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Sample records for electropolished niti shape

  1. Surface characteristics of sterilized electropolished NiTi shape memory alloy as biomaterials

    NASA Astrophysics Data System (ADS)

    Tabrizian, Maryam; Thierry, Benjamin; Savadogo, Omarou; Yahia, L'Hocine

    1999-05-01

    As a potential biomaterial for many medical applications, NiTi alloy derives its good biocompatibility and corrosion resistance from a homogeneous and protective oxide layer, mainly composed of TiO2, with little concentration of nickel. However, during corrosion testing at high potential, NiTi is susceptible to pitting corrosion, which may affect the amount of ions (nickel and titanium) released by the alloy and thus, may affect its biocompatibility. As a passivating treatment, electropolishing (EP) was demonstrated to decrease the amount of nickel on the surface and to remarkably improve the corrosion behavior of the alloy. After sterilization by ethylene oxide (EO), no modification of the promising corrosion behavior of electropolished NiTi were observed, although some surface modifications were reported. The corrosion resistance of ethylene oxide sterilized and electropolished samples ranked between that of the commonly used Ti6A14V and 316L (0.4 less than 1 less than 1.4 mV/SCE) implant alloys.

  2. 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.

  3. Shape Memory Behavior of Porous NiTi Alloy

    NASA Astrophysics Data System (ADS)

    Kaya, Mehmet; Çakmak, Ömer

    2016-04-01

    Shape memory behavior of porous NiTi alloy is dependent on the phases, and mechanical or thermal background. The phases change with solution heat treatment and aging. Fully reversible shape memory behavior was observed during thermal cycling, and recoverable strains increased with the increasing stress from 2 to 50 MPa. The porous NiTi sample shows recoverable transformation strain response under lower constant load.

  4. 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.

  5. 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. PMID:8894095

  6. 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.

  7. Effect of cathode shape on vertical buffered electropolishing for niobium SRF cavities

    NASA Astrophysics Data System (ADS)

    Jin, S.; Wu, A. T.; Lu, X. Y.; Rimmer, R. A.; Lin, L.; Zhao, K.; Mammosser, J.; Gao, J.

    2013-09-01

    This paper reports the research results of the effect of cathode shape during vertical buffered electropolishing (BEP) by employing a demountable single cell niobium (Nb) superconducting radio frequency (SRF) cavity. Several different cathode shapes such as, for instance, bar, ball, ellipsoid, and wheels of different diameters have been tested. Detailed electropolishing parameters including I-V characteristic, removal rate, surface roughness, and polishing uniformity at different locations inside the demountable cavity are measured. Similar studies are also done on conventional electropolishing (EP) for comparison. It is revealed that cathode shape has dominant effects for BEP especially on the obtaining of a suitable polishing condition and a uniform polishing rate in an Nb SRF single cell cavity. EP appears to have the same tendency. This paper demonstrates that a more homogeneous polishing result can be obtained by optimizing the electric field distribution inside the cavity through the modification of the cathode shape given the conditions that temperature and electrolyte flow are kept constant. Electric field distribution and electrolyte flow patterns inside the cavity are simulated via Poisson-Superfish and Solidworks respectively. With the optimal cathode shape, BEP shows a much faster polishing rate of ∼2.5 μm/min and is able to produce a smoother surface finish in the treatments of single cell cavities in comparison with EP.

  8. Effect of cathode shape on vertical buffered electropolishing for niobium SRF cavities

    SciTech Connect

    Jin, Song; Wu, Andy T.; Lu, Xiangyang; Rimmer, Robert A.; Lin, Lin; Zhao, K.; Mammosser, John D.; Gao, Jie

    2013-09-01

    This paper reports the research results of the effect of cathode shape during vertical buffered electropolishing (BEP) by employing a demountable single cell niobium (Nb) superconducting radio frequency (SRF) cavity. Several different cathode shapes such as, for instance, bar, ball, ellipsoid, and wheels of different diameters have been tested. Detailed electropolishing parameters including I–V characteristic, removal rate, surface roughness, and polishing uniformity at different locations inside the demountable cavity are measured. Similar studies are also done on conventional electropolishing (EP) for comparison. It is revealed that cathode shape has dominant effects for BEP especially on the obtaining of a suitable polishing condition and a uniform polishing rate in an Nb SRF single cell cavity. EP appears to have the same tendency. This paper demonstrates that a more homogeneous polishing result can be obtained by optimizing the electric field distribution inside the cavity through the modification of the cathode shape given the conditions that temperature and electrolyte flow are kept constant. Electric field distribution and electrolyte flow patterns inside the cavity are simulated via Poisson–Superfish and Solidworks respectively. With the optimal cathode shape, BEP shows a much faster polishing rate of ∼2.5 μm/min and is able to produce a smoother surface finish in the treatments of single cell cavities in comparison with EP.

  9. Effect of surface treatment and sterilization processes on the corrosion behavior of NiTi shape memory alloy.

    PubMed

    Thierry, B; Tabrizian, M; Trepanier, C; Savadogo, O; Yahia, L

    2000-09-15

    Nickel-titanium (NiTi) alloy derives its biocompatibility and good corrosion resistance from a homogeneous oxide layer mainly composed of TiO(2), with a very low concentration of nickel. In this article, we described the corrosion behavior of NiTi alloys after mechanical polishing, electropolishing, and sterilization processes using cyclic polarization and atomic absorption. As a preparative surface treatment, electropolishing decreased the amount of nickel on the surface and remarkably improved the corrosion behavior of the alloy by increasing the mean breakdown potential value and the reproducibility of the results (0.99 +/- 0.05 V/SCE vs. 0.53 +/- 0. 42). Ethylene oxide and Sterrad(R) sterilization techniques did not modify the corrosion resistance of electropolished NiTi, whereas a steam autoclave and, to a lesser extent, peracetic acid sterilization produced scattered breakdown potential. In comparing the corrosion resistance of common biomaterials, NiTi ranked between 316L stainless steel and Ti6A14V even after sterilization. Electropolished NiTi and 316L stainless-steel alloys released similar amounts of nickel after a few days of immersion in Hank's solution. Measurements by atomic absorption have shown that the amount of released nickel from passive dissolution was below the expected toxic level in the human body. Auger electron spectroscopy analyses indicated surface contamination by Ca and P on NiTi during immersion, but no significant modification in oxide thickness was observed. PMID:10880117

  10. 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. PMID:18937263

  11. Powder metallurgy technology of NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Dutkiewicz, J. M.; Maziarz, W.; Czeppe, T.; Lityńska, L.; Nowacki, W. K.; Gadaj, S. P.; Luckner, J.; Pieczyska, E. A.

    2008-05-01

    Powder metallurgy technology was elaborated for consolidation of shape memory NiTi powders. The shape memory alloy was compacted from the prealloyed powder delivered by Memry SA. The powder shows Ms = 10°C and As = -34°C as results from DSC measurements. The samples were hot pressed in the as delivered spherical particle's state. The hot compaction was performed in a specially constructed vacuum press, at temperature of 680°C and pressure of 400 MPa. The alloy powder was encapsulated in copper capsules prior to hot pressing to avoid oxidation or carbides formation. The alloy after hot vacuum compaction at 680°C (i.e. within the B2 NiTi stability range) has shown similar transformation range as the powder. The porosity of samples compacted in the as delivered state was only 1%. The samples tested in compression up to ɛ = 0.06 have shown partial superelastic effect due to martensitic reversible transform- ation which started at the stress above 300 MPa and returned back to ɛ = 0.015 after unloading. They have shown also a high ultimate compression strength of 1600 MPa. Measurements of the samples temperature changes during the process allowed to detect the temperature increase above 12°C for the strain rate 10-2 s-1 accompanied the exothermic martensite transformation during loading and the temperature decrease related to the reverse endothermic transformation during unloading.

  12. The effect of electropolishing on torque and force during simulated root canal preparation with ProTaper shaping files.

    PubMed

    Boessler, Claudia; Paque, Frank; Peters, Ove A

    2009-01-01

    Surface modifications of nickel-titanium instruments such as electropolishing may reduce fracture incidence but could potentially alter the instruments' mechanical properties. We studied the impact of two surface types, machined and electropolished, of ProTaper shaping files on torque and force during simulated root canal preparation. Pilot holes of 0.5-mm diameter were drilled perpendicularly through 3-mm thick human dentin discs and served as standardized simulated root canals (SSRCs). A total of 300 SSRCs were prepared with ProTaper Sx, S1, and S2 instruments using an automated testing platform. Maximum torque (in Ncm) and maximum force values (in N) were measured. In three experimental groups (Sx, S1, and S2) preparation of SSRCs was performed using electropolished versus machined instruments in the same dentin disc. For all three tested instruments, peak torque was higher for electropolished files; apically exerted forces were similar, except for Sx, in which machined instruments developed higher forces. We conclude that surface treatment by electropolishing alters the cutting ability of nickel-titanium rotary instruments. PMID:19084135

  13. 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. PMID:26952473

  14. Improving the bioactivity of NiTi shape memory alloy by heat and alkali treatment

    NASA Astrophysics Data System (ADS)

    Qiang, Wei; Zhen-duo, Cui; Xian-jin, Yang; Jie, Shi

    2008-11-01

    TiO 2 films were formed on an NiTi alloy surface by heat treatment in air at 600 °C. Heat treated NiTi shape memory alloys were subsequently alkali treated with 1 M, 3 M and 5 M NaOH solutions respectively, to improve their bioactivity. Then treated NiTi samples were soaked in 1.5SBF to evaluate their in vitro performance. The results showed that the 3 M NaOH treatment is the most appropriate method. A large amount of apatite formed within 1 day's soaking in 1.5SBF, after 7 day's soaking TiO 2/HA composite layer formed on the NiTi surface. SEM, XRD, FT-IR and TEM results showed that the morphology and microstructure are similar to the human bone apatite.

  15. 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. PMID:27040211

  16. Neutron diffraction study of NiTi during compressive deformation and after shape-memory recovery

    SciTech Connect

    Dunand, D.C.; Mari, D.; Bourke, M.A.M.; Goldstone, J.A.

    1995-09-01

    Neutron diffraction measurements of internal elastic strains and texture were performed during compressive deformation of martensitic NiTi deforming by twinning. Rietveld refinement of the diffraction spectrum was performed in order to obtain lattice parameter variations and preferred orientation of martensitic variants. The elastic internal strains, are proportional to the externally applied stress but strongly dependent on crystallographic orientation. Plastic deformation by matrix twinning is consistent with type I (1-1-1) twinning, whereby (100) and (011) planes tend to align perpendicular and parallel to the stress axis, respectively. The preferred orientation ratio r according to the model by March and Dollase is proportional to the macroscopic plastic strain for (100) and (011) planes for loading, unloading and shape-memory recovery. To the best of our knowledge, this is the first in situ bulk measurement of reversible twinning in NiTi. Finally, shape-memory recovery results in a marked change of NiTi cell parameters.

  17. Nanostructured Nb reinforced NiTi shape memory alloy composite with high strength and narrow hysteresis

    NASA Astrophysics Data System (ADS)

    Hao, Shijie; Cui, Lishan; Jiang, Daqiang; Yu, Cun; Jiang, Jiang; Shi, Xiaobin; Liu, Zhenyang; Wang, Shan; Wang, Yandong; Brown, Dennis E.; Ren, Yang

    2013-06-01

    An in-situ nanostructured Nb reinforced NiTi shape-memory alloy composite was fabricated by mechanical reduction of an as-cast Nb-NiTi eutectic alloy. The composite exhibits large elastic strain, high strength, narrow hysteresis, and high mechanical energy storage density and efficiency during tensile cycling. In situ synchrotron high-energy X-ray diffraction revealed that these superior properties were attributed to the strong coupling between nanostructured Nb and NiTi matrix during deformation. Furthermore, this study offers a good understanding of the deformation behavior of the nanoscale reinforcement embedded in the metal matrix deformed by stress-induced phase transformation.

  18. Tribological characteristics of ceramic conversion treated NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Ju, X.; Dong, H.

    2007-09-01

    NiTi shape memory alloys are very attractive for medical implants and devices (such as orthopaedic and orthodontic implants) and various actuators. However, wear is a major concern for such applications and a novel surface engineering process, ceramic conversion treatment, has recently been developed to address this problem. In this study, the tribological characteristics of ceramic conversion treated NiTi alloy have been systematically investigated under dry unidirectional wear, reciprocating-corrosion wear and fretting-corrosion wear condition. Based on the experimental results, the wear behaviour under different conditions is compared and wear mechanisms involved are discussed.

  19. Experimental Investigation on the Mechanical Instability of Superelastic NiTi Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Xiao, Yao; Zeng, Pan; Lei, Liping

    2016-06-01

    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.

  20. Fatigue properties of NiTi shape-memory alloy thin plates

    NASA Astrophysics Data System (ADS)

    Yamamoto, Hiroshi; Taya, Minoru; Liang, Yuanchang; Namli, Onur C.; Saito, Makoto

    2013-04-01

    The mechanical and fatigue characteristics of superelastic NiTi thin plates in the large strain area were obtained by tensile and pulsating 4-point bending tests to establish the design guidelines for the ferromagnetic shape memory alloy (FSMA) composite actuator and its fatigue life. The stress-strain curves of NiTi thin plates were found to be strain rate dependent. The finite element analysis (FEA) result using the stress-strain curve measured by tensile test is in good agreement with the experimental results of the 4-point bending tests. The relationship between the maximum bending strain and the number of cycles to failure in pulsating 4-point bending fatigue tests was obtained as well as an analysis of the fatigue fracture surfaces of NiTi thin plates.

  1. Wear Properties of Porous NiTi Orthopedic Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Wu, Shuilin; Liu, Xiangmei; Yeung, K. W. K.; Xu, Z. S.; Chung, C. Y.; Chu, Paul K.

    2012-12-01

    Porous NiTi shape memory alloy (SMA) scaffolds have great potential to be used as orthopedic implants because of their porous structure and superior physical properties. Its metallic nature provides it with better mechanical properties and Young's modulus close to that of natural bones. Besides allowing tissue ingrowth and transfer of nutrients, porous SMA possesses unique pseudoelastic properties compatible to natural hard tissues like bones and tendons, thus expediting in vivo osseointegration. However, the nickel release from debris and the metal surface may cause osteocytic osteolysis at the interface between the artificial implants and bone tissues. Subsequent mobilization may finally lead to implant failure. In this study, the wear properties of porous NiTi with different porosities processed at different treatment temperatures are determined. The results of the study show that the porosity, phase transformation temperature, and annealing temperature are major factors influencing the wear characteristics of porous NiTi SMA.

  2. Corrosion behavior of titanium nitride coated Ni-Ti shape memory surgical alloy.

    PubMed

    Starosvetsky, D; Gotman, I

    2001-07-01

    Nickel-titanium (NiTi, nitinol) shape memory alloy was nitrided using an original powder immersion reaction assisted coating (PIRAC) method in order to modify its surface properties. PIRAC nitriding method is based on annealing the samples in the atmosphere of highly reactive nitrogen supplied by decomposition of unstable nitride powders or, alternatively, by selective diffusion of the atmospheric nitrogen to the sample surface. Being a non-line-of-sight process, PIRAC nitriding allows uniform treatment of complex shape surgical implants. Hard two-layer titanium nitride (TiN)/Ti2, Ni coatings were obtained on NiTi surface after PIRAC anneals at 900 and 1000 degrees C. PIRAC coating procedure was found to considerably improve the corrosion behavior of NiTi alloy in Ringer's solution. In contrast to untreated nitinol, no pitting was observed in the samples PIRAC nitrided at 1000 degrees C, 1 h up to 1.1 V. The coated samples were also characterized by very low anodic currents in the passive region and by an exceedingly low metal ion release rate. The research results suggest that PIRAC nitriding procedure could improve the in vivo performance of NiTi alloys implanted into the human body. PMID:11396890

  3. 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.

  4. Effect of Deformation Mode on the Wear Behavior of NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Yan, Lina; Liu, Yong

    2016-05-01

    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.

  5. 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.

  6. X-ray diffraction study of the phase transformations in NiTi shape memory alloy

    SciTech Connect

    Uchil, J.; Fernandes, F.M. Braz . E-mail: kkmahesh@rediffmail.com

    2007-03-15

    The phase transformations occurring in heat-treated NiTi shape memory alloys have been studied through the analysis of variation in integrated peak area (integrated intensity) with temperature, under the XRD peak profiles in the transformation temperature range. For this purpose, integrated peak area under the prominent peak corresponding to (110) plane of the austenitic phase has been chosen. The results so obtained are compared with those got from the DSC method. The XRD method is found to be more sensitive.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-08-01

    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.

  9. 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.

  10. [NiTi shape-memory alloy cramp used in repair of skull defect].

    PubMed

    Wang, Z; Zhou, S; Tian, F

    1998-11-01

    Fixation of silicon-polyester fiber network on skull defect was usually difficult to handle and the fixation was unstable. In order to solve these problems, NiTi shape-memory alloy cramp was adopted and 101 patients with skull defects were selected for this clinical trial. Among them, there were 79 males and 22 females, and the age ranged from 12-55 years old. The area of skull defect ranged from 3 cm x 4 cm to 10 cm x 16 cm. All of these patients received repairing of the skull defects by silicon-polyester fiber network which was fixed by NiTi memory alloy cramps. After operation, there was no complication. One hundred patients were followed up for 1-8 years, in which 97 cases returned to their normal work, and only 2 cases had a transient dysfunction of frontal muscle for 2 months. In addition, There were no loosening of the cramps, displacement of plastic network and malignant degeneration. The NiTi shape-memory alloy cramps had the following advantages: 1. Simple operative procedure; 2. Rigid fixation; 3. Mild postoperative tissue reaction; 4. Few postoperative complication; 5. Favorable effect of skull repair; 6. No interference with CT and MRI image; 7. No carcinogenicity. PMID:10437089

  11. NiTi shape memory via solid-state nudge-elastic band

    NASA Astrophysics Data System (ADS)

    Zarkevich, Nikolai A.; Johnson, Duane D.

    2014-03-01

    We determine atomic mechanisms of the shape memory effect in NiTi from a generalized solid-state nudge elastic band (SSNEB) method. We consider transformation between the austenite B2 and the ground-state base-centered orthorhombic (BCO) structures. In these pathways we obtain the R-phase and discuss its structure. We confirm that BCO is the ground state, and determine the pathways to BCO martensite, which dictate transition barriers. While ideal B2 is unstable, we find a B2-like NiTi high-temperature solid phase with significant local displacement disorder, which is B2 on average. This B2-like phase appears to be entropically stabilized. This work is supported by the U.S. Department of Energy, Office of Basic Energy Science, Division of Materials Science and Engineering. Ames Laboratory is operated for the U.S. DOE by Iowa State University under contract DE-AC02-07CH11358.

  12. The combustion synthesis of Ni-Ti shape memory alloys

    SciTech Connect

    Moore, J.J.; Yi, H.C. )

    1990-08-01

    Combustion synthesis of Ni-Ti-series shape-memory alloys yields both time and energy savings over conventional production methods. The solidified combustion synthesis process products have been cold-rolled into plates which exhibit the shape-memory effect, and it was noted that shape-memory transition temperatures may be tailored over a -78 to 460 C temperature range through the substitution of a third element for Ni; this element may be Pd or Fe. Accounts are given of the experimental combustion syntheses of Ni-Ti-Fe and Ti-Ni-Pd. 24 refs.

  13. 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.

  14. 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.

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

    SciTech Connect

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

    2007-08-06

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

  16. Thermopower behavior for the shape memory alloy NiTi

    SciTech Connect

    Lee, J. Y.; McIntosh, G. C.; Kaiser, A. B.; Park, Y. W.; Kaack, M.; Pelzl, J.; Kim, Chul Koo; Nahm, Kyun

    2001-06-01

    We report thermopower measurements for the nickel titanium shape memory alloy Ni{sub 0.507}Ti{sub 0.493}. Our measurements reveal abrupt changes in the temperature dependence of thermopower, which correlate well with the structural phase transition between the austenitic and martensitic phases. These transition effects in thermopower are more clearly defined than in the resistivity, which is also reported. In the martensitic phase, thermopower exhibits standard metallic diffusion behavior with a nonlinearity, which is consistent with either a small peak in the density of states just below the Fermi level, as calculated by Kulkova, Egorushkin, and Kalchikhin [Solid State Commun. 77, 667 (1991)], or else electron{endash}phonon mass enhancement. For thermally or mechanically treated samples, the magnitude of the transition effects in thermopower are reduced. {copyright} 2001 American Institute of Physics.

  17. 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.

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

    DOE PAGESBeta

    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

  19. Shape-memory NiTi foams produced by replication of NaCl space-holders.

    PubMed

    Bansiddhi, A; Dunand, D C

    2008-11-01

    NiTi foams were created with a structure (32-36% open pores 70-400 microm in size) and mechanical properties (4-25 GPa stiffness, >1000 MPa compressive strength, >42% compressive ductility, and shape-memory strains up to 4%) useful for bone implant applications. A mixture of NiTi and NaCl powders was hot-isostatically pressed at 950 and 1065 degrees C and the NaCl phase was then dissolved in water. The resulting NiTi foams show interconnected pores that replicate the shape and size of the NaCl powders, indicating that NiTi powders densified significantly before NaCl melted at 801 degrees C. Densifying NiTi or other metal powders above the melting point of the space-holder permits the use of NaCl, with the following advantages compared with higher-melting, solid space-holders such as oxides and fluorides used to date: (i) no temperature limit for densification; (ii) lower cost; (iii) greater flexibility in powder (and thus pore) shape; (iv) faster dissolution; (v) reduced metal corrosion during dissolution; (vi) lower toxicity if space-holder residues remain in the foam. PMID:18678532

  20. Spray forming of NiTi and NiTiPd shape-memory alloys

    NASA Astrophysics Data System (ADS)

    Smith, Ronald; Mabe, James; Ruggeri, Robert; Noebe, Ronald

    2008-03-01

    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.

  1. 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.

  2. 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.

  3. Behavior of a Ni-Ti shape memory alloy under cyclic proportional and nonproportional loading

    NASA Astrophysics Data System (ADS)

    Lim, Tzishing Jesse

    Ni-Ti shape memory alloy behaves pseudoelastically above the austenite finish temperature, Af, due to stress-induced austenite-martensite phase transformation. In this work, novel multiaxial proportional and nonproportional loading experiments were conducted on a Ni-Ti shape memory alloy above the Af temperature. Several features of pseudoelasticity were highlighted, namely, the tension-compression asymmetry, near symmetry in both senses of shear, apparent strain rate dependence and relaxation (thermo-mechanical effects) and nonconformity to J2--J3 theory of phase transformation under nonproportional loading. Both a simplified representative volume element (RVE) numerical scheme and finite element (FE) modeling based on a micromechanical constitutive model were conducted in order to study the mechanics of phase transformation, interaction between different martensite variants, and intergranular interactions in a polycrystalline structure. In simulations, the austenite to martensite phase transformation can be quite accurately predicted for different modes of loading. Strain rate effects can also be quite accurately modeled; specimen heating/cooling due to latent heat generation/absorption during phase transformation is the primary cause of strain rate dependence.

  4. Oxide Scales Formed on NiTi and NiPtTi Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Garg, Anita; Rogers, Richard B.; Noebe, Ronald D.

    2011-01-01

    Ni-49Ti and Ni-30Pt-50Ti (at.%) shape memory alloys were oxidized isothermally in air over the temperature range of 500 to 900 C. The microstructure, composition, and phase content of the scales were studied by SEM, EDS, XRD, and metallography. Extensive plan view SEM/EDS identified various features of intact or spalled scale surfaces. The outer surface of the scale was a relatively pure TiO2 rutile structure, typified by a distinct highly striated and faceted crystal morphology. Crystal size increased significantly with temperature. Spalled regions exhibited some porosity and less distinct features. More detailed information was obtained by correlation of SEM/EDS studies of 700 C/100 hr cross-sections with XRD analyses of serial or taper-polishing of plan surfaces. Overall, multiple layers exhibited graded mixtures of NiO, TiO2, NiTiO3, Ni(Ti) or Pt(Ni,Ti) metal dispersoids, Ni3Ti or Pt3Ti depletion zones, and substrate, in that order. The NiTi alloy contained a 3 at.% Fe impurity that appeared in embedded localized Fe-Ti-rich oxides, while the NiPtTi alloy contained a 2 v/o dispersion of TiC that appeared in lower layers. The oxidation kinetics of both alloys (in a previous report) indicated parabolic growth and an activation energy (250 kJ/mole) near those reported in other Ti and NiTi studies. This is generally consistent with TiO2 existing as the primary scale constituent, as described here.

  5. Influence of Dynamic Compression on Phase Transformation of Martensitic NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    Shape memory alloys (SMAs) exhibit high damping capacity in both austenitic and martensitic phases, due to either a stress-induced martensite phase transformation or a stress-induced martensite variant reorientation, making them ideal candidates for vibration suppression devices to protect structural components from damage due to external forces. In this study, both quasi-static and dynamic compression was conducted on a martensitic NiTi SMA using a mechanical loading frame and on a Kolsky compression bar, respectively, to examine the relationship between microstructure and phase transformation characteristics of martensitic NiTi SMAs. Both endothermic and exothermic peaks disappear completely after experiencing deformation at a strain rate of 103 s-1 and to a strain of about 10 pct. The phase transformation peaks reappear after the deformed specimens were annealed at 873 K (600 °C) for 30 minutes. As compared to samples from quasi-static loading, where a large amount of twinning is observed with a small amount of grain distortion and fracture, samples from dynamic loading show much less twinning with a larger amount of grain distortion and fracture.

  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. Fracture modes during severe plastic deformation of NiTi shape memory alloys

    NASA Astrophysics Data System (ADS)

    Craciunescu, C. M.; Silva, R. J. C.; Fernandes, F. M. Braz

    2015-07-01

    The effects of severe plastic deformation on the surface micro-structural characteristics of NiTi shape memory alloys were observed after one single pass using the equal channel angular pressure technique. The analysis of the deformation and fracture showed distinct features related to the composition of the alloys, the temperature of the process, and the surface effects during the relative sliding in the die. In samples deformed at room temperature, the cracks initiated at the surface under tensile stress are amplified during the extrusion in the concurrent channel. The multiple cracks that develop during the friction process between the surfaces of the sample and channels of the die are the main cause for the fracture, even in materials that are less brittle, incorporating a smaller fraction of Ti2Ni precipitates and showing ductile fracture. A differential state of stress appears to exist in the deformed alloys starting from one surface to the other.

  8. 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. PMID:24928669

  9. A comparison of the shaping ability of reciprocating NiTi instruments in simulated curved canals

    PubMed Central

    Yoo, Young-Sil

    2012-01-01

    Objectives The study was to compare the shaping ability of Reciproc (VDW) and WaveOne (Dentsply Maillefer) instruments compared with ProTaper, Profile and hand instrument during the preparation of simulated root canals. Materials and Methods Five groups (n = 5) were established. Reciproc, WaveOne, ProTaper, Profile and K file (K-flexo file) were used to prepare the resin simulated canals. A series of preoperative and postoperative images were taken by a microscope and superimposed in 2 different layers. The amount of resin removed from both the inner and the outer sides of the canal was measured to the level of 10 mm from the apical tip, with a 1 mm increment. Results The mean of resin removal from the inner canal wall was not different from the outer canal wall for Reciproc and WaveOne groups at apical third (1 - 3 mm level). There was no difference in the change of working length and maintenance of canal curvature. NiTi instruments are superior to stainless-steel K file in their shaping ability. Conclusions Within the limitation of this present study, Reciproc and WaveOne instruments maintained the original canal curvature in curved canals better than ProTaper and Profile, which tend to transport towards the outer canal wall of the curve in the apical part of the canal. PMID:23430033

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    Shape memory alloys (SMAs) are a new generation of materials that exhibit unique nonlinear deformations due to a phase transformation which allows the material to return to its original shape after removal of stress or a change in temperature. These unique properties are the result of a martensitic/austenitic phase transformation through the application of temperature changes or applied stress. Many technological applications of austenitic SMAs involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity, but are limited due to poor fatigue life. In this paper, commercial pseudoelastic NiTi SMA wires (50.7 at.% Ni) were placed under different bending strains and examined using scanning electron microscopy and high-energy synchrotron radiation X-ray diffraction (SR-XRD). By observing the microstructure, phase transformation temperatures, surface texture and diffraction patterns along the wire, it is shown that the wire exhibits a strong anisotropic behavior whether on the tensile or compressive side of the bending axis and that the initiation of micro-cracks in the wires is localized on the compression side, but that crack propagation will still happen if the wire is reloaded in the opposite direction. In addition, lattice strains are examined for both the austenite and martensite phases.

  11. 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.

  12. 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.

  13. 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. PMID:25746282

  14. Challenges During Microstructural Analysis and Mechanical Testing of Small-Scale Pseudoelastic NiTi Structures

    NASA Astrophysics Data System (ADS)

    Hahn, S.; Wagner, M. F.-X.

    2016-06-01

    Most investigations on NiTi-based shape memory alloys involve large-scale bulk material; knowledge about the martensitic transformation in small-scale NiTi structures is still limited. In this paper, we study the microstructures of thin NiTi layers and their mechanical properties, and we discuss typical challenges that arise when experiments are performed on small samples. A physical vapor deposition (PVD) process was used to deposit thin NiTi wires with a cross section of 15 × 15 μm2 and dogbone-shaped samples 5 × 500 μm2. Microstructural properties were characterized by X-ray diffraction, electron backscatter diffraction, and scanning electron microscopy. Moreover, tensile tests were performed using optical strain measurements in order to observe martensite band formation during cyclic loading. The surfaces of the crystalline wires reflect the columnar growth of NiTi during deposition. The wires exhibit pseudoelastic material behavior during tensile testing. Fracture typically occurs along the columns because the column growth direction is perpendicular to the straining direction. Electropolishing removes these local stress raisers and hence increases fracture strains. Our results demonstrate that the pseudoelastic properties of the PVD-processed materials agree well with those of conventional NiTi, and that they provide new opportunities to study the fundamentals of martensitic transformation in small-scale model systems.

  15. Challenges During Microstructural Analysis and Mechanical Testing of Small-Scale Pseudoelastic NiTi Structures

    NASA Astrophysics Data System (ADS)

    Hahn, S.; Wagner, M. F.-X.

    2016-03-01

    Most investigations on NiTi-based shape memory alloys involve large-scale bulk material; knowledge about the martensitic transformation in small-scale NiTi structures is still limited. In this paper, we study the microstructures of thin NiTi layers and their mechanical properties, and we discuss typical challenges that arise when experiments are performed on small samples. A physical vapor deposition (PVD) process was used to deposit thin NiTi wires with a cross section of 15 × 15 μm2 and dogbone-shaped samples 5 × 500 μm2. Microstructural properties were characterized by X-ray diffraction, electron backscatter diffraction, and scanning electron microscopy. Moreover, tensile tests were performed using optical strain measurements in order to observe martensite band formation during cyclic loading. The surfaces of the crystalline wires reflect the columnar growth of NiTi during deposition. The wires exhibit pseudoelastic material behavior during tensile testing. Fracture typically occurs along the columns because the column growth direction is perpendicular to the straining direction. Electropolishing removes these local stress raisers and hence increases fracture strains. Our results demonstrate that the pseudoelastic properties of the PVD-processed materials agree well with those of conventional NiTi, and that they provide new opportunities to study the fundamentals of martensitic transformation in small-scale model systems.

  16. 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.

  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. 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.

  19. 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

  20. 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]. PMID:26380838

  1. Wafer-level integration of NiTi shape memory alloy on silicon using Au-Si eutectic bonding

    NASA Astrophysics Data System (ADS)

    Gradin, Henrik; Bushra, Sobia; Braun, Stefan; Stemme, Göran; van der Wijngaart, Wouter

    2013-01-01

    This paper reports on the wafer level integration of NiTi shape memory alloy (SMA) sheets with silicon substrates through Au-Si eutectic bonding. Different bond parameters, such as Au layer thicknesses and substrate surface treatments were evaluated. The amount of gold in the bond interface is the most important parameter to achieve a high bond yield; the amount can be determined by the barrier layers between the Au and Si or by the amount of Au deposition. Deposition of a gold layer of more than 1 μm thickness before bonding gives the most promising results. Through patterning of the SMA sheet and by limiting bonding to small areas, stresses created by the thermal mismatch between Si and NiTi are reduced. With a gold layer of 1 μm thickness and bond areas between 200 × 200 and 800 × 800 μm2 a high bond strength and a yield above 90% is demonstrated.

  2. 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.

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

    DOE PAGESBeta

    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 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

  4. 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.

  5. 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. PMID:24364947

  6. Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.

  7. 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

  8. Thermomechanical properties of Ni-Ti shape memory wires containing nanoscale precipitates induced by stress-assisted ageing.

    PubMed

    Cong, D Y; Saha, G; Barnett, M R

    2014-12-01

    This paper systematically examines the thermomechanical properties and phase transformation behaviour of slightly Ni-rich Ni-Ti biomedical shape memory wires containing homogeneously distributed nanoscale precipitates induced by stress-assisted ageing. In contrast to previous studies, particular attention is paid to the role of precipitates in impeding twin boundary movement (TBM) and its underlying mechanisms. The size and volume fraction of precipitates are altered by changing the ageing time. The martensitic transformation temperatures increase with prolonged ageing time, whereas the R-phase transformation temperature remains relatively unchanged. The stress-strain behaviour in different phase regions during both cooling and heating is comprehensively examined, and the underlying mechanisms for the temperature- and thermal-history-dependent behaviour are elucidated with the help of the established stress-temperature phase diagram. The effect of precipitates on TBM is explored by mechanical testing at 133K. It is revealed that the critical stress for TBM (σcr) increases with increasing ageing time. There is a considerable increase of 104MPa in σcr in the sample aged at 773K for 120min under 70MPa compared with the solution-treated sample, owing to the presence of precipitates. The Orowan strengthening model of twinning dislocations is insufficient to account for this increase in σcr. The back stress generation is the predominant mechanism for the interactions between precipitates and twin boundaries during TBM that give rise to the increase in σcr. Such results provide new insights into the thermomechanical properties of precipitate containing Ni-Ti biomedical shape memory wires, which are instructive for developing high-performance biomedical shape memory alloys. PMID:25159371

  9. 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

  10. Laser welding of NiTi shape memory alloy: Comparison of the similar and dissimilar joints to AISI 304 stainless steel

    NASA Astrophysics Data System (ADS)

    Mirshekari, G. R.; Saatchi, A.; Kermanpur, A.; Sadrnezhaad, S. K.

    2013-12-01

    The unique properties of NiTi alloy, such as its shape memory effect, super-elasticity and biocompatibility, make it ideal material for various applications such as aerospace, micro-electronics and medical device. In order to meet the requirement of increasing applications, great attention has been given to joining of this material to itself and to other materials during past few years. Laser welding has been known as a suitable joining technique for NiTi shape memory alloy. Hence, in this work, a comparative study on laser welding of NiTi wire to itself and to AISI 304 austenitic stainless steel wire has been made. Microstructures, mechanical properties and fracture morphologies of the laser joints were investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD), Vickers microhardness (HV0.2) and tensile testing techniques. The results showed that the NiTi-NiTi laser joint reached about 63% of the ultimate tensile strength of the as-received NiTi wire (i.e. 835 MPa) with rupture strain of about 16%. This joint also enabled the possibility to benefit from the pseudo-elastic properties of the NiTi component. However, tensile strength and ductility decreased significantly after dissimilar laser welding of NiTi to stainless steel due to the formation of brittle intermetallic compounds in the weld zone during laser welding. Therefore, a suitable modification process is required for improvement of the joint properties of the dissimilar welded wires.

  11. Experimental characterization and micromechanical modeling of superelastic response of a porous NiTi shape-memory alloy

    NASA Astrophysics Data System (ADS)

    Nemat-Nasser, Sia; Su, Yu; Guo, Wei-Guo; Isaacs, Jon

    2005-10-01

    Porous shape-memory alloys are usually brittle due to the presence of various nickel-titanium intermetallic compounds that are produced in the course of most commonly used synthesizing techniques. We consider here a porous NiTi shape-memory alloy (SMA), synthesized by spark-plasma sintering, that is ductile and displays full shape-memory effects over the entire appropriate range of strains. The porosity however is only 12% but the basic synthesizing technique has potential for producing shape-memory alloys with greater porosity that still are expected to display superelasticity and shape-memory effects. The current material has been characterized experimentally using quasi-static and dynamic tests at various initial temperatures, mostly within the superelastic strain range, but also into the plastic deformation regime of the stress-induced martensite phase. To obtain a relatively constant strain rate in the high strain-rate tests, a novel pulse-shaping technique is introduced. The results of the quasi-static experiments are compared with the predictions by a model that can be used to calculate the stress-strain response of porous NiTi shape-memory alloys during the austenite-to-martensite and reverse phase transformations in uniaxial quasi-static loading and unloading at constant temperatures. In the austenite-to-martensite transformation, the porous shape-memory alloy is modeled as a three-phase composite with the parent phase (austenite) as the matrix and the product phase (martensite) and the voids as the embedded inclusions, reversing the roles of austenite and martensite during the reverse transformation from fully martensite to fully austenite phase. The criterion of the stress-induced martensitic transformation and its reversal is based on equilibrium thermodynamics, balancing the thermodynamic driving force for the phase transformation, associated with the reduction of Gibbs' free energy, with the resistive force corresponding to the required energy to

  12. Mechanical behavior of an Ni-Ti shape memory alloy under axial-torsional proportional and nonproportional loading

    SciTech Connect

    Lim, T.J.; McDowell, D.L.

    1999-01-01

    Several biaxial proportional and nonproportional loading experiments are reported for thin-wall tubes of a pseudoelastic Ni-Ti shape memory alloy (SMA). In addition to the mechanical behavior, temperature was measured during the experiments. It is shown that the phase transformation exhibits asymmetrical behavior in the case of tension-compression cycling. The transformation strain rate is determined for selected histories by numerical differentiation of data. Under nonproportional loading, the rate of phase transformation does not follow a generalized J{sub 2}-J{sub 3} criteria based on results of micromechanical simulations for proportional loading. The role of simultaneous forward and reverse transformations on the nonproportional transformation response is examined using a simple micromechanical model, and the direction of the inelastic strain rate is adequately predicted. Load- and strain-controlled experiments at different strain rates, with and without hold times, are reported and coupled thermomechanical effects are studied.

  13. Phase Transformation Evolution in NiTi Shape Memory Alloy under Cyclic Nanoindentation Loadings at Dissimilar Rates

    PubMed Central

    Amini, Abbas; Cheng, Chun; Kan, Qianhua; Naebe, Minoo; Song, Haisheng

    2013-01-01

    Hysteresis energy decreased significantly as nanocrystalline NiTi shape memory alloy was under triangular cyclic nanoindentation loadings at high rate. Jagged curves evidenced discrete stress relaxations. With a large recovery state of maximum deformation in each cycle, this behavior concluded in several nucleation sites of phase transformation in stressed bulk. Additionally, the higher initial propagation velocity of interface and thermal activation volume, and higher levels of phase transition stress in subsequent cycles explained the monotonic decreasing trend of dissipated energy. In contrast, the dissipated energy showed an opposite increasing trend during triangular cyclic loadings at a low rate and 60 sec holding time after each unloading stage. Due to the isothermal loading rate and the holding time, a major part of the released latent heat was transferred during the cyclic loading resulting in an unchanged phase transition stress. This fact with the reorientation phenomenon explained the monotonic increasing trend of hysteresis energy. PMID:24336228

  14. Microstructure, Cyclic Deformation and Corrosion Behavior of Laser Welded NiTi Shape Memory Wires

    NASA Astrophysics Data System (ADS)

    Mirshekari, G. R.; Kermanpur, A.; Saatchi, A.; Sadrnezhaad, S. K.; Soleymani, A. P.

    2015-09-01

    The present paper reports the effects of Nd:YAG laser welding on the microstructure, phase transformation, cyclic deformation behavior, and corrosion resistance of Ti-55 wt.% Ni wire. The results showed that the laser welding altered the microstructure of the weld metal which mainly composed of columnar dendrites grown epitaxially from the fusion line. DSC results indicated that the onset of the transformation temperatures of the weld metal differed from that of the base metal. Cyclic stress-strain behavior of laser-welded NiTi wire was comparable to the as-received material; while a little reduction in the pseudo-elastic property was noted. The weld metal exhibited higher corrosion potential, lower corrosion current density, higher breakdown potential and wider passive region than the base metal. The weld metal was therefore more resistant to corrosion than the base metal.

  15. Shape memory Ni-Ti alloy swan-like bone connector for treatment of humeral shaft nonunion

    PubMed Central

    Su, Jia-can; Liu, Xin-wei; Yu, Bao-qing; Li, Zhuo-dong

    2009-01-01

    From August 1990 to December 2007, 156 patients with humeral shaft nonunion were treated with our patented Ni-Ti shape memory alloy swan-like memory pressure connector (SMC). The SMC device cooled with ice before implantation was warmed to 40–50°C after implantation to produce balanced axial and compression forces to stabilise the fracture three-dimensionally. This combined with autologous bone grafting achieved bone tissue regeneration in the fracture and promoted smooth recovery of joint function, with a nonunion healing rate of 98.7% after a single SMC implantation. Failure of nonunion healing occurred in only two cases but was successfully managed by a further operation. Complications were not found in any of these patients apart from four with pre-existing radial nerve injuries. These results demonstrate the effectiveness of the SMC device for the management of humeral shaft nonunion. The device provides continuous compression of the fracture with minimal trauma to the local blood supply. PMID:19198838

  16. 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.

  17. METHOD OF ELECTROPOLISHING URANIUM

    DOEpatents

    Walker, D.E.; Noland, R.A.

    1959-07-14

    A method of electropolishing the surface of uranium articles is presented. The process of this invention is carried out by immersing the uranium anticle into an electrolyte which contains from 35 to 65% by volume sulfuric acid, 1 to 20% by volume glycerine and 25 to 50% by volume of water. The article is made the anode in the cell and polished by electrolyzing at a voltage of from 10 to 15 volts. Discontinuing the electrolysis by intermittently withdrawing the anode from the electrolyte and removing any polarized film formed therein results in an especially bright surface.

  18. SmartFlex® NiTi Wires for Shape Memory Actuators

    NASA Astrophysics Data System (ADS)

    Fumagalli, L.; Butera, F.; Coda, A.

    2009-08-01

    Shape memory alloys (SMAs) are active metallic materials classified nowadays as “smart” or “intelligent” materials. One of their main areas of interest is that of actuators. The use of SMAs in actuators offers the opportunity to develop robust, simple, and lightweight elements that can represent an alternative to electro-magnetic actuators commonly used in several fields of industrial applications, such as automotive, appliances, etc. SAES Getters S.p.A. thanks to its vertically integrated process and to the scientific and quality approach, developed a NiTi-based wires family which can represent a solution for shape memory actuators. In this paper, the mechanical, thermal, and electrical response of these shape memory wires, with diameters ranging from 20 to 500 μm, will be examined and discussed, with particular focus on the design of the actuator. The thermo-mechanical properties have been investigated and measured by several methods. The most common and useful tests for these commercially available wires will be also described.

  19. 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.

  20. Superelasticity of NiTi Ring-Shaped Springs Induced by Aging for Cranioplasty Applications

    NASA Astrophysics Data System (ADS)

    Morawiec, Henryk Z.; Lekston, Zdzisław H.; Kobus, Kazimierz F.; Węgrzyn, Marek C.; Drugacz, Jan T.

    2009-08-01

    This paper concerns the application of titanium-nickel rings in modeling the cranium. After being fixed to the osseous margins, the ring’s expansion at the same time broadens and shortens the cranium vault. The rings formed from a straight superelastic wire, flattened to an ellipse, do not show the presence of a typical force plateau but rather a pseudoelastic loop during loading-unloading in the relationship between the force and the deflection. Based on the idea that superelasticity in more complex shape-springs may be induced by the precipitation hardening process, the further studies were carried out on alloys with higher nickel contents (51.06 at.% Ni). The rings that had been formed were welded and aged at an optimal temperature and time. The improved superelastic behavior during compression and unloading the rings was obtained by introducing small deformation by drawing the quenched wires before forming the rings and aging. Very positive clinical reshaping by long-term distraction with the superelastic ring-shaped springs was achieved in young children under one year and a less spectacular effect was observed in the group of older children.

  1. 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.

  2. Twinning-Induced Elasticity in NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Birk, Thorsten; Biswas, Somjeet; Frenzel, Jan; Eggeler, Gunther

    2016-03-01

    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.

  3. 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.

  4. Experimental characterization of Ni-Ti shape memory alloy wires under complex loading conditions

    NASA Astrophysics Data System (ADS)

    Prahlad, Harsha; Chopra, Inderjit

    1999-06-01

    Shape memory alloys (SMAs) have shown promise as high-force, high displacement actuators. Critical issues such as path- dependence, predictability and sensitivity to testing conditions, however, need to be addressed in order to design controllable actuators using SMAs. This paper presents research aimed at addressing some of design issues involving application of SMAs, particularly at actuators. Quasistatic experiments at constant stress, strain and temperature are consolidated on a critical stress-temperature diagram to delineate the regions of stability of the various phases of the material. The critical points from these quasistatic tests are found to be in excellent agreement with each other, and correlate relatively well with the constitutive models for SMA thermomechanical behavior. It is also observed that the state of the material is not unique at points along the transformation, and is dependent on the history of the material before the start of the test, individual test involved, the method of loading, and loading rates. Significant variation of the state of the material with different rates and conditions of loading are shown to further illustrate this point. This behavior is likely to be decisive in determining the dynamic behavior of the material, and underscores the need for approaches incorporating these issues for design of repeatable actuators.

  5. Texture and grain neighborhood effects on Ni-Ti shape memory alloy performance

    NASA Astrophysics Data System (ADS)

    Paranjape, Harshad; Anderson, Peter M.

    2014-10-01

    This work demonstrates how the statistical pseudoelastic performance of individual grains is affected by the local grain neighborhood in polycrystalline shape memory alloys (SMAs). This is achieved using a microstructural finite element (FE) model calibrated to homogenized Ti-50.9 at% Ni SMA. The results show a three-fold variation in the grain level axial transformation strain pT in randomly textured polycrystals, and a ˜20-30% reduction in average pT if plastically predeformed. A key outcome is a performance function to predict pT of a grain, based on the orientations of the grain and its neighbors. Two key strategies to improve polycrystalline SMA performance are identified. The first is to minimize the number of grain boundaries between high-and low-performing grains: plate and bamboo geometries achieve this. The second is to employ high-symmetry orientation relationships between these grains. The results draw on recent experimental studies of grain level performance and provide a theoretical framework to interpret future diffraction tomography studies.

  6. 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.

  7. Mechanical Behaviour of Umbrella-Shaped, Ni-Ti Memory Alloy Femoral Head Support Device during Implant Operation: A Finite Element Analysis Study

    PubMed Central

    Yi, Wei; Tian, Qing; Dai, Zhipeng; Liu, Xiaohu

    2014-01-01

    A new instrument used for treating femoral head osteonecrosis was recently proposed: the umbrella-shaped, Ni-Ti memory femoral head support device. The device has an efficacy rate of 82.35%. Traditional radiographic study provides limited information about the mechanical behaviour of the support device during an implant operation. Thus, this study proposes a finite element analysis method, which includes a 3-step formal head model construction scheme and a unique material assignment strategy for evaluating mechanical behaviour during an implant operation. Four different scenarios with different constraints, initial positions and bone qualities are analyzed using the simulation method. The max radium of the implanted device was consistent with observation data, which confirms the accuracy of the proposed method. To ensure that the device does not unexpectedly open and puncture the femoral head, the constraint on the impact device should be strong. The initial position of sleeve should be in the middle to reduce the damage to the decompression channel. The operation may fail because of poor bone quality caused by severe osteoporosis. The proposed finite element analysis method has proven to be an accurate tool for studying the mechanical behaviour of umbrella-shaped, Ni-Ti memory alloy femoral head support device during an implant operation. The 3-step construct scheme can be implemented with any kind of bone structure meshed with multiple element types. PMID:24960038

  8. 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. PMID:18431757

  9. 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.

  10. 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. PMID:23744099

  11. 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. PMID:16010037

  12. 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. PMID:23556847

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

    NASA Astrophysics Data System (ADS)

    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.

  14. 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.

  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. Atomistic modeling of ternary additions to NiTi and quaternary additions to Ni-Ti-Pd, Ni-Ti-Pt and Ni-Ti-Hf shape memory alloys

    NASA Astrophysics Data System (ADS)

    Mosca, H. O.; Bozzolo, G.; del Grosso, M. F.

    2012-08-01

    The behavior of ternary and quaternary additions to NiTi shape memory alloys is investigated using a quantum approximate method for the energetics. Ternary additions X to NiTi and quaternary additions to Ni-Ti-Pd, Ni-Ti-Pt, and Ni-Ti-Hf alloys, for X=Au, Pt, Ir, Os, Re, W, Ta,Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Zn, Cu, Co, Fe, Mn, V, Sc, Si, Al and Mg are considered. Bulk properties such as lattice parameter, energy of formation, and bulk modulus of the B2 alloys are studied for variations due to the presence of one or two simultaneous additives.

  17. A Review of the Various Surface Treatments of NiTi Instruments

    PubMed Central

    Mohammadi, Zahed; Soltani, Mohammad Karim; Shalavi, Sousan; Asgary, Saeed

    2014-01-01

    Since the introduction of engine-driven nickel-titanium (NiTi) instruments, attempts have been made to minimize or eliminate their inherent defects, increase their surface hardness/flexibility and also improve their resistance to cyclic fatigue and cutting efficiency. The various strategies of enhancing instrument surface include ion implantation, thermal nitridation, cryogenic treatment and electropolishing. The purpose of this paper was to review the metallurgy and crystal characteristics of NiTi alloy and to present a general over review of the published articles on surface treatment of NiTi endodontic instruments. PMID:25386201

  18. 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.

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

    PubMed

    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. PMID:27036816

  20. 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.

  1. Modeling of the Stress-Strain-Resistance Behaviour of Ni-Ti and Ni-Ti-Cu Shape Memory Alloys for use in Sensorless Actuator Position Control

    NASA Astrophysics Data System (ADS)

    Lynch, Brian

    Shape memory alloys have become increasingly popular for use in many engineering fields, including aerospace, robotics, and biomechanics. A major research focus is the application of Nitinol shape memory alloy wire as an actuator. While position and force control of shape memory alloy actuator wires has been successfully demonstrated in the past, most control algorithms have been developed using position feedback. Recently, it has been shown that there exists a significant correlation between the electrical resistance and strain of the material. This correlation has been used to model the strain as a function of the electrical resistance for use in predicting the actuator position for control purposes. However, the influence of applied stress as well as the presence of a third microstructure phase (R-phase) make modeling of the resistance-strain correlation difficult since hysteretic effects become more substantial. This thesis presents new models of the resistance-stress-strain behaviour of shape memory alloy for use in actuator position control. Characterization of the material behaviour was performed through experimental analysis, and used to develop the models based on empirical curve fitting. The models were then validated through simulation as well as application in a simple PID position control algorithm. Furthermore, two different alloys were investigated: a Ni-Ti alloy called Flexinol which exhibits significant hysteresis due to the presence of R-phase, as well as a Ni-Ti-Cu alloy which shows negligible hysteresis.

  2. Electropolishing at ANL/FNAL.

    SciTech Connect

    Kelly, M. P.; Gerbick, S. M.; Wu, G.; Bice, D.; Physics; FNAL

    2009-01-01

    A system for electropolishing of 1.3 GHz elliptical single- and nine-cell cavities is in operation at the joint ANL/FNAL cavity processing facility located at Argonne. The system is one peice of a larger 200 m2 complete single cavity processing and assembly facility which also includes clean rooms and high-pressure rinsing. Recently, the electropolishing system has been used to process a series of single and nine-cell cavities. For single cell cavities a good set of EP parameters has been demonstrated based on more than a half dozen complete processing and cold test cycles at ANL/FNAL. The lastest six single cell cavities each exceed EACC=35 MV/m and, at this gradient, have Q in the range 6 10{sup 9} - 1 10{sup 10}. The first nine cell cavities electropolished at ANL have not yet reached similar fields ({approx}23 MV/m-26 MV/m) and ongoing activities are focussed on demonstrating >30 MV/m in these cavities. Suitable nine cell EP parameters using the ANL/FNAL EP system including acid/water temperatures, flow rates, current, voltage, air flow etc. are all substantially different than for single-cell cavities and are discussed here.

  3. 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.

  4. Calcium Phosphate Growth at Electropolished Titanium Surfaces

    PubMed Central

    Ajami, Elnaz; Aguey-Zinsou, Kondo-Francois

    2012-01-01

    This work investigated the ability of electropolished Ti surface to induce Hydroxyapatite (HA) nucleation and growth in vitro via a biomimetic method in Simulated Body Fluid (SBF). The HA induction ability of Ti surface upon electropolishing was compared to that of Ti substrates modified with common chemical methods including alkali, acidic and hydrogen peroxide treatments. Our results revealed the excellent ability of electropolished Ti surfaces in inducing the formation of bone-like HA at the Ti/SBF interface. The chemical composition, crystallinity and thickness of the HA coating obtained on the electropolished Ti surface was found to be comparable to that achieved on the surface of alkali treated Ti substrate, one of the most effective and popular chemical treatments. The surface characteristics of electropolished Ti contributing to HA growth were discussed thoroughly. PMID:24955535

  5. 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.

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

    DOE PAGESBeta

    Benafan, O.; Padula, S. A.; Noebe, R. D.; Sisneros, T. A.; Vaidyanathan, R.

    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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    Benafan, O.; Padula, S. A.; Noebe, R. D.; Sisneros, T. A.; Vaidyanathan, R.

    2012-11-01

    Deformation of a B19' martensitic, polycrystalline Ni49.9Ti50.1 (at. %) shape memory alloy 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 situ neutron 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 dislocation 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.

  9. 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.

  10. Effects of Al2O3 Nanopowders on the Wear Behavior of NiTi Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Şahin, Y.; Öksüz, K. Emre

    2014-01-01

    TiNi shape memory alloy and its composite using δ-Al2O3 nanosize particles were prepared by the powder metallurgy method, and some mechanical properties like hardness, wear, and corrosion behavior were investigated. The experimental results exhibited that the lower wear rate was obtained for the nano-Al2O3-reinforced Ti alloy composite due to increased hardness, but the wear rate increased considerably with increasing the load over 25 N for Ti alloy. However, the best corrosion resistance was obtained for the base alloy, which is very important for implant applications.

  11. The Corrosion Resistance of Composite Arch Wire Laser-Welded By NiTi Shape Memory Alloy and Stainless Steel Wires with Cu Interlayer in Artificial Saliva with Protein

    PubMed Central

    Zhang, Chao; Sun, Xinhua; Hou, Xu; Li, Hongmei; Sun, Daqian

    2013-01-01

    In this paper, the corrosion resistance of laser-welded composite arch wire (CoAW) with Cu interlayer between NiTi shape memory alloy and stainless steel wire in artificial saliva with different concentrations of protein was studied. It was found that protein addition had a significant influence on the corrosion behavior of CoAW. Low concentration of protein caused the corrosion resistance of CoAW decrease in electrochemical corrosion and immersion corrosion tests. High concentration of protein could reduce this effect. PMID:23801895

  12. 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.

  13. Study of the Behavior of a Bell-Shaped Colonic Self-Expandable NiTi Stent under Peristaltic Movements

    PubMed Central

    Puértolas, José A.; López, Enrique

    2013-01-01

    Managing bowel obstruction produced by colon cancer requires an emergency intervention to patients usually in poor conditions, and it requires creating an intestinal stoma in most cases. Regardless of that the tumor may be resectable, a two-stage surgery is mandatory. To avoid these disadvantages, endoscopic placement of self-expanding stents has been introduced more than 10 years ago, as an alternative to relieve colonic obstruction. It can be used as a bridge to elective single-stage surgery avoiding a stoma or as a definitive palliative solution in patients with irresectable tumor or poor estimated survival. Stents must be capable of exerting an adequate radial pressure on the stenosed wall, keeping in mind that stent must not move or be crushed, guaranteeing an adequate lumen when affected by peristaltic waves. A finite element simulation of bell-shaped nitinol stent functionality has been done. Catheter introduction, releasing at position, and the effect of peristaltic wave were simulated. To check the reliability of the simulation, a clinical experimentation with porcine specimens was carried out. The stent presented a good deployment and flexibility. Stent behavior was excellent, expanding from the very narrow lumen corresponding to the maximum peristaltic pressure to the complete recovery of operative lumen when the pressure disappears. PMID:23841067

  14. 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.

