer fiber network. The matrix provides background rubber elasticity while the fiber network can transform between solid crystals and melt phases over the operative temperature range. As such it serves as a reversible "switching phase" that enables shape fixing and recovery. Shape memory elastomeric composites provide a new paradigm for the development of a wide array of active polymer composites that utilize the melt-crystal transition to achieve the shape memory effect. This potentially allows for material systems with much simpler chemistries than most shape memory polymers and thus can facilitate more rapid material development and insertion. It is therefore important to understand the thermomechanical behavior and to develop corresponding material models. In this paper, a 3D finite-deformation constitutive modeling framework was developed to describe the thermomechanical behavior of SMEC. The model is phenomenological, although inspired by micromechanical considerations of load transfer between the matrix and fiber phases of a composite system. It treats the matrix as an elastomer and the fibers as a complex solid that itself is an aggregate of melt and crystal phases that evolve from one to the other during a

  14. Critical behavior and magnetic entropy change at magnetic phase transitions in Ni50Mn35In14Si1 ferromagnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Das, R.; Alagarsamy, P.; Srinivasan, A.

    2014-12-01

    We have investigated critical behaviour and magnetocaloric effect in polycrystalline Ni50Mn35In14Si1 alloy near the second-order ferromagnetic phase transitions (SOPT) at austenite Curie temperature (TC,A) and at martensite Curie temperature (TC,M) by determining the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The field dependence of the maximum value of the magnetic entropy change (Δ SM) at the two TC's was estimated using the Maxwell relation as well as from the values of the critical exponents. Values of Δ SM obtained by these two methods at both the SOPT are in remarkable agreement with each other. The critical exponents have been determined by analysing isothermal magnetization data using two different methods, viz., the modified Arrott plot method and the Widom scaling relation. The scaling plots depicted on linear as well as logarithmic scales confirm the reliability of the values of critical exponents obtained. The values of the critical exponents of polycrystalline Ni50Mn35In14Si1 alloy at both the TC's are close to those predicted by mean-field theory confirming the presence of long-range magnetic ordering in the investigated alloy.

  15. 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.

  16. 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.

  17. 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.

  18. Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part 2; Effect of Thermal Cycling

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Noebe, R. D.

    2013-01-01

    This paper is the first report on the effect prior low temperature creep on the thermal cycling behavior of NiTi. The isothermal low temperature creep behavior of near-stoichiometric NiTi between 300 and 473 K was discussed in Part I. The effect of temperature cycling on its creep behavior is reported in the present paper (Part II). Temperature cycling tests were conducted between either 300 or 373 K and 473 K under a constant applied stress of either 250 or 350 MPa with hold times lasting at each temperature varying between 300 and 700 h. Each specimen was pre-crept either at 300 or at 473 K for several months under an identical applied stress as that used in the subsequent thermal cycling tests. Irrespective of the initial pre-crept microstructures, the specimens exhibited a considerable increase in strain with each thermal cycle so that the total strain continued to build-up to 15 to 20 percent after only 5 cycles. Creep strains were immeasurably small during the hold periods. It is demonstrated that the strains in the austenite and martensite are linearly correlated. Interestingly, the differential irrecoverable strain, in the material measured in either phase decreases with increasing number of cycles, similar to the well-known Manson-Coffin relation in low cycle fatigue. Both phases are shown to undergo strain hardening due to the development of residual stresses. Plots of true creep rate against absolute temperature showed distinct peaks and valleys during the cool-down and heat-up portions of the thermal cycles, respectively. Transformation temperatures determined from the creep data revealed that the austenitic start and finish temperatures were more sensitive to the pre-crept martensitic phase than to the pre-crept austenitic phase. The results are discussed in terms of a phenomenological model, where it is suggested that thermal cycling between the austenitic and martensitic phase temperatures or vice versa results in the deformation of the austenite and

  19. High-Temperature Shape Memory Polymers

    NASA Technical Reports Server (NTRS)

    Yoonessi, Mitra; Weiss, Robert A.

    2012-01-01

    physical conformation changes when exposed to an external stimulus, such as a change in temperature. Such materials have a permanent shape, but can be reshaped above a critical temperature and fixed into a temporary shape when cooled under stress to below the critical temperature. When reheated above the critical temperature (Tc, also sometimes called the triggering or switching temperature), the materials revert to the permanent shape. The current innovation involves a chemically treated (sulfonated, carboxylated, phosphonated, or other polar function group), high-temperature, semicrystalline thermoplastic poly(ether ether ketone) (Tg .140 C, Tm = 340 C) mix containing organometallic complexes (Zn++, Li+, or other metal, ammonium, or phosphonium salts), or high-temperature ionic liquids (e.g. hexafluorosilicate salt with 1-propyl-3- methyl imidazolium, Tm = 210 C) to form a network where dipolar or ionic interactions between the polymer and the low-molecular-weight or inorganic compound forms a complex that provides a physical crosslink. Hereafter, these compounds will be referred to as "additives". The polymer is semicrystalline, and the high-melt-point crystals provide a temporary crosslink that acts as a permanent crosslink just so long as the melting temperature is not exceeded. In this example case, the melting point is .340 C, and the shape memory critical temperature is between 150 and 250 C. PEEK is an engineering thermoplastic with a high Young fs modulus, nominally 3.6 GPa. An important aspect of the invention is the control of the PEEK functionalization (in this example, the sulfonation degree), and the thermal properties (i.e. melting point) of the additive, which determines the switching temperature. Because the compound is thermoplastic, it can be formed into the "permanent" shape by conventional plastics processing operations. In addition, the compound may be covalently cross - linked after forming the permanent shape by S-PEEK by applying ionizing

  20. Guide wire extension for shape memory polymer occlusion removal devices

    DOEpatents

    Maitland, Duncan J.; Small, IV, Ward; Hartman, Jonathan

    2009-11-03

    A flexible extension for a shape memory polymer occlusion removal device. A shape memory polymer instrument is transported through a vessel via a catheter. A flexible elongated unit is operatively connected to the distal end of the shape memory polymer instrument to enhance maneuverability through tortuous paths en route to the occlusion.

  1. [Shape-memory polymers for biomedical engineering applications].

    PubMed

    Zhu, Guangming; Liu, Zhongrang

    2005-10-01

    The latest progress in shape-memory polymer for biomedical engineering applications was summarized in this paper. The mechanism responsible for shape memory effect was analyzed in reference to the polymer structure. Also introduced and reviewed were the characteristics of some shape-memory polymers (polyurethane polycaprolactone and polylactide) and their applications in medical engineering.

