Increasing Nb Content Research Articles

Effects of Nb Addition on Microstructures and Mechanical Properties of Nbx-CoCrFeMnNi High Entropy Alloy Films

In the present work, Nbx-CoCrFeMnNi high entropy alloy films (HEAFs, 0 to 7.2 at.% Nb) were fabricated by radio frequency (RF) magnetron co-sputtering of CoCrFeMnNi alloy and Nb targets. The effects of Nb addition on the microstructures and mechanical properties of HEAFs were systematically investigated. For Nb-free film (0 at.% Nb), the face-centered cubic (FCC) peaks were identified in the X-ray diffraction (XRD) pattern. The addition of Nb resulted in a broadening of diffraction peaks, a decrease in peak intensity, and the vanishment of high-angle peaks. Transmission electron microscope (TEM) images indicated the formation of nanotwins at low Nb concentrations, and a transition from a single phase FCC solid solution to an amorphous phase was observed with the increasing Nb concentration. The films were strengthened with an increase in Nb concentration. Specifically, the hardness characterized by nanoindentation increased from 6.5 to 8.1 GPa. The compressive yield strength and fracture strength measured from micropillar compression tests were improved from 1.08 GPs and 2.56 GPa to 2.70 GPa and 5.76 GPa, respectively, whereas the fracture strain decreased from >29.4% (no fracture) to 15.8%. Additionally, shear banding was observed in the presence of amorphous phase.

Effect of Niobium on Ti–Sn Alloy for Implant Applications

Titanium (Ti) based alloys (e.g., Ti6Al4V) are extensively utilized in the field orthopedic and dental implant applications due to their enhanced bio-mechanical properties. Nevertheless, their resistance to corrosion requirements needs to be enhanced. Furthermore, existence of vanadium (V) and almunium (Al) elements causes cancer and alzymer respectively. Therefore, in this research Ti-Sn-Nb alloy was produced through the powder metallurgy (PM) route. Tin (Sn) and niobium (Nb) is chosen as an alloying element which replaces toxic Al and V elements. The effect Nb on the Ti–Sn–Nb alloy was studied. Three set of variations of Nb namely 5%, 7.5% & 10% were used for the improvement of properties of parent alloy. The particle dimensions of the parent alloy were analyzed through a laser particle analyzer (LPA). Morphology was studied through Scanning Electron Microscopy (SEM) and phases were determined through X-Ray Diffraction (XRD). Vicker (450SVA) tester was utilized to examine the effect on rigidity after the addition of Nb. The hardness of the alloy was decreasing and corrosion rate was increasing with an increase in Nb content. Furthermore, niobium addition enhances the ability of appetite formation when immersed in the Stimulated body fluid (SBF).

A moving-boundary dynamic model for in-situ alloyed and additive manufacturing TiAl-Nb alloys

Controlling the dissolution of the solid metal contact liquid metal or alloys is significantly important for some industrial processes, in particular for high temperature and long-time processes. A model for quantitatively evaluating the relationship between the dissolution thickness of Nb crucible and the increase of Nb concentration caused by dissolution is established based on the mass balance law, which supports in-situ alloyed and additive manufacturing process of TiAl-based alloys.

Microstructure and anti-corrosion performance of laser cladded Nb-modified Ni-based alloy coatings

In this work, Ni-based alloy coatings incorporated with Nb mass fractions of 0%, 3%, 6%, and 9% were successfully fabricated by laser cladding. The morphology, chemical composition, and phases of the obtained Nb-modified Ni-based coatings were characterized, and the effects of Nb contents on their electrochemical performance and immersion rates in 3.5 wt% NaCl solution were analyzed. The results show that the Ni-based coating with low Nb exhibits the most compact and refined microstructure, the best electrochemical passivation, and the lowest immersion corrosion rate of 3.30 × 10−3 mm/year. However, with increasing Nb content, the Laves phase is accumulated, and dendritic growth is promoted, which significantly decreases the coating passive stability and worsens the anti-corrosion performance.

