Increasing Niobium Content Research Articles

Microstructural study of additively-manufactured carbon steel-stainless steel 316L - Inconel 625 functionally graded material: Simulation and experimental approaches

This study aims to analyze the microstructure and present phases of functionally graded carbon steel - stainless steel 316L - Inconel 625 using experimental methods and computational software (JMatPro). Both FE-SEM and SEM-EDS equipment were employed to evaluate the materials. The JMatPro software accurately simulated the present phases and their formation temperatures. The microstructure in the plain carbon steel part formed the ferrite phase at 900 °C, while a small amount of pearlite structure formed at 700 °C, remaining stable at ambient temperature. Chromium phase in stainless steel 316 L layers increased with solidification, with a higher increase in the delta ferrite phase. Inconel 625 at 1130 °C, the Laves nucleated with austenite, stable up to ambient temperature. As liquid decreased, niobium and molybdenum accumulation increased, potentially leading to Laves formation. The significant increase in niobium content at the interface of stainless steel 316L-Inconel 625 is attributed to an increase in iron content. The research indicated a good correlation between the observed and predicted microstructures.

Insights on Niobium Micro-Alloyed Laser In Situ Synthesised Gamma Titanium Aluminide Alloys

The effects of micro-alloying gamma titanium aluminide (γ-TiAl) with niobium (Nb) using a laser melt pool as a melting pot are reported. The Optomec LENS machine was used to carry out the laser in situ alloying experiments where Nb, ranging from 6 to 10 (at. %), was added to the stable binary γ-TiAl alloy. The results of this study concluded that when a stable binary γ-TiAl alloy is micro-alloyed with Nb, there is a definite microstructural transformation, anneal twinning, promotion, and retardation of aluminium solubility in the dual and pure γ phases, respectively. Twinning in the as-built in situ alloyed ternary Ti–48Al–xNb was for the first time reported in this study. It was observed that 6 at. % Nb promoted twinning in the as-built sample, which inferred that the sample might have room temperature ductility. In fact, it was shown that the twins formed in the as-built sample dissipated with the addition of Nb. A heat treatment temperature of 1200 °C promoted anneal twinning only in the binary alloy, as confirmed by XRD data. Meanwhile, this twinning was absent in all the ternary alloys when they were heat treated to a temperature of 1200 °C. Anneal twinning was confirmed only for the alloy containing 8 Nb (at. %) at 1400 °C. Stalk faults, dislocations, and dislocation pile-ups were observed in the α2 phase of the alloys. Aluminium solubility was seen to increase in the α2 + γ (±49 at. %) phase alloy and sharply decrease in the pure γ (>49 at. %) phase alloys. Most importantly, this study determined that the laser in situ alloying process was highly exothermic. The heat gained by the reaction was found to increase with the increase in niobium content.

Niobium incorporation into rare-earth doped aluminophosphate glasses: Structural characterization, optical properties, and luminescence

Luminescent Rare Earth (RE3+) doped phosphate glasses with molar composition (1-x)(60P2O5 – 15ZnO – 5Al2O3 – 10BaO – 10PbO)-xNb2O5 (x = 0, 10, 20 and 30 wt%) doped with 1.0, 1.2 and 0.3 wt% of Eu2O3, Yb2O3 and Er2O3, respectively, were prepared by conventional melt cooling. The glasses were characterized by optical reflectance, Raman scattering, and multinuclear (31P, 27Al, and 93Nb) solid-state NMR spectroscopy. Monotonic 31P chemical shift changes as a function of Nb2O5 content are consistent with the successive formation of Nb-O-P linkages. Aluminum is found in four-, five-, and six-coordination, with a successive decrease in average coordination number with increasing niobium content, while 93Nb NMR indicates three distinct niobium environments in these glasses. Incorporation of Nb2O5 has the expected effects on refractive index values, optical basicity, optical electronegativity, Urbach Energy, and the indirect bandgap, while RE3+ emission properties are only slightly modified. Under UV excitation, narrow emission bands are observed arising from 5D0→7FJ (J = 0, 1, 2, 3, and 4) transitions of Eu3+. At least two distinct Eu3+ lifetime values are observed, suggesting a spread of different ionic environments within the glass structure. Co-doping with Er3+/Yb3+ promotes emission in the infrared region, with a emission band maximum near 1535 nm and a width of 30.65 nm under excitation at 980 nm. Based on the results, these glasses may be potential candidates for energy conversion from infrared or UV region to the visible region and also infrared solid-state emitters.

