Ti2Ni Alloy Research Articles

Microstructure and mechanical properties of Ti2Ni alloy fabricated by direct energy deposition

It is difficult to prepare Ti2Ni alloys using traditional single-wire arc additive manufacturing. In this study, a Ti2Ni alloy wall was fabricated in situ by double-wire arc additive manufacturing with pure Ti and Ni wires, and the resulting material has the potential to be applied to spacecraft and ground armor protection. In the stable region, the Ti: Ni content ratio was close to 2:1 after stabilization, indicating that the as-built wall was very close to the designed composition (Ti2Ni). From the top of the wall to the substrate, the microstructure evolved as follows: Ti2Ni + NiTi → Ti2Ni + NiTi + α-Ti → α-Ti + Ti2Ni. In the stable region, the hardness remained stable at approximately 660 HV0.5.

Erosion Resistance of BaZrO3-Y2O3 Two-Phase Crucibles against Highly Active Ti2Ni Alloys

Erosion Resistance of BaZrO3-Y2O3 Two-Phase Crucibles against Highly Active Ti2Ni Alloys

Interaction mechanism between BaZrO3/Y2O3 refractory and Ti2Ni alloy melts

Interaction mechanism between BaZrO3/Y2O3 refractory and Ti2Ni alloy melts

Role of Ca additive on the effect of phase composition and microstructure of BaZrO3 refractory and its interaction with titanium alloys

AbstractIn this study, the effect of different Ca additives (Ca(OH)2, CaO, and nano‐CaCO3) on the composition and microstructure of the fused BaZrO3 crucible were investigated, as well as their interaction with Ti2Ni alloy during vacuum induction melting. Results showed that the crucibles had the same phase compositions when the doping amounts of Ca additives were the same. Three kinds of Ca additives provided three different grain sizes of CaO precursors to participate in the solid solution reaction. When the doping amount of the Ca additive was 5.3 wt.%, the ZrO2 phase in the fused BaZrO3 was disappeared, and the CaZrO3 phase was founded. The composition of the crucibles doped with 7.7 wt.% Ca additives only consisted of Ba1‐xCaxZrO3 and CaZrO3 phase. The relative densities and erosion resistance of the crucibles were improved effectively with the increase of Ca additive content. Moreover, the crucible doped with 7.7 wt.% nano‐CaCO3 additive exhibited the highest density and the thinnest erosion layer. The Ba1‐xCaxZrO3 and CaZrO3 phases were dissolved by the alloy melt, according to the interaction analysis. In addition, the crucible doped with nano‐CaCO3 additive had a higher content of refractory element concentration in the alloy melts in comparision with the other two kinds of crucibles due to their higher number of pores.

Phase and microstructural evolution of BaZrO3‐CaZrO3 refractory and its interaction with titanium alloy melt

AbstractIn this study, the effect of CaZrO3 additives on the phase and microstructure of BaZrO3 refractory were investigated as well as the interaction with titanium alloy melts. Results revealed that no second phase was observed in the BaZrO3 refractory with 10 and 20 mol% CaZrO3 additives, respectively, and the incorporation CaZrO3 additives promoted the densification and the growth of grains due to the generation of BaZrO3‐CaZrO3 solid solutions. Whereas, the appearance of CaZrO3 phase was in the BaZrO3 refractory with 30 mol% additive, indicating that the additive content excessed the solid solubility limit in the BaZrO3 refractory. Interaction analysis indicated that CaZrO3 additive could improve the performance of BaZrO3 refractory for resisting the penetration of Ti2Ni alloy melt. Meanwhile, an increasing extent of melt contamination by the BaZrO3 refractory was also detected with the increasing content of CaZrO3 additive. According to the thermodynamic calculation, an obvious increase in Gibbs free energy of formation for the BaZrO3 refractory was confirmed with the CaZrO3 additive, resulting in the increasing extent of the dissolution‐corrosion between the refractory and the titanium alloy melts.