  15. The effects of plasma electrolytically oxidized NiTi on in vitro endothelialization.

    PubMed

    Huan, Z; Yu, H; Li, H; Ruiter, M S; Chang, J; Apachitei, I; Duszczyk, J; de Vries, C J M; Fratila-Apachitei, L E

    2016-05-01

    The role of biomaterials surface in controlling the interfacial biological events leading to implant integration is of key importance. In this study, the effects of NiTi surfaces treated by plasma electrolytic oxidation (PEO) on human umbilical vein endothelial cells (HUVECs) have been investigated. The changes in NiTi surface morphology and chemistry were assessed by SEM, XPS and cross-section TEM/EDX analyzes whereas the effects of the resultant surfaces on in vitro endothelialization and cell junction proteins have been evaluated by life/dead staining, SEM, cells counting, qPCR and immunofluorescence. The findings indicated that the PEO-treated NiTi, with a microporous morphology and oxide dominated surface chemistry, supports viability and proliferation of HUVECs. Numerous thin filopodia probing the microporous surface assisted cells attachment. In addition, claudin-5 and occludin have been upregulated and expression of vascular endothelial-cadherin was not suppressed on PEO-treated NiTi relative to the reference electropolished surfaces. The results of this study suggest that novel NiTi surfaces may be developed using the PEO process, which can be of benefit to atherosclerosis treatment. PMID:26878287

  16. Utility of magneto-electropolished ternary nitinol alloys for blood contacting applications.

    PubMed

    Pulletikurthi, Chandan; Munroe, Norman; Stewart, Danique; Haider, Waseem; Amruthaluri, Sushma; Rokicki, Ryszard; Dugrot, Manuel; Ramaswamy, Sharan

    2015-10-01

    The thrombogenicity of a biomaterial is mainly dependent on its surface characteristics, which dictates its interactions with blood. Surface properties such as composition, roughness wettability, surface free energy, and morphology will affect an implant material's hemocompatibility. Additionally, in the realm of metallic biomaterials, the specific composition of the alloy and its surface treatment are important factors that will affect the surface properties. The utility of magneto-electropolished (MEP) ternary Nitinol alloys, NiTiTa, and NiTiCr as blood contacting materials was investigated. The hemcompatibility of these alloys were compared to mechanically polished (MP) metallic biomaterial counterparts. In vitro thrombogenicity tests revealed significantly less platelet adherence on ternary MEP Nitinol, especially MEP NiTi10Ta as compared to the MP metals (p < 0.05). The enhanced anti-platelet-adhesive property of MEP NiTi10Ta was in part, attributed to the Ta2 O5 component of the alloy. Furthermore, the formation of a dense and mixed hydrophobic oxide layer during MEP is believed to have inhibited the adhesion of negatively charged platelets. In conclusion, MEP ternary Nitinol alloys can potentially be utilized for blood-contacting devices where, complications resulting from thrombogenicity can be minimized. PMID:25384352

  17. Surface Treatments of Nb by Buffered Electropolishing

    SciTech Connect

    Wu, Andy T.; Rimmer, Robert A.; Ciovati, Gianluigi; Manus, Robert L.; Reece, Charles E.; Williams, J. S.; Eozénou, F.; Jin, S.; Wang, E.

    2009-11-01

    Buffered electropolishing (BEP) is a Nb surface treatment technique developed at Jefferson Lab1. Experimental results obtained from flat Nb samples show2-4 that BEP can produce a surface finish much smoother than that produced by the conventional electropolishing (EP), while Nb removal rate can be as high as 4.67 μm/min. This new technique has been applied to the treatments of Nb SRF single cell cavity employing a vertical polishing system5 constructed at JLab as well as a horizontal polishing system at CEA Saclay. Preliminary results show that the accelerating gradient can reach 32 MV/m for a large grain cavity and 26.7 MV/m for a regular grain cavity. In this presentation, the latest progresses from the international collaboration between Peking University, CEA Saclay, and JLab on BEP will be summarized.

  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. Microstructural and mechanical challenges in biomedical NiTi

    NASA Astrophysics Data System (ADS)

    Franz-Xaver Wagner, Martin

    2010-07-01

    The mechanical behaviour of NiTi shape memory alloys superficially resembles that of certain biomaterials, such as bones or tissues: By virtue of a reversible martensitic phase transformation, NiTi alloys can recover relatively large strains; uniaxial stress-strain curves exhibit constant stress-plateaus (at several hundreds of MPa, depending on alloy composition and testing temperature) associated with the phase transition. These novel functional properties, in combination with high mechanical strength in ultra-fine grained NiTi and good biocompatibility, are utilized in various implants and medical devices. Yet - and quite similar to hierarchically structured biomaterials - the deformation behaviour of NiTi is intricately linked to distinct deformation processes on several length scales, and there remain significant gaps in our understanding of the microstructure-property relations. In the present paper, recent experimental and theoretical results from first-principles calculations, micromechanical modelling and nanoindentation are discussed with a focus on the role of inelastic deformation processes, twin boundaries and the interaction of plastic deformation and stress-induced phase transformations. These novel findings challenge our understanding of the fundamental mechanical properties of NiTi. They highlight the importance of inelastic deformation mechanisms for the overall mechanical properties and strength of NiTi.

  20. Porous NiTi for bone implants: A review

    PubMed Central

    Bansiddhi, A.; Sargeant, T.D.; Stupp, S.I.; Dunand, D.C.

    2011-01-01

    NiTi foams are unique among biocompatible porous metals because of their high recovery strain (due to the shape-memory or superelastic effects) and their low stiffness facilitating integration with bone structures. To optimize NiTi foams for bone implant applications, two key areas are under active study: synthesis of foams with optimal architectures, microstructure and mechanical properties; and tailoring of biological interactions through modifications of pore surfaces. This article reviews recent research on NiTi foams for bone replacement, focusing on three specific topics: (i) surface modifications designed to create bio-inert porous NiTi surfaces with low Ni release and corrosion, as well as bioactive surfaces to enhance and accelerate biological activity; (ii) In vitro and in vivo biocompatibility studies to confirm the long-term safety of porous NiTi implants; and (iii) biological evaluations for specific applications, such as in intervertebral fusion devices and bone tissue scaffolds. Possible future directions for bio-performance and processing studies are discussed that could lead to optimized porous NiTi implants. PMID:18348912

  1. Crack initiation and propagation in 50.9 at. pct Ni-Ti pseudoelastic shape-memory wires in bending-rotation fatigue

    NASA Astrophysics Data System (ADS)

    Sawaguchi, Tak Ahiro; Kausträter, Gregor; Yawny, Alejandro; Wagner, Martin; Eggeler, Gunther

    2003-12-01

    The structural fatigue of pseudoelastic Ni-Ti wires (50.9 at. pct Ni) was investigated using bending-rotation fatigue (BRF) tests, where a bent and otherwise unconstrained wire was forced to rotate at different rotational speeds. The number of cycles to failure ( N f ) was measured for different bending radii and wire thicknesses (1.0, 1.2, and 1.4 mm). The wires consisted of an alloy with a 50-nm grain size, no precipitates, and some TiC inclusions. In BRF tests, the surface of the wire is subjected to tension-compression cycles, and fatigue lives can be related to the maximum tension and compression strain amplitudes ( ɛ a ) in the wire surface. The resulting ɛ a - N f curves can be subdivided into three regimes. At ɛ a > 1 pct rupture occurs early (low N f ) and the fatigue-rupture characteristics were strongly dependent on ɛ a and the rotational speed (regime 1). For 0.75 pct < ɛ a < 1 pct, fatigue lives strongly increase and are characterized by a significant statistical scatter (regime 2). For ɛ a < 0.75 pct, no fatigue rupture occurs up to cycle numbers of 106 (regime 3). Using scanning electron microscopy (SEM), it was shown that surface cracks formed in regions with local stress raisers (such as inclusions and/or scratches). The growth of surface cracks during fatigue loading produced striations on the rupture surface; during final rupture, ductile voids form. The microstructural details of fatigue-damage accumulation during BRF testing are described and discussed.

  2. Effects of sterilization processes on NiTi alloy: surface characterization.

    PubMed

    Thierry, B; Tabrizian, M; Savadogo, O; Yahia, L

    2000-01-01

    Sterilization is required for using any device in contact with the human body. Numerous authors have studied device properties after sterilization and reported on bulk and surface modifications of many materials after processing. These surface modifications may in turn influence device biocompatibility. Still, data are missing on the effect of sterilization procedures on new biomaterials such as nickel-titanium (NiTi). Herein we report on the effect of dry heat, steam autoclaving, ethylene oxide, peracetic acid, and plasma-based sterilization techniques on the surface properties of NiTi. After processing electropolished NiTi disks with these techniques, surface analyses were performed by Auger electron spectroscopy (AES), atomic force microscopy (AFM), and contact angle measurements. AES analyses revealed a higher Ni concentration (6-7 vs. 1%) and a slightly thicker oxide layer on the surface for heat and ethylene oxide processed materials. Studies of surface topography by AFM showed up to a threefold increase of the surface roughness when disks were dry heat sterilized. An increase of the surface energy of up to 100% was calculated for plasma treated surfaces. Our results point out that some surface modifications are induced by sterilization procedures. Further work is required to assess the effect of these modifications on biocompatibility, and to determine the most appropriate methods to sterilize NiTi. PMID:10559750

  3. Electropolishing on small samples at Fermilab

    SciTech Connect

    Boffo, C.; Bauer, P.; Teid, T.; Geng, R.; /Cornell U., Phys. Dept.

    2005-07-01

    The electropolishing process (EP) is considered an essential step in the processing of high gradient SRF cavities. Studies on EP of small samples has been started at Fermilab as part of the SRF materials R&D program. A simple bench top setup was developed to understand the basic variables affecting the EP. In addition a setup for vertical EP of half cells, based on the Cornell design, was used and another one for dumbbells was designed and tested. Results and findings are reported.

  4. Microstructure, mechanical properties and superelasticity of biomedical porous NiTi alloy prepared by microwave sintering.

    PubMed

    Xu, J L; Bao, L Z; Liu, A H; Jin, X J; Tong, Y X; Luo, J M; Zhong, Z C; Zheng, Y F

    2015-01-01

    Porous NiTi alloys were prepared by microwave sintering using ammonium hydrogen carbonate (NH4HCO3) as the space holder agent to adjust the porosity in the range of 22-62%. The effects of porosities on the microstructure, hardness, compressive strength, bending strength, elastic modulus, phase transformation temperature and superelasticity of the porous NiTi alloys were investigated. The results showed that the porosities and average pore sizes of the porous NiTi alloys increased with increasing the contents of NH4HCO3. The porous NiTi alloys consisted of nearly single NiTi phase, with a very small amount of two secondary phases (Ni3Ti, NiTi2) when the porosities are lower than 50%. The amount of Ni3Ti and NiTi2 phases increased with further increasing of the porosity proportion. The porosities had few effects on the phase transformation temperatures of the porous NiTi alloys. By increasing the porosities, all of the hardness, compressive strength, elastic modulus, bending strength and superelasticity of the porous NiTi alloys decreased. However, the compressive strength and bending strength were higher or close to those of natural bone and the elastic modulus was close to the natural bone. The superelastic recovery strain of the trained porous NiTi alloys could reach between 3.1 and 4.7% at the pre-strain of 5%, even if the porosity was up to 62%. Moreover, partial shape memory effect was observed for all porosity levels under the experiment conditions. Therefore, the microwave sintered porous NiTi alloys could be a promising candidate for bone implant. PMID:25492002

  5. Reactive Ni/Ti nanolaminates

    SciTech Connect

    Adams, D. P.; Bai, M. M.; Rodriguez, M. A.; McDonald, J. P.; Jones, E. Jr.; Brewer, L.; Moore, J. J.

    2009-11-01

    Nickel/titanium nanolaminates fabricated by sputter deposition exhibited rapid, high-temperature synthesis. When heated locally, self-sustained reactions were produced in freestanding Ni/Ti multilayer foils characterized by average propagation speeds between approx0.1 and 1.4 m/s. The speed of a propagating reaction front was affected by total foil thickness and bilayer thickness (layer periodicity). In contrast to previous work with compacted Ni-Ti powders, no preheating of Ni/Ti foils was required to maintain self-propagating reactions. High-temperature synthesis was also stimulated by rapid global heating demonstrating low ignition temperatures (T{sub ig})approx300-400 deg. C for nanolaminates. Ignition temperature was influenced by bilayer thickness with more coarse laminate designs exhibiting increased T{sub ig}. Foils reacted in a vacuum apparatus developed either as single-phase B2 cubic NiTi (austenite) or as a mixed-phase structure that was composed of monoclinic B19{sup '} NiTi (martensite), hexagonal NiTi{sub 2}, and B2 NiTi. Single-phase, cubic B2 NiTi generally formed when the initial bilayer thickness was made small.

  6. Reproducibility Study of NiTi Parts Made by Metal Injection Molding

    NASA Astrophysics Data System (ADS)

    Bram, M.; Bitzer, M.; Buchkremer, H. P.; Stöver, D.

    2012-12-01

    Powder metallurgy (P/M) is an attractive manufacturing process for net-shaped NiTi parts considering the limited machinability of NiTi alloys. Nevertheless, the industrial implementation of P/M processing for NiTi alloys is not trivial. To become competitive to manufacturing of NiTi alloys based on established ingot metallurgy, combination of fully pronounced shape memory behavior with sufficient mechanical properties is required. Successful use of P/M technology is strongly influenced by high affinity of NiTi alloys for uptake of oxygen and carbon, which leads to the formation of oxygen-containing Ti2Ni and TiC phases coupled with increase of Ni content in the matrix. In the case of Ni-rich NiTi alloys, this increase leads to a shift of phase transformation temperatures to lower values. Furthermore, precipitation of Ni4Ti3 during cooling from sintering temperature is difficult to avoid. Even if these precipitates might be used to decrease the Ni:Ti ratio of the matrix balancing oxygen and carbon uptake, significant loss of ductility arises, especially in the case of finely dispersed Ni4Ti3 precipitates. In the present work, each step of P/M manufacturing is discussed regarding its influence on the specific properties of NiTi alloys. The work is based on the application of prealloyed, gas atomized NiTi powders. Metal injection molding was used for net-shaped manufacturing of tensile samples, which enabled detailed study of sintering behavior combined with investigation of shape memory and mechanical properties depending on particle size, oxygen and carbon content as well as precipitation of Ni4Ti3 phase.

  7. Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

    NASA Astrophysics Data System (ADS)

    Eozénou, F.; Boudigou, Y.; Carbonnier, P.; Charrier, J.-P.; Gasser, Y.; Maurice, L.; Peauger, F.; Roudier, D.; Servouin, C.; Muller, K.

    2014-08-01

    An advanced setup for vertical electropolishing of superconducting radio-frequency niobium elliptical cavities has been installed at CEA Saclay. Cavities are vertically electropolished with circulating standard HF-HF-H2SO4 electrolytes. Parameters such as voltage, cathode shape, acid flow, and temperature have been investigated. A low voltage (between 6 and 10 V depending on the cavity geometry), a high acid flow (25 L /min), and a low acid temperature (20° C) are considered as promising parameters. Such a recipe has been tested on single-cell and nine-cell International Linear Collider (ILC) as well as 704 MHz five-cell Super Proton Linac (SPL) cavities. Single-cell cavities showed similar performances at 1.6 K being either vertically or horizontally electropolished. The applied baking process provides similar benefit. An asymmetric removal is observed with faster removal in the upper half-cells. Multicell cavities (nine-cell ILC and five-cell SPL cavities) exhibit a standard Q0 value at low and medium accelerating fields though limited by power losses due to field emitted electrons.

  8. Mechanical Properties of Highly Porous NiTi Alloys

    NASA Astrophysics Data System (ADS)

    Bram, Martin; Köhl, Manuel; Buchkremer, Hans Peter; Stöver, Detlev

    2011-07-01

    Highly porous NiTi alloys with pseudoelastic properties are attractive candidates for biomedical implants, energy absorbers, or damping elements. Recently, a new method was developed for net-shape manufacturing of such alloys combining metal injection molding with the application of suitable space-holder materials. A comprehensive study of mechanical properties was conducted on samples with a porosity of 51% and a pore size in the range of 300-500 μm. At low deformations <6%, fully pronounced pseudoelasticity was found. Even at higher strains, a shape recovery of maximum 6% took place, on which the onset of irreversible plastic deformation was superposed. Results of static compression tests were also used to calculate the energy-absorbing capacity. Fatigue of porous NiTi was investigated by cyclic loading up to 230,000 stress reversals. The failure mechanisms responsible for a reduction of shape recovery after an increased number of load cycles are discussed.

  9. Study on Electro-Polishing Process by Niobium-Plate Sample With Artificial Pits

    SciTech Connect

    T. Saeki, H. Hayano, S. Kato, M. Nishiwaki, M. Sawabe, W.A. Clemens, R.L. Geng, R. Manus, P.V. Tyagi

    2011-07-01

    The Electro-polishing (EP) process is the best candidate of final surface-treatment for the production of ILC cavities. Nevertheless, the development of defects on the inner-surface of the Superconducting RF cavity during EP process has not been studied by experimental method. We made artificial pits on the surface of a Nb-plate sample and observed the development of the pit-shapes after each step of 30um-EP process where 120um was removed by EP in total. This article describes the results of this EP-test of Nb-sample with artificial pits.

  10. 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.

  11. 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.

  12. 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.

  13. A mechanistic study of copper electropolishing in phosphoric acid solutions

    NASA Astrophysics Data System (ADS)

    Mansson, Andrew

    The microelectronics industry is using copper as the interconnect material for microchips. A study of copper electropolishing is important for the process development of a new, low downforce approach, which is being developed to replace chemical mechanical polishing (CMP) of the copper overburden. A promising technology is a combination of electropolishing with conventional CMP. Electropolishing of copper in phosphoric acid has been studied for, more than 70 years. Previous work has shown that the polishing rate, as measured by current density is directly related to the viscosity of the electrolyte. Also, the limiting species is water. In this study, a multidimensional design of experiments was performed to develop an in-depth model of copper electropolishing. Phosphoric acid was mixed with alcohols of different molecular weight and related viscosity to investigate how the solvents' properties affected polishing. The alcohols used were methanol, ethanol, isopropanol, butanol, ethylene glycol, and glycerol. The limiting current densities and electrochemical behavior of each solution was measured by potentiodynamic and potentiostatic experiments. Also, the kinematic viscosity and density were measured to determine the dynamic viscosity to investigate the relationship of current density and viscosity. Water, methanol, ethanol, and isopropanol solutions were also examined at 20°C to 60°C. Next, the relative percentage of dissociated phosphoric acid was measured by Raman spectroscopy for each polishing solution. Raman spectroscopy was also used to measure the relative dissociation of phosphoric acid inside the polishing film. Additionally, wafers were electropolished and electrochemical mechanically polished to investigate the effects of the different solvents, fluid flow, current, and potential. The results of these experiments have shown that the molecular mass and the ability of the solvent to dissociate phosphoric acid are the primary electrolyte properties that

  14. Tensile deformation of NiTi wires.

    PubMed

    Gall, Ken; Tyber, Jeff; Brice, Valerie; Frick, Carl P; Maier, Hans J; Morgan, Neil

    2005-12-15

    We examine the structure and properties of cold drawn Ti-50.1 at % Ni and Ti-50.9 at % Ni shape memory alloy wires. Wires with both compositions possess a strong <111> fiber texture in the wire drawing direction, a grain size on the order of micrometers, and a high dislocation density. The more Ni rich wires contain fine second phase precipitates, while the wires with lower Ni content are relatively free of precipitates. The wire stress-strain response depends strongly on composition through operant deformation mechanisms, and cannot be explained based solely on measured differences in the transformation temperatures. We provide fundamental connections between the material structure, deformation mechanisms, and resulting stress-strain responses. The results help clarify some inconsistencies and common misconceptions in the literature. Ramifications on materials selection and design for emerging biomedical applications of NiTi shape memory alloys are discussed. PMID:16138359

  15. 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.

  16. Outgassing characteristics and microstructure of an electropolished stainless steel surface

    SciTech Connect

    Yoshimura, N.; Sato, T.; Adachi, S.; Kanazawa, T. )

    1990-03-01

    Outgassing characteristics of an electropolished stainless steel (304) pipe wall were investigated by an isolation method. The free outgassing rate after an {ital in} {ital situ} bakeout (150 {degree}C, 20 h) was estimated as low as 1.6{times}10{sup {minus}12} Pa l s{sup {minus}1}cm{sup {minus}2}. After the {ital in} {ital situ} bakeout, H{sub 2} molecules were steadily evolved from the pipe wall, whereas most of CO, C, CH{sub 4}, and CO{sub 2} molecules were emitted from the operating mass spectrometer and Bayard--Alpert gauge with incandescent filaments. Auger depth profile analysis revealed that the oxide layer of an electropolished surface was cleaner, thinner, and finer in microstructure than that of a buff-polished surface. This is the reason why an electropolished surface showed a very low outgassing rate.

  17. Creating poly(ethylene glycol) film on the surface of NiTi alloy by gamma irradiation

    NASA Astrophysics Data System (ADS)

    Yu, Hongyan; Yan, Jin; Ma, Huiling; Zeng, Xinmiao; Liu, Yang; Zhao, Xinqing

    2015-07-01

    NiTi alloy has been extensively utilized as biomaterials owing to its unique shape memory effect, superelasticity and biocompatibility. However, concern with the toxic and allergic responses of nickel potentially releasing from implants stimulated lots of researches of modification on NiTi alloy surface. Creating chemical bond attachment of bioorganic film on NiTi alloy surface could effectively inhibit Ni releasing and obtain bioactive functions for further application. In this work, to get a bioorganic surface, NiTi alloy was modified with poly(ethylene glycol) (PEG) film by gamma ray induced grafting or crosslinking. X-ray diffraction (XRD) spectrum, water contact angle geometer and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the NiTi surface. The results indicated that PEG was covalent bonded on NiTi alloy surface. Fluorescence microscope (FM) images for morphology of 1 day osteoblast culture on the PEG coated NiTi surface showed that PEG could improve cell proliferation on NiTi surface. Our work offers a way to introduce a bioorganic metal surface by gamma irradiation.

  18. Martensite transformation of epitaxial Ni-Ti films

    SciTech Connect

    Buschbeck, J.; Kozhanov, A.; Kawasaki, J. K.; James, R. D.; Palmstroem, C. J.

    2011-05-09

    The structure and phase transformations of thin Ni-Ti shape memory alloy films grown by molecular beam epitaxy are investigated for compositions from 43 to 56 at. % Ti. Despite the substrate constraint, temperature dependent x-ray diffraction and resistivity measurements reveal reversible, martensitic phase transformations. The results suggest that these occur by an in-plane shear which does not disturb the lattice coherence at interfaces.

  19. Electropolishing process development for PWR steam generator channel heads

    SciTech Connect

    Asay, R.H.; Graves, P.; Guastaferro, C.T.; Spalaris, C.N. )

    1991-04-01

    A broad range of process parameters was established to smoothen the surface of 309 L weld clad overlay, prototypic of surfaces common is channel heads of replacement PWR (pressurized water reactor) steam generators. Mechanical and electropolishing steps were studied to explore process boundaries, which result in acceptable degree of surface smoothness, without compromising metallurgical properties. Recommended processes and acceptance criteria established in this work, can be applied to electropolish steam generator channel heads. Smooth surfaces are less likely to retain radioactive species, and potentially develop lower radiation fields when these components are placed into service. 7 refs., 11 figs., 12 tabs.

  20. Mechanical Analysis of Hybrid Textile Composites with NiTi Wires

    NASA Astrophysics Data System (ADS)

    Villa, Elena; Arnaboldi, Sergio; Tuissi, Ausonio; Giacomelli, Marco; Turco, Elena

    2009-08-01

    Hybrid textile structures composed by polyamide (PA), Lycra (or Elastane EL), and NiTi thin wires were manufactured. The fabrics were realized by knitting Lycra (EL) as weft and warp filaments and a coupled PA/NiTi yarn through in-laying technique. Superelastic NiTi wire with diameter of 50 μm in both straight annealed and snake-like form and shape memory with a snake-like memorized form were used. The polyamide filament used coupled with the NiTi wire has a diameter around 140 μm, while the textile structure is composed by various Lycra filaments, characterized by different diameters. The textile structures were realized by a circular machine appropriately equipped and used in order to minimize problems related to the use of the thin NiTi alloy filament. To study the influence of NiTi filaments on mechanical properties, specimens taken from textile fabric were analyzed by using a DMA Q800 TA Instruments, equipped with a tension film clamp, in static and dynamic conditions. Force/strain measurements up to 150% in elongation and Tandelta versus frequency were carried out on fabrics with and without NiTi filaments. Finally, some tests strain recovery under load versus temperature are conducted.

  1. Status of the production electropolishing system at Jlab

    SciTech Connect

    John Mammosser; Jean Delayen; Julian Gordon; H. Phillips; Jeffrey Saunders; Tong Wang; Andy Wu; Anne-Marie Valente

    2003-05-01

    Jefferson Lab has installed, and is in the process of commissioning, a production electropolish system, sized for 805MHz SNS cavities. This paper describes the basic system design, plans for studying the effectiveness of polishing SNS high beta cavities and early results from cavity tests.

  2. Orientation contrast of secondary electron images from electropolished metals.

    PubMed

    Chen, D; Chang, C P; Loretto, M H

    2015-09-01

    Orientation contrast obtained by an in-lens secondary electron detector in a scanning electron microscope from electropolished/etched metals is reported. The imaging conditions for obtaining such orientation contrast are defined. The mechanism responsible for the formation of the orientation contrast is explained, and an application example of this new imaging method is given. PMID:25980953

  3. Improved technique for localizing electropolishing features novel nozzles

    NASA Technical Reports Server (NTRS)

    1964-01-01

    Impingement electropolishing is accomplished by use of an electrolyte film, which is evenly distributed by an insulated nozzle designed to match the contour of the workpiece to be treated. The workpiece is connected to the positive terminal of a generator and the nozzle to the negative terminal.

  4. The tribocorrosion behaviour of NiTi alloy

    NASA Astrophysics Data System (ADS)

    Kosec, Tadeja; Močnik, Petra; Legat, Andraž

    2014-01-01

    In biomedical applications, NiTi alloys are used mainly because of their favourable shape memory and superelastic properties. However, in many applications the tribocorrosion properties of these alloys can be of critical concern. For this reason the electrochemical and tribocorrosion properties of superelastic NiTi sheet and orthodontic archwire were studied, taking into account their microstructures and the effect of different surface finishes. In the case of the electrochemical tests, samples were tested in artificial saliva, whereas in the tribocorrosion tests the experiments were performed in ambient air, distilled water, and artificial saliva, the latter as a corrosive medium. In these tests, the total wear rate of the alloy samples was determined, together with the corresponding chemical and tribological contributions. It was confirmed that the microstructure of the investigated alloys had a significant effect on the measured electrochemical and tribocorrosion properties.

  5. Numerical Study on the Influence of Material Characteristics on Ni-Ti Endodontic Instrument Performance

    NASA Astrophysics Data System (ADS)

    Petrini, Lorenza; Necchi, Silvia; Taschieri, Silvio; Migliavacca, Francesco

    2009-08-01

    Ni-Ti rotary endodontic instruments ( files) are used in dentistry during the endodontic treatment to shape the root canal of the tooth while removing the pulp when infected. Up to now, the studies for evaluating their performances and drawbacks were mainly limited to experimental tests on product flexural and torsional resistance. This work exploits computational analyses for investigating the effects of materials with different mechanical properties on the behavior of rotary endodontic instruments. The aim is to understand the appropriate material choice to reduce the criticality of the treatment in particular clinical conditions. In particular, the interaction between an accurately modeled rotating file and differently shaped root canals during the clinical procedure was studied performing finite element analyses. Strains induced by the treatment on a file made of a “standard” Ni-Ti alloy (characterized by average properties of the pseudoelastic behavior), a “long” Ni-Ti alloy (characterized by wide transformation region), a “super” Ni-Ti alloy (characterized by an extended Hookian behavior without transformation region), and stainless steel were compared. The results accurately show the advantages of the use of Ni-Ti alloy with respect to stainless steel and the better performance of the “long” alloy in all the tested case.

  6. Analysis of the influence of electrolyte on surface finish in electropolished stainless steel

    NASA Astrophysics Data System (ADS)

    Hernando, M.; Núñez, P. J.; García, E.; Trujillo, R.

    2012-04-01

    Electropolishing is a surface finishing process of metals and alloys that enhances brilliant surface finishes with low surface roughness values. The most widely used electrolytes for the electropolishing of stainless steel are varying concentrations of phosphoric and sulphuric acid, and occasionally additives such as chromic acid. The objective of this study was to assess the performance of three commonly used industrial electrolytes in terms of the surface finish of electropolished stainless steel AISI 316L. Each electrolyte had varying sulphuric-phosphoric acid combinations with or without chromic acid. The following electropolishing conditions were assessed: current density, bath temperature, electropolishing time, and initial surface texture. The results revealed that adding chromic acid to the electrolyte did not significantly enhance surface finish, and electropolishing ranges were quite similar for all three electrolytes.

  7. Method and apparatus for spatially uniform electropolishing and electrolytic etching

    DOEpatents

    Mayer, Steven T.; Contolini, Robert J.; Bernhardt, Anthony F.

    1992-01-01

    In an electropolishing or electrolytic etching apparatus the anode is separated from the cathode to prevent bubble transport to the anode and to produce a uniform current distribution at the anode by means of a solid nonconducting anode-cathode barrier. The anode extends into the top of the barrier and the cathode is outside the barrier. A virtual cathode hole formed in the bottom of the barrier below the level of the cathode permits current flow while preventing bubble transport. The anode is rotatable and oriented horizontally facing down. An extended anode is formed by mounting the workpiece in a holder which extends the electropolishing or etching area beyond the edge of the workpiece to reduce edge effects at the workpiece. A reference electrode controls cell voltage. Endpoint detection and current shut-off stop polishing. Spatially uniform polishing or etching can be rapidly performed.

  8. Method and apparatus for spatially uniform electropolishing and electrolytic etching

    DOEpatents

    Mayer, S.T.; Contolini, R.J.; Bernhardt, A.F.

    1992-03-17

    In an electropolishing or electrolytic etching apparatus the anode is separated from the cathode to prevent bubble transport to the anode and to produce a uniform current distribution at the anode by means of a solid nonconducting anode-cathode barrier. The anode extends into the top of the barrier and the cathode is outside the barrier. A virtual cathode hole formed in the bottom of the barrier below the level of the cathode permits current flow while preventing bubble transport. The anode is rotatable and oriented horizontally facing down. An extended anode is formed by mounting the workpiece in a holder which extends the electropolishing or etching area beyond the edge of the workpiece to reduce edge effects at the workpiece. A reference electrode controls cell voltage. Endpoint detection and current shut-off stop polishing. Spatially uniform polishing or etching can be rapidly performed. 6 figs.

  9. Electropolishing the bore of metal capillary tubes: A technique for adjusting the critical flow.

    PubMed

    Stoffels, J J; Ells, D R

    1979-12-01

    A technique has been developed for electropolishing the bore of metal capillary tubes. Although developed specifically for stainless-steel tubes, the technique should be directly applicable to other metals. Tubes with inside diameter as small as 0.20 mm and 110 mm long have been successfully electropolished. The electropolishing technique can be used to increase the critical flow of a capillary tube in a controllable way. PMID:18699437

  10. Designing, Building and Testing of an Electropolishing Cell

    NASA Astrophysics Data System (ADS)

    Al-Ajlouni, M.; Al-Hamdan, A.

    During the work of this research, designing, building and testing of an electropolishing cell has been carried out. Various tests have been performed for three different materials namely, steel, aluminum and brass at different environment conditions in order to a better evaluation of electropolishing. These conditions include the effect of concentration of electrolytes, electrolytes temperature, power supplied and machining time. The results of these tests have been analyzed and performance curves have been drawn. The optimum temperatures and the optimum time have been obtained at which the maximum metal removal and the best surface quality is achieved. These temperature and time for Aluminum, Brass and Steel are T = 60, 50 and 75°C, t = 20, 40 and 50 min, respectively. Surface roughnesses of the specimens have been measured before and after electropolishing. The results showed a significant improvement that effect positively on strength, fatigue resistance and corrosion resistance. Many important conclusions have been extracted from these performance curves and some recommendations have been noted to help in future works.

  11. Tungsten inert gas (TIG) welding of Ni-rich NiTi plates: functional behavior

    NASA Astrophysics Data System (ADS)

    Oliveira, J. P.; Barbosa, D.; Braz Fernandes, F. M.; Miranda, R. M.

    2016-03-01

    It is often reported that, to successfully join NiTi shape memory alloys, fusion-based processes with reduced thermal affected regions (as in laser welding) are required. This paper describes an experimental study performed on the tungsten inert gas (TIG) welding of 1.5 mm thick plates of Ni-rich NiTi. The functional behavior of the joints was assessed. The superelasticity was analyzed by cycling tests at maximum imposed strains of 4, 8 and 12% and for a total of 600 cycles, without rupture. The superelastic plateau was observed, in the stress-strain curves, 30 MPa below that of the base material. Shape-memory effect was evidenced by bending tests with full recovery of the initial shape of the welded joints. In parallel, uniaxial tensile tests of the joints showed a tensile strength of 700 MPa and an elongation to rupture of 20%. The elongation is the highest reported for fusion-welding of NiTi, including laser welding. These results can be of great interest for the wide-spread inclusion of NiTi in complex shaped components requiring welding, since TIG is not an expensive process and is simple to operate and implement in industrial environments.

  12. Localized corrosion behaviour in simulated human body fluids of commercial Ni-Ti orthodontic wires.

    PubMed

    Rondelli, G; Vicentini, B

    1999-04-01

    The corrosion performances in simulated human body fluids of commercial equiatomic Ni-Ti orthodontic wires having various shape and size and produced by different manufacturers were evaluated; for comparison purposes wires made of stainless steel and of cobalt-based alloy were also examined. Potentiodynamic tests in artificial saliva at 40 degrees C indicated a sufficient pitting resistance for the Ni-Ti wires, similar to that of cobalt-based alloy wire; the stainless steel wire, instead, exhibited low pitting potential. Potentiodynamic tests at 40 degrees C in isotonic saline solution (0.9% NaCl) showed, for Ni-Ti and stainless steel wires, pitting potential values in the range approximately 200-400 mV and approximately 350 mV versus SCE, respectively: consequently, according to literature data (Hoar TP, Mears DC. Proc Roy Soc A 1996;294:486-510), these materials should be considered potentially susceptible to pitting; only the cobalt-based alloy should be immune from pitting. The localized corrosion potentials determined in the same environment by the ASTM F746 test (approximately 0-200 mV and 130 mV versus SCE for Ni-Ti and stainless steel, respectively) pointed out that for these materials an even higher risk of localized corrosion. Slight differences in localized corrosion behaviour among the various Ni-Ti wires were detected. PMID:10353661

  13. Micromachining NiTi tubes for use in medical devices by using a femtosecond laser

    NASA Astrophysics Data System (ADS)

    Hung, Chia-Hung; Chang, Fuh-Yu; Chang, Tien-Li; Chang, Yu-Ting; Huang, Kai-Wen; Liang, Po-Chin

    2015-03-01

    Recent growth in medical device technology has been substantially driven by developments in laser micromachining, which is a powerful fabrication technique in which nickel-titanium (Nitinol, NiTi) alloy materials that exhibit superelastic and shape memory properties are formed (e.g., self-expanding stents). In this study a NiTi tube curve surface process is proposed, involving a femtosecond laser process and a galvano-mirror scanner. The diameter of the NiTi tube was 5.116 mm, its thickness was 0.234 mm, and its length was 100 mm. The results indicated that during the machine process the ablation mechanism of the NiTi tubes was changed by altering the machining path. The path alteration enhanced the laser ablation rate from 12.3 to 26.7 μm/J. Thus the path alteration contributed to a wide kerf line, enabling the assisted air to efficiently remove the debris deposited at the bottom of the kerf during the laser ablation process. The results indicated that the NiTi tube curve process enhanced the laser ablation rate by two times and reduced the amount of energy accumulated within the materials by 50% or more. By altering the machining path using the scanning system, this process can decrease the production of heat affected zones (the accumulation of thermal energy) in medical device applications.

  14. Biomimetic Deposition of Apatite on Surface Chemically Modified Porous NiTi Shapememory Alloy

    NASA Astrophysics Data System (ADS)

    Wu, S. L.; Liu, X. M.; Chung, C. Y.; Chu, Paul K.; Chan, Y. L.; Yeung, K. W. K.; Chu, C. L.

    Porous NiTi shape memory alloy (SMA) with 48% porosity and an average pore size of 50-800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP). To enhance the surface bioactivity, the porous NiTi SMA was subjected to H2O2 and subsequent NaOH treatment. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses revealed that a porous sodium titanate (Na2TiO3) film had formed on the surface of the porous NiTi SMA. An apatite layer was deposited on this film after immersion in simulated body fluid at 37°C, while no apatite could be found on the surface of the untreated porous NiTi SMA. The formation of the apatite layer infers that the bioactivity of the porous NiTi SMA may be enhanced by surface chemical treatment, which is favorable for its application as bone implants.

  15. Free-standing NiTi alloy nanowires fabricated by nanoskiving.

    PubMed

    Hou, Huilong; Hamilton, Reginald F

    2015-08-28

    We report on free-standing NiTi alloy nanowires (120 nm × 75 nm) fabricated using a technique referred to as "nanoskiving", which complements conventional thin film sputter deposition with ultramicrotomy for thin sectioning. To date, the technique has been limited to pure metals without exploring metallic alloys. Leveraging the technique for the fabrication of shape memory alloy (SMA) nanostructures meets two critical requirements: compositional control (via film deposition) and controlled dimensions (via film deposition and programmable sectioning). Microstructure and composition analysis confirm continuity of the produced nanowires and Ni and Ti elemental uniformity. Free-standing NiTi nanowires are robust and remain intact throughout physical manipulation. The fabrication of NiTi alloy nanowires by nanoskiving will advance fundamental characterization of small scale SMA behavior. PMID:26203564

  16. Influence of the microstructure on electrochemical corrosion and nickel release in NiTi orthodontic archwires.

    PubMed

    Briceño, J; Romeu, A; Espinar, E; Llamas, J M; Gil, F J

    2013-12-01

    The aim of this work was to determine the influence of the present phases and the chemical composition on the corrosion behavior and the nickel ion release of the NiTi orthodontic archwires. Eight Ni-Ti archwires from six commercial brands, in the as-received condition, were studied. The chemical composition, roughness, microstructure and the proportion of the phases as well as the corrosion behavior were analyzed for each archwire. The nickel ion release was characterized in artificial saliva immersion settings ranging up to 4 weeks. The results show that the presence of the martensitic phase improves corrosion resistance and significantly decreases Ni release into exterior medium in comparison with the austenitic specimens. In spite of the partial loss of superelasticity produced in the martensitic phase, it 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. PMID:24094215

  17. Radiation Hardening of Ni-Ti Alloy Under Implantation of Inert Gases Heavy Ions

    NASA Astrophysics Data System (ADS)

    Poltavtseva, V.; Larionov, A.; Satpaev, D.; Gyngazova, M.

    2016-02-01

    The consistent patterns of changes in nano- and micro-hardness of Ni-Ti alloy with the shape memory effect after implantation of 40Ar8+ and 84Kr15+ ions depending on phase composition and implantation parameters have been experimentally studied. It has been shown that softening by 4 and 14% near the surface of the two-phase Ni-Ti alloy after implantation of 40Ar8+ and 84Kr15+ ions is connected with the differences in the nanostructure. Hardening of the near-surface layer of this alloy maximum by 118% at h = ∼3 pm and single-phase alloy in the entire region of the 40Ar8+ and 84Kr15+ ions range and in the out-range (h > Rp) area have been detected. The role of the current intensity of the ions beam in the change of nanohardness for the two-phase Ni-Ti alloy has been established.

  18. Dissimilar Laser Joining of NiTi SMA and MP35N Wires

    NASA Astrophysics Data System (ADS)

    Panton, Boyd; Pequegnat, Andrew; Zhou, Y. Norman

    2014-07-01

    The laser welding of NiTi alloy wire to MP35N wire was investigated to improve the understanding of dissimilar materials joining of NiTi shape memory alloys (SMAs), facilitating their future application in novel devices. Both positioning of the laser beam with respect to the joint's centerline and laser peak power were found to be critical variables affecting the physical and thermomechanical properties of the welded joint. Positioning of the laser beam was used to control the weld pool composition, while the laser beam intensity affected the pool size and mixing. These variables were shown to greatly affect hardness and susceptibility to cracking in the fusion zone, which heavily impacted the weld strength. With a lower peak power and the laser positioned over the MP35N wire, butt-welded wire joints were achieved with the ultimate load of 66 pct of the NiTi wire breaking load.

  19. Stable atomic structure of NiTi austenite

    NASA Astrophysics Data System (ADS)

    Zarkevich, Nikolai A.; Johnson, Duane D.

    2014-08-01

    Nitinol (NiTi), the most widely used shape-memory alloy, exhibits an austenite phase that has yet to be identified. The usually assumed austenitic structure is cubic B2, which has imaginary phonon modes, hence it is unstable. We suggest a stable austenitic structure that "on average" has B2 symmetry (observed by x-ray and neutron diffraction), but it exhibits finite atomic displacements from the ideal B2 sites. The proposed structure has a phonon spectrum that agrees with that from neutron scattering, has diffraction spectra in agreement with x-ray diffraction, and has an energy relative to the ground state that agrees with calorimetry data.

  20. Stable atomic structure of NiTi austenite

    SciTech Connect

    Zarkevich, Nikolai A; Johnson, Duane D

    2014-08-01

    Nitinol (NiTi), the most widely used shape-memory alloy, exhibits an austenite phase that has yet to be identified. The usually assumed austenitic structure is cubic B2, which has imaginary phonon modes, hence it is unstable. We suggest a stable austenitic structure that “on average” has B2 symmetry (observed by x-ray and neutron diffraction), but it exhibits finite atomic displacements from the ideal B2 sites. The proposed structure has a phonon spectrum that agrees with that from neutron scattering, has diffraction spectra in agreement with x-ray diffraction, and has an energy relative to the ground state that agrees with calorimetry data.

  1. Research and development for electropolishing of Nb for ILC accelerator cavities

    SciTech Connect

    Kelley, Michael J.

    2009-09-21

    The objectives of this project are to 1, Expand the scientific and technological understanding of the effect of post-treatment (electropolish, buffered chemical polish, low-temperature baking) on the surface of niobium; 2, Relate the knowledge to the performance of niobium superconducting radiofrequency accelerator cavities; and, 3, Thereby design and demonstrate an electropolish process that can be applied to complete cavities.

  2. Treatment of spent electropolishing solution for removal of cobalt-60

    SciTech Connect

    Taylor, P.A.; Youngblood, E.L.; Macon, R.J.

    1996-02-01

    The Irradiated Materials Examination and Testing (IMET) Facility at Oak Ridge National Laboratory electropolishes various types of irradiated metal specimens prior to examination of metallurgical and mechanical properties. The standard electropolishing solution used at IMET for most specimens consists of a 7:1 methanol/sulfuric acid mixture, with smaller amounts of a 3:1 methanol/nitric acid solution and a 10:6:1 methanol/2-butoxyethanol/perchloric acid solution also being used. Cobalt-60 is the primary source of gamma radiation in the spent solutions, with lesser amounts from manganese-54 and iron-59. A treatment method is needed to remove most of the Co-60 from these solutions to allow the waste solutions to be contact-handled for disposal. A wide range of adsorbents was tested for removing cobalt from the electropolishing solutions. No adsorbent was found that would treat full strength solution, but a complexing ion exchange resin (Chelex 100, BioRad Labs, or Amberlite IRC-718, Rohm and Haas Co.) will remove cobalt and other heavy metals from partially neutralized (pH=3) solution. A 5 wt% sodium hydroxide solution is used for pH adjustment, since more concentrated caustic caused sodium sulfate precipitates to form. Lab-scale column tests have shown that about 10 bed volumes of methanol/sulfuric acid solution, 30 bed volumes of methanol/nitric acid solution or 15 bed volumes of methanol/2-butoxyethanol/perchloric acid solution can be treated prior to initial Co-60 breakthrough.

  3. Effect of Surface Flow on Topography in Niobium Electropolishing

    SciTech Connect

    M.J. Kelley, C.E. Reece, L. Zhao

    2011-03-01

    Electropolishing (EP) is reliably delivering improved performance of multi-celled niobium SRF accelerator cavities, attributed to the smoother surface obtained. This superior leveling is a consequence of an etchant concentration gradient layer that arises in the HF-H2SO4 electrolyte adjacent to the niobium surface during polishing. Electrolyte circulation raises the prospect that fluid flow adjacent to the surface might affect the diffusion layer and impair EP performance. In this study, preliminary bench-top experiments with a moving electrode apparatus were conducted. We find that flow conditions approximating cavity EP show no effects attributable to depletion layer disruption.

  4. Alternate Electrolyte Composition for Electropolishing of Niobium Surfaces

    SciTech Connect

    Jean R. Delayen; John Mammosser; Larry Phillips; Andy T. Wu

    2001-09-01

    Electropolishing has shown promising results for the treatment of Nb cavities to be used in particle accelerators, particularly in the attainment of high surface electric fields. In support of the CEBAF Upgrade project and as part of a longer-term R and D program, we have investigated the properties of several electrolyte recipes. A particularly promising one consists of a mixture of lactic, sulfuric, and hydrofluoric acids. Initial tests reveal that smooth Nb surfaces can be achieved with no observable grain boundaries under optical microscope. We report on the results of the investigations of the parameters that control the polishing process using this particular acid mixture.

  5. Modeling, Simulation, Additive Manufacturing, and Experimental Evaluation of Solid and Porous NiTi

    NASA Astrophysics Data System (ADS)

    Taheri Andani, Mohsen

    In recent years, shape memory alloys (SMAs) have entered a wide range of engineering applications in fields such as aerospace and medical applications. Nickel-titanium (NiTi) is the most commonly used SMAs due to its excellent functional characteristics (shape memory effect and superelasticity behavior). These properties are based on a solid-solid phase transformation between martensite and austenite. Beside these two characteristics, low stiffness, biocompatibility and corrosion properties of NiTi make it an attractive candidate for biomedical applications (e.g., bone plates, bone screws, and vascular stents). It is well know that manufacturing and processing of NiTi is very challenging. The functional properties of NiTi are significantly affected by the impurity level and due to the high titanium content, NiTi are highly reactive. Therefore, high temperature processed parts through methods such as melting and casting which result in increased impurity levels have inadequate structural and functional properties. Furthermore, high ductility and elasticity of NiTi, adhesion, work hardening and spring back effects make machining quite challenging. These unfavorable effects for machining cause significant tool wear along with decreasing the quality of work piece. Recently, additive manufacturing (AM) has gained significant attention for manufacturing NiTi. Since AM can create a part directly from CAD data, it is predicted that AM can overcome most of the manufacturing difficulties. This technique provides the possibility of fabricating highly complex parts, which cannot be processed by any other methods. Curved holes, designed porosity, and lattice like structures are some examples of mentioned complex parts. This work investigates manufacturing superelastic NiTi by selective laser melting (SLM) technique (using PXM by Phenix/3D Systems). An extended experimental study is conducted on the effect of subsequent heat treatments with different aging conditions on phase

  6. Advance in Vertical Buffered Electropolishing on Niobium for Particle Accelerators*

    SciTech Connect

    A.T. Wu, S. Jin, J.D. Mammosser, C.E. Reece, R.A. Rimmer,L. Lin, X.Y. Lu, K. Zhao

    2011-09-01

    Niobium (Nb) is the most popular material that has been employed for making superconducting radio frequency (SRF) cavities to be used in various particle accelerators over the last couple of decades. One of the most important steps in fabricating Nb SRF cavities is the final chemical removal of 150 {mu}m of Nb from the inner surfaces of the SRF cavities. This is usually done by either buffered chemical polishing (BCP) or electropolishing (EP). Recently a new Nb surface treatment technique called buffered electropolishing (BEP) has been developed at Jefferson Lab. It has been demonstrated that BEP can produce the smoothest surface finish on Nb ever reported in the literature while realizing a Nb removal rate as high as 10 {mu}m/min that is more than 25 and 5 times quicker than those of EP and BCP(112) respectively. In this contribution, recent advance in optimizing and understanding BEP treatment technique is reviewed. Latest results from RF measurements on BEP treated Nb single cell cavities by our unique vertical polishing system will be reported.

  7. Cleaning Effectiveness of Three NiTi Rotary Instruments: A Focus on Biomaterial Properties

    PubMed Central

    Poggio, Claudio; Dagna, Alberto; Chiesa, Marco; Beltrami, Riccardo; Bianchi, Stefano

    2015-01-01

    Nickel-titanium (NiTi) instruments are commonly used for shaping the root canal system in endodontic practice. They are more flexible and have better cutting efficiency than conventional stainless steel files. The superelasticity of NiTi rotary files allows the clinicians to produce the desirable tapered root canal form with a reduced tendency to canal transportation and instrument fracture. HyFlex CM instruments are new NiTi rotary instruments with shape memory produced by an innovative methodology (patent pending) that uses a complex heating and cooling treatment that controls the material’s memory. The aim of the present study was to compare the cleaning efficacy of two conventional (Mtwo, Revo-S) Ni-Ti rotary instruments with HyFlex CM. 30 single-rooted freshly extracted teeth were divided into three groups. Root canals were shaped with three NiTi instruments (Mtwo, Revo-S and HyFlex CM) using 5.25% NaOCl and 17% EDTA solutions. Specimens were fractured longitudinally and prepared for SEM analysis at standard magnification of 1000×. The presence/absence of debris smear layer and the presence/absence of smear layer at coronal, middle, and apical third of each canal were evaluated using a 5-step scale for scores. Numeric data were analyzed using Kruskall-Wallis and Mann-Whitney U statistical tests and significance was predetermined at P < 0.05. This study revealed significant differences among the various groups. Despite some minor differences, all instruments removed smear layer and debris produced during instrumentation. HyFlex CM seem to be not so effective in promoting cleanliness of root canal walls and in removing smear layer from dentine if compared to Mtwo and Revo-S. PMID:25692796

  8. The Influence of Surface Nanocrystallization Induced by Shot Peening on Corrosion Behavior of NiTi Alloy

    NASA Astrophysics Data System (ADS)

    Olumi, S.; Sadrnezhaad, S. K.; Atai, M.

    2015-08-01

    Nickel-titanium (NiTi) shape memory alloys have been widely used as implant materials, due to their superior shape memory properties and similar mechanical behavior to bone tissue. The presence of nickel on the surface of nickel-titanium alloy and release of this ion in the body environment will result in some allergic reactions. In current study, we used shot pinning process to produce nanocrystalline nickel-titanium alloy with increased corrosion resistance. Field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) analysis, and atomic force microscopy were employed to investigate the surface features of samples. The quantitative chemical analysis of NiTi and modified NiTi samples was conducted by energy dispersive x-ray method. The electrochemical behavior of NiTi alloy was evaluated using the potentiodynamic polarization scan and electrochemical impedance spectroscopy tests in Ringer solution after and prior to the shot pining process. The result of XRD analysis of modified samples showed an average crystalline size of 23 nm. Moreover, FE-SEM confirmed the development of a nanostructured alloy induced by shot pinning process. Modification of NiTi alloy by shot-peening process resulted in corrosion resistance improvement and decrease in the corrosion rate, which consequently led to less release rate of the toxic nickel ions in the corrosive environment, compared to the non-modified samples.

  9. In Situ Phase Evolution of Ni/Ti Reactive Multilayers

    NASA Astrophysics Data System (ADS)

    Cavaleiro, A. J.; Ramos, A. S.; Martins, R. M. S.; Baetz, C.; Vieira, M. T.; Braz Fernandes, F. M.

    2014-07-01

    Joining shape-memory alloys (SMA) to other materials is strongly required in order to enlarge their fields of application. Fusion welding induces strong compositional and microstructural changes that significantly affect the shape-memory effect and the superelastic behavior of these alloys. The exothermic and in some cases self-propagating character of some nano-multilayer reactions is explored in this study as an alternative for joining SMA. To follow these very fast reactions, high brilliance sources, such as synchrotron radiation, are required. In situ high-resolution x-ray diffraction data, giving the phase evolution sequence with temperature of the Ni/Ti multilayer thin films under study, are presented. A correlation between the multilayer design and the tendency for the sequence of phase formation is established.

  10. Influence of electropolishing and anodic oxidation on morphology, chemical composition and corrosion resistance of niobium.

    PubMed

    Sowa, Maciej; Greń, Katarzyna; Kukharenko, Andrey I; Korotin, Danila M; Michalska, Joanna; Szyk-Warszyńska, Lilianna; Mosiałek, Michał; Zak, Jerzy; Pamuła, Elżbieta; Kurmaev, Ernst Z; Cholakh, Seif O; Simka, Wojciech

    2014-09-01

    The work presents results of the studies performed on electropolishing of pure niobium in a bath that contained: sulphuric acid, hydrofluoric acid, ethylene glycol and acetanilide. After the electropolishing, the specimens were subjected to anodic passivation in a 1moldm(-3) phosphoric acid solution at various voltages. The surface morphology, thickness, roughness and chemical composition of the resulting oxide layers were analysed. Thusly prepared niobium samples were additionally investigated in terms of their corrosion resistance in Ringer's solution. The electropolished niobium surface was determined to be smooth and lustrous. The anodisation led to the growth of barrier-like oxide layers, which were enriched in phosphorus species. PMID:25063150

  11. Microstructure and corrosion behavior of laser processed NiTi alloy.

    PubMed

    Marattukalam, Jithin J; Singh, Amit Kumar; Datta, Susmit; Das, Mitun; Balla, Vamsi Krishna; Bontha, Srikanth; Kalpathy, Sreeram K

    2015-12-01

    Laser Engineered Net Shaping (LENS™), a commercially available additive manufacturing technology, has been used to fabricate dense equiatomic NiTi alloy components. The primary aim of this work is to study the effect of laser power and scan speed on microstructure, phase constituents, hardness and corrosion behavior of laser processed NiTi alloy. The results showed retention of large amount of high-temperature austenite phase at room temperature due to high cooling rates associated with laser processing. The high amount of austenite in these samples increased the hardness. The grain size and corrosion resistance were found to increase with laser power. The surface energy of NiTi alloy, calculated using contact angles, decreased from 61 mN/m to 56 mN/m with increase in laser energy density from 20 J/mm(2) to 80 J/mm(2). The decrease in surface energy shifted the corrosion potentials to nobler direction and decreased the corrosion current. Under present experimental conditions the laser power found to have strong influence on microstructure, phase constituents and corrosion resistance of NiTi alloy. PMID:26354269

  12. Highly smooth Nb surfaces fabricated by buffered electropolishing

    SciTech Connect

    Andy T. Wu; John Mammossor; H. Phillips; Jean Delayen; Charles Reece; Amy Wilkerson; David Smith; Robert Ike

    2005-05-01

    It is demonstrated that highly smooth Nb surfaces can be obtained through Buffered ElectroPolishing (BEP) employing an electrolyte consisting of lactic, sulfuric, and hydrofluoric acids. Parameters that control the polishing process are optimized to achieve the smoothest surface finish with the help of surface observations using a scanning electron microscope and a Metallographic Optical Microscope (MOM). The polishing rate of BEP is determined to be 0.646 {micro}m/min that is much higher than 0.381 {micro}m/min achieved by the conventional ElectroPolishing (EP) process widely used in the Superconducting Radio Frequency (SRF) community. A high precision and large scan area 3-D profilometer is used to view morphology of the treated Nb surfaces. Statistical data, such as, rms, total indicator runout, and arithmetic mean deviation of the Nb surfaces are extracted from the profilometer images. It is found that Nb surfaces treated by BEP are an order of magnitude smoother than those treated by the optimized EP process. The chemical composition of the Nb surfaces after BEP is analyzed by static and dynamic Secondary Ion Mass Spectrometer (SIMS) systems. Cracking patterns of the Nb surfaces under different primary ion sources of Ga{sup +}, Au{sup +}, and Ar{sup +} are reported. The depth profile of the surface niobium oxides is studied through continuously monitoring niobium and its relevant oxides' peaks as a function of time. Dynamic SIMS results imply that the surface oxide structure of Nb may be more complicated than what usually believed and can be inhomogeneous. Preliminary results of BEP on Nb SRF single cell cavities and half-cells are reported. It is shown that smooth and bright surfaces can be obtained in 30 minutes when the electric field inside a SRF cavity is uniform during a BEP process. This study reveals that BEP is a highly promising technique for surface treatment on Nb SRF cavities to be used in particle accelerators.

  13. Removal of long-lived 222Rn daughters by electropolishing thin layers of stainless steel

    NASA Astrophysics Data System (ADS)

    Schnee, R. W.; Bowles, M. A.; Bunker, R.; McCabe, K.; White, J.; Cushman, P.; Pepin, M.; Guiseppe, V. E.

    2013-08-01

    Long-lived alpha and beta emitters in the 222Rn decay chain on detector surfaces may be the limiting background in many experiments attempting to detect dark matter or neutrinoless double beta decay. Removal of tens of microns of material via electropolishing has been shown to be effective at removing radon daughters implanted into material surfaces. Some applications, however, require the removal of uniform and significantly smaller thicknesses. Here, we demonstrate that electropolishing < 1 μm from stainless-steel plates reduces the contamination efficiently, by a factor > 100. Examination of electropolished wires with a scanning electron microscope confirms that the thickness removed is reproducible and reasonably uniform. Together, these tests demonstrate the effectiveness of removal of radon daughters for a proposed low-radiation, multi-wire proportional chamber (the BetaCage), without compromising the screener's energy resolution. More generally, electropolishing thin layers of stainless steel may effectively remove radon daughters without compromising precision-machined parts.

  14. Low-density open-cell foams in the NiTi system

    NASA Astrophysics Data System (ADS)

    Grummon, David S.; Shaw, John A.; Gremillet, Antoine

    2003-04-01

    It is shown that open-cell metallic foams having very low density, and that display martensite transformations required for shape memory and superelastic behavior, can be fabricated using a powder-metallurgy technique. Results are presented on experiments in which a polymeric precursor foam was coated with an equiatomic NiTi powder slurry and subsequently sintered to yield foams with relative densities as low as 0.039. Although contaminated with interstitial impurities, they displayed unambiguous calorimetric signature of the B2→B19' transformation. The results are of considerable significance to potential applications requiring ultralightweight structures with the unusual dissipative and strain-recovery properties of NiTi shape-memory materials.

