Increasing Nb Content Research Articles

Microstructural and Mechanical Properties of β-Type Ti–Nb–Sn Biomedical Alloys with Low Elastic Modulus

The microstructural and mechanical properties of β-type Ti85-xNb10+xSn5 (x = 0, 3, 6, 10 at.%) alloys with low elastic modulus were investigated. The experimental results show that the Ti85Nb10Sn5 and Ti75Nb20Sn5 alloys are composed of simple α and β phases, respectively; the Ti82Nb13Sn5 and Ti79Nb16Sn5 alloys are composed of β and α″ phases. The content of martensite phase decreases with the increase of Nb content. The Ti82Nb13Sn5 and Ti79Nb16Sn5 alloys show an inverse martensitic phase transition during heating. The Ti85Nb10Sn5 and Ti82Nb13Sn5 alloys with the small residual strain exhibit the good superelastic properties in 10-time cyclic loading. The reduced elastic modulus (Er) of the Ti75Nb20Sn5 alloy (61 GPa) measured by using the nanoindentation technique is 2–6 times of that of human bone (10–30 GPa), and is smaller than that of commercial Ti-6Al-4V biomedical alloy (120 GPa). The Ti75Nb20Sn5 alloy can be considered as a novel biomedical alloy. The wear resistance (H/Er) and anti-wear capability (H3/Er2) values of the four alloys are higher than those of the CP–Ti alloy (0.0238), which indicates that the present alloys have good wear resistance and anti-wear capability.

A Novel Series of Refractory High-Entropy Alloys Ti2ZrHf0.5VNbx with High Specific Yield Strength and Good Ductility

A series of Ti2ZrHf0.5VNbx (x = 0, 0.25, 0.5, 0.75 and 1.0) refractory high-entropy alloys were prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties. All the alloys displayed a simple BCC structure. The microstructures of the alloys changed from the initial single-phase columnar structure (x = 0) to dendrite microstructure (x > 0). At room temperature, all the alloys exhibited high ductility (with the compressive strains of more than 50%). With the increase in Nb content, the yield strength slightly decreased from 1160 to 980 MPa and the hardness dropped from 338 to 310 HV. Moreover, the alloys exhibited low density from 6.47 to 6.84 g/cm3 and high specific yield strength (SYS) from 143 to 179 kPa m3/kg. The comprehensive performance of ductility and SYS was superior to most of the reported high-entropy alloys. The yield strength of the alloys increased from 405 to 859 MPa and from 85 to 195 MPa with the addition of Nb element at 873 K and 1073 K, respectively.

One dimensional (1-D) signatures of nanopillars and nanowires in niobium doped zinc oxide (NZO) thin films prepared by aerosol assisted chemical vapour deposition (AACVD)

Abstract We report for the first time a facile synthesis of niobium (Nb) doped (1-D) ZnO nanopillars and nanowires by aerosol assisted chemical vapour deposition with improved structural and optical properties. The micro structural, vibrational and optical properties of Nb-doped ZnO were investigated by X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM)/Energy dispersive spectroscopy (EDS) and UV–Vis spectroscopy (UV/VIS). The results presented show that Nb doping and solvent choice can effectively control the growth of ZnO nanostructures as well as their reproducibility. The XRD results revealed that the highest estimated crystallite size of Nb doped ZnO was found to be 4.7 nm from depositions conducted in methanol and 5.4 nm from depositions conducted in toluene for 0.2 M% Nb doping. It is further explored that with an increase of Nb content, ZnO films show poor crystallinity with preferential orientation along the 0 0 2 plane. The change in morphology and local structure of ZnO also led to variations in the vibrational properties of the materials. Upon Nb doping, the A1 (LO) mode of ZnO was found to red shift and broaden, whereas a blue shift was found for the 2A1 (LO), 2E1 (LO) and 2LO vibrational modes. The UV–Visible spectroscopy of Nb doped ZnO revealed that excellent visible transmittance (∼89%) was achievable and witnessed an increase in band gap from 3.3 eV to 3.5 eV with increased Nb doping.

