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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]

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]

• The microstructure evolution of cold rolled Nb-5W-2Mo-1Zr alloy sheets is studied. • With the increase of deformation, the combination texture is formed eventually. • The mechanism of cold deformation of Nb-5W-2Mo-1Zr alloy is elucidated. In this study, the effect of cold rolling deformation from 10 % to 50 % was investigated on the microstructure evolution of Nb-5W-2Mo-1Zr alloy sheets. Microstructure observations showed that cold rolling deformation changed the texture of the sheets. At low deformation levels, the texture transitioned from an annealed {001} 〈1−10〉 orientation to a deformation-induced {112} 〈1−10〉 plate texture. As deformation increased, novel slip systems activated, transforming the deformation texture into a combination of {001} 〈1−10〉 and {111} 〈1−10〉 plate textures. In the grain interior, small-angle grain boundaries proliferated, the dislocation density intensified, and strain accumulated, resulting in the formation of fresh slip bands. [ABSTRACT FROM AUTHOR]

• A W-Cu composite and Nb alloy multi-material structure was fabricated using WAAM. • This structure exhibited no significant defects, such as porosity or cracks. • A hard Nb 3 W intermetallic phase formed at the interface. • The tensile strength achieved was 218 ± 3 MPa with an elongation of 5.7 ± 1 %. Integrating tungsten and niobium alloys into a single component offers synergistic benefits for fusion reactor applications. Additive manufacturing, particularly for components with complex geometries, further amplifies these advantages. This study examines the fabricability of a multi-material structure composed of a W–Cu composite and an Nb–Zr alloy using wire-arc additive manufacturing. The resulting W–Cu/Nb–Zr structure was free from significant defects like porosity or cracks, though the formation of hard intermetallic compounds was observed. Numerical analysis indicated considerable residual stress accumulation at the interface. During tensile testing, fractures occurred in the W–Cu composite near the interface, with the specimens exhibiting an ultimate tensile strength of 218 ± 3 MPa and an elongation of 5.7 ± 1 %. [ABSTRACT FROM AUTHOR]

• Multi-particles/multilayer synergistic design strategy for enhancing the high-temperature oxidation resistance. • In-situ Nb 2 O 5 -SiO 2 layer provides a good interface matching between the NbSi 2 layer and particle deposition layer. • The multi-particles exhibit an excellent coupling effect for retarding the oxidation rate of silicide coating. • "Hf-Yb" skeleton significantly improves the thermal stability and stress damage tolerance of the oxide layer. Multilayer composite design for thermal protective coating has proven to be promising for improving the high-temperature oxidation resistance of aerospace components. However, a series of problems such as the interface mismatch, dependable production method, and difficulty in forming a stable oxide scale, etc., make the scalable production of the multilayer composite coating with high efficiency, and low cost, along with achieving superior high-temperature oxidation resistance remains a long-time endeavor. Herein, a brand-new NbSi 2 /Nb 2 O 5 -SiO 2 /HfC-HfO 2 -MoSi 2 -Yb 2 O 3 multilayer protective ceramic coating is synthesized by the multi-particles/multilayer synergistic design strategy. The multi-particles outer layer acts as the first oxygen erosion barrier, while the in-situ Nb 2 O 5 -SiO 2 layer and the NbSi 2 bottom layer are the second and third oxygen shielding layer for niobium alloys separately. Moreover, the in-situ Nb 2 O 5 -SiO 2 layer also provides a good interface matching, and the co-existent multilayer makes a powerful thermal protection system. The incorporation of the high content of multi-particles in the outer layer is not only beneficial to reduce the inward oxygen flux through the oxygen diffusion barrier layer, but also improves the stress damage tolerance and thermal stability of the oxide scale by forming HfSiO 4 -Yb 2 O 3 -SiO 2 skeleton layer. Thereby, the multilayer-coated sample reduces the oxide scale thickness to 128 μm after being exposed to 1200 ℃ for 120 h, which is only 67 % compared to the NbSi 2 -coated sample (100 h, 192 μm), and simultaneously holding the intact structure after a short-time oxygen acetylene ablation above 1800 ℃. This work paves a new way to design next-generation thermal protective coatings with great potential for applications. [ABSTRACT FROM AUTHOR]

