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Data are presented from tensile tests of commercial Nb-based alloy C103 (Nb-10Hf-1Ti, by wt pct) at temperatures of 1550–1750 °C and true-strain rates of 3 × 10 - 5 to 3 × 10 - 3 s - 1 . Changes in strain rate generated pronounced short-term transients in flow stress. These transients are of the inverse type characteristic of solute drag creep (SDC). C103 produced large tensile elongations of 150–200 pct and strain hardened during plastic deformation. Test data provide an average strain-rate sensitivity of 0.29 and an activation energy for creep of 340 kJ/mol. Short-term transient data indicate a stress dependence for dislocation glide velocity of v ¯ ∝ σ 2.7 and for mobile dislocation density of ρ ∝ σ 0.7 . The deformed microstructure contains indistinct subgrains and steep strain gradients. All data indicate deformation by SDC controlled by the diffusion of Hf solute atoms for the range of conditions examined. Data from plastic flow transients suggest that creep rates for C103 available in the literature are likely from the primary creep region. When that is considered, data from the literature and the present study are in good agreement. [ABSTRACT FROM AUTHOR]

Tooth loss replacement using dental implants is becoming more frequent. Traditional dental implant materials such as commercially pure titanium and titanium aluminum vanadium alloys have well-proven mechanical and biological properties. New titanium alloying metals such as niobium provide improved mechanical properties such as lower elastic modulus while displaying comparable or even better biocompatibility. Hydroxyapatite coatings are a well-documented and widely used method for enhancing dental implants' surface characteristics and properties and could provide a useful tool for further enhancing titanium–niobium implant properties like osteointegration. Among several coating techniques, physical deposition methods and, in particular, vapour deposition ones are the most used due to their advantages compared to wet deposition techniques for hydroxyapatite coating of metallic surfaces like that of dental implants. Considering the scarcity of data concerning the in vivo evaluation of titanium–niobium biocompatibility and osteointegration and the lack of studies investigating coating these new proposed alloys with hydroxyapatite, this review aims to further knowledge on hydroxyapatite-coated titanium niobium alloys. [ABSTRACT FROM AUTHOR]

A novel TiB2-CeO2-modified (Nb,Mo,Cr,W)Si2 coating was prepared on a Nb-5W-2Mo-1Zr alloy substrate using two-step slurry sintering and halide-activated pack cementation to address the limitations of a single NbSi2 coating in meeting the service requirements of niobium alloys at elevated temperatures. At 1700 °C, the static oxidation life of the coating exceeded 20 h, thus indicating excellent high-temperature oxidation resistance. This was due to the formation of a TiO2-SiO2-Cr2O3 composite oxide film on the coating surface, which, due to low oxygen permeability, effectively prevented the inward infiltration of oxygen. Additionally, the dense structure of the composite coating further enhanced this protective effect. The composite coating was able to withstand over 1600 thermal shock cycles from room temperature to 1700 °C, and its excellent thermal shock performance could be attributed to the formation of MoSi2, CrSi2, and WSi2 from elements such as Mo, Cr, and W, which were added during modification. In addition to adjusting the difference in thermal expansion coefficients between the layers of composite coatings to reduce the thermal stress generated by thermal shock cycles, the formation of silicide compounds also improved the overall fracture toughness of the coating and thereby improved its thermal shock resistance. [ABSTRACT FROM AUTHOR]

Intermetallic titanium aluminides, leveraging the ordered γ-TiAl phase, attract increasing attention in aerospace and automotive engineering due to their favorable mechanical properties at high temperatures. Of particular interest are γ-TiAl-based alloys with a Niobium (Nb) concentration of 5–10 at.%. It is a key question how to model such ternary alloys at the atomic scale with molecular dynamics (MD) simulations to better understand (and subsequently optimize) the alloys. Here, we present a comparative analysis of ternary TiAlNb interatomic potentials developed by the moment tensor potential (MTP) and deep potential molecular dynamics (DeePMD) methods specifically for the above mentioned critical Nb concentration range. We introduce a novel dataset (TiAlNb dataset) for potential training that establishes a benchmark for the assessment of TiAlNb potentials. The potentials were evaluated through rigorous error analysis and performance metrics, alongside calculations of material properties such as elastic constants, equilibrium volume, and lattice constant. Additionally, we explore finite temperature properties including specific heat and thermal expansion with both potentials. Mechanical behaviors, such as uniaxial tension and the calculation of generalized stacking fault energy, are analyzed to determine the impact of Nb alloying in TiAl-based alloys. Our results indicate that Nb alloying generally enhances the ductility of TiAl-based alloys at the expense of reduced strength, with the notable exception of simulations using DeePMD for the γ-TiAl phase, where this trend does not apply. [ABSTRACT FROM AUTHOR]

This study aimed to investigate adhesive shear bond strength (SBS) on an ultrafine-grained niobium alloy (UFG-Nb) that is a potential dental implant material. SBS of three adhesive systems combined with three composites to UFG-Nb was compared to corresponding SBS to Ti-6Al-4V and to zirconia. Specimens of the substrates UFG-Nb, Ti-6Al-4V and zirconia with plane surfaces were sandblasted with Al2O3, cleaned and dried. Three adhesive systems (Futurabond U, Futurabond M + , Futurabond M + DCA; all VOCO GmbH, Cuxhaven, Germany) were applied each on specimens of each substrate and light cured. One composite (BifixSE, BifixQM, GrandioSO; all VOCO GmbH) was applied and light cured resulting in 27 groups (n = 10) for all substrate-adhesive-composite-combinations. SBS was measured after 24 h of storage. To simulate aging equally prepared specimens underwent 5000 thermocycles before SBS measurement. There was no significant difference in SBS within the non-aged groups. Among the artificially aged groups, GrandioSO-groups showed a greater variance of SBS than the other composites. All significant differences of corresponding UFG-Nb-, Ti-6Al-4V- and zirconia-groups with same adhesive-composite-combination (ACC) were observed between UFG-Nb and zirconia or Ti-6Al-4V and zirconia but never between the two metallic substrates. The similarity between these materials might show in their adhesive bonding behavior. As there were no differences comparing corresponding groups prior to and after artificial aging, it can be concluded that aging does not affect SBS to UFG-Nb, Ti-6Al-4V and zirconia using the tested ACCs. Adhesive bonding of established ACCs to UFG-Nb is possible resulting in SBS comparable to those on Ti-6Al-4V and zirconia surfaces. [ABSTRACT FROM AUTHOR]