Preparation of High Density BaZr<sub>0.97</sub>Y<sub>0.03</sub>O<sub>3-δ</sub> Ceramic and its Interaction with Titanium Melt

In this paper, the BaZrO3(BZ) and BaZr0.97Y0.03O3-δ(BZY3) powders were prepared by using the industrial grade BaCO3, ZrO2and Y2O3powders combining the conventional solid state reaction. The BaZrO3(BZ) and BaZr0.97Y0.03O3-δ(BZY3) ceramics were fabricated at 1750°C. The effect of ball milling time and sintering aid (TiO2) on the sinterability of BaZr0.97Y0.03O3-δ(BZY3) ceramics were investigated, and the improved stability of BaZrO3refractory with Y2O3additive were studied according to the refractory-metal interaction. The results revealed that the particle size of BZY3 powders decreased first and then increased with the increasing of ball milling time from 6h to 12h, and the minimum particle size was only 2.252μm at 8h. When 2wt.%TiO2was added, the sintered pellet of BZY3 was the most densest and the relative density was above 95%. After melting the Ti2Ni alloy on the BZY and BZ ceramics, the thickness erosion layer of BaZrO3and BZY3refractories and Ti2Ni alloy is approximately 50μm and 20μm respectively, showing that BZY3 was more stable than BaZrO3refractory.

Improved stability of BaZrO3 refractory with Y2O3 additive and its interaction with titanium melts

Two kinds of refractory (BaZrO3 and Y2O3 (Y)-doped BaZrO3) were prepared to melt two titanium alloys (TiNi and Ti2Ni), respectively. The influence of Y2O3 on the phase constitution and microstructure of BaZrO3, as well as the interaction between the refractory and the titanium alloys, were investigated using the XRD and SEM. The results revealed that the Y-doped BaZrO3 consisted of BaZr1-xYxO3 and Ba2YZrO6-d, no erosion phenomenon was observed for two kinds of refractory after melting TiNi alloys, however, a 275 μm thick reaction layer of BaZrO3 crucible was observed after melting Ti2Ni alloy, whereas, there existed only a 45 μm erosion layer for the Y-doped BaZrO3 crucible. The dissolution of BaZrO3 in the titanium melts was the main reason of the alloy-crucible interaction, and the dissolution equation was determined: TixNi(l)+x2BaZrO3(s)→TixNi[x2Zr,xO](l)+x2BaO(l), doping Y2O3 into BaZrO3 could reduce the dissolution amount of refractory in the titanium melts by improving its thermodynamic stability. This fact may imply that the Y-doped BaZrO3 was more suitable for induction melting of the titanium alloys.

Electrochemical properties of Ti2Ni hydrogen storage alloy

In this paper, the long cycling behavior, the kinetic and thermodynamic properties of Ti2Ni alloy used as negative electrode in nickel-metal hydride batteries have been studied by different electrochemical techniques. Several methods, such as, galvanostatic charge and discharge, the constant potential discharge and the potentiodynamic polarization are applied to characterize electrochemically the studied alloy. The studied electrodes are observed before and after electrochemical tests at different temperatures by scanning electron microscopy.The amorphous Ti2Ni is activated after five cycles and the achieved maximum discharge capacity is about 67 mAh g−1 at ambient temperature. Despite the low values of the maximum discharge capacity and the cycling stability (17%) and the steep decrease of the discharge capacity after activation, this alloy conserves a good stability lifetime during a long cycling. A good correlation is observed between the evolution of the discharge capacity and those of the redox parameters during a long cycling.The enthalpy change, the entropy change and the activation energy of the formation reaction of the Ti2Ni metal hydride are evaluated electrochemically. The found values of the enthalpy change, the entropy change and the activation energy are about −43.3 kJ mol−1, 51.7 J K−1 mol−1 and 34.9 kJ mol−1, respectively.

