Niobium Research Articles

Influence of alloying element Nb on the γ′ phase structure and mechanical properties of Co–8.8Al–9.8W alloy

Influence of alloying element Nb on the γ′ phase structure and mechanical properties of Co–8.8Al–9.8W alloy

Influence of β-Stabilizing Nb on Phase Stability and Phase Transformation in Ti-Zr Shape Memory Alloys: From the Viewpoint of the First-Principles Calculation

In the present study, the effect of the Nb element on the lattice parameters, phase stability and martensitic transformation behaviors of Ti-Zr-based shape memory alloys was extensively investigated using the first-principles calculation. The lattice parameters of both the β parent phase and α′ martensite phase gradually decreased with Nb content increasing. For the α″ martensite phase, the lattice constant (a) gradually increased with the increase in Nb content, whereas the lattice constants (b and c) continuously decreased due to the addition of Nb. Based on the formation energy and density of state, β→α′ martensitic transformation occurred, as the Nb content was not more than 12.5 at.%. However, the Ti-Zr-Nb shape memory alloys with a Nb content higher than 12.5 at.% possessed the β→α″ martensitic transformation. However, both the largest transformation strain and sensitivity of critical stress to temperature (dσ/dT) can be optimized by controlling 12.5 at.% Nb in the Ti-Zr-Nb shape memory alloy, which was favorable to obtaining the largest elastocaloric effect.

High-entropy strategy to suppress volumetric strain and enhance diffusion rate of Na3V2(PO4)2F3 cathode for durable and high-areal-capacity zinc-ion battery pouch cells

Aqueous zinc-ion batteries are pivotal contributors to the global energy transformation. Cathode materials with NASICON-type structures are promising candidates for zinc-ion batteries but are hindered by their low electrical conductivity, sluggish ionic diffusion, and structural instability. This work introduces a high-entropy, carbon-coated NASICON-type Na3V2(PO4)2F3 (HE-NVPF@C) cathode by incorporating five metal elements (Al, Zn, Mn, Cr, and Nb) mainly into the V sites of the VO4F2 octahedral structure. Systematic experimental and simulation studies of the Zn2+ storage mechanism in high-entropy NASICON-type cathode are presented for the first time. The high-entropy doping strategy contributes to significantly enhanced cycling stability by suppressing Jahn-Teller distortion, reducing lattice change during Zn2+ extraction and insertion, and decreasing the Zn2+ migration energy barrier. As a result, the HE-NVPF@C cathode demonstrates exceptional cycling stability over 6000 cycles at 20 C with a capacity loss of a mere 0.0031 % per cycle and a high areal capacity retention of 2.17 mAh cm−2. In addition, the pouch cell provides a long cycling lifespan with 90.8 % capacity retention at 5 C after 200 cycles. This feasible high-entropy approach broadens the perspective for developing practical zinc-ion batteries with a long cycle lifespan and high areal capacity.

Unveiling the strengthening effect of Nb in Ti3SiC2/Ti25Zr25Ni25Cu25 + Nb/GH3536 brazed joint

In order to achieve the ceramic/metal brazed joint with excellent mechanical properties, many kinds of high-entropy alloy (HEA) filler have been developed to acquire the joint. However, in some HEAs with high content of active element, such as Ti25Zr25Ni25Cu25 amorphous HEA, the metallurgical reaction between active element and base materials resulted in the formation of continuous intermetallics (IMCs) layer in the brazing seam inevitably, embrittling the brazed joint. In this study, Nb element was added into Ti25Zr25Ni25Cu25 amorphous HEA filler to improve the microstructure of Ti3SiC2/GH3536 brazed joint, promoting the application of Ti3SiC2 and GH3536 in the aerospace industry. After detailed characterizations, the strengthening effect of Nb in the brazed joint was unveiled. The formation of Nb-base solid solution in the brazing seam was achieved owing to the addition of Nb, which effectively inhibited the generation of large brittle IMCs bulk. Moreover, the Nb-strengthened ZrSi2 and Ni2Ti phases were generated in the reaction zone, which was also favor in promoting the mechanical properties of brazed joints. When Ti25Zr25Ni25Cu25 amorphous HEA filler with 20 vol% Nb was applied to braze Ti3SiC2 to GH3536, a maximum value of 85.36 ± 2.39 MPa for shear strength was achieved. This study illustrates the optimization mechanism of Nb in Ti25Zr25Ni25Cu25 +Nb composite filler and promotes the further application of Ti25Zr25Ni25Cu25 in brazing system.