This work investigated two titanium-based alloys with a constant tantalum content and variable contents of alloy additives – niobium and zirconium. The Ti-30Ta-10Zr-20Nb (wt.%) and Ti-30Ta-20Zr-10Nb (wt.%) alloys were obtained using a combination of powder metallurgy and arc melting methods. The influence of alloying additives on the structure and properties of the Ti-Ta-Nb-Zr system was studied using, among others: X-ray diffraction and scanning electron microscopy. The X-ray diffraction confirmed the single-β-phase structure of both alloys. In addition, the microscopic analysis revealed that a higher amount of zirconium favoured the formation of larger grains. However, the microhardness analysis indicated that the alloy with the higher niobium content had the higher microhardness. Importantly, the in vitro corrosion study revealed that the addition of niobium promoted the better corrosion resistance of the investigated alloy. [ABSTRACT FROM AUTHOR]

Biocompatible materials are natural or man-made substances kept in the body to turn a living cell into a working organ. Bone tissue and biocompatibility are emerging as an alternative approach to regenerating bone due to some distinct advantages over autografting and allografting. This research aimed to fabricate a novel porous scaffold Ti-Nb-Zr-Sn alloy that can be utilized as a bone substitute. Ti-Nb-Sn-Zr were selected by different weight ratios and synthesized using the powder metallurgy method. Zir- conium (Zr) is incorporated to get enhanced biological performance. The elements Ti, Nb with Zr, and Sn are utilized due to their excellent biocompatibility with the human body. The Ti-35Nb-7Zr-4Sn alloy has high tensile strength between 1042 and 1603 MPa by increasing Zr and Nb weight ratios. In addition, 35% Nb/7% Zr with 4% Sn composite show improved hardness, which is beneficial for resembling bone tissue and die-casting fittings in automobile applications. Fatigue and wear analysis is conducted to help us understand the behaviour of the Ti-Nb-Zr-Sn alloy. [ABSTRACT FROM AUTHOR]

This article studies the process of laser alloying of aluminum and alloy AL25 with metals: nickel, chromium, niobium, in a melting regime. Choice of metals for the study is made according to the criterion of efficiency of melt zone filling under laser treatment. Theoretical analysis of possible intermetallic phases within Al–Ni, Al–Cr, Al–Nb systems is performed, including physical parameters and crystallographic characteristics. Experimental studies by methods of metallography and X-ray diffraction analysis allows establishment of the spectrum of phases formed during alloying of aluminum from powders of these elements. They include both aluminum-rich intermetallics, and chemical compounds enriched with alloying metal. Alloying with niobium disilicide is also investigated to reveal differences in mechanisms of introducing chemical compounds into a laser-affected zone. On alloying with NbSi2 particles get into the melt zone directly from the powder (a mechanism of particle "flight"), and when alloying with pure metal intermetallic formation of occurs in situ during crystallization. On the basis of calculating the change in lattice spacing of aluminum the concentration of alloying metals within supersaturated solid solution is estimated. The increase in microhardness of alloying zones due to solid solution hardening and dispersion strengthening by intermetallic particles is established. [ABSTRACT FROM AUTHOR]

A family of TiHfZrNb high-entropy alloys has been considered novel biomaterials for high-performance, small-sized implants. The present work evaluates the role of niobium on passivation kinetics and electrochemical characteristics of passive film on TiHfZrNb alloys formed in Hanks' simulated body fluid by analyzing electrochemical data with three analytical models. Results confirm that higher niobium content in the alloys reinforces the compactness of the passive film by favoring the dominance of film formation and thickening mechanism over the dissolution mechanism. Higher niobium content enhances the passivation kinetics to rapidly form the first layer, and total surface coverage reinforces the capacitive-resistant behavior of the film by enrichment with niobium oxides and reduces the point defect density and their mobility across the film, lowering pitting initiation susceptibility. With the high resistance to dissolution and rapid repassivation ability in the aggressive Hanks' simulated body fluid, the TiHfZrNb alloys confirm their great potential as new materials for biomedical implants and warrant further biocompatibility testing. [ABSTRACT FROM AUTHOR]

The present work deals with the hot deformation behavior of commercial Nb alloy C-103 and its microstructure evolution during uniaxial compression tests in the temperature range of 700-1100°C and the strain rate range of 0.001-0.4 s-1. Strain rate sensitivity, calculated from the compression tests data, was almost constant and showed a negative value in the temperature range of 700-900°C but increased significantly beyond 900°C. Dynamic strain aging was found to have a predominant effect up to 900°C, beyond which dynamic recovery and oxidation influenced the compressive properties. The microstructure of the deformed samples showed indications of dynamic recrystallization within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. The 950-1000°C temperature range and strain rate range of 0.001-0.1 s-1 were suggested as suitable hot deformation conditions. The constitutive equation was established to describe the alloy's flow behavior, and the average activation energy for plastic flow was calculated to be 267 kJ/mol. [ABSTRACT FROM AUTHOR]