Influence of Gaseous Activation on Hydrogen Sorption Properties of TiNi and Ti2Ni Alloys

Ti-Ni-type alloy powders were prepared through mechanical alloying and annealing at 1382 K for 0.5 h of pure Ti and Ni elements. Samples were activated n-times (n is a number between 0 and 3) in two-stage process. The samples were initially heated for 12 h at 673 K in vacuum to remove impurities. In second step, materials were hydrogenated at a pressure of 3 MPa for 3 h. Phase components, microstructure, particle size, and hydrogen sorption properties of materials were investigated. X-ray diffraction analyses revealed the formation of TiNiH and Ti2NiH2.5 phases after hydrogenation. It was observed that cyclic hydrogenation process increased cell volume, resulting in fracturing of the powders. This effect was beneficial for hydrogen storage capacity due to creation of fresh reaction surfaces. Hydrogen activation of Ti-Ni-type alloys caused significant increase in concentration of absorbed hydrogen and improvement of hydrogen sorption kinetics.

Effect of multi-walled carbon nanotubes and palladium addition on the microstructural and electrochemical properties of the nanocrystalline Ti2Ni alloy

Ti2Ni-based nanocrystalline alloys and their nanocomposites were prepared by mechanical alloying and annealing at 750 °C for 0.5 h under an argon atmosphere. Shaker type ball mill was used. Ti2Ni alloy was chemically modified by Pd and multi-walled carbon nanotubes. The main aim of the study was to investigate the effect of chemical modification on electrochemical properties of Ti2Ni alloy. Structure, microstructure, composition and morphology of materials were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and atomic force microscopy. X-ray diffraction analysis revealed formation of main Ti2Ni phase structure crystallizing in a Fd3¯m space group. Transmission electron microscopy micrographs confirmed stability of tubular structure of MWCNTs after 1 min co-milling. All studied materials were tested as negative electrode for Ni-MHx rechargeable batteries. Electrochemical measurements revealed that materials with Pd have excellent activation properties. Ti2Ni + Pd + MWCNT is a material with the highest discharge capacity equaled 301 mAh/g. This is the highest capacity obtained so far for Ti2Ni-based materials. This capacity is related to lubricant and hydrogen transporting functions of multi-walled carbon nanotubes and anticorrosion and catalytic functions of Pd. Ti2Ni + Pd + MWCNT was also the material with the best cycle stability. Capacity retaining rate after 18th cycle equaled 75%.

Hydrogenation properties of nanostructured Ti2Ni-based alloys and nanocomposites

Mechanical alloying and annealing at 1023 K for 0.5 h under an argon atmosphere were used to prepare Ti2Ni-based nanocrystalline alloys and their nanocomposites. Ti2Ni alloy was chemically modified by Pd and multi-walled carbon nanotubes.An objective of the present study is to provide data on hydrogenation properties of Ti2Ni-based alloys and compounds containing Pd and/or multi-walled carbon nanotubes. Alloys and composites were characterized by X-ray diffraction, scanning electron microscopy equipped with an electron energy dispersive spectrometer, transmission electron microscopy, atomic force microscopy to evaluate phase composition, crystal structure, grain size, particle morphology and distribution of catalyst element. Hydrogenation/dehydrogenation properties and hydriding kinetics of materials were measured using a Sievert's apparatus.Hydrogenation properties of nanostructured Ti2Ni-based alloy and Ti2Ni-based nanocomposites were compared with those of the binary Ti2Ni compound. In present work we shown how mechanical alloying method and chemical modification by Pd and MWCNTs affected hydrogen storage properties of Ti2Ni alloy. The highest hydrogen capacity obtained for nanostructured Ti2Ni + Pd alloy equaled 2.1 wt.%. Up to our knowledge it is the highest hydrogen storage capacity obtained so far for Ti2Ni-based materials.

The Influence of Chemical Modification by Silver on Hydrogen Storage Properties of Nanocrystalline Ti2Ni Alloy

In this study mechanical alloying process with subsequent annealing at 750 ◦C for 0.5 h were used to produce Ti2Ni-based nanocrystalline alloys and composite. To improve electrochemical properties, Ti-Ni-based alloy was chemically modi ed by 5 wt% of silver powder. X-ray di raction analyses showed formation of nanocrystalline Ti2Ni main phase. Electrochemical studies revealed a positive e ect of chemical modi cation by silver on Ti2Ni alloy. All synthesized materials were used as negative electrodes for Ni-MHx batteries. The highest discharge capacity equaled 303 mAh/g, at 40 mA/g discharge current. All electrochemical measurements were done in 6 M KOH solution.