The MoNbTaW refractory multicomponent alloy (RMCA) retains good yield strength up to 1873K, but limited plasticity and high density at room temperature impede its utility in practical applications. Thus, a unique alloy design approach based on composition modification was used to improve these properties. Among the four constituent elements of the MoNbTaW alloy, Nb has good plasticity and lower density; hence a series of alloys with varying Nb content, namely Nb x (MoTaW) (1-x) with x = 0.4, 0.55, and 0.7 (designated as Nb 0.4 , Nb 0.55, and Nb 0.7 in this manuscript), were processed using vacuum arc melting. X-ray diffraction results showed that all the alloys formed as single-phase with the body-centered cubic crystal structure. The microstructures of these RMCAs are dendritic in nature with segregation of elements that decreased with heat treatment. The hardness values showed a decrease as the Nb content increased. The compressive yield strength values are 1251, 1055, and 945 MPa, and those of fractured strain are 10, 22, and 33 % for Nb 0.4 (MoTaW) 0.6 , Nb 0.55 (MoTaW) 0.45 , and Nb 0.7 (MoTaW) 0.3 respectively. The increase in plastic strain and toughness is due to the increment in the Nb concentration, which is directly interpreted as an enhancement in degree of plasticity. The average grain sizes of Nb 0.4, Nb 0.55, and Nb 0.7 RMCAs are measured to be 86 μm, 106 μm and 145 μm respectively. It was observed that 36 % of the grains are above 100 μm for Nb 0.4 alloy, whereas this fraction is increased to 49 % and 60 % for Nb 0.55 and Nb 0.7 alloys respectively, which indicates an increase in average grain size as well as fraction of coarser grains as the Nb content increases. Hence, the improvement in plasticity is attributed to the increase in the average grain size and broader grain distribution. Fracture surface analysis of all the compositions showed quasi-cleavage behavior. This study demonstrates that increasing the Nb concentration in the MoNbTaW RMCA enhances plasticity while decreasing density. In comparison to conventional niobium alloys like C103 and FS-85, the alloys of the present study had higher yield strength at the temperatures where the tests were carried out. The specific yield strength values of these alloys are found to be higher than commercially available Nb alloys. • Nb x (MoTaW) (1-x) RMCAs resulted in a single phase BCC structure. • With increasing Nb, flow stress and hardness decreased while plasticity increased. • RMCAs showed superior high-temperature flow stress than C103 and FS-85 Nb alloys. [ABSTRACT FROM AUTHOR]

With the rapid development of nuclear industry, advanced niobium alloys with high strength and irradiation resistance are urgently required. In this work, a new multi-component Nb 80 Mo 10 Zr 10 Cr 10 Al 5 B 0.1 alloy has been designed, and the yield strength in compression can reach ∼1100 MPa, and plastic strain is ∼11.3%. To reveal the irradiation damage mechanism, both the NbMoZrCrAlB alloy and pure Nb samples have been irradiated by Xe ion at 350 °C and 750 °C, with the fluence of 2.1 × 1015 ions/cm2. The average diameter of Xe bubble under 750 °C irradiation is only ∼2.92 nm in NbMoZrCrAlB alloy, which is smaller than that of pure Nb (∼ 9.22 nm). Consequently, the volume swelling ratio is only 0.04% in NbMoZrCrAlB alloy, which is largely lower than that of ∼0.65% in pure Nb. Meanwhile, both the average diameter and number density of dislocation loops in NbMoZrCrAlB alloy are obviously decreased compared with pure Nb at the same irradiation temperature. This result should arise from the severe lattice distortion and sluggish diffusion in present NbMoZrCrAlB alloy, which is similar with the high entropy alloy. The present work provides a reference for designing novel Nb based alloys for advanced nuclear materials. [Display omitted] • The yield stress of the novel Nb alloy can reach ∼1100 MPa. • The novel Nb alloy shows a low swelling(0.04%) at elevated temperature irradiation. • The novel Nb alloy shows a distinct decrease in number density of dislocation loops compared with pure Nb. [ABSTRACT FROM AUTHOR]

To protect niobium alloy against water-vapor corrosion at high temperatures, an innovative ZrO 2 -modified Yb 2 SiO 5 environmental barrier coating was prepared via supersonic atmosphere plasma spraying. The service life of the modified coating (50 h) is 10 times higher than the pristine due to the higher fracture toughness (2.07 MPa∙m1/2) to inhibit cracking during frequent thermal cycles. With exposure prolonging, the in-situ formation of (Zr,Yb)O 2 solid solution would weaken the fracture toughness of the coating by hindering the phase transformation of ZrO 2 from cubic to monoclinic, while improving the corrosion resistance of the coating by enhancing atomic bonding strength. • The water vapor corrosion behavior of the coatings was tested up to 1500 °C. • Higher fracture toughness of the ZrO 2 -modified Yb 2 SiO 5 coating (2.07 MPa∙m1/2) enabled the longer service life (50 h). • Disorder-to-order structural changes appeared in the (Zr,Yb) 2 solid solution caused by the rearrangement of Zr and Yb atoms. • The (Zr,Yb) 2 solid solution weakened the fracture toughness by inhibiting cubic-to-monoclinic phase transformation. • Improvement of the Zr-O and Yb-O atomic bonding strength leads to better corrosion resistance. [ABSTRACT FROM AUTHOR]