Effect of Doping Strategy on Electrochemical Performance of Grain Boundaries of Complex Perovskite Proton Conductor Ba3Ca1.18Nb1.82O−δ

In this study, the electrical conductivity and electrochemical performance of Ba3Ca1.18Nb1.82O9−δwere improved by substituting niobium (Nb) element with bismuth (Bi) and ytterbium (Yb) elements. Three different proton conductors, namely, Ba3Ca1.18Nb1.82O9−δ (BCN), Ba3Ca1.18Nb1.72Bi0.1O9−δ (BCNB), and Ba3Ca1.18Nb1.72Yb0.1O9−δ (BCNYb) were prepared by solid state sintering. The electrochemical performance of BCNYb was found to be the best at 400–800 °C in the wet atmosphere. Their ion transport properties were studied by using the defect equilibrium model. The results show the improvement in proton conductivity of BCNYb. Analysis of distribution of relaxation time reveals the improvement in the grain boundary properties of BCNYb. Single cells were prepared with BCN, BCNB, and BCNYb electrolytes, and the performance of the resulting fuel cells was tested. The BCNYb-based fuel cell shows excellent electrochemical performance, indicating its promising potential as a solid-state electrolyte with excellent properties.

The microstructure evolution and mechanical properties of WC-cu-10Ni-5Mn-3Sn cemented carbides containing NbC prepared by pressureless melt infiltration

WC-based cemented carbides with different contents of NbC (0, 0.6, 0.8, 1.0, 1.2, and 1.4 wt%) are prepared via pressureless melt infiltration at 1200 °C for 1.5 h. Microstructure evolution regularity of WC-based cemented carbide is investigated to establish the effect of NbC addition and microstructure peculiarities on mechanical properties (flexural strength, hardness, and impact toughness) of final product. Experimental results reveal that NbC firstly dissolves in binder alloy during melt infiltration, which slows down dissolution-precipitation reaction of WC, thus refining WC grains. With the increase in NbC content, average WC grain size shows varying trend, achieving the minimum (3.779 μm) at NbC addition of 1 wt%. When NbC is added in smaller amounts, Nb is mainly distributed throughout binder alloy. With the increase in NbC content, Nb elements tend to form aggregates and attach to WC particle boundaries. Some WC and NbC also decompose under experimental conditions. At NbC addition greater than 1 wt%, decomposition products (Nb, W, and C) combine with other elements in binder phase to form new phases such as (Nb,W)C, Ni2W4C, Nb2C, and Nb4Ni2C. These phases further act as bridges for WC grain coarsening. Meanwhile, excessive NbC is detrimental to mechanical properties of the alloy. With the increase in NbC content, hardness and flexural strength of the alloy increase and then decrease, reaching the maximum values of 93.4 HRA and 1808.786 MPa, respectively, at 1 wt% NbC addition. In turn, impact toughness of the alloy shows consistently downward trend. Therefore, changes in mechanical properties of WC-based cemented carbides are mainly related to WC grain size, the appearance of new phases in binder phase, and their morphology.

SYNTHESIS OF NANOSIZED PHASES WITH A GARNET STRUCTURE USING SUPERCRITICAL СО2 FLUID

A method was developed for the production of nanosized complex oxides and oxysulfides. The first stage uses supercritical СО2 fluid (SAS – supercritical antisolvent method). This approach makes it possible to obtain precursor-free complex oxides in a narrow nanoscale range. Nanosized rare-earth iron garnets with the general formula R3Fe5O12, where R is a rare earth element, were obtained and studied by physicochemical methods. The resulting samples have a size of less than 100 nm, exhibit ferromagnetic ordering, and can be used as soft magnetic materials. The multi-stage method for the preparation of complex oxysulfides was not previously demonstrated anywhere in the literature. The method involves three stages. At the first stage, a nanosized X-ray amorphous solid solution of the original salts is obtained using the SAS method. Then a nanosized X-ray amorphous component – the oxide phase – is obtained by annealing in a furnace. After this, the resulting oxide phase is mixed with the disulfide of a transition element (Nb, Mo), and high-temperature annealing is performed in an evacuated quartz ampoule. As a result, compact and nanosized phases of the composition Eu3Fe5-3/2xMox□1/2xO12-2xS2x and Eu3Fe5-3/2xNbx□1/2xO12-2xS2x, where x = 0.15, were obtained for the first time. The introduction of the sulfide component, namely NbS2, into the garnet structure increases its magnetic parameters by the factor of 1.5.