The conventional practice of heat-resistant nickel-alloys' brazing involves the utilization of industrial Ni-Cr-(B, Si)-based filler metals. However, employing filler metals within this system results in the formation of brittle compounds, specifically, silicides and borides of nickel, chromium, and other elements. These brittle phases have the potential to diminish the mechanical characteristics of brazed assemblies. This study investigates the feasibility of developing multicomponent high-entropy filler metals for brazing Nibased alloys (specifically, heat-resistant ones) without including boron and silicon in their composition. Utilizing computational methods and the updated Hume-Rothery rules, we identified a promising NiCoCrAl-(Ti, Nb) system. Various thermodynamic parameters are computed, and corresponding dependences on the alloying-components' content are established. The alloying limits of experimental alloys are determined, aligning with the criteria established for high-entropy alloys (HEA). Melting temperatures are calculated, and the liquidus-surface area of the NiCoCrAl-(Ti, Nb) system is delineated. Based on the research findings, it is determined that this alloy possesses a dendritic structure with some amount of eutectic component, and its melting temperature below 1220°C makes it suitable for brazing heatresistant nickel alloys. [ABSTRACT FROM AUTHOR]

The work is devoted to the study of bimetallic structures "titanium-steel" by electron beam freeform fabrication with the use of niobium and copper interlayers. A metallographic study of the deposited interlayers is carried out. The hardness distribution over the samples is shown. Technological issues according to deposition of niobium on titanium and steel on copper are pointed out. Tensile testing results reveal that the obtained structures have an ultimate tensile strength of 150–228 MPa and the fracture is located at the niobium-copper alloy side or at the niobium interlayer. The need to reduce the titanium content in niobium due to the occurrence of intergranular penetration of copper is demonstrated. [ABSTRACT FROM AUTHOR]

With advances in the thrust-weight ratio, the service temperature of gas turbine engines even exceeds 1500 °C, which is urgent for the development of high/superhigh-temperature thermal protection systems (TPSs) for long-term service. Niobium alloys are increasingly viewed as promising structural materials for high-temperature applications because of their superior high-temperature mechanical strength, but the “pest” catastrophic oxidation greatly restricts their further application. In this study, a HfC–HfO2-modified silicide coating was prepared via an innovative method of halide-activated pack cementation (HAPC) combined with liquid-plasma-assisted particle deposition and sintering of niobium alloys, resulting in a composite coating with excellent hot corrosion resistance and high-temperature oxidation resistance. This modified multilayer coating is characterized by the synergistic combination of a dense NbSi2 inner layer and a HfC–HfO2 porous outer layer, resulting in a significant improvement in high-temperature performance compared with that of the single NbSi2 coating. The corrosion gain of the composite coating is only 13.94 mg·cm−2 after a corrosion time of 200 h at 900 °C, and an intact oxide scale surface is observed after oxidation at 1500 °C for 500 min. This improvement is attributed to the formation of a robust Hf-rich skeleton provided by the deposited HfC–HfO2 layer, which can accelerate the formation of a highly stable corroded layer/oxide scale. In addition, multiple stress release mechanisms of the composite coating at high temperatures also provide substantial contributions to long-term service. All these merits make HfC–HfO2-modified composite coatings on niobium alloys competitive for the development of high/superhigh-temperature thermal protection systems for long-term service.

The economic importance, global market, primary resources and secondary sources of niobium are discussed in this paper. Niobium concentrate is the first commercial product of the enrichment process; however, the overwhelming majority of the niobium concentrate supply is processed into ferroniobium, which dominates international trade. In this form, niobium raw materials are used in the steel industry as an alloying agent (alloy additive). The production of\oxides and other compounds of niobium, such as carbides, alloys and metallic niobium are currently of much less commercial significance. The addition of a very small amount of niobium, of the order of 0.01%, changes the properties of steel fundamentally, increasing its strength, resistance to atmospheric factors or high temperatures, etc. The addition of niobium in other products also changes their properties, e.g. permanent magnets become superconductors. As a result, niobium is currently widely used around the world as a compo nent of sustainable technologies, which has a large positive impact on the environment by reducing the energy and material consumption of the manufacturing processes. The increase in the spectrum of niobium applications in advanced technologies, considered to be the technologies of the future, means that the widely recognized critical importance of niobium continues to grow. It can be assumed that the war between Ukraine and Russia will cause significant disturbances in the global metals market, including that for niobium. [ABSTRACT FROM AUTHOR]

The electrical characteristics of a point section of niobium oxide between a massive cathode made of a superconducting indium-tin alloy and a niobium film before the oxide breakdown and the nanocontact that appears after the breakdown of the oxide at room temperature have been studied. The dependencies of the point breakdown voltage of the oxide and the resistance of nanocontacts on the method of breakdown and the thickness of the oxide in the range of 15–60 nm have been established. In particular, a minimum value of the breakdown current has been established (about 1 μA), below which breakdown does not occur. The voltage-current characteristic (VCC) of the oxide has a semiconductor character and indicates the dependence of the breakdown voltage of the oxide on its polarity. The VCC of the nanocontact is nonlinear, which is associated with phase transitions in the nanocontact material caused by its heating by the transport current. [ABSTRACT FROM AUTHOR]

A novel NbSi 2 /Nb 2 O 5 -SiO 2 /MoSi 2 multilayer thermal protection ceramic coating is designed and fabricated via halide-activated pack cementation and liquid-plasma-assisted particle deposition and sintering technology, endowing the coating with multiple high-temperature protective properties. The incorporation of MoSi 2 nanoparticles not only gives superior high-temperature oxidation resistance/hot corrosion resistance of coating by forming a dense SiO 2 barrier layer, but also promotes passive radiative heat dissipation. When NbSi 2 /Nb 2 O 5 -SiO 2 /MoSi 2 coating was prolonged exposure to air at 1250 °C for 50 h of oxidation and at 900 °C for 100 h of corrosion, the mass gains are only 0.37 mg/cm2 and − 0.52 mg/cm2, respectively. The multilayer coating exhibits enhanced emissivity (>0.88) over the thermal infrared range of 3–20 µm, due to the lattice vibrational absorption-matching synergy of Nb 2 O 5 , SiO 2 , and MoSi 2 , as well as the mutual doping of SiO 2 /Nb 2 O 5 , mismatch of atoms at the interface, and a high degree of lattice distortion within the coating. [ABSTRACT FROM AUTHOR]