Langmuir isotherm adsorption theory is involved in the conventional model to predict the corrosion resistance of Nb and Nb alloys. It is illustrated that the anti-corrosion properties of Nb are dependent on the crystal plane, pH values and solution temperature. Nb(110) plane with the lowest E surf /ρ and the highest E esc present the slower dissolution of Nb atoms, and then exhibits the best anti-corrosion performance. Alloying with Cr, Cu, Mo, Ti and Ta destroys the stability of Nb(110) plane and thus degrades the corrosion resistance performances. Moreover, the anti-corrosion performance is improved with increasing pH values because of the decreasing coverage of H+ ions. The escape rate of Nb atoms will be accelerated at the elevating temperature, and thus the anti-corrosion performance be degraded. Therefore, an appropriate design of coating texture and solution environment could improve the anti-corrosion performances of bipolar plates. [Display omitted] • Langmuir theory is used to modify the current density equations of HER reaction. • The derived current density curves are consistent with the reported data. • The effect of crystal planes and environments on corrosion resistance is studied. • Corrosion resistances of Nb and Nb alloys in different solutions are predicted. [ABSTRACT FROM AUTHOR]

A continuous electron beam scanning process was used for the surface treatment on U-5.5Nb alloy, under various combinations of beam current, beam accelerating voltage, and scanning speed. The transverse cross-section characteristics of the resulting modification layers were metallographically measured to investigate the relationship between the electron beam processing parameters and the fusion zone geometry or the resolidification microstructure. Results showed that the resolidified modified layers were obtained with the bulk energy density (E 0 *) value exceeding 60.7 J/mm3. An "equiaxed-columnar-equiaxed" sandwich-type grain structure was formed in the resolidification fusion zone under the effects of local temperature gradient (G) and the growth rate (R). Different from that of traditional surface modified alloys, the cross-sectional microstructure of surface modified U-5.5Nb alloy consists of four characteristic areas: fusion zone (FZ), heat affected zone (HAZ), base metal (BM), and partially fusion zone (PFZ). The width (W) and depth (D) of the fusion zone had an almost linear increase with the bulk energy density (E 0 *). The Vickers hardness, Nb composition, and phase microstructures were also examined. The surface hardness values increased significantly following surface treatment, which was mainly attributed to phase transformation. [ABSTRACT FROM AUTHOR]

[Display omitted] The mechanism of formation of zirconium nitride-based ceramics in the single-stage high-temperature nitridation of Zr–Nb alloys with different niobium contents (0.1–10 at%) in a wide temperature range was determined using an oxidative constructing approach. In the process of nitridation, the segregation of a metallic niobium phase occurred with the subsequent formation of NbN. This should be taken into account when producing new high-temperature materials with unique functional properties [ABSTRACT FROM AUTHOR]

We report on atomic-scale analyses of grain boundary (GB) structures and segregation in Nb 3 Sn coatings on Nb, prepared by the vapor-diffusion process, for superconducting radiofrequency (SRF) cavity applications, utilizing atom-probe tomography, high-resolution scanning transmission electron-microscopy and first-principles calculations. We demonstrate that the chemical composition of Nb 3 Sn GBs is correlated strongly with the diffusion of Sn and Nb at GBs during the coating process. In a sample coated with a relatively large Sn flux, we observe an interfacial width of Sn segregation at a GB of ∼3 nm, with a maximum concentration of ∼35 at.%. After post-annealing at 1100 °C for 3 h, the Sn segregated at GBs disappears and Nb segregation is observed subsequently at GBs, indicating that Nb diffused into the Nb 3 Sn GBs from the Nb substrate. It is also demonstrated that the amount of Sn segregation in a Nb 3 Sn coating can be controlled by: (i) Sn flux; and (ii) the temperatures of the Nb substrates and Sn source, which may affect the overall kinetics including GB diffusion of Sn and Nb. An investigation of the correlation between the chemical compositions of GBs and Nb 3 Sn SRF cavity performance reveals that the Nb 3 Sn SRF cavities with the best performance (high-quality factors at high accelerating electric-field gradients) do not exhibit Sn segregation at GBs. Our results suggest that the chemical compositions of GBs in Nb 3 Sn coatings for SRF cavities can be controlled by GB engineering and can be utilized to optimize fabrication of high-quality Nb 3 Sn coatings for SRF cavities. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Two different structures of MoSi 2 coatings were prepared on Niobium based alloys by using a two step process. The as-deposited type(a) MoSi 2 coating structure consists of a MoSi 2 layer on the surface and a NbSi 2 layer underneath, while the type(b) MoSi 2 coating consists of an outer MoSi 2 layer and an inner unsiliconized Mo layer. The oxidation behaviors of the two different types MoSi 2 coatings were examined at 1200 °C for 100 h in air, and the mass gains of type(a) and type(b) MoSi 2 coated specimens were 0.64 mg/cm2 and 0.59 mg/cm2 respectively. The excellent oxidation resistance of both type(a) and type(b) MoSi 2 coated samples at 1200 °C was due to the formation of a dense and continuous SiO 2 scale during oxidation. As the CTE mismatch between the outer MoSi 2 coating and the inner layer, cracks distributed within both type(a) and type(b) MoSi 2 coating structures. [ABSTRACT FROM AUTHOR]