  2. Self-accommodation of B19' martensite in Ti-Ni shape memory alloys. Part III. Analysis of habit plane variant clusters by the geometrically nonlinear theory

    NASA Astrophysics Data System (ADS)

    Inamura, T.; Nishiura, T.; Kawano, H.; Hosoda, H.; Nishida, M.

    2012-06-01

    Competition between the invariant plane (IP) condition at the habit plane, the twin orientation relation (OR) and the kinematic compatibility (KC) at the junction plane (JP) of self-accommodated B19‧ martensite in Ti-Ni was investigated via the geometrically nonlinear theory to understand the habit plane variant (HPV) clusters presented in Parts I and II of this work. As the IP condition cannot be satisfied simultaneously with KC, an additional rotation Q is necessary to form compatible JPs for all HPV pairs. The rotation J necessary to form the exact twin OR between the major correspondence variants (CVs) in each HPV was also examined. The observed HPV cluster was not the cluster with the smallest Q but the one satisfying Q = J with a { ? 1}B19‧ type I twin at JP. Both Q and J are crucial to understanding the various HPV clusters in realistic transformations. Finally, a scheme for the ideal HPV cluster composed of six HPVs is also proposed.

  3. Self-accommodation of B19' martensite in Ti-Ni shape memory alloys - Part II. Characteristic interface structures between habit plane variants

    NASA Astrophysics Data System (ADS)

    Nishida, M.; Okunishi, E.; Nishiura, T.; Kawano, H.; Inamura, T.; S., Ii; Hara, T.

    2012-06-01

    Four characteristic interface microstructures between habit plane variants (HPVs) in the self-accommodation morphologies of B19‧ martensite in Ti-Ni alloys have been investigated by scanning transmission electron microscopy (STEM). The straight interface of a ? B19‧ type I twin is present at interface I. The relaxation of the transformation strain at interface II is achieved by a volume reduction of the minor correspondence variants (CVs) in the relevant habit plane variants (HPVs). The relaxation of the transformation strain at interface III is mainly due to the formation of a ? B19‧ type I twin between the two major CVs. Subsequently, local strain around the tips of the minor CVs perpendicular to the interface is released by the formation of micro-twins with the ⟨011⟩B19‧ type II and/or ? B19‧ type I relation. The major and minor CVs in each HPV are alternately connected through fine variants with the ? B19‧ type I twin relation parallel to interface IV. The results are compared with macroscopic observations and the predictions of PTMC analysis.

  4. Fast-Response-Time Shape-Memory-Effect Foam Actuators

    NASA Technical Reports Server (NTRS)

    Jardine, Peter

    2010-01-01

    Bulk shape memory alloys, such as Nitinol or CuAlZn, display strong recovery forces undergoing a phase transformation after being strained in their martensitic state. These recovery forces are used for actuation. As the phase transformation is thermally driven, the response time of the actuation can be slow, as the heat must be passively inserted or removed from the alloy. Shape memory alloy TiNi torque tubes have been investigated for at least 20 years and have demonstrated high actuation forces [3,000 in.-lb (approximately equal to 340 N-m) torques] and are very lightweight. However, they are not easy to attach to existing structures. Adhesives will fail in shear at low-torque loads and the TiNi is not weldable, so that mechanical crimp fits have been generally used. These are not reliable, especially in vibratory environments. The TiNi is also slow to heat up, as it can only be heated indirectly using heater and cooling must be done passively. This has restricted their use to on-off actuators where cycle times of approximately one minute is acceptable. Self-propagating high-temperature synthesis (SHS) has been used in the past to make porous TiNi metal foams. Shape Change Technologies has been able to train SHS derived TiNi to exhibit the shape memory effect. As it is an open-celled material, fast response times were observed when the material was heated using hot and cold fluids. A methodology was developed to make the open-celled porous TiNi foams as a tube with integrated hexagonal ends, which then becomes a torsional actuator with fast response times. Under processing developed independently, researchers were able to verify torques of 84 in.-lb (approximately equal to 9.5 Nm) using an actuator weighing 1.3 oz (approximately equal to 37 g) with very fast (less than 1/16th of a second) initial response times when hot and cold fluids were used to facilitate heat transfer. Integrated structural connections were added as part of the net shape process, eliminating

  5. Shape Memory Cellulose-Based Photonic Reflectors.

    PubMed

    Espinha, André; Guidetti, Giulia; Serrano, María C; Frka-Petesic, Bruno; Dumanli, Ahu Gümrah; Hamad, Wadood Y; Blanco, Álvaro; López, Cefe; Vignolini, Silvia

    2016-11-23

    Biopolymer-based composites enable to combine different functionalities using renewable materials and cost-effective routes. Here we fabricate novel thermoresponsive photonic films combining cellulose nanocrystals (CNCs) with a polydiolcitrate elastomer exhibiting shape memory properties, known as hydroxyl-dominant poly(dodecanediol-co-citrate) (PDDC-HD). Iridescent films of CNCs are first made by evaporation-induced self-assembly, then embedded in the PDDC-HD prepolymer, and finally cured to obtain a cross-linked composite with shape memory properties. The fabricated samples are characterized by polarized optical microscopy, scanning electron microscopy, and thermomechanical cycling. The obtained hybrid material combines both intense structural coloration and shape memory effect. The association of stiff cellulose nanocrystals and soft polydiolcitrate elastomer enhances the overall mechanical properties (increased modulus and reduced brittleness). This hybrid nanocomposite takes advantage of two promising materials and expands their possibilities to cover a wide range of potential applications as multiresponsive devices and sensors. As they perform from room to body temperatures, they could be also good candidates for biomedical applications.

