Nb Phase Research Articles

Microstructure and mechanical properties of a severely cold-rolled and annealed dual-phase compositionally complex alloy (CCA) with an exceptionally deformable Laves phase

A novel CCA was designed by substituting Nb in (FCC + C14 Laves) CoCrFeNi2.1(Nb)0.2 CCA by (Hf + Nb + Ta). The (HfNbTa)0.2 CCA was homogenized, heavily cold-rolled, and isothermally annealed at 800 °C and 1000 °C for different time intervals. The (HfNbTa)0.2 alloy revealed the presence of a Hf and Ni enriched cubic C15 Laves phase. The considerations of site occupancy behavior, formation energy, and highly off-stoichiometric composition stabilized the (Hf, Ni) rich cubic C15 Laves phase. In contrast to the brittle hexagonal C14 Laves phase in (Nb)0.2 CCA, the C15 Laves phase in (HfNbTa)0.2 CCA showed exceptional deformability owing to the high propensity for nano-twin formation. Meanwhile, the FCC matrix developed a deformation-induced nano-lamellar structure with a spacing of ∼45 nm. Annealing resulted in ultrafine recrystallized FCC matrix and precipitation of DO19 structured ε nano-precipitates. The isothermal grain growth kinetics revealed a high grain growth exponent (n) ∼7, which confirmed a Zener-drag mediated process due to the ε nano-precipitates. The Hall-Petch analysis of the hardness data showed relatively high friction stress originating from the dissolution of Hf, Nb, and Ta in the FCC matrix. A high Hall-Petch coefficient indicated increased shear stress for plastic flow across the boundaries, resulting from the elongated Laves phase at the boundaries. The highly deformable Laves phase, ultrafine grain size, and ε nano-precipitates resulted in high yield strength (∼975 MPa) and superior ductility (∼16 %) in the (HfNbTa)0.2 CCA, even surpassing the (Nb)0.2 CCA. It was envisaged that strong yet deformable Laves phases could pave the pathway for developing Laves phase-based CCAs for advanced structural applications.

Effects of Nb on Creep Properties and Hot Corrosion Resistance of New Alumina-Forming Austenitic Steels at 700 °C

Effects of Nb on the creep resistance and hot corrosion behavior of the Fe-25Cr-35Ni-2.5Al-xNb (x = 0, 0.6, 1.2) Alumina-Forming Austenitic stainless steels (AFA steels) at 700 °C were investigated. The addition of Nb promoted the precipitation of both nanoscale NbC and γ′-Ni3(Al, Nb) phases, which exhibited very low coarsening rate constants. The nanoscale NbC and γ′-Ni3(Al, Nb) phases effectively impeded the migration of dislocations and led to an improvement in creep performance of the Nb-addition AFA steel. The corrosion of AFA steels in Na2SO4-25%K2SO4 at 700 °C was primarily driven by an “oxidation-sulfidation” mechanism. The addition of Nb, serving as a third element, facilitated the formation of protective Cr2O3 and Al2O3 films, which improved the hot corrosion resistance performance. However, the formation Nb2O5 was found to compromise the compactness of the oxide film, which adversely affected the corrosion resistance.

Welding Heat-induced Microstructural Variations in Inconel 718 Superalloy: A Comparative Investigation between Conventionally Manufactured and 3D Printed Materials

This study focuses on the microstructural evolution of Inconel 718 superalloy, a precipitation-hardened superalloy, subjected to various manufacturing processes and subsequent thermal exposures. Conventional manufacturing methods such as casting and forging were compared with modern 3D printing techniques, notably wire-arc additive manufacturing. Subsequent treatments, including solution treatment and two-stage aging, as well as bead-on-plate welding, were performed to assess their effects on the microstructure of Inconel 718. The transformations of strengthening phases such as γ′(Ni3(Al,Ti)), γ″(Ni3Nb) and intermetallic δ(Ni3Nb) phases were observed to vary significantly under different thermal cycles, and these variations in phase transformation are anticipated to lead to a degradation in mechanical performance post-welding. Additionally, thermodynamic calculations using commercial Calphad software were utilized to investigate phase transformations in the welds, providing critical insights into how manufacturing processes and thermal exposures affect the stability and distribution of microstructural features, thereby highlighting the complexities of phase dynamics in this high-performance alloy.