White cast iron (WCIs) alloys were developed by adding Nb, Mo, and a combination of both (∼3 wt% Nb, ∼3 wt% Mo, ∼1 wt% Mo-2 wt% Nb) through melting and casting. The objective was to analyze the microstructural characteristics of the alloys, as well as the impact of reinforcing carbides on their mechanical and tribological properties. The alloy containing the highest percentage of niobium exhibited a refined microstructure, tending towards a eutectic structure, unlike the Mo-containing materials with totally hypoeutectic microstructures. The microstructural characteristics of the alloys and morphology of niobium carbides, as well as the percentage of M 7 C 3 eutectic carbides produced were affected by the varying percentages of Nb and the Mo–Nb combination. Moreover, thermodynamic simulations revealed that the NbC carbide precipitated before the M 7 C 3 eutectic carbides, austenite dendrites, and the MC (composed mainly of Nb containing bound Mo) carbide resulting from the Mo–Nb combination. The alloys containing Mo had similar bulk hardness values, while the alloy with the highest percentage of Nb showed a higher bulk hardness value. This was attributed to the effect of Nb on microstructure refinement and on the production of M 7 C 3 eutectic carbides from the alloy. Although there were different reinforcing carbides (NbC, MC and M 2 C), the differences in microstructural characteristics had no noticeable influence on the Charpy impact energy. Micro-scale abrasive wear test (conducted with SiC abrasive slurry) demonstrated that the reinforcing carbides MC and mainly NbC had a beneficial effect in blocking and preventing the progression of continuous micro-cuttings and formation of grooves. The M 7 C 3 and M 2 C carbides were less effective at protecting the matrix against the high-hardness SiC abrasive. [Display omitted] • White cast irons with added reinforcing carbide-forming were developed. • Microstructural changes had strong effects on the properties of alloys. • Reinforcing carbides had different effects on the properties of alloys. • Nb had multiple effects on the microstructural characteristics of the alloys. [ABSTRACT FROM AUTHOR]

In this study, the LPDS-coating charactered by the volcanic-like surface with micropores is synthetized on Nb alloys through halide activated pack cementation (HAPC) combined with a liquid-plasma-assisted particle deposition and sintering (LPDS) technology. Results show that the mass gain of NbSi 2 /Nb 2 O 5 -SiO 2 /HfC-HfO 2 coated sample (6.38 mg/cm2) is only 46% compared to NbSi 2 coated sample (13.8 mg/cm2) and holds the lowest oxidation rate (0.367 mg2·cm−4·h−1) during the isothermal oxidation process after 100 h at 1200°C. Besides, this multilayer coating also exhibits an enhanced oxyacetylene ablation resistance (the lowest mass ablation rate of −0.106 mg/s and a linear ablation rate of −0.333 μm/s) compared with NbSi 2 coating and NbSi 2 /Nb 2 O 5 -SiO 2 coating. Such superior high-temperature oxidation/oxyacetylene ablation resistance of multilayer coating are mainly ascribed to HfC oxygen-consuming phase combined with the oxide scale's high-temperature stability provided by the HfSiO 4 -HfO 2 -SiO 2 skeleton. • NbSi 2 /Nb 2 O 5 -SiO 2 /HfC-HfO 2 multilayer coating is designed to enhance the high-temperature oxidation/ablation resistance. • HfC particle is introduced into multilayer coating by a simple LPDS technique. • A dense oxygen diffusion barrier layer is formed by introducing HfC particle for retarding the oxide rate of coating. • HfSiO 4 -SiO 2 skeleton processes a large stress damage tolerance, exhibiting a strong high-temperature stability. [ABSTRACT FROM AUTHOR]