Effect of Microalloying on Microstructure and Mechanical Properties of Laser Weld of PHS Steel

The laser welded joint of 2000MPa cold rolled annealed hot pressed steel (PHS) is easy to break during cold rolling. In this paper, the laser welding method is used to butt weld four kinds of PHS2000 with a thickness of 3.5mm. The four kinds of PHS2000 steel are added with elements of 0% Nb, 0.04% Nb, 0.06% Nb + Cr and 0.08% Nb + Cr. The microstructure of the four kinds of welded joints is compared and analyzed. The mechanical properties of the four kinds of joints are compared through hardness test and tensile test. The results show that after adding 0.04% Nb, residual austenite appears in the weld zone and fully quenched zone, the width of columnar crystal decreases, the average hardness of the weld zone decreases from 595HV to 408HV, and the tensile strength increases from 608MPa to more than 800MPa. For chromium containing steel, the increase of niobium content can reduce the size of columnar crystal in weld zone.

ELECTRONIC STATES DENSITY, RESISTIVITY, AND PHASE COMPOSITION OF CaTiO3 PEROVSKITE WITH ISOMORPHIC IMPURITY OF NIOBIUM

The application of materials with a perovskite structure has currently become one of the most promising approaches for the development of photovoltaic systems. A method for high-speed synthesis (under 15 minutes) of CaTiO3 perovskite — TiO2 rutile with the possibility of concurrent doping of the product has been developed. The density of electronic states, phase composition features, and resistivity of niobium-doped perovskite (CaTiO3) were investigated. The calculations of the density of electronic states for niobium-doped CaTiO3 have shown that at low concentrations of niobium, the samples exhibit conductivity characteristic of semiconductors. Since niobium has one more valence electron compared to titanium, as the niobium content increases, the Fermi level shifts to the band of free states. This shift of the Fermi level should lead to a change in the nature of the conductivity of doped crystals, eventually transitioning to metallic conductivity at high concentrations of niobium. Composite analysis (СаТіО3+ТіО2) by X-ray diffraction has shown that the use of niobium as a doping element significantly accelerates the CaTiO3 synthesis reaction, and increases the perovskite concentration in the sample. The concentration of CaTiO3 in the sample the with niobium is 83 % vol. at a temperature of 900ºC and at a synthesis time of 5 min, whereas when using a mixture without Nb, the content of perovskite will be only 58 % vol. at a synthesis time of 12 min. X-ray phase analysis methods confirm the formation of a solid solution (doping) Ca(Ti,Nb)O3, resulting in the preparation of samples (СаТіО3+ТіО2) with resistivity inherent to semiconductors.

Microstructure, mechanical strength, chemical resistance, and antibacterial behavior of Ti–5Cu–x%Nb biomedical alloy

Titanium-based biomedical alloys are susceptible as they are used as a substitute for human bone. In this study, titanium alloy, Ti–5Cu–x%Nb (x = 0, 5, 10, 15) (%wt) was developed by powder metallurgy route. The effect of alloying niobium with Ti–5Cu alloy and its effect on the microstructure, mechanical strength, corrosion resistance, and antibacterial properties have been evaluated. The results show that the sintered alloy has both α-Ti and Ti2Cu phases. With increasing niobium content in the alloy, β-Ti was also detected. Additionally, it was found that the micro-hardness and compressive strength of the studied alloy was better than commercially pure titanium (cpTi), while the Young’s modulus was lower than cpTi. These properties are highly favorable for using this alloy to replicate the human cortical bone. The alloy was also tested for anticorrosive property in Ringer’s solution. The antibacterial activity was also examined for Staphylococcus aureus and Escherichia coli bacteria. The alloy showed promising anticorrosive and antibacterial ability.

