- The effect of an electric field on the microstructural development during combustion synthesis of TiNi-TiC composites
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The role of an externally imposed (contacting) electric field on the microstructural development during the synthesis of TiC-TiNi composites was investigated. Using elemental reactants, composites with 60 and 70 vol% TiNi were synthesized by the self-propagating combustion method. The field had a direct effect on the velocity and temperature of the combustion wave, and had an influence on the particle size of the TiC phase formed within the TiNi matrix. The average particle size increased by at least a factor of two (from about 2.5 to 5.5 μm for the 60 vol% TiNi samples and from 1.5 to 3.0 μm for the 70 vol% TiNi samples) as the field strength was increased from zero to about 5 V cm-1. Although higher temperatures and wave velocities result in higher temperature gradients and thus an anticipation of shorter residence time at the highest temperatures, the presence of a liquid phase has apparently a more direct effect on TiC particle growth. In cases where no liquid is present the results are different, as will be reported in a subsequent paper.
- Graeve, Olivia A.,Munir, Zuhair A.
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- Influence of heat of formation of B2/L12 intermetallic compounds on the milling energy for their formation during mechanical alloying
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In this paper an attempt has been made to arrive at a relation between the heat of formation of an intermetallic and the milling energy required for its formation during mechanical alloying. This has been demonstrated in case of B2 intermetallic compounds, namely, NiAl, FeAl, CoAl and MnAl. The milling energy corresponding to the start of formation of the compounds during mechanical alloying of the elemental blends is found to decrease linearly with the heat of formation of the intermetallics, calculated using the Miedema's model. Al3Zr, Ni3Al, Ni3Mn, CoFe, NiTi, Zr3Co are also synthesized in an attempt to test the strength of the hypothesis over a wider range of compounds as well as enthalpy of mixing. An attempt has been made to understand the mechanism of the compound formation.
- Abhik,Vivek,Udhayabanu,Murty
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- Effect of Zr additions on the electrode characteristics of nanocrystalline TiNi-type hydrogen storage alloys
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The effect of Zr on the structure and electrochemical properties of nanocrystalline TiNi-type alloys was studied. These materials were prepared by mechanical alloying (MA) followed by annealing. It was found that the respective replacement of Ni in nanocrystalline TiNi by Zr, and by Zr and Fe improved not only the discharge capacity but also the cycle life of these electrodes. In the nanocrystalline TiNi0.875Zr0.125, a powder discharge capacity up to 135 mA h g-1 was measured on the 10th cycle (at 40 mA g-1 discharge current). The studies show that the electrochemical properties of Ni-MH batteries are a function of the microstructure and the chemical composition of the used electrode materials.
- Makowiecka,Jankowska,Okonska,Jurczyk
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- Production of NiTi via the FFC cambridge process
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The FFC Cambridge process is a direct electrodeoxidation process used to reduce metal oxides to their constituent metals in a molten Ca Cl2 salt bath. NiTi O3 was used as a precursor (the first stable oxide to form upon blending and sintering NiO and Ti O2 powders) and was successfully reduced using the FFC Cambridge process at 1173 K and a constant cell voltage of -3.1 V to produce a NiTi alloy. This work builds on the literature work [Chinese Science Bulletin, 51, 2535 (2006)] through: (i) a predominance diagram calculated to show the regions of phase stability throughout the usable potential window of the Ca Cl2 salt; (ii) the investigation of a wide range of reduction times for a fixed cell voltage, elucidating several additional stable phases, to yield a complete and detailed reduction pathway. The reduction pathway for NiTi O3 was identified through the analysis of a series of partial reductions, with fully reduced NiTi formed after a period of 24 h. The first stage of the reaction involved the rapid formation of Ni and CaTi O3. The reduction then proceeded via the formation of the intermediate compounds Ni3 Ti and Ni2 Ti4O. All the NiTi O3 and Ni were consumed after a period of 6 h, while the intermediate compounds remained until the reaction was near completion. The experimental results related well to the thermodynamic predictions of the predominance diagram. A small variation in stoichiometry of the produced NiTi observed from the edge to the core of the samples was attributed to redeposition of Ti on the sample surface from the salt and a slightly Ti-rich NiTi O3 precursor material.