Microstructure characterization of plasma electrolytic oxidation coating on Hf-Nb-Ta-Zr high entropy alloy

The morphology, composition, and microstructure of plasma electrolytic oxidation (PEO) coating on Hf-Nb-Ta-Zr high entropy alloy (HEA) were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, glow discharge optical emission spectroscopy (GDOES) and transmission electron microscopy (TEM). The formation mechanism of PEO coating was analyzed. It was found that a dense PEO coating of ∼4 μm thick on the HEA surface was formed, which consisted of tetragonal and monoclinic ZrO2 phases, tetragonal and monoclinic HfO2 phases, Nb2O5 and Ta2O5 phases. The PEO coating from the alloy substrate to the surface contained five distinctive layers: amorphous barrier layer, nanocrystalline layer, columnar grain layer, amorphous outer layer, and top porous layer. Their formation was ascribed to the different cooling rates of the melt in the different depths of the discharge channel across the coating. Meanwhile, the formation of an amorphous barrier layer near the HEA substrate was also related to the mutual migration and diffusion of Hf4+, Nb5+, Ta5+, Zr4+ and O2− besides the rapid cooling of melt in the bottom of the discharge channel. The columnar grains of ∼70 nm wide were mainly composed of the monoclinic ZrO2 and monoclinic HfO2 phases, but both the amorphous layers enrich the Ta and Nb elements. It was believed that the high-content Ta and Nb in the HEA enhanced the formation of the amorphous layers.

Effect of trace niobium on the microstructure and properties of full-pearlite steel used in the high-strength hypereutectoid wire rods

The present study investigated the impact of 20–80 ppm Nb on the microstructure and properties of hypereutectoid pearlite steel. Remarkably, even trace amounts of Nb exhibited a favorable effect on the refinement of austenite grain. The addition of the Nb element resulted in a reduction of pearlite transition temperature, leading to a decrease of approximately 13% in lamellar spacing and 11% in the size of pearlite colonies. Furthermore, the dragging effect of the Nb element on the carbon atoms in hypereutectoid steel facilitated the control and refinement of network carbides. These findings offer valuable theoretical guidance for the production of ultra-high-strength wire rods. When the Nb content reached 80 ppm, it promoted the precipitation of (Ti, V)C, while simultaneously improving the morphology of square carbides. The grain refining strengthening mechanism accounted for about 70% of the overall strengthening effect observed in high carbon wire rods, with the influence of the Nb element primarily targeting grain refinement. Consequently, the incorporation of minute quantities of Nb presents a promising avenue for the development of ultra-high-strength hypereutectoid wire rods, offering significant potential for enhancing their strength properties.

The oxidation behavior and interfacial reaction between SiO2 coating and Ti45Al8.5Nb alloy

In this study, SiO2 coating was electrodeposited on Ti45Al8.5Nb alloy to enhance its oxidation resistance at 900 °C. The focus was on the interaction between SiO2 coating and the alloy substrate, and specifically, the role of the Nb element in this context. The formation of a SiO2/(Ti, Nb)O2/Ti5Si3 + Al2O3 three-layer oxide scale significantly inhibits the inward diffusion of oxygen. Beyond the characteristic Ti5Si3 + Al2O3 layer at the interface, the Nb2Al phase embedded within Ti5Si3 was observed. Concurrently, the presence of a (Ti, Nb)O2 layer was confirmed. The relationship between the coating thickness and oxidation resistance was also investigated. It was found that the thickness of the SiO2 coating affects the density of the oxide scale and the inward diffusion rate of oxygen. Moreover, due to the good adhesion to the substrate, the derived oxide scale exhibited good anti-peeling performance when subjected to a cyclic oxidation test.