Structure and electrochemical hydrogen storage properties of Ti2Ni alloy synthesized by ball milling

The structure and the electrochemical hydrogen storage properties of amorphous Ti2Ni alloy synthesized by ball milling and used as an anode in nickel–metal hydride batteries were studied. Nominal Ti2Ni was synthesized under argon atmosphere at room temperature using a planetary high-energy ball mill. The structural and morphological characterization of the amorphous Ti2Ni alloy is carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical characterization of the Ti2Ni electrodes is carried out by the galvanostatic charging and discharging, the constant potential discharge, the open circuit potential and the potentiodynamic polarization techniques.The Ti2Ni alloy activation requires only one cycle of charge and discharge, regardless of the temperature.The electrochemical discharge capacity of the Ti2Ni alloy, during the first eight cycles, and at a temperature of 30°C, remained practically unchanged and a good held cycling is observed. By increasing the temperature, the electrochemical discharge capacity loss after eight cycles undergoes an increase and it is more pronounced for the temperature 60°C.At 30°C, the anodic corrosion current density is 1mAcm−2 and then it undergoes a rapid drop, remaining substantially constant (0.06mAcm−2) in the range 40–60°C, before undergoing a slight increase to 70°C (0.3mAcm−2). This variation is in good agreement with the maximum electrochemical discharge capacity values found for the different temperatures.By increasing the temperature, the difference between the OCP curves corresponding to C/10 and C/30 regimes undergoes significant growth, reaching a maximum value (ΔEOCV=10.3mV) at 60°C before undergoing a decrease at 70°C.A good correlation is found between the evolutions of the corrosion current density with the maximum discharge capacity on one hand and on the other hand with the ΔEOCV, according to the temperature. The effect of temperature on the different electrochemical parameters (Icorr, Cmax, ΔEOCV) and the various correlations found between them allows us to optimize the performance of the battery and provide proper operation under the good experimental conditions.

Hydrogen storage characteristics of Ti2Ni alloy synthesized by the electro-deoxidation technique

Ti2Ni alloy was synthesized in the molten CaCl2 electrolyte by the electro-deoxidation method at 900 °C and the electrochemical hydrogen storage characteristics of the synthesized alloy was observed. The X-ray diffraction peaks indicated that stoichiometric oxides in TiO2–ZrO2–NiO mixture reduced to Ti3O5, CaTiO3, CaZrO3, Ni and Ti2O3 within 5 h electro-deoxidation process. Extension of the electro-deoxidation time to 10 h caused formations of TiO and equilibrium Ti2Ni phase. After 24 h electro-deoxidation the target alloy with the equilibrium Ti2Ni phase structure and the maximum amount of the dissolved Zr in it was obtained. It was observed that the synthesized alloy had maximum discharge capacity of 200 mA h g−1. Upon increase in the charge/discharge cycles, however, the discharge capacity decayed sharply. According to the gathered EIS data at various DODs, the rapid degradation in the electrode performance of Ti2Ni alloy was attributed to the developed barrier oxide layer on the electrode surface.

Electrochemical hydrogen storage properties of a non-equilibrium Ti2Ni alloy

A crystalline Ti2Ni alloy was mechanically milled and subsequently annealed to form a non-equilibrium Ti2Ni alloy. This non-equilibrium structure could restrain the formation of irreversible metal hydride during charging. Consequently, we demonstrated that the alloy had a discharge capacity of 336 mAh g−1, which was much higher than those of other Ti2Ni alloys reported in the literature and also higher than that of the commercial LaNi5–based alloy. An electrochemical hydrogen absorption–desorption mechanism of the alloy during cycling is also presented.