Niobium alloy C-103 is a refractory alloy used in the manufacturing of spacecraft propulsion components for its mechanical properties at elevated temperatures. Fair weldability makes C-103 additively manufacturable (printable) utilizing laser powder-bed fusion (L-PBF). Printed C-103 parts are often subjected to hot isostatic pressing (HIP) to obtain a microstructure with fewer defects and more isotropic properties. Brief exposures to high-temperature environments are common for C-103 parts; experimentally, a high-vacuum annealing (HVA) process was employed to identify changes from temperature effects apart from the HIP process. This study compares the effects of HVA and HIP processes on the microstructure (i.e., grain size, morphology), formation of precipitates, microhardness, and anisotropy of C-103 fabricated by L-PBF. The results showed recrystallization and texture changes occurred during HIP but not HVA, contributing to retained, albeit altered, anisotropy in the HVA-ed material. The microhardness of HVA-ed C-103 was greater and more anisotropic than HIP-ed for annealing temperatures below 1200°C. Hafnium oxide precipitates were observed in all the samples and which coarsened with increasing HVA temperature. Oxide area% determined via image analysis showed a strong negative correlation with microhardness. Overall, this paper presents novel findings on the effects of HVA and HIP on C-103 printed via L-PBF and forms a basis for future post-processing of C-103 parts. [ABSTRACT FROM AUTHOR]

The results of studying a composite material based on Nb–Si–C are presented. The alloy was obtained by aluminothermic self-propagating high-temperature synthesis. To prepare the initial charge a mixture of powders of commercial niobium pentoxide Nb2O5 and commercial silicon carbide SiC was used. The process of niobium oxide Nb2O5 reduction was implemented using an aluminum powder. The study of the Nb–Si–C ternary system is of interest in terms of obtaining high-temperature materials of new generation for gas turbine engine construction capable of replacing heat-resistant nickel alloys, as well as the potential possibility of forming MAX phases (Mn + 1AXn phases, where n = 1, 2, 3, ... ; M is the transition d-metal; A is the p-element; and X is carbon). The phase composition of the obtained Nb–Si–C composite was studied by X-ray diffraction. It has been shown that as a result of high-temperature synthesis NbC carbide and γ-Nb5Si3 and NbSi2 silicides are formed which are competing relative to the Nb2SiC MAX phase. The formation of Nb2SiC under the selected synthesis conditions was not detected. Using scanning electron microscopy and X-ray spectral analysis, the morphological distribution of the phases formed during high-temperature synthesis is analyzed in detail. It is shown that NbC carbide makes up the majority of the volume of the composite and is present in the form of pyramidal-shaped particles with a pyramid face size of ~10 μm. NbSi2 silicides are elongated rod-shaped particles with smooth edges measuring 30 × 80 μm; Nb5Si3 silicides do not have a specific shape. [ABSTRACT FROM AUTHOR]

This article presents the results of studies of the features of the development of thermoelastic martensitic transformations during cooling/heating in the free state and under load of Ti50Ni49.7−XNbXMo0.3 alloys (X = 0.5, 1.0 and 1.5 at% Nb) with shape memory effects. Using X-ray diffraction analysis, it was found that all the alloys studied at room temperature contained a multiphase mixture consisting of intermetallic compounds with the TiNi (B2, B19′), Ni56Ti29Nb15, and Ti2Ni compositions. Scanning electron microscopy was used to study the microstructure of TiNi (Nb,Mo) alloys and it was found that the distribution of fine Ni56Ti29Nb15 particles in the matrix depends significantly on the concentration of the alloying element. A correlation was established between changes in the structural-phase state in TiNi (Nb,Mo) alloys and the occurrence of the B2↔B19′ martensitic transition in the free state and under load. Based on physical and mechanical studies, the temperature ranges of the martensitic transformations (MT) in the free state and under load were established. Based on the thermodynamic description of the MT and the analysis of the characteristic temperatures of the MT, it was found that the MT mechanism is strongly dependent on the concentration of the alloying element. [ABSTRACT FROM AUTHOR]

Objective: To investigate the trends of research on niobium (Nb) in dentistry to determine its use in dental materials. Material and Methods: Electronic searches were carried out in six databases. Studies that evaluated niobium alloys in dentistry in vitro, in situ, and in vivo (humans and animals) were included. Data on publication year, authors, country, journal, study design, application area, niobium alloy, study approach, assay type and results (positive, negative and null compared to controls) were grouped and analyzed in VantagePoint™ and Excel. Descriptive analyses of frequency, cross-tables and co-occurrence matrices were performed. Results: After screening, 315 studies published between 1977 and 2021 were included, with an increase in publications between 2011 and 2021 (n=209; 66.3%). “Doi, H” was the top author (n=9; 2.8%), and Brazil was the most productive country (n=70; 22.2%). “Dental Materials” was the major contributing journal (n=24; 7.6%), and most studies were carried out in vitro (n=266; 84.4%), under implant surfaces (n=162; 51.4%), followed by dental prostheses (n=77; 24.4%) and restorative materials (n=27; 8.6%). The most common niobium was a ternary alloy (n=147; 46.7%), which was mainly tested in vitro via structural characterization or material improvement (n=131; 41.6%). Mechanical assays (n=114; 36.2%) were the most prevalent. Positive effects of niobium were found in 264 articles (83.8%), and negative effects were found in 13 articles (4.1%). Conclusion: The number of studies on niobium has increased over time, resulting in improvements in the mechanical properties of materials used in dental practice. [ABSTRACT FROM AUTHOR]