A novel TaMoNbCrTi refractory high-entropy alloy produced by powder metallurgy

The process of mechanical alloying (MA) and spark plasma sintering (SPS) were employed to manufacture a novel TaMoNbCrTi refractory high-entropy alloy. The investigation concentrated on how variations in sintering temperatures resulted in microstructural differences, which in turn altered the mechanical properties of TaMoNbCrTi. A BCC-structured solid solution phase was formed as a result of the MA process. During further sintering, the Cr2(Ta, Nb) phase and Ti(O, N) phase precipitated from the BCC phase. The Cr2(Ta, Nb) phase volume fraction declined and transitioned from a reticular distribution to a dispersed distribution as the sintering temperature rose. Additionally, a considerable enhancement in the Ti(O, N) phase size was observed. Because of the uniform distribution of the fine precipitated phases, the TaMoNbCrTi alloy sintered at 1200 °C demonstrated superior mechanical properties.

High strength diffusion bonding of Ti2AlNb to GH4169 with (TiZrHfNb)95Al5 high entropy interlayer

A high entropy interlayer (TiZrHfNb)95Al5 was designed for vacuum diffusion bonding of Ti2AlNb to GH4169. The influence of bonding temperature on the interfacial microstructure morphology, mechanical properties and fracture behaviour of the resultant joints was investigated. The evolution of microstructure and fracture mechanism were revealed. The typical interface microstructure of Ti2AlNb/B2/Solid solution/(Ti, Zr, Hf)2(Ni, Nb)+(Ti, Zr, Hf)(Ni, Nb)+(Ti, Zr, Hf)(Ni, Nb)2+Solid solution/(Ti, Zr, Hf)(Ni, Nb)+(Cr, Ni, Fe)ss/(Cr, Ni, Fe)ss/Cr-rich(Cr, Ni, Fe)ss/Ni-rich(Cr, Ni, Fe)ss/GH4169 was formed. As the bonding temperature increased, the thickness of interfacial reaction layer gradually increased, and the shear strength gradually increased until 980 °C, then decreased sharply. The highest shear strength reached 376 MPa at 980 °C for 90 min. The highest microhardness region of 11.79 GPa existed on the GH4169 side, which was mainly composed of (Ti, Zr, Hf)(Ni, Nb) and (Cr, Ni, Fe)ss phases. Meanwhile, the elastic modulus dramatically changed interface formed near this region. The fracture surface morphology indicated typical brittle fracture characteristics such as cleavage steps, transgranular fracture and intergranular fracture. According to the fracture analyses, major cracks initiated in the (Ti, Zr, Hf)(Ni, Nb) phase+(Ti, Zr, Hf)2(Ni, Nb) phase and gradually extended to the (Cr, Ni, Fe)ss phase. Thus, the major crack emerged region was located at the elastic modulus dramatically changed interface.

Crystallographic and electrical properties of mechanically rolled gold backed niobium target

This work demonstrates an excellent and high purity target film, realized by depositing uniformly thick mechanically rolled niobium (Nb) film over gold (Au) foil using indium (In) as adhesive layer (Nb/In/Au). The materials properties of the resulting foil in three layered Nb/In/Au structure, characterized using microscopic and spectroscopic techniques demonstrate presence of pure forms of the material contents and depict crystal phases of pure Au and Nb in Au and Nb/In/Au foils, respectively. This suggests the chemical inertness of Nb film towards oxidation during mechanical rolling and evidences formation of high purity Nb layer with precise crystallinity. The current-voltage (I–V) characteristics of Nb/In/Au foil measured at room temperature through a lateral device structure configuration with silver (Ag) top contacts exhibit ohmic conduction with surface resistivity of 2.5mΩm, indicating 127.3% increment after mechanical rolling of Nb on Au foil. The fabricated gold backed niobium target has been utilized in a recent nuclear level lifetime measurement experiment through Doppler shift attenuation method.

