NiTi Intermetallic Compound Research Articles

Mechanical and electrochemical properties of porous NiTi intermetallics synthesized via rapid thermal explosion

In this paper, porous NiTi intermetallic was synthesized via a modified thermal explosion (TE) method, utilizing Ni (74 μm, 38 μm, 5 μm, 100–200 nm) and Al element powders as raw material. The exothermic behavior and phase transition of porous NiTi intermetallic compounds were studied. The results showed that with the refinement of Ni particle size, the heat release decreased, and the Ti-74 μm sample was the product of two eutectic reactions. Their mechanical properties were verified by the Vickers hardness tester and universal testing machine, and the corrosion behavior of porous NiTi intermetallic compounds in phosphate-buffered saline (PBS) solution was studied by electrochemical tests. Among them, Ti-5 μm exhibits the most homogeneous microstructure and favorable mechanical properties, which has a porosity of 31.7 % and a compressive strength of 321.71 MPa. However, corrosion resistance is sacrificed due to the high open porosity. This study holds great promise for precise control microstructural characteristics and optimization of mechanical and electrochemical properties of porous NiTi intermetallics.

Structural, mechanical, and thermodynamic properties of Ni–Ti intermetallic compounds: First-principle calculation

Intermetallic compounds were applied widely in the fields of automotive and aerospace because of its excellent shape memory effect. In this work, the structural, mechanical, and thermodynamic properties of Ni–Ti intermetallic compounds are studied by first-principle calculation. The results show that Ti, NiTi3, NiTi2, NiTi, Ni4Ti3, Ni3Ti, Ni4Ti, and Ni are stable based on Born stable criterion. On the mechanical aspect, the bulk modulus of Ni–Ti intermetallic compounds increases with the rising electron density. Their ductility is ranked as follows: NiTi3 > Ni4Ti3 > NiTi2 > Ni4Ti > NiTi > Ni3Ti. And when the ratio of Ni and Ti is 3:1, it is the hardest. In addition, the Ni–Ti intermetallic compounds in this work are anisotropy, except NiTi2. On the thermodynamic aspect, the Debye temperature θD, melting point Tm, and minimum thermal conductivity kmin of Ni–Ti intermetallic compounds increase first and then decrease with the rising content of Ni. The θD and kmin of NiTi3 are the minimum among the Ni–Ti ICs mentioned above, and θD of Ni3Ti and kmin of NiTi are both the maximum. The melting point of Ni3Ti is 1940 K, it is the highest temperature.

Preparation of porous TiNi intermetallic compound and the corrosion behavior in NaCl solution

Porous TiNi intermetallic compounds have a promising future as biomaterials, with some challenges for their corrosion resistance. In this work, TiNi intermetallic compound was prepared by reactive synthesis of elemental powders. The evolution of the microstructure and phase composition of TiNi at different temperatures was studied. And the electrochemical corrosion behavior of TiNi intermetallic compound in NaCl solution was investigated by electrochemical tests. The results show the formation of a core-shell structure during the sintering process, where Ni is the core and Ti2Ni, TiNi and TiNi3 are the shells. With uniform diffusion, a large pore replaces the Ni core due to the Kirkendall effect. TiNi intermetallic compound has a well-developed open pore structure with an open pore ratio of 50.98%. TiNi intermetallic compound exhibits better corrosion resistance compared to Ni and Ti, which can be attributed to the generation of passivation film on the surface.

Preparation of Porous Tini Intermetallic Compound and the Corrosion Behavior in Nacl Solution

Preparation of Porous Tini Intermetallic Compound and the Corrosion Behavior in Nacl Solution

Preparation of Porous Tini Intermetallic Compound and the Corrosion Behavior in Nacl Solution

Preparation of Porous Tini Intermetallic Compound and the Corrosion Behavior in Nacl Solution

Molten Salt Synthesis of Intermetallic Compound TiNi Nanopowder Passivated by TiOx Shell Prepared from NiTiO3 for Catalytic Hydrogenation.