  15. Shape memory alloy film for deployment and control of membrane apertures

    NASA Astrophysics Data System (ADS)

    Hill, Lisa R.; Carman, Greg; Lee, Dong-Gun; Patrick, Brian

    2004-02-01

    Nickel Titanium (NiTi) film shape memory alloy (SMA) is integrated with space-qualified polymer and mesh materials for potential use as deployment mechanisms and actuation of flexible space apertures. SMA thin film is successfully applied to Astromesh metal mesh, Kapton, Upilex, and CP-1 polymer films. Sputter deposition of NiTi onto the substrate is used to validate the material system process and demonstrate the NiTi deployment capability. Although successful, the relatively high processing temperatures required to crystallize NiTi onto the substrates requires care. A second approach is demonstrated that deposits NiTi onto a silicon substrate, followed by coating the NiTi with the desired polymer, e.g. CP-1. Micro-electro-mechanical (MEMS) processing steps are then used to remove the silicon substrate beneath the NiTi, thus freeing up the composite membrane (i.e. NiTi + CP-1). Using MEMS fabrication techniques, a hot-shaped small dome shape structure is shaped into the NiTi before deposition of the CP-1 polymer. Activation of the integrated SMA/CP-1 produces deformation of this composite structure without damage. The test articles demonstrate the feasibility to both grossly deploy and locally actuate space-qualified polymer materials.

  16. The Effect of Thermal Annealing on Structural-phase Changes in the Ni-Ti Alloy Implanted with Krypton Ions

    NASA Astrophysics Data System (ADS)

    Poltavtseva, V. P.; Kislitsin, S. B.; Ghyngazov, S. A.

    2016-06-01

    The influence of thermal annealing within the temperature range 100-300°C on the structural-phase state of a Ni-Ti alloy with shape memory effect (SME) implanted with 84Kr ions at the energies E = 280 keV and 1.75 MeV/nucl and the fluences within 5·1012-1·1020 ion/m2 is investigated. For the samples modified by 84Kr ions at E = 1.75 MeV/nucl up to the fluences 1·1020 and 5·1012 ion/m2, the formation of a martensitic NiTi phase with the B19 ' structure, responsible for the SME, is revealed at the annealing temperatures 100 and 300°C, respectively, in the near-surface region corresponding to the outrange area. This is accompanied by the formation of nanosized NiTi particles in the R-phase. As the implantation fluence increases, the probability of their formation decreases. It is shown that annealing of the implanted structures can increase the strength of the Ni-Ti alloy. The degree of hardening is determined by the value of annealing temperature, and an increase in strength is primarily due to ordering of the radiation-induced defect structures (phases). A correlation between the onset temperature of a forward martensitic transition and the structural-phase state of the thermally annealed Ni-Ti alloy is established.

  17. Energetics of Single Substitutional Impurities in NiTi

    NASA Technical Reports Server (NTRS)

    Good, Brian S.; Noebe, Ronald

    2003-01-01

    Shape-memory alloys are of considerable current interest, with applications ranging from stents to Mars rover components. In this work, we present results on the energetics of single substitutional impurities in B2 NiTi. Specifically, energies of Pd, Pt, Zr and Hf impurities at both Ni and Ti sites are computed. All energies are computed using the CASTEP ab initio code, and, for comparison, using the quantum approximate energy method of Bozzolo, Ferrante and Smith. Atomistic relaxation in the vicinity of the impurities is investigated via quantum approximate Monte Carlo simulation, and in cases where the relaxation is found to be important, the resulting relaxations are applied to the ab initio calculations. We compare our results with available experimental work.

  18. Improving the oxidation resistance of 316L stainless steel in simulated pressurized water reactor primary water by electropolishing treatment

    NASA Astrophysics Data System (ADS)

    Han, Guangdong; Lu, Zhanpeng; Ru, Xiangkun; Chen, Junjie; Xiao, Qian; Tian, Yongwu

    2015-12-01

    The oxidation behavior of 316L stainless steel specimens after emery paper grounding, mechanical polishing, and electropolishing were investigated in simulated pressurized water reactor primary water at 310 °C for 120 and 500 h. Electropolishing afforded improved oxidation resistance especially during the early immersion stages. Duplex oxide films comprising a coarse Fe-rich outer layer and a fine Cr-rich inner layer formed on all specimens after 500 h of immersion. Only a compact layer was observed on the electropolished specimen after 120 h of immersion. The enrichment of chromium in the electropolished layer contributed to the passivity and protectiveness of the specimen.

  19. Investigation of differential surface removal due to electropolishing at JLab

    SciTech Connect

    Marhauser, Frank; Folkie, James; Reece, Charles

    2015-09-01

    Surface chemistry carried out for Superconducting Radio Frequency (SRF) cavities such as Buffered Chemical Polishing (BCP) and Electropolishing (EP) aims to uniformly remove the internal surface of a cavity along the entire structure and within each cell from equator to iris in order to obtain an equally etched surface. A uniform removal, however, is not readily achievable due to the complex fluid flow and varying temperatures of the acid mixture, which can lead to differential etching. This needs to be considered when envisaging a certain surface damage removal throughout the interior. The process-specific differential etching influences the target frequency set at the manufacturing stage as well as the field flatness and length of the as-built cavity. We report on analyses of JLab's present EP system using experimental data for six nine-cell cavities that have been processed recently in the frame of the LCLS-II high-Q development plan. In conjunction with numerical simulations, the differential etching and the impact on field flatness is assessed.

  20. Behavior of NiTi Wires for Dampers and Actuators in Extreme Conditions

    NASA Astrophysics Data System (ADS)

    Isalgue, A.; Auguet, C.; Grau, R.; Torra, V.; Cinca, N.; Fernandez, J.

    2015-09-01

    Shape memory alloys are considered smart materials because of their singular thermo-mechanical properties, due to a thermoelastic martensitic transformation, enabling possible uses as actuators (because of mechanical recovery induced from temperature changes) and as dampers (because of hysteresis). NiTi wires for dampers in Civil Engineering had been characterized and tested in facilities. Guaranteed performance needs to know behavior during fatigue life and knowledge of effects in the event of extreme conditions, as eventual overstraining. In this work, we check the possibilities to absorb mechanical energy on the fatigue life depending on stress level and explore the consequences of overstraining the material during installation, the possibilities of partial healing by moderate heating, and some effects of over-stressing the wires. The mechanical energy absorbed by the unit weight of damper wire might be very high during its lifetime if maximum stresses remain relatively low allowing high fatigue life. We show also some results on NiTi wire working as an actuator. The lifetime mechanical work performed by an actuator wire can be very high if applied stresses are limited. The overstraining produces relevant "residual" deformation, which can be to some extent reversed by moderate heating at zero stress. The reason for the observed characteristics seems to be that when external high stresses are applied to an NiTi wire, it undergoes some plastic deformation, leaving a distribution of internal stresses that alter the shape and position of the macroscopic stress-strain transformation path.

  1. An original architectured NiTi silicone rubber structure for biomedical applications.

    PubMed

    Rey, T; Le Cam, J-B; Chagnon, G; Favier, D; Rebouah, M; Razan, F; Robin, E; Didier, P; Heller, L; Faure, S; Janouchova, K

    2014-12-01

    This paper deals with composite structures for biomedical applications. For this purpose, an architectured tubular structure composed of Nickel Titanium (NiTi) Shape Memory Alloy (SMA) and silicone rubber was fabricated. One of the main interests of such structures is to ensure a good adhesion between its two constitutive materials. A previous study of the authors (Rey et al., 2014) has shown that the adhesion between NiTi and silicone rubber can be improved by an adhesion promoter or plasma treatment. However, adhesion promoters are often not biocompatible. Hence, plasma treatment is favored to be used in the present study. Three different gases were tested; air, argon and oxygen. The effects of these treatments on the maximum force required to pull-out a NiTi wire from the silicone rubber matrix were investigated by means of pull-out tests carried out with a self-developed device. Among the three gases, a higher maximum force was obtained for argon gas in the plasma treatment. A tube shaped architectured NiTi/silicone rubber structure was then produced using this treatment. The composite was tested by means of a bulge test. Results open a new way of investigations for architectured NiTi-silicone structures for biomechanical applications. PMID:25491818

  2. Growth of large single-crystalline two-dimensional boron nitride hexagons on electropolished copper.

    PubMed

    Tay, Roland Yingjie; Griep, Mark H; Mallick, Govind; Tsang, Siu Hon; Singh, Ram Sevak; Tumlin, Travis; Teo, Edwin Hang Tong; Karna, Shashi P

    2014-02-12

    Hexagonal-boron nitride (h-BN) or "white graphene" has many outstanding properties including high thermal conductivity, high mechanical strength, chemical inertness, and high electrical resistance, which open up a wide range of applications such as thermal interface material, protective coatings, and dielectric in nanoelectronics that easily exceed the current advertised benefits pertaining to the graphene-based applications. The development of h-BN films using chemical vapor deposition (CVD) has thus far led into nucleation of triangular or asymmetric diamond shapes on different metallic surfaces. Additionally, the average size of the triangular domains has remained relatively small (∼ 0.5 μm(2)) leading to a large number of grain boundaries and defects. While the morphology of Cu surfaces for CVD-grown graphene may have impacts on the nucleation density, domain sizes, thickness, and uniformity, the effects of the decreased roughness of Cu surface to develop h-BN films are unknown. Here, we report the growth and characterization of novel large area h-BN hexagons using highly electropolished Cu substrate under atmospheric pressure CVD conditions. We found that the nucleation density of h-BN is significantly reduced while domain sizes increase. In this study, the largest hexagonal-shape h-BN domain observed is 35 μm(2), which is an order of magnitude larger than a typical triangular domain. As the domains coalesce to form a continuous film, the larger grain size offers a more pristine and smoother film with lesser grain boundaries induced defects. PMID:24447201

  3. Thin film NiTi coatings on optical fiber Bragg sensors

    SciTech Connect

    Mohanchandra, K. P.; Karnani, S.; Emmons, M. C.; Carman, G. P.; Richards, W. L.

    2008-07-21

    This paper describes the sputter deposition and characterization of nickel titanium (NiTi) thin film shape memory alloy onto the surface of an optical fiber Bragg grating. The NiTi coating uniformity, crystallinity, and transformation temperatures are measured using scanning electron microscope, x-ray diffraction, and differential scanning calorimeter, respectively. The strain in the optical fiber is measured using centroid calculation of wavelength shifts. Results show distinct and abrupt changes in the optical fiber signal with the four related transformation temperatures represented by the austenite-martensite forward and reverse phase transformations. These tests demonstrate a coupling present between optical energy and thermal energy, i.e., a modified multiferroic material.

  4. The influence of electropolishing on the corrosion resistance of 316L stainless steel.

    PubMed

    Sutow, E J

    1980-09-01

    A study was conducted which examined the influence of electropolishing on the corrosion resistance of a cold rolled 316L stainless steel. Test specimens were surface prepared to a final mechanical finish of wetted 600 grit SiC paper, prior to electropolishing. An o-H3PO4/Glycerol/H2O electropolishing solution was employed for times of 15, 20, and 25 min. Control specimens were surface prepared only to the final mechanical finish. Anodic polarization tests were performed in a deaerated Ringer's solution (37 degrees C) which was acidified to pH 1, with HCl. The electropolished specimens demonstrated increased corrosion resistance, when compared to the control specimens. This was evidenced for the former by more anodic corrosion and breakdown potentials, and the absence of a dissolution peak which was observed for the control specimens at the initial polarization potentials. Surface hardness measurements indicated that this increase in corrosion resistance was produced, in part, by the removal of the cold worked surface layer produced by the mechanical finish. In terms of increasing corrosion resistance, no optimum electropolishing time was found within the 15-25 min treatment period. PMID:7349665

  5. Removal of long-lived Rn-222 daughters by electropolishing thin layers of stainless steel

    NASA Astrophysics Data System (ADS)

    Frascatore, J.; Schnee, R. W.; Bowles, M. A.; Bunker, R.; McCabe, K.; White, J.; Cushman, P.; Pepin, M.; Guiseppe, V. E.

    2013-10-01

    Long-lived daughter particles from the 222Rn decay chain may present a limiting background in dark matter detecting experiments. Electropolishing has proven to be an effective method at removing these daughter particles from material surfaces, particularly stainless steel. The removal of <1 μ m of stainless steel reduces the sample daughter contamination by a factor > 100. The total thickness removed due to electropolishing is fairly uniform, as observed by examining samples with a scanning electron microscope. Electropolishing can therefore be used for precision-machined equipment and applications which require the removal of uniform and significantly small thicknesses. Here, the relationship between thickness removed and removal of daughter contamination is studied, including corrections for systematic uncertainties produced by drifts in the digital scale calibration, alpha detector gain drifts, and grow-in of 210Po.

  6. Advanced Chinese NiTi alloy wire and clinical observations.

    PubMed

    Chen, R; Zhi, Y F; Arvystas, M G

    1992-01-01

    Chinese NiTi wire was studied on the bench with six other nickel-titanium-alloy wires. Bending and torsional tests were conducted and temperatures of phase transformation compared. The Chinese NiTi wire was found to have a low stiffness, high springback and constant bending and torsional moments on unloading, in a very large deformation region. It can produce a gentle, nearly constant force. These factors make it desirable for clinical application. Included in this paper are clinical observations of case selected from over 100 patients in current treatment with Chinese NiTi wires. Chinese NiTi wire reduced the leveling and alignment phase of treatment without discomfort to the patient. Chinese NiTi wire can be used in both children and adults. PMID:1445516

  7. The influence of heat treatment on the mechanical properties of Ni-Ti file materials.

    PubMed

    Miyara, Kana; Yahata, Yoshio; Hayashi, Yohsuke; Tsutsumi, Yusuke; Ebihara, Arata; Hanawa, Takao; Suda, Hideaki

    2014-01-01

    The purpose of this study was to investigate the influence of heat treatment on the mechanical properties of Ni-Ti file materials. Ni-Ti wire (1.00 mm ø) was processed into a conical shape with 0.30-mm diameter tip and 0.06 taper. Specimens were heated for 30 min at 300, 400, 450, 500 or 600°C. Non-heated specimens were used as controls. DSC, a cantilever-bending test and cyclic fatigue test were performed. Ms and Af for groups 400 and 450 were higher than those for others (p<0.05). The load/deflection ratios of groups 400, 450 and 500 were lower than that of group 600 (p<0.05). The bending load values at 2.0-mm deflection of groups 400, 450 and 500 were lower than those of group 300 and the control group (p<0.05). The NCFs of groups 400, 450 and 500 exceeded that of group 600(p<0.05). Changes in flexibility with heat treatment could improve the cyclic fatigue properties of Ni-Ti instruments. PMID:24492108

  8. Equation of state and mechanical response of NiTi during one-dimensional shock loading

    NASA Astrophysics Data System (ADS)

    Meziere, Y. J. E.; Millett, J. C. F.; Bourne, N. K.

    2006-08-01

    The equation of state and the mechanical response (dynamic tensile strength and dynamic shear strength) of the shape memory alloy NiTi have been investigated using plate impact. The Hugoniot has been extended with additional data and a nonlinear behavior of the Hugoniot (shock velocity-particle velocity) has been noted. A bilinear representation has been proposed for the trend. These two behaviors were attributed to the shock-induced phase transformation from B2 to monoclinic. However, this phase transformation seems to have no influence on the dynamic tensile strength. A minimum impact stress value was found necessary to create the spallation in NiTi but the pull back stress remains near constant above this value. A negative strain-rate dependency was also noted on the spallation. The shear strength (τ ) of NiTi appears to increase continuously with the impact stress. The evolution of τ behind the shock front seems to be linked to the phase transformation observed in determination of the Hugoniot. Indeed, It was observed that there was no change of τ until an impact stress value corresponding to the inflection point on the Hugoniot, followed by increase behind the shock front above this value.

  9. TEM studies of the nitrided/oxided Ni-Ti surface layer.

    PubMed

    Lelatko, J; Goryczka, T; Paczkowski, P; Wierzchoń, T; Morawiec, H

    2010-03-01

    TiN and TiO(2) coatings, which are known from their low chemical reactivity, high hardness and wear and corrosion resistance, are used for protecting the NiTi surface. In the present work, nearly equiatomic NiTi (50.6 at.%) shape memory alloy was covered with the layers obtained by nitriding under glow discharge at 1073 K. Additionally, at the end of the process some amount of oxygen was added. Characterization of the nitrided/oxided layers structure was carried out using transmission and scanning electron microscopy. The investigations were focused on the structure of the multilayer nitrided/oxided NiTi surface. The surface is formed from nanocrystalline and columnar grains of the TiN phase. Between the top layer and beta-NiTi substrate the interface Ti(2)Ni layer was formed. Addition of oxygen at the end of the process created a thin layer of TiO(2) phase nanograins at the surface of the TiN phase. In the same areas, small amount of amorphous phase was identified. The combination of nitriding and oxidation formed layers that reveal relatively high corrosion resistance. PMID:20500413

  10. Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

    PubMed Central

    Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

    2016-01-01

    NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

  11. Automated detection of a prostate Ni-Ti stent in electronic portal images

    SciTech Connect

    Carl, Jesper; Nielsen, Henning; Nielsen, Jane; Lund, Bente; Larsen, Erik Hoejkjaer

    2006-12-15

    Planning target volumes (PTV) in fractionated radiotherapy still have to be outlined with wide margins to the clinical target volume due to uncertainties arising from daily shift of the prostate position. A recently proposed new method of visualization of the prostate is based on insertion of a thermo-expandable Ni-Ti stent. The current study proposes a new detection algorithm for automated detection of the Ni-Ti stent in electronic portal images. The algorithm is based on the Ni-Ti stent having a cylindrical shape with a fixed diameter, which was used as the basis for an automated detection algorithm. The automated method uses enhancement of lines combined with a grayscale morphology operation that looks for enhanced pixels separated with a distance similar to the diameter of the stent. The images in this study are all from prostate cancer patients treated with radiotherapy in a previous study. Images of a stent inserted in a humanoid phantom demonstrated a localization accuracy of 0.4-0.7 mm which equals the pixel size in the image. The automated detection of the stent was compared to manual detection in 71 pairs of orthogonal images taken in nine patients. The algorithm was successful in 67 of 71 pairs of images. The method is fast, has a high success rate, good accuracy, and has a potential for unsupervised localization of the prostate before radiotherapy, which would enable automated repositioning before treatment and allow for the use of very tight PTV margins.

  12. Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires.

    PubMed

    Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

    2016-01-01

    NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19' martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19' martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

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

    PubMed Central

    Pan, Qiang; Cho, Chongdu

    2007-01-01

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

  14. Precipitation and surface adsorption of metal complexes during electropolishing. Theory and characterization with X-ray nanotomography and surface tension isotherms.

    PubMed

    Nave, Maryana I; Chen-Wiegart, Yu-chen Karen; Wang, Jun; Kornev, Konstantin G

    2015-09-21

    Electropolishing of metals often leads to supersaturation conditions resulting in precipitation of complex compounds. The solubility diagrams and Gibbs adsorption isotherms of the electropolishing products are thus very important to understand the thermodynamic mechanism of precipitation of reaction products. Electropolishing of tungsten wires in aqueous solutions of potassium hydroxide is used as an example illustrating the different thermodynamic scenarios of electropolishing. Electropolishing products are able to form highly viscous films immiscible with the surrounding electrolyte or porous shells adhered to the wire surface. Using X-ray nanotomography, we discovered a gel-like phase formed at the tungsten surface during electropolishing. The results of these studies suggest that the electropolishing products can form a rich library of compounds. The surface tension of the electrolyte depends on the metal oxide ions and alkali-metal complexes. PMID:26279498

  15. Removal of long-lived {sup 222}Rn daughters by electropolishing thin layers of stainless steel

    SciTech Connect

    Schnee, R. W.; Bowles, M. A.; Bunker, R.; McCabe, K.; White, J.; Cushman, P.; Pepin, M.; Guiseppe, V. E.

    2013-08-08

    Long-lived alpha and beta emitters in the {sup 222}Rn decay chain on detector surfaces may be the limiting background in many experiments attempting to detect dark matter or neutrinoless double beta decay. Removal of tens of microns of material via electropolishing has been shown to be effective at removing radon daughters implanted into material surfaces. Some applications, however, require the removal of uniform and significantly smaller thicknesses. Here, we demonstrate that electropolishing < 1 μm from stainless-steel plates reduces the contamination efficiently, by a factor > 100. Examination of electropolished wires with a scanning electron microscope confirms that the thickness removed is reproducible and reasonably uniform. Together, these tests demonstrate the effectiveness of removal of radon daughters for a proposed low-radiation, multi-wire proportional chamber (the BetaCage), without compromising the screener’s energy resolution. More generally, electropolishing thin layers of stainless steel may effectively remove radon daughters without compromising precision-machined parts.

  16. The effect of surfactants on the electropolishing behavior of copper in orthophosphoric acid

    NASA Astrophysics Data System (ADS)

    Taha, A. A.; Ahmed, A. M.; Rahman, H. H. Abdel; Abouzeid, F. M.

    2013-07-01

    The electropolishing behavior of copper was studied in orthophosphoric acid with Triton X-100, sodium dodecyl sulphate and cetyl pyridinium chloride as additives for improving the finish obtained on copper surface. This was investigated by measuring and comparing anode potential-limiting current relationships in solutions of gradually increasing concentration of surfactants. The addition of surfactants to the electropolishing solution results in a lower limiting current. This confirms the mass transport of dissolved species from the anode surface to the bulk of solution as the rate-determining step in the presence of three surfactants in all concentrations investigated. Scanning electron microscope (SEM), atomic force microscope (AFM) and measured brightness values were used to investigate the copper surface after electropolishing and the results were compared to polishing done in absence of surfactants. According to SEM images and brightness values, addition of Triton X-100 was effective to enhance levelling and brightening more than sodium dodecyl sulphate and cetyl pyridinium chloride. AFM analysis showed that the roughness values (Ra) for an electropolished copper surface, in presence of surfactants, is significantly lower than in absence of surfactants. Different reaction conditions and the physical properties of solutions are studied to obtain dimensionless correlation among all these parameters.

  17. Fatigue of pseudoelastic NiTi within the stress-induced transformation regime: a modified Coffin-Manson approach

    NASA Astrophysics Data System (ADS)

    Maletta, C.; Sgambitterra, E.; Furgiuele, F.; Casati, R.; Tuissi, A.

    2012-11-01

    Strain controlled fatigue tests of a pseudoelastic nickel-titanium (NiTi) shape memory alloy (SMA) have been carried out in this investigation. In particular, flat dog-bone shaped specimens, obtained from commercial NiTi sheets, have been analyzed, under pull-pull loading conditions, in two subsequent steps: (i) material stabilization and (ii) fatigue life estimation. The first step was carried out to obtain a stable pseudoelastic response of the SMA, i.e. with no residual deformations upon unloading, and it can be regarded as a preliminary processing condition of the alloy. Results on functional fatigue, i.e. in terms of stabilized pseudoelastic response, and on structural fatigue, in terms of cycles to failure, are reported and discussed. Furthermore, a modified Coffin-Manson approach for fatigue life estimation of SMAs is proposed, which takes into account the strain mechanisms involved during repeated stress-induced martensitic transformations.

  18. Aluminum-matrix composites with embedded Ni-Ti wires by ultrasonic consolidation

    NASA Astrophysics Data System (ADS)

    Hahnlen, Ryan; Dapino, Marcelo J.; Short, Matt; Graff, Karl

    2009-03-01

    [Smart Vehicle Workshop] This paper presents the development of active aluminum-matrix composites manufactured by Ultrasonic Additive Manufacturing (UAM), an emerging rapid prototyping process based on ultrasonic metal welding. Composites created through UAM experience process temperatures as low as 20°C, in contrast to current metal-matrix fabrication processes which require fusion of materials and hence reach temperatures of 500°C and above. UAM thus creates unprecedented opportunities to develop adaptive structures with seamlessly embedded smart materials and electronic components without degrading the properties that make embedding these materials and components attractive. This research focuses on three aspects of developing UAM Ni-Ti/Al composites which have not been accomplished before: (i) Characterization of the mechanical properties of the composite matrix; (ii) Investigation of Ni-Ti/Al composites as tunable stiffness materials and as strain sensors based on the shape memory effect; and (iii) Development of constitutive models for UAM Ni-Ti/Al composites. The mechanical characterization shows an increase in tensile strength of aluminum UAM builds over the parent material (Al 3003-H18), likely due to grain refinement caused by the UAM process. We demonstrate the ability to embed Ni-Ti wires up to 203 μm in diameter in an aluminum matrix, compared with only 100 μm in previous studies. The resulting Ni-Ti/Al UAM composites have cross sectional area ratios of up to 13.4% Ni-Ti. These composites exhibit a change in stiffness of 6% and a resistivity change of -3% when the Ni- Ti wires undergo martensite to austenite transformation. The Ni-Ti area ratios and associated strength of the shape memory effect are expected to increase as the UAM process becomes better understood and is perfected. The Brinson constitutive model for shape memory transformations is used to describe the stiffness and the strain sensing of Ni-Ti/Al composites in response to

  19. Transmission Kikuchi diffraction and transmission electron forescatter imaging of electropolished and FIB manufactured TEM specimens

    SciTech Connect

    Zieliński, W. Płociński, T.; Kurzydłowski, K.J.

    2015-06-15

    We present a study of the efficiency of the utility of scanning electron microscope (SEM)-based transmission methods for characterizing grain structure in thinned bulk metals. Foils of type 316 stainless steel were prepared by two methods commonly used for transmission electron microscopy — double-jet electropolishing and focused ion beam milling. A customized holder allowed positioning of the foils in a configuration appropriate for both transmission electron forward scatter diffraction, and for transmission imaging by the use of a forescatter detector with two diodes. We found that both crystallographic orientation maps and dark-field transmitted images could be obtained for specimens prepared by either method. However, for both methods, preparation-induced artifacts may affect the quality or accuracy of transmission SEM data, especially those acquired by the use of transmission Kikuchi diffraction. Generally, the quality of orientation data was better for specimens prepared by electropolishing, due to the absence of ion-induced damage. - Highlights: • The transmission imaging and diffraction techniques are emerging in scanning electron microscopy (SEM) as promising new field of materials characterization. • The manuscript titled: “Transmission Kikuchi Diffraction and Transmission Electron Forescatter Imaging of Electropolished and FIB Manufactured TEM Specimens” documents how different specimen thinning procedures can effect efficiency of transmission Kikuchi diffraction and transmission electron forescatter imaging. • The abilities to make precision crystallographic orientation maps and dark-field images in transmission was studied on electropolished versus focus ion beam manufactured TEM specimens. • Depending on the need, electropolished and focused ion beam technique may produce suitable specimens for transmission imaging and diffraction in SEM.

  20. Modeling the effects of stress state and crystal orientation on the stress-induced transformation of NiTi single crystals

    NASA Astrophysics Data System (ADS)

    Buchheit, T. E.; Wert, J. A.

    1994-11-01

    A model that combines the phenomenological theory of martensite with a generalized Schmid’s law has been used to predict the principal stress combinations required to induce the martensitic transformation in unconstrained NiTi shape memory alloy (SMA) single crystals. The transformation surfaces prescribed by the model are anisotropic and asymmetric, reflecting the unidirectional character of shear on individual martensite habit planes. Model predictions of the transformation strain as a function of stress axis orientation for a uniaxial applied stress further demonstrate the anisotropy of the stress-induced transformation in NiTi single crystals. Model results for the uniaxial stress case compare favorably with previously published experimental observations for aged NiTi single crystals.

  1. Modeling the effects of stress state and crystal orientation on the stress-induced transformation of NiTi single crystals

    SciTech Connect

    Buchheit, T.E.; Wert, J.A. . Dept. of Materials Science and Engineering)

    1994-11-01

    A model that combines the phenomenological theory of martensite with a generalized Schmid's law has been used to predict the principal stress combinations required to induce the martensitic transformation in unconstrained NiTi shape memory alloy (SMA) single crystals. The transformation surfaces prescribed by the model are anisotropic and asymmetric, reflecting the unidirectional character of shear on individual martensite habit planes. Model predictions of the transformation strain as a function of stress axis orientation for uniaxial applied stress further demonstrate the anisotropy of the stress-induced transformation in NiTi single crystals. Model results for the uniaxial stress case compare favorably with previously published experimental observations for aged NiTi single crystals.

  2. Remarkable biocompatibility enhancement of porous NiTi alloys by a new surface modification approach: in-situ nitriding and in vitro and in vivo evaluation.

    PubMed

    Li, H; Yuan, B; Gao, Y; Chung, C Y; Zhu, M

    2011-12-15

    An in-situ nitriding method has been developed to modify the outer surface and the pore walls of both open and closed pores of porous NiTi shape memory alloys (SMAs) as part of their sintering process. XRD and XPS examinations revealed that the modified layer is mainly TiN. The biocompatibility of the in-situ nitrided sample has been characterized by its corrosion resistance, cell adherence, and implant surgery. The in-situ nitrided porous NiTi SMAs exhibit much better corrosion resistance, cell adherence, and bone tissue induced capability than the porous NiTi alloys without surface modification. Furthermore, the released Ni ion content in the blood of rabbit is reduced greatly by the in-situ nitriding. The excellent biocompatibility of in-situ nitrided sample is attributed to the formation of the TiN layer on all the pore walls including both open and closed pores. PMID:21936044

  3. The Effect of Pre-Stressing on the Static Indentation Load Capacity of the Superelastic 60NiTi

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Moore, Lewis E., III; Clifton, Joshua S.

    2013-01-01

    Superelastic nickel-titanium alloys, such as 60NiTi (60Ni-40Ti by wt.%), are under development for use in mechanical components like rolling element bearings and gears. Compared to traditional bearing steels, these intermetallic alloys, when properly heat-treated, are hard but exhibit much lower elastic modulus (approx.100 GPa) and a much broader elastic deformation range (approx.3 percent or more). These material characteristics lead to high indentation static load capacity, which is important for certain applications especially space mechanisms. To ensure the maximum degree of elastic behavior, superelastic materials must be pre-stressed, a process referred to as "training" in shape memory effect (SME) terminology, at loads and stresses beyond expected use conditions. In this paper, static indentation load capacity tests are employed to assess the effects of pre-stressing on elastic response behavior of 60NiTi. The static load capacity is measured by pressing 12.7 mm diameter ceramic Si3N4 balls into highly polished, hardened 60NiTi flat plates that have previously been exposed to varying levels of pre-stress (up to 2.7 GPa) to determine the load that results in shallow but measurable (0.6 m, 25 in. deep) permanent dents. Hertz stress calculations are used to estimate contact stress. Without exposure to pre-stress, the 60NiTi surface can withstand an approximately 3400 kN load before significant denting (>0.4 m deep) occurs. When pre-stressed to 2.7 GPa, a static load of 4900 kN is required to achieve a comparable dent, a 30 percent increase. These results suggest that stressing contact surfaces prior to use enhances the static indentation load capacity of the superelastic 60NiTi. This approach may be adaptable to the engineering and manufacture of highly resilient mechanical components such as rolling element bearings.

  4. Comparative Study of Clinically Used NiTi Orthodontic Wires

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Zhang, Yang; Hao, Fengyu; Yang, Ke; Tan, Lili

    The purpose of the study was to comparatively investigate two NiTi orthodontic wires. It is valuable to determine the phase transformation temperature and corrosion characteristics of the orthodontic wires to further study the shape memory effect and corrosion resistance properties. Optical microscope and EDX analysis were used for microstructure characteristics and composition analysis. Differential scanning calorimetry (DSC) was carried out to identify the phase transformation behavior of the two wires. Electrochemical tests in artificial saliva at 37 ±1°C including polarization and electrochemical impedance spectroscopy (EIS) were used to assess the corrosion resistance and corrosion mechanism of the wires. It was found that the transformation temperature range of A-wire (imported) is narrower while the As and Af are close to the body temperature, which is more suitable in the orthodontic operation at early stage. The corrosion current density of A-wire is lower than that of B-wire (domestically made) while the corrosion potential is higher. EIS test results indicated that the corrosion mechanism was the same. However, the oxide layer formed on the surface of A-wire is more protective.

  5. Chinese NiTi wire--a new orthodontic alloy.

    PubMed

    Burstone, C J; Qin, B; Morton, J Y

    1985-06-01

    Chinese NiTi wire was studied by means of a bending test to determine wire stiffness, springback, and maximum bending moments. Chinese NiTi wire has an unusual deactivation curve (unlike steel and nitinol wires) in which relatively constant forces are produced over a long range of action. The characteristic flexural stiffness of NiTi wire is determined by the amount of activation. At large activations NiTi wires has a stiffness of only 7% that of a comparable stainless steel wire, and at small activations 28% of steel wire. For the same activation at large deflections, the forces produced are 36% that of a comparable nitinol wire. Chinese NiTi wire demonstrates phenomenal springback. It can be deflected 1.6 times as far as nitinol wire or 4.4 times as far as stainless steel wire without appreciable permanent deformation. NiTi wire is highly useful in clinical situations that require a low-stiffness wire with an extremely large springback. PMID:3890554

  6. Cutting Speed Dependent Microstructure and Transformation Behavior of NiTi Alloy in Dry and Cryogenic Machining

    NASA Astrophysics Data System (ADS)

    Kaynak, Y.; Karaca, H. E.; Jawahir, I. S.

    2015-01-01

    The effects of cutting speed in cryogenic and dry machining on the surface integrity characteristics (the affected layer, microhardness, transformation response, transformation temperature, and latent heat for transformation) of NiTi shape memory alloys are investigated. It has been found that the cutting speed has remarkable effects on the surface and subsurface properties of machined NiTi alloys. Increased cutting speed results in decreased subsurface hardness and increased latent heat for phase transformation. In general, the depth of affected layers decreases with increased cutting speed in dry and cryogenic machining. Chips show a similar behavior as affected layer in terms of transformation response and microhardness. Cryogenic machining is found to have greater effects on the surface and subsurface properties of the machined work material in comparison with dry machining at all given cutting speeds.

  7. Simulations of Mechanical Response of Superelastic NiTi Helical Spring and its Relation to Fatigue Resistance

    NASA Astrophysics Data System (ADS)

    Sedlák, P.; Frost, M.; Kruisová, A.; Hiřmanová, K.; Heller, L.; Šittner, P.

    2014-07-01

    Behavior of NiTi shape memory alloys under complex loading is still a subject of both experimental and theoretical investigations. One of the simplest geometries, in which the material is loaded in combined mode and which has also several practical applications, is a simple helical spring. In this contribution, mechanical response of NiTi superelastic spring is analyzed in detail by numerical simulation and the results are compared to experiments. The simulations show complex stress state, which develops during spring stretching. Analyzing fatigue tests with respect to simulated behavior allowed us to find relation between fatigue resistance and periodic changes in volume fraction of martensite induced by cyclic mechanical loading. The work also underlines an extension of the range of stroke amplitudes guaranteeing enhanced life performance of the spring when material transforms through the R-phase.

  8. Effect of Particle Size of Titanium and Nickel on the Synthesis of NiTi by TE-SHS

    NASA Astrophysics Data System (ADS)

    Novák, Pavel; Veselý, Tomáš; Marek, Ivo; Dvořák, Petr; Vojtěch, Vladimír; Salvetr, Pavel; Karlík, Miroslav; Haušild, Petr; Kopeček, Jaromír

    2016-04-01

    In this work, the influence of the particle size of nickel and titanium on the synthesis of NiTi shape memory alloy by self-propagating high-temperature synthesis (SHS) was investigated. It was found that coarse titanium and nickel powders undergo only a limited SHS reaction. On the other hand, too fine powders support the low-temperature diffusional formation of NiTi intermetallics at 773 K to 1073 K (500 °C to 800 °C) which could then suppress the SHS reaction. The optimum powder fraction of both nickel and titanium to achieve the most intensive SHS reaction is 25 to 45 µm. The influence of the particle size of both nickel and titanium on the reaction mechanism is discussed in terms of the microstructure evolution, phase, and chemical composition changes and thermal effects determined by differential thermal analysis.

  9. Recent developments in electropolishing and tumbling R&D at Fermilab

    SciTech Connect

    Cooper, C.; Brandt, J.; Cooley, L.; Ge, M.; Harms, E.; Khabiboulline, T.; Ozelis, J.; Boffo, C.; /Babcock Noell, Wuerzburg

    2009-10-01

    Fermi National Accelerator Lab (Fermilab) is continuing to improve its infrastructure for research and development on the processing of superconducting radio frequency cavities. A single cell 3.9 GHz electropolishing tool built at Fermilab and operated at an industrial partner was recently commissioned. The EP tool was used to produce a single cell 3.9 GHz cavity that reached an accelerating gradient of 30 MV/m with a quality factor of 5 x 10{sup 9}. A single cell 1.3 GHz cavity was also electropolished at the same industrial vendor using the vendor's vertical full-immersion technique. On their first and only attempt the vendor produced a single cell 1.3 GHz cavity that reached 30 MV/m with a quality factor of 1 x 10{sup 10}. These results will be detailed along with preliminary tumbling results.

  10. Fundamental Study of Micro-Defects in Electropolished EB-Welded and Hydroformed SRF Accelerating Structures

    SciTech Connect

    Sumption, Mike

    2014-08-29

    In the area of niobium elecropolishing fundamentals, we focused on understanding the influence of the surface topology, and geometry (with effects from gravity included. The formation of a viscous film is essential for the electropolishing process to take place. The exact nature and composition of the film formed on niobium is still unknown because of its solubility in the electrolyte. Extensive pitting may take place at surface where a stable film cannot form. This has to be taken into consideration while determining the speed with which the SRF cavities are rotated while EP. Hydrodynamic aspects must be taken into consideration while optimizing the polishing parameters. There is improvement in surface finish with polishing time. There is a huge change in surface quality when the EP time is increased from 2 hours to 4 hours but not much change takes place when the time is further increased to 6 hours. So keeping the economic points in view, about 100 um defect layer removal may be sufficient to get the desired performance. In the area of Electropolishing of untreated and treated niobium with Weld Joints we studied untreated and treated Nb, especially for the heat affected areas next to welded bumps, electropolished for different durations. The electropolishing of the untreated Nb caused the formation of pits on the surface at about 15 min but they disappeared when the electropolishing duration was more than 15 min. Electropolishing for 120 min smoothened the surface of untreated Nb by levelling the surface, but the severe formation of pits on the whole surface was found after 240 min. The treatment of Nb significantly changed the Nb surface morphology which was covered by grains of different size that looked light or dark in the optical microscope. The treated Nb was susceptible to pitting during the entire electropolishing starting from 15 min and the dark grains had more susceptibility to pitting than the light grains. In addition, electropolishing for 240 min

  11. Influence of electropolishing current densities on sulfur generation at niobium surface

    NASA Astrophysics Data System (ADS)

    Tyagi, P. V.; Nishiwaki, M.; Noguchi, T.; Sawabe, M.; Saeki, T.; Hayano, H.; Kato, S.

    2013-11-01

    We report the effect of different current densities on sulfur generation at Nb surface in the electropolishing (EP) with aged electrolyte. In this regard, we conducted a series of electropolishing (EP) experiments in aged EP electrolyte with high (≈50 mA/cm2) and low (≈30 mA/cm2) current densities on Nb surfaces. The experiments were carried out both for laboratory coupons and a real Nb single cell cavity with six witness samples located at three typical positions (equator, iris and beam pipe). Sample's surfaces were investigated by XPS (X-ray photoelectron spectroscopy), SEM (scanning electron microscope) and EDX (energy dispersive X-ray spectroscopy). The surface analysis showed that the EP with a high current density produced a huge amount of sulfate/sulfite particles at Nb surface whereas the EP with a low current density was very helpful to mitigate sulfate/sulfite at Nb surface in both the experiments.

  12. Impact of forming, welding, and electropolishing on pitting and the surface finish of SRF cavity niobium

    SciTech Connect

    Cooley, L.D.; Burk, D.; Cooper, C.; Dhanaraj, N.; Foley, M.; Ford, D.; Gould, K.; Hicks, D.; Novitski, R.; Romanenko, A.; Schuessler, R.; /Fermilab

    2010-07-01

    A broad range of coupon electropolishing experiments are described to ascertain the mechanism(s) by which large defects are formed near superconducting radiofrequency (SRF) cavity welds. Cold-worked vs. annealed metal, the presence of a weld, and several variations of electropolishing (EP) parameters were considered. Pitting is strongly promoted by cold work and agitation of the EP solution. Welding also promotes pitting, but less so compared with the other factors above. Temperature increase during EP did not strongly affect glossiness or pitting, but the reduced viscosity made the electrolyte more susceptible to agitation. The experiments suggest that several factors that are rather benign alone are combined by the cavity forming, welding, and processing sequence to promote the formation of defects such as pits. Process changes to mitigate these risks are discussed.

  13. Evaluation of electropolished stainless steel electrodes for use in DC high voltage photoelectron guns

    SciTech Connect

    BastaniNejad, Mahzad Elmustafa, Abdelmageed A.; Forman, Eric; Covert, Steven; Hansknecht, John; Hernandez-Garcia, Carlos; Poelker, Matthew; Das, Lopa; Kelley, Michael; Williams, Phillip

    2015-07-15

    DC high voltage photoelectron guns are used to produce polarized electron beams for accelerator-based nuclear and high-energy physics research. Low-level field emission (∼nA) from the cathode electrode degrades the vacuum within the photogun and reduces the photoelectron yield of the delicate GaAs-based photocathode used to produce the electron beams. High-level field emission (>μA) can cause significant damage the photogun. To minimize field emission, stainless steel electrodes are typically diamond-paste polished, a labor-intensive process often yielding field emission performance with a high degree of variability, sample to sample. As an alternative approach and as comparative study, the performance of electrodes electropolished by conventional commercially available methods is presented. Our observations indicate the electropolished electrodes exhibited less field emission upon the initial application of high voltage, but showed less improvement with gas conditioning compared to the diamond-paste polished electrodes. In contrast, the diamond-paste polished electrodes responded favorably to gas conditioning, and ultimately reached higher voltages and field strengths without field emission, compared to electrodes that were only electropolished. The best performing electrode was one that was both diamond-paste polished and electropolished, reaching a field strength of 18.7 MV/m while generating less than 100 pA of field emission. The authors speculate that the combined processes were the most effective at reducing both large and small scale topography. However, surface science evaluation indicates topography cannot be the only relevant parameter when it comes to predicting field emission performance.

  14. Study of electropolishing of ferrous alloys using rotating-disk electrodes

    NASA Astrophysics Data System (ADS)

    Hryniewich, T.; Muller, R. H.; Tobias, C. W.

    1981-06-01

    Studies were performed on the rotating disk electrode system under controlled electrochemical and hydrodynamic conditions to establish conditions at which the best surface finish, after electropolishing of different types of ferrous alloys, may be achieved. The investigations were made over a wide range of applied current density, mass loss, and current efficiency using pure iron, armco iron, steels 1018, 1028, 1040, 1060, 1080, 4141 and H13 and 01 toolsteels. Characteristics of the finished surfaces are described.

  15. Evaluation of electropolished stainless steel electrodes for use in DC high voltage photoelectron guns

    SciTech Connect

    BastaniNejad, Mahzad; Elmustafa, Abdelmageed A.; Forman, Eric; Covert, Steven; Hansknecht, John; Hernandez-Garcia, Carlos; Poelker, Matthew; Das, Lopa; Kelley, Michael; Williams, Phillip

    2015-07-01

    DC high voltage photoelectron guns are used to produce polarized electron beams for accelerator-based nuclear and high-energy physics research. Low-level field emission (~nA) from the cathode electrode degrades the vacuum within the photogun and reduces the photoelectron yield of the delicate GaAs-based photocathode used to produce the electron beams. High-level field emission (>μA) can cause significant damage the photogun. To minimize field emission, stainless steel electrodes are typically diamond-paste polished, a labor-intensive process often yielding field emission performance with a high degree of variability, sample to sample. As an alternative approach and as comparative study, the performance of electrodes electropolished by conventional commercially available methods is presented. Our observations indicate the electropolished electrodes exhibited less field emission upon the initial application of high voltage, but showed less improvement with gas conditioning compared to the diamond-paste polished electrodes. In contrast, the diamond-paste polished electrodes responded favorably to gas conditioning, and ultimately reached higher voltages and field strengths without field emission, compared to electrodes that were only electropolished. The best performing electrode was one that was both diamond-paste polished and electropolished, reaching a field strength of 18.7 MV/m while generating less than 100 pA of field emission. The speculate that the combined processes were the most effective at reducing both large and small scale topography. However, surface science evaluation indicates topography cannot be the only relevant parameter when it comes to predicting field emission performance.

  16. Processing and Damping Properties of Sputtered NiTi Thin Films for Tools in Machining Processes

    NASA Astrophysics Data System (ADS)

    Kahleyss, F.; de Miranda, R. Lima; Surmann, T.; Zamponi, C.; Machai, C.; Biermann, D.; Quandt, E.

    2011-07-01

    Nowadays, many manufacturing processes require the machining of complex forms with a high aspect ratio or cavities. Tools with a long overhang length are a common method to meet these requirements. Typical examples for this are boring bars for bore-turning and the milling with very long cutters. These tools tend to vibrate strongly due to their slender shape. The stress-induced transformation of austenite to martensite and the distinctive hysteresis loop allow the NiTi shape memory alloys (SMA) to absorb vibration energy. This article describes the innovative approach to dampen process vibrations by coating the tool shafts of cutting tools with long overhang with NiTi thin films. It explores how these thin films can be applied on polished tungsten carbide shafts and how their modal parameters are modified by these coatings. In a further step, this knowledge is used to calculate stability charts of corresponding machining processes. The study reported in this article identified the stabilizing effects of coatings with a thickness of 2-4 μm on milling processes. The minimum stability limit was increased by up to 200%.

  17. Rapid Laser Induced Crystallization of Amorphous NiTi Films Observed by Nanosecond Dynamic Transmission Electron Microscopy (DTEM)

    SciTech Connect

    LaGrange, T; Campbell, G H; Browning, N D; Reed, B W; Grummon, D S

    2010-03-01

    The crystallization processes of the as-deposited, amorphous NiTi thin films have been studied in detail using techniques such as differential scanning calorimetry and, in-situ TEM. The kinetic data have been analyzed in terms of Johnson-Mehl-Avrami-Kolomogrov (JMAK) semi-empirical formula. The kinetic parameters determined from this analysis have been useful in defining process control parameters for tailoring microstructural features and shape memory properties. Due to the commercial push to shrink thin film-based devices, unique processing techniques have been developed using laser-based annealing to spatially control the microstructure evolution down to sub-micron levels. Nanosecond, pulse laser annealing is particularly attractive since it limits the amount of peripheral heating and unwanted microstructural changes to underlying or surrounding material. However, crystallization under pulsed laser irradiation can differ significantly from conventional thermal annealing, e.g., slow heating in a furnace. This is especially true for amorphous NiTi materials and relevant for shape memory thin film based microelectromechanical systems (MEMS) applications. There is little to no data on the crystallization kinetics of NiTi under pulsed laser irradiation, primarily due to the high crystallization rates intrinsic to high temperature annealing and the spatial and temporal resolution limits of standard techniques. However, with the high time and spatial resolution capabilities of the dynamic transmission electron microscope (DTEM) constructed at Lawrence Livermore National Laboratory, the rapid nucleation events occurring from pulsed laser irradiation can be directly observed and nucleation rates can be quantified. This paper briefly explains the DTEM approach and how it used to investigate the pulsed laser induced crystallization processes in NiTi and to determine kinetic parameters.

  18. Design of energy absorbing materials and composite structures based on porous shape memory alloys (SE)

    NASA Astrophysics Data System (ADS)

    Zhao, Ying

    Recently, attention has been paid to porous shape memory alloys. This is because the alloys show large and recoverable deformation, i.e. superelasticity and shape memory effect. Due to their light weight and potential large deformations, porous shape memory alloys have been considered as excellent candidates for energy absorption materials. In the present study, porous NiTi alloy with several different porosities are processed by spark plasma sintering (SPS). The compression behavior of the porous NiTi is examined with an aim of using it for a possible high energy absorbing material. Two models for the macroscopic compression behavior of porous shape memory alloy (SMA) are presented in this work, where Eshelby's inhomogeneous inclusion method is used to predict the effective elastic and superelastic behavior of a porous SMA based on the assumption of stress-strain curve. The analytical results are compared with experimental data for porous NiTi with 13% porosity, resulting in a reasonably good agreement. Based on the study upon porous NiTi, an energy absorbing composite structure made of a concentric NiTi spring and a porous NiTi rod is presented in this PhD dissertation. Both NiTi spring and porous NiTi rod are of superelastic grade. Ductile porous NiTi cylindrical specimens are fabricated by spark plasma sintering. The composite structure exhibits not only high reversible force-displacement behavior for small to intermediate loading but also high energy absorbing property when subjected to large compressive loads. A model for the compressive force-displacement curve of the composite structure is presented. The predicted curve is compared to the experimental data, resulting in a reasonably good agreement.

  19. NOVEL CHARACTERIZATION OF THE ELECTROPOLISHING OF NIOBIUM WITH SULFURIC AND HYDROFLUORIC ACID MIXTURES

    SciTech Connect

    Hui Tian; Charles Reece; Michael Kelley; Sean Corcoran

    2008-02-12

    Niobium surfaces are commonly electropolished in an effort to obtain optimally smooth surfaces for high-field SRF cavity applications. We report the first use of controlled electrochemical analysis techniques to characterize electropolishing of Nb in a sulfuric and hydrofluoric acid electrolyte. Through the use of a reference electrode we are able to clearly distinguish the anode, cathode polarization potentials as well as the electrolyte voltage drop that sum to the applied power supply voltage. We then separate the temperature and HF concentration dependence of each. We also report the first use of Electrochemical Impedance Spectroscopy (EIS) on this system. EIS results are consistent with a presence of a compact salt film at the Nb/electrolyte interface that is responsible for the limiting current. Microscopic understanding of the basic Nb EP mechanism is expected to provide an appropriate foundation with which to optimize the preparation of high-field niobium cavity surfaces. The implication of EIS for monitoring Nb surface during electropolishing shows this technology could be potentially used as a source of on-line feedback.

  20. Removal of Long-Lived Radon Daughters by Electropolishing Thin Layers of Stainless Steel

    NASA Astrophysics Data System (ADS)

    White, James; Schnee, Richard; Bunker, Raymond; Bowles, Michael; Cushman, Priscilla; Epland, Matthew; Pepin, Mark; Guiseppe, Vince

    2012-10-01

    Long-lived alpha and beta emitters in the Radon decay chain on detector surfaces may be limiting background in many experiments attempting to detect dark matter or neutrinoless double beta decay. To screen detector surfaces for this radioactive contamination, a low-radiation, multi-wire proportional chamber (the BetaCage) is under construction. Removal of Pb-210 implanted on its 25-micron stainless steel wires without causing significant variation in the diameter of the wires is critical to the BetaCage's ultimate sensitivity. An apparatus to perform electropolishing trials to remove roughly a micron of material has been assembled. These trials have shown promising results. Stainless steel square samples implanted with Pb-210 have shown counts with a reduction factor greater than 10 after electropolishing according to gamma assay. Furthermore, alpha counting has produced similar results, with a reduction factor greater than 100. Lastly, the diameters of wires after electropolishing have remained sufficiently uniform, with reduction in thickness consistent with expectations.

  1. Innovative processes for electropolishing of medical devices made of stainless steels.

    PubMed

    Eliaz, Noam; Nissan, Oded

    2007-11-01

    Currently, many medical devices are made of implantable metals such as 316LVM stainless steel. Electropolishing is a common process to obtain a smooth surface, free of contaminants and more passive, which allows for minimizing the foreign body response and cell adhesion. However, polishing of small implants with a highly complicated geometry and nonuniform metallurgy might result in unsatisfactory results. The objective of this work was to develop an electropolishing process effective for complex metallic implants such as artificial heart valve frames and miniature glaucoma implants. Polishing in an ultrasonic bath and pulsed voltage polishing processes were studied and compared to the standard ASTM process. Current-voltage curves were constructed for different solutions and bath temperatures. The polished parts were evaluated by stereomicroscopy, optical microscopy, atomic force microscopy, noncontact surface profilometry, and X-ray diffraction. Pulse polishing was found useful in eliminating the erosion effects of gas bubbles in solution. Electropolishing in an ultrasonic bath was found useful when a rough, patterned surface is needed, e.g. for osseointegration purposes. Preliminary animal studies followed by histopathology indicated that the polished surfaces stimulated only a moderate body reaction, as desired in such applications. The pronounced dependence of the measured roughness values on both the measurement technique and scanned area should inspire the preparation of a new test-method standard. PMID:17567863

  2. Staphylococcus aureus adhesion to standard micro-rough and electropolished implant materials.

    PubMed

    Harris, Llinos G; Meredith, D Osian; Eschbach, Lukas; Richards, R Geoff

    2007-06-01

    Implant-associated infections can cause serious complications including osteomyelitis and soft tissue damage, and are a great problem due to the emergence of antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). In some cases, antibiotic-loaded beads which release the antibiotic locally have been used, however such systems may lead to the development of antibiotic-resistant bacteria, as seen with gentamicin-loaded beads. Hence modifying the actual metal implant surface to inhibit or reduce initial bacterial adhesion may be an alternative option. This study describes the visualisation and quantification of S. aureus adhering to standard micro-rough 'commercially pure' titanium (TS) and Ti-6Al-7Nb (NS) surfaces, electropolished titanium (TE) and Ti-6Al-7Nb (NE) surfaces, and standard electropolished stainless steel (SS). Qualitative and quantitative results of S. aureus on the different surfaces correlated with each other, and showed significantly more live bacteria on NS than on the other surfaces, whilst there was no significant difference between the amount of bacteria on TS, TE, NE and SS surfaces. The results showed a significant decrease in the amount of bacteria adhering to the NE compared to standard NS surfaces. Such an observation suggests that the NS surface encouraged S. aureus adhesion, and could lead to higher infection rates in vivo. Hence electropolishing Ti-6Al-7Nb surfaces could be advantageous in osteosynthesis areas in minimising bacterial adhesion and lowering the rate of infection. PMID:17268867

  3. 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

  4. 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. PMID:21991455

  5. Covalent Functionalization of NiTi Surfaces with Bioactive Peptide Amphiphile Nanofibers

    PubMed Central

    Sargeant, Timothy D.; Rao, Mukti S.; Koh, Chung-Yan

    2009-01-01

    Surface modification enables the creation of bioactive implants using traditional material substrates without altering the mechanical properties of the bulk material. For applications such as bone plates and stents, it is desirable to modify the surface of metal alloy substrates to facilitate cellular attachment, proliferation, and possibly differentiation. In this work we present a general strategy for altering the surface chemistry of nickel-titanium shape memory alloy (NiTi) in order to covalently attach self-assembled peptide amphiphile (PA) nanofibers with bioactive functions. Bioactivity in the systems studied here includes biological adhesion and proliferation of osteoblast and endothelial cell types. The optimized surface treatment creates a uniform TiO2 layer with low levels of Ni on the NiTi surface, which is subsequently covered with an aminopropylsilane coating using a novel, lower temperature vapor deposition method. This method produces an aminated surface suitable for covalent attachment of PA molecules containing terminal carboxylic acid groups. The functionalized NiTi surfaces have been characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and atomic force microscopy (AFM). These techniques offer evidence that the treated metal surfaces consist primarily of TiO2 with very little Ni, and also confirm the presence of the aminopropylsilane overlayer. Self-assembled PA nanofibers presenting the biological peptide adhesion sequence Arg-Gly-Asp-Ser are capable of covalently anchoring to the treated substrate, as demonstrated by spectrofluorimetry and AFM. Cell culture and scanning electron microscopy (SEM) demonstrate cellular adhesion, spreading, and proliferation on these functionalized metal surfaces. Furthermore, these experiments demonstrate that covalent attachment is crucial for creating robust PA nanofiber coatings, leading to confluent cell monolayers. PMID:18083225

  6. Self-centering and damping capabilities of a tension-compression device equipped with superelastic NiTi wires

    NASA Astrophysics Data System (ADS)

    Soul, H.; Yawny, A.

    2015-07-01

    The hysteretic damping capacity and high recoverable strains characterizing the superelastic response of shape memory alloys (SMA) make these materials attractive for protection systems of structures subjected to dynamic loads. A successful implementation however is conditioned by functional fatigue exhibited by the SMA when subjected to cyclic loading. The residual deformation upon cycling and the efficiency in material usage are the two most restrictive issues in this sense. In this paper, a device equipped with superelastic NiTi SMA wires and capable of supporting external tension compression loads with optimized properties is presented. It is shown how the introduction of the wires’ pre-straining allows for the absorption of deleterious residual deformation without affecting the self-centering capabilities upon unloading, in contrast with what occurs for pre-strained tendons. These features were experimentally verified in an in-scale prototype composed of two 1.2 mm diameter superelastic NiTi SMA wires. In order to numerically assess the dynamic response of a simple structure subjected to seismic excitations, a multilinear superelasticity model for the NiTi wires was developed.

  7. Resputtering Effect on Nanocrystalline Ni-Ti Alloy Films

    NASA Astrophysics Data System (ADS)

    Priydarshini, B. Geetha; Esakkiraja, N.; Aich, Shampa; Chakraborty, M.

    2016-04-01

    We report on the effect of resputtering on the properties of nanocrystalline Ni-Ti alloy thin films deposited using co-sputtering of Ni and Ti targets. In order to facilitate the formation of nanocrystalline phases, films were deposited at room temperature and 573 K (300 °C) with substrate bias voltage of -100 V. The influence of substrate material on the composition, surface topography microstructure, and phase formations of nanocrystalline Ni-Ti thin films was also systematically investigated. The preferential resputtering of Ti adatoms was lesser for Ni-Ti films deposited on quartz substrate owing to high surface roughness of 4.87 nm compared to roughness value of 1.27 nm for Si(100) substrate.