  6. Shape memory rubber bands & supramolecular ionic copolymers

    NASA Astrophysics Data System (ADS)

    Brostowitz, Nicole

    The primary focus of this dissertation is to understand the thermo-mechanical properties that govern shape memory in rubber blends. An ideal shape memory polymer (SMP) has a large entropic component that drives shape recovery with a distinct transition mechanism to control the recovery conditions. Polyisoprene rubber is highly elastic and shows shape memory behavior through strain induced crystallization above its glass transition temperature. However, this transition temperature is below 0°C and not suitable for most applications. Shape memory blends can tailor the transition temperature through selection of the switching phase. Most SMP blends require complicated synthesis routes or intensive compounding which would be inhibitive for production. A facile method was developed for fabrication of a robust shape memory polymer by swelling cross-linked natural rubber with stearic acid. Thermal, microscopic studies showed that stearic acid formed a percolated network of crystalline platelets within the natural rubber. Further investigation of the material interactions was carried out with a low molecular weight polyisoprene analog, squalene, and stearic acid gel. Tensile tests on the rubber band demonstrated the thermo-mechanical effect of swelling with stearic acid. Low hysteresis was observed under cyclic loading which indicated viability for the stearic acid swollen rubber band as an SMP. The microscopic crystals and the cross-linked rubber produce a temporary network and a permanent network, respectively. These two networks allow thermal shape memory cycling with deformation and recovery above the melting point of stearic acidand fixation below that point. Under manual, strain-controlled tensile deformation, the shape memory rubber bands exhibited fixity and recovery of 100% +/- 10%. The recovery properties of the SMP were studied under various loading conditions and a model was fit to describe the potential recovery with relation to the fixation. An additional

  7. Porous inorganic—organic shape memory polymers

    PubMed Central

    Zhang, Dawei; Burkes, William L.; Schoener, Cody A.; Grunlan, Melissa A.

    2012-01-01

    Thermoresponsive shape memory polymers (SMPs) are a type of stimuli-sensitive materials that switch from a temporary shape back to their permanent shape upon exposure to heat. While the majority of SMPs have been fabricated in the solid form, porous SMP foams exhibit distinct properties and are better suited for certain applications, including some in the biomedical field. Like solid SMPs, SMP foams have been restricted to a limited group of organic polymer systems. In this study, we prepared inorganic–organic SMP foams based on the photochemical cure of a macromer comprised of inorganic polydimethylsiloxane (PDMS) segments and organic poly(ε-caprolactone) (PCL) segments, diacrylated PCL40-block-PDMS37-block-PCL40. To achieve tunable pore size with high interconnectivity, the SMP foams were prepared via a refined solvent-casting/particulate-leaching (SCPL) method. By varying design parameters such as degree of salt fusion, macromer concentration in the solvent and salt particle size, the SMP foams with excellent shape memory behavior and tunable pore size, pore morphology, and modulus were obtained. PMID:22956854

  8. Triple shape memory effect of star-shaped polyurethane.

    PubMed

    Yang, Xifeng; Wang, Lin; Wang, Wenxi; Chen, Hongmei; Yang, Guang; Zhou, Shaobing

    2014-05-14

    In this study, we synthesized one type of star-shaped polyurethane (SPU) with star-shaped poly(ε-caprolactone) (SPCL) containing different arm numbers as soft segment and 4,4'-diphenyl methane diisocyanate (MDI) as well as chain extender 1,4-butylene glycol (BDO) as hard segment. Proton nuclear magnetic resonance (1H-NMR) confirmed the chemical structure of the material. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results indicated that both the melting temperature (Tm) and transition temperature (Ttrans) of SPU decreased with the hard segment composition increase. X-ray diffraction (XRD) results demonstrated that the increase of the crystallinity of SPU following the raised arm numbers endowed a high shape fixity of six-arm star-shaped polyurethane (6S-PU) and a wide melting temperature range, which resulted in an excellent triple-shape memory effect of 6S-PU. The in vitro cytotoxicity assay evaluated with osteoblasts through Alamar blue assay demonstrates that this copolymer possessed good cytocompatibility. This material can be potentially used as a new smart material in the field of biomaterials.

  9. Characterization of varied geometry shape memory alloy beams

    NASA Astrophysics Data System (ADS)

    Gravatt, Lynn M.; Mabe, James H.; Calkins, Frederick T.; Hartl, Darren J.

    2010-04-01

    Shape Memory Alloys (SMA) have proven to be a lightweight, low cost alternative to conventional actuators for a number of commercial applications. Future applications will require a more complex shape changes and a detailed understanding of the performance of more complex SMA actuators is required. The purpose of this study is to validate engineering models and design practices for SMA beams of various configurations for future applications. Until now, SMA actuators have been fabricated into relatively simple beam shapes. Boeing is now fabricating beams with more complicated geometries in order to determine their strength and shape memory characteristics. These more complicated shapes will allow for lighter and more compact SMA actuators as well as provide more complex shape control. Some of the geometries evaluated include vertical and horizontal I-beams, sine wave and linear wave beams, a truss, and a beam perforated with circular holes along the length. A total of six beams were tested; each was a complex shape made from 57% Nickel by weight with the remainder composed of Titanium (57NiTi). Each sample was put through a number of characterization tests. These include a 3-point bend tests to determine force/displacement properties, and thermal cycling under a range of isobaric loads to determine actuator properties. Experimental results were then compared to modeled results. Test results for one representative beam were used to calibrate a 3-D constitutive model implemented in an finite element framework. It is shown that the calibrated analysis tool is accurate in predicting the response of the other beams. Finally, the actuation work capabilities of the beams are compared using a second round of finite element anaylysis.

  10. Release mechanism utilizing shape memory polymer material

    DOEpatents

    Lee, Abraham P.; Northrup, M. Allen; Ciarlo, Dino R.; Krulevitch, Peter A.; Benett, William J.

    2000-01-01

    Microfabricated therapeutic actuators are fabricated using a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a specified temperature (Tg). At a temperature above temperature Tg material is soft and can be easily reshaped into another configuration. As the temperature is lowered below temperature Tg the new shape is fixed and locked in as long as the material stays below temperature Tg. Upon reheating the material to a temperature above Tg, the material will return to its original shape. By the use of such SMP material, SMP microtubing can be used as a release actuator for the delivery of embolic coils through catheters into aneurysms, for example. The microtubing can be manufactured in various sizes and the phase change temperature Tg is determinate for an intended temperature target and intended use.

  11. Synthesis and electrochemical behavior of nanostructured cauliflower-shape Co-Ni/Co-Ni oxides composites

    SciTech Connect

    Gupta, Vinay Kawaguchi, Toshikazu; Miura, Norio

    2009-01-08

    Nanostructured Co-Ni/Co-Ni oxides were electrochemically deposited onto stainless steel electrode by electrochemical method and characterized for their structural and supercapacitive properties. The SEM images indicated that the obtained Co-Ni/Co-Ni oxides had cauliflower-type nanostructure. The X-ray diffraction pattern showed the formation of Co{sub 3}O{sub 4}, NiO, Co and Ni. The EDX elemental mapping images indicated that Ni, Co and O are distributed uniformly. The deposited Co-Ni/Co-Ni oxides showed good supercapacitive characteristics with a specific capacitance of 331 F/g at 1 mA/cm{sup 2} current density in 1 M KOH electrolyte. A mechanism of the formation of cauliflower-shape Co-Ni/Co-Ni oxides was proposed. A variety of promising applications in the fields such as energy storage devices and sensors can be envisioned from Co-Ni/Co-Ni oxides.