- Jackson, Ben,Jackson, Martin,Dye, David,Inman, Douglas,Dashwood, Richard
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- Studies of electrochemical properties of TiNi alloy used as an MH electrode - I. Discharge capacity
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The electrochemical properties of TiNi alloy used as an MH electrode were investigated. A mathematical model for the electrochemical discharge capacity of TiNi electrode was developed. The model was used to study the effects of various parameters on the discharge capacity, and cycle life. The predicted results from the model fit well with the experimental results. Increasing the discharge current density and charge/discharge cycling current density decreases the discharge capacity, but a high charge/ discharge cycling current density increases the cycle life of the hydride electrode. Increasing the exchange current density, or the diffusion coefficient of hydrogen or reducing the particle size increases the discharge capacity. Upon increasing the discharge current density the controlling steps of discharge capacity change from hydrogen diffusion in α phase (including oxide film) to the charge-transfer reaction on the hydride electrode surface. However for the TiNi alloy electrode the discharge capacity still depends mainly on the diffusion ability of hydrogen even at high discharge current density (200 mA/g). There exists an optimum dissolved hydrogen content of the α phase, Coptαβ, at which the discharge capacity reaches a maximum value. Also Coptαβ increases with increasing discharge current density.
- Wang,Lei,Wang
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- Electrochemical hydriding of amorphous and nanocrystalline TiNi-based alloys
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Amorphous and nanocrystalline TiNi1-xMx (M = Co, Fe, Sn; x = 0 and 0.2) alloys were synthesized by mechanical alloying. Powder particles with an average diameter of about 5 μm were produced. X-ray diffraction analysis showed that aft
- Drenchev, Boris,Spassov, Tony
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- Production of NiTi shape memory alloys via electro-deoxidation utilizing an inert anode
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NiTi shape memory alloys (SMA) with equiatomic composition of Ni and Ti were prepared by electro-deoxidation, in molten calcium chloride, at 950 °C. Constant voltage electro-deoxidation was conducted using a NiTiO3 cathode, and either a carbon anode or a novel CaRuO3/CaTiO 3 composite inert anode. Both anode materials successfully allowed NiTi shape memory alloy to be obtained. The primary difference is that molecular oxygen was produced on the inert anode, instead of environmentally undesired CO2 greenhouse gases on the carbon anode. Indeed, it was found that carbon could successfully be substituted with conductive calcium titanate-calcium ruthenate composites for electro-deoxidation. Furthermore, DSC was used to analyze the phase transformation of NiTi shape memory alloys, with results revealing the existence of reversible martensite-austenite phase transformations during the cooling and heating process.
- Jiao, Shuqiang,Zhang, Linlin,Zhu, Hongmin,Fray, Derek J.
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- Electrochemical and electronic properties of nanocrystalline TiNi 1 - XMx (M = Mg, Mn, Zr; X = 0, 0.125, 0.25) ternary alloys
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Nanocrystalline TiNi1 - xMx (M = Mg, Mn, Zr; x = 0, 0.125, 0.25) ternary alloys were prepared by mechanical alloying (MA) followed by annealing. The effect of Mg, Mn and Zr on the structure and electrochemical properties of nanocrystalline TiNi-type alloys was studied. It was found that the respective replacement of Ni in TiNi by Mg, Mn or Zr improved not only the discharge capacity but also the cycle life of these electrodes. In the nanocrystalline TiNi0.875Mn0.125 powder the discharge capacity up to 151 mA h g-1 on the 10th cycle was measured (at 40 mA g-1 discharge current). The studies show, that the electrochemical properties of nanocrystalline MH electrodes are a function of the chemical composition of the used materials. The band structure has been studied by the Tight Binding version of the Linear Muffin-Tin orbitals method in the Atomic Sphere Approximation (TB LMTO ASA).