Microstructure and electrical properties of Nb‐doped SrTiO3‐BiFeO3 based lead‐free ceramics

AbstractIn this work, Nb‐doped 0.75SrTiO3‐0.25BiFeO3 (ST‐BF) lead‐free ceramics are designed and synthesized using a conventional solid‐state reaction method. The influence of Nb doping on the microstructure, dielectric, and electrical properties are systematically investigated. With the increase of Nb concentration, the crystal structure of ST‐BF remains pseudo‐cubic as exhibited in the X‐ray diffraction patterns. The grain size is found to increase from 0.33 to 6.23 μm, and then decrease to 1.88 μm by Nb doping, along with a clear heterogeneous core–shell microstructure. A relatively low dielectric loss (∼0.1, at 1 kHz) and a stable dielectric constant (∼700, at 1 kHz) are obtained for the 0.03 Nb‐doped ST‐BF composition at room temperature. Impedance spectroscopy analysis shows that Nb doping in ST‐BF increases the total resistivity, forming an electrically conductive core and a nonconductive shell, with enhanced activation energy. The results may provide a feasible approach to develop novel ST‐based lead‐free dielectric ceramics for capacitor applications.

Influence of Nb on the Structure and High Temperature Performance of Billet for High-Rise Structural Steel

Reasonable control of the niobium (Nb) content in steel slabs is of great significance for improving the surface quality of the slabs. In this study, a Gleeble-3500 thermal simulation testing machine was used to test the high-temperature mechanical properties of steel slabs with four different Nb contents (A: 0.006%, B: 0.031%, C: 0.050%, D: 0.065%) and to analyze the effect of Nb on the high-temperature performance of the steel slabs. Optical microscopy and transmission electron microscopy (TEM) were used to study the microstructure of the casting slabs with different Nb contents and the precipitation in the samples after heat treatment at different temperatures. The results of the study show that the microstructure of the cast slab is mainly composed of ferrite and pearlite. The distribution of each of the two structures was found to become more uniform and a significant improvement in yield strength was observed with increasing Nb content. After heat treatment, the precipitates in the high-rise structural steel were mainly square and star shaped Nb(C,N) precipitates. Increasing the Nb content was found to increase the amount of precipitates in steel. Beyond a threshold, increasing the Nb content did not increase the amount of precipitates. However, the size of the precipitates increased.

Microstructures and mechanical properties of Ti–Al–V–Nb alloys with cluster formula manufactured by laser additive manufacturing

Ti–Al–V–Nb alloys with the cluster formula, 12[Al–Ti12](AlTi2)+5[Al–Ti14](V,Nb)2Ti, were designed by replacing V with Nb based on the Ti–6Al–4V alloy. Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.% were prepared by laser additive manufacturing to examine their formability, microstructure, and mechanical properties. For single-track cladding layers, the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability. The alloy, Ti–5.96Al–1.94V– 3.54Nb (wt.%), exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder. The microstructures of the bulk samples contained similar columnar β-phase grains, regardless of Nb content. These grains grew epitaxially from the Ti substrate along the deposition direction, with basket-weave α-phase laths within the columnar grains. The α-phase size increased with increasing Nb contents, but its uniformity decreased. Along the deposition direction, the Vickers hardness increased from the substrate to the surface. The Ti–5.96Al–1.94V–3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between the α-phase size and its content among the designed alloys.

High Temperature Dry Tribological Behavior of Nb-Microalloyed Bearing Steel 100Cr6.