The pivotal role of metal implants within the host's body following reconstructive surgery hinges primarily on the initial phase of the process: the adhesion of host cells to the implant's surface and the subsequent colonization by these cells. Notably, titanium alloys represent a significant class of materials used for crafting metal implants. This study, however, marks the first investigation into how the phase composition of titanium alloys, encompassing the volume fractions of the α, β, and ω phases, influences cell adhesion to the implant's surface. Moreover, the research delves into the examination of induced hemolysis and cytotoxicity. To manipulate the phase composition of titanium alloys, various parameters were altered, including the chemical composition of titanium alloys with iron and niobium, annealing temperature, and high-pressure torsion parameters. By systematically adjusting these experimental parameters, we were able to discern the distinct impact of phase composition. As a result, the study unveiled that the colonization of the surfaces of the examined Ti–Nb and Ti–Fe alloys by human multipotent mesenchymal stromal cells exhibits an upward trend with the increasing proportion of the ω phase, concurrently accompanied by a decrease in the α and β phases. These findings signify a new avenue for advancing Ti-based alloys for both permanent implants and temporary fixtures, capitalizing on the ability to regulate the volume fractions of the α, β, and ω phases. Furthermore, the promising characteristics of the ω phase suggest the potential emergence of a third generation of biocompatible Ti alloys, the ω-based materials, following the first-generation α-Ti alloys and second-generation β alloys. [ABSTRACT FROM AUTHOR]

This paper reports a study whose object was material of the weld. The nature of changes in the microstructure of the weld material, which are caused by changes in the supplied energy, alloying elements and heat removal from the melt area, was investigated. Welding was performed with an electron beam at Uacc=60 kV, Ieb=90 mA, with an elliptical sweep of 3×4 mm. The speed of electron beam movement veb was varied from 7 to 15 mm·s-1. The temperature of the experimental welded samples T0 was varied from 300 K to 673 K. Ti-TiB alloy (a microcomposite alloy with reinforcing TiB fibers) was welded with Ti-TiB alloys, T110, and with niobium. One of the tasks of welding this alloy was to preserve and optimize the structure of this type in the weld. Grinding of boride fibers, loss of their initial orientation, and formation of a dendritic or cellular microstructure was observed in the weld. Using the methods of raster electron microscopy and micro-X-ray spectral analysis, the microstructure of the weld material was investigated and the dimensional characteristics of TiB fibers under different welding conditions were determined. The analysis of changes in the microstructure of the weld material, the average length ᶏ and the thickness ȩ of the boride fibers in the material of the joints made at different velocities of electron beam movement and initial temperatures T0 was carried out. It was established that the growth of the ratio ȩ/ᶏ from 0.04–0.07 to 0.1–0.27 is accompanied by significant changes in the micro-structure and the mechanism of formation of eutectic phases. It is shown that the process that determines the formation of the micro-structure of the weld material was the eutectic breakdown with the determining influence of the temperature gradient, crystallization rate, supercooling, concentration inhomogeneities, and alloying impurities. [ABSTRACT FROM AUTHOR]

The present study investigated existing and potential approaches for hot cracking analysis of cast alloys and showed a promising and very applicable new specimen for high alloyed steels. The reliability of this specimen has been demonstrated by adding niobium to alloy HH (ASTM A297), or alloy 1.4837 (ISO 11973). Niobium shows a very positive impact on hot cracking behavior and can thereby reduce scrap in steel foundries. Amounts above 0.6 wt% niobium can reduce the size and number of hot cracks significantly. The reduction of hot cracking tendency was quantified by the cracking factor CFNb2. The positive effect is associated with the reduction in solidification interval length that was measured by thermal analysis and the observed "healing" of cracks in the microsections. Both effects are promoted by niobium. The promotion of the ferritic solidification seems to have no positive impact on the hot cracking behavior. [ABSTRACT FROM AUTHOR]

Nickel- and cobalt-based superalloys are commonly used as turbine materials for high-temperature applications. However, their maximum operating temperature is limited to about 1100 °C. Therefore, to improve turbine efficiency, current research is focused on designing materials that can withstand higher temperatures. Niobium-based alloys can be considered as promising candidates because of their exceptional properties at elevated temperatures. The conventional approach to alloy design relies on phase diagrams and structure–property data of limited alloys and extrapolates this information into unexplored compositional space. In this work, we harness machine learning and provide an efficient design strategy for finding promising niobium-based alloy compositions with high yield and ultimate tensile strength. Unlike standard composition-based features, we use domain knowledge-based custom features and achieve higher prediction accuracy. We apply Bayesian optimization to screen out novel Nb-based quaternary and quinary alloy compositions and find these compositions have superior predicted strength over a range of temperatures. We develop a detailed design flow and include Python programming code, which could be helpful for accelerating alloy design in a limited alloy data regime. [ABSTRACT FROM AUTHOR]

Nb alloys with high strength and relatively low density are sought for high-temperature applications. However, due to strain softening, conventional Nb alloys often exhibit insufficient high-temperature strengths. Here we report a strategy to design a novel lightweight and thermally-stable Nb alloy by combining the notion of eutectics and refractory carbide. The resulting Nb2MoWC0.96 eutectic alloy exhibits a high-temperature specific compressive strength of 77.2 MPa/·cm3·g1 at 1673 K with a retained engineering plasticity of 37.5%, both are notably higher than the existing Nb and Nb-containing alloys. This work demonstrates that both the strength and plasticity of Nb alloys can be further optimized with refractory carbide and eutectics.