Titanium-nickel alloy is an attractive material due to its unique properties of shape memory effect, superior elasticity, and biocompatibility. Generally, Ti-Ni alloy powders are prepared from pure elemental powders of Ti and Ni as starting materials, but it is an energy-intensive process to obtain pure titanium. In this study, intermetallic compound TiNi powder passivated by TiOx shell was prepared by directly reducing a commercial NiTiO3 using CaH2 reducing agent in a molten LiCl at 650 °C. Analyses by X-ray diffraction, scanning electron microscopy/transmission electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the powder had a core-shell structure, with the core of TiNi and the shell of TiOx-rich composition with scarce metallic Ni nicely catalyzing hydrogenation reactions with good recyclability and stability.

Microwave versus Conventional Sintering of NiTi Alloys Processed by Mechanical Alloying.

The present study shows a comparison between two sintering processes, microwave and conventional sintering, for the manufacture of NiTi porous specimens starting from powder mixtures of nickel and titanium hydrogenation–dehydrogenation (HDH) milled by mechanical alloying for a short time (25 min). The samples were sintered at 850 °C for 15 min and 120 min, respectively. Both samples exhibited porosity, and the pore size results are within the range of the human bone. The NiTi intermetallic compound (B2, R-phase, and B19′) was detected in both sintered samples through X-ray diffraction (XRD) and electron backscattering diffraction (EBSD) on scanning electron microscopic (SEM). Two-step phase transformation occurred in both sintering processes with cooling and heating, the latter occurring with an overlap of the peaks, according to the differential scanning calorimetry (DSC) results. From scanning electron microscopy/electron backscatter diffraction, the R-phase and B2/B19′ were detected in microwave and conventional sintering, respectively. The instrumented ultramicrohardness results show the highest elastic work values for the conventionally sintered sample. It was observed throughout this investigation that using mechanical alloying (MA) powders enabled, in both sintering processes, good results, such as intermetallic formation and densification in the range for biomedical applications.

Enhancing the phase stability of TiNi intermetallic compound via nanocrystallization in an irradiated multicomponent vanadium alloy

Intermetallic compounds often have a low radiation tolerance due to the low recombination rate of radiation-induced defects. In the present work, we designed a novel multicomponent vanadium-based alloy (MVA), V34Ti25Cr10Ni30Pd1, containing a micron-scale TiNi matrix phase with VCr nanoprecipitates (NPs) and a micron-scale VCr matrix phase with TiNi NPs. The MVA was irradiated with 6 MeV Ti3+ ions with a radiation dose of 5×1015ions/cm2 at room temperature. Results indicated that the micron-scale intermetallic TiNi matrix along with VCr NPs inside both became amorphous, while the micron-scale VCr matrix including numerous intermetallic TiNi NPs both exhibited a high structural stability after ion irradiation. The intermetallic TiNi matrix becomes amorphous due to the accumulation of radiation-induced defects, and the intermetallic TiNi NPs in VCr matrix have a high stability of crystallographic structure due to high-density interfaces between NPs and matrix. These results indicate that the phase stability of TiNi intermetallic compound is increased after nanocrystallization. Besides, the discrepancy of two matrix phases including precipitates after ion irradiation, and the underlying mechanisms are discussed in detail in this work. This work gives a guidance for designing new vanadium alloys and intermetallic compounds with enhanced structural stability under ion irradiation.

Synthesis and microstructure, properties characterization of Ni-Ti-Cu/Cu-Al functionally graded coating on Mg-Li alloy by laser cladding