Nb-based C103 is an increasingly relevant material for aerospace applications due to recent advances in additive manufacturing (AM). AM enabled complex component geometries, along with the associated surface roughness, are a challenge to the survival of environmental barrier coatings (EBCs), like R512E. EBCs are necessary to provide protection for the oxidation susceptible C103 substrates in elevated temperature, oxidizing environments. This work leveraged cyclic thermal exposures to understand the role of AM surface finish on the residual stress, the oxidation protection mechanisms, and the survivability of the R512E coated C103, with insight into the corner geometry-dependent performance supported by finite element modeling (FEM). The experimental characterization indicated that the rough surface finish from AM resulted in increased voids within the build layers in the diffusion formed coating, which in conjunction with tensile residual stress along the substrate interface, negated the coating protection during thermal cycling. Conversely, the coating applied to prepared surfaces indicated survivability throughout the exposures. Furthermore, the coating's experimental corner-dependent performance was consistent with the FEM results, highlighted by increased damage around sharp corners with improved coating performance at a fillet corner. These experimental and model results inform the surface and corner preparation requirements to leverage the benefits of AM in R512E coated C103 for elevated temperature applications. • Rough, L-DED C103 surface features caused increased damage in as-cured coating. • Spallation and coating protection negated due to AM substrate surface features. • Coating applied to substrates with prepared surfaces survived high heat flux torch. • Residual stress results revealed crack initiating stress and gradients at interface. • Modeled stress increase was consistent with local coating damage at sharp corners. [ABSTRACT FROM AUTHOR]

A NbSi 2 /Nb 2 O 5 -SiO 2 /SiC multilayer coating was developed on niobium alloys to improve the hot anti-corrosion and infrared thermal radiation performance simultaneously. This novel modified silicide coating includes a NbSi 2 inner layer, a Nb 2 O 5 -SiO 2 pre-oxidation intermediate layer, and a SiC particle deposition and sintering outer layer, showing a strong multilayer synergistic. This multilayer design strategy endows the coating a high emissivity above 0.9 at 700 °C across the entire range of wavelength (3–20 μm), significantly enhancing the infrared thermal radiation performance than that of the NbSi 2 coating and PEO-coating. Accordingly, the enhanced infrared radiation performance is ascribed to the synergistic effects of vibrational absorption between the Nb 2 O 5 , SiO 2 and SiC phase in the ceramic outer layer over multiple bands, as well as the porous surface structure of LPDS-coating; Meanwhile, the as-prepared LPDS-coated specimen exhibits an excellent anti-corrosion performance with a mass gain of −0.56 mg/cm2 under the hot corroded environment for 100 h. The improved hot anti-corrosion performance is main the result of a synergistic effect between a dense pre-oxidation layer and a continuous SiO 2 film layer with self-sealing, as well as the SiC providing an extra Si source substantially. A novel NbSi 2 /Nb 2 O 5 -SiO 2 /SiC multilayer protective ceramic coating has been designed and prepared on silicide coating by using a one-step liquid-plasma-assisted particle deposition and sintering (LPDS) technology, which achieves a superior hot corrosion resistance and infrared thermal radiation performance. [Display omitted] • NbSi 2 /Nb 2 O 5 -SiO 2 /SiC coating is designed and constructed through a new multilayer co-growing strategy. • The incorporation of SiC nanoparticles gives superior hot corrosion resistance of the coating. • The enhanced hot corrosion resistance is mainly ascribed to the formed SiO 2 molten salts barrier layer. • The incorporation of SiC nanoparticles improves the high-temperature broadband emissivity (>0.9). [ABSTRACT FROM AUTHOR]