100Cr6 steel is one of the most widely used bearing steels and a representative of first-generation bearing steel. Many engineering applications require rolling bearings to run at a high temperature. Therefore, it is necessary to improve the high temperature properties of 100Cr6 steel. In this paper, the effect of Nb on high temperature dry tribological behavior, including worn surface and friction coefficient, was analyzed by a wear test when Nb content was 0.018% and 0.040%. The results show that the microstructure is refined gradually, the hardness is improved, and wear volume decreases by 31.8% at most with the increase of Nb content. At 50 °C, the friction coefficient of 100Cr6 steel can be reduced by adding a small amount of Nb, but this effect will be weakened if the content of Nb is too high. In addition, excess Nb increases the hard precipitation of NbC, which aggravates the abrasive wear and leads to the increase in the depth of the worn surface. At 125 °C, the effect of Nb on tribological properties is weaker. With the increase of temperature, the steel substrate softens, and the oxide particles increase, which aggravates the abrasive wear and oxidation wear and makes the wear volume increase significantly.

Electronic Mechanism of Martensitic Transformation in Nb-doped NiTi Alloys: A First-Principles Investigation.

The effect of Nb on the crystal structures and electronic mechanism of martensitic transformation in Ni50Ti50–xNbx alloys is investigated by first principles. The lattice parameters, the formation energy, the middle eigenvalue of the transformation stretch tensor (λ2), and the energy difference between the parent and martensite (ΔE) as a function of Nb content x (x = 0, 2.08, 6.25, 8.33, 10.42, 12.5, 18.75) are calculated. Lattice parameters increase with the increase of Nb content. The formation energies of the parent B2 phase, martensite orthorhombic B19, and monoclinic B19′ increase with the increase of Nb content. It is also found that at ≤10.42 at. % Nb, the martensite stable phase is monoclinic structure B19′; at >10.42 at. % Nb, the orthorhombic crystal structure B19 is formed. The energy difference between the parent and martensite means that the transformation temperature decreases with increasing Nb concentration at Nb ≤ 10.42 at. % and increases at >10.42 at. % Nb. The λ2 of the NiTiNb alloys have the same value of about 0.95 with low Nb content. Furthermore, the electronic structure mechanisms behind the martensitic transformations are discussed in detail based on the density of states.

Lattice instability of B-site substituted SrTiO3 crystals studied by terahertz time-domain spectroscopic ellipsometry

The B-site substituted quantum paraelectric strontium titanate, SrTiO3 (STO), crystals with the perovskite structure were studied regarding their dielectric properties in the terahertz frequency range. When Ti4+ ions at the B-site are substituted by heterovalent Nb5+ ions, free electrons are introduced and the conductivity increases. The complex dielectric constants were accurately determined by the terahertz time-domain spectroscopic ellipsometry. The dielectric spectra were analyzed by the damped harmonic oscillator model for a ferroelectric soft mode and the Drude-Smith model for free electrons. The soft mode frequency and the plasma frequency increased with the increasing Nb content. The square of the plasma frequency is proportional to the concentration of free electrons. It was found that the change in the ferroelectric soft mode frequency is approximately proportional to the concentration of free electrons. This fact suggests that the increase in the free electrons by donor-doping suppresses the ferroelectric instability.

Cracking mechanism and a novel strategy to eliminate cracks in TiAl alloy additively manufactured by selective laser melting

Additive manufacturing of TiAl alloys by selective laser melting (SLM) remains a challenge due to serious cracking during the print process. In this work, the cracking mechanism of the SLM-fabricated Ti-48Al-2Cr-2Nb alloy is studied. Experimental results show that the cracks mainly occurred in the Nb-poor regions and near the interfaces between α2 and B2 phases. A novel strategy to eliminate cracks is thus proposed: eliminating the Nb-poor regions and reducing the interface between different phases. It is found that by increasing Nb content, a nearly α2 single-phase structure without heterogeneous interface formed along with the elimination of Nb-poor regions in the SLM-fabricated Ti–48Al–2Cr–8Nb alloy. The as-SLMed alloy is crack-free and of high strength, verifying the effectiveness of the proposed strategy.