  12. Carbon plasma immersion ion implantation of nickel-titanium shape memory alloys.

    PubMed

    Poon, R W Y; Yeung, K W K; Liu, X Y; Chu, P K; Chung, C Y; Lu, W W; Cheung, K M C; Chan, D

    2005-05-01

    Nickel-titanium (NiTi) shape memory alloys possess super-elasticity in addition to the well-known shape memory effect and are potentially suitable for orthopedic implants. However, a critical concern is the release of harmful Ni ions from the implants into the living tissues. We propose to enhance the corrosion resistance and other surface and biological properties of NiTi using carbon plasma immersion ion implantation and deposition (PIII&D). Our corrosion and simulated body fluid tests indicate that either an ion-mixed amorphous carbon coating fabricated by PIII&D or direct carbon PIII can drastically improve the corrosion resistance and block the out-diffusion of Ni from the materials. Our tribological tests show that the treated surfaces are mechanically more superior and cytotoxicity tests reveal that both sets of plasma-treated samples favor adhesion and proliferation of osteoblasts.

  13. 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.

  14. Improving of Mechanical and Shape-Memory Properties in Hyperbranched Epoxy Shape-Memory Polymers

    NASA Astrophysics Data System (ADS)

    Santiago, David; Fabregat-Sanjuan, Albert; Ferrando, Francesc; De la Flor, Silvia

    2016-09-01

    A series of shape-memory epoxy polymers were synthesized using an aliphatic amine and two different commercial hyperbranched poly(ethyleneimine)s with different molecular weights as crosslinking agents. Thermal, mechanical, and shape-memory properties in materials modified with different hyperbranched polymers were analyzed and compared in order to establish the effect of the structure and the molecular weight of the hyperbranched polymers used. The presence of hyperbranched polymers led to more heterogeneous networks, and the crosslinking densities of which increase as the hyperbranched polymer content increases. The transition temperatures can be tailored from 56 to 117 °C depending on the molecular weight and content of the hyperbranched polymer. The mechanical properties showed excellent values in all formulations at room temperature and, specially, at T_{{g}}^{{E^' with stress at break as high as 15 MPa and strain at break as high as 60 %. The shape-memory performances revealed recovery ratios around 95 %, fixity ratios around 97 %, and shape-recovery velocities as high as 22 %/min. The results obtained in this study reveal that hyperbranched polymers with different molecular weights can be used to enhance the thermal and mechanical properties of epoxy-based SMPs while keeping excellent shape-memory properties.

  15. 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.

  16. 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.

  17. High performance shape memory effect in nitinol wire for actuators with increased operating temperature range

    NASA Astrophysics Data System (ADS)

    Casati, Riccardo; Biffi, Carlo Alberto; Vedani, Maurizio; Tuissi, Ausonio

    2014-07-01

    In this research, the high performance shape memory effect (HP-SME) is experimented on a shape memory NiTi wire, with austenite finish temperature higher than room temperature. The HP-SME consists in the thermal cycling of stress induced martensite and it allows achieving mechanical work higher than that produced by conventional shape memory actuators based on the heating/cooling of detwinned martensite. The Nitinol wire was able to recover about 5.5% of deformation under a stress of 600 MPa and to withstand about 5000 cycles before failure. HP-SME path increased the operating temperature of the shape memory actuator wire. Functioning temperatures higher than 100°C was reached.

  18. 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.

  19. 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

  20. Multiresponsive Shape Memory Blends and Nanocomposites Based on Starch.

    PubMed

    Sessini, Valentina; Raquez, Jean-Marie; Lo Re, Giada; Mincheva, Rosica; Kenny, José Maria; Dubois, Philippe; Peponi, Laura

    2016-08-03

    Smart multiresponsive bionanocomposites with both humidity- and thermally activated shape-memory effects, based on blends of ethylene-vinyl acetate (EVA) and thermoplastic starch (TPS) are designed. Thermo- and humidity-mechanical cyclic experiments are performed in order to demonstrate the humidity- as well as thermally activated shape memory properties of the starch-based materials. In particular, the induced-crystallization is used in order to thermally activate the EVA shape memory response. The shape memory results of both blends and their nanocomposites reflect the excellent ability to both humidity- and thermally activated recover of the initial shape with values higher than 80 and 90%, respectively.

  1. 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.

  2. Modelling the phase diagram of magnetic shape memory Heusler alloys

    NASA Astrophysics Data System (ADS)

    Entel, P.; Buchelnikov, V. D.; Khovailo, V. V.; Zayak, A. T.; Adeagbo, W. A.; Gruner, M. E.; Herper, H. C.; Wassermann, E. F.

    2006-03-01

    We have modelled the phase diagram of magnetic shape memory alloys of the Heusler type by using the phenomenological Ginzburg-Landau theory. When fixing the parameters by realistic values taken from experiment we are able to reproduce most details of, for example, the phase diagram of Ni2+xMn1-xGa in the (T, x) plane. We present the results of ab initio calculations of the electronic and phonon properties of several ferromagnetic Heusler alloys, which allow one to characterize the structural changes associated with the martensitic instability leading to the modulated and tetragonal phases. From the ab initio investigations emerges a complex pattern of the interplay of magic valence electron per atom numbers (Hume-Rothery rules for magnetic ternary alloys), Fermi surface nesting and phonon instability. As the main result, we find that the driving force for structural transformations is considerably enhanced by the extremely low lying optical modes of Ni in the Ni-based Heusler alloys, which interfere with the acoustical modes enhancing phonon softening of the TA2 mode. In contrast, the ferromagnetic Co-based Heusler alloys show no tendency for phonon softening.

  3. Methods of Making and Using Shape Memory Polymer Composite Patches

    NASA Technical Reports Server (NTRS)

    Hood, Patrick J.

    2011-01-01

    A method of repairing a composite component having a damaged area including: laying a composite patch over the damaged area: activating the shape memory polymer resin to easily and quickly mold said patch to said damaged area; deactivating said shape memory polymer so that said composite patch retains the molded shape; and bonding said composite patch to said damaged part.

  4. 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

  5. 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.