  8. NiTi superelastic orthodontic archwires with polyamide coating.

    PubMed

    Bravo, L A; de Cabañes, A González; Manero, J M; Rúperez, E; Gil, F Javier

    2014-02-01

    Twenty orthodontic archwires with 55.2% Ni and 44.8% Ti (% weight) were subjected to a dipping treatment to coat the NiTi surface by a polyamide polymer. It has been selected a Polyamide 11 due to its remarkable long lasting performance. The transformation temperatures as well as the transformation stresses of the NiTi alloy were determined in order to know whether the coating process can alter its properties. The adhesive wear tests have been demonstrated that the wear rates as well as the dynamic friction coefficients μ of polymer coated wires are much lower than metallic wires. The corrosion studies have shown that the use of this polymer, as coating, seals the NiTi surface to prevent corrosion and the release of nickel ions. The average decrease of Ni ions release due to this coating is around 85%. PMID:24154920

  9. Inclusions Size-based Fatigue Life Prediction Model of NiTi Alloy for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Urbano, Marco Fabrizio; Cadelli, Andrea; Sczerzenie, Frank; Luccarelli, Pietro; Beretta, Stefano; Coda, Alberto

    2015-06-01

    Current standards consider the size and distribution of inclusions in semi-finished material, but do not place requirements on final biomedical devices made of NiTi shape memory alloys. In this paper, we analyze this by comparing the fatigue performances of NiTi superelastic wires obtained by different processes through a simple bilinear model of fatigue response in terms of strain life. The fracture surfaces of failed wires are analyzed through SEM microscopy and data regarding the presence of particles, and their morphology is recorded and analyzed using Type-I extreme value distribution. The results show a strong correlation between the fatigue limit of wires (in terms of strain) and the predicted extreme values of inclusions at fracture origin. Then, following the concept of treating the inclusions as `small cracks,' a simple relationship between fatigue limit strain range and inclusion size is proposed based on ΔKth data from the literature. The model is compared with the fatigue data obtained from the tested wires.

  10. Enhanced corrosion resistance and cellular behavior of ultrafine-grained biomedical NiTi alloy with a novel SrO-SiO2-TiO2 sol-gel coating

    NASA Astrophysics Data System (ADS)

    Zheng, C. Y.; Nie, F. L.; Zheng, Y. F.; Cheng, Y.; Wei, S. C.; Ruan, Liqun; Valiev, R. Z.

    2011-04-01

    NiTi alloy has a unique combination of mechanical properties, shape memory effects and superelastic behavior that makes it attractive for several biomedical applications. In recent years, concerns about its biocompatibility have been aroused due to the toxic or side effect of released nickel ions, which restricts its application as an implant material. Bulk ultrafine-grained Ni50.8Ti49.2 alloy (UFG NiTi) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study. A homogeneous and smooth SrO-SiO2-TiO2 sol-gel coating without cracks was fabricated on its surface by dip-coating method with the aim of increasing its corrosion resistance and cytocompatibility. Electrochemical tests in simulated body fluid (SBF) showed that the pitting corrosion potential of UFG NiTi was increased from 393 mV(SCE) to 1800 mV(SCE) after coated with SrO-SiO2-TiO2 film and the corrosion current density decreased from 3.41 μA/cm2 to 0.629 μA/cm2. Meanwhile, the sol-gel coating significantly decreased the release of nickel ions of UFG NiTi when soaked in SBF. UFG NiTi with SrO-SiO2-TiO2 sol-gel coating exhibited enhanced osteoblast-like cells attachment, spreading and proliferation compared with UFG NiTi without coating and CG NiTi.

  11. Engine Performance of Precision-forged, Electropolished and Machined Blades of Nimonic 80 and 80A Alloys

    NASA Technical Reports Server (NTRS)

    Sikora, Paul F; Johnston, James R

    1955-01-01

    An investigation was conducted to determine the effect of electropolishing precision-forged blades and of machining blades from oversize forgings on the engine performance of Nimonic 80 and Nimonic 80A turbine blades. These blades, along with precision-forged blades, were run in a J33-9 turbojet engine. The tests resulted in the following conclusions: (1) Electropolishing of precision-forged blades did not improve engine life relative to the life of nonelectropolished blades. (2) Machining blades from oversize forgings did not improve the engine life of precision-forged blades. (3) The precision-forging and heat-treating practice used in fabricating the blades investigated was such that the surface roughness and oxide penetration was so slight, approximately 0.0005 inch in depth, as to preclude any benefits derived from surface removal by electropolishing or machining.

  12. Evaluation of electropolished stainless steel electrodes for use in DC high voltage photoelectron guns

    DOE PAGESBeta

    BastaniNejad, Mahzad; Elmustafa, Abdelmageed A.; Forman, Eric; Covert, Steven; Hansknecht, John; Hernandez-Garcia, Carlos; Poelker, Matthew; Das, Lopa; Kelley, Michael; Williams, Phillip

    2015-07-01

    DC high voltage photoelectron guns are used to produce polarized electron beams for accelerator-based nuclear and high-energy physics research. Low-level field emission (~nA) from the cathode electrode degrades the vacuum within the photogun and reduces the photoelectron yield of the delicate GaAs-based photocathode used to produce the electron beams. High-level field emission (>μA) can cause significant damage the photogun. To minimize field emission, stainless steel electrodes are typically diamond-paste polished, a labor-intensive process often yielding field emission performance with a high degree of variability, sample to sample. As an alternative approach and as comparative study, the performance of electrodes electropolishedmore » by conventional commercially available methods is presented. Our observations indicate the electropolished electrodes exhibited less field emission upon the initial application of high voltage, but showed less improvement with gas conditioning compared to the diamond-paste polished electrodes. In contrast, the diamond-paste polished electrodes responded favorably to gas conditioning, and ultimately reached higher voltages and field strengths without field emission, compared to electrodes that were only electropolished. The best performing electrode was one that was both diamond-paste polished and electropolished, reaching a field strength of 18.7 MV/m while generating less than 100 pA of field emission. The speculate that the combined processes were the most effective at reducing both large and small scale topography. However, surface science evaluation indicates topography cannot be the only relevant parameter when it comes to predicting field emission performance.« less

  13. A comparison of EDS microanalysis in FIB-prepared and electropolished TEM thin foils.

    PubMed

    Hutchinson, C R; Hackenberg, R E; Shiflet, G J

    2003-01-01

    This paper reports the results of a fine-probe EDS microanalytical study of cellular precipitation in a Cu-Ti binary alloy. Compositional profiles across the solute depleted Cu-rich FCC lamellae and the Cu4Ti lamellae within isothermally formed cellular colonies were measured in a FEG-TEM from thin-foil specimens prepared by conventional electropolishing and by a technique using a Ga+ focused ion-beam (FIB). The Cliff-Lorimer ratio method, with an absorption correction, was employed to quantify the compositions. Two FIB samples were prepared with different orientations of the lamellae with respect to the ion-milling direction. The compositional profiles across the Cu-rich FCC lamellae and the Cu4Ti compound lamellae in both the FIB-prepared samples and the electropolished sample were, within experimental error, numerically equivalent. The composition of the Cu4Ti compound phase lamellae was very close to the ideal stoichiometric composition of 20 at % Ti. It is concluded that for this system, and for the specimen preparation procedures used in this study, the Ga+ ion-milling process has had no detectable effect on the chemistry changes across the interlamellar interface at the scale studied. These results indicate that the possible sources of chemical artifacts which include redeposition, preferential sputtering and ion-induced atomic migration can be minimized if several precautions are taken during milling in the FIB. Consistent with previous investigators, it was also found that the ion-milling process does introduce significant structural artifacts (e.g., dislocations) into the softer FCC Cu-rich phase compared with a specimen produced by conventional electropolishing. PMID:12489594

  14. High current density electropolishing in the preparation of highly smooth substrate tapes for coated conductors

    SciTech Connect

    Kreiskott, Sascha; Matias, Vladimir; Arendt, Paul N.; Foltyn, Stephen R.; Bronisz, Lawrence E.

    2009-03-31

    A continuous process of forming a highly smooth surface on a metallic tape by passing a metallic tape having an initial roughness through an acid bath contained within a polishing section of an electropolishing unit over a pre-selected period of time, and, passing a mean surface current density of at least 0.18 amperes per square centimeter through the metallic tape during the period of time the metallic tape is in the acid bath whereby the roughness of the metallic tape is reduced. Such a highly smooth metallic tape can serve as a base substrate in subsequent formation of a superconductive coated conductor.

  15. 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.

  16. 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.

  17. Site preference of ternary alloying additions to NiTi: Fe, Pt, Pd, Au, Al, Cu, Zr and Hf

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Noebe, Ronald D.; Mosca, Hugo O.

    2004-01-01

    Atomistic modeling of the site substitution behavior of Pd in NiTi (J. Alloys and Comp. (2004), in press) has been extended to examine the behavior of several other alloying additions, namely, Fe, Pt, Au, Al, Cu, Zr and Hf in this important shape memory alloy. It was found that all elements, to a varying degree, displayed absolute preference for available sites in the deficient sublattice. How- ever, the energetics of the different substitutional schemes, coupled with large scale simulations indicate that the general trend in all cases is for the ternary addition to want to form stronger ordered structures with Ti.

  18. Electro and Magneto-Electropolished Surface Micro-Patterning on Binary and Ternary Nitinol

    PubMed Central

    Munroe, Norman; McGoron, Anthony

    2012-01-01

    In this study, an Atomic Force Microscopy (AFM) roughness analysis was performed on non-commercial Nitinol alloys with Electropolished (EP) and Magneto-Electropolished (MEP) surface treatments and commercially available stents by measuring Root-Mean-Square (RMS), Average Roughness (Ra), and Surface Area (SA) values at various dimensional areas on the alloy surfaces, ranging from (800 × 800 nm) to (115 × 115μm), and (800 × 800 nm) to (40 × 40 μm) on the commercial stents. Results showed that NiTi-Ta 10 wt% with an EP surface treatment yielded the highest overall roughness, while the NiTi-Cu 10 wt% alloy had the lowest roughness when analyzed over (115 × 115 μm). Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis revealed unique surface morphologies for surface treated alloys, as well as an aggregation of ternary elements Cr and Cu at grain boundaries in MEP and EP surface treated alloys, and non-surface treated alloys. Such surface micro-patterning on ternary Nitinol alloys could increase cellular adhesion and accelerate surface endothelialization of endovascular stents, thus reducing the likelihood of in-stent restenosis and provide insight into hemodynamic flow regimes and the corrosion behavior of an implantable device influenced from such surface micro-patterns. PMID:22754200

  19. Use of electropolishing for enhanced metallic specimen preparation for electron backscatter diffraction analysis

    SciTech Connect

    Wynick, G.L.; Boehlert, C.J. . E-mail: boehlert@egr.msu.edu

    2005-09-15

    The effects of mechanical polishing with Al{sub 2}O{sub 3} and colloidal SiO{sub 2} followed by electropolishing were studied for preparation of metal alloy specimens for Electron Backscatter Diffraction (EBSD). The alloys studied were Inconel 718, a commonly used nickel-based superalloy, and a Ti-Al-Nb alloy (nominally Ti-22Al-28Nb(at.%)). Atomic Force Microscopy was used to measure the surface topography to attempt to correlate nano-scale surface roughness with EBSD pattern quality. The results suggest that mechanically polishing with Al{sub 2}O{sub 3} followed by electropolishing for a short time can produce EBSD pattern confidence indices and image quality values that are equal to or better than those produced by mechanically polishing with colloidal SiO{sub 2} alone. The data suggests that surface roughness on the scale considered here has much less effect on EBSD pattern quality than had been previously believed. The data suggests that removing the surface damage is more critical than reduction of topography for EBSD.

  20. Investigation on Crack Tip Transformation in NiTi Alloys: Effect of the Temperature

    NASA Astrophysics Data System (ADS)

    Sgambitterra, Emanuele; Maletta, Carmine; Furgiuele, Franco

    2015-06-01

    The effect of the temperature on crack tip transformation in Nickel-Titanium (NiTi) shape memory alloys was analyzed in this work by means of experimental and analytical approaches. In particular, single edge crack specimens were analyzed for two different values of the testing temperature in the pseudoelastic regime of the alloy, i.e., T = 298 K and T = 338 K. The thermal-dependent phase transition mechanisms occurring at the crack tip region were studied by analyzing data obtained from digital image correlation as well as by nanoindentation experiments performed near the crack tip. Finally, experimental results were compared with predictions of a recent analytical model. Results revealed that an increase in temperature causes a decrease of the phase transformation zone and that both the techniques are well suitable in capturing the thermal effect on the phase transformation mechanisms near the crack tip.

  1. Effects of surface finish and mechanical training on Ni-Ti sheets for elastocaloric cooling

    NASA Astrophysics Data System (ADS)

    Engelbrecht, Kurt; Tušek, Jaka; Sanna, Simone; Eriksen, Dan; Mishin, Oleg V.; Bahl, Christian R. H.; Pryds, Nini

    2016-06-01

    Elastocaloric cooling has emerged as a promising alternative to vapor compression in recent years. Although the technology has the potential to be more efficient than current technologies, there are many technical challenges that must be overcome to realize devices with high performance and acceptable durability. We study the effects of surface finish and training techniques on dog bone shaped polycrystalline samples of NiTi. The fatigue life of several samples with four different surface finishes was measured and it was shown that a smooth surface, especially at the edges, greatly improved fatigue life. The effects of training both on the structure of the materials and the thermal response to an applied strain was studied. The load profile for the first few cycles was shown to change the thermal response to strain, the structure of the material at failure while the final structure of the material was weakly influenced by the surface finish.

  2. Rheological study of feed stock for NiTi alloy molded parts

    NASA Astrophysics Data System (ADS)

    Subuki, I.; Abdullah, Z.; Razali, R.; Ismail, M. H.

    2015-12-01

    A rheological behaviour of the powder-binder mixture is one of essential analysis upon to success of Metal Injection Moulding (MIM) process. The purpose of this experimental work is to investigate the rheological behavior of feedstock containing mixtures of elemental Ni and Ti powders mixed with composite binder of palm stearin (PS) and polyethylene (PE) binder system. An equiatomic Ni-Ti (50-50) ratio was used in the present work for all formulations owing to excellent shape memory behaviour. The experimental rheological result indicated that all the feedstocks exhibited pseudo plastic flow behaviour; viscosity decreasing with temperature and shear rate. Increasing the powder loading resulted in higher viscosity, particularly at the low-range of shear rate. Owing to pseudo-plastic flow, it was found that the feedstock prepared exhibit promising rheological properties, thus resulting successfully injection moulding at an optimum temperature of 130°C.

  3. On the Mechanisms for Martensite Formation in YAG Laser Welded Austenitic NiTi

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Extensive work has been reported on the microstructure of laser-welded NiTi alloys either superelastic or with shape memory effect, motivated by the fact that the microstructure affects the functional properties. However, some effects of laser beam/material interaction with these alloys have not yet been discussed. This paper aims to discuss the mechanisms for the occurrence of martensite in the heat-affected zone and in the fusion zone at room temperature, while the base material is fully austenitic. For this purpose, synchrotron radiation was used together with a simple thermal analytic mathematical model. Two distinct mechanisms are proposed for the presence of martensite in different zones of a weld, which affects the mechanical and functional behavior of a welded component.

  4. Mechanical Behavior of a NiTi Endodontic File During Insertion in an Anatomic Root Canal Using Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Legrand, V.; Moyne, S.; Pino, L.; Arbab Chirani, S.; Calloch, S.; Chevalier, V.; Arbab Chirani, R.

    2015-12-01

    Superelastic NiTi shape memory alloys (SMA) have biomedical applications including rotary endodontic files. These alloys are used thanks to their flexibility, which is due to solid-solid martensitic transformation. Unfortunately, the intracanal file separation can occur during canal preparation. To avoid this problem and to have a good idea of the mechanical behavior of these instruments, finite elements simulations taking into account the real shape of root canals are proposed in this study. This is possible by using a well-adapted model describing all the particularities of SMA and representative limit conditions. The behavior model has been validated in previous studies under complex loadings. It is implemented in ABAQUS® finite elements software. The anatomic shapes of root canals are extracted by microtomography using a real tooth. They are applied as limit conditions in realized simulations to be as near as possible to clinical conditions. The mechanical behavior of an endodontic file is then simulated during insertion in a root canal without and with rotation. This permits to obtain different information like the loading applied to the instrument during its use, the stress, and the phase transformation fields through the file. This is useful not only for clinical use but also for new NiTi endodontic instruments design.

  5. Chemical analysis of nickel-titanium rotary instruments with and without electropolishing after cleaning procedures with sodium hypochlorite.

    PubMed

    Bonaccorso, Antonio; Schäfer, Edgar; Condorelli, Guglielmo Guido; Cantatore, Giuseppe; Tripi, Teresa Roberta

    2008-11-01

    The aim of this study was to chemically analyze rotary nickel-titanium instruments with and without electropolishing after cleaning procedures with NaOCl. To evaluate the effect of 5.25% NaOCl on electropolished RaCe instruments, a total of 18 instruments were tested. A control group of 18 nonelectropolished RaCe instruments was used. The surface of each instrument was analyzed before and after cleaning in NaOCl by using energy dispersive x-ray analysis, Auger electron spectroscopy, and scanning electron microscopy. Surface defects were recorded, and a chi(2) test was used for statistical analysis. After immersion in NaOCl, the nonelectropolished and electropolished files showed a significant increase of iron deposits as a result of galvanic corrosion of the shaft (P < .05). The nonelectropolished files showed marked presence of NaCl deposits in the machining marks and microcracks. As regards the chemical nature of the surface, the electropolished files had an oxide increase compared with the low oxide concentration (mainly TiO2) before cleaning. The nonelectropolished files already possessed higher oxides concentration (TiO2 and NiO) before NaOCl cleaning. NaOCl treatment affects the chemical composition of the surface and, in particular for nonelectropolished instruments, of the bulk exposed through machining marks and fabrication microcracks. PMID:18928855

  6. Field test and evaluation of electropolishing and preoxidation processes for Type-316 stainless steel nuclear-grade piping. Final report

    SciTech Connect

    Spalaris, C.N.; Wang, M.J.

    1985-03-01

    Pretreatment of BWR replacement recirculation piping by electropolishing or preoxidation greatly reduces radiation buildup. Now, examination of full-scale samples pretreated by both processes shows that neither treatment degrades the integrity of the pipe steel or lessens its resistance to stress corrosion cracking.

  7. Effect of Post Weld Heat Treatment on Mechanical and Corrosion Behaviors of NiTi and Stainless Steel Laser-Welded Wires

    NASA Astrophysics Data System (ADS)

    Mirshekari, G. R.; Saatchi, A.; Kermanpur, A.; Sadrnezhaad, S. K.

    2016-06-01

    Effects of post weld heat treatment (PWHT) on mechanical properties and corrosion behavior of NiTi shape memory wire, laser welded to the 304 stainless steel wire were investigated. The results showed that PWHT at 200 °C increased corrosion resistance and tensile strength of the joint up to ~1.8 times that of the as-weld joint, with no heat treatment. On the contrary, precipitation of neoteric intermetallic compounds like Fe2Ti, Cr2Ti, FeNi, Ni3Ti, and Ti2Ni in the welded region deteriorated these properties, when PWHT was conducted at 400 °C. Due to the vital effects of the PWHT performed after the laser welding, careful control of the PWHT temperature was found to be a prerequisite for achievement of desirable properties in the dissimilar NiTi-304 stainless steel laser-welded wires.

  8. Effect of Post Weld Heat Treatment on Mechanical and Corrosion Behaviors of NiTi and Stainless Steel Laser-Welded Wires

    NASA Astrophysics Data System (ADS)

    Mirshekari, G. R.; Saatchi, A.; Kermanpur, A.; Sadrnezhaad, S. K.

    2016-04-01

    Effects of post weld heat treatment (PWHT) on mechanical properties and corrosion behavior of NiTi shape memory wire, laser welded to the 304 stainless steel wire were investigated. The results showed that PWHT at 200 °C increased corrosion resistance and tensile strength of the joint up to ~1.8 times that of the as-weld joint, with no heat treatment. On the contrary, precipitation of neoteric intermetallic compounds like Fe2Ti, Cr2Ti, FeNi, Ni3Ti, and Ti2Ni in the welded region deteriorated these properties, when PWHT was conducted at 400 °C. Due to the vital effects of the PWHT performed after the laser welding, careful control of the PWHT temperature was found to be a prerequisite for achievement of desirable properties in the dissimilar NiTi-304 stainless steel laser-welded wires.

  9. Influence of Addition of Nb on Phase Transformation, Microstructure and Mechanical Properties of Equiatomic NiTi SMA

    NASA Astrophysics Data System (ADS)

    Jiang, Shuyong; Liang, Yulong; Zhang, Yanqiu; Zhao, Yanan; Zhao, Chengzhi

    2016-08-01

    Three novel NiTiNb shape memory alloys, which possess a nominal chemical composition of Ni50-x/2-Ti50-x/2-Nb x (at.%) where x stands for 2, 4 and 6, respectively, were designed in order to investigate the influence of the addition of Nb on phase transformation, microstructure and mechanical properties of equiatomic NiTi shape memory alloy. All the three NiTiNb shape memory alloys contain B2 austenite phase, B19' martensite phase and β-Nb precipitate phase. Martensite type II twin can be observed in the case of Ni49Ti49Nb2 alloy. In the case of Ni48Ti48Nb4 alloy, there exists a boundary between Ti2Ni precipitate phase and β-Nb precipitate phase. As for Ni47Ti47Nb6 alloy, it can be observed that there exists an orientation relationship of [01bar{1}]_{{β{{ - Nb}}}} //[01bar{1}]_{{B2}} between β-Nb precipitate phase and B2 austenite matrix. The increase in Nb content contributes to enhancing the yield stress of NiTiNb shape memory alloy, but it leads to the decrease in compression fracture stress. The addition of Nb to equiatomic NiTi shape memory alloy does not have a significant influence on the transformation hysteresis of the alloy, which is attributed to the fact that NiTiNb shape memory alloy is not subjected to plastic deformation and hence β-Nb precipitate phase is unable to relax the elastic strain in the martensite interface.

  10. Influence of Different Thermo-mechanical Cycling Routes on Recovery Stresses of Annealed NiTi Wires

    NASA Astrophysics Data System (ADS)

    Yan, X. J.; Ge, Y. L.; Van Humbeeck, J.

    2016-01-01

    In this study, the influence of different thermo-mechanical cycling routes on recovery stresses of annealed NiTi wires has been investigated by using a dynamic mechanical analyzer. The as-received wire was annealed in Argon atmosphere in the temperature range of 350 to 900 °C. Differential scanning calorimeter was used to study the martensite transformation. In route I, the sample is deformed to 2% pre-strain and recovery stress is measured after unloading. In route II, the sample undergoes 3% deformation followed by a free shape recovery and then is reloaded to 2% pre-strain and recovery stress is measured after unloading. In route III, the sample undergoes a constrained thermal cycling at 3% pre-strain followed by a free shape recovery and then recovery stress is measured at 2% pre-strain. The results show that both route II and III can improve the recovery stresses. Route III has higher recovery stresses than route II for samples annealed at 550-700 °C. The improvements of recovery stresses under route II and III are partly attributed to the decrease of A s temperatures after thermo-mechanical cycling. Such information is essential for the proper use of NiTi alloys in smart structures, intelligent controllers, and memory devices.

  11. Photo-induced ultrathin electropolishing layers on silicon: formation, composition and structural properties

    NASA Astrophysics Data System (ADS)

    Jungblut, H.; Lewerenz, H. J.

    2000-12-01

    The properties of electropolishing layers formed on illuminated n-Si(111) in dilute NH4F are analysed using a combined (photo) electrochemistry/UHV surface analysis system. Evaluation of thickness d and composition dependencies on potential U and pH shows increasing d at lower pH (d=25 Å at 3 V, pH 3) and for U>3 V at pH 4.9 (d=7 Å, U=5 V). Fluorides, oxyfluorides, hydroxides and oxides of Si are found in the films. The surprising observation that thicker films transmit higher currents is discussed. UP spectra (He II) reveal a valence band offset between Si and the oxidic layer of 5.2 eV.

  12. Exploiting new electrochemical understanding of niobium electropolishing for improved performance of SRF cavities for CEBAF

    SciTech Connect

    Reece, Charles E.; Tian, Hui

    2010-09-01

    Recent incorporation of analytic electrochemistry into the development of protocols for electropolishing niobium SRF cavities has yielded new insights for optimizing this process for consistent, high-performance results. Use of reference electrodes in the electrolyte, electrochemical impedance spectroscopy (EIS), rotating disk electrodes (RDE), and controlled sample temperatures has greatly clarified the process dynamics over the empirical understanding developed via years of practice. Minimizing RF losses at high operational gradients is very valuable for CW linacs. Jefferson Lab is applying these new insights to the low-loss 7-cell cavity design developed for the CEBAF 12 GeV Upgrade. Together with controlled cleaning and assembly techniques to guard against field-emission-causing particulates, the resulting process is yielding consistent cavity performance that exceeds project requirements. Cavity tests show BCS-limited Q well above 30 MV/m. Detailed process data, interpretation, and resulting rf performance data will be presented.

  13. Surface characterization of Nb samples electropolished together with real superconducting rf accelerator cavities

    DOE PAGESBeta

    Xin Zhao; Geng, Rong -Li; Tyagi, P. V.; Hayano, Hitoshi; Kato, Shigeki; Nishiwaki, Michiru; Saeki, Takayuki; Sawabe, Motoaki

    2010-12-30

    Here, we report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive X-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granulesmore » with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.« less

  14. In situ X-ray nanotomography of metal surfaces during electropolishing

    DOE PAGESBeta

    Nave, Maryana I.; Allen, Jason P.; Karen Chen-Wiegart, Yu-chen; Wang, Jun; Kalidindi, Surya R.; Kornev, Konstantin G.

    2015-10-15

    A low voltage electropolishing of metal wires is attractive for nanotechnology because it provides centimeter long and micrometer thick probes with the tip radius of tens of nanometers. Using X-ray nanotomography we studied morphological transformations of the surface of tungsten wires in a specially designed electrochemical cell where the wire is vertically submersed into the KOH electrolyte. We show that stability and uniformity of the probe span is supported by a porous shell growing at the surface of tungsten oxide and shielding the wire surface from flowing electrolyte. We discovered that the kinetics of shell growth at the triple line,more » where meniscus meets the wire, is very different from that of the bulk of electrolyte. Many metals follow similar electrochemical transformations hence the discovered morphological transformations of metal surfaces are expected to play significant role in many natural and technological applications.« less

  15. In situ X-ray nanotomography of metal surfaces during electropolishing

    NASA Astrophysics Data System (ADS)

    Nave, Maryana I.; Allen, Jason P.; Karen Chen-Wiegart, Yu-Chen; Wang, Jun; Kalidindi, Surya R.; Kornev, Konstantin G.

    2015-10-01

    A low voltage electropolishing of metal wires is attractive for nanotechnology because it provides centimeter long and micrometer thick probes with the tip radius of tens of nanometers. Using X-ray nanotomography we studied morphological transformations of the surface of tungsten wires in a specially designed electrochemical cell where the wire is vertically submersed into the KOH electrolyte. It is shown that stability and uniformity of the probe span is supported by a porous shell growing at the surface of tungsten oxide and shielding the wire surface from flowing electrolyte. It is discovered that the kinetics of shell growth at the triple line, where meniscus meets the wire, is very different from that of the bulk of electrolyte. Many metals follow similar electrochemical transformations hence the discovered morphological transformations of metal surfaces are expected to play significant role in many natural and technological applications.

  16. Simulation of nonlinear superconducting rf losses derived from characteristic topography of etched and electropolished niobium surfaces

    NASA Astrophysics Data System (ADS)

    Xu, Chen; Reece, Charles E.; Kelley, Michael J.

    2016-03-01

    A simplified numerical model has been developed to simulate nonlinear superconducting radiofrequency (SRF) losses on Nb surfaces. This study focuses exclusively on excessive surface resistance (Rs ) losses due to the microscopic topographical magnetic field enhancements. When the enhanced local surface magnetic field exceeds the superconducting critical transition magnetic field Hc , small volumes of surface material may become normal conducting and increase the effective surface resistance without inducing a quench. We seek to build an improved quantitative characterization of this qualitative model. Using topographic data from typical buffered chemical polish (BCP)- and electropolish (EP)-treated fine grain niobium, we have estimated the resulting field-dependent losses and extrapolated this model to the implications for cavity performance. The model predictions correspond well to the characteristic BCP versus EP high field Q0 performance differences for fine grain niobium. We describe the algorithm of the model, its limitations, and the effects of this nonlinear loss contribution on SRF cavity performance.

  17. Annealing to Mitigate Pitting in Electropolished Niobium Coupons and SRF Cavities

    SciTech Connect

    Cooley, L.D.; Hahn, E.; Hicks, D.; Romanenko, A.; Schuessler, R.; Thompson, C.; /Fermilab

    2011-06-08

    Ongoing studies at Fermilab investigate whether dislocations and other factors instigate pitting during cavity electropolishing (EP), despite careful processing controls and the inherent leveling mechanism of EP itself. Here, cold-worked niobium coupons, which exhibited increased tendencies for pitting in our past study, were annealed in a high vacuum furnace and subsequently processed by EP. Laser confocal scanning microscopy and special defect counting algorithms were used to assess the population of pits formed. Hardness measurements indicated that annealing for 2 hours at 800 C produced recovery, whereas annealing for 12 hours at 600 C did not, as is consistent with known changes for cavities annealed in a similar way. The 800 C anneal was effective in some cases but not others, and we discuss reasons why tendencies for pitting remain. We discuss implications for cavities and continued work to understand pitting.

  18. Surface characterization of Nb samples electropolished together with real superconducting rf accelerator cavities

    SciTech Connect

    Xin Zhao; Geng, Rong -Li; Tyagi, P. V.; Hayano, Hitoshi; Kato, Shigeki; Nishiwaki, Michiru; Saeki, Takayuki; Sawabe, Motoaki

    2010-12-30

    Here, we report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive X-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granules with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.

  19. In situ X-ray nanotomography of metal surfaces during electropolishing

    SciTech Connect

    Nave, Maryana I.; Allen, Jason P.; Karen Chen-Wiegart, Yu-chen; Wang, Jun; Kalidindi, Surya R.; Kornev, Konstantin G.

    2015-10-15

    A low voltage electropolishing of metal wires is attractive for nanotechnology because it provides centimeter long and micrometer thick probes with the tip radius of tens of nanometers. Using X-ray nanotomography we studied morphological transformations of the surface of tungsten wires in a specially designed electrochemical cell where the wire is vertically submersed into the KOH electrolyte. We show that stability and uniformity of the probe span is supported by a porous shell growing at the surface of tungsten oxide and shielding the wire surface from flowing electrolyte. We discovered that the kinetics of shell growth at the triple line, where meniscus meets the wire, is very different from that of the bulk of electrolyte. Many metals follow similar electrochemical transformations hence the discovered morphological transformations of metal surfaces are expected to play significant role in many natural and technological applications.

  20. In situ X-ray nanotomography of metal surfaces during electropolishing

    PubMed Central

    Nave, Maryana I.; Allen, Jason P.; Karen Chen-Wiegart, Yu-chen; Wang, Jun; Kalidindi, Surya R.; Kornev, Konstantin G.

    2015-01-01

    A low voltage electropolishing of metal wires is attractive for nanotechnology because it provides centimeter long and micrometer thick probes with the tip radius of tens of nanometers. Using X-ray nanotomography we studied morphological transformations of the surface of tungsten wires in a specially designed electrochemical cell where the wire is vertically submersed into the KOH electrolyte. It is shown that stability and uniformity of the probe span is supported by a porous shell growing at the surface of tungsten oxide and shielding the wire surface from flowing electrolyte. It is discovered that the kinetics of shell growth at the triple line, where meniscus meets the wire, is very different from that of the bulk of electrolyte. Many metals follow similar electrochemical transformations hence the discovered morphological transformations of metal surfaces are expected to play significant role in many natural and technological applications. PMID:26469184

  1. Surface Form Memory in NiTi: Energy Density of Constrained Recovery During Indent Replication

    NASA Astrophysics Data System (ADS)

    Fei, Xueling; O'Connell, Corey J.; Grummon, David S.; Cheng, Yang-Tse

    2009-08-01

    Spherical indentation of NiTi shape memory alloys (SMA) to depths greater than about 3% of the indenter radius results in two-way shape-memory training in a deformation zone beneath the indent. If deep spherical or cylindrical indents are subsequently machined away just sufficiently to remove traces of the original indent (in the martensitic condition), a thermally induced and cyclically reversible flat-to-protruded surface topography is enabled. We term the phenomenon surface form memory. The amplitude of cyclic protrusions, or ‘exdents’, is related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Dislocation generation in this zone is thought to underlie the observed two-way shape-memory (TWSME) training effect. In this article, we show that these cyclic exdents can perform appreciable mechanical work when displacing under load against a base-metal substrate (constrained recovery). This “non-Hertzian” indentation, which appears to be able to exert the full energy density of SMA actuation, may have use for assembly of micromachines, bond-release, microforging, microjoining, electrical switching, microconnectors, and variable heat transfer devices, among many other potential applications.

  2. The implantation of a Nickel-Titanium shape memory alloy ameliorates vertebral body compression fractures: a cadaveric study

    PubMed Central

    Chen, Bo; Zheng, Yue-Huang; Zheng, Tao; Sun, Chang-Hui; Lu, Jiong; Cao, Peng; Zhou, Jian-Hua

    2015-01-01

    Objective: To evaluate the effect of a Nickel-Titanium (Ni-Ti) shape memory alloy in the treatment of vertebral body compression fractures. Methods: The experimental thoracic-lumbar fracture units were made with adult human fresh-frozen vertebral specimens. A total of 30 fresh-frozen vertebral units were randomly assigned to 3 experimental groups: control group, percutaneous kyphoplasty group (PKP group), and percutaneous Ni-Ti shape memory alloys implant group (Ni-Ti implant group). Vertebral height and ultimate compression load of the vertebral body before and after procedures were measured to determine the restoration of vertebral heights and compressive strength, respectively. Results: The Ni-Ti implant group achieved a vertebrae endplate reduction effect comparable to the PKP group. The vertebral height of the PKP group was restored from 2.01±0.21 cm to 2.27±0.18 cm after procedure, whereas that of the Ni-Ti implant group was restored from 2.00±0.18 cm to 2.31±0.17 cm. The ultimate loads of the vertebrae body of the PKP and the Ni-Ti implant groups were 2880.75±126.17 N and 2888.00±144.69 N, respectively, both of which were statistically significantly higher than that of the control group (2017.17±163.71 N). There was no significant difference in ultimate compression load of vertebrae body between the Ni-Ti implant and PKP groups. Conclusions: The implantation of Ni-Ti shape memory alloys of vertebral body induced effective endplate reduction, restored vertebral height, and provided immediate biomechanical spinal stability. PMID:26629241

  3. NITI Needs Assessment Study. A Study of the Postsecondary Educational Needs of Merged Area I.

    ERIC Educational Resources Information Center

    Ratcliff, James L.

    The study described in this report was conducted to determine whether the present mix of vocational-technical and adult educational programs and services at Northeast Iowa Technical Institute (NITI) was optimal in meeting the needs of the constituents and clients of the college. Particular attention was given to the question of whether NITI would…

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

    NASA Astrophysics Data System (ADS)

    Zhang, Yijun

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

  5. Basic Electropolishing Process Research and Development in Support of Improved Reliable Performance SRF Cavities for the Future Accelerator

    SciTech Connect

    H. Tian, C.E. Reece,M.J. Kelley

    2009-05-01

    Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nanosmoothness. Electropolishing is the technique of choice to be developed for high-field superconducting radiofrequency cavities. Electrochemical impedance spectroscopy (EIS) and related techniques point to the electropolishing mechanism of Nb in a sulfuric and hydrofluoric acid electrolyte of controlled by a compact surface salt film under F- diffusion-limited mass transport control. These and other findings are currently guiding a systematic characterization to form the basis for cavity process optimization, such as flowrate, electrolyte composition and temperature. This integrated analysis is expected to provide optimum EP parameter sets for a controlled, reproducible and uniform surface leveling for Nb SRF cavities.

  6. A Study on Micro-Machining Technology for the Machining of NiTi: Five-Axis Micro-Milling and Micro Deep-Hole Drilling

    NASA Astrophysics Data System (ADS)

    Biermann, D.; Kahleyss, F.; Krebs, E.; Upmeier, T.

    2011-07-01

    Micro-sized applications are gaining more and more relevance for NiTi-based shape memory alloys (SMA). Different types of micro-machining offer unique possibilities for the manufacturing of NiTi components. The advantage of machining is the low thermal influence on the workpiece. This is important, because the phase transformation temperatures of NiTi SMAs can be changed and the components may need extensive post manufacturing. The article offers a simulation-based approach to optimize five-axis micro-milling processes with respect to the special material properties of NiTi SMA. Especially, the influence of the various tool inclination angles is considered for introducing an intelligent tool inclination optimization algorithm. Furthermore, aspects of micro deep-hole drilling of SMAs are discussed. Tools with diameters as small as 0.5 mm are used. The possible length-to-diameter ratio reaches up to 50. This process offers new possibilities in the manufacturing of microstents. The study concentrates on the influence of the cutting speed, the feed and the tool design on the tool wear and the quality of the drilled holes.

  7. Phase transformation studies in unirradiated and proton beam irradiated Ni-Ti alloy between 25 and 100°C

    NASA Astrophysics Data System (ADS)

    Ayub, Rana; Afzal, Naveed; Ahmad, R.

    2012-06-01

    The stress-induced phase transformation characteristics of unirradiated and proton beam irradiated NiTi alloy were investigated at different tests temperatures. The wire-shaped NiTi specimens were irradiated by 2 MeV proton beam for 30 min at room temperature to a flux of 1019 protons/m2 s. Engineering stress-strain (S-S) curves of both unirradiated and irradiated specimens were obtained using a materials testing machine at 25, 50, 75 and 100°C. The results indicate a single-stage phase transformation from austenite to martensite (B2-B19‧) in unirraidated specimens at all the test temperatures. In contrast, in the case of the irradiated specimens, a two-stage austenite-rhombohedral-martensite (B2-R-B19‧) phase transformation is observed at 25 and 50°C. The B2-R-B19‧ phase transformation, however, is found to change into B2-B19‧ transformation at 75 and 100°C. The stress required to initiate the B19‧ phase transformation (σMS) and the plateau range are found to be lower in irradiated specimens compared with those of the unirradiated specimens. The results obtained are discussed on the basis of the formation of Ni4Ti3 precipitates in irradiated specimens and their consequences on the phase transformations.

  8. Static and Cyclic Load-Deflection Characteristics of NiTi Orthodontic Archwires Using Modified Bending Tests

    NASA Astrophysics Data System (ADS)

    Nili Ahmadabadi, Mahmoud; Shahhoseini, Tahereh; Habibi-Parsa, Mohamad; Haj-Fathalian, Maryam; Hoseinzadeh-Nik, Tahereh; Ghadirian, Hananeh

    2009-08-01

    Near-equiatomic nickel-titanium (nitinol) has the ability to return to a former shape when subjected to an appropriate thermomechanical procedure. One of the most successful applications of nitinol is orthodontic archwire. One of the suitable characteristics of these wires is superelasticity, a phenomenon that allows better-tolerated loading conditions during clinical therapy. Superelastic nitinol wires deliver clinically desired light continuous force enabling effective tooth movement with minimal damage for periodontal tissues. In this research, a special three-point bending fixture was invented and designed to determine the superelastic property in simulated clinical conditions, where the wire samples were held in the fixture similar to an oral cavity. In this experimental study, the load-deflection characteristics of superelastic NiTi commercial wires were studied through three-point bending test. The superelastic behavior was investigated by focusing on bending time, temperature, and number of cycles which affects the energy dissipating capacity. Experimental results show that the NiTi archwires are well suited for cyclic load-unload dental applications. Results show reduction in superelastic property for used archwires after long-time static bending.

  9. Evolution of phase transformations after multiple steps of marforming in Ti-rich Ni-Ti SMA

    NASA Astrophysics Data System (ADS)

    Paula, A. S.; Mahesh, K. K.; Braz Fernandes, F. M.

    2008-05-01

    The phase transformations associated with Shape Memory Effect (SME) can be one step, B19' (martensite) ↔ B2 (austenite), or two/multiple steps which include the intermediate R phase, depending on the thermal and thermomechanical history of the alloy. The transformation temperatures are generally observed above room temperature in Ti-rich Ni-Ti alloys, while those observed in Ni-rich alloys occur below room temperature. The goal of the present work is to investigate the phase transformations evolution in Ti-Rich Ni-Ti SMA (Ni-51 at % Ti) when subjected to two distinct thermal treatments (500°C for 30 minutes in air and 800°C for 300 minutes in vacuum) and subsequently multiple steps of marforming thermomechanical treatments intercalated with thermal treatments (500°C for 30 minutes in air) and subsequent four distinct final thermal treatments (400, 450, 500 or 600°C for 30 minutes in air). Further, the stability of phase transformations in the initial ten thermal cycles of these thermomechanically treated samples is also studied. Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) were used to identify the transformation temperatures and the phases that are present after the thermomechanical treatments.

  10. Corrosion and wear properties of laser surface modified NiTi with Mo and ZrO 2

    NASA Astrophysics Data System (ADS)

    Ng, K. W.; Man, H. C.; Yue, T. M.

    2008-08-01

    Because of its biocompatibility, superelasticity and shape memory characteristics, NiTi alloys have been gaining immense interest in the medical field. However, there is still concern on the corrosion resistance of this alloy if it is going to be implanted in the human body for a long time. Titanium is not toxic but nickel is carcinogenic and is implicated in various reactions including allergic response and degeneration of muscle tissue. Debris from wear and the subsequent release of Ni + ions due to corrosion in the body system are fatal issues for long-term application of this alloy in the human body. This paper reports the corrosion and wear properties of laser surface modified NiTi using Mo and ZrO 2 as surface alloying elements, respectively. The modified layers which are free from microcracks and porosity, act as both physical barrier to nickel release and enhance the bulk properties, such as hardness, wear resistance, and corrosion resistance. The electrochemical performance of the surface modified alloy was studied in Hanks' solution. Electrochemical impedance spectroscopy was measured.

  11. Effect of intrinsic damping on vibration transmissibility of nickel-titanium shape memory alloy springs

    SciTech Connect

    Graesser, E.J.

    1995-11-01

    A research study was undertaken to measure the transmissibility of nickel-titanium (NI-Ti) shape memory alloy (SMA) springs and to compare the results to corresponding data on steel and IN-CONEL springs. It was motivated by interest in an effective metal alternative to rubber-based machinery isolation mounts, with possible active control features. Ni-Ti was used due to its well-known properties of shape memory and high intrinsic damping. Acceleration transmissibility was measured on a spring-mass system. Due to the distributed mass in the spring oils, standing waves occurred at high frequencies. However, due to the high intrinsic damping in Ni-Ti, the standing wave resonance peaks were as much as 20 dB lower than corresponding peaks in steel and INCONEL springs. Thus, the capability of Ni-Ti springs for high frequency acoustic isolation is significantly better than that of steel or INCONEL. Also, it is judged that the Ni-Ti material could be used in a variety of other isolation mount designs with a high likelihood for further improvement in passive isolation properties. In addition, it may be possible to use the shape memory effect (SME) in active control concepts.

  12. TEM studies of the nitrided Ni-Ti surface layer.

    PubMed

    Lelatko, J; Paczkowski, P; Wierzchoń, T; Morawiec, H

    2006-09-01

    The structure of surface layer, obtained on the nearly equiatomic Ni-Ti alloy after nitriding under glow discharge conditions at temperatures 700 or 800 degrees C, was investigated. The structural characterization of the intruded layer was performed on cross-sectional thin foils by the use of the transmission and scanning electron microscopes. The obtained results show that the nitrided layers consist mainly of the nanocrystalline TiN phase and small amount of Ti(2)N. Between the nitrided layers and beta-NiTi matrix an intermediate Ti(2)Ni phase layer was observed. PMID:17059538

  13. Influence of Electropolishing and Magnetoelectropolishing on Corrosion and Biocompatibility of Titanium Implants

    NASA Astrophysics Data System (ADS)

    Rahman, Zia ur; Pompa, Luis; Haider, Waseem

    2014-11-01

    Titanium alloys are playing a vital role in the field of biomaterials due to their excellent corrosion resistance and biocompatibility. These alloys enhance the quality and longevity of human life by replacing or treating various parts of the body. However, as these materials are in constant contact with the aggressive body fluids, corrosion of these alloys leads to metal ions release. These ions leach to the adjacent tissues and result in adverse biological reactions and mechanical failure of implant. Surface modifications are used to improve corrosion resistance and biological activity without changing their bulk properties. In this investigation, electropolishing and magnetoelectropolishing were carried out on commercially pure titanium, Ti6Al4V, and Ti6Al4V-ELI. These surface modifications are known to effect surface charge, chemistry, morphology; wettability, corrosion resistance, and biocompatibility of these materials. In vitro cyclic potentiodynamic polarization tests were conducted in phosphate buffer saline in compliance with ASTM standard F-2129-12. The surface morphology, roughness, and wettability of these alloys were studied using scanning electron microscope, atomic force microscope, and contact angle meter, respectively. Moreover, biocompatibility of titanium alloys was assessed by growing MC3T3 pre-osteoblast cells on them.

  14. Surface analyses of electropolished niobium samples for superconducting radio frequency cavity

    SciTech Connect

    Tyagi, P. V.; Nishiwaki, M.; Saeki, T.; Sawabe, M.; Hayano, H.; Noguchi, T.; Kato, S.

    2010-07-15

    The performance of superconducting radio frequency niobium cavities is sometimes limited by contaminations present on the cavity surface. In the recent years extensive research has been done to enhance the cavity performance by applying improved surface treatments such as mechanical grinding, electropolishing (EP), chemical polishing, tumbling, etc., followed by various rinsing methods such as ultrasonic pure water rinse, alcoholic rinse, high pressure water rinse, hydrogen per oxide rinse, etc. Although good cavity performance has been obtained lately by various post-EP cleaning methods, the detailed nature about the surface contaminants is still not fully characterized. Further efforts in this area are desired. Prior x-ray photoelectron spectroscopy (XPS) analyses of EPed niobium samples treated with fresh EP acid, demonstrated that the surfaces were covered mainly with the niobium oxide (Nb{sub 2}O{sub 5}) along with carbon, in addition a small quantity of sulfur and fluorine were also found in secondary ion mass spectroscopy (SIMS) analysis. In this article, the authors present the analyses of surface contaminations for a series of EPed niobium samples located at various positions of a single cell niobium cavity followed by ultrapure water rinsing as well as our endeavor to understand the aging effect of EP acid solution in terms of contaminations presence at the inner surface of the cavity with the help of surface analytical tools such as XPS, SIMS, and scanning electron microscope at KEK.

  15. Studies on the Electro-Polishing process with Nb sample plates at KEK

    SciTech Connect

    Saeki, Takayuki; Funahashi, Y.; Hayano, Hitoshi; Kato, Seigo; Nishiwaki, Michiru; Sawabe, Motoaki; Ueno, Kenji; Watanabe, K.; Clemens, William A.; Geng, Rongli; Manus, Robert L.; Tyagi, Puneet

    2009-11-01

    In this article, two subjects would be described. the first subject is on the production of stains on the surface of Nb sample plates in Electro-polishing (EP) process and the second subject is on the development of defects/pits in the EP process on the surface of a Nb sample plate. Recently, some 9-cell cavities were treated with new EP acid at KEK and the performance of these cavities were limited by heavy field emissions. On the inside surface of these cavities, brown stains were observed. We made an effort to reproduce the brown stains on Nb sample plates with an EP setup in laboratory with varying the concentration of Nibium in the EP acid. We found that the brown stains would appear only when processed with new EP acid. In the second subject, we made artificial pits on the surface of a Nb-sample plate and observed the development of the pits after each step of 30um-EP process where 120um was removed in total by the EP process. This article describes these series EP-tests with Nb sample plates at KEK.

  16. Launch Load Resistant Spacecraft Mechanism Bearings Made From NiTi Superelastic Intermetallic Materials

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Moore, Lewis E.

    2014-01-01

    Compared to conventional bearing materials (tool steel and ceramics), emerging Superelastic Intermetallic Materials (SIMs), such as 60NiTi, have significantly lower elastic modulus and enhanced strain capability. They are also immune to atmospheric corrosion (rusting). This offers the potential for increased resilience and superior ability to withstand static indentation load without damage. In this paper, the static load capacity of hardened 60NiTi 50mm bore ball-bearing races are measured to correlate existing flat-plate indentation load capacity data to an actual bearing geometry through the Hertz stress relations. The results confirmed the validity of using the Hertz stress relations to model 60NiTi contacts; 60NiTi exhibits a static stress capability (3.1GPa) between that of 440C (2.4GPa) and REX20 (3.8GPa) tool steel. When the reduced modulus and extended strain capability are taken into account, 60NiTi is shown to withstand higher loads than other bearing materials. To quantify this effect, a notional space mechanism, a 5kg mass reaction wheel, was modeled with respect to launch load capability when supported on 440C, 60NiTi and REX20 tool steel bearings. For this application, the use of REX20 bearings increased the static load capability of the mechanism by a factor of three while the use of 60NiTi bearings resulted in an order of magnitude improvement compared to the baseline 440C stainless steel bearings.

  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. Deformation attending internal nitridation of Ni-Ti alloys

    SciTech Connect

    Savva, G.C.; Weatherly, G.C.; Kirkaldy, J.S.

    1996-04-01

    Net volume increase attending precipitation is the source of a number of interesting deformation processes including creep and grain boundary sliding. Grain boundary sliding, a common high temperature deformation process, was observed in Ni-Al but was absent in Ni-Ti and Ag-In. It appears that in Ni-Ti, Ni is preferentially transported outwards along dislocation pipes and some twin boundaries countercurrent to a bulk stress driven vacancy flow (similar to the Nabarro-Herring creep attributed to Ni-Al). Some Ti may be preferentially transported outward by grain boundaries since at compositions near the transition to a superficial scale of TiN outward solute diffusion is significant. A strong element of Ni surface diffusion is involved in redistributing extruded Ni and producing facetted surface features. In respect to Ti diffusion towards the surface the authors have to record a distinction between the process and the classical Wagner models of frontal internal oxidation which applies to Ag-In and Ni-Al.

  19. Features of radiation damage of Ni-Ti alloy under exposure to heavy ions of gaseous elements

    NASA Astrophysics Data System (ADS)

    Poltavtseva, V. P.; Kislitsin, S. B.; Satpayev, D. A.; Mylnikova, T. S.; Chernyavskii, A. V.

    2015-04-01

    The consistent patterns of changes in structural and phase state, hardening and temperature ranges of martensitic transformations in Ni-Ti alloy with the shape memory effect after implantation of heavy ions 16O3+, 40Ar8+ and 84Kr15+ under comparable parameters have been experimentally studied. It is found that under the impact of 84Kr15+ ions, a two-layer surface structure with radiation-hardened second layer is formed, radiation-stimulated phase transformation B19'→B2 occurs in the near-surface layer and out-range area, and the martensitic transformation temperature increases toward higher values after implantation of 40Ar8+ and 84Kr15+ ions.

  20. The super-elastic Japanese NiTi alloy wire for use in orthodontics. Part III. Studies on the Japanese NiTi alloy coil springs.

    PubMed

    Miura, F; Mogi, M; Ohura, Y; Karibe, M

    1988-08-01

    Closed and open Japanese nickel titanium (NiTi) alloy coil springs were fabricated from the Japanese NiTi alloy wire. The closed coil springs were subjected to a tensile test and the open coil springs were subjected to a compression test to evaluate the mechanical properties. At the same time, a test with the commercially available steel coil springs also was done. It was clearly established that the Japanese NiTi alloy coil springs exhibited superior springback and super-elastic properties similar to the properties of the Japanese NiTi alloy arch wires. In addition, it was shown that the load value of super-elastic activity can be effectively controlled by changing the diameter of the wire, the size of lumen, the martensite transformation temperature, and the pitch of the open coil spring. The most important characteristic of the Japanese NiTi alloy coil springs is the ability to exert a very long range of constant light, continuous force. It is possible to use this coil selectively to obtain optimal tooth movement. PMID:3165245

  1. Design of two-way reversible bending actuator based on a shape memory alloy/shape memory polymer composite

    NASA Astrophysics Data System (ADS)

    Taya, Minoru; Liang, Yuanchang; Namli, Onur C.; Tamagawa, Hirohisa; Howie, Tucker

    2013-10-01

    The design of a reversible bending actuator based on a SMA/SMP composite is presented. The SMA/SMP composite is made of SMA NiTi wires with a bent ‘U’-shape in the austenite phase embedded in an epoxy SMP matrix which has a memorized flat shape. The bending motion is caused by heating the composite above TAf to activate the NiTi recovery. Upon cooling, the softening from the austenite to R-phase transformation results in a relaxation of the composite towards its original flat shape. In the three-point bending measurement the composite was able to exhibit a reversible deflection of 1.3 mm on a support with a 10 mm span. In addition, a material model for predicting the composite’s deflection is presented and predicts the experimental results reasonably well. The model also estimates the in-plane internal force and the degree of the SMA phase transformation.

  2. Fatigue of NiTi SMA–pulley system using Taguchi and ANOVA

    NASA Astrophysics Data System (ADS)

    Mohd Jani, Jaronie; Leary, Martin; Subic, Aleksandar

    2016-05-01

    Shape memory alloy (SMA) actuators can be integrated with a pulley system to provide mechanical advantage and to reduce packaging space; however, there appears to be no formal investigation of the effect of a pulley system on SMA structural or functional fatigue. In this work, cyclic testing was conducted on nickel–titanium (NiTi) SMA actuators on a pulley system and a control experiment (without pulley). Both structural and functional fatigues were monitored until fracture, or a maximum of 1E5 cycles were achieved for each experimental condition. The Taguchi method and analysis of the variance (ANOVA) were used to optimise the SMA–pulley system configurations. In general, one-way ANOVA at the 95% confidence level showed no significant difference between the structural or functional fatigue of SMA–pulley actuators and SMA actuators without pulley. Within the sample of SMA–pulley actuators, the effect of activation duration had the greatest significance for both structural and functional fatigue, and the pulley configuration (angle of wrap and sheave diameter) had a greater statistical significance than load magnitude for functional fatigue. This work identified that structural and functional fatigue performance of SMA–pulley systems is optimised by maximising sheave diameter and using an intermediate wrap-angle, with minimal load and activation duration. However, these parameters may not be compatible with commercial imperatives. A test was completed for a commercially optimal SMA–pulley configuration. This novel observation will be applicable to many areas of SMA–pulley system applications development.

  3. Simulating Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi

    NASA Technical Reports Server (NTRS)

    Manchiraju, Sivom; Gaydosh, Darrell J.; Noebe, Ronald D.; Anderson, Peter M.

    2011-01-01

    A microstructure-based FEM model that couples crystal plasticity, crystallographic descriptions of the B2-B19' martensitic phase transformation, and anisotropic elasticity is used to simulate thermal cycling and isothermal deformation in polycrystalline NiTi (49.9at% Ni). The model inputs include anisotropic elastic properties, polycrystalline texture, DSC data, and a subset of isothermal deformation and load-biased thermal cycling data. A key experimental trend is captured.namely, the transformation strain during thermal cycling is predicted to reach a peak with increasing bias stress, due to the onset of plasticity at larger bias stress. Plasticity induces internal stress that affects both thermal cycling and isothermal deformation responses. Affected thermal cycling features include hysteretic width, two-way shape memory effect, and evolution of texture with increasing bias stress. Affected isothermal deformation features include increased hardening during loading and retained martensite after unloading. These trends are not captured by microstructural models that lack plasticity, nor are they all captured in a robust manner by phenomenological approaches. Despite this advance in microstructural modeling, quantitative differences exist, such as underprediction of open loop strain during thermal cycling.

  4. Crystallization study of amorphous sputtered NiTi bi-layer thin film

    SciTech Connect

    Mohri, Maryam; Nili-Ahmadabadi, Mahmoud; Chakravadhanula, Venkata Sai Kiran

    2015-05-15

    The crystallization of Ni-rich/NiTiCu bi-layer thin film deposited by magnetron sputtering from two separate alloy targets was investigated. To achieve the shape memory effect, the NiTi thin films deposited at room temperature with amorphous structure were annealed at 773 K for 15, 30, and 60 min for crystallization. Characterization of the films was carried out by differential scanning calorimetry to indicate the crystallization temperature, grazing incidence X-ray diffraction to identify the phase structures, atomic force microscopy to evaluate surface morphology, scanning transmission electron microscopy to study the cross section of the thin films. The results show that the structure of the annealed thin films strongly depends on the temperature and time of the annealing. Crystalline grains nucleated first at the surface and then grew inward to form columnar grains. Furthermore, the crystallization behavior was markedly affected by composition variations. - Highlights: • A developed bi-layer Ni45TiCu5/Ni50.8Ti was deposited on Si substrate and crystallized. • During crystallization, The Ni{sub 45}TiCu{sub 5} layer is thermally less stable than the Ni-rich layer. • The activation energy is 302 and 464 kJ/mol for Cu-rich and Ni-rich layer in bi-layer, respectively.

  5. Influence of TiN coating on the biocompatibility of medical NiTi alloy.

    PubMed

    Jin, Shi; Zhang, Yang; Wang, Qiang; Zhang, Dan; Zhang, Song

    2013-01-01

    The biocompatibility of TiN coated nickel-titanium shape memory alloy (NiTi-SMA) was evaluated to compare with that of the uncoated NiTi-SMA. Based on the orthodontic clinical application, the surface properties and biocompatibility were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), wettability test, mechanical test and in vitro tests including MTT, cell apoptosis and cell adhesion tests. It was observed that the bonding between the substrate and TiN coating is excellent. The roughness and wettability increased as for the TiN coating compared with the uncoated NiTi-SMA. MTT test showed no significant difference between the coated and uncoated NiTi-SMA, however the percentage of early cell apoptosis was significantly higher as for the uncoated NiTi alloy. SEM results showed that TiN coating could enhance the cell attachment, spreading and proliferation on NiTi-SMA. The results indicated that TiN coating bonded with the substrate well and could lead to a better biocompatibility. PMID:23010039

  6. Sectioning of contaminated components for decontamination by vibratory finishing and electropolishing

    SciTech Connect

    Fetrow, L.K.; Allen, R.P.