Structure and electrochemical hydrogen storage properties of A2B-type Ti–Zr–Ni alloys

Elemental substitution of part Ti by Zr has been carried out for Ti2Ni alloy to form Ti2−xZrxNi (x = 0, 0.2, 0.4) alloys. Mechanical milling and subsequent heat treatment have been used to prepare non-equilibrium Ti–Zr–Ni alloys. The effects of Zr addition on the structure and discharge properties of Ti2Ni alloy were investigated. The addition of Zr could enhance the discharge capacity of the non-equilibrium Ti2Ni alloy at electrolyte temperatures of 313 and 333 K. For instance, the non-equlibrium Ti1.6Zr0.4Ni alloy had a stable discharge capacity of about 210 mAh/g at 313 K. However, the protective surface layer formed during heat treatment was destroyed at a high electrolyte temperature of 333 K, and thus a severe capacity loss during cycling.

Structural evolution and electrochemical hydrogenation behavior of Ti 2Ni alloy

The structure, morphology, and electrochemical hydrogenation behavior of Ti 2Ni alloy, prepared by an induction melting method, have been systematically investigated. The results of X-ray diffraction showed that hydrogen absorption led to a significant inelastic lattice expansion of the alloy. The alloy had a maximum discharge capacity of 235.5 mAh/g at a current density of 60 mA/g and a high rate dischargeability of 73.3% at 300 mA/g. The increase in the electrolyte temperature induced a decrease in discharge capacity, a decay of cycle life, an increase and subsequently a decrease in exchange current density, and an enhancement of hydrogen diffusion. Moreover, the alloy with a smaller particle size showed a higher discharge capacity. The mechanism for the capacity loss of the alloy during charge and discharge cycling was studied. The apparent activation energy for hydrogen diffusion within the bulk alloy was 10.7 kJ/mol.

Ti2Ni alloy: a potential candidate for hydrogen storage in nickel/metal hydride secondary batteries

An amorphous Ti2Ni alloy, prepared by mechanical milling of a crystalline Ti2Ni alloy, was heat-treated at several temperatures. The crystalline behavior of the amorphous alloy was studied , relative to a multi-stage crystallization mode, using X-ray diffraction, differential scanning calorimetry, and electron diffraction. X-Ray photoelectron spectroscopy was performed to analyze the surface structure of the alloys. The alloy that was heat-treated at 693 K, with a non-equilibrium bulk structure and a protective surface layer, has a high discharge capacity and good cycling stability. The issue of severe capacity loss of Ti2Ni-based alloys, which has caused problems for many years, has been significantly improved.

Effect of Mechanical Milling on the Structure and Electrochemical Properties of Ti2Ni Alloy in an Alkaline Battery

Mechanical milling (MM) has been used to treat the crystalline Ti2Ni alloy prepared by solid-state sintering. Changes of the structure, morphology, and electrochemical properties were investigated. The particle size of the alloy decreases first and then increases after the milling. Moreover, MM contributes to a decrease in grain size and the formation and increase of the amorphous phase by increasing the milling time, resulting in improvements of the antipulverization ability and cycle life after the milling. The result of linear polarization indicates that the exchange current density, determined by the competition between the specific surface area and amorphous phase, increases first and then decreases. The amorphous phase is beneficial to hydrogen diffusion according to the result of potential-step measurement. The electrochemical properties of Ti2Ni alloy are significantly improved by the non-equilibrium processing technology.

Effect of the modification of metal-hydride electrodes based on Ti2Ni alloys on their discharge characteristics

We have developed a new computerized PGStat-8 device for the high-cycle charge-discharge of electrodes under galvanostatic or potentiostatic conditions and, with its help, have investigated the charge-discharge characteristics of metal-hydride electrodes based on Ti2Ni-type alloys. We show the effect of partial replacement Ti → Zr or V and Ni → Co or Cu, modification with oxygen, homogenizing annealing, polymeric addition, and metallic binder on the discharge capacity and cyclic stability of the prepared metal-hydride electrodes.