  6. Thermal energy conversion by coupled shape memory and piezoelectric effects

    NASA Astrophysics Data System (ADS)

    Zakharov, Dmitry; Lebedev, Gor; Cugat, Orphee; Delamare, Jerome; Viala, Bernard; Lafont, Thomas; Gimeno, Leticia; Shelyakov, Alexander

    2012-09-01

    This work gives experimental evidence of a promising method of thermal-to-electric energy conversion by coupling shape memory effect (SME) and direct piezoelectric effect (DPE) for harvesting quasi-static ambient temperature variations. Two original prototypes of thermal energy harvesters have been fabricated and tested experimentally. The first is a hybrid laminated composite consisting of TiNiCu shape memory alloy (SMA) and macro fiber composite piezoelectric. This composite comprises 0.1 cm3 of active materials and harvests 75 µJ of energy for each temperature variation of 60 °C. The second prototype is a SME/DPE ‘machine’ which uses the thermally induced linear strains of the SMA to bend a bulk PZT ceramic plate through a specially designed mechanical structure. The SME/DPE ‘machine’ with 0.2 cm3 of active material harvests 90 µJ over a temperature increase of 35 °C (60 µJ when cooling). In contrast to pyroelectric materials, such harvesters are also compatible with both small and slow temperature variations.

  7. Biaxial Fatigue Behavior of Niti Shape Memory Alloy

    DTIC Science & Technology

    2005-03-01

    M06 Abstract Nitinol is a shape memory alloy (SMA) capable of martensite-to-austenite phase transformations enabling shape-memory behavior. Shape...memory properties make Nitinol a strong candidate material for use in aircraft applications such as actuators. Structural integrity and reliability...torsion fatigue behavior of Nitinol at room temperature. Monotonic tests in tension and torsion were conducted to typify uni-directional stress-strain

  8. Surface form memory by indentation-planarization training of nickel titanium shape memory alloys

    NASA Astrophysics Data System (ADS)

    Fei, Xueling

    Shape memory alloys respond to deformation by indentation with strong two-way cyclic displacements on heating and cooling. Shallow indents can vanish on heating, and deeper indents will change depth when thermally cycled. In the present work, following indentation by an added step of surface planarization can furthermore produce what has been termed "Surface Form Memory" or SFM. The term SFM describes an effect that causes one surface form to reversibly transform to another, under thermal excitation. The term surface form is meant to distinguish between say, flat and "bumpy" surfaces, on a scale much larger than the intrinsic surface roughness. Surface protrusions, or 'exdents' may reach an amplitude near 20% of the initial indent depth, and may be created on nano to macroscopic size scales. The surface form memory effect may have special applications into novel optical, microelectromechanical, and tribological systems. Surface deformation of a NiTi shape memory alloy (SMA) was accomplished using spherical, cylindrical, pyramidal, and flat punch indenters. Single indents and indent arrays have been made. The amplitude of SFM after planarization was found to be related to the size of the subsurface deformation zone and can be maximized by thermal cycling, multiple indentations, by changing indent depth and spacing, and by varying indentation temperature parameters. The spatial extent of the subsurface deformation zone was studied by both experimental methods and finite element modeling. Methods such as successive front and back thinning probed the size of the deformation zone directly, while finite element modeling provided stress-strain information supporting the conclusion that the deformation zone responsible for the two-way effect was a slip zone that had plastic strains larger than 7%. NiTi SFM, when studied in constrained recovery experiments, showed an energy density up to 10 MJ/m3, which is about the same as that of a conventional NiTi actuator. This proves

  9. Apparatus for loading shape memory gripper mechanisms

    DOEpatents

    Lee, Abraham P.; Benett, William J.; Schumann, Daniel L.; Krulevitch, Peter A.; Fitch, Joseph P.

    2001-01-01

    A method and apparatus for loading deposit material, such as an embolic coil, into a shape memory polymer (SMP) gripping/release mechanism. The apparatus enables the application of uniform pressure to secure a grip by the SMP mechanism on the deposit material via differential pressure between, for example, vacuum within the SMP mechanism and hydrostatic water pressure on the exterior of the SMP mechanism. The SMP tubing material of the mechanism is heated to above the glass transformation temperature (Tg) while reshaping, and subsequently cooled to below Tg to freeze the shape. The heating and/or cooling may, for example, be provided by the same water applied for pressurization or the heating can be applied by optical fibers packaged to the SMP mechanism for directing a laser beam, for example, thereunto. At a point of use, the deposit material is released from the SMP mechanism by reheating the SMP material to above the temperature Tg whereby it returns to its initial shape. The reheating of the SM material may be carried out by injecting heated fluid (water) through an associated catheter or by optical fibers and an associated beam of laser light, for example.

  10. 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.

  11. Titanium-nickel shape memory alloy foams for bone tissue engineering.

    PubMed

    Xiong, J Y; Li, Y C; Wang, X J; Hodgson, P D; Wen, C E

    2008-07-01

    Titanium-nickel (TiNi) shape memory alloy (SMA) foams with an open-cell porous structure were fabricated by space-holder sintering process and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The mechanical properties and shape memory properties of the TiNi foam samples were investigated using compressive test. Results indicate that the plateau stresses and elastic moduli of the foams under compression decrease with the increase of their porosities. The plateau stresses and elastic moduli are measured to be from 1.9 to 38.3 MPa and from 30 to 860 MPa for the TiNi foam samples with porosities ranged from 71% to 87%, respectively. The mechanical properties of the TiNi alloy foams can be tailored to match those of bone. The TiNi alloy foams exhibit shape memory effect (SME), and it is found that the recoverable strain due to SME decreases with the increase of foam porosity.

  12. Shaped Ni nanoparticles with an unconventional hcp crystalline structure.

    PubMed

    Kim, Chanyeon; Kim, Cheonghee; Lee, Kangtaek; Lee, Hyunjoo

    2014-06-18

    Hourglass-shaped Ni nanoparticles were synthesized with a hexagonal close packed (hcp) structure. The unconventional crystalline structure could be stabilized by intensive utilization of hexadecylamine. The dense organic layer on the surface protected the meta-stable crystalline structure.

  13. 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.

  14. 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.

  15. Shape memory polymers with high and low temperature resistant properties

    NASA Astrophysics Data System (ADS)

    Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong

    2015-09-01

    High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to -150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed.

  16. Shape memory polymers with high and low temperature resistant properties

    PubMed Central

    Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong

    2015-01-01

    High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to −150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed. PMID:26382318

  17. Shape memory polymers with high and low temperature resistant properties.

    PubMed

    Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong

    2015-09-18

    High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to -150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed.

  18. 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.