- Szajek,Makowiecka,Jankowska,Jurczyk
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- Two-stage transformation of aluminum-containing NiTi
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Measurements of electrical resistivity, ultrasonic velocity and attenuation for equiatomic NiTi and Ni50Ti49Al1 were performed in order to characterize the thermoelastic martensitic transformation during cooling. The NiTi shows a one-stage transformation, essentially, because a premartensitic phenomenon is negligibly faint. The ultrasonic anomalies in NiTi appear near the temperature at a faint resistivity-peak, which correspond to lattice softening at the start temperature of martensitic transformation from the high-temperature phase to the low-temperature phase. The resistivity of Ni50Ti49Al1 has a negative temperature coefficient over the wide temperature range from room temperature to154K, and indicates a large peak. Such an anomaly in resistivity corresponds to an enhanced premartensitic phenomenon, where ultrasonic anomalies caused by a two-stage transformation are observed which accompany a large change in electrical resistivity. However, a resistivity peak in the aluminum-containing NiTi is formed at lower temperature than those at ultrasonic anomalies by over 40K, and the temperature at the resistivity peak is not one characterizing the transformation behavior. It proved helpful to measure the ultrasonic properties in comparison with the electrical resistivity in order to characterize successive transformations in the temperature range of a premartensitic phenomenon of NiTi enhanced by addition of aluminum.
- Matsumoto, Hitoshi,Abe, Hiroshi,Morikawa, Yuki
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- Shape memory effect in sputtered Ti-Ni thin films
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The microstructure and electrical transport properties of Ti-Ni granular films have been investigated with X-ray diffraction and DC resistivity measurements, respectively. Samples with the eutectoid composition (~50at%Ni) were grown by RF magnetron sputtering on a heated sample holder. These films comprised Ti2Ni,TiNi3 and TiNi granular phases, their relative proportions and microstructures critically depending on the substrate temperature. A majoritary metastable TiNi phase was obtained in samples grown at temperatures above 600°, as inferred from the discussion of the X-ray diffraction plots. These crystalline films showed the hysteretic behaviour of the electrical resistance which is attributed to the characteristic shape memory effect of such a binary alloy. Besides, the DC resistivity measurements are accomplished in Joule-heated samples by which efficiently modify their microgranular structure from amorphous to crystalline, or even stabilize the TiNi phase after a flash annealing.
- Arranz,Riveiro
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- Amorphization by mechanical alloying: The role of mixtures of intermetallics
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This paper reports selected results on the systematics and mechanisms of amorphization by mechanical alloying of mixtures of intermetallic compound powders. Mechanical alloying was carried out on mixtures of 'line' intermetallic compounds (i.e. those having a narrow range of homogeneity) in Cr-Ti, Mn-Ti, Cu-Ti, Fe-Ti, Co-Ti, Ni-Ti, Cu-Zr, Ni-Zr and Mn-Si. Amorphization by mechanical alloying was observed to be complete, to the resolution of X-ray diffraction, for intermetallic compound mixtures in all the above systems except Cr-Ti, which exhibited partial amorphization, and Mn-Si, which showed no amorphization. The amorphization tendencies could not be predicted from calculated enthalpies of mixing for the amorphous alloys, all of which were negative, or from calculated differences in free energy between the amorphous phase and the mixture of equilibrium intermetallic compounds. Preliminary transmission electron microscopy studies of the evolution of the amorphous phase for the system NiZr2+Ni11Zr9→a-Ni40Zr60 revealed an amorphous halo-like region surrounding the transforming intermetallic particles in a amorphous matrix. Energy dispersive X-ray analysis measurements indicate that the halo-like region has a composition which falls between those of the intermetallic particle and the amorphous matrix.