Electrochemical coatings of chromium modified with diamond nanoparticles applied directly on niobium-aluminum alloy were obtained. Diamond nanoparticles produced by detonation synthesis were used. Chromium coatings were deposited on a monolithic composite with a complex structure based on niobium and aluminum alloys, called later matrix for short. Standard chromium electrolyte and electrolyte with diamond nanoparticles concentration of 10 g/L were used. The surface morphology of the chromium coating was investigated with an atomic force microscope and NanoScope V system (Bruker Inc., Germany). Analyzes were performed by scanning electron microscope, Bruker Inc. system and PolyvarMet metallographic microscope. The microhardness was measured using PolyvarMet 4000 microhardness tester. The obtained results of the microhardness are 6800 MPa in the chromium layer and 1400 and 6400 MPa in the matrix. The average thickness of the chromium coatings modified with diamond nanoparticles is 40–45 µm. [ABSTRACT FROM AUTHOR]

This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining (PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications. Three processes are involved simultaneously i.e. spark erosion, chemical etching, and abrasive grinding for removal of material while the classical electrochemical discharge machining process involves double actions i.e. spark erosion, and chemical etching. The powder-mixed electrolyte process resulted in rapid material removal along with a better surface finish as compared to the classical microelectrochemical discharge machining (MECDM). Further, the results are optimized through a multiobjective optimization approach and study of the surface topography of the hole wall surface obtained at optimized parameters. In the selected range of experimental parameters, PMECDM shows a higher material removal rate (MRR) and lower surface roughness (Ra) (MRR: 2.8 mg/min and Ra of 0.61 mm) as compared to the MECDM process (MRR: 2.01 mg/min and corresponding Ra of 1.11 µm). A detailed analysis of the results is presented in this paper. [ABSTRACT FROM AUTHOR]

This work investigated two titanium-based alloys with a constant tantalum content and variable contents of alloy additives - niobium and zirconium. The Ti-30Ta-10Zr-20Nb (wt.%) and Ti-30Ta-20Zr-10Nb (wt.%) alloys were obtained using a combination of powder metallurgy and arc melting methods. The influence of alloying additives on the structure and properties of the Ti-Ta-Nb-Zr system was studied using, among others: X-ray diffraction and scanning electron microscopy. The X-ray diffraction confirmed the single-ß-phase structure of both alloys. In addition, the microscopic analysis revealed that a higher amount of zirconium favoured the formation of larger grains. However, the microhardness analysis indicated that the alloy with the higher niobium content had the higher microhardness. Importantly, the in vitro corrosion study revealed that the addition of niobium promoted the better corrosion resistance of the investigated alloy. [ABSTRACT FROM AUTHOR]

Results of detailed investigations by the method of transmission electron microscopy are presented, and evaluation was performed in the system of chemical composition→structure→properties of welded joints produced by electron beam welding of experimental high-temperature multicomponent titanium alloys doped by niobium and silicon. It was found that in order to eliminate the gradient by strength and fracture toughness, it is necessary to ensure formation of a homogeneous dispersed platelike structure at uniform distribution of the density of dislocations and phase precipitate particles. Such a structure will ensure a high level of mechanical properties and crack resistance of metal in titanium alloy welded joints. 20 Ref., 2 Tabl., 6 Fig. [ABSTRACT FROM AUTHOR]

Novel spark plasma sintering (SPS) of W–Ti–Al–V–Cu containing Nb-based alloys, representing a new generation of refractory materials, are novel candidates for structural applications. Ni superalloys are currently used at temperatures close to their melting point. Therefore, a novel generation of refractory alloys is being applied at even higher temperatures. When compared to other refractory metals for applications in higher temperature environments, Nb-based alloys have shown great prominence owing to higher melting point. However, their applications have not yet been widely implemented. Indeed, there is a lack of research which might improve some restrictive aspects of Nb alloys, such as low temperature oxidation resistance as well as poor fracture toughness and ductility. To fill this gap, novel alloys with composition Nb-xW-15(Ti6Al4V)–1Cu (x = 5, 10 and 15 wt.%) were developed via SPS at 1400 and 1500 °C (with and without pre-compression). The alloys microstructure, density, hardness and oxidation resistance were characterized. X-ray diffraction and energy dispersive spectroscopy microanalysis confirmed the formation of Nb, Ti and W solid phases solution, as well as intermetallic, AlTi3, TiO2 and TiC compounds. The highest densification (97.5%) was obtained in the alloy with the highest content of 15 wt.% W sintered at 1500 °C and pre-compressed. Despite a lower hardness, it exhibited a parabolic oxidation kinetics from the beginning of the oxidation test. This behavior was attributed to the higher amount of Nb2O5, which increased the oxidation resistance of the alloy.

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The addition of refractory metals represents a promising approach for development of future high-entropy alloys (HEAs). Niobium and molybdenum are particularly suitable additives for increasing hardness as well as wear and corrosion resistance. In the context of surface protection applications, eutectic high-entropy alloys (EHEAs) with their homogeneous property profile are of specific interest. In the present work, two EHEAs were developed starting from the alloy Al0.3CoCrFeNi using electric arc melting. Following mechanical and microstructural characterization, the two alloys were found to have the compositions Al0.3CoCrFeNiMo0.75 and Al0.3CoCrFeNiNb0.5. For thermal spray processing, powders of the above alloys were prepared by inert gas atomization. The coatings produced by high-velocity oxy-fuel spraying (HVOF) were characterized and evaluated compared with castings, allowing process–structure–property relationships to be derived. Based on the results, statements on possible application potential can be made. [ABSTRACT FROM AUTHOR]

The aerospace components operating in hot sections of aero-engines and combustors experience extreme environments. Typically, the components are subjected to high service temperatures exceeding 1100°C and oxidizing conditions. Protective coatings are essential for preventing oxidation-induced dimensional degradation of the components and enhancing their high temperature capability as well as durability. Defence Metallurgical Research Laboratory (DMRL) has developed a variety of metallic and ceramic Thermal Barrier Coating (TBC) systems for Ni-base superalloys, and refractory Nb-alloys for strategic aerospace applications involving ultra-high temperatures and high flow velocities. These coatings have demonstrated significant effectiveness against thermal degradation at temperatures as high as 2000 °C during oxidation in static air as well as in dynamic conditions involving high flow velocities (Mach > 2). The present article provides an overview of the advanced oxidation resistant and thermal barrier coatings developed in DMRL. The effectiveness of the TBCs in preventing dimensional degradation of the metallic and composite substrate materials has been evaluated at the laboratory scale. The developed TBCs have the potential for use in aero-engines and propulsion systems of hypervelocity vehicles. [ABSTRACT FROM AUTHOR]