    1981-09-01

    This report summarizes work conducted to develop, adapt, and evaluate a variety of techniques for sectioning glove boxes, chemical processing equipment, pipes, ducts, and other contaminated components in preparation for decontamination by vibratory finishing and electropolishing. These sectioning studies were conducted with a special 10-ft x 20-ft x 10-ft stainless-steel, walk-in glove box equipped for either hands-on operation via gloves and personnel entry, or remote operation using master slave manipulators and a bridge crane. Several sectioning techniques have been evaluated with respect to effectiveness, versatility, secondary waste generation, and capability for remote operation. The methods include wet and dry plasma arc torch cutting, mechanical sawing and nibbling, abrasive cutting, and hydraulic shearing and punching. The results of these comparison studies show that the plasma arc torch is a very rapid and effective metal cutting tool for size reduction applications. However, its use to prepare material for decontamination should be minimized because of problems with smoke generation, torch manipulation, waste generation, and entrainment of contamination. Mechanical saws eliminate all but the waste generation problem, but are very slow and labor intensive. Mechanical nibblers are fast and produce a waste form that can be decontaminated, but are limited with respect to the geometry and thickness of material that can be sectioned. High-speed abrasive saws provide high cutting rates, but produce nontreatable waste from the cut as well as from blade wear. Hydraulic shearing rapidly produces sectioned material in the small sizes required for decontamination by vibratory finishing. The kerf material also can be decontaminated. However, the glove box first must be sectioned into relatively narrow strips by one of the other techniques.

  7. Corrosion resistance of stressed NiTi and stainless steel orthodontic wires in acid artificial saliva.

    PubMed

    Huang, Her-Hsiung

    2003-09-15

    The purpose of this study was to investigate the corrosion resistance of stressed NiTi and stainless steel orthodontic wires using cyclic potentiodynamic and potentiostatic tests in acid artificial saliva at 37 degrees C. An atomic force microscope was used to measure the 3-D surface topography of as-received wires. Scanning electron microscope observations were carried out before and after the cyclic potentiodynamic tests. The surface chemical analysis was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy after the potentiostatic tests. The cyclic potentiodynamic test results showed that the pH had a significant influence on the corrosion parameters of the stressed NiTi and stainless steel wires (p < 0.05). The pitting potential, protection potential, and passive range of stressed NiTi and stainless steel wires decreased on decreasing pH, whereas the passive current density increased on decreasing pH. The load had no significant influence on the above corrosion parameters (p > 0.05). For all pH and load conditions, stainless steel wire showed higher pitting potential and wider passive range than NiTi wire (p < 0.001), whereas NiTi wire had lower passive current density than stainless steel wire (p < 0.001). The corrosion resistance of the stressed NiTi and stainless steel wires was related to the surface characterizations, including surface defect and passive film. PMID:12926035

  8. Characterization of PEG-Like Macromolecular Coatings on Plasma Modified NiTi Alloy

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Gao, Jiacheng; Chang, Peng; Wang, Jianhua

    2008-04-01

    A poly (ethylene glycol) (PEG-like) coating was developed to improve the biocompatibility of Nickel-Titanium (NiTi) alloy implants. The PEG-like macromolecular coatings were deposited on NiTi substrates at a room temperature of 298 K through a ECR (electron-cyclotron resonance) cold-plasma enhanced chemical vapor deposition method using tetraglyme (CH3-O-(CH2-CH2-O)4-CH3) as a precursor. A power supply with a frequency of 2.45 GHz was applied to ignite the plasma with Ar(argon) used as the carrier gas. Based on the atomic force microscopy (AFM) studies, a thin smooth coating on NiTi substrates with highly amorphous functional groups on the modified NiTi surfaces were mainly the same accumulated stoichiometric ratio of C and O with PEG. The vitro studies showed that platelet-rich plasma (PRP) adsorption on the modified NiTi alloy surface was significantly reduced. This study indicated that plasma surface modification changes the surface components of NiTi alloy and subsequently improves its biocompatibility.

  9. Effect of nano-hydroxyapatite reinforcement in mechanically alloyed NiTi composites for biomedical implant.

    PubMed

    Akmal, Muhammad; Raza, Ahmad; Khan, Muhammad Mudasser; Khan, M Imran; Hussain, Muhammad Asif

    2016-11-01

    Equi-atomic NiTi alloy composites reinforced with 0, 2, 4 and 6vol.% nano-hydroxyapatite (HA) were successfully synthesized using pressureless sintering. Pure Ni and Ti elements were ball milled for 10h in order to produce a mechanically alloyed equi-atomic NiTi alloy (MA-NiTi). Mechanically alloyed NiTi and HA powders were blended, compacted and then sintered for 3h at 1325K. The sintered density varied inversely with volume percent of HA reinforcement. The X-Ray diffraction spectra and SEM images showed the formation of multiple phases like NiTi, NiTi2, Ni3Ti, and Ni4Ti3. The back scattered-SEM image analysis confirmed the presence of Ni-rich and Ti-rich phases with increasing HA content. The 6vol.% HA reinforced composite showed Ni3Ti as the major phase having the highest hardness value which can be attributed to the presence of relatively harder phases along with higher HA content as a reinforcement. The composite of MA-NiTi with 2vol.% HA manifested the most desirable results in the form of better sintering density mainly due to the minute decomposition of NiTi into other phases. Therefore, the 2vol.% reinforced MA-NiTi composite can be exploited as a novel material for manufacturing biomedical implants. PMID:27523992

  10. Buffered Electropolishing – A New Way for Achieving Extremely Smooth Surface Finish on Nb SRF Cavities to be Used in Particle Accelerators

    SciTech Connect

    Hui Tian, Charles Reece, Michael Kelley

    2009-05-01

    Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nano-smoothness. Electropolishing (EP) is the technique of choice to be developed for high-field superconducting radio frequency (SRF) cavities. Electrochemical impedance spectroscopy (EIS) and related techniques point to the electropolishing mechanism of Nb in a sulphuric and hydrofluoric acid electrolyte controlled by a compact surface salt film under F- diffusion-limited mass transport control. These and other findings are guiding a systematic characterization to form the basis for cavities process optimization.

  11. Effect of Pore Size and Porosity on the Biomechanical Properties and Cytocompatibility of Porous NiTi Alloys

    PubMed Central

    Jian, Yu-Tao; Yang, Yue; Tian, Tian; Stanford, Clark; Zhang, Xin-Ping; Zhao, Ke

    2015-01-01

    Five types of porous Nickel-Titanium (NiTi) alloy samples of different porosities and pore sizes were fabricated. According to compressive and fracture strengths, three groups of porous NiTi alloy samples underwent further cytocompatibility experiments. Porous NiTi alloys exhibited a lower Young’s modulus (2.0 GPa ~ 0.8 GPa). Both compressive strength (108.8 MPa ~ 56.2 MPa) and fracture strength (64.6 MPa ~ 41.6 MPa) decreased gradually with increasing mean pore size (MPS). Cells grew and spread well on all porous NiTi alloy samples. Cells attached more strongly on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cell adhesion on porous NiTi alloys was correlated negatively to MPS (277.2 μm ~ 566.5 μm; p < 0.05). More cells proliferated on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cellular ALP activity on all porous NiTi alloy samples was higher than on control group and blank group (p < 0.05). The porous NiTi alloys with optimized pore size could be a potential orthopedic material. PMID:26047515

  12. 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

  13. Sulfuric acid-methanol electrolytes as an alternative to sulfuric-hydrofluoric acid mixtures for electropolishing of niobium

    SciTech Connect

    Zhao, Xin; Corcoran, Sean G.; Kelley, Michael J.

    2011-06-01

    Attainment of the greatest possible interior surface smoothness is critical to meeting the performance demands placed upon niobium superconducting radiofrequency (SRF) accelerator cavities by next generation projects. Electropolishing with HF-H{sub 2}SO{sub 4} electrolytes yields cavities that meet SRF performance goals, but a less-hazardous, more environmentally-friendly process is desirable. Reported studies of EP on chemically-similar tantalum describe the use of sulfuric acid-methanol electrolytes as an HF-free alternative. Reported here are the results of experiments on niobium samples with this electrolyte. Voltammetry experiments indicate a current plateau whose voltage range expands with increasing acid concentration and decreasing temperature. Impedance spectroscopy indicates that a compact salt film is responsible for the current plateau. Equivalent findings in electropolishing chemically-similar tantalum with this electrolyte were interpreted due to as mass transfer limitation by diffusion of Ta ions away from the anode surface. We infer that a similar mechanism is at work here. Conditions were found that yield leveling and brightening comparable to that obtained with HF-H{sub 2}SO{sub 4} mixtures.

  14. The influence of passivation and electropolishing on the performance of medical grade stainless steels in static and fatigue loading.

    PubMed

    Weldon, L M; McHugh, P E; Carroll, W; Costello, E; O'Bradaigh, C

    2005-02-01

    The effects of surface passivation and electropolishing on the mechanical performance of a group of biomedical grade stainless steels have been investigated. Surface roughness measurements showed that the treatments had a significant effect on the final surface finish. However, static mechanical testing demonstrated no difference in static mechanical properties, regardless of surface treatment. High cycle fatigue testing was carried out at a frequency of 120 Hz with a load ratio of R=0.1, in both air and a simulated in vivo wet corrosive environment. 316LVM (cold worked) proved superior to 316L (annealed) in fatigue performance, in both dry and wet environments. The fatigue performance of both materials did depend on the surface treatment, with electropolishing resulting in better performance than passivation. The fatigue performance of both materials was significantly better in the dry environment in comparison to the wet environment. The dry-to-wet deterioration in fatigue performance was somewhat dependent on the surface treatment for the 316L material but almost independent of surface treatment for the 316LVM material. Significant surface pitting and damage was evident for 316L during fatigue in the wet environment, whereas almost no pitting and damage was observed for 316LVM. PMID:15744598

  15. Microscopic Shape Memory and Superelastic Effects in Shape Memory Alloys and Thin Films Studied by Indentation Techniques

    NASA Astrophysics Data System (ADS)

    Ni, Wangyang; Cheng, Yang-Tse; Grummon, David S.

    2003-03-01

    Although shape memory alloys were discovered more than 50 years ago, there is a growing interest in shape memory thin films and coatings for applications ranging from MEMs to tribology. While the macroscopic shape memory (SM) and superelastic (SE) behavior of NiTi alloys are well known, very few studies have been conducted to investigate the SM and SE effects at the micro- and nano-meter length scales. In this presentation, instrumented indentation experiments with spherical, Vickers, and Berkovich indenters were used to study the mechanical behavior of NiTi alloys and thin films at the micro- and nano- meter scales. The indentation load-displacement curves for the shape memory and superelastic NiTi were obtained under a range of indentation conditions. The SM effect was quantified by the depth recovery ratio of the indents measured by a surface profilometer and atomic force microscope; the SE effect was determined by the ratio of reversible work to total work. We show that SM and SE effects exist under both spherical and pyramidal indenters for a wide range of indentation loads and depths. However, the magnitude of these effects depends strongly on indenter geometry. These observations were rationalized using the concept of representative strain and maximum strain under the spherical and pyramidal indenters. These studies provide new insights into the mechanisms of SM and SE effects at multiple length scales.

  16. Improvements of anti-corrosion and mechanical properties of NiTi orthopedic materials by acetylene, nitrogen and oxygen plasma immersion ion implantation

    NASA Astrophysics Data System (ADS)

    Poon, Ray W. Y.; Ho, Joan P. Y.; Liu, Xuanyong; Chung, C. Y.; Chu, Paul K.; Yeung, Kelvin W. K.; Lu, William W.; Cheung, Kenneth M. C.

    2005-08-01

    Nickel-titanium shape memory alloys (NiTi) are useful materials in orthopedics and orthodontics due to their unique super-elasticity and shape memory effects. However, the problem associated with the release of harmful Ni ions to human tissues and fluids has been raising safety concern. Hence, it is necessary to produce a surface barrier to impede the out-diffusion of Ni ions from the materials. We have conducted acetylene, nitrogen and oxygen plasma immersion ion implantation (PIII) into NiTi alloys in an attempt to improve the surface properties. All the implanted and annealed samples surfaces exhibit outstanding corrosion and Ni out-diffusion resistance. Besides, the implanted layers are mechanically stronger than the substrate underneath. XPS analyses disclose that the layer formed by C2H2 PIII is composed of mainly TiCx with increasing Ti to C concentration ratios towards the bulk. The nitrogen PIII layer is observed to be TiN, whereas the oxygen PIII layer is composed of oxides of Ti4+, Ti3+ and Ti2+.

  17. Launch Load Resistant Spacecraft Mechanism Bearings Made From NiTi Superelastic Intermetallic Materials

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Moore, Lewis E., III

    2014-01-01

    Compared to conventional bearing materials (tool steel and ceramics), emerging Superelastic Intermetallic Materials (SIMs), such as 60NiTi, have significantly lower elastic modulus and enhanced strain capability. They are also immune to atmospheric corrosion (rusting). This offers the potential for increased resilience and superior ability to withstand static indentation load without damage. In this paper, the static load capacity of hardened 60NiTi 50-mm-bore ball bearing races are measured to correlate existing flat-plate indentation load capacity data to an actual bearing geometry through the Hertz stress relations. The results confirmed the validity of using the Hertz stress relations to model 60NiTi contacts; 60NiTi exhibits a static stress capability (approximately 3.1 GPa) between that of 440C (2.4 GPa) and REX20 (3.8 GPa) tool steel. When the reduced modulus and extended strain capability are taken into account, 60NiTi is shown to withstand higher loads than other bearing materials. To quantify this effect, a notional space mechanism, a 5-kg mass reaction wheel, was modeled with respect to launch load capability when supported on standard (catalogue geometry) design 440C; 60NiTi and REX20 tool steel bearings. For this application, the use of REX20 bearings increased the static load capability of the mechanism by a factor of three while the use of 60NiTi bearings resulted in an order of magnitude improvement compared to the baseline 440C stainless steel bearings

  18. 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.

  19. Electropolishing of Re-melted SLM Stainless Steel 316L Parts Using Deep Eutectic Solvents: 3 × 3 Full Factorial Design

    NASA Astrophysics Data System (ADS)

    Alrbaey, K.; Wimpenny, D. I.; Al-Barzinjy, A. A.; Moroz, A.

    2016-07-01

    This three-level three-factor full factorial study describes the effects of electropolishing using deep eutectic solvents on the surface roughness of re-melted 316L stainless steel samples produced by the selective laser melting (SLM) powder bed fusion additive manufacturing method. An improvement in the surface finish of re-melted stainless steel 316L parts was achieved by optimizing the processing parameters for a relatively environmentally friendly (`green') electropolishing process using a Choline Chloride ionic electrolyte. The results show that further improvement of the response value-average surface roughness ( Ra) can be obtained by electropolishing after re-melting to yield a 75% improvement compared to the as-built Ra. The best Ra value was less than 0.5 μm, obtained with a potential of 4 V, maintained for 30 min at 40 °C. Electropolishing has been shown to be effective at removing the residual oxide film formed during the re-melting process. The material dissolution during the process is not homogenous and is directed preferentially toward the iron and nickel, leaving the surface rich in chromium with potentially enhanced properties. The re-melted and polished surface of the samples gave an approximately 20% improvement in fatigue life at low stresses (approximately 570 MPa). The results of the study demonstrate that a combination of re-melting and electropolishing provides a flexible method for surface texture improvement which is capable of delivering a significant improvement in surface finish while holding the dimensional accuracy of parts within an acceptable range.

  20. Electropolishing of Re-melted SLM Stainless Steel 316L Parts Using Deep Eutectic Solvents: 3 × 3 Full Factorial Design

    NASA Astrophysics Data System (ADS)

    Alrbaey, K.; Wimpenny, D. I.; Al-Barzinjy, A. A.; Moroz, A.

    2016-05-01

    This three-level three-factor full factorial study describes the effects of electropolishing using deep eutectic solvents on the surface roughness of re-melted 316L stainless steel samples produced by the selective laser melting (SLM) powder bed fusion additive manufacturing method. An improvement in the surface finish of re-melted stainless steel 316L parts was achieved by optimizing the processing parameters for a relatively environmentally friendly (`green') electropolishing process using a Choline Chloride ionic electrolyte. The results show that further improvement of the response value-average surface roughness (Ra) can be obtained by electropolishing after re-melting to yield a 75% improvement compared to the as-built Ra. The best Ra value was less than 0.5 μm, obtained with a potential of 4 V, maintained for 30 min at 40 °C. Electropolishing has been shown to be effective at removing the residual oxide film formed during the re-melting process. The material dissolution during the process is not homogenous and is directed preferentially toward the iron and nickel, leaving the surface rich in chromium with potentially enhanced properties. The re-melted and polished surface of the samples gave an approximately 20% improvement in fatigue life at low stresses (approximately 570 MPa). The results of the study demonstrate that a combination of re-melting and electropolishing provides a flexible method for surface texture improvement which is capable of delivering a significant improvement in surface finish while holding the dimensional accuracy of parts within an acceptable range.

  1. Monitoring Tensile Fatigue of Superelastic NiTi Wire in Liquids by Electrochemical Potential

    NASA Astrophysics Data System (ADS)

    Racek, Jan; Stora, Marc; Šittner, Petr; Heller, Luděk; Kopeček, Jaromir; Petrenec, Martin

    2015-06-01

    Fatigue of superelastic NiTi wires was investigated by cyclic tension in simulated biofluid. The state of the surface of the fatigued NiTi wire was monitored by following the evolution of the electrochemical open circuit potential (OCP) together with macroscopic stresses and strains. The ceramic TiO2 oxide layer on the NiTi wire surface cannot withstand the large transformation strain and fractures in the first cycle. Based on the analysis of the results of in situ OCP experiments and SEM observation of cracks, it is claimed that the cycled wire surface develops mechanochemical reactions at the NiTi/liquid interface leading to cumulative generation of hydrogen, uptake of the hydrogen by the NiTi matrix, local loss of the matrix strength, crack transfer into the NiTi matrix, accelerated crack growth, and ultimately to the brittle fracture of the wire. Fatigue degradation is thus claimed to originate from the mechanochemical processes occurring at the excessively deforming surface not from the accumulation of defects due to energy dissipative bulk deformation processes. Ironically, combination of the two exciting properties of NiTi—superelasticity due to martensitic transformation and biocompatibility due to the protective TiO2 surface oxide layer—leads to excessive fatigue damage during cyclic mechanical loading in biofluids.

  2. Biocompatibility of the micro-patterned NiTi surface produced by femtosecond laser

    NASA Astrophysics Data System (ADS)

    Liang, Chunyong; Wang, Hongshui; Yang, Jianjun; Li, Baoe; Yang, Yang; Li, Haipeng

    2012-11-01

    Biocompatibility of the micro-patterned NiTi surface produced by femtosecond laser (FSL) was studied in this work. The surface characteristics of the laser treated NiTi alloys were investigated by scanning electron microscopy (SEM), atom force microscopy (AFM), X-ray diffractometry (XRD) and X-ray photoelectron spectrum (XPS). The biocompatibility was evaluated by in vitro cell culture test. The results showed that, grooves, ripples, which covered by nanoparticles were formed on the sample surfaces, and the Ni/Ti ratio on the alloy surface increased with increasing laser energy. The crystal structure was not changed by laser treatment. However, the cell culture test proved that the micro-patterns induced by FSL were beneficial to improve the biocompatibility of NiTi alloys: the growth of osteoblasts oriented along the grooves, a large amount of synapses and filopodias were formed due to the ripples, holes and nanoparticles on the alloy surface, and the proliferation rate and alkaline phosphatase (ALP) content of cells were increased after FSL treatment. However, due to the toxicity of Ni ions on cell growth, the NiTi alloy surface should not be treated by laser fluence of more than 3.82 J/cm2 to obtain the ideal biocompatibility.

  3. Effect of temperature on the orthodontic clinical applications of niti closed-coil springs

    PubMed Central

    Espinar-Escalona, Eduardo; Llamas-Carreras, José M.; Barrera-Mora, José M.; Abalos-Lasbrucci, Camilo

    2013-01-01

    NiTi spring coils were used to obtain large deformation under a constant force. The device consists on a NiTi coil spring, superelastic at body temperature, in order to have a stress plateau during the austenitic retransformation during the unloading. The temperature variations induced changes in the spring force. Objectives: The aim of this study is to investigate the effect of the temperature variations in the spring forces and corrosion behaviour simulating the ingestion hot/cold drinks and food. Study Design: The springs were subjected to a tensile force using universal testing machine MTS-Adamel (100 N load cell). All tests were performed in artificial saliva maintained at different temperatures. The corrosion tests were performed according to the ISO-standard 10993-15:2000. Results: The increase in temperature of 18oC induced an increase in the spring force of 30%. However, when the temperature returns to 37oC the distraction force recovers near the initial level. After cooling down the spring to 15oC, the force decreased by 46%. This investigation show as the temperature increase, the corrosion potential shifts towards negative values and the corrosion density is rising. Conclusions: The changes of the temperatures do not modify the superelastic behaviour of the NiTi closed-coil springs. The corrosion potential of NiTi in artificial saliva is decreasing by the rise of the temperatures. Key words:Superelasticity, NiTi, springs, orthodontic, coils, recovery, temperature. PMID:23722142

  4. In vitro surface corrosion of stainless steel and NiTi orthodontic appliances.

    PubMed

    Shin, Ji-Soo; Oh, Keun-Taek; Hwang, Chung-Ju

    2003-04-01

    Simulated fixed orthodontic appliances were constructed, immersed and incubated in artificial saliva for periods up to three months. Two types of stainless steel archwires and two types of NiTi wires were used. The surface corrosion of the archwires was determined macroscopically, with scanning electron microscopy, and with spectrophotometry. The deposits on the wires were identified with X-ray diffraction. Uniform corrosion was observed on stainless steel wires, and a slight colour change was detected on the NiTi wires beneath stainless steel ligatures. The corrosion product on the stainless steel wires increased with immersion time, and the surface oxide films were easily detached from the underlying matrix. Crevice corrosion was observed under deposits of oxide, and at the interface between bracket and band. Such corrosion may weaken a wire or weld leading to fracture. In contrast, the NiTi archwires did not corrode, and there was no significant difference in surface morphology. The stainless steel archwires showed a significant loss of reflectance after heat treatment and immersion in artificial saliva. The NiTi archwires had the same reflectance before and after the immersion test. NiTi archwires are significantly more stable and resistant to corrosion than stainless steel archwires. PMID:12790351

  5. Comparison of apical microleakage using Ni-Ti with stainless steel finger spreaders

    PubMed Central

    Shahi, Shahriar; Shakouie, Sahar; Rahimi, Saeed; Yavari, Hamid Reza; Mohammadi, Narmin; Abdolrahimi, Majid

    2009-01-01

    INTRODUCTION: The purpose of this in vitro study was to compare apical microleakage after obturation with Nickel-Titanium (NiTi) compared to Stainless Steel (SS) finger spreaders. MATERIALS AND METHODS: Eighty straight single-rooted human teeth were instrumented using step-back technique. The specimens were randomly divided into four groups. The two experimental groups (n=30) and the negative control group (n=10) were obturated by lateral condensation technique with Ariadent gutta-percha and AH26 sealer. The roots in the positive control group (n=10) were instrumented but not obturated. In one group, SS and in another group NiTi spreaders were used. Microleakage evaluation was conducted using dye penetration method t-test was used for statistical analysis. RESULTS: The results showed statistically significant differences between NiTi and SS groups (P=0.022), with the greatest dye penetration in SS group and the least in NiTi group. CONCLUSION: According to the results of the present study using NiTi spreader decrease apical microleakage in endodontically treated teeth. [Iranian Endodontic Journal 2009;4(4):149-51] PMID:24019837

  6. Electrophoretic deposition of double-layer HA/Al composite coating on NiTi.

    PubMed

    Karimi, Esmaeil; Khalil-Allafi, Jafar; Khalili, Vida

    2016-01-01

    In order to improve the bioactivity of NiTi alloys, which are being known as the suitable materials for biomedical applications, numerous NiTi disks were electrophoretically coated by hetero-coagulated hydroxyapatite/aluminum composite coatings in three main voltages from suspensions with different Al concentrations. In this paper, the amount of Ni ions release and bioactivity of prepared samples as well as bonding strength of the coating to substrate were investigated. The surface characterization of the coating by XRD, EDX, SEM, and FTIR showed that HA particles bonded by Al particles. It caused the formation of a free crack coating on NiTi disks. Moreover, the bonding strength of HA/Al coatings to NiTi substrate were improved by two times as compared to that of the pure HA coatings. Immersing of coated samples in SBF for 1 week showed that apatite formation ability was improved on HA/Al composite coating and Ni ions release from the surface of composite coating decreased. These results induce the appropriate bioactivity and biocompatibility of the deposited HA/Al composite coatings on NiTi disks. PMID:26478383

  7. Improved endothelialization of NiTi alloy by VEGF functionalized nanocoating.

    PubMed

    Shen, Weixing; Cai, Kaiyong; Yang, Zaixiang; Yan, Ying; Yang, Weihu; Liu, Peng

    2012-06-01

    To improve surface endothelialization of NiTi alloy substrate, a nano-structured coating functionalized with vascular endothelial growth factor (VEGF) was fabricated via polydopamine (PDOP) as intermediate layer. The successful preparation of VEGF conjugated nanocoating was demonstrated by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), respectively. Inductively coupled plasma mass spectrometry (ICP-MS) test showed that the formed nanocoating significantly reduced the release of Ni ion from NiTi alloy in simulated body fluid. The biological behaviors of endothelial cells adhered to modified NiTi alloy substrates, including cell proliferation, cell spreading and production of nitric oxide and prostacyclin were investigated in vitro. The results suggest that surface functionalization of NiTi alloy substrate with VEGF is beneficial for cell growth. The approach presented here affords an alternative for surface modification of NiTi implants applied as heart and vascular implant devices. PMID:22387019

  8. Two-spring model for active compression textiles with integrated NiTi coil actuators

    NASA Astrophysics Data System (ADS)

    Holschuh, B.; Newman, D.

    2015-03-01

    This paper describes the development and implementation of a two-spring model to predict the performance of hybrid compression textiles combining passive elastic fabrics and integrated NiTi shape memory alloy (SMA) coil actuators. An analytic model that treats passive fabric-SMA coil systems as conjoined linear springs is presented to predict garment passive and active counter-pressure as a function of 11 design variables. For a fixed SMA coil design (encompassing five design variables), the model predicts that passive fabric material modulus, initial length, width and thickness determine both passive counter-pressure magnitude and activation stroke length, and that passive and active pressures are highly dependent on the relative unstretched lengths of the conjoined SMA-fabric system compared to the total limb circumference. Several passive fabrics were tested to determine their moduli and to generally assess the fabric linearity model assumption: two fabrics (spandex and neoprene) were found to behave linearly up to 200% strain, while two other fabrics (flat polyester elastic and a tri-laminate Lycra) were found to be nonlinear in the same strain envelope. Five hypothetical compression tourniquet designs are presented using experimentally determined fabric characteristics and previously studied SMA actuators developed at MIT. The performance of each tourniquet design is discussed with a specific focus on mechanical counter-pressure (MCP) space suit design requirements, with designs presented that achieve the full MCP design specification (\\gt 29.6 kPa) while minimizing (\\lt 5 mm) garment thickness. The modeling framework developed in this effort enables compression garment designers to tailor counter-pressure and activation stroke properties of active compression garments based on a variety of design parameters to meet a wide range of performance specifications.

  9. Effect of Electropolishing and Low-Temperature Baking on the Superconducting Properties of Large-Grain Niobium

    SciTech Connect

    A. S. Dhavale, G. Ciovati, G. R. Myneni

    2011-03-01

    Measurements of superconducting properties such as bulk and surface critical fields and thermal conductivity have been carried out in the temperature range from 2 K to 8 K on large-grain samples of different purity and on a high-purity fine-grain sample, for comparison. The samples were treated by electropolishing and low temperature baking (120° C, 48 h). While the residual resistivity ratio changed by a factor of ~3 among the samples, no significant variation was found in their superconducting properties. The onset field for flux penetration at 2 K, Hffp, measured within a ~30 µm depth from the surface, was ~160 mT, close to the bulk value. The baking effect was mainly to increase the field range up to which a coherent superconducting phase persists on the surface, above the upper critical field.

  10. Surface Characterization of Nb Samples Electro-polished Together With Real Superconducting Radio-frequency Accelerator Cavities

    DOE PAGESBeta

    Xin Zhao; Geng, Rongli; Tyagi, P. V.; Hayano, Hitoshi; Kato, Shigeki; Nishiwaki, Michiru; Saeki, Takayuki; Sawabe, Motoaki

    2010-12-01

    We report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive X-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granules withmore » a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.« less

  11. Efficacy and safety of a NiTi CAR 27 compression ring for end-to-end anastomosis compared with conventional staplers: A real-world analysis in Chinese colorectal cancer patients

    PubMed Central

    Lu, Zhenhai; Peng, Jianhong; Li, Cong; Wang, Fulong; Jiang, Wu; Fan, Wenhua; Lin, Junzhong; Wu, Xiaojun; Wan, Desen; Pan, Zhizhong

    2016-01-01

    OBJECTIVES: This study aimed to evaluate the safety and efficacy of a new nickel-titanium shape memory alloy compression anastomosis ring, NiTi CAR 27, in constructing an anastomosis for colorectal cancer resection compared with conventional staples. METHODS: In total, 234 consecutive patients diagnosed with colorectal cancer receiving sigmoidectomy and anterior resection for end-to-end anastomosis from May 2010 to June 2012 were retrospectively analyzed. The postoperative clinical parameters, postoperative complications and 3-year overall survival in 77 patients using a NiTi CAR 27 compression ring (CAR group) and 157 patients with conventional circular staplers (STA group) were compared. RESULTS: There were no statistically significant differences between the patients in the two groups in terms of general demographics and tumor features. A clinically apparent anastomotic leak occurred in 2 patients (2.6%) in the CAR group and in 5 patients (3.2%) in the STA group (p=0.804). These eight patients received a temporary diverting ileostomy. One patient (1.3%) in the CAR group was diagnosed with anastomotic stricture through an electronic colonoscopy after 3 months postoperatively. The incidence of postoperative intestinal obstruction was comparable between the two groups (p=0.192). With a median follow-up duration of 39.6 months, the 3-year overall survival rate was 83.1% in the CAR group and 89.0% in the STA group (p=0.152). CONCLUSIONS: NiTi CAR 27 is safe and effective for colorectal end-to-end anastomosis. Its use is equivalent to that of the conventional circular staplers. This study suggests that NiTi CAR 27 may be a beneficial alternative in colorectal anastomosis in Chinese colorectal cancer patients. PMID:27276395

  12. Degradation and fracture of Ni-Ti superelastic wire in an oral cavity.

    PubMed

    Yokoyama, K; Hamada, K; Moriyama, K; Asaoka, K

    2001-08-01

    Superelastic Ni-Ti wire is widely used in orthodontic clinics, but delayed fracture in the oral cavity has been observed. Because hydrogen embrittlement is known to cause damage to Ti alloy systems, orthodontic wires were charged with hydrogen using an electro-chemical system in saline. Tensile tests were carried out, and fracture surfaces were observed after hydrogen charging. The strength of the Co-Cr alloy and stainless steel used in orthodontic treatment, was not affected by the hydrogen charging. However, Ni-Ti wire showed significant decreases in strength. The critical stress of martensite transformation was increased with increasing hydrogen charging, and the alloy was embrittled. The fractured surface of the alloys with severe hydrogen charging exhibited dimple patterns similar to those in the alloys from patients. In view of the galvanic current in the mouth, the fracture of the Ni-Ti alloys might be attributed to the degradation of the mechanical properties due to hydrogen absorption. PMID:11456065

  13. Molecular dynamics study of the melting curve of NiTi alloy under pressure

    NASA Astrophysics Data System (ADS)

    Zeng, Zhao-Yi; Hu, Cui-E.; Cai, Ling-Cang; Chen, Xiang-Rong; Jing, Fu-Qian

    2011-02-01

    The melting curve of NiTi alloy was predicted by using molecular dynamics simulations combining with the embedded atom model potential. The calculated thermal equation of state consists well with our previous results obtained from quasiharmonic Debye approximation. Fitting the well-known Simon form to our Tm data yields the melting curves for NiTi: 1850(1 + P/21.938)0.328 (for one-phase method) and 1575(1 + P/7.476)0.305 (for two-phase method). The two-phase simulations can effectively eliminate the superheating in one-phase simulations. At 1 bar, the melting temperature of NiTi is 1575 ± 25 K and the corresponding melting slope is 64 K/GPa.

  14. Development and application of a Ni-Ti interatomic potential with high predictive accuracy of the martensitic phase transition

    NASA Astrophysics Data System (ADS)

    Ko, Won-Seok; Grabowski, Blazej; Neugebauer, Jörg

    2015-10-01

    Phase transitions in nickel-titanium shape-memory alloys are investigated by means of atomistic simulations. A second nearest-neighbor modified embedded-atom method interatomic potential for the binary nickel-titanium system is determined by improving the unary descriptions of pure nickel and pure titanium, especially regarding the physical properties at finite temperatures. The resulting potential reproduces accurately the hexagonal-close-packed to body-centered-cubic phase transition in Ti and the martensitic B 2 -B 19' transformation in equiatomic NiTi. Subsequent large-scale molecular-dynamics simulations validate that the developed potential can be successfully applied for studies on temperature- and stress-induced martensitic phase transitions related to core applications of shape-memory alloys. A simulation of the temperature-induced phase transition provides insights into the effect of sizes and constraints on the formation of nanotwinned martensite structures with multiple domains. A simulation of the stress-induced phase transition of a nanosized pillar indicates a full recovery of the initial structure after the loading and unloading processes, illustrating a superelastic behavior of the target system.

  15. Crack-closing of cement mortar beams using NiTi cold-drawn SMA short fibers

    NASA Astrophysics Data System (ADS)

    Choi, Eunsoo; Kim, Dong Joo; Chung, Young-Soo; Kim, Hee Sun; Jung, Chungsung

    2015-01-01

    In this study, crack-closing tests of mortar beams reinforced by shape memory alloy (SMA) short fibers were performed. For this purpose, NiTi SMA fibers with a diameter of 0.965 mm and a length of 30 mm were made from SMA wires of 1.0 mm diameter by cold drawing. Four types of SMA fibers were prepared, namely, straight and dog-bone-shaped fiber and the two types of fibers with paper wrapping in the middle of the fibers. The paper provides an unbonded length of 15 mm. For bending tests, six types of mortar beams with the dimensions of 40 mm × 40 mm × 160 mm (B×H×L) were prepared. The SMA fibers were placed at the bottom center of the beams along with an artificial crack of 10 mm depth and 1 mm thickness. This study investigated the influence of SMA fibers on the flexural strength of the beams from the measured force- deflection curves. After cracking, the beams were heated at the bottom by fire to activate the SMA fibers. Then, the beams recovered the deflection, and the cracks were closed. This study evaluated crack-closing capacity using the degree of crack recovery and deflection-recovery factor. The first factor is estimated from the crack-width before and after crack-closing, and the second one is obtained from the downward deflection due to loading and the upward deflection due to the closing force of the SMA fibers.

  16. Prestressing effect of cold-drawn short NiTi SMA fibres in steel reinforced mortar beams

    NASA Astrophysics Data System (ADS)

    Choi, Eunsoo; Kim, Dong Joo; Hwang, Jin-Ha; Kim, Woo Jin

    2016-08-01

    This study investigated the prestressing effect of cold-drawn short NiTi shape memory alloy (SMA) fibres in steel reinforced mortar beams. The SMA fibres were mixed with 1.5% volume content in a mortar matrix with the compressive strength of 50 MPa. The SMA fibres had an average length of 34 mm, and they were manufactured with a dog-bone shape: the diameters of the end- and middle-parts were 1.024 and 1.0 mm, respectively. Twenty mortar beams with the dimensions of 40 mm × 40 mm × 160 mm (B × H × L) were prepared. Two types of tests were conducted. One was to investigate the prestressing effect of the SMA fibres, and the beams with the SMA fibres were heated at the bottom. The other was to assess the bending behaviour of the beams prestressed by the SMA fibres. The SMA fibres induced upward deflection and cracking at the top surface by heating at the bottom; thus, they achieved an obvious prestressing effect. The beams that were prestressed by the SMA fibres did not show a significant difference in bending behaviour from that of the SMA fibre reinforced beams that were not subjected to heating. Stress analysis of the beams indicated that the prestressing effect decreased in relation to the cooling temperature.

  17. Corrosion resistance of porous NiTi biomedical alloy in simulated body fluids

    NASA Astrophysics Data System (ADS)

    Stergioudi, F.; Vogiatzis, C. A.; Pavlidou, E.; Skolianos, S.; Michailidis, N.

    2016-09-01

    The corrosion performance of two porous NiTi in physiological and Hank’s solutions was investigated by potentiodynamic polarization, cyclic polarization and impedance spectroscopy. Electric models simulating the corrosion mechanism at early stages of immersion were proposed, accounting for both microstructural observations and electrochemical results. Results indicate that both porous samples were susceptible to localized corrosion. The porosity increase (from 7% to 18%) resulted in larger and wider pore openings, thus favoring the corrosion resistance of 18% porous NiTi. Strengthening of corrosion resistance was observed in Hank’s solution. The pore morphology and micro-galvanic corrosion phenomena were determining factors affecting the corrosion resistance.

  18. Enhancement of NiTi superelastic endodontic instruments by TiO2 coating.

    PubMed

    Aun, Diego Pinheiro; Peixoto, Isabella Faria da Cunha; Houmard, Manuel; Buono, Vicente Tadeu Lopes

    2016-11-01

    Rotary nickel-titanium (NiTi) endodontic instruments were coated with a nanometric flexible TiO2 layer through dip-coating sol-gel. Control groups and coated samples of superelastic NiTi instruments model RaCe 25/0.06 (0.25mm tip-diameter, 6% conicity) were comparatively investigated with respect to the cutting efficiency, fatigue life, and corrosion resistance. Results showed an improvement in cutting efficiency for the coated samples and a high resistance to corrosion in NaClO. The coated instruments showed a better performance in fatigue life after corrosion. PMID:27524067

  19. Theoretical determination of twin boundaries in R-phase of Ni-Ti shape memory alloys

    NASA Astrophysics Data System (ADS)

    H, C. Yi; M, Zhu; D, Z. Yang

    1988-06-01

    Twin boundaries among different variants in Nitinal R-phase were determined using group decomposition theory. It was found that there are four variants in the R-phase. The four variants may form three types of self-accommodation group. The four variants are twin related with {100}p and {100}p as twin planes. These results are in good agreement with the experiment data.

  20. Development and experimental evaluation of a novel annuloplasty ring with a shape memory alloy core

    NASA Astrophysics Data System (ADS)

    Purser, Molly Ferris

    A novel annuloplasty ring with a shape memory alloy core has been developed to facilitate minimally invasive mitral valve repair. In its activated (austenitic) phase, this prototype ring provides comparable mechanical properties as commercial semi-rigid rings. In its pre-activated (martensitic) phase, this ring is flexible enough to be introduced through an 8 mm trocar and easily manipulated with robotic instruments within the confines of a left atrial model. The core is constructed of 0.508 mm diameter NiTi, which is maintained below its M s temperature (24°C) during deployment and suturing. After suturing, the stiffener is heated to its Af temperature (37°C, normal human body temperature) enabling the NiTi to retain its optimal geometry and stiffness characteristics indefinitely. The NiTi core is shape set in a furnace to the appropriate size and optimal geometry during fabrication. The ring is cooled in a saline bath prior to surgery, making it compliant and easy to manipulate. Evaluation of the ring included mechanical testing, robotic evaluation, static pressure testing, dynamic flow testing and fatigue testing. Experimental results suggest that the NiTi core ring could be a viable alternative to flexible bands in robot-assisted mitral valve repair.

  1. The Characterization of Thin Film Nickel Titanium Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Harris Odum, Nicole Latrice

    Shape memory alloys (SMA) are able to recover their original shape through the appropriate heat or stress exposure after enduring mechanical deformation at a low temperature. Numerous alloy systems have been discovered which produce this unique feature like TiNb, AgCd, NiAl, NiTi, and CuZnAl. Since their discovery, bulk scale SMAs have undergone extensive material property investigations and are employed in real world applications. However, its thin film counterparts have been modestly investigated and applied. Researchers have introduced numerous theoretical microelectromechanical system (MEMS) devices; yet, the research community's overall unfamiliarity with the thin film properties has delayed growth in this area. In addition, it has been difficult to outline efficient thin film processing techniques. In this dissertation, NiTi thin film processing and characterization techniques will be outlined and discussed. NiTi thin films---1 mum thick---were produced using sputter deposition techniques. Substrate bound thin films were deposited to analysis the surface using Scanning Electron Microscopy; the film composition was obtained using Energy Dispersive Spectroscopy; the phases were identified using X-ray diffraction; and the transformation temperatures acquired using resistivity testing. Microfabrication processing and sputter deposition were employed to develop tensile membranes for membrane deflection experimentation to gain insight on the mechanical properties of the thin films. The incorporation of these findings will aid in the movement of SMA microactuation devices from theory to fruition and greatly benefit industries such as medicinal and aeronautical.

  2. Phase transformations in nickel-rich nickel-titanium alloys: Influence of strain-rate, temperature, thermomechanical treatment and nickel composition on the shape memory and superelastic characteristics

    NASA Astrophysics Data System (ADS)

    Adharapurapu, Raghavendra R.

    Nearly four decades of academic research and industrial interest on Nitinol has largely focused on the superelastic applications in the bio-medical sector and in the development of 'smart' shape-memory based sensors involving the low-strain rate (˜0.001/s) response of NiTi. It is only within the last decade that there has been a growing interest in the exploitation of Nitinol towards high-strain rate applications such as seismic damping, blast-mitigation or energy-absorbing applications. However, a systematic study of the influence of high-strain rate and temperature on the shape memory characteristics of NiTi is severely lacking. The current research program reports the findings on: (1) The phase-transformation mechanisms in Ni-rich Ni-Ti alloys. These include (a) diffusionless multiple-stage martensitic transformations and (b) diffusion-based phase transformations that govern the precipitation reactions in Ni-rich alloys and the overall time-temperature-transformation (TTT) curves. (2) The systematic study of the high-strain rate response of Ni-rich NiTi alloys as a function of temperature (between -196°C and 400°C) and thermomechanical treatment, viz., fully annealed, work-hardened and precipitation hardened conditions. Two Ni-rich Nitinol alloys, a commercial 50.8-NiTi (at.%) and a new 55-NiTi (at.%), were selected for the study, since the Ni composition determines the precipitation processes and, critically, the transformation temperatures in NiTi alloys. It was observed that the presence of dislocations (through work-hardening) and the presence of Ni-rich precipitates (through age-hardening) contribute to a more complex two-stage or multiple-stage transformations and also improve the overall strength of the NiTi alloy. Based on the microstructural changes, such as recovery, recrystallization and precipitation formation in 50.8-NiTi alloys, the current work uniquely provides a unified and general understanding of the various multiple-stage transformations

  3. Electromagnetic heating of a shape memory alloy translator

    NASA Astrophysics Data System (ADS)

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

    1996-03-01

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

  4. Effects of oxygen plasma source ion implantation on microstructure evolution and mechanical properties of nickel-titanium shape memory alloy

    NASA Astrophysics Data System (ADS)

    Tan, Lizhen

    Near-equiatomic NiTi is an important shape memory alloy used in both medical and non-medical applications, which are dependent upon the surface characteristics of NiTi. The work presented here is the first use of plasma source ion implantation with oxygen as the incident species to modify the surface structure of NiTi shape memory alloy. Two levels of voltage bias and three levels of ion dose were employed to investigate the effect of processing parameters on surface microstructure and surface-related properties. Several surface analytical techniques, Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), were employed to analyze the effects of the surface modification on surface characteristics including oxide thickness, oxide constitution, phase distribution, morphology and topography. A two-layer surface structure consisting of an oxide layer and a precipitate accommodation layer was observed on modified NiTi. The surface morphology, roughness and hydrophilicity, which are considered to play important roles in affecting protein adsorption behavior, were found to be altered by surface modification. The effects of surface modification on surface-related properties including corrosion resistance, hardness and wear resistance were evaluated by cyclic potentiodynamic polarization tests, Knoop hardness microindentation and fretting wear tests, respectively. The optimum corrosion and wear resistance of NiTi were achieved with ion implantation under high bias and moderate dose. Archard's equation was modified by incorporating the pseudoelasticity effect on wear resistance in addition to hardness. The modified Archard's equation better describes the fretting wear resistance of NiTi. A combination of nanoindentation and AES was employed to understand the relationship between mechanical properties and composition of the modified material.

  5. Characterization of a 3D multi-mechanism SMA material model for the prediction of the cyclic "evolutionary" response of NiTi for use in actuations

    NASA Astrophysics Data System (ADS)

    Dhakal, Binod

    The intermetallic NiTi-based alloys are known as Shape Memory material. They exhibit unique ability to remember a shape after large deformation. They are desirable in various engineering applications, such as actuators, biomedical devices, vibration damping, etc, as they can absorb and dissipate mechanical/thermal energies by undergoing a reversible hysteretic shape change under the applied mechanical/thermal cyclic loadings. This reflects the effect of micro-structural changes occurring during phase transformation between Austenite(A) and Martensite(M), as well as differently-oriented M-variants. As typically utilized in applications, a particular shape memory alloy (SMA) device or component operates under a large number of thermo-mechanical cycles, hence, the importance of accounting for the cyclic behavior characteristics in modeling and characterization of these systems. A detailed study of the multi-mechanism-based, comprehensive, thus complex modeling framework (by Saleeb et al) and the determination of its material parameters responsible for the physical significance of the shape memory effect are made. This formulation utilizes multiple, inelastic mechanisms to regulate the partitioning of energy dissipation and storage governing the evolutionary thermo-mechanical behavior. Equipped with the understanding of the physical significance of the model parameters and utilizing the SMA modeling strategy effectively, a comprehensive characterization of the evolutionary, cyclic response of the complex real SMA, known as 55NiTi (Ni49.9Ti50.1) is carried out. The detailed comparisons between the SMA model and experimental results provided the necessary validation of the modeling capabilities of the framework to calibrate the complex alloys like 55NiTi. In addition, the details of interplays between the internal mechanisms to describe the material behavior within all the important response characteristic regions provides a convenient means to compliment the theoretical

  6. Electropolishing of stainless steels in a choline chloride based ionic liquid: an electrochemical study with surface characterisation using SEM and atomic force microscopy.

    PubMed

    Abbott, Andrew P; Capper, Glen; McKenzie, Katy J; Glidle, Andrew; Ryder, Karl S

    2006-09-28

    We have studied the anodic dissolution (electropolishing) of various stainless steel alloys in an ionic liquid comprising a 2 : 1 stoichiometric mix of ethylene glycol (EG) and choline chloride. We have used a combination of electrochemical and spectroscopic methods together with in situ liquid probe microscopy. We discuss the role and influence of the surface oxide passivation layer, characterized here by X-ray photoelectron spectroscopy (XPS) and linear sweep voltammetry, on the polishing process. We address the question of dealloying during the polish in order to contribute to our understanding of the viability of the ionic liquid as a replacement industrial electropolishing medium; the current commercial process uses a corrosive mixture of phosphoric and sulfuric acids. Also, we present data from ex situ and in situ liquid AFM studies giving both a qualitative and quantitative insight into the nature and scale of morphological changes at the steel surface during the polishing process. PMID:16971989

  7. 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.

  8. Effect of Cr and Cu addition on corrosion behavior of Ni-Ti alloys.

    PubMed

    Iijima, M; Endo, K; Ohno, H; Mizoguchi, I

    1998-03-01

    The corrosion behavior of three Ni-Ti alloys with compositions as commercial super-elastic orthodontic wires was investigated using polished plate specimens. Corrosion resistance was estimated by potentiodynamic polarization measurement in 0.9% NaCl and 1% lactic acid solutions and analysis of released metals by atomic absorption spectrophotometry. The influence of Cr and Cu addition on the structure of the surface oxide film was examined by X-ray photoelectron spectroscopy (XPS). Addition of 0.19 at% Cr had little effect on the structure of the oxide films and the corrosion resistance of the Ni-Ti alloys. For Ni-Ti-5Cu-0.3Cr alloy, the metallic Cu was enriched at the alloy/oxide film interface, resulting in increased susceptibility to pitting corrosion above +1000 mV. However, the passive current density and the amount of released Ni were not significantly increased by the addition of Cu. The study showed that small amounts of Cr and Cu added to change the super-elastic characteristics do not change the corrosion resistance of the Ni-Ti alloy freely immersed in simulated physiological environments. PMID:9663060

  9. Revealing ultralarge and localized elastic lattice strains in Nb nanowires embedded in NiTi matrix

    PubMed Central

    Zang, Ketao; Mao, Shengcheng; Cai, Jixiang; Liu, Yinong; Li, Haixin; Hao, Shijie; Jiang, Daqiang; Cui, Lishan

    2015-01-01

    Freestanding nanowires have been found to exhibit ultra-large elastic strains (4 to 7%) and ultra-high strengths, but exploiting their intrinsic superior mechanical properties in bulk forms has proven to be difficult. A recent study has demonstrated that ultra-large elastic strains of ~6% can be achieved in Nb nanowires embedded in a NiTi matrix, on the principle of lattice strain matching. To verify this hypothesis, this study investigated the elastic deformation behavior of a Nb nanowire embedded in NiTi matrix by means of in situ transmission electron microscopic measurement during tensile deformation. The experimental work revealed that ultra-large local elastic lattice strains of up to 8% are induced in the Nb nanowire in regions adjacent to stress-induced martensite domains in the NiTi matrix, whilst other parts of the nanowires exhibit much reduced lattice strains when adjacent to the untransformed austenite in the NiTi matrix. These observations provide a direct evidence of the proposed mechanism of lattice strain matching, thus a novel approach to designing nanocomposites of superior mechanical properties. PMID:26625854

  10. Static Indentation Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Moore, Lewis E., III; Clifton, Joshua S.

    2012-01-01

    The nickel-rich, binary nickel-titanium alloys, such as 60NiTi (60Ni-40Ti by wt%), are emerging as viable materials for use in mechanical components like rolling element bearings and gears. 60NiTi is a superelastic material that simultaneously exhibits high hardness and a relatively low elastic modulus (approx.100 GPa). These properties result in the potential to endure extremely high indentation loads such as those encountered in bearings, gears and other mechanical components. In such applications, quantifying the load that results in permanent deformation that can affect component performance and life is important. In this paper, the static load capacity is measured by conducting indentation experiments in which 12.7 mm diameter balls made from the ceramic Si3N4 are pressed into highly polished, hardened 60NiTi flat plates. Hertz stress calculations are used to estimate contact stress. The results show that the 60NiTi surface can withstand an approximately 3400 kN load before significant denting (>0.6 microns deep) occurs. This load capacity is approximately twice that of high performance bearing steels suggesting that the potential exists to make highly resilient bearings and components from such materials.

  11. Capability of Sputtered Micro-patterned NiTi Thick Films

    NASA Astrophysics Data System (ADS)

    Bechtold, Christoph; Lima de Miranda, Rodrigo; Quandt, Eckhard

    2015-09-01

    Today, most NiTi devices are manufactured by a combination of conventional metal fabrication steps, e.g., melting, extrusion, cold working, etc., and are subsequently structured by high accuracy laser cutting. This combination has been proven to be very successful; however, there are several limitations to this fabrication route, e.g., in respect to the fabrication of more complex device designs, device miniaturization or the combination of different materials for the integration of further functionality. These issues have to be addressed in order to develop new devices and applications. The fabrication of micro-patterned films using magnetron sputtering, UV lithography, and wet etching has great potential to overcome limitations of conventional device manufacturing. Due to its fabrication characteristics, this method allows the production of devices with complex designs, high structural accuracy, smooth edge profile, at layer thicknesses up to 75 µm. The aim of this study is to present recent developments in the field of NiTi thin film technology, its advantages and limitations, as well as new possible applications in the medical and in non-medical fields. These developments include among others NiTi scaffold structures covered with NiTi membranes for their potential use as filters, heart valve components or aneurysm treatments, as well as micro-actuators for consumable electronics or automotive applications.

  12. Surface modification of NiTi by plasma based ion implantation for application in harsh environments

    NASA Astrophysics Data System (ADS)

    Oliveira, R. M.; Fernandes, B. B.; Carreri, F. C.; Gonçalves, J. A. N.; Ueda, M.; Silva, M. M. N. F.; Silva, M. M.; Pichon, L.; Camargo, E. N.; Otubo, J.

    2012-12-01

    The substitution of conventional components for NiTi in distinct devices such as actuators, valves, connectors, stents, orthodontic arc-wires, e.g., usually demands some kind of treatment to be performed on the surface of the alloy. A typical case is of biomaterials made of NiTi, in which the main drawback is the Ni out-diffusion, an issue that has been satisfactorily addressed by plasma based ion implantation (PBII). Even though PBII can tailor selective surface properties of diverse materials, usually, only thin modified layers are attained. When NiTi alloys are to be used in the harsh space environment, as is the case of devices designed to remotely release the solar panels and antenna arrays of satellites, e.g., superior mechanical and tribological properties are demanded. For this case the thickness of the modified layer must be larger than the one commonly achieved by conventional PBII. In this paper, new nitrogen PBII set up was used to treat samples of NiTi in moderate temperature of 450 °C, with negative voltage pulses of 7 kV/250 Hz/20 μs, in a process lasting 1 h. A rich nitrogen atomic concentration of 85 at.% was achieved on the near surface and nitrogen diffused at least for 11 μm depth. Tribological properties as well as corrosion resistance were evaluated.

  13. Blast Coating of Superelastic NiTi Wire with PTFE to Enhance Wear Properties

    NASA Astrophysics Data System (ADS)

    Dunne, Conor F.; Roche, Kevin; Twomey, Barry; Hodgson, Darel; Stanton, Kenneth T.

    2015-03-01

    This work investigates the deposition of polytetrafluoroethylene (PTFE) onto a superelastic NiTi wire using an ambient temperature-coating technique known as CoBlast. The process utilises a stream of abrasive (Al2O3) and a coating medium (PTFE) sprayed simultaneously at the surface of the substrate. Superelastic NiTi wire is used in guidewire applications, and PTFE coatings are commonly applied to reduce damage to vessel walls during insertion and removal, and to aid in accurate positioning by minimising the force required to advance, retract or rotate the wire. The CoBlast coated wires were compared to wire treated with PTFE only. The coated samples were examined using variety of techniques: X-ray diffraction (XRD), microscopy, surface roughness, wear testing and flexural tests. The CoBlast coated samples had an adherent coating with a significant resistance to wear compared to the samples coated with PTFE only. The XRD revealed that the process gave rise to a stress-induced martensite phase in the NiTi which may enhance mechanical properties. The study indicates that the CoBlast process can be used to deposit thin adherent coatings of PTFE onto the surface of superelastic NiTi.

  14. Surface modification of AISI H13 tool steel by laser cladding with NiTi powder

    NASA Astrophysics Data System (ADS)

    Norhafzan, B.; Aqida, S. N.; Chikarakara, E.; Brabazon, D.

    2016-04-01

    This paper presents laser cladding of NiTi powder on AISI H13 tool steel surface for surface properties enhancement. The cladding process was conducted using Rofin DC-015 diffusion-cooled CO2 laser system with wavelength of 10.6 µm. NiTi powder was pre-placed on H13 tool steel surface. The laser beam was focused with a spot size of 90 µm on the sample surface. Laser parameters were set to 1515 and 1138 W peak power, 18 and 24 % duty cycle and 2300-3500 Hz laser pulse repetition frequency. Hardness properties of the modified layer were characterized by Wilson Hardness tester. Metallographic study and chemical composition were conducted using field emission scanning electron microscope and energy-dispersive X-ray spectrometer (EDXS) analysis. Results showed that hardness of NiTi clad layer increased three times that of the substrate material. The EDXS analysis detected NiTi phase presence in the modified layer up to 9.8 wt%. The metallographic study shows high metallurgical bonding between substrate and modified layer. These findings are significant to both increased hardness and erosion resistance of high-wear-resistant components and elongating their lifetime.

  15. Surface Modification of NiTi Alloy via Cathodic Plasma Electrolytic Deposition and its Effect on Ni Ion Release and Osteoblast Behaviors

    NASA Astrophysics Data System (ADS)

    Yan, Ying; Cai, Kaiyong; Yang, Weihu; Liu, Peng

    2013-07-01

    To reduce Ni ion release and improve biocompatibility of NiTi alloy, the cathodic plasma electrolytic deposition (CPED) technique was used to fabricate ceramic coating onto a NiTi alloy surface. The formation of a coating with a rough and micro-textured surface was confirmed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. An inductively coupled plasma mass spectrometry test showed that the formed coating significantly reduced the release of Ni ions from the NiTi alloy in simulated body fluid. The influence of CPED treated NiTi substrates on the biological behaviors of osteoblasts, including cell adhesion, cell viability, and osteogenic differentiation function (alkaline phosphatase), was investigated in vitro. Immunofluorescence staining of nuclei revealed that the CPED treated NiTi alloy was favorable for cell growth. Osteoblasts on CPED modified NiTi alloy showed greater cell viability than those for the native NiTi substrate after 4 and 7 days cultures. More importantly, osteoblasts cultured onto a modified NiTi sample displayed significantly higher differentiation levels of alkaline phosphatase. The results suggested that surface functionalization of NiTi alloy with ceramic coating via the CPED technique was beneficial for cell proliferation and differentiation. The approach presented here is useful for NiTi implants to enhance bone osseointegration and reduce Ni ion release in vitro.

  16. Enhancing the electrical properties of a flexible transparent graphene-based field-effect transistor using electropolished copper foil for graphene growth.