Use of first principles and Thermo-Calc to identify potential low elastic modulus titanium-based alloys for biomedical applications

High alloyed β-phase stabilised titanium alloys are known to have low elastic moduli comparable to that of the human bone (≈30 GPa). The β-phase in titanium alloys exhibits an elastic modulus of about 60-80 GPa, which is nearly half that of α-phase (100-120 GPa). In this work, an attempt to develop a β-phase titanium-based alloy through first-principles calculations and Thermo-Calc calculations for biomedical applications was conducted. First-principles calculations were performed using the CASTEP code on a simple 2-atom bcc unit cell to predict the theoretical elastic modulus and mechanical stability of the Ti-Nb-Ta-Zr (TNTZ) system at 0 K. Thermo-Calc was used to determine the phase proportion diagrams of the proposed alloys at 500℃. The alloy comprised Ti-Nbx-Ta25-Zr5 (x = 5, 10, 20, 30, 40) (at.%). The theoretical results suggested that increasing niobium content introduced both mechanical (cʹ > 0) stability of the alloys. Alloy Ti-Nb5-Ta25-Zr5 gave the lowest elastic modulus of 55.23 ± 24.45 GPa which is half the elastic modulus of pure titanium (α phase). The phase proportion diagrams showed that up to 58.6 mol.% of β phase was retained at 20 at.% Nb, although the Voigt-Reuss-Hill Young’s modulus calculated from first principles increased with increasing niobium content while the α/β phase transformation temperature decreased down to 551.3℃ at 40 at.% Nb.

Laves phase precipitation and sigma phase transformation in a duplex stainless steel microalloyed with niobium.

Duplex stainless steels are used to replace austenitic steels in industrial applications, especially in the chemical industry where corrosion resistance in chloride-containing media is an important requirement. According to literature, niobium has a great influence on the transformation of the phases of these steels (ferrite, austenite and sigma). Given the interest in evaluating this property in terms of wear resistance and corrosion of the material, the aim of this study was to evaluate the effect of niobium on the formation in austenitic-ferritic stainless steel SEW 410 Nr 1.4517 after heat treatment at 850ºC for 15, 30 and 60 minutes. The niobium contents studied were 0.2; 0.5 and 1.5 wt%. Measurements of microhardness, electrochemical tests in saline solution containing 3.5% sodium chloride and wear resistance were carried out. The results show that an increase in niobium content and sigma phase leads to an increase in hardness and wear resistance, associated with a decrease in corrosion potential. Therefore, the use of niobium in austeno-ferritic stainless steel is recommended when wear resistance is an important factor to be considered.

The Precipitation of Niobium Carbide and Its Influence on the Structure of HT250 for Automobile Wheel Hubs

Improving the strength of grey cast iron wheel hubs will improve the safety of automobiles and have a great significance for energy saving and environmental protection. This paper systematically compares the calculation results of Python-based precipitation calculation and JmatPro software simulation with experiments. The results show that with a low mass fraction of niobium (0.098%) cuboid Niobium Carbide (NbC) precipitates do not form in the liquid phase; however, an elongated NbC niobium-rich phase may form during the solidification process and in the solid phase. However, cuboid NbC precipitates can be precipitated from the liquid phase when the niobium mass fraction is higher (0.27%, 0.46%). These results indicate that with the increasing niobium content the amount, particle size, and initial precipitation temperature of niobium carbide precipitated in the matrix structure will increase. According to the observation and statistical analysis of the microstructure, it is found that tensile strength will be improved with an increase in niobium content due to the refinement of the graphite and pearlite interlamellar spacing. In this paper, adding less than 0.32% of Nb to grey cast iron is recommended, considering the comprehensive cost and the effect of niobium in the material structure.