Effect of Nb on microstructure and mechanical properties of Ti-xNb-4Zr–8Sn alloys

Ti-xNb-4Zr–8Sn (x = 16, 20, 24, 28, 36 wt%) alloys were fabricated using vacuum arc furnace melting with subsequent hot rolling and solution treatment. Tensile tests were conducted to evaluate the mechanical properties of the Ti-xNb-4Zr–8Sn alloys. The microstructural and phase composition were examined using scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDX), X-ray diffraction (XRD), and transmission electron microscope (TEM). The results show that the Nb content strongly affects the microstructure and the mechanical properties of the Ti-xNb-4Zr–8Sn alloys. With the increase of Nb content, more β phase occurs in the alloy due to the stabilizing effect of Nb, and the alloys evolve from α''+β (Nb: 16, 20, 24 wt%) duplex-phase structure to a single β (Nb: 28, 36 wt%) phase structure. The Young's modulus decreases first with the increase of Nb and then increases when the Nb content increases over 24 wt%. The Ti–24Nb–4Zr–8Sn alloy shows the minimum Young's modules of 45 GPa. The tensile strength (UTS) of the alloys decreases with the increase of Nb content. The effect of Nb content on the microstructure and the mechanical properties of the quaternary alloys are elucidated, and the affecting mechanism is discussed in this study.

Oxygen addition in biomedical Ti–Nb alloys with low Nb contents: Effect on the microstructure and mechanical properties

Ti–Nb alloys have been widely researched for biomedical applications because of their excellent mechanical properties, corrosion resistance, and superior biocompatibility. In this investigation, the influence of oxygen content on the microstructure and mechanical properties of Ti–Nb alloys with relatively low Nb contents was evaluated. Arc-melted Ti–Nb–O ingots (Nb contents were 15, 17.5, 20, and 22.5 wt% and O contents were 0.15, 0.25, and 0.40 wt%) were hot-rolled and solution-treated at 1200 °C for 1 h, followed by furnace cooling. These samples were characterized by scanning electron microscopy, differential scanning calorimetry, compression tests, and measuring hardness and Young's modulus. The furnace-cooled alloys exhibited typical α + β microstructures, in which the thickness of the α plates decreased with increasing Nb content and increased slightly with increasing oxygen content. A similar behavior was observed for the apparent β-transus, which decreased with increasing Nb content, and increased with increasing oxygen content. The obtained hardness and 0.2% compressive yield stress improved with increasing concentrations of alloying elements. This was due to the solid-solution strengthening promoted by Nb and oxygen, and microstructural refinement induced by Nb addition. The Young's modulus was found to increase very slowly with increasing oxygen content. Owing to the enhancement in yield stress and the small change in elastic modulus with increasing oxygen content, alloys can be designed and produced with high mechanical strength/Young's modulus ratios, favoring their application as biomaterials.

The in-situ β phase reinforced Ti/Zr-based bulk metallic glass matrix composite by selective laser melting

In this study, in-situ β phase reinforced Ti/Zr-based BMGCs without toxic element Be, (Ti0.65Zr0.35-yNby)100-xCux (x = 5, 10, y = 0.05, 0.1, at. %), were prepared via selective laser melting (SLM). The effect of Cu and Nb contents on phase formation, microstructure, and compressive mechanical properties were studied, and the microcrack formation mechanism in the deposits with lower Cu content (5 at. %) was also investigated. With the increase of Cu content from 5 to 10 at. %, the volume fraction of β phase decreased, while the volume fraction of amorphous phase and (Ti, Zr)2Cu phase increased. Meanwhile, the amorphous phase presented a more continuous network-shaped morphology. Compared with the content of Cu element, the variation of Nb content had a minor effect on the phase precipitation and microstructure evolution. With the increase of Nb content, β phase became more stable, which may cause the increase of compression fracture strain. In addition, the microstructure with a good connectivity of β phase in the center zone of the molten pool had a higher deformation capacity than that in the edge zone of molten pool, where β phase was isolated by the amorphous phase network. There are some solidification microcracks existing in Cu5Nb4.75 and Cu5Nb9.5 deposits. Because of a higher |dT/d(fS1/2)| near fS1/2 = 1, the liquid phase cannot feed the liquid channel between β phases in time, liquid film is ruptured, and solidification crack forms.