- Lee, P. Y.,Jang, J.,Koch, C. C.
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- Isothermal section of the phase diagram of the La-Ni-Ti ternary system at 673 K
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The isothermal section of the phase diagram of the ternary system La-Ni-Ti was investigated by X-ray diffraction, differential thermal analysis, optical microscopy and electron microscopy techniques. It consists of 14 single-phase regions, 25 two-phase re
- Jingqi, Liu,Ke, Geng
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- Effect of crystallographic orientation of nanocrystalline TiN on structural, electrical and mechanical properties of TiN/NiTi thin films
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Nanocrystalline TiN/NiTi thin films have been grown on silicon substrate by dc magnetron sputtering to improve the surface and mechanical properties of NiTi based shape memory alloys without sacrificing the phase transformation effect. Interestingly, the
- Kumar, Ashvani,Singh, Devendra,Kumar, Ravi,Kaur, Davinder
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- Pore characteristics of porous NiTi alloy fabricated by combustion synthesis
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Biomedical porous NiTi shape memory alloy (SMA) is a promising implant material. The pore characteristics, such as pore morphology and distribution, mean pore size and porosity of porous NiTi SMA fabricated by combustion synthesis were investigated in this paper by optical microscopy, scanning electron microscopy (SEM), image processing and density determination and the mechanism of pore formation was proposed. The result indicated that pore morphology and distribution of porous NiTi SMA exhibited features of isotropy or anisotropy, depending upon preheating temperature during synthesis. Mean pore size and porosity range was 300-600 μm and 60-64% respectively, and open porosity ratio was bigger than 90% which indicates that porous NiTi SMA is suitable for biomedical application.
- Li,Rong,Li
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- Optical properties and electronic structures of B2 and B19′ phases of equiatomic Ni-Ti alloys
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The dielectric functions of equiatomic Ni-Ti alloys were measured by spectroscopic ellipsometry in the energy range of 1.5-5.4 eV at ~423 and at ~25 K. The peak at ~2.26 eV in the B19′ (monoclinic structure) optical conductivity spectrum has a slightly larger magnitude than in the B2 (cubic CsCl structure) phase, while the shoulder at ~3.5 eV becomes weaker and almost indiscernible upon martensitic transformation. A new structure develops at ~2.85 eV in the B19′ phase; however, it is also very weak. The band structures and the optical conductivity were calculated in both phases using the linearized-augmented-plane-wave method within the local-density approximation. k points near the Γ-X-M plane in the B2 phase and the corresponding k-points in B19′ phase contribute significantly to all three structures. The difference between the two spectra is due to the transitions between the folded-back bands from the B2 phase because of the larger unit cell of the B19′ phase and the change in the electronic energy spectrum near the Fermi level. The overall optical properties of Ni-Ti alloys in the measured energy range are rather insensitive to the martensitic transformation because the states far from the Fermi level are mainly involved in the interband transitions. 1999 The American Physical Society.
- Rhee, Joo Yull,Harmon,Lynch
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- Nickel-metal hydride battery using nanocrystalline TiFe-type hydrogen storage alloys
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Mechanical alloying (MA) process was used to synthesize nanocrystalline TiFe-type alloys. XRD analysis showed that, firstly, after 20 h of milling, the starting mixture of the elements had transformed into an amorphous phase and, secondly, the annealing i
- Jankowska,Makowiecka,Jurczyk
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- Nanocrystalline titanium-type metal hydride electrodes prepared by mechanical alloying
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Mechanical alloying (MA) was employed to produce nanocrystalline TiFe1-xNix alloys (x=0, 0.25, 0.5, 0.75 and 1.0). XRD analysis showed that, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase. Following annealing in high purity argon at 750°C for 0.5 h, XRD confirmed the formation of the CsCl-type structures with crystallite sizes of about 50 nm. These materials were used as negative electrodes for a Ni-MHx battery. With increasing nickel content in TiFe1-xNix, the material shows an increase in discharge capacity which passes through a maximum for x=0.75. In the nanocrystalline TiFe0.25Ni0.75 powder, discharge capacities of up to 155 mA h g-1 (at 40 mA g-1 discharge current) were measured. The titanium-based hydrogen storage alloys are attractive for secondary batteries, because of inexpensive raw materials.