    PubMed

    Tsai, Lei-Wei; Tai, Nyan-Hwa

    2014-07-01

    Flexible transparent graphene-based field-effect transistors (Gr-FETs) were fabricated using large-area single-layer graphene synthesized through low-pressure chemical vapor deposition on a pretreated copper (Cu) foil, followed by transfer of the graphene from the Cu foil to a poly(ethylene terephthalate) (PET) substrate. The electropolishing method was adopted to smooth the surface of the Cu foil, which is a crucial factor because it affects the defect density of graphene films on the PET substrate after transfer and the electronic transport property of the graphene-based devices. The influence of the electropolishing process on the graphene properties was examined using a Raman spectroscope, a scanning electron microscope, and an optical microscope. When the electropolishing process was adopted to improve the graphene quality, the carrier mobility of the flexible transparent Gr-FETs was enhanced from 90 to 340 cm(2)/(V s). Furthermore, variation of the carrier mobility was lower than 10% when the bending radius of the flexible device was decreased from 6.0 to 1.0 cm. PMID:24922088

  17. A bridge column with superelastic NiTi SMA and replaceable rubber hinge for earthquake damage mitigation

    NASA Astrophysics Data System (ADS)

    Varela, Sebastian; ‘Saiid’ Saiidi, M.

    2016-07-01

    This paper reports a unique concept for resilient bridge columns that can undergo intense earthquake loading and remain functional with minimal damage and residual drift. In this concept, the column is designed so that its components can be easily disassembled and reassembled to facilitate material recycling and component reuse. This is meant to foster sustainability of bridge systems while minimizing monetary losses from earthquakes. Self-centering and energy dissipation in the column were provided by unbonded superelastic nickel–titanium (NiTi) shape memory alloy bars placed inside a plastic hinge element made of rubber. This replaceable plastic hinge was in turn attached to a concrete-filled carbon fiber-reinforced polymer tube and a precast concrete footing that were designed to behave elastically. The proposed concept was evaluated experimentally by testing a ¼-scale column model under simulated near-fault earthquake motions on a shake table. After testing, the model was disassembled, reassembled and tested again. The seismic performance of the reassembled model was found to be comparable to that of the ‘virgin’ model. A relatively simple computational model of the column tested that was developed in OpenSees was able to match some of the key experimental response parameters.

  18. Pickling of laser-cut NiTi slotted tube stents: Effect on surface morphology, dimension changes and mechanical behaviour

    NASA Astrophysics Data System (ADS)

    Zhao, H.; Stalmans, R.; van Humbeeck, J.; de Scheerder, I.

    2003-10-01

    Production of the NiTi slotted tube stents by laser cutting leads to strong burr formation and depositions on the material surface. Acid pickling is one of the major methods to remove the burr and the depositions. In this study, as a pre-treatment of polishing the NiTi stents, pickling was tested for various times in an acid solution at room temperature. Its effect on the surface morphology, dimension changes, and mechanical behaviour of the NiTi stents was evaluated. The burr and depositions could be removed practically. The removal (weight loss) of the material increases linearly with the pickling time. The burr and depositions were removed totally from the cutting zone when pickling time reached a specific value. Experimental relations among weight loss, dimensions, mechanical properties and pickling time of the NiTi stents were established.

  19. Parametric study and characterization of the isobaric thermomechanical transformation fatigue of nickel-rich NiTi SMA actuators

    NASA Astrophysics Data System (ADS)

    Bertacchini, Olivier W.; Schick, Justin; Lagoudas, Dimitris C.

    2009-03-01

    The recent development of various aerospace applications utilizing Ni-rich NiTi Shape memory Alloys (SMAs) as actuators motivated the need to characterize the cyclic response and the transformation fatigue behavior of such alloys. The fatigue life validation and certification of new designs is required in order to be implemented and used in future applications. For that purpose, a custom built fatigue test frame was designed to perform isobaric thermally induced transformation cycles on small dogbones SMA actuators (test gauge cross-section up to: 1.270 x 0.508 mm2). A parametric study on the cyclic response and transformation fatigue behavior of Ni-rich NiTi SMAs led to the optimization of several material/process and test parameters, namely: the applied stress range, the heat treatment, the heat treatment environment and the specimen thickness. However, fatigue testing was performed in a chilled waterless glycol environment maintained at a temperature of 5°C that showed evidence of corrosion-assisted transformation fatigue failure. Therefore, it was necessary to build a fatigue test frame that would employ a dry and inert cooling methodology to get away from any detrimental interactions between the specimens and the cooling medium (corrosion). The selected cooling method was gaseous nitrogen, sprayed into a thermally insulated chamber, maintaining a temperature of -20°C. The design of the gaseous nitrogen cooling was done in such a way that the actuation frequency is similar to the one obtained using the original design (~ 0.1 Hz). For both cooling methods, Joule resistive heating was used to heat the specimens. In addition and motivated by the difference in surface quality resulting from different material processing such as EDM wire cutting and heat treatments, EDM recast layer and oxide layer were removed. The removal was followed by an ultra-fine polish (0.05 μm) that was performed on a subset of the fatigue specimens. Experimental results are presented

  20. 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.

  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. The underlying biological mechanisms of biocompatibility differences between bare and TiN-coated NiTi alloys.

    PubMed

    Lifeng, Zhao; Yan, Hong; Dayun, Yang; Xiaoying, Lü; Tingfei, Xi; Deyuan, Zhang; Ying, Hong; Jinfeng, Yuan

    2011-04-01

    TiN coating has been demonstrated to improve the biocompatibility of bare NiTi alloys; however, essential biocompatibility differences between NiTi alloys before and after TiN coating are not known so far. In this study, to explore the underlying biological mechanisms of biocompatibility differences between them, the changes of bare and TiN-coated NiTi alloys in surface chemical composition, morphology, hydrophilicity, Ni ions release, cytotoxicity, apoptosis, and gene expression profiles were compared using energy-dispersive spectroscopy, scanning electron microscopy, contact angle, surface energy, Ni ions release analysis, the methylthiazoltetrazolium (MTT) method, flow cytometry and microarray methods, respectively. Pathways binding to networks and real-time polymerase chain reaction (PCR) were employed to analyze and validate the microarray data, respectively. It was found that, compared with the bare NiTi alloys, TiN coating significantly decreased Ni ions content on the surfaces of the NiTi alloys and reduced the release of Ni ions from the alloys, attenuated the inhibition of Ni ions to the expression of genes associated with anti-inflammatory, and also suppressed the promotion of Ni ions to the expression of apoptosis-related genes. Moreover, TiN coating distinctly improved the hydrophilicity and uniformity of the surfaces of the NiTi alloys, and contributed to the expression of genes participating in cell adhesion and other physiological activities. These results indicate that the TiN-coated NiTi alloys will help overcome the shortcomings of NiTi alloys used in clinical application currently, and can be expected to be a replacement of biomaterials for a medical device field. PMID:21441653

  3. Shape memory alloys: New materials for future engineering

    NASA Technical Reports Server (NTRS)

    Hornbogen, E.

    1988-01-01

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

  4. 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. PMID:15585228

  5. Effect of Upper-Cycle Temperature on the Load-Biased, Strain-Temperature Response of NiTi

    NASA Technical Reports Server (NTRS)

    Padula, Santo, II; Noebe, Ronald; Bigelow, Glen; Qiu, Shipeng; Vaidyanathan, Raj; Gaydosh, Darrell; Garg, Anita

    2011-01-01

    Over the past decade, interest in shape memory alloy based actuators has increased as the primary benefits of these solid-state devices have become more apparent. However, much is still unknown about the characteristic behavior of these materials when used in actuator applications. Recently we have shown that the maximum temperature reached during thermal cycling under isobaric conditions could significantly affect the observed mechanical response of NiTi (55 wt% Ni), especially the amount of transformation strain available for actuation and thus work output. The investigation we report here extends that original work to ascertain whether further increases in the upper-cycle temperature would produce additional changes in the work output of the material, which has a stress-free austenite finish temperature of 113 C, and to determine the optimum cyclic conditions. Thus, isobaric, thermal-cycle experiments were conducted on the aforementioned alloy at various stresses from 50-300 MPa using upper-cycle temperatures of 165, 200, 230, 260, 290, 320 and 350 C. The data indicated that the amount of applied stress influenced the transformation strain, as would be expected. However, the maximum temperature reached during the thermal excursion also plays an equally significant role in determining the transformation strain, with the maximum transformation strain observed during thermal cycling to 290 C. In situ neutron diffraction at stress and temperature showed that the differences in transformation strain were mostly related to changes in martensite texture when cycling to different upper-cycle temperatures. Hence, understanding this effect is important to optimizing the operation of SMA-based actuators and could lead to new methods for processing and training shape memory alloys for optimal performance.

  6. Effect of Upper-Cycle Temperature on the Load-Biased, Strain-Temperature Response of NiTi

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    Over the past decade, interest in shape memory alloy based actuators has increased as the primary benefits of these solid-state devices have become more apparent. However, much is still unknown about the characteristic behavior of these materials when used in actuator applications. Recently we have shown that the maximum temperature reached during thermal cycling under isobaric conditions could significantly affect the observed mechanical response of NiTi (55 wt% Ni), especially the amount of transformation strain available for actuation and thus work output. This investigation extends that original work to ascertain whether further increases in the upper-cycle temperature would produce additional improvement in the work output of the material, which has a stress-free Af of 113 oC, and to determine the optimum cyclic conditions. Thus, isobaric, thermal-cycle experiments were conducted in the aforementioned alloy at various stress levels from 50-300 MPa using upper-cycle temperatures of 165, 200, 230, 260, 290, 320 and 350 oC. The data indicated that the amount of applied stress influenced the transformation strain available in the system, as would be expected. However, the maximum temperature reached during the thermal excursion also plays a role in determining the transformation strain, with the maximum transformation strain being developed by thermal cycling to 290 oC. In situ, neutron diffraction showed that the differences in transformation strain were related to differences in martensite texture within the microstructure when cycling to different upper-cycle temperatures. Hence, understanding this effect is important to optimizing the operation of SMA-based actuators and could lead to new methods for processing and training shape memory alloys for optimal performance.

  7. Construction of extracellular microenvironment to improve surface endothelialization of NiTi alloy substrate.

    PubMed

    Liu, Peng; Zhao, Yongchun; Yan, Ying; Hu, Yan; Yang, Weihu; Cai, Kaiyong

    2015-10-01

    To mimic extracellular microenvironment of endothelial cell, a bioactive multilayered structure of gelatin/chitosan pair, embedding with vascular endothelial growth factor (VEGF), was constructed onto NiTi alloy substrate surface via a layer-by-layer assembly technique. The successful fabrication of the multilayered structure was demonstrated by scanning electron microscopy, atomic force microscopy, contact angle measurement, attenuated total reflection-fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The growth behaviors of endothelial cells on various NiTi alloy substrates were investigated in vitro. Cytoskeleton observation, MTT assay, and wound healing assay proved that the VEGF-embedded multilayer structure positively stimulated adhesion, proliferation and motogenic responses of endothelial cells. More importantly, the present system promoted the nitric oxide production of endothelial cells. The approach affords an alternative to construct extracellular microenvironment for improving surface endothelialization of a cardiovascular implant. PMID:26117732

  8. Tribological behavior of NiTi alloy against 52100 steel and WC at elevated temperatures

    SciTech Connect

    Abedini, M.; Ghasemi, H.M.; Ahmadabadi, M. Nili

    2010-07-15

    The dry tribological behavior of a Ti-50.3 at.% Ni alloy at temperatures of 25 deg. C, 50 deg. C and 200 deg. C was studied. The wear tests were performed on a high temperature pin-on-disk tribometer using 52100 steel and tungsten carbide pins. The worn surfaces of the NiTi alloy were examined by scanning electron microscope. The results showed that in the wear tests involving steel pins, the wear rate of the NiTi decreased as the wear testing temperature was increased. However, for the NiTi/WC contact, a reverse trend was observed. There was also a large decrease in the coefficient of friction for the NiTi/steel contact with increasing wear testing temperature. The formation of compact tribological layers could be the main reason for the reduction of the wear rate and coefficient of friction of the NiTi/steel contact at higher wear testing temperatures.

  9. Ion beam mixing in binary amorphous metallic alloys. [Cu-Er; Ni-Ti

    SciTech Connect

    Hahn, H.; Averback, R.S.; Diaz de la Rubia, T.; Okamoto, P.R.

    1985-12-01

    Ion beam mixing (IM) was measured in homogeneous amorphous metallic alloys of Cu-Er and Ni-Ti as a function of temperature using tracer impurities, i.e., the so-called ''marker geometry''. In Cu-Er, a strong temperature dependence in IM was observed between 80 and 373K, indicating that radiation-enhanced diffusion mechanisms are operative in this metallic glass. Phase separation of the Cu-Er alloy was also observed under irradiation as Er segregated to the vacuum and SiO2 interfaces of the specimen. At low-temperatures, the amount of mixing in amorphous Ni-Ti is similar to that in pure Ni or Ti, but it is much greater in Cu-Er than in either Cu or Er.

  10. Metallurgical characterization, galvanic corrosion, and ionic release of orthodontic brackets coupled with Ni-Ti archwires.

    PubMed

    Darabara, Myrsini S; Bourithis, Lefteris I; Zinelis, Spiros; Papadimitriou, George D

    2007-04-01

    In orthodontics, a combination of metallic alloys is placed into the oral cavity during medical treatment and thus the corrosion resistance and ionic release of these appliances is of vital importance. The aim of this study is to investigate the elemental composition, microstructure, hardness, corrosion properties, and ionic release of commercially available orthodontic brackets and Copper Ni-Ti archwires. Following the assessment of the elemental composition of the orthodontic wire (Copper Ni-Ti) and the six different brackets (Micro Loc, Equilibrium, OptiMESH(XRT), Gemini, Orthos2, and Rematitan), cyclic polarization curves were obtained for each material to estimate the susceptibility of each alloy to pitting corrosion in 1M lactic acid. Galvanic corrosion between the orthodontic wire and each bracket took place in 1M lactic acid for 28 days at 37 degrees C and then the ionic concentration of Nickel and Chromium was studied. The orthodontic wire is made up from a Ni-Ti alloy with copper additions, while the orthodontic brackets are manufactured by different stainless steel grades or titanium alloys. All tested wires and brackets with the exception of Gemini are not susceptible to pitting corrosion. In galvanic corrosion, following exposure for 28 days, the lowest potential difference (approximately 250 mV) appears for the orthodontic wire Copper Ni-Ti and the bracket made up from pure titanium (Rematitan) or from the stainless steel AISI 316 grade (Micro Loc). Following completion of the galvanic corrosion experiments, measurable quantities of chromium and nickel ions were found in the residual lactic acid solution. PMID:16969817

  11. Bone Cell–materials Interactions and Ni Ion Release of Anodized Equiatomic NiTi Alloy

    PubMed Central

    Bernard, Sheldon A.; Balla, Vamsi Krishna; Davies, Neal M.; Bose, Susmita; Bandyopadhyay, Amit

    2011-01-01

    Laser processed NiTi alloy was anodized for different durations in H2SO4 electrolyte with varying pH to create biocompatible surfaces with low Ni ion release as well as bioactive surfaces to enhance biocompatibility and bone cell-materials interactions. The anodized surfaces were assessed for their in vitro cell-materials interactions using human fetal osteoblast (hFOB) cells for 3, 7 and 11 days, and Ni ion release up to 8 weeks in simulated body fluids. The results were correlated with surface morphologies of anodized surfaces characterized using field-emission scanning electron microscopy (FESEM). The results show that the anodization creates a surface with nano/micro roughness depending on anodization conditions. The hydrophilicity of NiTi surface was found to improve after anodization due to lower contact angles in cell media, which dropped from 32° to < 5°. The improved wettability of anodized surfaces is further corroborated by their high surface energy comparable to that of cp Ti. Relatively high surface energy, especially polar component, and nano/micro surface features of anodized surfaces significantly increased the number of living cells and their adherence and growth on these surfaces. Finally, a significant drop in Ni ion release from 268 ± 11 to 136 ± 15 ppb was observed for NiTi surfaces after anodization. This work indicates that anodization of NiTi alloy has a positive influence on the surface energy and surface morphology, which in turn improve bone cell-materials interactions and reduce Ni ion release in vitro. PMID:21232641

  12. Superelastic NiTi springs for corrective skull operations in children with craniosynostosis.

    PubMed

    Morawiec, H Z; Lekston, Z H; Kobus, K F; Wegrzyn, M C; Drugacz, J T

    2007-09-01

    This paper concerns the formation and characterization of superelastic springs and rings of NiTi alloys for long-term skull correction. Superelastic properties of the rings were induced in the process of ageing of the already formed rings which cause hardening of parent phase by the precipitation of coherent Ni(4)Ti(3) particles. The efficacy of the worked out springs and rings were successfully proved in several clinical applications. PMID:17483902

  13. Repairing cracks developed in mortar beams reinforced by cold-drawn NiTi or NiTiNb SMA fibers

    NASA Astrophysics Data System (ADS)

    Choi, Eunsoo; Kim, Dong Joo; Youn, Heejung; Nam, Tae-hyun

    2015-12-01

    In this study, mortar beams reinforced by shape memory alloy (SMA) fibers of NiTi and NiTiNb alloys were prepared to perform crack-repairing tests using three-point bending tests. The SMA fibers had a length of 30 mm, and their types were straight, dog-bone, and dog-bone with paper wrapping. For the bending tests, twelve types of mortar beams with the dimensions of 40 mm × 40 mm × 160 mm (B × H × L) were prepared. Half of them had a top steel reinforcement, and equal numbers of beams were assigned to the NiTi and NiTiNb fibers. Five SMA fibers were located at the bottom center of the beams along with an artificial crack of 10 mm depth and 1 mm thickness. Epoxy was used to fill the cracks to bond the cracked surfaces using injection, and a hot-gun was used to heat the SMA fibers in the cracks. The crack widths were measured before and after the cracks were repaired, and force-displacement curves were obtained to assess the flexural strength recovery ratio of the beams. It does not appear that the crack-closing capacity of SMA fibers is a crucial factor to recover the flexural strength in repaired beams. However, adequate application of epoxy is critical for repairing cracks, and the residual stress of SMA fibers seems to contribute to increase flexural strength of repaired beams. The residual stress of SMA fibers functions as prestress on mortar and delays the initiation of cracking.

  14. Computational Modeling to Predict Fatigue Behavior of NiTi Stents: What Do We Need?

    PubMed Central

    Dordoni, Elena; Petrini, Lorenza; Wu, Wei; Migliavacca, Francesco; Dubini, Gabriele; Pennati, Giancarlo

    2015-01-01

    NiTi (nickel-titanium) stents are nowadays commonly used for the percutaneous treatment of peripheral arterial disease. However, their effectiveness is still debated in the clinical field. In fact a peculiar cyclic biomechanical environment is created before and after stent implantation, with the risk of device fatigue failure. An accurate study of the device fatigue behavior is of primary importance to ensure a successful stenting procedure. Regulatory authorities recognize the possibility of performing computational analyses instead of experimental tests for the assessment of medical devices. However, confidence in numerical methods is only possible after verification and validation of the models used. For the case of NiTi stents, mechanical properties are strongly dependent on the device dimensions and the whole treatments undergone during manufacturing process. Hence, special attention should be paid to the accuracy of the description of the device geometry and the material properties implementation into the numerical code, as well as to the definition of the fatigue limit. In this paper, a path for setting up an effective numerical model for NiTi stent fatigue assessment is proposed and the results of its application in a specific case study are illustrated. PMID:26011245

  15. Hydrogen embrittlement of work-hardened Ni-Ti alloy in fluoride solutions.

    PubMed

    Yokoyama, Ken'ichi; Kaneko, Kazuyuki; Ogawa, Toshio; Moriyama, Keiji; Asaoka, Kenzo; Sakai, Jun'ichi

    2005-01-01

    Hydrogen embrittlement of work-hardened Ni-Ti alloy has been examined in acidulated phosphate fluoride (APF) solutions. Upon immersion in a 2.0% APF solution with a pH of 5.0, tensile strength decreased markedly with immersion time. Moreover, the fracture mode changed from ductile to brittle due to brittle layer formation at the peripheral part of the cross section of the specimen. The amount of absorbed hydrogen increased linearly with immersion time, and it reached above 5000 mass ppm after 24 h. The hydrogen desorption temperature of the immersed specimens shifted from 450 degrees C to a lower temperature with immersion time. As the amount of absorbed hydrogen was larger than 500 mass ppm, the degradation of mechanical properties was recognized. Although the tensile properties and fracture mode scarcely change in a 0.2% APF solution, the slight reduction in hardness and hydrogen absorption of several hundreds mass ppm were observed. The results of the present study imply that work-hardened Ni-Ti alloy is less sensitive to hydrogen embrittlement compared with Ni-Ti superelastic alloy. PMID:15193885

  16. Delayed fracture of Ni-Ti superelastic alloys in acidic and neutral fluoride solutions.

    PubMed

    Yokoyama, Ken'ichi; Kaneko, Kazuyuki; Moriyama, Keiji; Asaoka, Kenzo; Sakai, Jun'ichi; Nagumo, Michihiko

    2004-04-01

    Hydrogen-related degradation of the mechanical properties of a Ni-Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni-Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen-related degradation of performance of Ni-Ti superelastic alloys occurs in the presence of fluoride. PMID:14999757

  17. Calculation of defect properties of NiTi and FeTi

    SciTech Connect

    Lutton, R.T.; Sabochick, M.J. . Dept. of Engineering Physics); Lam, N.Q. )

    1990-12-01

    The energies and configurations of interstitials and vacancies in the B2 ordered compounds NiTi and FeTi were calculated using atomistic simulation. The stable configuration of a vacancy after the removal of an Ni atom was a vacant Ni site; similarly, the removal of an Fe atom in FeTi resulted in a vacant Fe site. Removal of a Ti atom in both compounds, however, resulted in a vacant Ni or Fe site and an adjacent antisite defect. The effective vacancy formation energies in NiTi and FeTi were calculated to be 1.48 and 1.07 eV, respectively. Interstitials in NiTi formed split {l angle}111{r angle} configurations consisting of a Ni-Ni dumbbell oriented in the {l angle}111{r angle} direction with one or two adjacent antisite defects. The Fe interstitial in FeTi had a similar configuration, except the dumbbell contained Fe atoms. The Ti interstitial in FeTi formed an {l angle}110{r angle} Fe-Fe dumbbell. 8 refs., 2 tabs.

  18. Thermo-mechanical Response and Damping Behavior of Shape Memory Alloy-MAX Phase Composites

    NASA Astrophysics Data System (ADS)

    Kothalkar, Ankush Dilip; Benitez, Rogelio; Hu, Liangfa; Radovic, Miladin; Karaman, Ibrahim

    2014-05-01

    NiTi/Ti3SiC2 interpenetrating composites that combine two unique material systems—a shape memory alloy (SMA) and a MAX phase—demonstrating two different pseudoelastic mechanisms, were processed using spark plasma sintering. The goal of mixing these two material systems was to enhance the damping behavior and thermo-mechanical response of the composite by combining two pseudoelastic mechanisms, i.e., reversible stress-induced martensitic transformation in SMA and reversible incipient kink band formation in MAX phase. Equal volume fractions of equiatomic NiTi and Ti3SiC2 were used. Microstructural characterization was conducted using scanning electron microscopy to study the distribution of NiTi, Ti3SiC2, and remnant porosity in the composite. Thermo-mechanical testing in the form of thermal cycles under constant stress levels was performed in order to characterize shape memory behavior and thereby introducing residual stresses in the composites. Evolution of two-way shape memory effect was studied and related to the presence of residual stresses in the composites. Damping behavior, implying the energy dissipation per loading-unloading cycle under increasing compressive stresses, of pure NiTi, pure Ti3SiC2, as-sintered, and thermo-mechanically cycled (TC) NiTi/Ti3SiC2 composites, was investigated and compared to the literature data. In this study, the highest energy dissipation was observed for the TC composite followed by the as-sintered (AS) composite, pure NiTi, and pure Ti3SiC2 when compared at the same applied stress levels. Both the AS and TC composites showed higher damping up to 200 MPa stress than any of the metal—MAX phase composites reported in the literature to date. The ability to enhance the performance of the composite by controlling the thermo-mechanical loading paths was further discussed.

  19. 60NiTi Intermetallic Material Evaluation for Lightweight and Corrosion Resistant Spherical Sliding Bearings for Aerospace Applications

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Jefferson, Michael

    2015-01-01

    NASA Glenn Research Center and the Kamatics subsidiary of the Kaman Corporation conducted the experimental evaluation of spherical sliding bearings made with 60NiTi inner races. The goal of the project was to assess the feasibility of manufacturing lightweight, corrosion resistant bearings utilizing 60NiTi for aerospace and industrial applications. NASA produced the bearings in collaboration with Abbott Ball Corporation and Kamatics fabricated bearing assemblies utilizing their standard reinforced polymer liner material. The assembled bearings were tested in oscillatory motion at a load of 4.54kN (10,000 lb), according to the requirements of the plain bearing specification SAE AS81820. Several test bearings were exposed to hydraulic fluid or aircraft deicing fluid prior to and during testing. The results show that the 60NiTi bearings exhibit tribological performance comparable to conventional stainless steel (440C) bearings. Further, exposure of 60NiTi bearings to the contaminant fluids had no apparent performance effect. It is concluded that 60NiTi is a feasible bearing material for aerospace and industrial spherical bearing applications.

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

    PubMed

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

    2016-03-01

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

  1. Effects of heat treatment on shape-setting and non-linearmechanical properties of Nitinol stent

    NASA Astrophysics Data System (ADS)

    Liu, Xiaopeng; Wang, Yinong; Qi, Min; Yang, Dazhi

    2007-07-01

    NiTi shape memory alloy is a temperature sensitive material with non-linear mechanical properties and good biocompatibility, which can be used for medical devices such as stent, catheter guide wire and orthodontic wire. The majority of nitinol stents are of the self-expanding type basing on the superelasticity. Nitinol stents are shape set into the open condition and compressed and inserted into the delivery catheter. Additional the shape-setting treatment can be used as a tool to accurately tune the transformation temperatures and mechanical properties. In this study, different heat treatments have been performed on the Ti-50.7at%Ni alloy wires. And results of shape-setting, austenite transformation finish temperature and non-linear mechanical property of NiTi shape memory alloy at body temperature have been investigated. The experimental results show that the proper shape-setting temperature should be chosen between 450-550 °C. And the shape-setting results were stabilization when the NiTi wires were constrain-treated at 500 and 550°C and ageing time longer than 10 minutes. The austenite finish temperatures increased with ageing time and increased first and then decreased with ageing temperature. The peak values were obtained at 400°C. When the heat treatments was performed at the same temperature, both the upper plateau stresses and lower plateau stresses decreased with the ageing time. Most of treated nitinol wires owned good recovery ability at body temperature and the permanent sets were less than 0.05% when short time ageing treatment was performed at 500°C.

  2. Reduction of Ni release and improvement of the friction behaviour of NiTi orthodontic archwires by oxidation treatments.

    PubMed

    Espinar, E; Llamas, J M; Michiardi, A; Ginebra, M P; Gil, F J

    2011-05-01

    This work studies NiTi orthodontic archwires that have been treated using a new oxidation treatment for obtaining Ni-free surfaces. The titanium oxide on the surface significantly improves corrosion resistance and decreases nickel ion release, while barely affecting transformation temperatures. This oxidation treatment avoids the allergic reactions or toxicity in the surrounding tissues produced by the chemical degradation of the NiTi. In the other hand, the lack of low friction coefficient for the NiTi superelastic archwires makes difficult the optimal use of these materials in Orthodontic applications. In this study, the decrease of this friction coefficient has been achieved by means of oxidation treatment. Transformation temperatures, friction coefficient and ion release have been determined. PMID:21437639

  3. Structural phase states in NiTi near-surface layers modified by electron and ion beams

    SciTech Connect

    Meisner, Ludmila Meisner, Stanislav; Mironov, Yurii Kashin, Oleg Lotkov, Aleksandr; Kudryashov, Andrey

    2014-11-14

    The paper considers the effects arising on X-ray diffraction patterns taken in different diffraction geometries and how these effects can be interpreted to judge structural states in NiTi near-surface regions after electron and ion beam treatment. It is shown that qualitative and quantitative analysis of phase composition, lattice parameters of main phases, elastic stress states, and their in-depth variation requires X-ray diffraction patterns in both symmetric Bragg–Brentano and asymmetric Lambot–Vassamilleta geometries with variation in X-ray wavelengths and imaging conditions (with and with no β-filter). These techniques of structural phase analysis are more efficient when the thickness of modified NiTi surface layers is 1–10 μm (after electron beam treatment) and requires special imaging conditions when the thickness of modified NiTi surface layers is no greater than 1 μm (after ion beam treatment)

  4. 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.

  5. Midpoint Shapes.

    ERIC Educational Resources Information Center

    Welchman, Rosamond; Urso, Josephine

    2000-01-01

    Emphasizes the importance of children exploring hands-on and minds-on mathematics. Presents a midpoint shape activity for students to explore the midpoint shape of familiar quadrilaterals, such as squares and rectangles. (KHR)

  6. 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).

  7. Cell adhesion on NiTi thin film sputter-deposited meshes.

    PubMed

    Loger, K; Engel, A; Haupt, J; Li, Q; Lima de Miranda, R; Quandt, E; Lutter, G; Selhuber-Unkel, C

    2016-02-01

    Scaffolds for tissue engineering enable the possibility to fabricate and form biomedical implants in vitro, which fulfill special functionality in vivo. In this study, free-standing Nickel–Titanium(NiTi) thin film mesheswere produced by means of magnetron sputter deposition.Meshes contained precisely defined rhombic holes in the size of 440 to 1309 μm2 and a strut width ranging from 5.3 to 9.2 μm. The effective mechanical properties of the microstructured superelastic NiTi thin film were examined by tensile testing. These results will be adapted for the design of the holes in the film. The influence of hole and strut dimensions on the adhesion of sheep autologous cells (CD133+) was studied after 24 h and after seven days of incubation. Optical analysis using fluorescence microscopy and scanning electron microscopy showed that cell adhesion depends on the structural parameters of the mesh. After 7 days in cell culture a large part of the mesh was covered with aligned fibrous material. Cell adhesion is particularly facilitated on meshes with small rhombic holes of 440 μm2 and a strut width of 5.3 μm. Our results demonstrate that free-standing NiTi thin film meshes have a promising potential for applicationsin cardiovascular tissue engineering, particularly for the fabrication of heart valves. PMID:26652414

  8. In vitro mesenchymal stem cell responses on laser-welded NiTi alloy.

    PubMed

    Chan, C W; Hussain, I; Waugh, D G; Lawrence, J; Man, H C

    2013-04-01

    The biocompatibility of NiTi after laser welding was studied by examining the in vitro (mesenchymal stem cell) MSC responses at different sets of time varying from early (4 to 12h) to intermediate phases (1 and 4 days) of cell culture. The effects of physical (surface roughness and topography) and chemical (surface Ti/Ni ratio) changes as a consequence of laser welding in different regions (WZ, HAZ, and BM) on the cell morphology and cell coverage were studied. The results in this research indicated that the morphology of MSCs was affected primarily by the topographical factors in the WZ: the well-defined and directional dendritic pattern and the presence of deeper grooves. The morphology of MSCs was not significantly modulated by surface roughness. Despite the possible initial Ni release in the medium during the cell culture, no toxic effect seemed to cause to MSCs as evidenced by the success of adhesion and spreading of the cells onto different regions in the laser weldment. The good biocompatibility of the NiTi laser weldment has been firstly reported in this study. PMID:23827581

  9. The influence of bracket type on the force delivery of Ni-Ti archwires.

    PubMed

    Hemingway, R; Williams, R L; Hunt, J A; Rudge, S J

    2001-06-01

    This study investigated the force delivery of an 0.014 inch nickel-titanium (Ni-Ti) archwire used in combination with a range of commercially available bracket systems, and using a model based on an 'ideal' mandibular archform. The model aimed to replicate the clinical interbracket span. The force delivery was measured at four different sites on an archwire for one batch of 10 nickel titanium archwires from one manufacturer, using one bracket/archwire combination. The four sites represented the lateral incisor, canine, second premolar and first molar positions. Force delivery was also measured for a further four different bracket designs at four different sites on the archwire using five fresh wires of the same archwire type. The wires were loaded with an M5 Nene Universal testing machine. The results demonstrate that the peak and plateau force, both of which are clinically important, are dependent on several factors of the archwire/bracket combination. The results showed that 20 per cent of the batch of 10 wires behaved differently by delivering a higher peak force. There was a statistically significant difference (P < 0.05) between the four bracket/archwire combinations for the peak forces delivered, but there was very little difference between the four bracket/archwire unloading force delivery values. The wires delivered a predictable force on the unloading curves, but self-ligating brackets may not develop sufficient strain within the wire to take full advantage of the superelastic effect of Ni-Ti wires. PMID:11471266

  10. Failure Analysis and Recovery of a 50-mm Highly Elastic Intermetallic NiTi Ball Bearing for an ISS Application

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Howard, S. Adam; Moore, Lewis

    2016-01-01

    Ball bearings used inside the ISS Distillation Assembly centrifuge require superior corrosion and shock resistance to withstand acidic wastewater exposure and heavy spacecraft launch related loads. These requirements challenge conventional steel bearings and provide an ideal pathfinder application for 50-mm bore, deep-groove ball bearings made from the corrosion immune and highly elastic intermetallic material 60NiTi. During early ground testing in 2014 one 60NiTi bearing unexpectedly and catastrophically failed after operating for only 200 hr. A second bearing running on the same shaft was completely unaffected. An investigation into the root cause of the failure determined that an excessively tight press fit of the bearing outer race coupled with NiTi's relatively low elastic modulus were key contributing factors. The proposed failure mode was successfully replicated by experiment. To further corroborate the root cause theory, a successful bearing life test using improved installation practices (selective fitting) was conducted. The results show that NiTi bearings are suitable for space applications provided that care is taken to accommodate their unique material characteristics.

  11. Synthesis and characterization of hybrid micro/nano-structured NiTi surfaces by a combination of etching and anodizing

    NASA Astrophysics Data System (ADS)

    Huan, Z.; Fratila-Apachitei, L. E.; Apachitei, I.; Duszczyk, J.

    2014-02-01

    The purpose of this study was to generate hybrid micro/nano-structures on biomedical nickel-titanium alloy (NiTi). To achieve this, NiTi surfaces were firstly electrochemically etched and then anodized in fluoride-containing electrolyte. With the etching process, the NiTi surface was micro-roughened through the formation of micropits uniformly distributed over the entire surface. Following the subsequent anodizing process, self-organized nanotube structures enriched in TiO2 could be superimposed on the etched surface under specific conditions. Furthermore, the anodizing treatment significantly reduced water contact angles and increased the surface free energy compared to the surfaces prior to anodizing. The results of this study show for the first time that it is possible to create hybrid micro/nano-structures on biomedical NiTi alloys by combining electrochemical etching and anodizing under controlled conditions. These novel structures are expected to significantly enhance the surface biofunctionality of the material when compared to conventional implant devices with either micro- or nano-structured surfaces.

  12. Effects of focused ion beam milling on the compressive behavior of directionally solidified micro-pillars and the nanoindentation response of an electro-polished surface

    SciTech Connect

    Shim, Sang Hoon; Bei, Hongbin; Miller, Michael K; Pharr, George Mathews; George, Easo P

    2009-01-01

    Focused ion beam (FIB) milling is the typical way in which micro-pillars are fabricated to study small-scale plasticity and size effects in uniaxial compression. However, FIB milling can introduce defects into the milled pillars. To investigate the effects of FIB damage on mechanical behavior, we tested Mo-alloy micro-pillars that were FIB milled following directional solidification, and compared their compressive response to pillars that were not FIB milled. We also FIB milled at glancing incidence a Mo-alloy single-crystal surface, and compared its nanoindentation response to an electro-polished surface of the same crystal. Consequences for the interpretation of data obtained from FIB milled micro-pillars are discussed.

  13. [In vitro investigation of three NiTi rotary instruments].

    PubMed

    Pataky, Gergely; Bartha, Károly

    2013-06-01

    The purpose of our study was to compare the shaping ability of three nickel-titanium rotary instruments (RaCe/FKG Dentaire/, ProTaper /Dentsply-Maillefer/ and M(two)/VDW/) by measuring the asymmetry that occurs in curved canals during instrumentation. Eight simulated canals in resin blocks (Morita Europe) were prepared in each group by the same operator according to the instructions of the manufacturers. We used M(two) direct (VDW-Sirona) contra-angle with torque control function. Copious irrigation of the canals was performed with the use of Chloramine B solution and File-Eze (Ultradent) was used for lubrication. We accomplished our measurements on the pre- and postoperatively scanned images of the resin blocks with the aid of Image Tool for Windows 3.0 (UTHSCSA). Measuring points were assigned along the curvature of the canal axis line to represent 1 millimeter distance from the apex and from each other. The centre of the curvature was edited and radius lines were drawn from the centre through the measuring points. We determined the value of the preparation asymmetry at the levels of these measuring points along the radius lines. RaCe prepared with the greatest asymmetry at the first, second, fourth and fifth measuring points, at the third level ProTaper produced the highest value of asymmetry. In general M(two) prepared with the lowest asymmetry while it proved as a safe instrument system. The main disadvantage about ProTaper was the high risk of fracture. The RaCe sequence used in this study showed great asymmetry values at the apical area. PMID:24344560

  14. Effect of Surface Alloying by Silicon on the Corrosion Resistance and Biocompatibility of the Binary NiTi

    NASA Astrophysics Data System (ADS)

    Psakhie, S. G.; Meisner, S. N.; Lotkov, A. I.; Meisner, L. L.; Tverdokhlebova, A. V.

    2014-07-01

    This paper presents the study on changes in element and phase compositions in the near-surface layer and on surface topography of the NiTi specimens after the silicon ion-beam treatment. The effect of these parameters of the near-surface layer on corrosion properties in biochemical solutions and biocompatibility with mesenchymal stem cells of rat marrow is studied. Ion-beam surface modification of the specimens was performed by a DIANA-3 implanter (Tomsk, Russia), using single-ion-beam pulses under oil-free pumping and high vacuum (10-4 Pa) conditions in a high-dose ion implantation regime. The fluence made 2 × 1017 cm-2, at an average accelerating voltage of 60 kV, and pulse repetition frequency of 50 Hz. The silicon ion-beam treatment of specimen surfaces is shown to bring about a nearly twofold improvement in the corrosion resistance of the material to attack by aqueous solutions of NaCl (artificial body fluid) and human plasma and a drastic decrease in the nickel concentration after immersion of the specimens into the solutions for ~3400 and ~6000 h, respectively (for the artificial plasma solution, a nearly 20-fold decrease in the Ni concentration is observed). It is shown that improvement of NiTi corrosion resistance after treatment by Si ions occurs mainly due to the formation of two-layer composite coating based on Ti oxides (outer layer) on the NiTi surface and adjacent inner layer of oxides, carbides, and silicides of the NiTi alloy components. Inner layer with high silicon concentration serves as a barrier layer preventing nickel penetration into biomedium. This, in our opinion, is the main reason why the NiTi alloy exhibits no cytotoxic properties after ion modification of its surface and leads to the biocompatibility improvement at the cellular level, respectively.

  15. Novel far infrared imaging sensor based on the use of titanium-nickel shape memory alloys

    NASA Astrophysics Data System (ADS)

    Ho, Ho-Pui; Chung, Jonathan C. Y.; Ng, Ki-Cheong; Cheng, K. L.; Wu, Shu-Yuen

    2002-11-01

    In this paper we describe a novel imaging sensor design1 that uses the thermo-mechanical properties of nickel-titanium (NiTi) shape memory alloys (SMAs) for detecting far infrared radiation (FIR). A thin NiTi SMA cantilever is coated with a FIR absorbing layer on one surface, while the other is coated with a highly reflecting metallic layers such as gold. Upon absorption of FIR, the temperature of the cantilever changes. This causes the tilt angle of the cantilever to change as well. The deflection is very large if the temperature change coincides with the temperature range of the phase transformation of the NiTi SMA. The detection of the mechanical movements in the cantilever is achieved by illuminating the reflective side using a visible laser beam. A Michelson interferometer is used to covert the reflected light into optical modulation. In doing this, very small displacement in the cantilever can be visualized as laser intensity variation. A single element device has been fabricated for this purpose and our initial experimental results have demonstrated the successful detection of FIR. An estimation of angular deflection per unit change of temperature suggests that our approach can offer sensitivity higher than the reported design based on the use of bi-material strips. We envisage that a two-dimensional array of such devices can lead to the possibility of realizing a practical low-cost infrared imaging device operating under room temperature conditions.

  16. A stabilized, high stress self-biasing shape memory alloy actuator

    NASA Astrophysics Data System (ADS)

    Panton, B.; Zhou, Y. N.; Khan, M. I.

    2016-09-01

    A shape memory alloy (SMA) actuator that is biased internally would not need an external bias to achieve multiple actuation cycles. This would reduce cost, complexity and weight compared to standard one-way SMAs. The self-biasing actuators that have been developed to date have a lack of geometric and actuation stability. The current study developed a self-biasing NiTi actuator using a laser based vaporization process to alter the bulk composition of different regions. The martensitic laser processed NiTi region was the actuator, and un-processed austenitic base metal region was the internal bias. It was discovered that the laser processed region of the self-biasing actuator was unstable during high stress thermomechanical cycling due to the coarse grained microstructure. Cold-working of the half martensitic and half austenitic component resulted in similar deformation characteristics to single phase NiTi, which enabled the formation of a uniform nanocrystalline microstructure in both regions. When thermomechanically cycled 6000 times under stresses ranging from 180 to 400 MPa, it was discovered that this treated self-biasing actuator exhibited the stabilization behavior of traditional one-way actuators. This behavior was due to the uniform nanocrystalline microstructure, which impeded dislocation activity and ensured minimal plastic deformation.

  17. Microstructure of cryogenically treated martensitic shape memory nickel-titanium alloy

    PubMed Central

    Vinothkumar, Thilla Sekar; Kandaswamy, Deivanayagam; Prabhakaran, Gopalakrishnan; Rajadurai, Arunachalam

    2015-01-01

    Context: Recent introduction of shape memory (SM) nickel-titanium (NiTi) alloy into endodontics is a major breakthrough. Although the flexibility of these instruments was enhanced, fracture of rotary endodontic instruments during instrumentation is an important challenge for the operator. Implementation of supplementary manufacturing methods that would improve the fatigue life of the instrument is desirable. Aim: The purpose of this study was to investigate the role of dry cryogenic treatment (CT) conditions on the microstructure of martensitic SM NiTi alloy. Materials and Methods: Experiments were conducted on Ni-51 wt% Ti-49 wt% SM alloy. Five cylindrical specimens and five sheet specimens were subjected to different CT conditions: Deep CT (DCT) 24 group: −185°C; 24 h, DCT 6 group: −185°C; 6 h, shallow CT (SCT) 24 group: −80°C, 24 h, SCT 6 group: −80°C, 6 h and control group. Microstructure of surface was observed on cylindrical specimens with an optical microscope and scanning electron microscope at different magnifications. Subsurface structure was analyzed on sheet specimens using X-ray diffraction (XRD). Results: Microstructures of all SM NiTi specimens had equiaxed grains (approximately 25 μm) with well-defined boundaries and precipitates. XRD patterns of cryogenically treated specimens revealed accentuation of austenite and martensite peaks. The volume of martensite and its crystallite size was relatively more in DCT 24 specimen. Conclusions: DCT with 24 h soaking period increases the martensite content of the SM NiTi alloy without altering the grain size. PMID:26180413

  18. Temperature-dependent quantitative 3{omega} scanning thermal microscopy: Local thermal conductivity changes in NiTi microstructures induced by martensite-austenite phase transition

    SciTech Connect

    Chirtoc, M.; Gibkes, J.; Wernhardt, R.; Pelzl, J.; Wieck, A.

    2008-09-15

    We develop the theoretical description of 3{omega} signals from the resistive Wollaston thermal probe (ThP) of a scanning thermal microscope (SThM) in terms of an equivalent low-pass filter. The normalized amplitude and phase frequency spectra are completely characterized by a single parameter, the crossover frequency f{sub c}(k) depending on the sample thermal conductivity k. The application concerns polycrystalline NiTi shape memory alloy microstructured by focused Ga ion beam milling and implantation. The calibration of the ThP combined with a novel two-step normalization procedure allowed quantitative exploitation of 3{omega} signal variations as small as -1.75% in amplitude and 0.60 deg. in phase upon heating the sample from room temperature to 100 deg. C. This corresponds to k increase of 23.9% that is consistent with the expected thermal conductivity variation due to martensite-austenite structural phase transition. To our knowledge this is for the first time that SThM 3{omega} phase information is used quantitatively as well. The static, calibrated 3{omega} measurements are complementary to 3{omega} SThM images of the patterned sample surface. The local SThM measurement of temperature-dependent thermal conductivity opens the possibility to imaging structural phase transitions at submicron scale.

  19. Three-dimensional phase field simulation of the morphology and growth kinetics of Ni4Ti3 precipitates in a NiTi alloy

    NASA Astrophysics Data System (ADS)

    Ke, C. B.; Cao, S.; Zhang, X. P.

    2014-07-01

    A three-dimensional phase field model is applied to study the morphology and growth kinetics of Ni4Ti3 precipitates, as well as the Ni concentration distribution feature, during the aging of a NiTi alloy. The model can reproduce well the multiple-variants morphology of Ni4Ti3 precipitates. The diameter-to-thickness ratio of lenticular Ni4Ti3 precipitates in the equilibrium shape is 4.2. Simulation results show that the Ni depletion region near the face of Ni4Ti3 precipitates is broader than that near the edge of the precipitates, and both the depletion level of Ni concentration and the length of the Ni depletion region adjacent to the precipitates increase with the aging time. The growth of the precipitate diameter and thickness can be described by the power-law fitting equation, with growth exponent m = 0.47 for the diameter and m = 0.46 for the thickness, which are in good agreement with those obtained in previous experimental and analytical studies.

  20. 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.

  1. Schapiro Shapes

    ERIC Educational Resources Information Center

    O'Connell, Emily

    2009-01-01

    This article describes a lesson on Schapiro Shapes. Schapiro Shapes is based on the art of Miriam Schapiro, who created a number of works of figures in action. Using the basic concepts of this project, students learn to create their own figures and styles. (Contains 1 online resource.)

  2. Micromechanics of stress-induced martensitic transformation in mono- and polycrystalline shape memory alloys: Ni-Ti

    SciTech Connect

    Liang, Y.; Taya, M.; Mori, T.

    1999-07-01

    Stress-induced martensitic transformation in single crystals and polycrystals are examined on the basis of micromechanics. A simple method to find a stress- and elastic energy-free martensite plate (combined variant), which consists of two variants, is presented. External and internal stresses preferentially produce a combined variant, to which the stresses supply the largest work upon its formation. Using the chemical energy change with temperature, the phase boundary between the parent and martensitic phases is determined in stress-temperature diagrams. The method is extended to a polycrystal, modeled as an aggregate of spherical grains. The grains constitute axisymmetric multiple fiber textures and a uniaxial load is applied to the fiber axis. The occurrence and progress of transformation are followed by examining a stress state in the grains. The stress is the sum of the external stress and internal stress. The difference in the fraction of transformation and, thus, in transformation strains between the grains causes the internal stress, which is calculated with the average field method. After a short transition stage, all the grains start to transform, and the external uniaxial stress to continue the transformation increases linearly thereafter. The external stress at the end of the transition is defined as the macroscopic yield stress due to the transformation in polycrystals. The yield stress tends to saturate, as the number of the textures increases.

  3. 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.

  4. Hydrogen embrittlement of Ni-Ti superelastic alloy in fluoride solution.

    PubMed

    Yokoyama, Ken'ichi; Kaneko, Kazuyuki; Moriyama, Keiji; Asaoka, Kenzo; Sakai, Jun'ichi; Nagumo, Michihiko

    2003-05-01

    Hydrogen embrittlement of Ni-Ti superelastic alloy in a fluoride solution (0.2% APF) has been investigated by means of a tensile test (after immersion) and hydrogen thermal desorption analysis. Upon immersion, the tensile strength of the alloy decreased to the critical stress level of martensite transformation. Hydrogen desorption of the immersed specimens appeared with a peak at around 500 degrees C. The amount of absorbed hydrogen in the alloy ranged from 100 to 1000 mass ppm when immersed in the fluoride solution for 2 to 24 h. The immersion in the fluoride solution led to the degradation of mechanical properties due to hydrogen embrittlement. The results of the present study imply that one reason that Ti and its alloys fracture in the oral cavity is the fact that hydrogen is absorbed in a fluoride solution, such as prophylactic agents. PMID:12734810

  5. The role of the martensite transformation for the mechanical amorphization of NiTi

    SciTech Connect

    Ewert, J.C.; Boehm, I.; Haider, F.; Peter, R.

    1997-05-01

    Mechanical amorphization by cold rolling and uniaxial deformation of the intermetallic compound NiTi was studied by TEM and DSC. In cold rolled samples it could be clearly shown that amorphization occurs and that the amorphous regions recrystallize at T {approx} 350 C. In uniaxially deformed material a microstructure similar to that of cold rolled samples and a DSC-peak at the same temperature was found. In the TEM, extended amorphous regions could only be identified after a moderate heat treatment at 250 C. After deformation at temperatures above room temperature, a considerably lower degree of amorphization was found, and the fraction of amorphous volume was found to depend on the martensite transition temperature of the material.

  6. Characterization of Inclusions in VIM/VAR NiTi Alloys

    NASA Astrophysics Data System (ADS)

    Coda, A.; Zilio, S.; Norwich, D.; Sczerzenie, F.

    2012-12-01

    Inclusions content is important for the mechanical behavior and performances of NiTi-based products particularly in fatigue-rated devices. Higher inclusions content has been correlated to reductions in transformation temperatures and strain recovery under mechanical or thermo-mechanical cycling. Moreover, most fatigue fractures show inclusions at the initiation site. However, there is a general lack of information on the nature and characteristics of such inclusions, especially those typically recognized as intermetallics oxides. In this study, the common scanning electron microscopy technique has been used to investigate the chemistry and morphology of inclusions in commercial standard VIM/VAR binary NiTi alloys. The defined experimental procedure, results, and their significance will be presented and discussed.

  7. Influence of Surface Morphology on the Torsion Fracture of NiTi Endodontic Instruments

    NASA Astrophysics Data System (ADS)

    Elias, Carlos; Lopes, Helio; Vieira, Victor; Souza, Leticia; Vieira, Márcia

    2014-07-01

    This study analyzed the influences of manufacturing process (twisting and machining) and surface finishing on the angular distortion, maximum torque, and toughness of two NiTi endodontic instruments (Race—FKG Dentaire and TF—Twisted Files, SybronEndo). Statistical analysis of results showed that TF instruments (twisted) had higher distortion angle ( p < 0.05) and lower maximum torque to fracture ( p < 0.05) than Race instruments (machined). SEM analysis of fractured instruments showed a surface morphology characteristic of ductile fracture, with plastic deformation in the helical shafts. The results suggest that both instruments are equally suitable for clinical applications. This study is purely scientific as it evaluates only some material properties, and is not intended to endorse a commercial product.

  8. Failure of ProTaper rotary Ni-Ti instruments used by undergraduate students

    PubMed Central

    Duran-Sindreu, Fernando; Morello-Castro, Sergio; Mercade-Bellido, Montserrat; Bueno-Martínez, Rufino; Roig-Cayón, Miguel

    2012-01-01

    Objective: To evaluate the effect of number of uses, angle and radius of curvature and type of instrument on the fracture of ProTaper rotary instruments when used by undergraduate students. Study Design: Three hundred and seventy-six molars, with a total of 1114 root canals, extracted were instrumented by undergraduate students using ProTaper instruments according to the manufacturer´s recommendations. When fracture occurred, data were collected concerning the number of uses, type of instrument, level of fracture, angle and radius of curvature. ANOVA test were used to determine the influence of type of instrument in the incidence of instrument fracture. Logistic regression model was used to determine the influence of number of uses, angle and radius of curvature in the incidence of instrument fracture. Significance was set at p< 0.05. Results: A total of 37 Ni-Ti rotary instruments fractured during the treatment. Fracture occurred in 9.84% (37/376) of the teeth treated and 3.32% of the canals prepared with Ni-Ti rotary instruments (37/1114). A decrease in the radius of curvature of the canal significantly increased the likelihood of fracture (p=0.0001). Instrument fracture significantly increased as the number of uses increased (p=0.0037). No significant differences were found between the 6 types of ProTaper instruments (p=0.8). A reduction in the angle of curvature did not produce a significant decrease in the incidence of instrument separation (p=0.08). Conclusions: The results of this study imply that instrument fracture is linked to radius of curvature and number of uses. Key words:Fracture, ProTaper ®, root canal preparation, undergraduate students. PMID:24558555

  9. Ion irradiation induced solid-state amorphous reaction in Ni/Ti multilayers

    NASA Astrophysics Data System (ADS)

    Milosavljević, Momir; Toprek, Dragan; Obradović, Marko; Grce, Ana; Peruško, Davor; Dražič, Goran; Kovač, Janez; Homewood, Kevin P.

    2013-03-01

    The effects of Ar ion irradiation on interfacial reactions induced in Ni/Ti multilayers were investigated. Structures consisting of 10 alternate Ni (˜26 nm) and Ti (˜20 nm) layers of a total thickness ˜230 nm were deposited by ion sputtering on Si (1 0 0) wafers. Argon irradiations were done at 180 keV, to the doses of 1-6 × 1016 ions/cm2, the samples being held at room temperature. The projected implanted ion range is 86 ± 36 nm, maximum energy loss is closer to the surface, and maximum displacements per atom (dpa) from 47 to 284 for Ni and 26 to 156 for Ti. Characterizations of samples were performed by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). It is shown that ion irradiation induced a progressed intermixing in the mostly affected zone already for the lowest dose, the thickness of the mix increasing linearly with the irradiation dose. The mixed phase is fully amorphous, starting with a higher concentration of Ni (which is the diffusing species) from the initial stages, and saturating at Ni:Ti˜66:34. A thick amorphous layer (˜127 nm) formed towards the surface region of the structure for the irradiation dose of 4 × 1016 ions/cm2 remains stable with increasing the dose to 6 × 1016 ions/cm2, which introduces up to 6-7 at.% of Ar within the mix. The results are discussed in light of the existing models. They can be interesting for introducing a selective and controlled solid-state reaction and towards further studies of ion irradiation stability of amorphous Ni-Ti phase.

  10. Laser surface treatment of polyamide and NiTi alloy and the effects on mesenchymal stem cell response

    NASA Astrophysics Data System (ADS)

    Waugh, D. G.; Lawrence, J.; Shukla, P.; Chan, C.; Hussain, I.; Man, H. C.; Smith, G. C.

    2015-07-01

    Mesenchymal stem cells (MSCs) are known to play important roles in development, post-natal growth, repair, and regeneration of mesenchymal tissues. What is more, surface treatments are widely reported to affect the biomimetic nature of materials. This paper will detail, discuss and compare laser surface treatment of polyamide (Polyamide 6,6), using a 60 W CO2 laser, and NiTi alloy, using a 100 W fiber laser, and the effects of these treatments on mesenchymal stem cell response. The surface morphology and composition of the polyamide and NiTi alloy were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. MSC cell morphology cell counting and viability measurements were done by employing a haemocytometer and MTT colorimetric assay. The success of enhanced adhesion and spreading of the MSCs on each of the laser surface treated samples, when compared to as-received samples, is evidenced in this work.

  11. Influence of Soft Drinks with Low pH on Different Ni-Ti Orthodontic Archwire Surface Patterns

    NASA Astrophysics Data System (ADS)

    Abalos, C.; Paul, A.; Mendoza, A.; Solano, E.; Palazon, C.; Gil, F. J.

    2013-03-01

    The aim of this study was to determine the influence of soft drinks on the surface of Ni-Ti archwires and their corrosion behavior. Archwires with different patterns (smooth, scratch, dimple, and crack) were selected and characterized by scanning electron microscopy and laser confocal microscopy. Immersion tests were performed in artificial saliva (pH 6.7) with a soft drink with a pH of 2.5 for 28 days. The results showed an increase in the surface defects and/or roughness of the dimple, crack and scratch patterns with the immersion times, and a decrease in corrosion resistance. A relationship between the surface pattern and the extent of the corrosion in Ni-Ti archwires with soft drinks at low pH has been demonstrated. Pattern should be taken into account in future studies, and manufacturing processes that produce surface defects (especially cracks) should be avoided.

  12. Coating NiTi archwires with diamond-like carbon films: reducing fluoride-induced corrosion and improving frictional properties.

    PubMed

    Huang, S Y; Huang, J J; Kang, T; Diao, D F; Duan, Y Z

    2013-10-01

    This study aims to coat diamond-like carbon (DLC) films onto nickel-titanium (NiTi) orthodontic archwires. The film protects against fluoride-induced corrosion and will improve orthodontic friction. 'Mirror-confinement-type electron cyclotron resonance plasma sputtering' was utilized to deposit DLC films onto NiTi archwires. The influence of a fluoride-containing environment on the surface topography and the friction force between the brackets and archwires were investigated. The results confirmed the superior nature of the DLC coating, with less surface roughness variation for DLC-coated archwires after immersion in a high fluoride ion environment. Friction tests also showed that applying a DLC coating significantly decreased the fretting wear and the coefficient of friction, both in ambient air and artificial saliva. Thus, DLC coatings are recommended to reduce fluoride-induced corrosion and improve orthodontic friction. PMID:23793493

  13. Influence of microstructure on the shape memory properties of two titanium-lean, nickel-titanium-platinum high temperature shape memory alloys

    NASA Astrophysics Data System (ADS)

    Hudish, Grant A.