Wetting behavior of Ti-Ni-xNb filler alloy on (HfTaZrNbTi)C high-entropy carbide ceramic

Exploring the wetting behavior of active filler alloys on high-entropy ceramic is critical to clarifying the solid/liquid interface reaction mechanism and guiding the preparation of high-performance composites. The wetting and spreading behaviors of the molten Ti-Ni-xNb filler alloys, both without and with different Nb concentrations, on (HfTaZrNbTi)C high-entropy carbide (HEC) ceramic were investigated at 1330 °C under a vacuum atmosphere using a sessile drop method. The wetting process of the Ti-Ni-xNb filler alloys was characterized by four distinct stages: (i) adhesion stage, (ii) rapid decreasing stage, (iii) sluggish spreading stage, and (iv) final equilibrium stage. The Ti-Ni-xNb filler alloys all exhibited good wettability on the HEC ceramic, with the final contact angle remaining around 47-48°. The interfacial structure was identified as a sequence of HEC/Ti-based HEC’ diffusion layer/TiCx reaction layer/Ti2Ni layer/alloy droplet in all wetting systems. Notably, the introduced Nb element participated in the interfacial reactions between HEC and the filler alloy, modifying the morphology of the solidified droplet and accelerating the rapidly decreasing stage of the alloys on the ceramic. Nb atoms replaced some of the Ti atoms in the TiCx reaction layer, which restrained the atomic diffusion, leading to the formation of thinner reaction layers. The spreading kinetics were initially governed by interfacial reactions and later by the diffusion of Ti and Ni into the ceramic substrate, exhibiting a transition from reaction-controlled to diffusion-controlled spreading.

Disentangling the Roles of Subducted Volatile Contributions and Mantle Source Heterogeneity in the Production of Magmas Beneath the Washington Cascades

AbstractThe compositional diversity of primitive arc basalts has long inspired questions regarding the drivers of magmatism in subduction zones, including the roles of decompression melting, mantle heterogeneity, and the amount and composition of slab‐derived materials. This contribution presents the volatile (H2O, Cl, and S), major, and trace element compositions of melt inclusions from basaltic magmas erupted at three volcanic centers in the Washington Cascades: Mount St. Helens (two basaltic tephras, 2.0–1.7 ka), Indian Heaven Volcanic Field (two <600 ka basaltic hyaloclastite tuffs), and Glacier Peak (late Pleistocene to Holocene basaltic tephra from Whitechuck and Indian Pass cones). Compositions corrected to be in equilibrium with mantle olivine display variability in Nb and trace element ratios indicative of mantle source variability that impressively spans nearly the entire range of arc magmas globally. All volcanic centers have magmas with H2O and Cl contributions from the downgoing plate that overlap with other Cascade Arc segments. Volatile abundances and trace element ratios support a model of melting of a highly variably mantle wedge driven by a subduction component of variably saline fluid and/or slab partial melt. Magmas from Glacier Peak in northern Washington have unusually high Th/Yb ratios that are similar to Lassen region basalts, indicating possible contributions of “subcreted” metasediments that geophysical data suggest are not present beneath central Oregon and southern Washington. This data set adds to the growing inventory of primitive magma volatile concentrations and provides insight into spatial distributions of mantle heterogeneity and the role of slab components in the petrogenesis of arc magmas.

First-principles study of the interaction of solutes with ∑3(11-1) symmetric tilt grain boundaries in α-Fe

Abstract The structural, cohesive and magnetic properties of a symmetric Σ3(70.53)[011](11-1) tilt grain boundary in pure bcc iron and with commonly used alloying elements (Si, Co, Mn, Ti, Cu, Mo, Nb, V, Cr and Ni) by means of density functional theory calculations are studied. Solubility and segregation energies were calculated for different positions of dissolved atoms. Calculations show a tendency for impurities to segregate near the boundary. It was found that the substituting Co, Cu and Ni in the layer adjacent to the boundary have an embrittling effect, while other atoms enhance the cohesion of the grains. Magnetic moments on GB atoms are significantly higher than those on bulk atoms.