In this research, the effect of weld fluid flow in molten pool on the formation and behavior of intermetallic compounds NbNi 3 and Nb 7 Ni 6 and HfO 2 precipitates in dissimilar electron beam welding of niobium base alloy C-103 to nickel was investigated. It was observed that due to the large difference in the melting temperature of the base metals, nickel contributed 82% by volume and C-103 contributed 18% by volume in weld zone. In the weld zone and attached to the C-103 base metal, a thin and continuous intermetallic zone was formed, including the initial phase of NbNi 3 and the eutectic structure of NbNi 3 +Nb 7 Ni 6. In the areas after the continuous intermetallic layer in welding, the initial phase of NbNi 3 and the eutectic structure of NbNi 3 +γ-Ni are formed. During welding, HfO 2 particles in the C-103 base metal enter the molten pool due to the weld fluid flow and remain as white precipitates in the welding zone and close to C-103. In addition to these precipitates, nanometer precipitates of HfO 2 are also observed in the weld, which are formed in-situ in the weld due to the reaction of hafnium with dissolved oxygen in the melt. In the central zone of the weld, continuous band-shaped intermetallic layers can be observed which have been removed from the wall of C-103 due to the fluid flow of the molten pool and moved towards the central zone of the weld. These layers act as nucleus in the center of the molten pool and solidification occurs from their surface. At first, solidification begins with the planar growth of the initial phase of NbNi 3 , and then cellular and columnar dendritic growth occurs. At the end of solidification, the eutectic structure of NbNi 3 +γ-Ni forms between cells and dendritic branches. Due to the presence of intermetallic compounds NbNi 3 and Nb 7 Ni 6 as well as HfO 2 nanometer precipitates in the weld, the hardness of the weld zone was higher than that of the base metals. • The effect of weld fluid flow on the formation mechanism of NbNi 3 , Nb 7 Ni 6 , and HfO 2 precipitates was investigated. • In the welded zone the initial phase are NbNi 3 and the eutectic structure of NbNi 3 + Nb 7 Ni 6. • Cellular growth occurs and NbNi 3 solidified cells grow in direction perpendicular to the continuous intermetallic layers. • Dendritic growth is observed and finally, the eutectic structure of NbNi 3 + Ni is formed between cells and dendrites. • The tensile strength of the weld was obtained as 119.5 MPa and the failure occurred from this part. [ABSTRACT FROM AUTHOR]

Recent efforts to develop Refractory Multi-Principal Element Alloys (RMPEAs) for high temperature applications have led to a renewed interest in elucidating fundamental properties of refractory metals. These metals can dissolve high concentrations of interstitial oxygen to the detriment of their mechanical properties and oxidation resistance. Strategies are therefore sought to control the oxygen solubility of refractory alloys. Even in simple dilute refractory alloys, the underlying mechanisms driving binding energies between substitutional solutes and oxygen is not fully understood. We have used first principles calculations of Nb-X-O alloys to examine the interactions between interstitial oxygen and dilute substitutional solutes X = Al, Si, Sc, Ti, V, Cr, Y, Zr, Mo, Ru, Hf, Ta, W, and Re in BCC Nb. Electronegativity differences drive charge transfer between the Nb matrix and both the substitutional and interstitial solutes. This transfer of charge results in strong electrostatic interactions at short distances that play a key role in determining X-O binding energies. The solute misfit volume, which leads to local straining of the surrounding BCC Nb lattice, is also found to have a strong effect on the X-O binding energies. Finally, we identify a repulsive interaction, of significance for a subset of X-O pairs, that arises from a closed-shell hybridization between localized orbitals on solutes. [Display omitted] [ABSTRACT FROM AUTHOR]

Ternary alloys of general composition (TiFe) 100-x M x (M = Co, Nb) have been synthesized from pure metals through high-energy ball milling. The maximum concentration of alloying components allowing formation of single phase TiFe-type compounds has been defined as 2 at.%. The hydrogenation behavior of the mechanical alloys in comparison with the arc-melted ones of the same composition has been studied by a combination of volumetric and calorimetric techniques. Influence of the alloy composition and the synthesis mode on the crystal structure of TiFe and its hydrides has been evaluated. It has been shown that the thermochemical method based on calorimetric titration provides more accurate information about phase transformations in the nanocrystalline metal hydride systems. The obtained results show that the third components slightly affect the hydrogen storage performance of non-equilibrium mechanical alloys in contrast with alloys produced by conventional melting. • Single phase mechanical alloys TiFe Co and TiFe Nb have been synthesized. • Hydrogenation features were studied by PCI measurement and calorimetric titration. • Structure parameters of the hydride phases have been defined through XRD. • Concentration limits of phase regions have been evaluated calorimetrically. • Mechanical alloying reduces the impact of additives. [ABSTRACT FROM AUTHOR]

The paper presents the results of investigations concerning the formation and high temperature oxidation behavior of silico-boronized coatings on C103 Nb-base alloy. The coatings were obtained by boronizing and subsequent siliconizing using pack cementation method which resulted in the formation of inner NbB 2 and outer NbSi 2 layers. The coated C103 alloy was subject to isothermal oxidation test at 1100 °C for 1000 h during which the coating provided protection against high temperature oxidation of the base material. The oxidation behavior was studied using SEM and STEM methods and the samples from the metal-scale interface were prepared by Focused Ion Beam method. It was shown that during high temperature exposure the reaction between the NbSi 2 and NbB 2 layers results in the formation of Nb 5 Si 3 and T2 phases. The oxidation process is hindered at the front of this reaction where mixed oxide scale was found consisting of Nb 2 O 5 , NbO 2 and borosilicate glass. • Microstructural characterization of silico-boronized coatings on C103 is presented. • The coatings on C103 alloy contain outer NbSi 2 and inner NbB 2 layers. • Obtained coatings provide high temperature oxidation protection up to 1000 h at 1100 °C. • Formation of borosilicate glass during high temperature oxidation was observed. [ABSTRACT FROM AUTHOR]