The bottleneck challenge of preparing laser cladded coating on Mg-Li alloys is the evaporation and dilution of substrate, which seriously affect the performance of coatings. In order to solve these deficiencies, Ni-Ti-Cu/Cu-Al functionally graded coating was proposed in this work. The graded coating with excellent performance was successfully prepared on Mg-Li alloy. More remarkable, the top-layer was not affected by dilution and substrate evaporation. The top-layer was mainly composed of Ni3Ti and NiTi intermetallic compounds, as well as TiNi0.8Cu0.2 phase that dispersed on the surface of Ni3Ti. Typical hypoeutectic structure was found in the interlayer, which was composed of Li3Mg7 and CuMg2. Furthermore, the corrosion and wear resistance of Mg-Li alloy were greatly improved. Specifically, the wear volume of the top-layer and interlayer is reduced by 98.04% and 82.41% than that of substrate, respectively. The corrosion potential of the top-layer (-242 mV) and the interlayer (-991 mV) are 1311 mV and 562 mV higher than that of the substrate (-1553 mV), while the corrosion current density of the top-layer (2.71 × 10-7 A·cm−2) and the interlayer (1.93 × 10-6 A·cm−2) are about three and two orders of magnitude lower than that of the substrate (2.53 × 10-4 A·cm−2).

Dissolution and isothermal solidification behaviour of commercially pure titanium brazed using a pure nickel filler under TLPB conditions

Transient liquid phase bonding of Ti using elemental Ni foils represents a potential low-cost manufacturing route to join aerospace components. To fully develop this technique, the dissolution behaviour and kinetics of isothermal solidification in Ti/Ni joints were determined in this study. During heating, Ti-Ni intermetallic compounds form at the solid/liquid interface, which slows down the dissolution of the Ni foil, while promoting diffusion of Ni into the Ti base metal. These two features limit the amount of liquid gap widening that occurs during initial heating such that it only reaches 55% of the theoretical maximum. Once at the braze temperature of 1050 °C, the rate of isothermal solidification becomes constant with the square root of braze time. The IS rate in the Ti-Ni joints was twice as high as that reported for Ti-Cu joints. Comparison of experimental IS rates with model predictions indicated excellent agreement and demonstrated that the difference in IS rate in Ti-Ni compared to Ti-Cu was largely due to a higher rate of diffusion of Ni in Ti compared to Cu in Ti. The actual time required to achieve isothermal solidification depended both on the amount of dissolution/gap widening and on the rate of IS.

Коэффициент Пуассона TiNi

A review of the literature data and methods for calculating the Poisson coefficient of the TiNi intermetallic compound in the poly- and single-crystal state is performed. The results of our own research are also presented. Significant variability of the presented data is noted, due to differences in the thermomechanical processing of the alloys and the measurement and calculation methods used. By averaging the matrices of elastic constants and compliance coefficients using the Voigt, Reuss, and Hill approximations, we obtained the values of the parameters of the effective elastic properties of TiNi polycrystals and calculated the Poisson’s ratio. Using analytical expressions to calculate the values of the extreme values, the extrema of the Poisson’s ratio of cubic TiNi crystals are determined for standard orientations. Based on a number of data, TiNi crystals are auxetics (materials having negative Poisson’s ratio values), on the basis of others they are not. We found that TiNi crystals belong to the so-called partial auxetics, in this case the signs of the inequalities (s12 < 0, s = s11 + s12 − s44/2 > 0 or s12 > 0, s = s11 + s12 − s44/2 < 0) are opposite. The values of the Poisson’s ratio TiNi averaged over the transverse directions of deformation are analyzed. Isosurfaces of the Poisson’s ratio and their sections are presented using the ELATE computational graphic package and the MATHCAD computer algebra program. Aspects of TiNi elastic anisotropy, its parameters, and their relationship with martensitic transformations in TiNi and alloys based on it are discussed.

Rapid Growth of TiNi intermetallic compound within undercooled Ti50Ni50 alloy under electrostatic levitation condition

The undercooling dependence of the solidification mechanism was systematically explored by the electrostatic levitation (ESL) facility. During the experiments, the maximum undercooling reached up to 406 K (0.26 TL) and the growth velocity of the primary TiNi phase was in-situ determined at various undercoolings. At the initial increase of alloy undercooling, the value of growth velocity sluggishly rose followed by a power function. In this case, the primary TiNi phase preferentially developed as the equiaxed dendrite, then the remnant liquid participated as Ti2Ni and α-Ti phases on the grain boundary. Once the undercooling exceeded the critical value of 350 K, the growth velocity of the primary phase displayed a sharply increase tendency. Meanwhile, the TEM results demonstrated that the precipitation of the intermetallic Ti2Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.