    Because of NiTi's superior properties (work output, strength, ductility, recoverable strain, etc.) it is the base system of choice for development of derivative high-temperature shape memory alloys (HTSMAs). Ternary additions of Hf, Zr, Pt, Pd, and Au can be made, in quantities greater than ≈ 10 at.%, to increase the transformation temperature of Ni-Ti based SMAs. Pt as an alloying addition is attractive because of (1) its efficiency in raising the martensitic transformation temperature, (2) the relatively stable properties during thermal cycling of Pt-containing Nitinol (NiTi), and (3) the high work outputs of Ni-Ti-Pt alloys relative to other HTSMAs. Platinum containing samples of NiTi were thermally processed to explore the utility of Ti-lean precipitates for matrix strengthening and stabilization of shape memory properties during thermomechanical cycling. Two alloys, Ti48.5Ni30.5Pt 21 and Ti49.5Ni29.5Pt21, were heat treated for 1, 5, 24 and 100h at 500, 550, 600, 650, and 700°C and examined using SEM, EDS, DTA, XRD and TEM techniques. Two relevant precipitate phases, the PL and Ti2(Ni,Pt)3 phases, were identified, characterized and the thermodynamic stability and relevant behavior during thermal processing determined. Samples were then subjected to thermomechanical testing that consisted of two parts, (1) two thermal cycles (75°C to 500°C to 75°C) each at stresses of 0, 50, 100, 150, 200, 250, and 300MPa, and (2) 100 thermal cycles at 200MPa. With this combination of systematic microstructural characterization and isobaric thermal cycling, the link between microstructure and shape memory performance was made. The influence the PL and Ti2(Ni,Pt)3 phases have on properties such as martensitic transformation temperatures, transformation strain, and accumulated irrecoverable strain are explained and discussed. Specifically, it was found that the P L-phase suppresses transformation temperatures and strains through a matrix strengthening effect, but also

  14. The influence of FeTi and NiTi intermetallide additions on high-temperature oxidation of permalloy alloy

    SciTech Connect

    Klimenko, V.N.; Lavrenko, V.A.; Panasyuk, O.A.; Blasova, O.V.; Protsenko, T.G.

    1995-11-01

    As a rule powder metallurgy Permalloy alloys are used in production of parts for electronic instruments. For the purpose of controlling the magnetic and electrical properties and also the wear (in the case of production of magnetic heads) and corrosion resistance appropriate additions of metals or such compounds as carbides and oxides are added to the alloy. In this work use of FeTi and NiTi intermetallides produced by reaction sintering of powders of pure metals in a protective atmosphere as alloying additions to Permalloy is recommended. The size of the original powders is less than 100 {mu}m. For reaction sintering at temperature 50{degrees}C above the eutectic temperature in the Ti-TiFe and TiNi-Ni systems was selected. The contents of titanium, iron, and oxygen in the FeTi alloy is 51.9, 45.7, and 2.4 wt.%, respectively, and of titanium, nickel, and oxygen in the NiTi alloy 59.6, 31.9, and 4.6 wt.%. High-temperature oxidation in air up to 1300{degrees}C with a rate of change in temperature of 15{degrees}C of type 78N Permalloy with additions of FeTi and NiTi alloys was investigated with use of methods of differential thermal and differential thermogravimetric analyses on an OD-103 derivatograph under nonisothermal conditions. The reaction products were studied by x-ray diffraction phase analysis on a DRON-3 instrument in CoK{sub {alpha}}-radiation. Pure 78N alloy powder with a composition of 78.1% Ni + 19.3% Fe (specimen 1) and also with additions of 1% FeTi (specimen 2) and 1% NiTi (specimen 3) were subjected to oxidation.

  15. 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.

  16. Highly Porous NiTi with Isotropic Pore Morphology Fabricated by Self-Propagated High-Temperature Synthesis

    NASA Astrophysics Data System (ADS)

    Hosseini, S. A.; Alizadeh, M.; Ghasemi, A.; Meshkot, M. A.

    2013-02-01

    Highly porous NiTi with isotropic pore morphology has been successfully produced by self-propagating high-temperature synthesis of elemental Ni/Ti metallic powders. The effects of adding urea and NaCl as temporary pore fillers were investigated on pore morphology, microstructure, chemical composition, and the phase transformation temperatures of specimens. These parameters were studied by optical microscopy, scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry (DSC). Highly porous specimens were obtained with up to 83% total porosity and pore sizes between 300 and 500 μm in diameter. Results show pore characteristics were improved from anisotropic to isotropic and pore morphology was changed from channel-like to irregular by adding pore filler powders. Furthermore, the highly porous specimens produced when using urea as a space holder, were of more uniform composition in comparison to NaCl. DSC results showed that a two-step martensitic phase transformation takes place during the cooling cycles and the austenite finish temperature ( A f) is close to human body temperature. Compression test results reveal that the compressive strength of highly porous NiTi is about 155 MPa and recoverable strain about 6% in superelasticity regime.

  17. Anomalous temperature dependence of yield stress and work hardening coefficient of B2-stabilized NiTi alloys

    SciTech Connect

    Hosoda, Hideki; Mishima, Yoshinao; Suzuki, Tomoo

    1997-12-31

    Yield stress and work hardening coefficient of B2-stabilized NiTi alloys are investigated using compression tests. Compositions of NiTi alloys are based on Ni-49mol.%Ti, to which Cr, Co and Al are chosen as ternary elements which reduce martensitic transformation temperatures of the B2 phase. Mechanical tests are carried out in liquid nitrogen at 77 K, air at room temperature (R.T.) and in an argon atmosphere between 473 K and 873 K. Only at 77 K, some alloys show characteristic stress-strain curves which indicate stress induced martensitic transformation (SIMT), but the others do not. Work hardening coefficient is found to be between 2 and 11GPa in all the test temperature range. The values are extremely high compared with Young`s modulus of B2 NiTi. Yield stress and work hardening coefficient increase with test temperature between R.T. and about 650 K in most alloys. The anomalous temperature dependence of mechanical properties is not related to SIMT but to precipitation hardening and/or anomalous dislocation motion similar to B2-type CoTi. Solution hardening by adding ternary elements is evaluated to be small for Cr and Co additions, and large for Al addition, depending on difference in atomic size of the ternary element with respect to Ni or Ti.

  18. Reliability performance of titanium sputter coated Ni-Ti arch wires: mechanical performance and nickel release evaluation.

    PubMed

    Anuradha, P; Varma, N K Sapna; Balakrishnan, Avinash

    2015-01-01

    The present research was aimed at developing surface coatings on NiTi archwires capable of protection against nickel release and to investigate the stability, mechanical performance and prevention of nickel release of titanium sputter coated NiTi arch wires. Coated and uncoated specimens immersed in artificial saliva were subjected to critical evaluation of parameters such as surface analysis, mechanical testing, element release, friction coefficient and adhesion of the coating. Titanium coatings exhibited high reliability on exposure even for a prolonged period of 30 days in artificial saliva. The coatings were found to be relatively stable on linear scratch test with reduced frictional coefficient compared to uncoated samples. Titanium sputtering adhered well with the Ni-Ti substrates at the molecular level, this was further confirmed by Inductive coupled plasma emission spectroscopy (ICPE) analysis which showed no dissolution of nickel in the artificial saliva. Titanium sputter coatings seem to be promising for nickel sensitive patients. The study confirmed the superior nature of the coating, evident as reduced surface roughness, friction coefficient, good adhesion and minimal hardness and elastic modulus variations in artificial saliva over a given time period. PMID:26484557

  19. Effects of additions of small amounts of fourth elements on structure, crystal structure and shape recovery of Cu-Zn-Al shape memory alloys

    SciTech Connect

    Zhang, M.R. |; Yang, D.Z.; Tadaki, T.; Hirotsu, Y.

    1997-01-15

    Cu-based shape memory alloys (SMAs) are particularly interesting, compared to Ni-Ti SMAs because of their low cost and relatively ease process. However, there are important problems to be solved, such as intergranular fracture due to large grain size, stabilization of martensite, etc. In the present work, the influences of additions only less than 1 mass% of several fourth elements, such as Mn, Fe, Co, Ni, and Y, to two kinds of Cu-Zn-Al SMAs, i.e., Cu-30Zn-4Al and Cu-25Zn-7Al on their structure, crystal structure and shape recovery have been examined in order to know what elements are the most effective for the thermal stability of the parent and martensite phases and the shape memory capacity.

  20. Effect of dry cryogenic treatment on Vickers hardness and wear resistance of new martensitic shape memory nickel-titanium alloy

    PubMed Central

    Vinothkumar, Thilla Sekar; Kandaswamy, Deivanayagam; Prabhakaran, Gopalakrishnan; Rajadurai, Arunachalam

    2015-01-01

    Objectives: The aim of this study is to investigate the role of dry cryogenic treatment (CT) temperature and time on the Vickers hardness and wear resistance of new martensitic shape memory (SM) nickel-titanium (NiTi) alloy. The null hypothesis tested was that there is no difference in Vickers hardness and wear resistance between SM NiTi alloys following CT under two soaking temperatures and times. Materials and Methods: The composition and the phase transformation behavior of the alloy were examined by X-ray energy dispersive spectroscopy and differential scanning calorimetry, respectively. Fifteen cylindrical specimens and 50 sheet specimens were subjected to different CT conditions: Deep cryogenic treatment (DCT) 24 group: −185°C, 24 h; DCT six group: −185°C, 6 h; shallow cryogenic treatment (SCT) 24 group: −80°C, 24 h; SCT six group: −80°C, 6 h; and control group. Wear resistance was assessed from weight loss before and after reciprocatory wet sliding wear. Results: The as-received SM NiTi alloy contained 50.8 wt% nickel and possessed austenite finish temperature (Af) of 45.76°C. Reduction in Vickers hardness of specimens in DCT 24 group was highly significant (P < 0.01; Tukey's honest significant difference [HSD]). The weight loss was significantly higher in DCT 24 group (P < 0.05; Tukey's HSD). Conclusion: Deep dry CT with 24 h soaking period significantly reduces the hardness and wear resistance of SM NiTi alloy. PMID:26929689

  1. Evaluation of Mechanical and Physical Properties of Clinically Used and Recycled Superelastic NiTi Wires

    PubMed Central

    Bavikati, Venkata Naidu; Mandava, Prasad; Killamsetty, Sai Sandeep; Nettam, Venkatesh; Karnati, Praveen Kumar Reddy

    2016-01-01

    Introduction The initial leveling and aligning phase has been simplified with the introduction of superelastic nickel-titanium archwires. The relatively high cost of these wires has prompted some of the clinicians to reuse them after sterilization. The quantitative changes in the surface properties of superelastic ‘NiTi’ wires after clinical application and recycling by autoclave method have not been established in earlier studies. Aim To quantify the changes in mechanical and physical properties of four different commercially available superelastic nitinol (NiTi) archwires after clinical usage and recycling. Materials and Methods The superelastic ‘NiTi archwires obtained from four different manufacturers: Group I-GAC (McMinnville, USA); Group II- 3M Company (California, USA); Group III- G&H Company(Franklin, USA) and Group IV- American Orthodontics (AO) (Sheboygan, USA) were selected for the study. Each of the four groups comprised of 20 samples of wire with 10 of them selected randomly as control and remaining 10 as test specimen in each group. The experimental archwires were placed on selected patients for a period of three months followed by Standard Autoclave sterilization at 121°C and 15 to 20 psi pressure for 20 minutes and were retrieved. The tensile strength was evaluated by Instron-Universal Testing Machine. The quantification of changes in surface roughness was investigated by grid method using Scanning Electron Microscope (SEM). The Control Wires (C) were evaluated at initial time “T1” where as the Experimental sample of wires (T) were subjected to testing at an initial time ‘T1’ and after clinical usage and sterilization at ‘T2’ Statistical Analysis Paired t-test was used for intra-group comparison and one way ANOVA and Post Hoc Tukey tests were used for inter-group comparison. Results There was significant decrease in tensile strength (p = 0.0015 to 0.001) and surface roughness (p< 0.001) between control and experimental arch wires

  2. 60NiTi Intermetallic Material Evaluation for Lightweight and Corrosion Resistant Spherical Sliding Bearings for Aerospace Applications, Report on NASA-Kamatics SAA3-1288

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Jefferson, Michael

    2015-01-01

    Under NASA Space Act Agreement (SAA3-1288), NASA Glenn Research Center and the Kamatics subsidiary of the Kaman Corporation conducted the experimental evaluation of spherical sliding bearings made with 60NiTi inner races. The goal of the project was to assess the feasibility of manufacturing lightweight, corrosion resistant bearings utilizing 60NiTi for aerospace and industrial applications. NASA produced the bearings in collaboration with Abbott Ball Corporation and Kamatics fabricated bearing assemblies utilizing their standard reinforced polymer liner material. The assembled bearings were tested in oscillatory motion at a load of 4.54 kN (10,000 lb), according to the requirements of the plain bearing specification SAE AS81820. Several test bearings were exposed to hydraulic fluid or aircraft deicing fluid prior to and during testing. The results show that the 60NiTi bearings exhibit tribological performance comparable to conventional stainless steel (440C) bearings. Further, exposure of 60NiTi bearings to the contaminant fluids had no apparent performance effect. It is concluded that 60NiTi is a feasible bearing material for aerospace and industrial spherical bearing applications.

  3. Phase composition in NiTi near-surface layers after electron beam treatment and its variation depending on beam energy density

    SciTech Connect

    Ostapenko, Marina G.; Meisner, Ludmila L.; Lotkov, Aleksandr I. E-mail: egu@ispms.tsc.ru; Gudimova, Ekaterina Y. E-mail: egu@ispms.tsc.ru

    2014-11-14

    In the work, we study the mechanisms of structural phase state formation in NiTi surface layers after low-energy pulsed electron beam irradiation depending on the electron beam energy density. It is revealed that after electron beam treatment of the NiTi specimens at energy densities E{sub 1} = 15 J/cm{sup 2}, E{sub 2} = 20 J/cm{sup 2}, and E{sub 3} = 30 J/cm{sup 2}, a series of effects is observed: the absence of the Ti2Ni phase and the presence of new peaks correspond to the B19′ martensite phase with monoclinic structure. Estimation of the relative volume content of the B2 and B19′ phases from the total intensity of their peaks shows that the percentage of the martensite phase increases from ∼5 vol.% in the NiTi specimen irradiated at E{sub 1} = 15 J/cm{sup 2} to ∼80 vol.% in the NiTi specimen irradiated at E{sub 3} = 30 J/cm{sup 2}. It is found that in the NiTi specimens irradiated at E ≤ 20 J/cm{sup 2}, the layer that contains a martensite phase resides not on the surface but at some depth from it.

  4. SEM analysis of defects and wear on Ni-Ti rotary instruments.

    PubMed

    Arantes, Werington Borges; da Silva, Celso Monteiro; Lage-Marques, José Luiz; Habitante, Sandramarcia; da Rosa, Luiz Carlos Laureano; de Medeiros, João Marcelo Ferreira

    2014-01-01

    SEM analysis of endodontic instruments from a Ni-Ti rotary system was assessed, before and after using them, considering their defects and deformations. Twenty Twisted File®, BioRąCe®, Mtwo®, and EndoWave® instruments were micrographed at 190× magnification. The files were washed and micrographed again to view alterations as to the presence or absence of irregular edges, grooves, microcavities, and scraping. Simulated root canal preparations were performed using these instruments. The instruments were cleaned and received a microscopic analysis after being used five times. After analysis tests were tested using Fisher's exact test and Kappa to evaluate the concordance among examiners. There was a statistically significant difference with respect to deformations between Twisted File® and other instruments (p < 0.05). There was no statistically significant difference in strains between the other groups (p > 0.05). All Twisted File® instruments showed the same defects; however damage were lower than those found in BioRace® and Mtwo®. The Endowave® did not show the same defects. In accordance with the data we conclude that the presence of defects was higher in Twisted File® instruments as the instruments and BioRace® Mtwo® brand, the defect rate was smaller and Endowave® instruments had no defects. Regarding the presence of wear after five uses among the groups all instruments showed changes in their cutting blades. PMID:24395626

  5. Load bearing and stiffness tailored NiTi implants produced by additive manufacturing: a simulation study

    NASA Astrophysics Data System (ADS)

    Rahmanian, Rasool; Shayesteh Moghaddam, Narges; Haberland, Christoph; Dean, David; Miller, Michael; Elahinia, Mohammad

    2014-03-01

    Common metals for stable long-term implants (e.g. stainless steel, Titanium and Titanium alloys) are much stiffer than spongy cancellous and even stiffer than cortical bone. When bone and implant are loaded this stiffness mismatch results in stress shielding and as a consequence, degradation of surrounding bony structure can lead to disassociation of the implant. Due to its lower stiffness and high reversible deformability, which is associated with the superelastic behavior, NiTi is an attractive biomaterial for load bearing implants. However, the stiffness of austenitic Nitinol is closer to that of bone but still too high. Additive manufacturing provides, in addition to the fabrication of patient specific implants, the ability to solve the stiffness mismatch by adding engineered porosity to the implant. This in turn allows for the design of different stiffness profiles in one implant tailored to the physiological load conditions. This work covers a fundamental approach to bring this vision to reality. At first modeling of the mechanical behavior of different scaffold designs are presented as a proof of concept of stiffness tailoring. Based on these results different Nitinol scaffolds can be produced by additive manufacturing.

  6. Surface roughness and interface width scaling of magnetron sputter deposited Ni/Ti multilayers

    SciTech Connect

    Maidul Haque, S.; Biswas, A.; Tokas, R. B.; Bhattacharyya, D.; Sahoo, N. K.; Bhattacharya, Debarati

    2013-09-14

    Using an indigenously built r.f. magnetron sputtering system, several single layer Ti and Ni films have been deposited at varying deposition conditions. All the samples have been characterized by Grazing Incidence X-ray Reflectivity (GIXR) and Atomic Force Microscopy to estimate their thickness, density, and roughness and a power law dependence of the surface roughness on the film thickness has been established. Subsequently, at optimized deposition condition of Ti and Ni, four Ni/Ti multilayers of 11-layer, 21-layer, 31-layer, and 51-layer having different bilayer thickness have been deposited. The multilayer samples have been characterized by GIXR and neutron reflectivity measurements and the experimental data have been fitted assuming an appropriate sample structure. A power law correlation between the interface width and bilayer thickness has been observed for the multilayer samples, which was explained in the light of alternate roughening/smoothening of multilayers and assuming that at the interface the growth “restarts” every time.

  7. Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi: Simulations vs. Experiment

    NASA Technical Reports Server (NTRS)

    Manchiraju, Sivom; Gaydosh, Darrell; Benafan, Othmane; Noebe, Ronald; Vaidyanathan, Raj; Anderson, Peter M.

    2011-01-01

    A recent microstructure-based FEM model that couples crystal-based plasticity, the B2<-> MB190 phase transformation and anisotropic elasticity at the grain scale is calibrated to recent data for polycrystalline NiTi (49.9 at.% Ni). Inputs include anisotropic elastic properties, texture and differential scanning calorimetry data, as well as a subset of recent isothermal deformation and load-biased thermal cycling data. The model is assessed against additional experimental data. Several experimental trends are captured - in particular, the transformation strain during thermal cycling monotonically increases and reaches a peak with increasing bias stress. This is achieved, in part, by modifying the martensite hardening matrix proposed by Patoor et al. [Patoor E, Eberhardt A, Berveiller M. J Phys IV 1996;6:277]. Some experimental trends are underestimated - in particular, the ratcheting of macrostrain during thermal cycling. This may reflect a model limitation that transformation-plasticity coupling is captured on a coarse (grain) scale but not on a fine (martensitic plate) scale.

  8. Corrosion behavior and surface structure of orthodontic Ni-Ti alloy wires.

    PubMed

    Iijima, M; Endo, K; Ohno, H; Yonekura, Y; Mizoguchi, I

    2001-03-01

    The corrosion behaviors of a commercial Ni-Ti alloy orthodontic wire and a polished plate with same composition in 0.9% NaCl and 1% lactic acid solutions were examined using an electrochemical technique, an analysis of released ions, and a surface analysis by X-ray photoelectron spectroscopy (XPS). The effect of polishing the wire on the corrosion was also examined. The XPS analysis demonstrated the presence of a thick oxide film mainly composed of TiO2 with trace amounts of Ni hydroxide, which had formed on the wire surface during the heat treatment and subsequent pickling processes. This oxide layer contributed to the higher resistance of the as-received wire to both general and localized corrosion in 0.9% NaCl solution, compared with that of the polished plate and the polished wire. The thick oxide layer, however, was not stable and did not protect the orthodontic wire from corrosion in 0.1% lactic acid solution. PMID:11441483

  9. Transition between internal and external nitridation of Ni-Ti alloys

    SciTech Connect

    Savva, G.C.; Weatherly, G.C.; Kirkaldy, J.S.

    1996-06-01

    A series of Ni-Ti alloys ranging in composition from 0.1 to 5 wt pct Ti were annealed in nitrogen gas or a nitrogen/argon gas mixture between 800 C and 1,020 C. The evolution of surface and subscale structures, along with the diffusion profile of Ti in Ni, were investigated using scanning electron microscopy and energy dispersive X-ray analysis (EDX), respectively. A strong extrusion of Ni to accommodate the excess volume of internal TiN precipitation was observed between 0.5 and 1.0 wt pct Ti at 1,020 C, where a continuous superficial layer of stoichiometric TiN begins to form. A finite difference computational algorithm was developed based upon a ternary model of simultaneous diffusion and precipitation, which generates the concentration profile of Ti in Ni and the particle distribution of TiN and subsumes a transition from internal to external nitridation. Because there is a dearth of independent thermodynamic and kinetic data on this system, the authors were forced to use parameters established by a selected minimal set of their own experiments to predict outcomes for the main body of experimental work, thereby obtaining satisfactory closure between theory and experiment.

  10. Elastocaloric effect of Ni-Ti wire for application in a cooling device

    NASA Astrophysics Data System (ADS)

    Tušek, J.; Engelbrecht, K.; Mikkelsen, L. P.; Pryds, N.

    2015-03-01

    We report on the elastocaloric effect of a superelastic Ni-Ti wire to be used in a cooling device. Initially, each evaluated wire was subjected to 400 loading/unloading training cycles in order to stabilize its superelastic behavior. The wires were trained at different temperatures, which lead to different stabilized superelastic behaviors. The stabilized (trained) wires were further tested isothermally (at low strain-rate) and adiabatically (at high strain-rate) at different temperatures (from 312 K to 342 K). We studied the impact of the training temperature and resulting superelastic behavior on the adiabatic temperature changes. The largest measured adiabatic temperature change during loading was 25 K with a corresponding 21 K change during unloading (at 322 K). A special focus was put on the irreversibilities in the adiabatic temperature changes between loading and unloading. It was shown that there are two sources of the temperature irreversibilities: the hysteresis (and related entropy generation) and the temporary residual strain immediately after unloading, respectively. The latter results in the temporary bending of the wire and reduced negative adiabatic temperature change. The paper also shows the impact of the applied strain on the adiabatic temperature changes as well as the distribution of the elastocaloric effect over the wire during loading in the case of two wires trained at different temperatures and the virgin wire, respectively. In the end, we propose guidelines about the required material properties for an efficient elastocaloric cooling device.

  11. The Influence of the R-Phase on the Superelastic Behavior of NiTi

    NASA Astrophysics Data System (ADS)

    Duerig, T. W.; Bhattacharya, K.

    2015-06-01

    Approximately equiatomic Ni-Ti alloys, or Nitinol, can transform upon cooling or when stressed from a parent ordered cubic (B2) Austenite phase into two martensitic structures: a monoclinic structure commonly referred to as simply martensite and a rhombohedrally distorted martensite referred to as the R-phase. While the former is often more stable, the R-phase presents a substantially lower barrier to formation, creating an interesting competition for the succession of Austenite. This competition has markedly different outcomes depending upon whether Austenite instability is caused by cooling or by the application of stress. While medical applications are generally used isothermally, most characterization is done using thermal scans such as differential scanning calorimetry. This leads to frequent and significant misunderstandings regarding plateau stresses in particular. The purpose of this paper is to discuss the competition between these two martensites as the parent Austenite phase loses stability, and to clarify how tests can be properly conducted and interpreted to avoid confusion. To that end, the examples shown are not selected to be ideal or theoretical, but rather to illustrate complexities typical of those found in medical devices, such as cold worked conditions that make peaks difficult to interpret and "plateaus" ill-defined. Finally, a stress-induced M ⇒ R ⇒ M sequence will be discussed.

  12. Influence of topographical features on the fluoride corrosion of Ni-Ti orthodontic archwires.

    PubMed

    Abalos, C; Paúl, A; Mendoza, A; Solano, E; Gil, F J

    2011-12-01

    Different manufacturing processes of Ni-Ti archwires respond differently to corrosion due to the surface conditions involved. In this study, several topographical features and their influence upon fluoride corrosion were studied. Four topographies (smooth, dimple, scratch, and crack) according to the main surface defect were characterized (n = 40). Static corrosion tests were performed in artificial saliva with fluorated prophylactic gel (12500 ppm) for 28 days. The surface was characterized by SEM and laser confocal microscopy. Standard electrochemical corrosion (open circuit potential, corrosion potential and corrosion current density) was performed. Statistical analysis was carried out using the ANOVA test (α ≤ 0.05). An increase was observed in the surface defects and/or roughness of the cracked and scratched surfaces. These defects produced an important increase in corrosion behavior. The best surfaces for the orthodontic archwires were the smooth and dimpled surfaces, respectively. The increase in defects was independent of roughness. Manufacturing processes that produce surface cracks should be avoided in orthodontic applications. PMID:22042458

  13. Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

    NASA Astrophysics Data System (ADS)

    Elkhal Letaief, Wissem; Hassine, Tarek; Gamaoun, Fehmi

    2016-03-01

    The relaxation behavior under tensile loading of a superelastic NiTi alloy was investigated after hydrogen charging with respect to aging from one to 77 days in air at room temperature. The specimens were immersed for 3 h in a 0.9 % NaCl aqueous solution and then relaxed with an imposed strain of 4.8 %—which results in half of the martensite transformation—for different strain rates of 10-4, 10-3, and 5 × 10-3 s-1. For the non-charged specimens, the relaxed stress at the beginning exhibited a temporary dependence on the strain rates and then reached the same equilibrium stress after 2.5 h. After hydrogen charging, this equilibrium stress did not vary for the as-charged specimen. Nevertheless, the greater the aging period is the greater the equilibrium stress is. This behavior can be attributed to the diffusion of hydrogen into the entire specimen, which hinders the relaxation mechanism of the martensite bands.

  14. Comparison of cyclic fatigue resistance between different NiTi instruments with 4% taper.

    PubMed

    Ersoy, Ibrahim; Kol, Elif; Demirhan Uygun, Ahmet; Tanriver, Mehmet; Seckin, Fatih

    2016-05-01

    The aim of this study was to make a comparison between the cyclic fatigue (CF) resistance of F360, twisted files (TF), FlexMaster (FM) and RaCE instruments with 4% taper. A total of 40 instruments were evaluated 8 mm from the tip. A stainless steel block with a simulated canal of 1.5 mm diameter, and a 60° angle of curvature was tested using CF testing. One-way ANOVA and posthoc Tukey's test (P < 0.05) were used. The F 360 files showed the highest CF resistance while the TF files had greater CF resistance than the FM and RaCE (P < 0.05). There was no significant difference between the FM and RaCE (P > 0.05). F360 instruments with a double S cross-section had the highest CF resistance among the group. The TF led the NiTi rotary files to be more resistant to fatigue than the FM and RaCE instruments. Microsc. Res. Tech. 79:345-348, 2016. © 2016 Wiley Periodicals, Inc. PMID:26864386

  15. Biocompatibility of sol-gel-derived titania-silica coated intramedullary NiTi nails.

    PubMed

    Muhonen, V; Kujala, S; Vuotikka, A; Aäritalo, V; Peltola, T; Areva, S; Närhi, T; Tuukkanen, J

    2009-02-01

    We investigated bone response to sol-gel-derived titania-silica coated functional intramedullary NiTi nails that applied a continuous bending force. Nails 26 mm in length, either straight or with a radius of curvature of 28 or 15 mm, were implanted in the cooled martensite form from a proximal to distal direction into the medullary cavity of the right femur in 40 Sprague-Dawley rats. Body temperature restored the austenite form, causing the curved implants to generate a bending force on the bone. The femurs were examined after 24 weeks. Bone length measurements did not reveal any bowing or shortening of the bone in the experimental groups. The results from histomorphometry demonstrated that the stronger bending force, together with sol-gel surface treatment, resulted in more bone deposition around the implant and the formation of significantly less fibrous tissue. Straight intramedullary nails, even those with a titania-silica coating, were poorly attached when compared to the implants with a curved austenite structure. PMID:18838349

  16. Locality and rapidity of the ultra-large elastic deformation of Nb nanowires in a NiTi phase-transforming matrix

    SciTech Connect

    Wang, Shan; Cui, Lishan; Hao, Shijie; Jiang, Daqiang; Liu, Yinong; Liu, Zhenyang; Mao, Shengcheng; Han, Xiaodong; Ren, Yang

    2014-10-24

    This study investigated the elastic deformation behaviour of Nb nanowires embedded in a NiTi matrix. The Nb nanowires exhibited an ultra-large elastic deformation, which is found to be dictated by the martensitic transformation of the NiTi matrix, thus exhibiting unique characteristics of locality and rapidity. These are in clear contrast to our conventional observation of elastic deformations of crystalline solids, which is a homogeneous lattice distortion with a strain rate controlled by the applied strain. The Nb nanowires are also found to exhibit elastic-plastic deformation accompanying the martensitic transformation of the NiTi matrix in the case when the transformation strain of the matrix over-matches the elastic strain limit of the nanowires, or exhibit only elastic deformation in the case of under-matching. Such insight provides an important opportunity for elastic strain engineering and composite design.

  17. Locality and rapidity of the ultra-large elastic deformation of Nb nanowires in a NiTi phase-transforming matrix

    DOE PAGESBeta

    Wang, Shan; Cui, Lishan; Hao, Shijie; Jiang, Daqiang; Liu, Yinong; Liu, Zhenyang; Mao, Shengcheng; Han, Xiaodong; Ren, Yang

    2014-10-24

    This study investigated the elastic deformation behaviour of Nb nanowires embedded in a NiTi matrix. The Nb nanowires exhibited an ultra-large elastic deformation, which is found to be dictated by the martensitic transformation of the NiTi matrix, thus exhibiting unique characteristics of locality and rapidity. These are in clear contrast to our conventional observation of elastic deformations of crystalline solids, which is a homogeneous lattice distortion with a strain rate controlled by the applied strain. The Nb nanowires are also found to exhibit elastic-plastic deformation accompanying the martensitic transformation of the NiTi matrix in the case when the transformation strainmore » of the matrix over-matches the elastic strain limit of the nanowires, or exhibit only elastic deformation in the case of under-matching. Such insight provides an important opportunity for elastic strain engineering and composite design.« less

  18. Locality and rapidity of the ultra-large elastic deformation of Nb nanowires in a NiTi phase-transforming matrix

    PubMed Central

    Wang, Shan; Cui, Lishan; Hao, Shijie; Jiang, Daqiang; Liu, Yinong; Liu, Zhenyang; Mao, Shengcheng; Han, Xiaodong; Ren, Yang

    2014-01-01

    This study investigated the elastic deformation behaviour of Nb nanowires embedded in a NiTi matrix. The Nb nanowires exhibited an ultra-large elastic deformation, which is found to be dictated by the martensitic transformation of the NiTi matrix, thus exhibiting unique characteristics of locality and rapidity. These are in clear contrast to our conventional observation of elastic deformations of crystalline solids, which is a homogeneous lattice distortion with a strain rate controlled by the applied strain. The Nb nanowires are also found to exhibit elastic-plastic deformation accompanying the martensitic transformation of the NiTi matrix in the case when the transformation strain of the matrix over-matches the elastic strain limit of the nanowires, or exhibit only elastic deformation in the case of under-matching. Such insight provides an important opportunity for elastic strain engineering and composite design. PMID:25341619

  19. Embedded Shape Memory Alloy Particles for the Self-Sensing of Fatigue Crack Growth in an Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Leser, William Paul

    Future aerospace vehicles will be built using novel materials for mission conditions that are difficult to replicate in a laboratory. Structural health monitoring and condition-based maintenance will be critical to ensure the reliability of such vehicles. A multi-functional aluminum alloy containing embedded shape memory alloy (SMA) particles to detect fatigue crack growth is proposed. The regions of intensified strain near the tip of a growing fatigue crack cause the SMA particles to undergo a solid-to-solid phase transformation from austenite to martensite, releasing a detectable and identifiable acoustic emission (AE) signal that can be used to locate the crack in the affected component. This study investigates the AE response of two SMA systems, Ni-Ti, and Co-Ni-Al. Tensile (Ni-Ti) and compressive (Co-Ni-Al) tests were conducted to study the strain-induced transformation response in both of the alloy systems. It was found that the critical stress for transformation in both SMA systems was easily identified by a burst of AE activity during both transformation and reverse transformation. AE signals from these experiments were collected for use as training data for a Bayesian classifier to be used to identify transformation signals in a Al7050 matrix with embedded SMA particles. The Al/SMA composite was made by vacuum hot pressing SMA powder between aluminum plates. The effect of hot pressing temperature and subsequent heat treatments (solutionizing and peak aging) on the SMA particles was studied. It was found that, at the temperatures required, Co-Ni-Al developed a second phase that restricted the transformation from austenite to martensite, thus rendering it ineffective as a candidate for the embedded particles. Conversely, Ni-Ti did survive the embedding process and it was found that the solutionizing heat treatment applied after hot pressing was the main driver in determining the final transformation temperatures for the Ni-Ti particles. The effect of hot

  20. Design and application of shape memory actuators

    NASA Astrophysics Data System (ADS)

    Mertmann, M.; Vergani, G.

    2008-05-01

    The use of shape memory alloys in actuators allows the development of robust, simple and lightweight elements for application in a multitude of different industries. Over the years, the intermetallic compound Nickel-Titanium (NiTi or Nitinol) together with its ternary and quaternary derivates has gained general acceptance as a standard alloy. Even though as many as 99% of all shape memory actuator applications make use of Nitinol there are certain properties of this alloy system which require further research in order to find improvements and new markets: • Lack of higher transformation temperatures in the available alloys in order to open the field of automotive applications (Mf temperature > 80 °C) • Non-linearity in the electrical resistivity in order to improve the controllability of the actuator, • Wide hysteresis in the temperature-vs.-strain behaviour, which has a signi-ficant effect on both, the dynamics of the actuator and its controllability. Hence, there is a constant strive in the field towards an improvement of the related properties. However, these improvements are not always just alloy composition related. There is also a tremendous potential in the thermomechanical treatment of the material and in the design of the actuator. Significant improvement steps are already possible if the usage of the existent materials is optimized for the projected application and if the actuator system is designed in the most efficient way. This paper provides an overview about existent designs, applications and alloys for use in actuators, as well as examples of new shape memory actuator application with improved performance. It also gives an overview about general design rules and reflects about the strengths of the material and the related opportunities for its application.

  1. PEEK (polyether-ether-ketone)-coated nitinol wire: Film stability for biocompatibility applications

    NASA Astrophysics Data System (ADS)

    Sheiko, Nataliia; Kékicheff, Patrick; Marie, Pascal; Schmutz, Marc; Jacomine, Leandro; Perrin-Schmitt, Fabienne

    2016-12-01

    High quality biocompatible poly-ether-ether-ketone (PEEK) coatings were produced on NiTi shape memory alloy wires using dipping deposition from colloidal aqueous PEEK dispersions after substrate surface treatment. The surface morphology and microstructure were investigated by Scanning Electron Microscopy at every step of the process from the as-received Nitinol substrate to the ultimate PEEK-coated NiTi wire. Nanoscratch tests were carried out to access the adhesive behavior of the polymer coated film to the NiTi. The results indicate that the optimum process conditions in cleaning, chemical etching, and electropolishing the NiTi, were the most important and determining parameters to be achieved. Thus, high quality PEEK coatings were obtained on NiTi wires, straight or curved (even with a U-shape) with a homogeneous microstructure along the wire length and a uniform thickness of 12 μm without any development of cracks or the presence of large voids. The biocompatibility of the PEEK coating film was checked in fibrobast cultured cells. The coating remains stable in biological environment with negligible Ni ion release, no cytotoxicity, and no delamination observed with time.

  2. A novel approach to determine the effect of irrigation on temperature and failure of Ni-Ti endodontic rotary files

    PubMed Central

    Mousavi, Sayed Ali; Kargar-Dehnavi, Vida; Mousavi, Sayed Amir

    2012-01-01

    Background: Nickel-titanium (Ni-Ti) rotary instrument files are important devices in Endodontics in root canal preparation. Ni-Ti file breakage is a critical and problematic issue and irrigation techniques were applied to decrease risk of file failure root. The aim of the present study was to compare the temperature gradient change of different irrigation solutions with Ni-Ti rotary instrument system during root canal preparation and also to define their effects on the file failure. Materials and Methods: A novel computerized instrumentation was utilized and thirty standard (ProFile #25/.04) files were divided into three groups and subjected to a filing in the root canal test. Changes in temperature on teeth under constant instrumental conditions with custom-designed computerized experimental apparatus were measured by using a temperature sensor bonded to the apical hole. A rotary instrument for canal preparation in three series of solution was used and the changes in temperature after each solution were compared. Finally, the file failure results were mentored according to each step of test. Comparisons were performed between group status clinically by using ANOVA (t) test, once the sample showed up normal and differences of P<0.01 were considered significant. All data collected were computerized and analyzed for frequency, distribution, and statistical description. Results: There was a decrease in the temperature of the instruments, which were immersed in 5% NaOCl, when compared with the water group (P<0.01). There was also a decrease in the temperature of the instruments immersed in water, when compared with the no solution group (P<0.01). Test results showed that sodium hypochlorite, water, or air of root canals does alter the properties of gradual temperature change and contributes to the failure of the instruments. Conclusion: By immersing the file in 5% NaOCl, the temperature gradient decreased and instrument failure was reduced. PMID:23087732

  3. Dental students' perceptions about the endodontic treatments performed using NiTi rotary instruments and hand stainless steel files.

    PubMed

    Martins, Renata Castro; Seijo, Marília Oliveira Saraiva; Ferreira, Efigênia Ferreira; Paiva, Saul Martins; Ribeiro Sobrinho, Antônio Paulino

    2012-01-01

    This study evaluated the perceptions of Brazilian undergraduate dental students about the endodontic treatments performed using NiTi rotary instruments and hand stainless steel. Data were collected using a questionnaire administered to undergraduate dental students enrolled in endodontic disciplines. The students were divided into 3 groups: G1, students who had treated straight canals with SS hand instruments; G2, students who had treated curved canals with SS hand instruments; and G3, students who had treated both straight and curved canals with NiTi rotary instruments. The number of endodontic treatments performed, types of treated teeth, students' learning, time spent, encountered difficulties, quality of endodontic treatment and characteristics of the employed technique were analyzed. There was a 91.3% rate of return for the questionnaires. Mandibular molars were the most frequently treated teeth, followed by maxillary incisors. The Kruskal-Wallis test showed no differences in learning (p=0.528) or in the characteristics of the technique employed (p=0.560) among the three groups. G3 students performed a greater number of endodontic treatments (p<0.001) in a smaller time (p<0.001) than did G1 and G2 students. Difficulties were reported primarily by students in G2 and G3 compared with G1 (p=0.048). The quality of endodontic treatments differed only between G1 and G2 (p=0.045). The use of NiTi rotary instruments should be included in undergraduate dental curriculum, contributing to the increase of patients assisted and consequently to improve the clinical experience of the students. PMID:23338269

  4. Ti-TiC-TiC/DLC gradient nano-composite film on a biomedical NiTi alloy.

    PubMed

    Zheng, Yufeng; Liu, Dong; Liu, Xiliang; Li, Li

    2008-12-01

    Ti-TiC-TiC/diamond-like carbon (DLC) gradient nano-composite films have been prepared on NiTi alloy substrates by the technique of plasma immersion ion implantation and deposition (PIIID) combined with plasma-enhanced chemical vapor deposition (PECVD). The influence of negative bias voltage applied to the substrate (from -100 V to -500 V) on the chemical structure, microstructure, mechanical properties and corrosion resistance was investigated by Raman spectrum, x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), x-ray diffraction (XRD), friction coefficient test, scratch test, nano-indentation test and anodic polarization experiments. The Raman spectrum and XPS results showed that the doped films kept an amorphous DLC structure. TEM observation revealed that nanometer TiC particles were surrounded by the amorphous DLC. With the increase of bias voltage, the ratio of sp(2)/sp(3) first decreased, reaching a minimum value at -200 V, and then increased. The nano-indentation results showed that the hardness of the Ti-TiC-TiC/DLC gradient films reached the maximum value at -200 V when TiC particles reached the maximum content in the films. The friction coefficient test and scratch test indicated that Ti-TiC-TiC/DLC gradient films had a low friction coefficient and high bonding strength with the NiTi substrates. Combined with anodic polarization curves and SEM observation, it was found that the corrosion resistance of the Ti-TiC-TiC/DLC gradient films was much better than that of the bare NiTi alloy. PMID:19029600

  5. The structure of the NiTi surface layers after the ion-plasma alloying of Ta

    SciTech Connect

    Poletika, T. M. Girsova, S. L.; Meisner, L. L. Meisner, S. N.; Schmidt, E. Yu.

    2015-10-27

    The effect of the Ta-ion beam implantation on the micro- and nanostructures of the surface layers of NiTi alloy was investigated using transmission electron microscopy and Auger spectroscopy. It is found that the elements are distributed non-uniformly with depth, so that the sublayers differ significantly in structure. The modified surface layer was found to consist of two sublayers, i.e. the upper oxide layer and the lower-lying amorphous layer that contains a maximum of Ta atoms.

  6. Stress-induced martensitic transformations in NiTi and NiTi-TiC composites investigated by neutron diffraction

    SciTech Connect

    Vaidyanathan, R.; Bourke, M.A.M.; Dunand, D.C.

    1998-12-31

    Superelastic NiTi (51.0 at% Ni) with 0, 10 and 20 vol% TiC particles were deformed under uniaxial compression as neutron diffraction spectra were simultaneously obtained. The experiments yielded in-situ measurements of the thermoelastic stress-induced transformation. A detailed Rietveld determination is made of the phase fractions and the evolving strains in the reinforcing TiC particles and the austenite as it transforms to martensite on loading (and its subsequent back transformation on unloading). These strains are used to shed light on the phenomenon of load transfer in composites where the matrix undergoes a stress-induced phase transformation.

  7. Equilibrium Shaping

    NASA Astrophysics Data System (ADS)

    Izzo, Dario; Petazzi, Lorenzo

    2006-08-01

    We present a satellite path planning technique able to make identical spacecraft aquire a given configuration. The technique exploits a behaviour-based approach to achieve an autonomous and distributed control over the relative geometry making use of limited sensorial information. A desired velocity is defined for each satellite as a sum of different contributions coming from generic high level behaviours: forcing the final desired configuration the behaviours are further defined by an inverse dynamic calculation dubbed Equilibrium Shaping. We show how considering only three different kind of behaviours it is possible to acquire a number of interesting formations and we set down the theoretical framework to find the entire set. We find that allowing a limited amount of communication the technique may be used also to form complex lattice structures. Several control feedbacks able to track the desired velocities are introduced and discussed. Our results suggest that sliding mode control is particularly appropriate in connection with the developed technique.

  8. Finite Element Analysis of a Copper Single Crystal Shape Memory Alloy-Based Endodontic Instruments

    NASA Astrophysics Data System (ADS)

    Vincent, Marin; Thiebaud, Frédéric; Bel Haj Khalifa, Saifeddine; Engels-Deutsch, Marc; Ben Zineb, Tarak

    2015-10-01

    The aim of the present paper is the development of endodontic Cu-based single crystal Shape Memory Alloy (SMA) instruments in order to eliminate the antimicrobial and mechanical deficiencies observed with the conventional Nickel-Titane (NiTi) SMA files. A thermomechanical constitutive law, already developed and implemented in a finite element code by our research group, is adopted for the simulation of the single crystal SMA behavior. The corresponding material parameters were identified starting from experimental results for a tensile test at room temperature. A computer-aided design geometry has been achieved and considered for a finite element structural analysis of the endodontic Cu-based single crystal SMA files. They are meshed with tetrahedral continuum elements to improve the computation time and the accuracy of results. The geometric parameters tested in this study are the length of the active blade, the rod length, the pitch, the taper, the tip diameter, and the rod diameter. For each set of adopted parameters, a finite element model is built and tested in a combined bending-torsion loading in accordance with ISO 3630-1 norm. The numerical analysis based on finite element procedure allowed purposing an optimal geometry suitable for Cu-based single crystal SMA endodontic files. The same analysis was carried out for the classical NiTi SMA files and a comparison was made between the two kinds of files. It showed that Cu-based single crystal SMA files are less stiff than the NiTi files. The Cu-based endodontic files could be used to improve the root canal treatments. However, the finite element analysis brought out the need for further investigation based on experiments.

  9. 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.

  10. Fabrication of Ni-Ti-O nanotube arrays by anodization of NiTi alloy and their potential applications.

    PubMed

    Hang, Ruiqiang; Liu, Yanlian; Zhao, Lingzhou; Gao, Ang; Bai, Long; Huang, Xiaobo; Zhang, Xiangyu; Tang, Bin; Chu, Paul K

    2014-01-01

    Nickel-titanium-oxide (Ni-Ti-O) nanotube arrays (NTAs) prepared on nearly equiatomic NiTi alloy shall have broad application potential such as for energy storage and biomedicine, but their precise structure control is a great challenge because of the high content of alloying element of Ni, a non-valve metal that cannot form a compact electronic insulating passive layer when anodized. In the present work, we systemically investigated the influence of various anodization parameters on the formation and structure of Ni-Ti-O NTAs and their potential applications. Our results show that well controlled NTAs can be fabricated during relatively wide ranges of the anodization voltage (5-90 V), electrolyte temperature (10-50°C) and electrolyte NH4F content (0.025-0.8 wt%) but within a narrow window of the electrolyte H2O content (0.0-1.0 vol%). Through modulating these parameters, the Ni-Ti-O NTAs with different diameter (15-70 nm) and length (45-1320 nm) can be produced in a controlled manner. Regarding potential applications, the Ni-Ti-O NTAs may be used as electrodes for electrochemical energy storage and non-enzymic glucose detection, and may constitute nanoscaled biofunctional coating to improve the biological performance of NiTi based biomedical implants. PMID:25520180

  11. The effect of crystallographic texture on stress-induced martensitic transformation in NiTi: A computational analysis.

    PubMed

    Weafer, F M; Guo, Y; Bruzzi, M S

    2016-01-01

    NiTi׳s superelasticity is exploited in a number of biomedical devices, in particular self-expanding endovascular stents. These stents are often laser-cut from textured micro-tubing; texture is the distribution of crystallographic grain orientations in a polycrystalline material which has been experimentally shown to have a marked influence on mechanical properties. This study offers a computational examination into the effect of texture on the stress-induced martensite transformation (SIMT) in a micro-dogbone NiTi specimen subject to tensile loading. Finite Element Analysis (FEA) is employed to simulate the transformational behaviour of the specimen on a micro-scale level. To represent a realistic grain structure in the FEA model, grains present in a 200µm×290µm test site located at the centre edge of the specimen were identified using Scanning Electron Microscopy (SEM). Grains are assumed to have homogenous behaviour with properties varying according to their crystallographic orientation to the loading direction. Required material properties were extracted from uniaxial stress-strain curves of single crystals for each crystallographic orientation for input into the in-built UMAT/Nitinol. The orientation of each grain in the test site was identified using Electron Back-Scatter Diffraction (EBSD) techniques. In this way, a quantitative explanation is offered to the effect of crystallographic texture on SIMT. Finally, the evolution of grains in the specimen, during the transformation process, was experimentally investigated by means of an in-situ SEM tensile test. PMID:26334356

  12. Atomistic simulation of radiation-induced amorphization of the B2 ordered intermetallic compound NiTi

    SciTech Connect

    Sabochick, M.J. . Dept. of Engineering Physics); Lam, N.Q. )

    1990-12-01

    Amorphization of the B2 intermetallic compound NiTi under electron irradiation has been investigated using molecular dynamics. The effect of irradiation was simulated using two processes: (1) Ni and Ti atoms were exchanged, resulting in chemical disorder, and (2) Frenkel pairs were introduced, leading to the formation of stable point defects and also chemical disorder upon mutual recombination of interstitials and vacancies. After {approximately}0.4 exchanges per atom, the first process resulted in an energy increase of approximately 0.11 eV/atom and a volume increase of 1.91%. On the other hand, after introducing {approximately}0.5 Frenkel pairs per atom, the second process led to smaller increases of 0.092 eV/atom in energy and 1.43% in volume. The calculated radial distribution functions (RDFs) were essentially identical to each other and to the calculated RDF of a quenched liquid. The structure factor, however, showed that long-range order was still present after atom exchanges, while the introduction of Frenkel pairs resulted in the loss of long-range order. It was concluded that point defects are necessary for amorphization to occur in NiTi, although chemical disorder alone is capable of storing enough energy to make the transition possible. 18 refs., 3 figs.

  13. Fabrication of Ni-Ti-O nanotube arrays by anodization of NiTi alloy and their potential applications

    PubMed Central

    Hang, Ruiqiang; Liu, Yanlian; Zhao, Lingzhou; Gao, Ang; Bai, Long; Huang, Xiaobo; Zhang, Xiangyu; Tang, Bin; Chu, Paul K.

    2014-01-01

    Nickel-titanium-oxide (Ni-Ti-O) nanotube arrays (NTAs) prepared on nearly equiatomic NiTi alloy shall have broad application potential such as for energy storage and biomedicine, but their precise structure control is a great challenge because of the high content of alloying element of Ni, a non-valve metal that cannot form a compact electronic insulating passive layer when anodized. In the present work, we systemically investigated the influence of various anodization parameters on the formation and structure of Ni-Ti-O NTAs and their potential applications. Our results show that well controlled NTAs can be fabricated during relatively wide ranges of the anodization voltage (5–90 V), electrolyte temperature (10–50°C) and electrolyte NH4F content (0.025–0.8 wt%) but within a narrow window of the electrolyte H2O content (0.0–1.0 vol%). Through modulating these parameters, the Ni-Ti-O NTAs with different diameter (15–70 nm) and length (45–1320 nm) can be produced in a controlled manner. Regarding potential applications, the Ni-Ti-O NTAs may be used as electrodes for electrochemical energy storage and non-enzymic glucose detection, and may constitute nanoscaled biofunctional coating to improve the biological performance of NiTi based biomedical implants. PMID:25520180

  14. Investigation on the evolution of microstructure and texture of electroplated Ni-Ti composite coating by Rietveld method

    NASA Astrophysics Data System (ADS)

    Zhao, Yuantao; Cai, Fei; Wang, Chengxi; Chai, Ze; Zhu, Kaiyuan; Xu, Zhou; Jiang, Chuanhai

    2015-10-01

    Rietveld refinement was utilized to investigate the evolution of microstructure and texture of the Ni-Ti composite coatings electroplated at different applied current densities. Scanning Electron Microscope and Energy Dispersive Spectroscopy were utilized to investigate the morphology and chemical composition of the coatings. Relative texture coefficients (RTC) and measured pole figures were utilized to investigate the texture evolution of the coatings. The results showed that the surface morphology of the coatings changed from a colonial structure to a polyhedral one. And the incorporated Ti content decreased with increasing applied current density. As the applied current density increased, the crystallite sizes increased and their distribution got less uniform, and the microstrain and dislocation density decreased. The results of simulated pole figures obtained from Rietveld refinement illustrated that the texture of the coatings changed from no obvious texture to a strong [2 0 0] fiber texture with increasing applied current density. The texture evolution obtained from simulated pole figures was confirmed by the result of RTC and the measured pole figures. The evolutions of the microstructure and texture were derived from the change of the applied current density and incorporated Ti content in the Ni-Ti composite coatings.

  15. Selective Tumor Cell Inhibition Effect of Ni-Ti Layered Double Hydroxides Thin Films Driven by the Reversed pH Gradients of Tumor Cells.

    PubMed

    Wang, Donghui; Ge, Naijian; Li, Jinhua; Qiao, Yuqin; Zhu, Hongqin; Liu, Xuanyong

    2015-04-22

    Nitinol is widely fabricated as stents for the palliation treatment of many kinds of cancers. It is of great importance to develop nitinol stents with selective tumor cell inhibition effects. In this work, a series of pH sensitive films composed of Ni(OH)2 and Ni-Ti layered double hydroxide (Ni-Ti LDH) with different Ni/Ti ratios were prepared on the surface of nitinol via hydrothermal treatment. The films with specific Ni/Ti ratios would release a large amount of nickel ions under acidic environments but were relatively stable in neutral or weak alkaline medium. Cell viability tests showed that the films can effectively inhibit the growth of cancer cells but have little adverse effects to normal cells. Besides, extraordinarily high intracellular nickel content and reactive oxygen species (ROS) level were found in cancer cells, indicating the death of cancer cells may be induced by the excessive intake of nickel ions. Such selective cancer cell inhibition effect of the films is supposed to relate with the reversed pH gradients of tumor cells. PMID:25825800

  16. The wear properties and adhesion strength of the diamond-like carbon film coated on SUS, Ti and Ni-Ti with plasma pre-treatment.

    PubMed

    Ozeki, K; Masuzawa, T; Hirakuri, K K

    2010-01-01

    Diamond-like carbon (DLC) films were deposited on stainless steel (SUS), titanium (Ti) and nickel titanium (Ni-Ti) substrates using a radiofrequency plasma chemical vapour deposition method. Prior to DLC coating, the substrates were exposed to O2 and N2 plasma to enhance the adhesion strength of the DLC film to the substrate. After the plasma pre-treatment, the chemical composition and the wettability of the substrate surface was investigated by X-ray photoelectron spectroscopy (XPS) and water contact angle measurement, respectively. A pull-out test and a ball-on-disc test were carried out to evaluate the adhesion strength and the wear properties of the DLC-coated substrates. The XPS results showed that the N2 and O2 plasma pre-treatment produced nitride and oxide on the substrate surfaces, such as TiO2, TiO, Fe2O3, CrN and TiNO. In the pull-out test, the adhesion strengths of the DLC film to the SUS, Ti and Ni-Ti substrates were improved with the plasma pre-treatment. In the ball-on-disc test, the DLC coated SUS, Ti and Ni-Ti substrates without the plasma pre-treatment showed severe film failure following the test. The DLC coated SUS and Ni-Ti substrates with the N2 plasma pre-treatment showed good wear resistance, compared with that with the O2 plasma pre-treatment. PMID:20448301

  17. Niti CAR 27 Versus a Conventional End-to-End Anastomosis Stapler in a Laparoscopic Anterior Resection for Sigmoid Colon Cancer

    PubMed Central

    Kwag, Seung-Jin; Kim, Jun-Gi; Kang, Won-Kyung; Lee, Jin-Kwon

    2014-01-01

    Purpose The Niti CAR 27 (ColonRing) uses compression to create an anastomosis. This study aimed to investigate the safety and the effectiveness of the anastomosis created with the Niti CAR 27 in a laparoscopic anterior resection for sigmoid colon cancer. Methods In a single-center study, 157 consecutive patients who received an operation between March 2010 and December 2011 were retrospectively assessed. The Niti CAR 27 (CAR group, 63 patients) colorectal anastomoses were compared with the conventional double-stapled (CDS group, 94 patients) colorectal anastomoses. Intraoperative, immediate postoperative and 6-month follow-up data were recorded. Results There were no statistically significant differences between the two groups in terms of age, gender, tumor location and other clinical characteristics. One patient (1.6%) in the CAR group and 2 patients (2.1%) in the CDS group experienced complications of anastomotic leakage (P = 0.647). These three patients underwent a diverting loop ileostomy. There were 2 cases (2.1%) of bleeding at the anastomosis site in the CDS group. All patients underwent a follow-up colonoscopy (median, 6 months). One patient in the CAR group experienced anastomotic stricture (1.6% vs. 0%; P = 0.401). This complication was solved by using balloon dilatation. Conclusion Anastomosis using the Niti CAR 27 device in a laparoscopic anterior resection for sigmoid colon cancer is safe and feasible. Its use is equivalent to that of the conventional double-stapler. PMID:24851217

  18. Enhanced corrosion resistance and hemocompatibility of biomedical NiTi alloy by atmospheric-pressure plasma polymerized fluorine-rich coating

    NASA Astrophysics Data System (ADS)

    Li, Penghui; Li, Limin; Wang, Wenhao; Jin, Weihong; Liu, Xiangmei; Yeung, Kelvin W. K.; Chu, Paul K.

    2014-04-01

    To improve the corrosion resistance and hemocompatibility of biomedical NiTi alloy, hydrophobic polymer coatings are deposited by plasma polymerization in the presence of a fluorine-containing precursor using an atmospheric-pressure plasma jet. This process takes place at a low temperature in air and can be used to deposit fluoropolymer films using organic compounds that cannot be achieved by conventional polymerization techniques. The composition and chemical states of the polymer coatings are characterized by fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the coated and bare NiTi samples is assessed and compared by polarization tests and electrochemical impedance spectroscopy (EIS) in physiological solutions including simulated body fluids (SBF) and Dulbecco's Modified Eagle's medium (DMEM). The corrosion resistance of the coated NiTi alloy is evidently improved. Protein adsorption and platelet adhesion tests reveal that the adsorption ratio of albumin to fibrinogen is increased and the number of adherent platelets on the coating is greatly reduced. The plasma polymerized coating renders NiTi better in vitro hemocompatibility and is promising as a protective and hemocompatible coating on cardiovascular implants.

  19. Strategies for Self-Repairing Shape Memory Alloy Actuators

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  20. 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

  1. A thermomechanical model accounting for the behavior of shape memory alloys in finite deformations

    NASA Astrophysics Data System (ADS)

    Haller, Laviniu; Nedjar, Boumedienne; Moumni, Ziad; Vedinaş, Ioan; Trană, Eugen

    2016-07-01

    Shape memory alloys (SMA) comport an interesting behavior. They can undertake large strains and then recover their undeformed shape by heating. In this context, one of the aspects that challenged many researchers was the development of a mathematical model to predict the behavior of a known SMA under real-life conditions, or finite strain. This paper is aimed at working out a finite strain mathematical model for a Ni-Ti SMA, under the superelastic experiment conditions and under uniaxial mechanical loading, based on the Zaki-Moumni 3D mathematical model developed under the small perturbations assumption. Within the current article, a comparison between experimental findings and calculated results is also investigated. The proposed finite strain mathematical model shows good agreement with experimental data.