Austempered ductile iron (ADI) is a heat-treated nodular iron variant that has for a given strength level much higher elongation than conventional iron with spheroidized graphite. This paper considers the effect of niobium addition on the graphite microstructure, bainite microstructure, bainite transformation process and properties such as hardness and impact toughness under given heat-treatment conditions. The resulting properties are significant with regard to the wear resistance of the material. The effects of niobium addition on the graphite morphology can be understood based on a detailed precipitation analysis of the niobium precipitation behavior in the liquid phase. Niobium influences the temperature and kinetics of pearlite as well as bainite transformation. Furthermore, niobium refines the bainite microstructure generated during austempering treatment. It was found that niobium addition in the range of 0.2–0.5 wt percent allows obtaining an optimum combination of hardness, impact toughness and wear resistance. [ABSTRACT FROM AUTHOR]

Abstract Oxidation behaviors of halide activated pack cementation (HAPC) silicide coatings on niobium alloy were elaborately studied by experimental and theoretical analysis. The HAPC process was performed with a commonly applied powder pack of Si, NH 4 F, and Al 2 O 3 filler. Adsorptive Al 2 O 3 particles from the pack from HAPC process played a positive role against oxidation at 700 °C (the so-called pest temperature). Above this temperature, the passion behavior rather than pulverization gradually appeared by the occurrence of seal-healing SiO 2. However, the seal-healing effect was meanwhile weakened by the generation of the volatilized Si-O (g) species when the temperature rose up to the eutectic point of Nb 2 O 5 -SiO 2 system. Continuously temperature-elevated (1500–1700 °C) oxidation overwhelmingly destroyed the surface protective scale by the depletion of melting Nb 2 O 5 and the volatilization of SiO 2 (g), leading to a catastrophic failure of structural integrity for the coated samples. Highlights • Oxidation behaviors of silicide coating on Nb alloy were comparatively investigated. • Adsorptive particles block the oxidation at the so-called pest temperature. • Nb 2 O 5 was restricted by the seal-healing SiO 2 at 700–1200 °C. • Seal-healing effect was weakened near eutectic point of the Nb 2 O 5 -SiO 2 system. • Surface scale was overwhelmingly destroyed at temperatures above the eutectic point. [ABSTRACT FROM AUTHOR]

Abstract A specimen with a newly designed composition was produced using shielded metal arc welding by changing the Nb content. To evaluate the susceptibility of ductility-dip cracking (DDC), tensile test and hardness measurement were performed, and to examine the behaviors of precipitates during heat treatment, the microstructures were observed using an optical microscope and a scanning electron microscope. As the Nb content increased, the hardness of the specimen improved through solution hardening, and as the hardness increased, the yield strength in the tensile test results increased. Furthermore, as the Nb content increased, the amount of Cr-rich carbide precipitated at the grain boundary decreased and the amount of transgranular Nb-rich carbides increased. This increased the susceptibility of DDC and the critical strain at which the DDC begins to appear at tension increased. The microstructure analysis of a specimen heat-treated at 715 °C revealed that the intergranular Cr-rich carbides became continuous and coarse through the diffusion of Cr, and the tensile test results showed that DDC occurred at a strain lower than that of the as-weld specimen. In the specimen heat-treated at 1100 °C, the intergranular Cr-rich carbides were melted and the intergranular precipitates were removed. Highlights • DDC susceptibility decreases as the amount of carbide increases at grain boundaries. • As the Nb content increased, the amount of Cr-rich carbide decreased. • The amount of carbide at grain boundary increases during the heat treatment. • The carbide is melted during the heat treatment at a temperature near the melting point. [ABSTRACT FROM AUTHOR]