Nb alloys with high strength and relatively low density are sought for high-temperature applications. However, due to strain softening, conventional Nb alloys often exhibit insufficient high-temperature strengths. Here we report a strategy to design a novel lightweight and thermally-stable Nb alloy by combining the notion of eutectics and refractory carbide. The resulting Nb2MoWC0.96 eutectic alloy exhibits a high-temperature specific compressive strength of 77.2 MPa/·cm3·g1 at 1673 K with a retained engineering plasticity of 37.5%, both are notably higher than the existing Nb and Nb-containing alloys. This work demonstrates that both the strength and plasticity of Nb alloys can be further optimized with refractory carbide and eutectics. Combining the notion of eutectics with refractory carbide makes high strength, large plasticity Nb alloy with good microstructural stability. [ABSTRACT FROM AUTHOR]

Multi-functional integrated thermal protection coating is a promising approach for the high-temperature protection of niobium alloy while facing multiple extremely harsh environments, while hard to avoid the complex/multi-step preparation process. Particularly, a simultaneous demonstration of multi-functional features is still challenging. Herein, a novel HfC-HfO 2 -MoSi 2 -Yb 2 O 3 multi-functional layer has been fabricated on the NbSi 2 layer surface via plasma-assisted particle deposition manufacturing, endowing the modified silicide-based multilayer composite coating with multiple thermal protective characteristics. The composite coating shows excellent hot corrosion resistance with a corrosion gain of 3.56 mg cm−2 after 200 h, the intact coating structure after three thermal cycles of fast rise and fall from 25 °C–1800 °C, and a high thermal emissivity of above 0.9, as well as the good high-temperature oxidation resistance and ablation resistance demonstrated in our previous study. The superior multiple thermal protective characteristics are attributed to the synergistic effects of multi-functional particles. HfC particle provides the anti-ablation skeleton, MoSi 2 particle provides more SiO 2 glass phase and seals defects, Yb 2 O 3 particle acts as the stabilizer of glass network, and matching vibration absorption of multiphase/multi-chemical bonds endow the high emissivity of coating. Our work paves the new way and provides an inexpensive and environmentally friendly approach for the development of a new class of multi-functional integrated thermal protection materials. [ABSTRACT FROM AUTHOR]

A low-grade ore containing 4 % niobium and 7 % titanium has been extracted from Bayan Obo tailing, but its potential has not been fully utilized. This study aims to recover the niobium and titanium elements from this low-grade ores in the form of their carbides. The process involves reducing niobium and titanium to (Nb,Ti)C through a carbothermal process. During this process, iron and silicon are also reduced to Fe-Si intermetallic compounds, allowing (Nb,Ti)C to diffuse into them. Subsequently, selective electrochemical oxidation is used to separate (Nb,Ti)C from the Fe-Si intermetallic compounds in an aqueous ferrous sulfate solution. The Fe-Si intermetallic compounds are first oxidized to the Fe 3 Si phase, and then to the Fe 5 Si 3 phase in the solution with pH 0.35. The (Nb,Ti)C/matrix interfaces are identified as the preferred site of electrochemical pitting corrosion. By exploiting the electrochemical oxidation reaction of iron in the matrix, (Nb,Ti)C powders are separated along these interfaces. The by-products of this process are FeSi alloys, which are evaluated for their electrocatalytic properties in oxygen evolution reactions. It is found that the Fe 5 Si 3 alloy by-product exhibits good electrocatalytic activity and kinetics in the oxygen evolution reaction, demonstrating its potential for practical applications. [Display omitted] • An innovative technology was proposed to utilize low-grade niobium ores. • Two high-value materials, (Nb,Ti)C and Fe 5 Si 3 OER catalyst, was extracted. • The (Nb,Ti)C/matrix interfaces are identified as the preferred corrosion sites. [ABSTRACT FROM AUTHOR]

Niobium alloys play an indispensable role in aerospace technology. However, traditional niobium alloys has unsatisfactory or high-temperature strength or limited room-temperature. This work introduces Nb 2 Mo x W y C 0.25 alloys with strength-plasticity balance by optimizing refractory alloy elements and eutectic carbides drawing on the design concepts of eutectic high-entropy alloys. The influence of Mo and W contents on the microstructure and mechanical properties of the alloys was studied. The Nb 2 Mo x W y C 0.25 alloy contain body-centered cubic (BCC) primary phase and eutectic structures composed of BCC and carbide phases with semi-coherent interfaces. Appropriate additions of Mo and W refine the grain size of the primary BCC phase and cause the carbide phase to evolve from Nb 2 C to NbC. The Nb 2 Mo 0.5 W 0.5 C 0.25 hypoeutectic niobium alloy composed of BCC and Nb 2 C phases with a relatively small lattice mismatch has a room-temperature yield strength of 1.27 ± 0.04 GPa, compressive strength of 2.03 ± 0.06 GPa, and a fracture strain of 17.8 ± 2.2 %. Solid solution strengthening in the BCC phase and second-phase strengthening of the carbide phase simultaneously enhance the alloy. The fine grain strengthening, reduced crack origination at low mismatch interface, and the crack tip by soft BCC at the phase interface improve the plasticity simultaneously. This paper provides a method to improve the room-temperature plasticity and strength of refractory niobium alloys, laying the foundation for the industrial application of refractory niobium alloys. • By adjusting the content of Mo and W, Nb 2 Mo x W y C 0.25 forms a eutectic structure composed of BCC and carbide phases with semi-coherent interfaces, enhancing its performance. • Nb 2 Mo 0.5 W 0.5 C 0.25 hypoeutectic niobium alloy has a yield strength of 1.27 GPa, compressive strength of 2.03 GPa, and a fracture strain of 17.8 %. • Solid solution strengthening in the BCC phase and second-phase strengthening of the carbide phase simultaneously enhance the alloy. The fine grain strengthening and the crack tip by soft BCC at the phase interface improve the plasticity simultaneously. [ABSTRACT FROM AUTHOR]