  19. Magnetically Controlled Shape Memory Behaviour—Materials and Applications

    NASA Astrophysics Data System (ADS)

    Gandy, A. P.; Sheikh, A.; Neumann, K.; Neumann, K.-U.; Pooley, D.; Ziebeck, K. R. A.

    2008-06-01

    For most metals a microscopic change in shape occurs above the elastic limit by the irreversible creation and movement of dislocations. However a large number of metallic systems undergo structural, martensitic, phase transformations which are diffusionless, displacive first order transitions from a high-temperature phase to one of lower symmetry below a certain temperature TM. These transitions which have been studied for more than a century are of vital importance because of their key role in producing shape memory phenomena enabling the system to reverse large deformations in the martensitic phase by heating into the austenite phase. In addition to a change in shape (displacement) the effect can also produce a force or a combination of both. Materials having this unique property are increasing being used in medical applications—scoliosis correction, arterial clips, stents, orthodontic wire, orthopaedic implants etc. The structural phase transition essential for shape memory behaviour is usually activated by a change in temperature or applied stress. However for many applications such as for actuators the transformation is not sufficiently rapid. Poor energy conversion also limits the applicability of many shape memory alloys. In medicine a change of temperature or pressure is often inappropriate and new ferromagnetic materials are being considered in which the phenomena can be controlled by an applied magnetic field at constant temperature. In order to achieve this, it is important to optimise three fundamental parameters. These are the saturation magnetisation σs, the Curie temperature Tc and the martensitic temperature TM. Here, σs is important because the magnetic pressure driving the twin boundary motion is 2σsH. Furthermore the material must be in the martensitic state at the operating temperature which should be at or above room temperature. This may be achieved by alloying or controlling the stoichiometry. Recently new intermetallic compounds based

  20. Actuation curvature limits for a composite beam with embedded shape memory alloy wires

    NASA Astrophysics Data System (ADS)

    Naghashian, S.; Fox, B. L.; Barnett, M. R.

    2014-06-01

    Shape memory alloy composites were manufactured using NiTi wires and woven glass fiber pre-impregnated fabrics. A closed form analytical model was developed to investigate the curvature achievable during actuation. The experimental results of actuation showed reasonable agreement with the model. Actuation temperatures were between ˜55 and 110 °C, curvatures of 0.25-0.5 m-1 were obtained and the stresses in the wires were estimated to have reached 265 MPa during actuation. An actuation curvature map was produced, which shows the actuation limits and approximate temperature-curvature curves for the general case of a composite containing shape memory alloy wires.

  1. Residual stresses in injection molded shape memory polymer parts

    NASA Astrophysics Data System (ADS)

    Katmer, Sukran; Esen, Huseyin; Karatas, Cetin

    2016-03-01

    Shape memory polymers (SMPs) are materials which have shape memory effect (SME). SME is a property which has the ability to change shape when induced by a stimulator such as temperature, moisture, pH, electric current, magnetic field, light, etc. A process, known as programming, is applied to SMP parts in order to alter them from their permanent shape to their temporary shape. In this study we investigated effects of injection molding and programming processes on residual stresses in molded thermoplastic polyurethane shape memory polymer, experimentally. The residual stresses were measured by layer removal method. The study shows that injection molding and programming process conditions have significantly influence on residual stresses in molded shape memory polyurethane parts.

  2. Development of Nano Processing Technology for Shape Memory Alloy Fibers

    DTIC Science & Technology

    2011-01-30

    Final Report AOARD-09-4037 (FA2386-09-1-4037) Title: Development of nano processing technology for shape memory alloy fibers PI: Hiroyuki...4. TITLE AND SUBTITLE Development of nano processing technology for shape memory alloy fibers 5a. CONTRACT NUMBER FA23860914037 5b. GRANT NUMBER

  3. AC Electric Field Activated Shape Memory Polymer Composite

    NASA Technical Reports Server (NTRS)

    Kang, Jin Ho; Siochi, Emilie J.; Penner, Ronald K.; Turner, Travis L.

    2011-01-01

    Shape memory materials have drawn interest for applications like intelligent medical devices, deployable space structures and morphing structures. Compared to other shape memory materials like shape memory alloys (SMAs) or shape memory ceramics (SMCs), shape memory polymers (SMPs) have high elastic deformation that is amenable to tailored of mechanical properties, have lower density, and are easily processed. However, SMPs have low recovery stress and long response times. A new shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive fillers to enhance its thermo-mechanical characteristics. A new composition of shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive functionalized graphene sheets (FGS) to enhance its thermo-mechanical characteristics. The elastic modulus of LaRC-SMPC is approximately 2.7 GPa at room temperature and 4.3 MPa above its glass transition temperature. Conductive FGSs-doped LaRC-SMPC exhibited higher conductivity compared to pristine LaRC SMP. Applying an electric field at between 0.1 Hz and 1 kHz induced faster heating to activate the LaRC-SMPC s shape memory effect relative to applying DC electric field or AC electric field at frequencies exceeding1 kHz.

  4. SHADE: A Shape-Memory-Activated Device Promoting Ankle Dorsiflexion

    NASA Astrophysics Data System (ADS)

    Pittaccio, S.; Viscuso, S.; Rossini, M.; Magoni, L.; Pirovano, S.; Villa, E.; Besseghini, S.; Molteni, F.

    2009-08-01

    Acute post-stroke rehabilitation protocols include passive mobilization as a means to prevent contractures. A device (SHADE) that provides repetitive passive motion to a flaccid ankle by using shape memory alloy actuators could be of great help in providing this treatment. A suitable actuator was designed as a cartridge of approximately 150 × 20 × 15 mm, containing 2.5 m of 0.25 mm diameter NiTi wire. This actuator was activated by Joule’s effect employing a 7 s current input at 0.7 A, which provided 10 N through 76 mm displacement. Cooling and reset by natural convection took 30 s. A prototype of SHADE was assembled with two thermoplastic shells hinged together at the ankle and strapped on the shin and foot. Two actuators were fixed on the upper shell while an inextensible thread connected each NiTi wire to the foot shell. The passive ankle motion (passive range of motion, PROM) generated by SHADE was evaluated optoelectronically on three flaccid patients (58 ± 5 years old); acceptability was assessed by a questionnaire presented to further three flaccid patients (44 ± 11.5 years old) who used SHADE for 5 days, 30 min a day. SHADE was well accepted by all patients, produced good PROM, and caused no pain. The results prove that suitable limb mobilization can be produced by SMA actuators.