Ab initio study of transition paths between (meta)stable phases of Nb and Ta-substituted Nb

<i>Ab initio</i> study of transition paths between (meta)stable phases of Nb and Ta-substituted Nb

Structure and Ionic Conductivity of Ga and Nb Dual Doped LLZO Synthesized by Sol-Gel Method

More and more attention has been focused on Li7La3Zr2O12 (LLZO) because of the high ionic conductivity and excellent chemical stability. It is great significance to find suitable dopants for locking cubic LLZO and improving the conductivity of Li+ ions. The uniform nano powder can be obtained by the sol gel synthetic method, which is conducive to maintaining high sintering activity. In this work, Ga and Nb dual doped LLZO solid electrolyte powders were synthesized via sol gel method, and Ga and Nb dual doped LLZO solid electrolyte ceramic were obtained via traditional solid state sintering method. The phase and microstructure of Ga and Nb co-doped LLZO solid electrolyte were analyzed by combine X-ray diffraction with scanning electron microscope. The impedance of Ga and Nb dual doped LLZO (Li6.8-3xGaxLa3Zr1.8Nb0.2O12 (0≤x≤0.3)) solid electrolyte was measured by the electrochemical workstation, and then the conductivity was calculated. The results show that when the doping amount of Ga is x=0.2, it is a pure cubic LLZO structure with the highest conductivity value of 3.7×10-4 S cm-1 (tested at room temperature) due to the sample has a high relative density and reaches the optimal Li+ vacancy concentration.

Extremely large magnetoresistance with coexistence of a nontrivial Berry phase in Nb0.5Ta0.5P: an experimental and theoretical study

We synthesized Nb0.5Ta0.5P, exhibiting XMR at low temperatures with charge carrier compensation up to 50 K. SdH oscillations reveal multiple Fermi pockets and non-zero Berry phase. SOC effects were analyzed via band structure calculations.

Understanding the oxidation resistance of zirconium alloy at 1000°C based on the formation of a Zr-Sn intermetallic phase and co-precipitation of Sn and Nb

The oxidation behavior of zirconium alloy in high-temperature steam plays a dominant role in the operation of nuclear reactors under accident conditions. The present work investigated the effect of Sn on the oxidation behavior of zirconium alloys in high-temperature steam at 1000 °C. The results of scanning electron microscopy (SEM), metallographic microscopy and synchrotron X-ray diffraction (S-XRD) analyses show that there are three layers in the oxidized sample, including prior β-Zr, α-Zr(O) and ZrO2. High resolution analyses conducted in these layers by transmission electron microscopy (TEM) show that Sn atoms segregate around the oxide-metal (O-M interface and Zr-Sn intermetallic precipitates only present in the oxide film. Clear atomic arrangements of Zr5Sn3 were obtained by TEM, resulting in accurate identification of the Zr-Sn intermetallic phase. Also, TEM energy dispersive spectroscopy (EDS) maps show that Zr-Sn particles invariably accompany the segregation or precipitation of Nb. However, no clear precipitation sequence was observed, which suggests that a co-precipitation mechanism of Sn and Nb is in operation. As oxidation proceeds, nanovoids next to the Zr-Sn intermetallic particles were observed accompanied by local areas deficient in oxygen, identified as ZrO. Combining the interdiffusion trend obtained by Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, a mechanism for the transformation from the Zr-Sn intermetallic precipitates to nanovoids was proposed. This proposed mechanism may shed new light into the role of Sn in the oxidation resistance of zirconium alloy under LOCA conditions.

Origin of carbonatite-related niobium deposits: Insights from pyrochlore geochemistry