+Effect of niobium on microstructure and properties of 6016 aluminum alloy

6016 aluminum alloys with different niobium contents were prepared by smelting and casting. The alloys were rolled and heat treated, and the effect of niobium on microstructures and properties of the alloys were studied. The results show that the as-cast alloy consists of Mn-rich phases, Cu-rich phases, Mg-rich phases, Si-rich phases and small blocks of Zn-rich phases, and Nb element is solidly dissolved in these phases and matrix. After solution and pre-aging treatment, recrystallization occurs in the rolled alloy. The grain size of the rolled alloy is obviously smaller than that of the as-cast alloy, and the second phase precipitates dispersively. After solution treatment or solution treatment + pre-aging treatment, the tensile strength and plasticity of the alloy are significantly improved. With the increase of niobium content, the number and size of the second phase increase. The alloy with 1%Nb in T4P condition has the better comprehensive mechanical properties, and its elongation after fracture, tensile strength, yield strength, plastic strain ratio and strain hardening index are as following respectively: 34.20%, 372.77MPa, 208.54MPa, 0.82, 0.32.

Quantitative analysis of microstructure and mechanical properties of Nb–V microalloyed high-strength seismic reinforcement with different Nb additions

Abstract HRB500E seismic steel bars are mainly used in high-rise buildings near the seismic zone. The influence of different niobium contents (0–0.023%) on the microstructure and mechanical properties of HRB500E seismic reinforcement was studied. Results showed that the grain size of ferrite was between 3.6 and 8.3 μm when only V was added. Meanwhile, as the niobium content increases, the ferrite particles are further refined. After adding niobium, the grain contribution increased by 9%. The addition of niobium significantly refined the grain size of HRB500E seismic reinforcement. The second-phase nano-elliptic precipitate is NbC. The precipitated phase is dispersed on the grain boundary and the matrix, and the dislocation density on the matrix promotes the precipitation of NbC particles along the dislocation line. The second-phase precipitation of niobium can form an effective pinning effect and then refine the pearlite spacing. The microhardness and the tensile strength also significantly improved. The yield strength increased from 509 to 570 MPa.

Microstructure, Mechanical Properties, and Corrosion Behavior of Ultra-Low Carbon Bainite Steel with Different Niobium Content.

Four types of ultra-low carbon bainite (ULCB) steels were obtained using unified production methods to investigate solely the effect of niobium content on the performance of ULCB steels. Tensile testing, low-temperature impact toughness testing, corrosion weight-loss method, polarization curves, electrochemical impedance spectroscopy (EIS), and the corresponding organizational observations were realized. The results indicate that the microstructure of the four steels comprise granular bainite and quite a few martensite/austenite (M/A) elements. The niobium content affects bainite morphology and the size, quantity, and distribution of M/A elements. The elongation, yield strength, and tensile strength of the four types of ULCB steels are above 20%, 500 MPa, and 650 MPa, respectively. The impact toughness of the four types of ULCB steels at −40 °C is lower than 10 J. Steel with Nb content of 0.0692% has better comprehensive property, and maximum charge transfer resistance in 3.5 wt.% NaCl solution at the initial corrosion stage. The corrosion products on the surface of steel with higher niobium content are much smoother and denser than those steel with lower niobium content after 240 h of corrosion. The degree of corrosion decreases gradually with the increase of niobium content at the later stage of corrosion.

The Effects of Nb Addition on the Oxidation Behavior of Ni–Fe–Cr Alloys at 800 °C

High temperature oxidation of Ni–18Fe–19Cr alloys with different Nb contents (based on the chemical composition of Alloy718) was investigated to elucidate the effect of Nb on oxidation kinetics and scale formation after exposure at 800 °C in air. The experimental results indicated that the oxidation kinetics decreased with increasing niobium content. Rapid establishment of an external Cr2O3 scale was interpreted by the formation of a continuous CrNbO4 layer at the metal-oxide interface, which acts as a diffusion barrier for inward oxygen and outward Fe and Ni diffusion and is of benefit for the establishment of an external Cr2O3 scale. The early establishment of this diffusion barrier prevented internal oxidation of chromium and reduced the growth of the outer Ni2FeO4 oxide scale. The beneficial effect of Nb could be attributed to effectively increasing the volume fraction of internal oxide precipitates, which are favorable for rapid establishment of an external Cr2O3 scale.