- Jurczyk,Jankowska,Nowak,Jakubowicz
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- Investigation of the Zr1-yTiy(Cr1-xNix)2-H2 system 0.0≤y≤1.0 and 0.0≤x≤1.0 Phase composition analysis and thermodynamic properties
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The Zr1-yTiy(Cr1-xNix)2 compounds were synthesized and characterized by means of X-ray powder diffraction. From the Rietveld analysis carried out on the alloys, we determined the phase abundancy and refined the crystal structure. The system crystallized with hexagonal C14-type structure for nickel content less than x=1.0 with some amount of additional phases (ZrNi, Zr9Ni11, Zr7Ni10, TiNi) and pure metals (Ni and Cr). For higher nickel concentrations, the system crystallized in the cubic C15-type structure. The amount of additional phases increased with increasing nickel and titanium content. The Pressure-Composition-Temperature measurements using a volumetric method were carried out at 313 K on some selected alloys. The single phase systems were found to absorb a large amount of hydrogen (H/M≤1.8 wt.%) but had very poor kinetics. The multiphase systems were found to behave as a single phase (presence of single plateau), have a relatively good hydrogen capacity (H/M≤1.4 wt.%) and exhibit faster kinetics. A linear correlation between the heat of formation of the Zr1-yTiy(Cr1-xNix)2 hydrides estimated from the band structure model and the unit cell volume of the alloys determined from the X-ray Rietveld analysis was obtained. It shows a decrease of hydride stability with increasing unit cell volume.
- Bououdina,Enoki,Akiba
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- Electrochemical properties of sealed Ni-MH batteries using nanocrystalline TiFe-type anodes
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Mechanical alloying (MA) process was introduced to produce nanocrystalline TiFe0.25Ni0.75 and TiNi alloys. XRD analysis showed that, firstly, after 20 h of milling, the starting mixture of the elements had transformed into an amorphous phase and, secondly, the annealing in high purity argon at 700°C for 0.5 h led to formation of the CsCl-type structures with a crystallite size of about 25 nm. These materials were used as negative electrodes for sealed nickel-metal hydride (Ni-MH) batteries. The results show that the sealed battery using the nanocrystalline TiFe0.25Ni 0.75 alloy has about 1.5 times the capacity of the TiNi one.
- Jankowska,Jurczyk
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- Localized modes of hydrogen and deuterium in NiTiHx and NiTiDx
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The localized vibrations of hydrogen and deuterium in the shape-memory alloy NiTi were investigated by neutron spectroscopy. Measurements were carried out on two hydrogenated samples (NiTiH0.02 and NiTiH1.3) and one deuterated sample
- Stuhr, U.,Schmidt, R.,Wipf, H.,Herget, G.,Muellner, M.,et al.
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- Enhancement of a peak in electrical resistivity of NiTi alloy in early stage of transformation cycles
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For a better understanding of the transformation behavior on the equiatomic NiTi alloy, the measurement of electrical resistivity was performed in the early stage of transformation cycles, and was compared with the calorimetric measurement. A faint peak in electrical resistivity is observed during the first cooling, at which the temperature is much higher in comparison with the exothermic peak. With increasing transformation cycles, the peak in electrical resistivity is enhanced, at which the temperature is close to the start temperature of the transformation from the intermediate phase to the low-temperature phase. The transformation and the reverse one show a thermal hysteresis of 30 K, and the low-temperature phase is transformed directly to the high-temperature phase, even with increasing transformation cycles. An increase in electrical resistivity with the transformation is detected in the temperature range of the low-temperature phase, which is attributable to the defects induced during the transformation. It is thought on the transformation in the early stage of transformation cycles that the transformation-induced defects play complicated roles such as the electron scattering and the stabilization of the intermediate phase to result in a peak in electrical resistivity.