Oxygen-rich combustion behaviors and mechanisms of a new Ni-Cr-based superalloy fabricated by selective laser melting

The mechanical and combustion behavior of a new Ni-Cr-based superalloy, fabricated by selective laser melting in an atmosphere with an oxygen concentration greater than 99.5 %, was investigated through the analysis of microstructural morphology, elements distribution and combustion kinetics. The results show that heat treatment eliminated the anisotropy of the as-built microstructures and improved the tensile strength. The studied superalloy can be ignited with a combustion threshold of about 2.5 MPa–3 MPa. The burning length and burning rate increase with the increase of pressure. The selective combustion of Al, Ti, Nb, Cr, Fe, Mo, and Cu elements occurred, resulting in the dissolution of γ′, γ", and δ precipitates and formation of holes at the grain boundaries in the heat-affected zone. The microstructures exhibit large elongated grains in the melting zone and column grains in the heat-affected zone along the heat dissipation direction. The combustion products are a mixture of oxides exhibiting dendritic structures in terms of selective combustion, density, and melting point. The findings from this study enhance our comprehension of the combustion process in nickel-based superalloys, offering valuable data and guidance for the advancement of new oxygen-rich combustion-resistant superalloys.

Petrogenesis of microgranular enclaves in the A-type granitoid Krasnopol intrusion (Mazury Complex, northeastern Poland): Evidence of magma mixing

The origin of magmatic microgranular enclaves has been investigated in the Mesoproterozoic granitoid Krasnopol intrusion (1.5 Ga), part of the AMCG (anorthosite–mangerite–charnockite–granite) Mazury Complex in the East European Craton (NE Poland). The granitoids are ferroan and metaluminous, and display the typical characteristics of A-type granites, with high contents of Zr, Nb, Ga and rare earth elements (REEs). The enclaves are metaluminous and have a broad compositional range with two groups distinguished: silica-poor (45–50 wt% SiO2) and silica-rich (54 to 59 wt% SiO2), the latter overlapping in composition with the granitoid samples. The silica-poor enclaves are enriched in REEs compared to the silica-rich type, while the silica-rich enclaves exhibit trace-element patterns similar to those of the granitoids. Initial whole rock εNd values range between -3.8 and -4.0 for the granitoids and give a slightly wider range from -2.6 to -3.8 for the enclaves. The 87Sr/86Sr initial values vary from 0.7084 to 0.7138 for the granitoids and between 0.7052 and 0.7075 for the enclaves and indicate that the granitoids and enclaves are not isotopically identical. These may suggest that the two magmatic systems represented by the granitoid host rock and the enclaves, were probably derived from different sources, but with sufficient interaction, which led to a progressive change in the composition of the enclaves towards intermediate composition. We suggest that the mafic melts of the enclaves were generated at the base of the thickened crust through partial melting of the lower crustal source, with a significant contribution from mantle material. The increase in temperature resulted in anatexis of the lower crust and the formation of the granitoid parental magma.

Effect of micron/nano Nb particles on high-temperature oxidation behavior of TiAl alloy/thermal barrier coating system

In this study, the effect of NiCoCrAlY bond coating modified by micron- and nano-sized Nb particles on the oxidation behavior of a TiAl alloy/thermal barrier coating (TBC) system was investigated. The results show that the addition of micron-sized Nb particles slightly decreased the oxidation resistance of the TNM/TBC system, while the addition of nano-sized Nb particles significantly increased the oxidation resistance. The growth stress from the oxidation of micron-sized Nb particles and the Kirkendall effect lead to localized thickening (tumor effect) of the thermally grown oxide (TGO). Severe internal oxidation occurs in the bond coating modified by micron-sized Nb particles, greatly reducing the mechanical properties and antioxidant properties of the TNM/TBC system. However, these micron-sized Nb particles are deposited at the bond coating/TiAl matrix interface, acting as an in-situ diffusion barrier and partially hindering element interdiffusion. Conversely, nano-sized Nb particles induce the formation of fine columnar crystals in the TGO and promote the external diffusion of Al elements, thereby maintaining a low growth rate and excellent continuity of the TGO. Additionally, the Nb element dissolves into the matrix phase, and the formation of nano Nb-Al₂O₃ core-shell structures effectively improves the deformation resistance and failure resistance of the bond coating.