The carbonatite-related Nb deposits of the Alto Paranaíba Igneous Province (APIP) in central Brazil, currently account for ∼92 % of the global Nb production. In the APIP, pyrochlore is abundant in magnetite–apatite–tetraferriphlogopite ± carbonate rocks or phoscorites, occurring as interbedded layers with carbonatites in the lower hypogene zone, feeding dike swarms of phoscorite and calcite carbonatite, and late-stage carbothermal veins in the upper hypogene zone. The origin of the phoscorite-carbonatite association can be explained by three hypotheses: (1) crystal segregation from fractional crystallization, (2) liquid immiscibility, and/or (3) phoscoritic magma formation after basement metasomatism (fenitization). However, it is not well understood whether pyrochlore formation is limited to a carbonatitic event, carbohydrothermal, or both, and this gap of knowledge is addressed in this work. To investigate the petrogenesis of pyrochlore-rich phoscorite, cathodoluminescence (CL) images, chemical maps, and LA-ICP-MS data were acquired of pyrochlore crystals from magmatic and carbothermal rocks from the Boa Vista Nb mine, Catalão II Complex. In the Boa Vista mine, oscillatory and patchy zoning were identified as primary pyrochlore textures commonly recorded at the lower hypogene zone, while secondary dissolution, skeletal and zonation-free textures are registered at shallower depths in the upper hypogene zone. Calciopyrochlore is the dominant Nb phase at the Boa Vista mine, with only two kenopyrochlore outliers. The pyrochlore CI chondrite-normalized REE distribution is consistent with geochemical results of the carbonatite and phoscorite rocks, indicating a magmatic origin for pyrochlore and the presence of pyrochlore antecrysts in carbothermal veins. The Sr/Y vs La and Na vs Ce diagrams in pyrochlore indicate a continuous fractionation pattern, with some mixtures of antecrysts and primary phases. An examination of intercumulus calcite using CL provide evidence of carbonatitic magma residues within tetraferriphlogopite phoscorite dikes and suggests that alkaline–carbonate-rich fluids played a role in transporting heavy minerals (i.e., magnetite, apatite, pyrochlore). Consequently, the textural and chemical evidence in the Boa Vista Nb mine indicates that the origin of pyrochlore-rich phoscorites is the result of physical segregation of heavy minerals from a carbonatite magma by fractional crystallization, leading to the emplacement of pyrochlore-rich carbonatite and phoscorite dikes. The implications at Catalão II may extend to other APIP alkaline-carbonatite complexes, as they share a genetic connection, and should motivate further studies focusing on pyrochlore geochemistry in other carbonatite-related Nb deposits, which will be crucial for advancing our knowledge of global Nb metallogenesis.

Structural transformation behavior in a high Nb–TiAl alloy additively manufactured by laser powder bed fusion

High Nb–TiAl alloys fabricated using laser powder bed fusion (LPBF) exhibit a metastable α2 phase due to the rapid cooling rate of the LPBF process. However, the understanding of the structural transformation behavior in LPBF-fabricated high Nb–TiAl alloys remains limited. In this work, a high Nb–TiAl alloy with a nominal composition of Ti–48Al–2Cr–8Nb (at. %) was additively manufactured using LPBF. The structural transformation from metastable α2 phase to γ phase was then studied by the in-situ high-temperature x-ray diffraction (XRD), in-situ heating transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Furthermore, the phase composition and microstructure of the samples annealed at different temperatures were determined by XRD and electron backscatter diffraction (EBSD). Our findings demonstrate that the α2 phase in LPBF-fabricated high Nb–TiAl alloy remains stable up to 873 K, after which it decomposes and forms fine γ lamellar colonies along with a disordered γ′ phase as an intermediate phase. Notably, the transition from α2 to γ′ phase is reversible. In contrast, the formation of the γ phase is irreversible and persists down to room temperature. It is also found that the changes in grain size and phase composition of the LPBF-fabricated high Nb–TiAl alloy have a significant impact on its hardness. This study provides valuable insights into the structural transformation behavior of additively manufactured high Nb–TiAl alloys by LPBF, offering guidance for regulating their structure and properties.

Unveiling the Degradation of Pt/NbOx/C Catalysts in PEMFCs via In Situ X-ray Absorption Spectroscopy

Among the class of the catalyst that is composed of metal nanoparticles supported on metal oxides (MMO), the Pt/NbOx/C system has shown promising oxygen reduction reaction (ORR) activities as a cathode of proton exchange membrane fuel cells (PEMFCs). Herein, we have studied a series of Pt/NbOx/C catalysts prepared via physical vapor deposition and unraveled the nature of the metal and metal oxide interaction (MMOI) by characterizing this system under reactive conditions. By conducting in situ X-ray absorption spectroscopy (XAS) experiments, we demonstrate that Pt preferably interacts with O but not Nb in the Pt/NbOx/C system. As such, Pt-O interaction benefits the ORR activity via an electronic effect rather than a strain effect. We have also provided clear evidence for the formation of metallic Nb phase at the early stage of PEMFC operation, which led to severe particle growth of Pt after long-term PEMFC operation.