(Invited) Electronic Properties of ABO4 Photo-Catalysts Under Nb-Substitution and Phase/Pressure-Related Distortions

Both SbTaO4 and SbNbO4 in the orthorhombic α-Sb2O4 phase have demonstrated pure water splitting as photo-catalysts. Previous experimental studies have shown a significant difference in reported bandgap values for SbTaO4 such as 3.71 eV and 2.28 eV. We have studied SbTa1-xNbxO4 (x = 0, 0.25, 0.5, 0.75, 1) in the tetragonal, orthorhombic, and monoclinic phases. The resulting Sb3+ M 5+O-2 4 material can be classified as a ns2 md0 ternary metal oxide. We have studied the effects of structural symmetry related distortions on the band gaps and overall energetics of SbMO4 compounds (M = Ta, Nb). Evolution of the electronic structures was studied as one transitions from a system of 4d bands to 5d bands, and whether this has any effect on the Sb oxidation state or its lone pair s electrons. From the atomic point of view, electronic correlation energy is higher in Ta 5d than in Nb 4d, and Nb 4d band is higher in energy than Ta 5d. These were examined in terms of oxidation states in their respective solids. We look at the effects of increasing Nb concentration on the electronic structure of SbTa1-xNbxO4 alloy with emphasis on polyhedral and overall cell distortions. We decouple the effects caused by the presence of different nd cations from those caused by distortions and reorientation of various polyhedra. BiVO4 Belongs to the same group of materials; we will also present the electronic structure changes caused by Nb incorporation in BiVO4 and the application of external pressure. Through the analyses of the chemical-potential landscape, we have determined the single-phase stability zone of BiVO4 with the Nb doping. Application of external pressure improved the single-phase stability zone. We have also focused on the local structural distortions near the Nb doping site, especially on the BiO8 octahedra. We have shown here that pressure-induced symmetrization of BiO8 dodecahedron could lower the electron’s effective mass and therefore can help to improve the photo-conduction property of BiVO4. This work is supported by NSF-award # 1609811. We also acknowledge the computational time from Texas Advanced Computing Center (TACC).

Investigation of the in vitro corrosion behavior and biocompatibility of niobium (Nb)-reinforced hydroxyapatite (HA) coating on CoCr alloy for medical implants

Abstract

Numerical investigation on photoelectric properties of Nb,N Co-doped TiO2

The unit cell structure, defect formation energy and photoelectric properties of intrinsic TiO2 and different (Nb, N) co-doped molar ratios are studied by using the first principle. Firstly, the crystal structure and defect formation energy of intrinsic TiO2 and each doped system are calculated and analyzed. It is found that as the Nb doped amount increases, the unit cell volume and formation energy also increase, but it is easier to form defects in an oxygen-rich environment. Then, the electronic structure, state of density and photoelectric properties of intrinsic TiO2 and each doped system were calculated and analyzed. It was found that Nb caused the Fermi level to enter the conduction band in the (Nb, N) co-doped TiO2, the increase of Nb content makes it form an N-type semiconductor with higher electron concentration, and N has the effect of significantly reducing the forbidden band width and increasing the light absorption coefficient.

Influence of Nb concentration on the structure, stability, and electronic and mechanical properties of D022 Al3Ti by first-principles calculations and experiments

The crystal structure, stability, and electronic and mechanical properties of D022 Al3Ti-Al3Nb pseudobinary solid solution were systematically investigated by a first-principles method and experiment. The calculated formation energies demonstrated that all the Al3(Ti1-xNbx) (0 ≤ x ≤ 1) solid solutions considered are thermodynamically stable and that the stability decreases monotonously with increasing Nb concentration. Lattice parameter a of Al3(Ti1-xNbx) exhibits strong negative deviation from a linear composition dependence, while the trend is reversed for lattice parameter c. Study of the mechanical properties (including the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and Debye temperature) reveals that Nb atom substitution in Al3Ti enhances the mechanical stability and strength. The analysis of calculated electronic structures reveals that the metallic behavior of Al3(Ti1-xNbx) depends on the Nb concentration. Experimentally, Al3(Ti1-xNbx) was synthesized and was characterized by means of X-ray diffraction and scanning electron microscopy. Rietveld refinement results confirmed that the lattice parameters are in the range of our previous calculated values. The differences between the calculated and experimental lattice parameters are also discussed in detail.