Effects of alloying element on the interface stability of fcc-Fe/NbC by first principles investigation

Interfacial segregation engineering is widely used as a means of regulating the strength and toughness of materials. In this paper, the effect of alloying elements on the interfacial segregation and interfacial bonding properties of fcc-Fe/NbC is investigated with the precipitated phase NbC in austenitic heat-resistant steel. The results show that there are eighteen interfacial configurations between the fcc-Fe and NbC phase, and the stability of the interface with Nb terminal is better than that of C terminal according to the calculation results of separation work and interface energy. Al atom is easy to segregate on the surface of austenite, while the alloy elements Mo, Nb, Cr, Ti, Mn, Y and Zr tend to segregate in the austenite matrix. The segregation of alloy elements Mo, Nb, Cr and Ti can enhance the hybridization between the d orbits of Fe and Nb atoms at the interface, thus promoting the bonding strength of the interface, while the segregation of Mn, Al, Y and Zr reduces the covalent interaction of the interface atoms, which weakens the bond strength at the interface. The above results have important practical significance for improving and regulating the composition and interfacial properties of heat-resistant steels.

Phase evolution in Ni-based superalloy K439B during thermal process

Based on the difference in element distribution and diffusion in various regions, the phase transformation of the as-cast, heat-treated and long-term aged K439B superalloys was investigated. Ti, Nb, Ta and Al elements segregated to the interdendritic regions, whereas W, Co and Cr elements segregated to the dendrite core regions in the as-cast alloy. During thermal process, the γ/γ' eutectic and the irregular γ' phase formed in the as-cast alloy completely dissolved into γ matrix. Subsequently, the reprecipitated spherical γ' phase gradually grew up and tended to be cubic. γ' phase was surrounded by the dislocations and a few stacking faults, which reduced the elastic strain energy in the long-term aged alloy. In addition, the degeneration of MC carbide was caused by a discrepancy in element diffusion rate and driving force in the interdendritic and grain boundary regions. The degeneration of MC carbide promoted the precipitation of γ' phase, M23C6 carbide and η phase, M23C6 carbide precipitated from γ matrix and γ' phase transformed into η phase. The preferential precipitation of M23C6 carbide was related to the difference in crystal structure, precipitation temperature range and Gibbs free energy.

Editorial for Special Issue “Rare Metal Ore Formations and Rare Metal Metallogeny”

Rare metals (usually defined as including elements such as Li, Rb, Cs, Be, Sn, Nb, Ta, Zr, Y, U, and rare-earth elements) are included in the list of “critical mineral resources” by major economies around the world [...]

Nb/Mn co‐doping enhances the pyroelectric properties of Na0.5Bi4.5Ti4O15 ceramics for infrared detection

AbstractThe pyroelectric effect has wide applications in various fields, such as infrared imaging, detection, alarms, and the expanding field of smart homes. The rapid advancement of smart systems, focusing on miniaturization and integration, requires pyroelectric infrared detectors with high pyroelectric coefficients and Curie temperatures to meet the requirements of integrated processes. However, the Curie temperature of commercial lead zirconate titanate is limited to <230°C, urgently looking for a breakthrough. Here, we explore pyroelectricity in Na0.5Bi4.5Ti4O15 (NBT) ceramics, characterized by a high Curie temperature (∼660°C). We systematically examined the crystal structure modifications and defect dipole effects of the Nb/Mn‐co‐doped NBT. The lattice expansion, distortion of the TiO6 octahedra, and structural transformation tendency from the orthorhombic to tetragonal phase facilitate dipole movements with increasing temperature. Furthermore, the Mn and Nb elements result in the formation of MnTi“–VO·· and NbTi·–MnTi” –NbTi· defect dipoles, inducing additional polarization changes in response to temperature variations. Finally, a significantly improved pyroelectric coefficient of 110 µC m2 K–1 and remarkable temperature stability from 25°C to 300°C is achieved in NBTM‐5Nb ceramics. This co‐doping strategy for enhancing pyroelectric performance can be expanded to other systems and substantially contribute to advancing high‐performance materials for infrared detection.