Effects of Nb and Mo content on mechanical properties of Ti-Nb-Mo-Ta alloys by two-step pressure-free and hot isostatic pressing sintering

The Ti-(15-30) Nb-(2-11) Mo-3.5Ta (wt.%) alloys with the composition interval of 5.0 wt.% for Nb and 3.0 wt.% for Mo were prepared by a two-step sintering method from blended elemental powders. After pressure-free sintering and hot isostatic pressing, fully dense Ti-Nb-Mo-Ta alloys with favourable compressive properties were obtained, rendering the alloys suitable to be used as structural or biomedical materials. The phase constituent, microstructure, and compressive properties were investigated for these Ti-Nb-Mo-Ta alloys. With the increasing Nb or Mo content, the volume fraction of the α phase and the grain size of the β phase decreased. The yield strength of the Ti-Nb-Mo-Ta alloys first declined and then increased with the increase of Nb or Mo content. As for the strain at failure, it increased monotonously for the Ti-xNb-8Mo- 3.5Ta alloys with the addition of Nb, and it first increased and then decreased for the Ti-25Nb-yMo-3.5Ta alloys with the addition of Mo. After analysing and comparing the variation trend of volume fraction of α phase, grain size, yield strength and strain at failure, the dominant strengthening mechanisms of the Ti-xNb-yMo-3.5Ta alloys were interpreted. The dominating mechanism was second-phase strengthening for the alloys with lower alloying elements content, and it changed to solid solution strengthening with the increase of alloying elements content.

Structural, morphological, and optical studies of hydrothermally synthesized Nb-added TiO2 for DSSC application

Herein, titanium dioxide (TiO2) nanoparticles doped with various concentrations (0–7 wt %) of niobium (Nb) are hydrothermally synthesized and used effectively as a photoelectrode for application in dye-sensitized solar cells (DSSCs). The rutile-to-anatase phase transition, accompanied by a change in crystallite size from 23.75 to 9.77 nm, is confirmed via X-ray diffraction (XRD) and Fourier transform (FT)-Raman spectroscopy. In addition, the prepared Nb–TiO2 nanoparticles exhibit a spherical morphology with a mean grain diameter of 43.38–50.69 nm. Further, X-ray photoelectron spectroscopy (XPS) indicates a shift in the Fermi level of the TiO2 towards the conduction band minimum, and an increase in the bandgap from 2.69 to 2.88 eV, with increasing Nb concentration. The resulting increases in the short-circuit current density (JSC) and open circuit voltage (VOC) with the increased injection and conductivity of electrons lead to the enhancement of the DSSC performance. EIS measurements represents the effect of Nb doping on charge transporting and recombination behavior of DSSCs. Moreover, the Nb–TiO2-based DSSCs provide a better power conversion performance as compared to that of the pristine TiO2.

Effect of niobium content on irradiation microstructure and hardening in FeCrAl-based alloys

• The evolution of dislocation loop with niobium content in FeCrAl alloys was discussed. • The formation of laves phase resulted in the decrease of Mo content and the increase of Cr content in the matrix of the FeCrAl alloys. • Nb addition increased nanoindentation hardness and reduced irradiation hardening in the FeCrAl alloys . Iron-chromium-aluminum (FeCrAl) alloys with different content of niobium (Nb)—0, 0.4 wt%, 0.8 wt%, and 1.2 wt%—were designed and prepared. All samples were then irradiated with 2.4 MeV Fe 2+ ion to the dose of 1 and 15 displacements per atom (dpa) at 400 °C. The formations of dislocation loops induced by self-ion irradiation in these alloys were investigated by transmission electron microscopy (TEM). Nano-indentation tests were used to assess the hardness and irradiation hardening of samples. For the samples before irradiation, the (Fe, Cr) 2 (Nb, Mo) Laves phases density and the nano-indentation hardness increased with increasing Nb content of the samples. After irradiation to 1 and 15 dpa, both of a /2<111> and a <100> dislocation loops were produced but no voids or αˊ phase were found in all samples. With increasing Nb content of the samples, the size of dislocation loops increased first and then decreased, while the total volume number density decreased and then increased. The fraction of a <100> dislocation loops increased first and then decreased with increasing Nb content, and increased with increasing irradiation dose. Dislocation networks and the amorphization of the Laves phases were observed in the samples with irradiation dose of 15 dpa. Irradiation hardening of Nb free samples was two to four times that of Nb containing samples, and the irradiation hardening increased with increasing Nb content of Nb containing samples. The experimental results indicate that the increase of Nb content in FeCrAl alloys can increase the density of Laves phases, leading to the decrease of Mo content and increase of Cr content in the matrix. The competition between the two types of solutes affects the nucleation and growth of the dislocation loops.