Synthesis of Sr1+2xLa1‐2xFe1‐xNbxO4 (x=0, 0.1, 0.3, and 0.5) by Sol‐gel Method: Structural, Magnetic, and Dielectric Properties

AbstractOne – layered Ruddlesden‐Popper phase Sr1+2xLa1‐2xFe1‐xNbxO4 doped with niobium was synthesized using a sol‐gel method for various Nb concentrations (x=0, 0.1, 0.3, and 0.5). Single‐phase samples could be observed with x=0 and 0.1, while x=0.3 and 0.5 contain additional phases. Microstructure results showed that the increase of niobium content corresponded to a decrease in the grain size of the samples. The magnetic measurements indicated that antiferromagnetic interactions of doped samples had decreased. The dielectric constant of the samples decreased as x increased due to the increase in conductivity. The origin of conduction in the samples might be caused by hopping conduction due to the mixed oxidation states of iron with charge +3 and +4.

Effects of niobium (Nb) on mechanical properties of laser coated Nitinol (NiTi) used for surface modification of Ti6A14V alloy

Abstract:Laser surface treatment is widely used as an engineering technique due to its special characteristics and several advantages over other surface modification techniques. In the present study, elemental mechanically pre-alloyed powder consisting of Niobium, Titanium and Nickel was deposited onto a grade 5 Titanium alloy substrates to form a high wear resistance coating. This was such that the surface mechanical properties of the base metal can be improved. The fabricated samples were characterised using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), Differential Scanning Calorimeter (DSC), micro hardness tester and wear machine. The deposited coatings were well bonded and consisted of various phases. Hardness was seen decrease with increase in Nb content while wear resistance increasing with increase in niobium content.

The essential role of niobium in high manganese austenitic steel for application in liquefied natural gas tanks

Five high manganese austenitic steels with different niobium additions were designed, and the essential role of niobium in high manganese austenitic steel has been elucidated by means of electron back-scatter diffraction, transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy. Regardless of niobium content, NbC carbides can be formed during hot rolling in the temperature range of 1100-970 °C, whereas these NbC carbides are at 100-nm scale. Furthermore, the dynamic strain aging can be effectively restrained once the niobium is added. It is found that the niobium addition of 0.05 wt% greatly lowers tensile ductility and deteriorates cryogenic impact toughness, whereas both tensile ductility and cryogenic impact toughness are slightly sacrificed with further increasing niobium content. In addition, it is found that the grain refinement effect of niobium in high manganese austenitic steels is rather weak. Moreover, there is a steep increase in yield strength only when the niobium content reaches 0.29 wt%, and the sharp increase in yield strength is due to the formation of heterogeneous microstructure consisting of recrystallized or strong recovered grains and dislocation tangled or lath structured grains, indicating that the essential role of niobium in high manganese austenitic steels is that it suppresses recovery and recrystallization, and its solid-solution strengthening, grain refinement, and precipitation hardening effects are relatively weak.

Impact of Nb(V) Substitution on the Structure and Optical and Photoelectrochemical Properties of the Cu5(Ta1- xNb x)11O30 Solid Solution.