Effect of niobium addition in FeCoNiCuNbx high-entropy alloys

Abstract

Magnetoresistance and thermoelectric transport in EuTi1-xNbxO3

We report the impact of Nb substitution in EuTi1-xNbxO3 (x = 0, 0.01, 0.03, 0.06 and 0.1) on the magnetization, resistivity, magnetoresistance (MR), thermopower (S) and thermal conductivity (κ) over a wide temperature range (T = 390–2.5 K). Partial replacement of Ti by Nb weakens the antiferromagnetic coupling between Eu-4f spins, drastically reduces low-temperature resistivity and induces insulator-metal transition above the Neel temperature. MR is negative and decreases from 20% for x = 0.01–0.5% for x = 0.1 at 2.5 K but the sign of MR changes to positive at higher temperatures for x = 0.06 and 0.1. The negative MR is suggested due to spin-dependent scattering of Ti-3d conduction electrons by localized Eu-4f spins and we fitted the experimental data to a theoretical model. The negative sign of S asserts electron doping. The values of S and κ systematically decrease with increasing Nb content. κ(T) is analyzed using the Debye-Callaway model.

Effects of Nb on Superelasticity and Low Modulus Properties of Metastable β-Type Ti-Nb-Ta-Zr Biomedical Alloys

In this work, a series of Ti-xNb-2Ta-3Zr (x = 25, 30, 35, 40 wt.%) alloys are designed, and the transformation of β-phase to α″ martensitic, β-phase stability, microstructure, mechanical properties and corrosion performance of these alloys are investigated. The phase analysis shows as the Nb content increases, the α″ phase in these alloys decreases, while the intensity of the two main peaks β(110) and β(211) of Ti-40Nb-2Ta-3Zr alloy is reduced. These results can be attributed to the variation of β-phase stability caused by Nb element of alloy and cold rolling process. The mechanical properties test shows that the elastic modulus (52 GPa) of the Ti-35Nb-2Ta-3Zr alloy is the lowest and the elongation (18.8%) is the maximum. In addition, the alloy is susceptible to β-phase elastic deformation and stress-induced martensitic transformation resulting in the highest recovery strain of the alloy (66.87%). The polarization curves show that the Ti-35Nb-2Ta-3Zr alloy has the highest corrosion potential (− 0.34 V) and the lowest corrosion current density (0.21 μA cm−2) exhibiting the best corrosion resistance.

Microstructure, phase composition and mechanical properties of new, low cost Ti-Mn-Nb alloys for biomedical applications

A group of new Ti-7Mn-xNb alloys with Nb contents varying from 0 to 10 wt% were fabricated by conventional press and sinter powder metallurgy processing from blended elemental powders. The effect of Nb content on the sintering and phase stability as well as microstructure and mechanical characteristics of the alloys was investigated. Microstructural studies and phase analysis showed a two-phase microstructure composed of α and β phases in all alloys. However, addition of Nb up to 10 wt% enhanced the stability of the β phase hindering the transformation to α during furnace cooling and increasing the proportion of retained β. Sintering and densification of the Ti-7Mn-xNb alloys was enhanced by the fast diffusing Mn and negatively impacted by the slow diffusing Nb due to the reliance of solid sintering processes on diffusion. Nonetheless, the relative densities of the Ti-7Mn-xNb alloys with up to 10 wt% Nb were higher than that of the sintered CP-Ti. The compressive strength and hardness of the alloys varied in the range of (1842–2127 MPa) and (341–375 Hv) respectively. It was also observed that with increasing Nb contents, the elastic modulus decreased, while compressive strain increased due to stabilisation of a greater proportion of the β phase. The results showed that the low-cost Ti-7Mn-xNb alloys possess superior properties to those of CP-Ti and a number of other Ti based alloys developed for biomedical implant applications.