- Matsumoto, Hitoshi
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- Combustion synthesis of TiNi intermetallic compounds: Part 1. Determination of heat of fusion of TiNi and heat capacity of liquid TiNi
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The synthesis of the TiNi intermetallic compound using the thermal explosion mode of the combustion synthesis technique has been used to determine the heat of fusion, δHm (7.77 kcal mol-1), of the TiNi intermetallic and the heat capa
- Yi,Moore
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- Microstructure of TiNi shape-memory alloy synthesized by explosive shock-wave compression of Ti-Ni powder mixture
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Cylinders of TiNi shape-memory alloy were synthesized from mixtures of equiatomic fine irregular titanium and nickel powders by explosive-wave compression with a detonation velocity of about 6500 m s 1. B2 type parent phase, R phase, B19′ type martensite, Ti2Ni, Ti3Ni4 and Ti2Ni3 phases were observed in this as-synthesized material. In the B2 matrix high density dislocations existed. The Burgers vectors of many dislocations were determined to be parallel to 〈111〉 directions. The R phase variants formed (001) B2 twinning structure. The substructure of the B19′ martensite was (001) B19′ type I twin and stacking faults on the (001) B19′ plane. When increasing the temperature of the as-synthesized material in a differential scanning calorimeter, no B19′ → R → B2 transitions were observed on the temperature range -50 to 100°C. However, B2 → B19′(R) transitions occurred during the cooling cycle. After heat treating the specimen at 800°C for 1 h and then ageing at 400°C for 10 min, both B2 → R → B19′ and B19′(R) → B2 phase transitions were observed.
- Han, Xiaodong,Zou, Wenhui,Wang, Renhui,Jin, Sing,Zhang, Ze,Li, Tongchun,Yang, Dazhi
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- 573 K and 773 K isothermal sections of the phase diagram of the Pr-Ni-Ti ternary system
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The 573 K and 773 K isothermal sections of the phase diagram of the Pr-Ni-Ti ternary system were investigated by X-ray diffraction, differential thermal analysis, optical microscopy and electron microscopy techniques. The 573 K isothermal section was rest
- Zhong, Xiaping,Yang, Zhao,Liu, Jingqi
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- The electronic and electrochemical properties of the TiFe-based alloys
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Ti(Fe,M)-based alloys (M = Ni, Mo, Cr, Co) were mechanically alloyed (MA) under an argon atmosphere to synthesize nanostructured materials. XRD analysis showed that, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase. Following the annealing in high purity argon at 750 °C for 0.5 h, XRD confirmed the formation of CsCl-type structures with crystallite sizes of about 30 nm. These materials were used as negative electrodes for a Ni-MHx battery. The alloying elements of the 3d transition metals, Ni, Mo, Cr and Co, were substituted for iron atoms, and the structural, electronic and electrochemical properties were studied. With increasing nickel content in TiFe1-xNix, the material showed an increase in discharge capacity which passed through a maximum for x = 3/4. In the nanocrystalline TiNi0.6Fe0.1Mo0.1Cr0.1Co0.1 powder, a discharge capacity of up to 135 mA h g-1 (at 40 mA g-1 discharge current) was measured. For this composition the capacity degraded much more slowly with cycling in comparison to other studied compositions. The electronic structure was studied by the tight-binding version of the linear muffin-tin method in the atomic sphere approximation (TB-LMTO ASA). In the TiFe1-xNix alloys, increasing the content of the Ni impurities extended the valence bands and increased the density of states at the Fermi level. Similar effects were observed for the TiNi1/2Fe1/8Mo1/8Cr1/8Co1/8 system. Mechanical alloying proved to be a suitable procedure for obtaining TiFe-based alloy electrodes for Ni-MHx batteries. Elsevier Science B.V. All rights reserved.