  5. Biomedical Applications of Thermally Activated Shape Memory Polymers

    SciTech Connect

    Small IV, W; Singhal, P; Wilson, T S; Maitland, D J

    2009-04-10

    Shape memory polymers (SMPs) are smart materials that can remember a primary shape and can return to this primary shape from a deformed secondary shape when given an appropriate stimulus. This property allows them to be delivered in a compact form via minimally invasive surgeries in humans, and deployed to achieve complex final shapes. Here we review the various biomedical applications of SMPs and the challenges they face with respect to actuation and biocompatibility. While shape memory behavior has been demonstrated with heat, light and chemical environment, here we focus our discussion on thermally stimulated SMPs.

  6. Biomedical applications of thermally activated shape memory polymers†

    PubMed Central

    Small, Ward; Singhal, Pooja; Wilson, Thomas S.

    2011-01-01

    Shape memory polymers (SMPs) are smart materials that can remember a primary shape and can return to this primary shape from a deformed secondary shape when given an appropriate stimulus. This property allows them to be delivered in a compact form via minimally invasive surgeries in humans, and deployed to achieve complex final shapes. Here we review the various biomedical applications of SMPs and the challenges they face with respect to actuation and biocompatibility. While shape memory behavior has been demonstrated with heat, light and chemical environment, here we focus our discussion on thermally stimulated SMPs. PMID:21258605

  7. Residual stresses in shape memory alloy fiber reinforced aluminium matrix composite

    NASA Astrophysics Data System (ADS)

    Tsz Loong, Tang; Jamian, Saifulnizan; Ismail, Al Emran; Nur, Nik Hisyammudin Muhd; Watanabe, Yoshimi

    2017-01-01

    Process-induced residual stress in shape memory alloy (SMA) fiber reinforced aluminum (Al) matrix composite was simulated by ANSYS APDL. The manufacturing process of the composite named as NiTi/Al is start with loading and unloading process of nickel titanium (NiTi) wire as SMA to generate a residual plastic strain. Then, this plastic deformed NiTi wire would be embedded into Al to become a composite. Lastly, the composite is heated form 289 K to 363 K and then cooled back to 300 K. Residual stress is generated in composite because of shape memory effect of NiTi and mismatch of thermal coefficient between NiTi wire and Al matrix of composite. ANSYS APDL has been used to simulate the distribution of residual stress and strain in this process. A sensitivity test has been done to determine the optimum number of nodes and elements used. Hence, the number of nodes and elements used are 15680 and 13680, respectively. Furthermore, the distribution of residual stress and strain of nickel fiber reinforced aluminium matrix composite (Ni/Al) and titanium fiber reinforced aluminium matrix composite (Ti/Al) under same simulation process also has been simulated by ANSYS APDL as comparison to NiTi/Al. The simulation results show that compressive residual stress is generated on Al matrix of Ni/Al, Ti/Al and NiTi/Al during heating and cooling process. Besides that, they also have similar trend of residual stress distribution but difference in term of value. For Ni/Al and Ti/Al, they are 0.4% difference on their maximum compressive residual stress at 363K. At same circumstance, NiTi/Al has higher residual stress value which is about 425% higher than Ni/Al and Ti/Al composite. This implies that shape memory effect of NiTi fiber reinforced in composite able to generated higher compressive residual stress in Al matrix, hence able to enhance tensile property of the composite.

  8. Stress serration and arch-shaped Lüders stress plateau behaviour of Ti-50.8 at% Ni wire prepared by selective electrical resistance over-aging

    NASA Astrophysics Data System (ADS)

    Meng, Qinglin; Wu, Zhigang; Bakhtiari, Reza; Zhang, Junsong; Yang, Hong; Liu, Yinong

    2016-11-01

    Joule heating of NiTi shape memory alloy wires is a commonly applied technique for heat treatment and shape setting in many applications. Another innovative use of this method is to produce functionally graded NiTi. In this study, NiTi wires with spatially varied shape memory characteristics along the length were created by electrical resistance over-aging of a Ni-rich superelastic NiTi alloy. The stress-strain behaviour of such wires exhibited some new and unique characteristics during the stress-induced martensitic transformation, including two discrete stress plateaus, stress serration during transition between the two stress plateaus and an arch-shaped stress plateau in the over-aged section. These unique features have direct implications to design using NiTi alloys and the underlying mechanisms are explained in this study.

  9. Shape-memory-actuated compliant control surface

    NASA Astrophysics Data System (ADS)

    Maclean, Brian J.; Carpenter, Bernie F.; Draper, Jerry L.; Misra, Mohan S.

    1993-09-01

    Advanced submarine stern configurations require a variety of control surfaces to actively manage aftbody boundary layer flow, vorticity, propulsor inflow and intrapropulsor flow, as well as vehicle attitude. Two necessary attributes of advanced control surface designs include (1) integrated actuation to provide placement flexibility at remote locations with minimal structural interfacing and control interconnects, and (2) improved lift efficiency and flow using variable or adaptive camber control. To demonstrate these attributes, a shape memory alloy (SMA) actuated compliant control fin (CCF) with a planform area of 620 sq. cm was developed for evaluation as rudder and sternplane appendages on a radio control submarine model at velocities up to 5.1 m/s (Reynolds No. approximately equals 1,000,000) and up to 0.2 Hz full cycle actuation. A completely fixed root design was developed to reduce turbulence at the hull/fine interface, with compliant deformation of the foil to improve flow characteristics over the baseline full-flying and trailing-edge-flap designs.

  10. Dynamic Characterization of Shape Memory Titanium Alloys

    NASA Astrophysics Data System (ADS)

    Joshi, V. S.; Imam, M. A.

    2004-07-01

    Evaluation of high strain rate behavior of materials at pre-fracture strains is very important where the materials are considered for ballistic applications. High compression strain rate response of shape memory titanium alloy including a typical titanium alloy are determined using the split Hopkinson pressure bar (SHPB). The conventional SHPB technique has been routinely used for measuring high strain rate properties of high strength materials. A split Hopkinson bar consisting of 10-mm diameter Maraging 350 alloy incident, transmitter, and striker bars was used to determine the compressive response of these alloys. Attempts are underway to use this technique to extract useful information required to design a material for improving its impact resistance. Initial test results performed on these different titanium alloys show an interesting trend with change of composition. Attempts were made to compare the stress-strain data of these alloys with the published data for titanium alloys. Stress-strain data and changes resulting in the microstructure from strain rates in the regime 1800-4000/s are presented.

  11. 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'.