Microstructure and wear resistance of a Ni-WC composite coating on titanium grade 2 obtained by electroplating and electron beam remelting

To improve the hardness and wear resistance of titanium grade 2 (TA2), Ni-WC pre-coating by electroplating was prepared on the surface of TA2 substrate in advance, and then electron beam remelting was conducted. The microstructure of the coating was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM results showed that the coating was strongly attached to the TA2 substrate that and the Ti-Ni intermetallic compounds were evenly distributed with in the coating. Moreover, TEM results showed that WC did not undergo chemical decomposition during the remelting process and did not participate in the reaction of the Ti-Ni system. After electron beam remelting, the hardness significantly increased: the maximum Vickers hardness of the coating was 745 HV0.1, which was near 6 times higher than that of the TA2 substrate (approximately 130 HV0.1). A ball-on-disk wear test was carried out with the TA2 substrate and the coatings. The wear rates of the TA2 substrate and the coating were 7.034 × 10−4 and 2.596 × 10−5 mm3N−1 m−1, respectively. Thus, compared with the TA2 substrate, the coating notably improved the wear resistance.

Influence of welding parameters on microstructure and mechanical properties of electron beam welded Ti60 to GH3128 joint with a Cu interlayer

Effects of welding parameters on the microstructure and mechanical properties of Ti/Cu/Ni joint welded by electron beam were investigated. High welding heat input increased the melting quantity of Ti60 titanium alloy and promoted the formation of Ti–Cu intermetallic compounds (IMC) such as Ti2Cu and Ti3Cu4, increasing the brittleness of the joints. Low welding heat input was not conducive to the complete melting of the copper interlayer, and the unmelted copper reduced the performance of the joints. Under the optimal welding parameters, Ti–Ni IMCs in the weld would be replaced by (Cu, Ni) solid solutions ((Cu, Ni)ss). However, Ti–Cu IMC layers cannot be eliminated entirely by changing the welding parameters. The maximum tensile strength of the joints was 201 MPa. The fracture of the joints occurred at the Ti–Cu IMC layer, which was a typical brittle fracture.

Dissimilar jointing of TA15 to Inconel718 by laser additive manufacturing using Nb/Cu bilayer

High quality jointing of TA15 titanium alloy and Inconel718 (IN718) nickel based superalloy has a widespread application prospect in the aerospace industry. In the present work, we adopted a laser additive manufacturing (LAM) technique to joint dissimilar materials of TA15 and IN718, and to restrain the formation of Ti-Ni intermetallic compounds and macroscopic cracking via Nb/Cu bilayer. Research results showed that the presence of Nb/Cu bilayer was very helpful to impede the formation of brittle Ti-Ni phases and macroscopic cracking between TA15 and IN718. Microstructure results indicated that high quality metallurgical bonds were formed at the interfaces of adjacent materials. Micro-hardness results presented that the Nb/Cu bilayer was able to obtain a good plastic transition from TA15 to IN718. The tensile strength of the jointing with the Nb/Cu bilayer was 434 MPa, indicating the bonding strength exceeded that of the Nb interlayer.

First-principles investigation on ideal strength of B2 NiAl and NiTi alloys**Project supported by the Science Challenge Project, China (Grant No. TZ2018002) and the Fundamental Research Funds for the Central Universities, China (Grant No. FRF-TP-18-013A3).

For B2 NiAl and NiTi intermetallic compounds, the ideal stress–strain image is lack from the perspective of elastic constants. We use first-principles calculation to investigate the ideal strength and elastic behavior under the tensile and shear loads. The relation between the ideal strength and elastic constants is found. The uniaxial tension of NiAl and NiTi along crystal direction leads to the change from tetragonal path to orthogonal path, which is driven by the vanishing of the shear constant C66. The shear failure under {110} shear deformation occurring in process of tension may result in a small ideal tensile strength (∼2 GPa) for NiTi. The unlikeness in the ideal strength of NiAl and NiTi alloys is discussed based on the charge density difference.