[Display omitted] • Room temperature moduli of most Nb-alloys agree well with mole fraction weighted rule-of-mixture calculations. • A single, linear temperature dependence of the elastic properties is suggested for all Nb-alloys considered in this study. • A single Smith-Palmer equation adequately describes the thermal conductivity most of the Nb-based alloys investigated. • Thermal conductivity of WC-3009 is significantly lower than the thermal conductivity than the other Nb-alloys investigated. • A performance index is introduced for lightweight, panel-shaped applications subject to thermal gradients or transients. There is renewed interest in refractory alloys that possess higher service temperatures than incumbent Ni-based superalloys (⪆1100 °C). Thermophysical property data for six Nb-alloys are gathered from the literature and reviewed, and new data are provided for two Hf-containing Nb-alloys; elastic modulus, thermal expansion, thermal conductivity, and heat capacity are presented for C103, and new thermal conductivity data are provided for a higher strength alloy, WC-3009. Comparisons with Ni-superalloys and other refractory-metal based alloys provide context. Physics-based models are provided that describe the temperature dependencies of the Young's modulus, coefficient of thermal expansion and density, and thermal conductivity; such that fair comparisons can be made across alloys for any given condition. The results suggest a need for improved understanding of the temperature dependence of the elastic modulus. A performance index is introduced for making informed materials selection decisions in the context of lightweight, panel-shaped applications subjected to sharp thermal transients or steep thermal gradients, and the significant strain rate sensitivity of Nb-alloys is highlighted. Ultimately, the relative value of current commercial alloy, C103, as well as the promise of specific Nb-W-Zr alloys are highlighted. [ABSTRACT FROM AUTHOR]

Zirconium-niobium alloy is widely used in pressurized-water-reactors (PWRs) due to its excellent performance. Herein, the effects of Nb on the formation, migration, and clustering of vacancies/interstitials in Zr-Nb solid solution are studied using first-principles calculations. Nb lowers the formation energy of Zr interstitials and significantly enhances the anisotropy of Zr interstitial migration in the vicinity. Nb shows thermodynamic attraction to vacancies while causes a significant decrease in the vacancy migration barrier, which enhances the mobility of vacancies around Nb. In addition, we find that the vacancy-mediated Nb migration is anisotropic, and these Nb-vacancy interactions play an important role in revealing the mechanism of the precipitation of needle-like Nb phases under high irradiation fluences. Finally, we verified the anisotropic attraction of Nb to vacancies with CI-NEB method. These findings will contribute to a more in-depth comprehension on the mechanism how Nb influences the evolution process of irradiation defects in Zr-Nb alloys. [ABSTRACT FROM AUTHOR]

This paper presents a new method of modelling that combines several approaches to anticipate the softening of nickel-niobium alloys during dynamic recrystallization (DRX). The study employs an extensive dataset obtained from hot torsion deformation tests conducted on high-purity nickel and six nickel-niobium alloys. The niobium concentration in these alloys varies from 0.01 to 10 wt % (Matougui et al., 2013). The hybrid technique integrates the Avrami model to provide early predictions about the kinetics of recrystallization and then uses mechanistic modelling to assess the progression of softening caused by dynamic recrystallization (DRX). The integrated technique is improved by using Gaussian process regression analysis, which investigates the softening properties and offers useful insights into the effects of niobium additions on dynamic softening behaviour. This unique hybrid framework combines multiple modelling tools to reveal intricate connections impacted by solute addition, therefore enhancing our comprehension of the physical events that take place during the hot deformation of superalloys. The use of empirical, mechanistic, and machine learning methods in this hybrid model provides a more thorough and detailed investigation of DRX processes in these alloys. [Display omitted] • Hybrid model combines machine learning and Avrami formalism for recrystallization kinetics. • Zener-Hollomon values increase with Nb content, affecting strain rate sensitivity in Ni-Nb alloys. • Novel approach integrates empirical, mechanistic, and machine learning methods for DRX modelling. • Model provides insights for optimizing industrial superalloy production processes. [ABSTRACT FROM AUTHOR]

Niobium (Nb)-based alloys have not yet been considered to replace nickel (Ni)-based alloys as engineering component in high temperature applications. In spite of its elevate melting temperature, Nb is known for very limited oxidation resistance as well as lower fracture toughness and ductility. These disadvantages combined with relatively high cost, have not favor the high temperature engineering applications of Nb-based alloys. Therefore, for the first time, the present work developed spark plasma sintered novel Nb-based alloys with additions of Ni, Cu and WC, that allowed them to compete with conventional, Ni-based alloys. Alloys with composition Nb-xNi-2Cu–2WC (x = 5, 10 and 15 wt.%) were fabricated by sintering at 1000, 1100 and 1200 °C. The novel alloys microstructure, porosity, hardness and oxidation resistance were characterized and evaluated. X-ray diffraction analysis revealed the formation of Nb2C, δ Ni3Nb intermetallic. Nb alloy with 10 wt.% Ni spark plasma sintering at 1200 °C displayed superior properties of 97% densification, 1205 Vickers hardness, coherent granular Nb2O5 oxides, and 1.84 × 10−7 g2cm4.s−1 oxidation parabolic rate, as compared to other common Nb alloys and some conventional Ni-based alloys for high temperature applications.