Role of Nb elements in SiCf/SiC/(CoFeNiCrMn)100-xNbx/GH536 brazed joints: Joint residual stress transfer and pinning of dislocations

Brazing is a critical method to address the challenge of connecting composite materials to metals. This study joined SiCf/SiC composites and GH536 superalloy using (CoFeNiCrMn)100-xNbx high-entropy alloy filler with varying Nb element contents successfully. The microstructural evolution and mechanical property changes of brazed joints were systematically investigated. Notably, when the Nb element content in the filler reached 12 %, a diffuse distribution of Nb(s, s) emerged in the joint, playing a vital role in effectively transferring residual stress on the SiCf/SiC side. This effect is attributed to the disparity in thermal expansion coefficients between the Nb(s, s) and face-centered cubic (FCC) phases. The resulting joint exhibited remarkable room temperature and high temperature shear strengths of 89.7 MPa and 49.7 MPa, respectively. Furthermore, the presence of Nb(s, s) in the brazing seam proved to impede the movement of dislocations during joint fracture. This work introduces a new technical paradigm for aero-engine manufacturing.

Deposition-controlled phase separation in CuNb metallic alloys

Vapor co-deposited metal nanocomposites with immiscible components have shown to have several superior properties including mechanical performance, radiation tolerance, and enhanced functionalities. The morphology and structural design of these nanocomposites are important in determining the expression of these properties. The conditions used to deposit thin film nanocomposites are the governing factors in determining the final nanostructure. In this work, we link the effects of process gas pressure, substrate temperature, and sputtering target power on resultant Cu/Nb thin film nanostructures. We find that for films with equiatomic phase fractions of Cu and Nb, inhomogeneous precipitate segregation dominated the structure at lower substrate temperature depositions while higher temperatures distributed the Cu and Nb phases more uniformly. Increasing process gas pressure during deposition lead to a spatially homogeneous, nanocrystalline structure of Cu/Nb. In situ annealing of this sample shows that the phase separated morphology of the two immiscible materials depends on the initial composition. Finally, compositions of Cu and Nb that were highly disparate lead to interface segregation of the minority phase. The morphological evolution observed in the Cu/Nb system is compatible with modified structural zone models for immiscible thin film systems.

Evolution of CrCx Ceramic Induced by Laser Direct Energy Deposition Multilayered Gradient Ni204-dr60 Coating.

The manufacturing process for many large components of machines leads to a difference in their properties and performances based on changes in location. Functionally graded materials can meet these requirements and address the issue of generation and expansion of interface cracks. Ni204-dr60 gradient coatings were successfully fabricated using laser direct energy deposition (LDED). Microstructure mechanism evolution and microhardness of the gradient coating were comprehensively investigated. The change in the precipitated phase at the grain boundary and the intergranular zones resulted in a change in microstructural characteristics and also affected the microhardness distribution. The reinforced phase of the Ni204 → dr60 gradient zone from Ni204 to dr60 gradually precipitated and was rich in Mo and Nb phase, lath-shaped CrCx phase, network-shaped CrCx phase, block shape (Ni, Si) (C, B) phase, block CrCx phase, and block Cr (B, C) phase. The gradient coating thus acts as a potential candidate to effectively solve the problem of crack generation at the interface of dr60 and the substrate.

Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;: Percentage Effect of T/H Phase and Evaluation of Catalytic Activity, a Preliminary Study

Due to its similar characteristics to titanium, niobium has become an attractive alternative in photocatalytic processes. Research indicates that titania has an optimal percentage of phases resulting in a commercial catalyst, P25, that contains more than 70% anatase with a minor amount of rutile and a small amount of amorphous phase. On the other hand, for Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;, percentage optimization was little explored in the literature, which consists of studying the phases obtained via heat treatment individually and in different percentages via chemometric studies. In this context, the present research proposes to study the T/H phases of Nb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; and their mixture. The catalysts were used to assess the catalytic activity in salicylic acid (SA) degradation. The results demonstrated that a theoretical mixture of T/H phase, with an optimal ratio of 69.1% of the H phase, had more significant SA degradation than the tests with the pure phases. The mixture was able to degrade 87.9% of SA in 60 minutes.