A family of solid solutions, Cu5(Ta1- xNb x)11O30 (0 ≤ x ≤ 0.4), was investigated as p-type semiconductors for their band gaps and energies and for their activity for the reduction of water to molecular hydrogen. Compositions from 0 to 40 mol % niobium were prepared in high purity by solid-state methods, accompanied by only very small increases in the lattice parameters of ∼0.05% and with the niobium and tantalum cations disordered over the same atomic sites. However, an increasing niobium content causes a significant decrease in the bandgap size from ∼2.58 to ∼2.05 eV owing to the decreasing conduction band energies. Linear-sweep voltammetry showed an increase in cathodic photocurrents with niobium content and applied negative potential of up to -0.6 mA/cm2 (pH ∼7.3; AM 1.5 G light filter with an irradiation intensity of ∼100 mW/cm2). The cathodic photocurrents could be partially stabilized by heating the polycrystalline films in air at 550 °C for 1 h to produce surface nanoislands of CuO or using protecting layers of aluminum-doped zinc oxide and titania. Aqueous suspensions of the Cu5(Ta1- xNb x)11O30 powders were also found to be active for hydrogen production under visible-light irradiation in a 20% aqueous methanol solution with the highest apparent quantum yields for the 10% and 20% Nb-substituted samples. Electronic structure calculations show that the increased photocurrents and hydroen evolution activities of the solid solutions arise near the percolation threshold of the niobate/tantalate framework wherein the Nb cations establish an extended -O-Nb-O-Nb-O- diffusion pathway for the minority carriers. The latter also reveals a novel pathway for enhancing charge separation as a function of the niobium-oxide connectivity. Thus, these results illustrate the advantages of using solid solutions to achieve the smaller bandgap sizes and band energies that are needed for solar-driven photocatalytic reactions.

Relationship between Structure, Phase Composition, and Physicomechanical Properties of Quenched Ti–Nb Alloys

Transmission electron microscopy, X-ray diffraction analysis, and microindentation were used to study the changes in the structure, phase composition, elastic modulus, and hardness of the Ti–(9.6–34) at % Nb alloys after quenching in water from heating temperatures corresponding to the β region. The relationship between the physicomechanical properties (elastic modulus, microhardness) and the volume fraction of metastable phases detected in Ti–Nb alloys after quenching from the β region has been shown. It has been noted that the Ti–13.3 at % Nb alloy with a structure in which the ω phase with anomalous morphology in the form of massive plates is formed after quenching is characterized by maximum values of elastic modulus and microdurometric characteristics. The growth of the elastic modulus of the metastable β solid solution with increasing niobium content in alloys with a decrease in the average distance between the niobium–niobium atoms in the bcc structure has been justified. The possibility for calculating the elastic modulus of quenched Ti–Nb alloys based on the additive contributions of the elastic moduli of phases detected after quenching, which are proportional to their volume fractions has been considered.

Synthesis and ion exchange properties of zirconogermanates

AbstractPure and Nb-doped zirconium germanate materials of composition K2-xZr1-xNbxGe3O9.H2O where x = 0, 0.1, 0.2 and 0.25 with the structure of the mineral umbite have been successfully synthesised. The parent material displays negligible ion exchange of K+ for Cs+ but the doped materials shows much improved exchange. Synchrotron X-ray diffraction shows substantial peak splitting which varies with increasing niobium content. Preliminary Rietveld refinements suggest a two phase model with a caesium and potassium rich doped umbite phase.

Effect of Nb addition on microstructure and corrosion resistance of novel stainless steels fabricated by direct laser metal deposition

The study demonstrated the successful fabrication of novel stainless steels by direct laser metal deposition with the aim of investigating the impact of niobium content (Nb = 0, 0.25, 0.75, 1.25 wt%) on their microstructure and electrochemical properties. The microstructure and phase evolution of the as-built stainless steels were studied using scanning electron microscope (SEM) and electron back-scatter diffraction (EBSD). Corrosion behavior of the samples was evaluated using electrochemical workstation in 3.5 wt% NaCl. Experimental results have shown that the crystal structure of as-built stainless steels was BCC with a small trace of dispersive carbides and FCC phase. Grain refinement was observed with increasing niobium content. Large-angle boundaries were obtained in different Nb-containing samples with distribution from 50° to 60°. An increase in niobium content extremely improved the corrosion resistance of as-built stainless steels and the as-built samples with 1.25 wt% exhibited the best corrosion resistance among the tested samples as indicated by its lowest corrosion rate, which was an order of magnitude lower than that of Nb-free samples.