Effect of niobium doping on the dielectric and nonlinear current–voltage characteristics of [formula omitted] ceramics

The effect of Nb5+ on the crystallographic structure, electrical properties and the dielectric behaviour of Na0.5La0.5Cu3Ti(4−x)NbxO12 ceramics prepared via the solid-state reaction method were investigated. Rietveld refinement of the powder diffraction data confirmed a cubic, single phase structure with space group Im3. A low frequency Debye-type relaxation is observed for the Nb-doped samples in addition to the usually observed high frequency relaxation. The grain boundary resistance decreased significantly with increasing Nb5+ dopant. The reduced grain boundary resistivity was found to be responsible for the decrease in the potential barrier at the grain boundary as observed from the overall variation of current density-electric field (J–E) characteristics. The dielectric constant at low Frequency is increased with increasing Nb content. The dielectric behaviour of the compound is explained on the basis of the Internal Barrier Layer Capacitance (IBLC) model.

An application of differential injection to fabricate functionally graded Ti-Nb alloys using DED-CLAD® process

The aim of this paper is twofold: firstly, to compare the microstructural and the mechanical properties of Ti-44Nb samples manufactured pre-alloyed powder and differential injection, and secondly, to demonstrate the feasibility of the differential injection method included in the DED-CLAD® process, to manufacture functionally graded Ti-Nb alloys. Functionally graded materials (FGM) are promising new materials which are perfectly adapted to custom-made parts with various properties for specific applications. In FGMs, titanium and niobium ratios were modified in different steps to create the variation in alloy composition owing to a double-powder feeder. Mechanical analysis and SEM observations show the variation along the deposition depending on the chemical composition. Chemical analysis revealed the homogeneous repartition of the powder mixture as well as the nominal composition of each deposition. Mechanical tests showed a decrease of the microhardness with the increase of Nb content. The elastic modulus was found to be the lowest for Ti-40Nb.

Effect of alloying elements on the precipitation of δ phase in Ni-Nb-Cr-Mo alloys

Effect of alloying elements on precipitation of δ phase in Ni-Nb-Cr-Mo alloys has been studied using thermodynamic method. It is found that an increase of Al/Ti ratio or (Al+Ti) content will inhibit the precipitation of δ phase obviously. When the Al/Ti ratio (exceed 1) or (Al+Ti) content increases, Nb content in δ phase increases, while the Mo content decreases. The mole fraction of δ phase increases obviously with increase of Nb content, however, it is nearly not affected by B content. Artificial neural network (ANN) method is tentatively applied to predict the multielement additions on mechanical properties in these alloys. A suitable composition of Al, Ti and B is suggested which obviously promotes stress-rupture life. The theoretical simulation results are finally verified through experiments.

Synthesis and Characterization of AlCoCrFeNiNbx High-Entropy Alloy Coatings by Laser Cladding

AlCoCrFeNiNbx (x in molar ratio x = 0, 0.25, 0.5, 0.75, and 1.0) high-entropy alloy (HEA) coatings were manufactured on 304 stainless steel by laser cladding. The constituent phases, microstructures, chemical composition, micro-hardness and wear resistance of the HEA coatings were investigated respectively by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), a Vickers hardness tester and a friction/wear testing machine. It was found that an AlCoCrFeNi alloy coating without Nb consisted of body-centered-cubic (BCC) and order BCC (B2) phases, while the AlCoCrFeNiNbx (x > 0) alloy coatings consisted of BCC, B2 and Laves phases. Microstructures of the AlCoCrFeNiNbx alloy coatings evolved from equiaxed grain (x = 0) to hypoeutectic (0.25 ≤ x < 0.75), then to full eutectic (x = 0.75), and finally to hypereutectic (x > 0.75). With increasing Nb content, the Vickers hardness values increased. AlCoCrFeNiNb0.75 alloy coating with a fully eutectic microstructure demonstrated the best wear resistance among the AlCoCrFeNiNbx (x ≥ 0) alloy coatings.