- Szajek,Jurczyk,Jankowska
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- Compressive property of porous NiTi alloy synthesized by combustion synthesis
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Porous NiTi shape memory alloy (SMA) is a promising biomedical material applied as a human implant. Compressive properties of porous NiTi SMAs fabricated by combustion synthesis were investigated in this paper by compression tests. The results indicated that the nominal ultimate compressive strength and strain of porous NiTi SMAs were dependent on porosity and independent on strain rate. The compressive strength of porous NiTi SMA met the basic strength demand of human cancellous bone with corresponding porosity. Elsevier Science B.V. All rights reserved.
- Li, Yong-Hua,Rong, Li-Jian,Li, Yi-Yi
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- Experimental investigation in the quaternary systems Ti-Ni-Al-N and Ti-Ni-Al-O
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The experimental evaluation of phase equilibria in the Ti-Ni-Al-N and Ti-Ni-Al-O phase diagrams are based on alloy samples, which were prepared of elemental powder blends by argon-levitation melting in a Hukin crucible. The experimental investigation employed X-ray powder diffraction, metallography, SEM, and EMPA techniques in the as-cast state as well as after annealing at 900°C. Two quaternary compounds Ti3NiAl2N and Ti3NiAl2O deriving from the filled Ti2Ni type (η phase) were observed. The novel phases are in equilibrium with the Ti2Ni-type solid solution phase (Ti(1-x)Al(x))2Ni, which exhibits a maximum solubility of 14 at % Al in binary Ti2Ni. Atom order in all these phases was monitored by quantitative X-ray powder diffraction (Rietveld analyses). The difference of X-ray spectra among the various phases deriving from parent Ti2Ni type was analyzed and the complex atom site occupation mode was discussed in terms of the general classification scheme for η phases. (C) 2000 Academic Press.
- Huneau,Ding,Rogl,Bauer,Ding,Bohn
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- Combustion synthesis of TiNi intermetallic compounds: Part 2. Effect of TiO2 formation
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Equiatomic titanium and nickel compacted powders were synthesized into a TiNi intermetallic compound using a thermal explosion mode of the self-propagating high-temperature synthesis (SHS) method in air. It was found that the combustion temperature (Tsub
- Yi, H. C.,Moore, J. J.
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- Electrochemical stability of orthopedic porous NiTi shape memory alloys treated by different surface modification techniques
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The complex surface morphology and large exposed surface area induce electrochemical instability on porous NiTi shape memory alloys in human body fluids. Consequently, leaching of toxic nickel ions from the alloys impede wider applications of the material
- Wu, Shuilin,Liu, Xiangmei,Hu, Tao,Jiang, Jiang,Chu, Paul K.,Yeung,Chung,Chu,Xu, Zushun,Lu,Cheung,Luk
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- Ultrasonic attenuation in NiTi near the martensitic transformation temperature
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In the present paper, measurements of electrical resistivity, ultrasonic velocity and attenuation for the equiatomic NiTi were made over a wider temperature range; and it was emphasized that the ultrasonic attenuations during cooling and heating have characteristic temperature dependences in comparison with the resistivity and the velocity. The equiatomic NiTi alloy was prepared form nickel (purity, 99.99%) and titanium (purity, 99.9%) by electron-beam melting.