  2. The Effect of Indenter Ball Radius on the Static Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Moore, Lewis E.

    2014-01-01

    Static load capacity is a critical design parameter for rolling element bearings used in space mechanisms because of the potential for Brinell (surface dent) damage due to shock and vibration loading events during rocket launch. Brinell damage to bearing raceways can lead to torque variations (noise) and reduced bearing life. The growing use of ceramic rolling elements with high stiffness in hybrid bearings exacerbates the situation. A new family of hard yet resilient materials based upon nickel-titanium is emerging to address such bearing challenges. 60NiTi is a superelastic material that simultaneously exhibits high hardness and a relatively low elastic modulus (approx. 100 GPa) and has been shown to endure higher indentation loads than conventional and high performance steel. Indentation load capacity has been reported for relatively large (12.7 mm diameter) ceramic (Si3N4) indenter balls pressed against flat plates of 60NiTi. In order to develop damage load threshold criteria applicable to a wide range of bearing designs and sizes, the effects of indenter ball radius and the accuracy of interpolation of the Hertz contact stress relations for 60NiTi must be ascertained. In this paper, results of indentation tests involving ceramic balls ranging from 6.4 to 12.7 mm in diameter and highly polished 60NiTi flat plates are presented. When the resulting dent depth data for all the indenter ball sizes are normalized using the Hertz equations, the data (dent depth versus stress) are comparable. Thus when designing bearings made from 60NiTi, the Hertz stress relations can be applied with relative confidence over a range of rolling element sizes and internal geometries.

  3. The Effect of Indenter Ball Radius on the Static Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Moore, Lewis E.; Clifton, Joshua S.

    2014-01-01

    Static load capacity is a critical design parameter for rolling element bearings used in space mechanisms because of the potential for Brinell (surface dent) damage due to shock and vibration loading events during rocket launch. Brinell damage to bearing raceways can lead to torque variations (noise) and reduced bearing life. The growing use of ceramic rolling elements with high stiffness in hybrid bearings exacerbates the situation. A new family of hard yet resilient materials based upon nickel-titanium is emerging to address such bearing challenges. 60NiTi is a superelastic material that simultaneously exhibits high hardness and a relatively low elastic modulus (100GPa) and has been shown to endure higher indentation loads than conventional and high performance steel. Indentation load capacity has been reported for relatively large (12.7mm diameter) ceramic (Si3N4) indenter balls pressed against flat plates of 60NiTi. In order to develop damage load threshold criteria applicable to a wide range of bearing designs and sizes, the effects of indenter ball radius and the accuracy of interpolation of the Hertz contact stress relations for 60NiTi must be ascertained. In this paper, results of indentation tests involving ceramic balls ranging from 6.4 to 12.7mm in diameter and highly polished 60NiTi flat plates are presented. When the resulting dent depth data for all the indenter ball sizes are normalized using the Hertz equations, the data (dent depth vs. stress) are comparable. Thus when designing bearings made from 60NiTi, the Hertz stress relations can be applied with relative confidence over a range of rolling element sizes and internal geometries.

  4. The Effect of Indenter Ball Radius on the Static Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Moore, Lewis E., III; Clifton, Joshua S.

    2014-01-01

    Static load capacity is a critical design parameter for rolling element bearings used in space mechanisms because of the potential for Brinell (surface dent) damage due to shock and vibration loading events during rocket launch. Brinell damage to bearing raceways can lead to torque variations (noise) and reduced bearing life. The growing use of ceramic rolling elements with high stiffness in hybrid bearings exacerbates the situation. A new family of hard yet resilient materials based upon nickel-titanium is emerging to address such bearing challenges. 60NiTi is a superelastic material that simultaneously exhibits high hardness and a relatively low elastic modulus (approx. 100 GigaPascals) and has been shown to endure higher indentation loads than conventional and high performance steel. Indentation load capacity has been reported for relatively large (12.7 millimeters diameter) ceramic (Si3N4) indenter balls pressed against flat plates of 60NiTi. In order to develop damage load threshold criteria applicable to a wide range of bearing designs and sizes, the effects of indenter ball radius and the accuracy of interpolation of the Hertz contact stress relations for 60NiTi must be ascertained. In this paper, results of indentation tests involving ceramic balls ranging from 6.4 to 12.7 mm in diameter and highly polished 60NiTi flat plates are presented. When the resulting dent depth data for all the indenter ball sizes are normalized using the Hertz equations, the data (dent depth versus stress) are comparable. Thus when designing bearings made from 60NiTi, the Hertz stress relations can be applied with relative confidence over a range of rolling element sizes and internal geometries.

  5. Superordinate Shape Classification Using Natural Shape Statistics

    ERIC Educational Resources Information Center

    Wilder, John; Feldman, Jacob; Singh, Manish

    2011-01-01

    This paper investigates the classification of shapes into broad natural categories such as "animal" or "leaf". We asked whether such coarse classifications can be achieved by a simple statistical classification of the shape skeleton. We surveyed databases of natural shapes, extracting shape skeletons and tabulating their parameters within each…

  6. Fabrication and Characterization of Nitinol-Copper Shape Memory Alloy Bimorph Actuators

    NASA Astrophysics Data System (ADS)

    Wongweerayoot, E.; Srituravanich, W.; Pimpin, A.

    2015-02-01

    This study aims to examine the effect of annealing conditions on nitinol (NiTi) characteristics and applies this knowledge to fabricate a NiTi-copper shape memory alloy bimorph actuator. The effect of the annealing conditions was investigated at various temperatures, i.e., 500, 600, and 650 °C, for 30 min. With the characterizations using x-ray diffraction, energy dispersive spectroscopy, and differential scanning calorimetry techniques, the results showed that annealing temperatures at 600 and 650 °C were able to appropriately form the crystalline structure of NiTi. However, at these high annealing temperatures, the oxide on a surface was unavoidable. In the fabrication of actuator, the annealing at 650 °C for 30 min was chosen, and it was performed at two pre-stressing conditions, i.e., straight and curved molds. From static and dynamic response experiments, the results suggested that the annealing temperature significantly affected the deflection of the actuator. On the other hand, the effect of pre-stressing conditions was relatively small. Furthermore, the micro gripper consisting of two NiTi-copper bimorph actuators successfully demonstrated for the viability of small object manipulation as the gripper was able to grasp and hold a small plastic ball with its weight of around 0.5 mg.

  7. Modeling and cyclic behavior of segmental bridge column connected with shape memory alloy bars

    NASA Astrophysics Data System (ADS)

    Roh, Hwasung; Reinhorn, Andrei M.; Lee, Jong Seh

    2012-09-01

    This paper examines the quasi-static cyclic behavior, lateral strength and equivalent damping capacities of a system of post-tensioned segmental bridge columns tied with large diameter martensitic Shape Memory Alloy (SMA) link-bars. Moment-curvature constitutive relationships are formulated and analysis tools are developed for the PT column, including a modified four-spring model prepared for the SMA bars. The suggested system is exemplified using a column with an aspect ratio of 7.5 and twelve 36.5 mm diameter NiTi martensitic SMA bars. A post-tensioning force of 40% to 60% of the tendon yield strength is applied in order to obtain a self re-centering system, considering the residual stress of the martensitic SMA bars. The cyclic response results show that the lateral strength remains consistently around 10% of the total vertical load and the equivalent viscous damping ratios reach 10%-12% of critical. When large diameter NiTi superelastic SMA bars are incorporated into the column system, the cyclic response varies substantially. The creep behavior of the superelastic SMA bar is accounted for since it affects the re-centering capability of the column. Two examples are presented to emphasize the modeling sensitivities for these special bars and quantify their cyclic behavior effects within the column assembly.

  8. 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.

  9. New developments in actuator materials as reflected in magnetically controlled shape memory alloys and high-strength shape memory steels

    NASA Astrophysics Data System (ADS)

    Ullakko, Kari; Yakovenko, Peter G.; Gavriljuk, Valentin G.

    1996-05-01

    Shape memory alloys (SMA) are applied as actuator materials in smart structures and in fastening and pre-stressing devices. Shape memory alloys can be divided into three groups: one-way alloys, two-way alloys and magnetically controlled SMAs. The magnetically controlled SMAs recently suggested by one of the present authors are potential actuator materials for smart structures because they may provide rapid strokes with large amplitudes under precise control. The most extensively applied conventional SMAs are Ni-Ti and Cu- based alloys. Iron-based shape memory alloys, especially Fe-Mn-Si steels, are becoming more and more important in engineering applications due to their low price. The properties of Fe- Mn-Si steels have been improved by alloying, for example, with Cr, Ni and Co. Nitrogen alloying was shown to significantly improve shape memory, mechanical and corrosion properties of Fe-Mn-Si-based steels. Tensile strengths over 1500 MPa, recovery stresses of 300 MPa and recoverable strains of 4% have been attained. In fasteners made from these steels, stresses of 700 MPa were reached. The beneficial effect of nitrogen alloying on shape memory and mechanical properties is based on the decrease of stacking fault energy and increase of the strength of austenite caused by nitrogen atoms. Nitrogen alloyed Fe-Mn-Si- based steels are expected to be employed as actuator materials in pre-stressing and fastening applications in many fields of engineering. Nitrogen alloyed shape memory steels possess good manufacturing properties and weldability, and they are economical to process using conventional industrial methods.

  10. About the Transformation Phase Zones of Shape Memory Alloys' Fracture Tests on Single Edge-Cracked Specimen

    NASA Astrophysics Data System (ADS)

    Taillebot, V.; Lexcellent, C.; Vacher, P.

    2012-03-01

    The thermomechanical behavior of shape memory alloys is now well mastered. However, a hindrance to their sustainable use is the lack of knowledge of their fracture behavior. With the aim of filling this partial gap, fracture tests on edge-cracked specimens in NiTi have been made. Particular attention was paid to determine the phase transformation zones in the vicinity of the crack tip. In one hand, experimental kinematic fields are observed using digital image correlation showing strain localization around the crack tip. In the other hand, an analytical prediction, based on a modified equivalent stress criterion and taking into account the asymmetric behavior of shape memory alloys in tension-compression, provides shape and size of transformation outset zones. Experimental results are relatively in agreement with our analytical modeling.

  11. On the effects of geometry, defects, and material asymmetry on the mechanical response of shape memory alloy cellular lattice structures

    NASA Astrophysics Data System (ADS)

    Karamooz Ravari, M. R.; Nasr Esfahani, S.; Taheri Andani, M.; Kadkhodaei, M.; Ghaei, A.; Karaca, H.; Elahinia, M.

    2016-02-01

    Shape memory alloy (such as NiTi) cellular lattice structures are a new class of advanced materials with many potential applications. The cost of fabrication of these structures however is high. It is therefore necessary to develop modeling methods to predict the functional behavior of these alloys before fabrication. The main aim of the present study is to assess the effects of geometry, microstructural imperfections and material asymmetric response of dense shape memory alloys on the mechanical response of cellular structures. To this end, several cellular and dense NiTi samples are fabricated using a selective laser melting process. Both cellular and dense specimens were tested in compression in order to obtain their stress-strain response. For modeling purposes, a three -dimensional (3D) constitutive model based on microplane theory which is able to describe the material asymmetry was employed. Five finite element models based on unit cell and multi-cell methods were generated to predict the mechanical response of cellular lattices. The results show the considerable effects of the microstructural imperfections on the mechanical response of the cellular lattice structures. The asymmetric material response of the bulk material also affects the mechanical response of the corresponding cellular structure.

  12. Improve the corrosion and cytotoxic behavior of NiTi implants with use of the ion beam technologies

    SciTech Connect

    Meisner, L. L. Meisner, S. N.; Matveeva, V. A.; Matveev, A. L.

    2015-11-17

    The corrosion resistance behavior and cytotoxicity of binary NiTi-base alloy specimens subjected to surface modification by silicon ion beams and the proliferative ability of mesenchymal stem cells (MSC) of rat marrow on an ion-implanted surface of the alloy have been studied. The silicon ion beam processing of specimen surfaces is shown to bring about a nearly two-fold improvement in the corrosion resistance of the material to attack by acqueous solutions of NaCl and human plasma and a drastic decrease in the nickel concentration after immersion of the specimens into the solutions for ∼3400 and ∼6000 h, respectively. It is found that MSC proliferation strongly depends on the surface structure, roughness and chemical condition of NiTi implants.

  13. Generalized melting criterion for amorphization. [NiZr, NiZr[sub 2], NiTi, FeTi

    SciTech Connect

    Devanathan, R. Northwestern Univ., Evanston, IL . Dept. of Materials Science and Engineering); Lam, N.Q.; Okamoto, P.R. ); Meshii, M. . Dept. of Materials Science and Engineering)

    1992-12-01

    We present a thermodynamic model of solid-state amorphization based on a generalization of the well-known Lindemann criterion. The original Lindemann criterion proposes that melting occurs when the root-mean-square amplitude of thermal displacement exceeds a critical value. This criterion can be generalized to include solid-state amorphization by taking into account the static displacements. In an effort to verify the generalized melting criterion, we have performed molecular dynamics simulations of radiation-induced amorphization in NiZr, NiZr[sub 2], NiTi and FeTi using embedded-atom potentials. The average shear elastic constant G was calculated as a function of the total mean-square atomic displacement following random atom-exchanges and introduction of Frenkel pairs. Results provide strong support for the generalized melting criterion.

  14. Calorimetry study of the synthesis of amorphous Ni-Ti alloys by mechanical alloying. [Ni33 Ti67

    SciTech Connect

    Schwarz, R.B.; Petrich, R.R.

    1988-01-01

    We synthesized amorphous Ni/sub 33/Ti/sub 67/ alloy powder by ball milling (a) a mixture of elemental nickel and titanium powders and (b) powders of the crystalline intermetallic NiTi/sub 2/. We characterized the reaction products as a function of ball-milling time by differential scanning calorimetry and x-ray diffraction. The measurements suggest that in process (a) the amorphous alloy forms by a solid-state interdiffusion reaction at the clean Ni/Ti interfaces generated by the mechanical attrition. In process (b), the crystalline alloy powder stores energy in the form of chemical disorder and lattice and point defects. The crystal-to-amorphous transformation occurs when the stored energy reaches a critical value. The achievement of the critical stored energy competes with the dynamic recovery of the lattice. 23 refs., 7 figs.

  15. Improve the corrosion and cytotoxic behavior of NiTi implants with use of the ion beam technologies

    NASA Astrophysics Data System (ADS)

    Meisner, L. L.; Matveeva, V. A.; Meisner, S. N.; Matveev, A. L.

    2015-11-01

    The corrosion resistance behavior and cytotoxicity of binary NiTi-base alloy specimens subjected to surface modification by silicon ion beams and the proliferative ability of mesenchymal stem cells (MSC) of rat marrow on an ion-implanted surface of the alloy have been studied. The silicon ion beam processing of specimen surfaces is shown to bring about a nearly two-fold improvement in the corrosion resistance of the material to attack by acqueous solutions of NaCl and human plasma and a drastic decrease in the nickel concentration after immersion of the specimens into the solutions for ˜3400 and ˜6000 h, respectively. It is found that MSC proliferation strongly depends on the surface structure, roughness and chemical condition of NiTi implants.

  16. Resilient and Corrosion-Proof Rolling Element Bearings Made from Superelastic Ni-Ti Alloys for Aerospace

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher

    2014-01-01

    Mechanical components (bearings, gears, mechanisms) typically utilize hardened construction materials to minimize wear and attain long life. In such components, loaded contact points (e.g., meshing gear teeth, bearing balls-raceway contacts) experience high contact stresses. The combination of high hardness and high elastic modulus often leads to damaging contact stress and denting, particularly during transient overload events such as shock impacts that occur during the launching of space vehicles or the landing of aircraft. In this webinar, Dr. DellaCorte will introduce the results of a research project that employs a superelastic alloy, Ni-Ti for rolling element bearing applications. Bearings and components made from such alloys can alleviate many problems encountered in advanced aerospace applications and may solve many terrestrial applications as well

  17. Evaluation of canine retraction following periodontal distraction using NiTi coil spring and implants – A clinical study

    PubMed Central

    Khanna, Rohit; Tikku, Tripti; Sachan, Kiran; Maurya, R.P.; Verma, Geeta; Ojha, Vivek

    2014-01-01

    Objective To evaluate the amount of canine retraction with periodontal distraction using miniscrew implants and NiTi coil spring. Material and method Sample comprised of 25 patients who were scheduled for all 1st premolar extraction (13 males and 12 females), in the age range of 16–22 years with mean age 18.8 ± 2.7 years. For each patient left side served as control side (Group I) and right side as experimental side (Group II). At the time of first premolar extraction, periodontal distraction was performed only on the experimental side, followed by retraction of canine from mini-implant by closed NiTi coil spring on both the sides. “Nemotech” software was used to evaluate the amount of canine retraction for a period of 3 months. Results Significantly higher amount of tooth movement was seen from T0–T1 and from T1–T2 in Group II for the maxillary parameters 3C-5C, 6CF-3C, 3C-I/3C-J and for the mandibular parameter 6CF″-3C″. Whereas no significant amount of tooth movement was observed for maxillary and mandibular parameters between T2-T3 except for 6CF″-3C″ (p ≤ 0.01) which was significantly higher for the Group II. Conclusion There was accelerated canine retraction on the periodontal distraction side as compared to the control side, with negligible anchorage loss. PMID:25737943

  18. Energetic shape recovery associated with martensitic transformation in shape-memory alloys

    SciTech Connect

    Golestaneh, A.A.

    1980-01-01

    The present paper contains an investigation of the mechanical energy associated with the transformation of the stress-induced martensite, ..beta..', to the parent phase, ..beta.., during the shape recovery (SR) of a deformed shape-memory (SM) material. We describe a heat-mechanical energy converter, or solid-state engine, which operates by this SR phenomenon. The energy output of such an engine is expressed in terms of a fraction ..cap alpha.. of the latent heat ..delta..H of the martensitic reaction. This ..cap alpha.. is found to depend on two parameters. One is the difference between the ..delta..H of the ..beta..' ..-->.. ..beta.. reaction and the ..delta..H of the transformation of the quench-induced martensite, ..gamma..', to ..beta.., the other is the fraction of ..gamma..' which can be transformed via the channel ..gamma..' ..-->.. ..beta..' ..-->.. ..beta.. instead of the direct channel ..gamma..' ..-->.. ..beta... Moreover, it is shown that within certain ranges of temperature T and applied strain epsilon, the heat-mechanical energy balance equation leads to an expression identical in form to the Clapeyron-Clausius equation, which is usually valid for a first-order transition. Within these epsilon and T ranges the coefficient ..cap alpha.. is also found to be equal to log (T/sub csigma//T/sub c/) where T/sub csigma/ and T/sub c/ are the SR critical temperatures with and without the presence of an applied stress sigma, respectively. We discuss the role of the ..gamma..' martensite in this process and explain the so-called two-way SR phenomenon. In addition, the parameters that limit the output of the SR energy are evaluated. This output depends sensitively on both ..cap alpha.. and the material characteristic temperature h = C/sup -1/..delta..H, where C is the specific heat. For a solid-state engine made with the Ni-Ti SM alloy, the efficiency is found to be limited to about 5%.

  19. 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.

  20. Thermomechanical characterization of Ni-rich NiTi fabricated by selective laser melting

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    This study presents the shape memory behavior of as-fabricated and solution annealed Ni50.8Ti49.2 alloys fabricated using the selective laser melting (SLM) technique. Results were compared to the initial ingot that was used to fabricate powders. Optical microscopy was employed to reveal the microstructure. The shape memory effect under constant compressive stress and isothermal compressive stress cycling tests were utilized to investigate the shape memory characteristics of the initial ingot and fabricated alloys. It was revealed that the SLM method and post heat treatments can be used to tailor the microstructure and shape memory response. Partial superelasticity was observed after the SLM process. Solutionizing the fabricated samples increased the strength and improved the superelasticity but slightly decreased the recoverable strain.

  1. One-dimensional shape memory alloy models for use with reinforced composite structures

    NASA Astrophysics Data System (ADS)

    Zak, A. J.; Cartmell, M. P.; Ostachowicz, W. M.; Wiercigroch, M.

    2003-06-01

    In this paper three models of the shape memory alloy behaviour have been presented and re-investigated. The models are attributed to Tanaka, Liang and Rogers, and Brinson, and have been used extensively in the literature for studying the static or dynamic performance of different composite material structures with embedded shape memory alloy components. The major differences and similarities between these models have been emphasised and examined in the paper. A simple experimental rig was designed and manufactured to gain additional insight into the main mechanics governing the shape memory alloy (SMA) mechanical properties. Data obtained from the experimental measurements on Ni-Ti wires have been used in the numerical simulation for validation purposes. It has been found that the three models all agree well in their predictions of the superelastic behaviour at higher temperatures, above the austenite finish temperature when shape memory alloys stay in the fully austenitic phase. However, at low temperatures, when the alloys stay in the fully martensitic phase, some difficulties may be encountered. The model developed by Brinson introduces two new state variables and therefore two different mechanisms for the instigation of stress-induced and temperature-induced martensite. This enables more accurate predictions of the superelastic behaviour. In general, it can be recommended that for investigations of the shape memory and superelastic behaviour of shape memory alloy components the Brinson model, or refinements based on the Brinson model, should be applied.

  2. Shape-Shifting Plastic

    SciTech Connect

    2015-05-20

    A new plastic developed by ORNL and Washington State University transforms from its original shape through a series of temporary shapes and returns to its initial form. The shape-shifting process is controlled through changes in temperature

  3. Development of a flexible nanocomposite TiO2 film as a protective coating for bioapplications of superelastic NiTi alloys

    NASA Astrophysics Data System (ADS)

    Aun, Diego Pinheiro; Houmard, Manuel; Mermoux, Michel; Latu-Romain, Laurence; Joud, Jean-Charles; Berthomé, Gregory; Buono, Vicente Tadeu Lopes

    2016-07-01

    An experimental procedure to coat superelastic NiTi alloys with flexible TiO2 protective nanocomposite films using sol-gel technology was developed in this work to improve the metal biocompatibility without deteriorating its superelastic mechanical properties. The coatings were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and glazing incidence X-ray diffraction. The elasticity of the film was tested in coated specimens submitted to three-point bending tests. A short densification by thermal treatment at 500 °C for 10 min yielded a bilayer film consisting of a 50 nm-thick crystallized TiO2 at the inner interface with another 50-nm-thick amorphous oxide film at the outer interface. This bilayer could sustain over 6.4% strain without cracking and could thus be used to coat biomedical instruments as well as other devices made with superelastic NiTi alloys.

  4. Structure of the near-surface layer of NiTi on the meso- and microscale levels after ion-beam surface treatment

    SciTech Connect

    Meisner, L. L. Meisner, S. N.; Poletika, T. M. Girsova, S. L.; Tverdichlebova, A. V.; Shulepov, I. A.

    2014-11-14

    Using the EBSD, SEM and TEM methods, the structure of surface layer of polycrystalline NiTi alloy samples was examined after the modification of material surface by the pulsed action of mean-energy silicon ion beam. It was found that the ion beam treatment would cause grain fragmentation of the near-surface layer to a depth 5÷50 μm; a higher extent of fragmentation was observed in grains whose close-packed planes were oriented approximately in the same direction as the ion beam was. The effect of high-intensity ion beam treatment on the anisotropic behavior of polycrystalline NiTi alloy and the mechanisms involved were also examined.

  5. In vitro evaluation of diamond-like carbon coatings with a Si/SiC x interlayer on surgical NiTi alloy

    NASA Astrophysics Data System (ADS)

    Liu, C. L.; Chu, Paul K.; Yang, D. Z.

    2007-04-01

    Diamond-like carbon (DLC) coatings were produced with a Si/SiCx interlayer by a hybrid plasma immersion ion implantation and deposition process to improve the adhesion between the carbon layer and surgical NiTi alloy substrate. The structure, mechanical properties, corrosion resistance and biocompatibility of the coatings were evaluated in vitro by Raman spectroscopy, pin-on-disk tests, potentiodynamic polarization tests and simulated fluid immersion tests. The DLC coatings with a Si/SiCx interlayer of a suitable thickness have better adhesion, lower friction coefficients and enhanced corrosion resistance. In the simulated body fluid tests, the coatings exhibit effective corrosion protection and good biocompatibility as indicated by PC12 cell cultures. DLC films fabricated on a Si/SiCx interlayer have high potential as protective coatings for biomedical NiTi materials.

  6. Tooth - abnormal shape

    MedlinePlus

    Hutchinson incisors; Abnormal tooth shape; Peg teeth; Mulberry teeth; Conical teeth ... The appearance of normal teeth varies, especially the molars. ... conditions. Specific diseases can affect tooth shape, tooth ...

  7. Tooth - abnormal shape

    MedlinePlus

    Hutchinson incisors; Abnormal tooth shape; Peg teeth; Mulberry teeth; Conical teeth ... from many different conditions. Specific diseases can affect tooth shape, tooth color, time of appearance, or absence ...

  8. Characterization of mechanical properties of hydroxyapatite-silicon-multi walled carbon nano tubes composite coatings synthesized by EPD on NiTi alloys for biomedical application.

    PubMed

    Khalili, Vida; Khalil-Allafi, Jafar; Sengstock, Christina; Motemani, Yahya; Paulsen, Alexander; Frenzel, Jan; Eggeler, Gunther; Köller, Manfred

    2016-06-01

    Release of Ni(1+) ions from NiTi alloy into tissue environment, biological response on the surface of NiTi and the allergic reaction of atopic people towards Ni are challengeable issues for biomedical application. In this study, composite coatings of hydroxyapatite-silicon multi walled carbon nano-tubes with 20wt% Silicon and 1wt% multi walled carbon nano-tubes of HA were deposited on a NiTi substrate using electrophoretic methods. The SEM images of coated samples exhibit a continuous and compact morphology for hydroxyapatite-silicon and hydroxyapatite-silicon-multi walled carbon nano-tubes coatings. Nano-indentation analysis on different locations of coatings represents the highest elastic modulus (45.8GPa) for HA-Si-MWCNTs which is between the elastic modulus of NiTi substrate (66.5GPa) and bone tissue (≈30GPa). This results in decrease of stress gradient on coating-substrate-bone interfaces during performance. The results of nano-scratch analysis show the highest critical distance of delamination (2.5mm) and normal load before failure (837mN) as well as highest critical contact pressure for hydroxyapatite-silicon-multi walled carbon nano-tubes coating. The cell culture results show that human mesenchymal stem cells are able to adhere and proliferate on the pure hydroxyapatite and composite coatings. The presence of both silicon and multi walled carbon nano-tubes (CS3) in the hydroxyapatite coating induce more adherence of viable human mesenchymal stem cells in contrast to the HA coated samples with only silicon (CS2). These results make hydroxyapatite-silicon-multi walled carbon nano-tubes a promising composite coating for future bone implant application. PMID:26897095

  9. Influence of Friction Resistance on Expression of Superelastic Properties of Initial NiTi Wires in "Reduced Friction" and Conventional Bracket Systems.

    PubMed

    Reznikov, Natalie; Har-Zion, Gilad; Barkana, Idit; Abed, Yosef; Redlich, Meir

    2010-01-01

    Objectives. The aim of this study was to assess the influence of resistance to sliding on expression of superelastic properties of NiTi wires. Methods and Materials. A three-point bending test was performed for 0.014 NiTi wire engaged in self-ligating (Damon, SmartClip, In-Ovation) and conventional brackets (Victory) ligated with regular and reduced friction modules (Slide). The wire was deflected in the buccal direction and allowed to straighten. The maximum load, unloading plateau and unloading capacity were registered. Results. The lowest activation load was required in the active self-ligating group (In-Ovation 2.2 ± 0.4 N) and reduced friction module group (Victory/Slide 2.9 ± 0.4 N), followed by the passive self-ligating systems (Damon 3.6 ± 0.7 N, SmartClip 3.7 ± 0.4 N). Higher activation load was obtained in the conventionally ligated group (Victory/module 4.5 ± 0.4 N). Unloading plateau phase with the load magnitude ranging from 1.27 ± 0.4 N (In-Ovation) to 1.627 ± 0.4 N (Slide) was distinct in all groups but one (Victory). Conclusions. Higher friction at flanking points reduces the net force delivered by the wire. Unloading plateau phase of NiTi load-deflection curve disappears in the conventionally ligated group thus indicating to an incomplete expression of NiTi superelastic properties. A rigid passive bracket clip amplifies resistance to sliding in an active configuration and produces a permanent deflection of the wire. PMID:20981153

  10. TEM investigation of the surface layer structure [111]{sub B2} of the single NiTi crystal modified by the Si-ion beam implantation

    SciTech Connect

    Girsova, S. L. Poletika, T. M.; Meisner, S. N. Meisner, L. L.

    2015-10-27

    The study was carried on for the single NiTi crystals subjected to the Si-ion beam implantation. Using the transmission electron microscopy technique (TEM), the surface layer structure [111]{sub B2} was examined for the treated material. The modified near-surface sublayers were found to have different composition. Thus the uppermost sublayer contained mostly oxides; the lower-lying modified sublayer material was in an amorphous state and the thin underlying sublayer had a defect structure.

  11. Assessing the morphology of selective laser melted NiTi-scaffolds for a three-dimensional quantification of the one-way shape memory effect

    NASA Astrophysics Data System (ADS)

    Bormann, Therese; de Wild, Michael; Beckmann, Felix; Müller, Bert

    2013-04-01

    NiTi is promising for the use as bone scaffold, because the pseudoelasticity or the one- and two-way shape memory effect in the physiological window can mechanically stimulate the adherent cells. Such stimuli can enhance osseointegration and might reduce stress shielding associated with load bearing implants. The present study is based on the additive manufacturing technique of selective laser melting (SLM) to fabricate three-dimensional NiTi scaffolds. We demonstrate that the morphology of the scaffolds can be quantified using synchrotron radiation-based micro computed tomography (SRμCT) and sophisticated registration software. Comparing the CAD file with the SLM scaffolds, quality factors are derived. With respect to the CAD file, the overlap corresponds to (92.5 +/- 0.6) %. (7.4 +/- 0.42) % of material was missing and (48.9 +/- 2.3) % of excess material found. This means that the actual scaffold is less porous than expected, a fact that has to be considered for the scaffold design. In order to quantify the shape memory effect during the shape recovery process, we acquired radiographs rotating an initially deformed scaffold in angular steps of 0.2 degree during controlled heating. The continuously acquired radiographs were combined to tomography data, showing that the quality factors evolved with temperature as the scaffold height, measured by conventional thermo-mechanical analysis. Furthermore, the data comprise the presence of compressive and tensile local strains in the three-dimensional scaffolds to be compared with the physiological situation.

  12. The effect of 5% sodium hypochlorite, 17% EDTA and triphala on two different rotary Ni-Ti instruments: An AFM and EDS analysis

    PubMed Central

    Prasad, Pramod Siva; Sam, Jonathan Emi; Kumar, Arvind; Kannan

    2014-01-01

    Aim: To use Atomic Force Microscope and Energy Dispersive X-ray Spectroscopy to evaluate the effect of 5% NaOCl, 17% EDTA and triphala on ProTaper and iRaCe rotary Ni-Ti instruments. Methodology: A total of eight Ni-Ti rotary files, four files each of ProTaper - S2 (Dentsply) and iRaCe - R3 (FKG DENTAIRE) were used. Three out of four files each from ProTaper and iRaCe were immersed in 5% NaOCl, 17% EDTA and Triphala separately for five minutes. The Roughness average (Ra), Root Mean Square (RMS) and Mean Height of Roughness Profile Elements (Rc) of the scanned profiles were then recorded using AFM and the elemental composition was evaluated with EDS. Data were analyzed by Student's t test, One Way ANOVA and Duncan's Multiple Range Test. Results: Topographic irregularities at the nanometric scale were observed for all files. Files immersed in EDTA and NaOCl showed highly significant surface roughness than untreated files. Conclusion: Short-term contact with 17% EDTA and 5% NaOCl can cause significant surface deterioration of ProTaper and iRaCe rotary NiTi files. AFM proves to be a suitable method for evaluating the instrument surface. PMID:25298649

  13. Detection of Procedural Errors with Stainless Steel and NiTi Instruments by Undergraduate Students Using Conventional Radiograph and Cone Beam Computed Tomography

    PubMed Central

    Alves, Regis Augusto Aleixo; Souza, João Batista; Gonçalves Alencar, Ana Helena; Pécora, Jesus Djalma; Estrela, Carlos

    2013-01-01

    Introduction This study investigated procedural errors made during root canal preparation using stainless steel and nickel-titanium (NiTi) instruments by undergraduate students, using two diagnostic imaging methods. Materials and Methods Sixty human molars were divided into three groups (n=20; group 1: K-Flexofile, group 2: K3, and group 3: BioRace). The root canals were filled with gutta-percha and AH Plus. Periapical radiographs and cone beam computed tomography (CBCT) images were obtained to detect procedural errors made by undergraduate students during root canal preparation. Two examiners evaluated the presence or absence of fractured instruments, perforations and canal transportations. The agreement between observers was assessed using the kappa coefficient. The Kolmogorov-Smirnov, Fisher exact, ANOVA and Tukey tests were used for statistical analysis. The level of significance was set at 5%. Results There were no significant differences in detecting procedural errors between two- and three-dimensional diagnostic imaging methods. There were no significant differences in procedural errors between stainless steel and NiTi instruments. Mean preparation time was recorded in minutes, and results were significantly different between the three groups. NiTi instruments had the lowest mean preparation time. Conclusion Both periapical radiographs and CBCT identified procedural errors, however, three-dimensional images offered more diagnostic resources. The frequency of procedural errors was low for any of the endodontic instruments despite being used by inexperienced operators. PMID:24171022

  14. Observation and prediction of the deformation and fracture of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Creuziger, Adam

    This thesis explores the deformation and fracture behavior of two common shape memory alloys (SMAs), CuAlNi and NiTi. Millimeter, micrometer and nanometer scale features are observed and compared with crystallographic theory of martensite (CTM) predictions and finite element models. Observed fracture behavior, in conjunction with theory and modeling, shed light on the fracture behavior and deformation in shape memory materials. The in plane and out of plane deformations are quantitatively measured and compared with good agreement to predictions from the CTM. For deformation where the stress state was unknown, predicted martensite plates correlated well with observed features. When the stress state could be calculated using finite element analysis (FEA), an available work criterion was used to predict which type of martensite plate would form; with good agreement in arbitrarily oriented, notched CuAlNi samples. The out of plane deformation caused during transformation was quantitatively investigated and agrees well with the average strain of twinned martensite. Using a FEA model of a tapered martensite, the effect of boundary conditions on the out of plane deformation angle was explored. Some limitations on the available work criterion were found. The direction of the out of plane deformation near the notch is consistently such that the area directly ahead of the notch sinks downward. This effect, and the wide martensite plates observed after fracture occurs, indicate the role boundary conditions have on the transformation observed. These effects are not taken into account in the current available work criterion. In single crystal NiTi, the available work criterion was not predictive of the deformations observed in uniaxial tension or in notched samples. However, available work predictions were useful in predicting the fracture properties of notched single crystal NiTi samples, a capability not previously demonstrated. Investigation into the grain boundary fracture

  15. Modeling the transformation stress of constrained shape memory alloy single crystals

    SciTech Connect

    Comstock, R.J. Jr.; Buchheit, T.E.; Somerday, M.; Wert, J.A.

    1996-09-01

    Shape memory alloys (SMA) are a unique class of engineering materials that can be further exploited with accurate polycrystal constitutive models. Previous investigators have modeled stress-induced martensite formation in unconstrained single crystals. Understanding stress-induced martensite formation in constrained single crystals is the next step towards the development of a constitutive model for textured polycrystalline SMA. Such models have been previously developed for imposition of axisymmetric strain on a polycrystal with random crystal orientation; the present paper expands the constrained single crystal SMA model to encompass arbitrary imposed strains. To evaluate the model, axisymmetric tension and compression strains and pure shear strain are imposed on three SMA: NiTi, Cu-Al-Ni ({beta}{sub 1}{yields}{gamma}{prime}{sub 1}) and Ni-Al. Model results are then used to understand the anisotropy and asymmetry of transformation stress in the three SMA considered. Finally, the impact of the present results on polycrystal behavior is addressed.

  16. Modeling the stress-induced transformation behavior of shape memory alloy single crystals

    SciTech Connect

    Buchheit, T.E.; Kumpf, S.L.; Wert, J.A.

    1995-11-01

    The phenomenological theory of martensite crystallography has been used to determine habit plane/shear direction combinations for stress-induced transformation of NiTi, Cu-Ni-Al and NiAl shape memory alloys (SMA) to twin-related martensite correspondence variant pairs. By considering the habit plane/shear direction combinations as unidirectional shear systems, generalized Schmid`s law is then used to predict the mechanical response of unconstrained single crystals of each SMA. Model results include axial transformation strain, and plane stress transformation surfaces as a function of crystal orientation. Comparison of the predicted mechanical response results with the habit plane/shear direction combinations reveals a link between the anisotropy and asymmetry of the mechanical response of SMA single crystals, and the crystallography of the martensitic transformation.

  17. Energy-based fatigue model for shape memory alloys including thermomechanical coupling

    NASA Astrophysics Data System (ADS)

    Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

    2016-03-01

    This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

  18. An innovative approach to achieve re-centering and ductility of cement mortar beams through randomly distributed pseudo-elastic shape memory alloy fibers

    NASA Astrophysics Data System (ADS)

    Shajil, N.; Srinivasan, S. M.; Santhanam, M.

    2012-04-01

    Fibers can play a major role in post cracking behavior of concrete members, because of their ability to bridge cracks and distribute the stress across the crack. Addition of steel fibers in mortar and concrete can improve toughness of the structural member and impart significant energy dissipation through slow pull out. However, steel fibers undergo plastic deformation at low strain levels, and cannot regain their shape upon unloading. This is a major disadvantage in strong cyclic loading conditions, such as those caused by earthquakes, where self-centering ability of the fibers is a desired characteristic in addition to ductility of the reinforced cement concrete. Fibers made from an alternative material such as shape memory alloy (SMA) could offer a scope for re-centering, thus improving performance especially after a severe loading has occurred. In this study, the load-deformation characteristics of SMA fiber reinforced cement mortar beams under cyclic loading conditions were investigated to assess the re-centering performance. This study involved experiments on prismatic members, and related analysis for the assessment and prediction of re-centering. The performances of NiTi fiber reinforced mortars are compared with mortars with same volume fraction of steel fibers. Since re-entrant corners and beam columns joints are prone to failure during a strong ground motion, a study was conducted to determine the behavior of these reinforced with NiTi fiber. Comparison is made with the results of steel fiber reinforced cases. NiTi fibers showed significantly improved re-centering and energy dissipation characteristics compared to the steel fibers.

  19. 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.

  20. Woven type smart soft composite beam with in-plane shape retention

    NASA Astrophysics Data System (ADS)

    Wu, Renzhe; Han, Min-Woo; Lee, Gil-Yong; Ahn, Sung-Hoon

    2013-12-01

    Shape memory alloy (SMA) wire embedded composites (SMAECs) are widely used as morphing structures in small-size and high-output systems. However, conventional SMAECs cannot keep deformed shapes without additional energy. In this paper, a new kind of smart structure named the woven type smart soft composite (SSC) beam is introduced, which is not only capable of morphing, but also maintaining its deformed shape without additional energy. The woven type SSC beam consists of two parts: woven wires and matrix. The selected woven wires are nitinol (Ni-Ti) SMA wires and glass fibers, while the matrix part is polydimethylsiloxane (PDMS). In order to evaluate the performance of the woven type SSC beam in areas such as in-plane deformation, blocking force and repeatability, a beam-shape specimen is prepared of size 100 mm (length) × 8 mm (width) ×3 mm (thickness). The fabricated SSC beam achieved 21 mm deformation and 16 mm shape retention. Blocking force was measured using a dynamometer, and was about 60 mN. In the repeatability test, it recovered almost the same position when its cooling time was 90 s more. Consequently, the woven type SSC beam can be applied to bio-mimicking, soft morphing actuators, consuming less energy than traditional SMAECs.

  1. 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.

  2. Comparative evaluation of pentraxin 3 levels in GCF during canine retraction with active tieback and NiTi coil spring: An in vivo study

    PubMed Central

    Patel, Pratik; Shanthraj, Ravi; Bhagyalakshmi, A; Garg, Nekta; Vallakati, Anisha

    2016-01-01

    Objectives: To compare the levels of pentraxin 3 (PTX-3) in gingival crevicular fluid (GCF) in patients undergoing orthodontic canine retraction with active tieback and nickel titanium (NiTi) coil spring. Materials and Methods: Fifteen patients of the age group 15–25 years with first premolar extraction undergoing canine retraction were selected. One month after placement of 0.019” × 0.025” stainless steel wire, canine retraction was started with active tieback (150 g force) on upper right quadrant and NiTi coil spring (150 g force) on upper left quadrant. GCF samples were collected 1 h before commencement of canine retraction and thereafter at intervals of 1 h, 1 day, 1 week, and 2 weeks after application of force. The collected GCF was eluted from the microcapillary pipette in 100 μl phosphate-buffered saline (pH 5–7.2). The samples were analyzed for PTX-3 levels by the ELISA technique. Results: The mean levels of PTX-3 at 1 h before canine retraction (baseline) was 1.30 ± 0.22 ng/ml and at 1 h 1.66 ± 0.33 ng/ml, 1 day 2.65 ± 0.09 ng/ml, 1 week 1.96 ± 0.15 ng/ml, and 2 weeks 1.37 ± 0.18 ng/ml in active tieback group. The mean levels of PTX-3 at 1 h before canine retraction was 1.32 ± 0.30 ng/ml, and at 1 h 1.71 ± 0.39 ng/ml, 1 day 2.78 ± 0.12 ng/ml, 1 week 2.52 ± 0.18 ng/ml, and 2 weeks 2.12 ± 0.17 ng/ml in NiTi coil spring group. A significant difference of P < 0.001 was found in PTX-3 levels in GCF during canine retraction between active tieback and NiTi coil spring at 1 day, 1 week, and 2 weeks. Conclusion: The results showed that PTX-3 levels increased from 1 h after application of orthodontic force and reached peak at 1 day, followed by a gradual decrease at 1 week and 2 weeks in both active tie back and NiTi coil spring groups. PMID:27127751

  3. Finite element modeling of indentation-induced superelastic effect using a three-dimensional constitutive model for shape memory materials with plasticity

    SciTech Connect

    Zhang, Yijun; Cheng, Yang-Tse; Grummon, David S.

    2007-03-01

    Indentation-induced shape memory and superelastic effects are recently discovered thermo-mechanical behaviors that may find important applications in many areas of science and engineering. Theoretical understanding of these phenomena is challenging because both martensitic phase transformation and slip plasticity exist under complex contact loading conditions. In this paper, we develop a three-dimensional constitutive model of shape memory alloys with plasticity. Spherical indentation-induced superelasticity in a NiTi shape memory alloy was simulated and compared to experimental results on load-displacement curves and recovery ratios. We show that shallow indents have complete recovery upon unloading, where the size of the phase transformation region is about two times the contact radius. Deep indents have only partial recovery when plastic deformation becomes more prevalent in the indent-affected zone.

  4. Functional Response of NiTi Elements for Smart Micro-actuation Applications

    NASA Astrophysics Data System (ADS)

    Biffi, C. A.; Nespoli, A.; Previtali, B.; Villa, E.; Tuissi, A.

    2014-07-01

    Shape memory alloys (SMAs) can be considered a good candidate for actuation applications in the current micro-technology field. In the micro-scale, the temporal response of the SMA actuators can be improved, because of faster cooling during the austenite-martensite transformation. One of the most investigated geometries for this purpose has been the snake-like arrangement, which allows high strokes with considerable forces to be obtained. In this work, SMA elements for micro-actuators were patterned by laser machining in a snake-like shape. Subsequent surface chemical etching was adopted to improve the functional properties of the micro-elements. Calorimetric analysis and thermo-mechanical response of 90 μm thick SMA elements were reported for the evaluation of their functional performances. Moreover, the effect of post-thermal treatment and grain orientation were also evaluated on the final performances.

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

    NASA Astrophysics Data System (ADS)

    Zare, Fateme; Kadkhodaei, Mahmoud; Salafian, Iman

    2015-04-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  9. Tension, compression, and bending of superelastic shape memory alloy tubes

    NASA Astrophysics Data System (ADS)

    Reedlunn, Benjamin; Churchill, Christopher B.; Nelson, Emily E.; Shaw, John A.; Daly, Samantha H.

    2014-02-01

    While many uniaxial tension experiments of shape memory alloys (SMAs) have been published in the literature, relatively few experimental studies address their behavior in compression or bending, despite the prevalence of this latter deformation mode in applications. In this study, superelastic NiTi tubes from a single lot of material were characterized in tension, compression, and pure bending, which allowed us to make direct comparisons between the deformation modes for the first time. Custom built fixtures were used to overcome some long-standing experimental difficulties with performing well-controlled loading and accurate measurements during uniaxial compression (avoiding buckling) and large-rotation bending. In all experiments, the isothermal, global, mechanical responses were measured, and stereo digital image correlation (DIC) was used to measure the evolution of the strain fields on the tube's outer surface.As is characteristic of textured NiTi, our tubes exhibited significant tension-compression asymmetry in their uniaxial responses. Stress-induced transformations in tension exhibited flat force plateaus accompanied by strain localization and propagation. No such localization, however, was observed in compression, and the stress "plateaus" during compression always maintained a positive tangent modulus. While our uniaxial results are similar to the observations of previous researchers, the DIC strain measurements provided details of localized strain behavior with more clarity and allowed more quantitative measurements to be made. Consistent with the tension-compression asymmetry, our bending experiments showed a significant shift of the neutral axis towards the compression side. Furthermore, the tube exhibited strain localization on the tension side, but no localization on the compression side during bending. This is a new observation that has not been explored before. Detailed analysis of the strain distribution across the tube diameter revealed that the

  10. Degradation of the mechanical properties of orthodontic NiTi alloys in the oral environment: an in vitro study.

    PubMed

    Rerhrhaye, Wiam; Bahije, Loubna; El Mabrouk, Khalil; Zaoui, Fatima; Marzouk, Nadia

    2014-09-01

    Appropriate characterization studies are needed to demonstrate the mechanical and biological effects of interaction between archwires and the oral environment. The aim of this study was to investigate, in vitro, the impact of this acidic and fluoridated environment on the electrochemical behavior and the mechanical properties of orthodontic alloys in nickel titanium and in stainless steel (controls) for the following parameters: Young's modulus (E), elastic limit (σe) and the maximum tensile load (σm). Six samples of each archwire alloy were used to assess these parameters. An Instron universal test apparatus (model - 88512) was used for the traction tests on the wires after immersion in solutions at different concentrations of fluoride and at various pH levels. Observations were made using an electron scanning microscope (ESM) to evaluate the surface and an ICP (inductively coupled plasma) mass spectroscopy analysis was made to quantify the substances released into the immersion solution. For the NiTi archwires, immersion in the fluoridated and acidic medium showed a statistically significant reduction of the Young's modulus (E), the elastic limit (σe) and the maximum tensile load (σm). Similarly, a higher level of released nickel proportionate to the increase in the fluoride concentration and acidity was observed in the immersion solutions. ESM observations revealed the status of the surface of the different alloys and the presence of corrosive pitting. PMID:25127751

  11. Inhibition of hydrogen embrittlement of Ni-Ti superelastic alloy in acid fluoride solution by hydrogen peroxide addition.

    PubMed

    Yokoyama, Ken'ichi; Yazaki, Yushin; Sakai, Jun'ichi

    2011-09-01

    Inhibition of the hydrogen embrittlement of Ni-Ti superelastic alloy in an acidulated phosphate fluoride (APF) solution has been attempted by adding various amounts of H(2)O(2). In a 0.2% APF solution, hydrogen absorption is markedly inhibited by adding H(2)O(2), although corrosion is slightly enhanced by increasing the amount of added H(2)O(2). By adding a small amount of H(2)O(2) (0.001 M), in the early stage of immersion, hydrogen embrittlement is inhibited and corrosion is only slightly enhanced. Upon adding H(2)O(2), it appears that the dominant cathodic reactions change from hydrogen evolution to H(2)O(2) reduction reactions, or the surface conditions of the alloy are changed by H(2)O(2) with a high oxidation capability, thereby inhibiting hydrogen absorption. The present study clearly indicates that infinitesimal addition of H(2)O(2) into acid fluoride solutions is effective for the inhibition of the hydrogen embrittlement of the alloy. PMID:21630433

  12. Ab initio studies of the structural, elastic, electronic and thermal properties of NiTi2 intermetallic

    NASA Astrophysics Data System (ADS)

    Toprek, Dragan; Belosevic-Cavor, Jelena; Koteski, Vasil

    2015-10-01

    First principles calculations were performed in the framework of the density functional theory (DFT) using the Full Potential-Linear Augment Plane Wave method (FP-LAPW) within the generalized gradient approximation (GGA) to predict the structural, electronic, elastic and thermal properties of NiTi2 intermetallic compound. By using the Wien2k all-electron code, calculations of the ground state and electronic properties such as lattice constants, bulk modulus, presure derivative of bulk modulus, total energies and density of states were also included. The elastic constants and mechanical properties such as Poisson's ratio, Young's modulus and shear modulus are estimated from the calculated elastic constants of the single crystal. Through the quasi-harmonic Debye model, the preasure and temperature dependences of the linear expansion coefficient, bulk modulus and heat capacity have been investigated. Finally, the Debye temperature has been estimated from the average sound velocity according to the predicted polycrystal bulk properties and from the single crystal elastic constants.

  13. MR-CT registration using a Ni-Ti prostate stent in image-guided radiotherapy of prostate cancer

    SciTech Connect

    Korsager, Anne Sofie; Ostergaard, Lasse Riis; Carl, Jesper

    2013-06-15

    Purpose: In image-guided radiotherapy of prostate cancer defining the clinical target volume often relies on magnetic resonance (MR). The task of transferring the clinical target volume from MR to standard planning computed tomography (CT) is not trivial due to prostate mobility. In this paper, an automatic local registration approach is proposed based on a newly developed removable Ni-Ti prostate stent.Methods: The registration uses the voxel similarity measure mutual information in a two-step approach where the pelvic bones are used to establish an initial registration for the local registration.Results: In a phantom study, the accuracy was measured to 0.97 mm and visual inspection showed accurate registration of all 30 data sets. The consistency of the registration was examined where translation and rotation displacements yield a rotation error of 0.41 Degree-Sign {+-} 0.45 Degree-Sign and a translation error of 1.67 {+-} 2.24 mm.Conclusions: This study demonstrated the feasibility for an automatic local MR-CT registration using the prostate stent.

  14. Resilient and Corrosion-Proof Rolling Element Bearings Made from Superelastic Ni-Ti Alloys for Aerospace Mechanism Applications

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Noebe, Ronald D.; Stanford, Malcolm; Padula, Santo A.

    2011-01-01

    Mechanical components (bearings, gears, mechanisms) typically utilize hard materials to minimize wear and attain long life. In such components, heavily loaded contact points (e.g., meshing gear teeth, bearing ball-raceway contacts) experience high contact stresses. The combination of high hardness, heavy loads and high elastic modulus often leads to damaging contact stress. In addition, mechanical component materials, such as tool steel or silicon nitride exhibit limited recoverable strain (typically less than 1 percent). These material attributes can lead to Brinell damage (e.g., denting) particularly during transient overload events such as shock impacts that occur during the launching of space vehicles or the landing of aircraft. In this paper, a superelastic alloy, 60NiTi, is considered for rolling element bearing applications. A series of Rockwell and Brinell hardness, compressive strength, fatigue and tribology tests are conducted and reported. The combination of high hardness, moderate elastic modulus, large recoverable strain, low density, and intrinsic corrosion immunity provide a path to bearings largely impervious to shock load damage. It is anticipated that bearings and components made from alloys with such attributes can alleviate many problems encountered in advanced aerospace applications.

  15. The atomic-scale nucleation mechanism of NiTi metallic glasses upon isothermal annealing studied via molecular dynamics simulations.

    PubMed

    Li, Yang; Li, JiaHao; Liu, BaiXin

    2015-10-28

    Nucleation is one of the most essential transformation paths in phase transition and exerts a significant influence on the crystallization process. Molecular dynamics simulations were performed to investigate the atomic-scale nucleation mechanisms of NiTi metallic glasses upon devitrification at various temperatures (700 K, 750 K, 800 K, and 850 K). Our simulations reveal that at 700 K and 750 K, nucleation is polynuclear with high nucleation density, while at 800 K it is mononuclear. The underlying nucleation mechanisms have been clarified, manifesting that nucleation can be induced either by the initial ordered clusters (IOCs) or by the other precursors of nuclei evolved directly from the supercooled liquid. IOCs and other precursors stem from the thermal fluctuations of bond orientational order in supercooled liquids during the quenching process and during the annealing process, respectively. The simulation results not only elucidate the underlying nucleation mechanisms varied with temperature, but also unveil the origin of nucleation. These discoveries offer new insights into the devitrification mechanism of metallic glasses. PMID:26414845

  16. Application of fiber Bragg grating sensors in monitoring fatigue failure of NiTi rotary endodontic instruments

    NASA Astrophysics Data System (ADS)

    Liu, C. Y.; Shin, C. S.

    2011-11-01

    NiTi endodontic rotary instruments subjected to alternating tension and compression stress in root canals may fracture without prior warning. Once broken, extracting the fractured part from the canal is a difficult job and is annoying to both the patient and the dentist. Warning of an imminent fracture during clinical use will be a great help to avoid medical and legal complications. A monitoring system employing Fiber Bragg Grating (FBG) sensors has been attempted. The reason of using FBG is its small size which is very promising in integrating with the handpiece of the endodontic equipment. When cracking developed in an rotary instrument, we expect the natural vibration frequency of the instrument changes. If we can pick up the stress wave transmitted through the structural components of the rotary instruments, we may be able to detect the occurrence of a crack. In the current work, we found that we can successfully locate the operation period in the time domain by picking up and analyzing the sound wave using FBG. Furthermore, by employing Fast Fourier Transform (FFT) on the signal, we can reveal the energy variation and the frequency shifting phenomenon in specific section of frequency domain. For some characteristic frequencies, it was found that the energy and frequency varied in a well-defined pattern during the period of crack growth. It is hoped that with these information, the fatigue failure of rotary instruments can be closely monitored to avoid/alleviate the occurrence of unexpected fracture during clinical use.

  17. Application of fiber Bragg grating sensors in monitoring fatigue failure of NiTi rotary endodontic instruments

    NASA Astrophysics Data System (ADS)

    Liu, C. Y.; Shin, C. S.

    2012-04-01

    NiTi endodontic rotary instruments subjected to alternating tension and compression stress in root canals may fracture without prior warning. Once broken, extracting the fractured part from the canal is a difficult job and is annoying to both the patient and the dentist. Warning of an imminent fracture during clinical use will be a great help to avoid medical and legal complications. A monitoring system employing Fiber Bragg Grating (FBG) sensors has been attempted. The reason of using FBG is its small size which is very promising in integrating with the handpiece of the endodontic equipment. When cracking developed in an rotary instrument, we expect the natural vibration frequency of the instrument changes. If we can pick up the stress wave transmitted through the structural components of the rotary instruments, we may be able to detect the occurrence of a crack. In the current work, we found that we can successfully locate the operation period in the time domain by picking up and analyzing the sound wave using FBG. Furthermore, by employing Fast Fourier Transform (FFT) on the signal, we can reveal the energy variation and the frequency shifting phenomenon in specific section of frequency domain. For some characteristic frequencies, it was found that the energy and frequency varied in a well-defined pattern during the period of crack growth. It is hoped that with these information, the fatigue failure of rotary instruments can be closely monitored to avoid/alleviate the occurrence of unexpected fracture during clinical use.

  18. 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

  19. 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.

  20. Comparison of the shaping ability of GT® Series X, Twisted Files and AlphaKite rotary nickel-titanium systems in simulated canals

    PubMed Central

    2013-01-01

    Background Efforts to improve the performance of rotary NiTi instruments by enhancing the properties of NiTi alloy, or their manufacturing processes rather than changes in instrument geometries have been reported. The aim of this study was to compare in-vitro the shaping ability of three different rotary nickel-titanium instruments produced by different manufacturing methods. Methods Thirty simulated root canals with a curvature of 35˚ in resin blocks were prepared with three different rotary NiTi systems: AK- AlphaKite (Gebr. Brasseler, Germany), GTX- GT® Series X (Dentsply, Germany) and TF- Twisted Files (SybronEndo, USA). The canals were prepared according to the manufacturers’ instructions. Pre- and post-instrumentation images were recorded and assessment of canal curvature modifications was carried out with an image analysis program (GSA, Germany). The preparation time and incidence of procedural errors were recorded. Instruments were evaluated under a microscope with 15 × magnifications (Carl Zeiss OPMI Pro Ergo, Germany) for signs of deformation. The Data were statistically analyzed using SPSS (Wilcoxon and Mann–Whitney U-tests, at a confidence interval of 95%). Results Less canal transportation was produced by TF apically, although the difference among the groups was not statistically significant. GTX removed the greatest amount of resin from the middle and coronal parts of the canal and the difference among the groups was statistically significant (p < 0.05). The shortest preparation time was registered with TF (444 s) and the longest with GTX (714 s), the difference among the groups was statistically significant (p < 0.05). During the preparation of the canals no instrument fractured. Eleven instruments of TF and one of AK were deformed. Conclusion Under the conditions of this study, all rotary NiTi instruments maintained the working length and prepared a well-shaped root canal. The least canal transportation was produced by AK. GTX