CoCrFeMnNi high-entropy alloys reinforced with Laves phase by adding Nb and Ti elements

Abstract

Effect of Nb-doping on the structural and electrical properties of Ba0.97La0.02Ti1-xNb4x/5O3 ceramics at room temperature synthesized by molten-salt method

We, herein, report on the structural and electrical properties of Ba0,97La0.02Ti1-xNb4x/5O3 ceramics prepared by the molten-salt method. The XRD patterns of the samples at room temperature showed a single perovskite phase having a tetragonal structure with a P4/mmm space group. The electrical properties were studied by complex impedance spectroscopy in the frequency range (1–107Hz) at room temperature. The real and imaginary parts of impedance decreased with increasing Nb concentration. The complex impedance plot exhibited a single impedance semicircle for each compound, identified over the high and medium frequencies followed by a linear section, at low frequency, is explained by Warburg's element. The study of the normalization curves of impedance and electrical modulus showed a mismatch of both peaks, which suggests the presence of short-range motion of charge carriers. The electrical conductivity decreased with increasing niobium amount and the experimental data were fitted using Jonscher's universal power law. The exponent n is slightly superior to 1, indicating that the hopping occurs between neighboring sites.

Electronic Properties of SbTa1-xNbxO4: Phase-Related Distortions

We have studied the effects of structural symmetry related distortions on the band gaps and overall energetics of SbMO4 compounds (M = Ta, Nb). Evolution of the electronic structures was studied as one transitions gradually from a system of 4d bands to 5d bands, and whether this has any effect on the Sb oxidation state or its lone pair s electrons. From the atomic point of view, electronic correlation energy is higher in Ta 5d than in Nb 4d, and Nb 4d bands are higher in energy than Ta 5d. These were examined in terms of oxidation states in their respective solids and mixed alloys. We look at the effects of increasing Nb concentration on the electronic structures of SbTa1-xNbxO4 alloys with emphasis on polyhedral interactions and overall cell distortions. We decouple the effects caused by the presence of different nd cations from those caused by distortions and reorientation of various polyhedra.

Hydrodeoxygenation of phenol over Ni/Ce1-xNbxO2 catalysts

This work investigated the effect of different niobium concentration on the performance of Ni/Ce1-xNbxO2 catalyst for hydrodeoxygenation of phenol in gas phase at 300 °C. Also, the structural modification promoted by Nb addition was studied by several techniques. In situ X-ray diffraction and Raman analyses indicated that high niobium concentration lead to Nb2O5 oxide with hexagonal structure, while in situ X-ray photoelectron spectroscopy (XPS) experiments indicated an enrichment of the surface with Nb. In general, the incorporation of niobium changed the lattice parameter of ceria and promoted the formation of oxygen vacancies as observed by XPS and X-ray absorption near edge structure (XANES) analyses, which favored the activity of the sample. Increasing Nb content increased the selectivity to deoxygenated products (benzene). The superior benzene selectivity is likely due to the higher interaction between the oxygen of phenol molecule and the oxophilic sites represented by the Nb5+ cations of the support that promotes the hydrogenation of carbonyl group.

Nanotubes from the Misfit Compound Alloy LaS-NbxTa(1–x)S2

Misfit layered compounds (MLC) with the composition (LaS)1.15TaS2 (for simplicity denoted as LaS-TaS2) and LaS-NbS2 were prepared and studied in the past. Nanotubes of LaS-TaS2 could be easily synthesized, while tubular structure of the LaS-NbS2 were found to be rather rare in the product. To understand this riddle, quaternary alloys of LaS-NbxTa(1–x)S2 with ascending Nb concentration were prepared herein in the form of nanotubes (and platelets). Not surprisingly, the concentration of these quaternary nanotubes shrank (and the relative density of platelets increased) with increasing Nb content in the precursor. The structure and chemical composition of such nanotubes was elucidated by electron microscopy. Conceivably, the TaS2 in the MLC compounds LnS-TaS2 (Ln = lanthanide atom) crystallizes in the 2H polytype. High resolution transmission electron microscopy showed however that, invariably, MLC nanotubes prepared from 80 at% Nb content in the precursor belonged to the 1T polytype. Raman spectroscopy of i...