- Matsumoto, Hitoshi,Ishiguro, Hisayuki
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- The thermochemical behavior of some binary shape memory alloys by high temperature direct synthesis calorimetry
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The standard enthalpies of formation of some shape memory alloys have been measured by high temperature direct synthesis calorimetry at 1373 K. The following results (in kJ/mol of atoms) are reported: CoCr (-0.3 ± 2.9); CuMn (-3.7 ± 3.2); Cu3Sn
- Meschel,Pavlu,Nash
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p. 5256 - 5262
(2011/06/25)
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- A study on microstructure and porosity of NiTi alloy implants produced by SHS
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In this study, Ni and Ti with 50.5 at.% Ni powders were blended for 12 h and cold pressed in the different pressures (50, 75 and 100 MPa). Then, the porous NiTi alloy compacts obtained were synthesized by SHS (self-propagating high-temperature synthesis)
- Tosun, Gul,Ozler, Latif,Kaya, Mehmet,Orhan, Nuri
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p. 605 - 611
(2010/03/23)
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- The effect of solution treatment under loading on the microstructure and phase transformation behavior of porous NiTi shape memory alloy fabricated by SHS
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Porous NiTi shape memory alloy (SMA) was fabricated by self-propagating high-temperature synthesis (SHS). With this study, a new solution treatment "solution treatment under loading" was applied to porous NiTi SMA fabricated by SHS to determine microstruc
- Kaya, Mehmet,Orhan, Nuri,Kurt, Bulent,Khan, Tahir I.
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p. 378 - 382
(2009/10/23)
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- Synthesis of NiTi intermetallics by self-propagating combustion
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The production of NiTi intermetallic compounds from elemental powder compacts was conducted by self-propagating high-temperature synthesis (SHS) in this study. Effects of initial sample density, preheating temperature, and Ni particle size on the combustion characteristics, as well as on the final composition and morphology of products were studied. For the samples with densities between 50 and 60% theoretical maximum density (TMD) under preheating temperatures in the range of 100-300°C, the synthesis process showed two consecutive combustion stages, including the propagation of combustion front and the subsequent bulk combustion. Under these conditions, high-density products containing NiTi as the major phase with small amounts of secondary phases of NiTi2 and Ni3Ti were obtained. However, porous combustion products with a significant amount of unreacted Ni were produced from the 45% TMD samples under preheating temperatures of 100 and 150°C, due to the lack of the second combustion stage. The amount of unreacted Ni in the final composition was greatly reduced by increasing the initial sample density and preheating temperature, or by using smaller Ni particles in the samples. In addition, the use of smaller Ni particles also led to an increase in the product density up to about 95% relative to the density of NiTi intermetallic.
- Yeh,Sung
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- Hydrogenation characteristics of ternary alloys containing Ti4Ni2X (X = O, N, C)
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Ti2Ni-based alloys containing oxygen, nitrogen and carbon were investigated regarding their metallographic structures and hydrogenation characteristics. The alloy samples containing these non-metal elements had multi-phase structures composed o
- Takeshita, Hiroyuki T.,Tanaka, Hideaki,Kuriyama, Nobuhiro,Sakai, Tetsuo,Uehara, Itsuki,Haruta, Masatake
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p. 188 - 193
(2008/10/08)
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- TiNi-H System at Elevated Hydrogen Pressures
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The TiNi-H system was studied at pressures 0.1-15 MPa and temperatures 20-450°C. The most hydrogen-rich compositions obtained at 20°C are TiNiH10 at 10 MPa and TiNiH15 at 15 MPa. The system contains no two-phase regions. Sorption isotherms for the Ti2Ni-H and TiNi3-H systems were measured at hydrogen pressures up to 8.5 and 9.5 MPa, respectively. The hydrogen sorption behavior of TiNiHx differs from that of conventional hydrides of metals and alloys.
- Fadeev,Syasin
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p. 1306 - 1309
(2008/10/08)
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- PHASE RELATIONS AND DIFFUSION PATHS IN THE Ti-Ni-Fe SYSTEM AT 900 degree C.
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A study was made of the 900 degree C cross section through the ternary phase diagram Ti-Ni-Fe by means of the diffusion couple technique and by investigating equilibrated alloys. The course of a number of diffusion paths was established. Use was made of optical, microprobe, and X-ray analyses. Some hitherto unaccountable results mentioned in the literature have been explained.
- Van Loo,Vrolijk,Bastin
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p. 121 - 130
(2008/10/09)
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