  12. Styrene-based shape memory foam: fabrication and mathematical modeling

    NASA Astrophysics Data System (ADS)

    Yao, Yongtao; Zhou, Tianyang; Qin, Chao; Liu, Yanju; Leng, Jinsong

    2016-10-01

    Shape memory polymer foam is a promising kind of structure in the biomedical and aerospace field. Shape memory styrene foam with uniform and controlled open-cell structure was successfully fabricated using a salt particulate leaching method. Shape recovery capability exists for foam programming in both high-temperature compression and low-temperature compression (Shape recovery properties such as shape fixing property and shape recovery ratio were also characterized. In order to provide guidance for the future fabrication of shape memory foam, the theories of Gibson and Ashby as well as differential micromechanics theory were applied to predict Young’s modulus and the mechanical behavior of SMP styrene foams during the compression process.

  13. Cellular Shape Memory Alloy Structures: Experiments & Modeling (Part 1)

    DTIC Science & Technology

    2012-08-01

    AFOSR  Grant  #FA9550-­‐08-­‐1-­‐0313 Cellular  Shape  Memory   Alloy  Structures:   Experiments  &  Modeling J.  Shaw  (UM...2012 4. TITLE AND SUBTITLE Cellular Shape Memory Alloy Structures: Experiments & Modeling (Part 1) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c...dense,  0.37  g/cc) Combine benefits of light-weight cellular structures with Shape Memory Alloy (SMA) adaptive behavior CombinaKon •Amplified

  14. Modeling shape-memory behavior of dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Xiao, Rui

    2016-04-01

    In this study, we present a constitutive model to couple the shape memory and dielectric behaviors of polymers. The model adopted multiple relaxation processes and temperature-dependent relaxation time to describe the glass transition behaviors. The model was applied to simulate the thermal-mechanical-electrical behaviors of the dielectric elastomer VHB 4905. We investigated the influence of deformation temperature, voltage rate, relaxation time on the electromechanical and shape-memory behavior of dielectric elastomers. This work provides a method for combining the shape-memory properties and electroactive polymers, which can expand the applications of these soft active materials.

  15. Spooled packaging of shape memory alloy actuators

    NASA Astrophysics Data System (ADS)

    Redmond, John A.

    A vast cross-section of transportation, manufacturing, consumer product, and medical technologies rely heavily on actuation. Accordingly, progress in these industries is often strongly coupled to the advancement of actuation technologies. As the field of actuation continues to evolve, smart materials show significant promise for satisfying the growing needs of industry. In particular, shape memory alloy (SMA) wire actuators present an opportunity for low-cost, high performance actuation, but until now, they have been limited or restricted from use in many otherwise suitable applications by the difficulty in packaging the SMA wires within tight or unusually shaped form constraints. To address this packaging problem, SMA wires can be spool-packaged by wrapping around mandrels to make the actuator more compact or by redirecting around multiple mandrels to customize SMA wire pathways to unusual form factors. The goal of this dissertation is to develop the scientific knowledge base for spooled packaging of low-cost SMA wire actuators that enables high, predictable performance within compact, customizable form factors. In developing the scientific knowledge base, this dissertation defines a systematic general representation of single and multiple mandrel spool-packaged SMA actuators and provides tools for their analysis, understanding, and synthesis. A quasi-static analytical model distills the underlying mechanics down to the three effects of friction, bending, and binding, which enables prediction of the behavior of generic spool-packaged SMA actuators with specifiable geometric, loading, frictional, and SMA material parameters. An extensive experimental and simulation-based parameter study establishes the necessary understanding of how primary design tradeoffs between performance, packaging, and cost are governed by the underlying mechanics of spooled actuators. A design methodology outlines a systematic approach to synthesizing high performance SMA wire actuators

  16. The quintuple-shape memory effect in electrospun nanofiber membranes

    NASA Astrophysics Data System (ADS)

    Zhang, Fenghua; Zhang, Zhichun; Liu, Yanju; Lu, Haibao; Leng, Jinsong

    2013-08-01

    Shape memory fibrous membranes (SMFMs) are an emerging class of active polymers, which are capable of switching from a temporary shape to their permanent shape upon appropriate stimulation. Quintuple-shape memory membranes based on the thermoplastic polymer Nafion, with a stable fibrous structure, are achieved via electrospinning technology, and possess a broad transition temperature. The recovery of multiple temporary shapes of electrospun membranes can be triggered by heat in a single triple-, quadruple-, quintuple-shape memory cycle, respectively. The fiber morphology and nanometer size provide unprecedented design flexibility for the adjustable morphing effect. SMFMs enable complex deformations at need, having a wide potential application field including smart textiles, artificial intelligence robots, bio-medical engineering, aerospace technologies, etc in the future.

  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. Novel Processing for Creating 3D Architectured Porous Shape Memory Alloy

    DTIC Science & Technology

    2013-03-01

    Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 15. SUBJECT TERMS shape memory alloy, powder metallurgy , digital image...were used as a spaceholder with powder metallography. High carbon steel wires were chosen with a wire diameter of 400 μm. The wires were orthogonally...similar to the method detailed above, in that a composite of NiTi powders and a steel spaceholder frame is created, and the frame is electrochemically

  19. Equilibrium shape of graphene domains on Ni(111)

    NASA Astrophysics Data System (ADS)

    Li, Meifang; Hannon, James B.; Tromp, Rudoff M.; Sun, Jiebing; Li, Junwen; Shenoy, Vivek B.; Chason, Eric

    2013-07-01

    We have determined the equilibrium shape of graphene domains grown on Ni(111) via carbon segregation at 925∘C. In situ, spatially resolved electron diffraction measurements were used to determine the crystallographic orientation of the edges of the graphene domains. In contrast to recent theoretical predictions of a nearly circular shape, we show that graphene domains, which nucleate with random shapes, all evolve toward a triangular equilibrium shape with “zigzag” edges. Only one of the two possible zigzag edge orientations is observed.

  20. The applications and research progresses of nickel-titanium shape memory alloy in reconstructive surgery.

    PubMed

    Li, Qiang; Zeng, Yanjun; Tang, Xiaoying

    2010-06-01

    In spite of some good successes and excellent researches of nickel-titanium shape memory alloy (NiTi-SMA) in reconstructive surgery, there are still serious limitations to the clinical applications of NiTi alloy today. The potential leakage of elements and ions could be toxic to cells, tissues and organs. This review discussed the properties, clinical applications, corrosion performance, biocompatibility, the possible preventive measures to improve corrosion resistance by surface/structure modifications and the long-term challenges of using SMAs.