Microstructural and mechanical properties of inconel 600/ZrB2-SiC joints brazed with AgCu/Cu-foam/AgCu/Ti multi-layered composite filler

A set of AgCu/Cu-foam/AgCu/Ti multi-layered composite fillers was designed and employed to braze the Inconel 600 alloy and ZrB2-SiC ceramic. Microstructures, formation mechanism and shear strengths of the joints were investigated in detail with and without the addition of Ti foil. The shear strengths of the brazed joints were improved substantially with the presence of Ti foils. A maximum gain of 150 % was reached from 77 MPa to 198 MPa after introducing the Ti foil and brazing the joint at a 1173 K for 15 min. The mechanical property enhancement is attributed to a newly formed TiC phase, release of residual stress, and barrier effect of Cu foam to inhibit formation of Ti-Ni intermetallic compounds.

Synthesis of NiTi alloy powders for powder-based additive manufacturing

Spherical powders of NiTi intermetallic compound were obtained from elemental powders by mechanical alloying at various modes followed by plasma spheroidization. The obtained powders were analyzed in terms of its chemical composition, sizes, morphology and microstructure. The plasma spheroidized NiTi powder was found to contain from 5.5% to 8.7% of the Ti2Ni phase in the form of a dendritic structure. It was also found that an increase in the mechanical alloying time leads to a more uniform distribution of elements in the powder, however, it significantly increases the iron impurity originating from the grinding of steel balls. Furthermore, granulometric composition of the synthesized powders was observed to depend on the size of the initial particles before spheroidization.

Joints of TiBw/Ti6Al4V composites- Inconel 718 alloys dissimilar joining using Nb and Cu interlayers

Dissimilar joining of TiBw/Ti6Al4V composites to Inconel 718 superalloys were explored using interlayers of Nb and Cu. It was difficult to gain good joints by using Nb interlayer. High thermal conductivity of Nb and particular assembly mode made more heat concentrated between Nb interlayer and Inconel 718 base metal, thus the connection between Nb and TiBw/Ti6Al4V composite was poor. While joints with good appearance and excellent mechanical properties could be obtained with Cu interlayer, and Ti-Cu, Ti-Ni-Cu and Ti-Ni intermetallic compounds could be found. The shear strength of the joints would be greatly improved in joints with Cu interlayer of 0.2 mm, because retained Cu-based solid solution in the joints could relieve the residual stress to a certain extent, and the maximum shear strength was 616 MPa (90 A, 100 mm/min, 0.2 mm). The formation of joints mainly depended on the formation of intermetallic compounds and solid solutions during welding. In addition, TiB whisker (TiBw) in TiBw/Ti6Al4V composites played a role in promoting the formation of intermetallic compounds in the joint reaction layer.

Effect of Synthesis Mode and Ni Particle Size on Microstructural Aspects and Hardness Properties of Combustion-Synthesized NiTi

NiTi intermetallic compound was fabricated via two modes of the combustion synthesis process, namely, thermal explosion (TE) and self-propagating synthesis (SHS). The effect of combustion synthesis mode as well as Ni particle size on the microstructure and microhardness of the final products was investigated. The phases in the products were determined using XRD technique, and microstructural investigations were performed using optical as well as SEM-EDS in order to make a comparison between microstructural evolutions in each mode, other conditions being constant. The analyses showed that the desired B2(NiTi) was successfully formed as the primary phase in all samples, and no unreacted Ni or Ti powders were present. The main secondary phase was NiTi2 which was invariably present in all samples; however, the percentage as well as the morphology of the detrimental NiTi2 phase was found out to be controllable by the mode of combustion as well as Ni particle size. A comparison between the two modes revealed that samples produced by TE showed coarse dendrites in the microstructure; they also presented higher average microhardness values. The SHS-synthesized samples exhibited microstructures similar to those observed in heat-treated and homogenized NiTi obtained from methods such as vacuum arc remelting and vacuum induction melting, and contained finely dispersed NiTi2 particles. It was shown that a decrease in Ni particle size presented a grain refining effect on NiTi2 in both modes.