Effect of Nb contents on microstructure characteristics and yielding behavior of Fe–4Mn–2Al-0.2C steel

The microstructure characteristics and yielding behavior of two Fe–4Mn–2Al-0.2C steels with different Nb contents, i.e. 0.02 wt% and 0.1 wt%, were investigated in the present study. The results show that the increase of Nb content will bring about 50–100 MPa more fine-grain strengthening effect. But on the other hand, Nb promotes the precipitation of cementite and delays recrystallization, so that the stability of austenite decreases and presents a single lathy morphology. The partial martensitic transformation of austenite in the cooling process promotes the diffusion of carbon from martensite to retained austenite, and causes the segregation of carbon at the austenite phase boundaries, leading to the Lüders effect. The steel with 0.02 wt% Nb undergoes a more persistent TRIP effect during the deformation process due to two austenite morphologies with higher volume fractions and exhibits excellent comprehensive mechanical properties with the yield strength of 570 MPa, ultimate tensile strength of 1011 MPa, total elongation of 35.6% and product of strength and elongation of 36 GPa·% after intercritical annealing at 725 °C for 30 min without the appearance of Lüders effect. Thus, this paper is of great importance to the effect of Nb contents on microstructure and yielding behavior of medium Mn steels.

Effect of Ti and Nb Contents on Microstructure and Mechanical Properties of HfZrVTaMoWTixNby Refractory High‐Entropy Alloys

Refractory high‐entropy alloys (RHEAs) with excellent high‐temperature performance are attractive for high‐temperature structural applications. However, many RHEAs suffer from high density and poor room temperature (RT) malleability. Herein, the effects of Ti and Nb contents on the phase equilibrium and mechanical properties of HfZrVTaMoWTixNby RHEAs are studied to achieve unique balanced properties in a wide temperature range. With the increase of Ti or Nb content, the Laves phase precipitation is suppressed and RT malleability is improved. Particularly, the HfZrVTaMoWTi2Nb2 RHEA without Laves precipitates exhibits a high yield strength of 1.7 GPa and a compressive strain of ∼30% at RT. Moreover, it retains a high systemic yield strength of 31 MPa cm3 g−1 at 1200 °C, which is nearly three times that of HfZrTaTiNb and nearly equal to that of MoWTaNb, suggesting its potential applicability at elevated temperatures.

Influence of Nb2O5 doping to energy-storage properties of (Na0.5Bi0.5)0.705Ba0.045Sr0.25TiO3 lead-free ferroelectric ceramics

The powder samples of (Na0.5Bi0.5)0.705Ba0.045Sr0.25TiO3-xNb2O5 (NBBSNT) were synthesized by a wet solid-phase method. The effects of Nb-doping on morphology, ferroelectric and dielectric properties of samples were investigated. Typical surface morphologies by scanning electron microscopy for the NBTBZN ceramics showed grain size decreasing. Dielectric measurements revealed that the depolarization temperature and Curie temperature shifted to lower temperature. With the increase of Nb content, the ferroelectric hysteresis loops became much slimmer, coupled with the reduction in remnant polarization and coercive field. Energy storage density of 0.855 J/cm3 and the energy storage efficiency of 74.26% were obtained for NBBSNT with x = 0.09.