Modelling of thermal behaviour in niobium during electron beam welding

Niobium (Nb) has been the subject of extensive research for its application as a crucial material for various complex engineering systems. The increased usage of Nb has prompted extensive research into new ways to join it. Previous works done by researchers on niobium joining majorly involves the use of laser welding technology. In recent years, electron beam welding (EBW) has emerged as one of the most effective joining methods, with a poor understanding of the dynamics though. This study aimed to enhance our understanding of the EBW of Nb plates through the development of a novel finite-element multiphysics model and a molecular dynamics analysis. To understand the heat transmission during the welding process, this study developed heat distribution and temperature contour maps. Variations of several process parameters on heat distribution and beam stabilisation were also noted during the finite element analysis. This study also comprehends the physics behind the creation of keyhole geometry. Molecular dynamics analysis introduced Voronoi clusters and radial distribution function graphs to explain the successful macro- and atomistic evolution of the heat distribution during electron beam welding of pure niobium. The research in this literature discusses the experimentation correlated with computational and molecular dynamics modelling. The finite element modelling and the atomistic simulation provide the relation between heat dissipation through the liquid and solid phases of pure Nb and its behaviour at the molecular level. Niobium has a growing future potential in various engineering domains ranging from uses in spacecraft structures to heavy drilling machinery due to its astonishing thermal properties. These structures perform in extreme thermal conditions and thus addition of niobium in these systems can improve their integrity under such environment. EBW has proven to be a very efficient method for joining of materials and thus can be used for highly sophisticated equipment with marginal error. The studies can help provide useful insight in joining of Niobium and its alloys with near perfection which have been used extensively in recent times.

A novel method to design Nb(W)–Ti–Co(Fe) alloy membrane with high hydrogen permeability and strong resistance to hydrogen embrittlement

A hydrogen permeable Nb43W5Ti27Co20Fe5 alloy membrane was designed and its microstructure and hydrogen transportation performances were systematically studied. W mainly dissolves into primary body-centered cubic (bcc)-(Nb) phases, while Fe is captured in eutectic structures. Substituting Nb with W leads to a substantial reduction in hydrogen solubility and substituting Co with Fe negligibly affects hydrogen solubility. The W and Fe substitutions contribute to an enhanced intrinsic hydrogen diffusion coefficient D∗. The designed Nb43W5Ti27Co20Fe5 alloy membrane exhibits lower hydrogen solubility and higher hydrogen permeability at temperatures below 623 K than that of the original Nb48Ti27Co25 alloy membrane. No hydrogen-induced failures were found for the designed Nb43W5Ti27Co20Fe5 alloy membrane during cooling to room temperature and under long-term hydrogen permeation at 673 K for 72 h, whereas the original alloy membrane failed at 444 K during cooling to room temperature and after 19 h during hydrogen permeation at 673 K. The designed Nb43W5Ti27Co20Fe5 alloy membrane exhibits high hydrogen permeability and strong resistance to hydrogen embrittlement.

Weldability study of 304HCu stainless steel using varestraint and “Gleeble” based hot ductility tests

The susceptibilities of 304HCu SS to solidification and liquation cracking are assessed in the current work and the underlying mechanisms are clarified. The development of γ + Nb4C3 eutectic along the interdendritic areas in the fusion zone is attributed for solidification cracking in this stainless steel. To forecast and rank the susceptibility of an alloy to solidification cracking, a novel technique is put forth and experimentally confirmed. Using the measured temperature gradient, welding speed and Scheil's solidification module, a relationship between the liquid fraction and mushy zone width is derived. Liquation cracking susceptibility evaluated using “Gleeble™” based hot ductility test is observed to be high which is attributed to the constitutional liquation of primary Nb(C,N) and secondary M23C6 phases present in the base metal. Further, the influence of phosphorus on the local solidus temperature in the partially melted zone of the alloy is discussed in the context of liquation cracking.