Abstract A ternary immiscible nanostructured Cu-Al-Nb alloy was fabricated by friction stir processing of mechanically compacted pellets. Subsequently, aging was carried out at 563 K for various times. The material exhibited hardness of ~4.3 ± 0.1 GPa in the peak-aged condition (aging for 6 h), which is remarkable among Cu-based ternary immiscible alloys. The excellent strength of the material is attributed to Hall-Petch strengthening due to the extremely refined nanocrystalline structure, coupled with precipitation strengthening due to a uniform distribution of nano-scale Al- and Nb-rich precipitates or clusters, as confirmed by X-ray diffraction and microstructural characterization. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Highlights • The Niobium is component of metal alloys, used in various industry sectors. • The use of Nb in the steel industry shows that 90.2% is used in the manufacture of high-strength steel. • The LCA tool can be used in the metallurgy from the extraction of the ore, production and disposal. • The exploitation of raw materials through mining is responsible for impacts caused to the environment. Abstract In recent decades, environmental issues and the emphasis on sustainable development has resulted in increasing pressure to use natural resources more efficiently and reduce the generation and emission of industrial waste. Therefore, the metallurgical industry has focused on the exploration and processing of Niobium (Nb). The use of Nb in heat treatments at high temperatures as superalloys began in 1970. During recent years, the application of Nb for different uses, such as micro-alloyed steels, superalloys, thin films, medical implants, titanium and aluminium alloys, superconductors and copper alloys, and electrolytic and ceramic capacitors, has increased steadily. In this study, life cycle assessment tools were used to develop a diagrams which as proposed as a model for the LCA of Nb. For this propose, LCA tools were used to develop diagram of the beneficiation process of ore containing Nb, and quantify the mass balance with respect to the finished products and solid, liquid, and gaseous waste. The data showed that 2200 kg of FeNb and 300 kg of Nb 2 O 5 were produced from 100 t of ore containing 2.5% of Nb, and that ore beneficiation damages the environment. Moreover, the use of Nb is essential in the metallurgical industry for the advancement of numerous fields in science and technology. [ABSTRACT FROM AUTHOR]

• Successful fabrication of TZM-NbZr1 bimetallic structure using wire-based DED. • Fabricated structure did not form any cracks and intermetallic compounds. • Non-uniformly distributed pores in NbZr1 matrix near to TZM-NbZr1 interface. • Ultimate tensile strength of 249 ± 126 MPa with elongation less than 6 % was achieved. The outcome of this study highlights the feasibility of additively manufactured bimetallic structures from refractory alloys for high-temperature applications. Using a wire-based directed energy deposition (DED) process, a bimetallic structure composed of molybdenum alloy (TZM) and niobium alloy (NbZr1) was successfully fabricated. The TZM-NbZr1 interface displayed no significant defects, such as cracks or delamination, and showed no presence of intermetallic compounds. A few pores were observed on the deposited NbZr1 side near the interface. During uniaxial tensile testing, the specimen's failure occurred on the NbZr1 side in close proximity to the interface, resulting in an ultimate tensile strength of 249 ± 126 MPa and an elongation of less than 6 %. [ABSTRACT FROM AUTHOR]

GH3535 and 2 wt.% Nb-modified GH3535 (Nb-GH3535) alloys were irradiated with 1.2 MeV He ion at fluences of 1 × 1016, 3 × 1016 and 1 × 1017 ions/cm2 at 750 °C. Microstructural changes, including the formation of He bubbles and superlattice phases, as well as the irradiation-induced hardening, were investigated by TEM and nanoindentation. Notably, Nb-GH3535 exhibited a smaller size and lower number density of He bubbles, especially at higher fluences, indicating the inhibitory effect of Nb on bubble evolution. First-principles calculations revealed that the presence of Nb inhibits the combination of He atoms and vacancies, reducing their diffusion rate and consequently impeding the nucleation and growth of He bubbles. Furthermore, the addition of Nb facilitates the irradiation-induced precipitation of the superlattice phase, leading to a higher degree of total hardening in Nb-GH3535 alloy. [ABSTRACT FROM AUTHOR]

This study aims to analyze the influence of niobium and zirconium in the structure, microstructure, and mechanical properties of quaternary Ti-25Ta-Zr-Nb alloys system: Ti-25Ta, Ti-25Ta-10Zr-15Nb, and Ti-25Ta-20Zr-30Nb (wt%). The structural and microstructural analyses were performed using X-ray diffraction, as well as optical, scanning and transmission electron microscopy. Rietveld method was used for calculating the volume fractions of crystalline phases and values of β lattice parameters. Williamson-Hall's equation calculated the micro-strain and average size of the β-phase crystallite. The mechanical properties were analyzed by microhardness and Young's modulus measurements. The results show that the different heat treatments influence the structure of the materials and the mechanical properties: Rapid cooling treatments induced the formation of α″ and β for Ti-25Ta-10Zr-15Nb (TTZN1), while the treatments with slow cooling induced the formation of α phases. The Ti-25Ta-20Zr-30Nb (TTZN2) alloy is a stable β, so heat treatments could not change the crystalline structure. To Ti-25Ta alloy, in all study conditions, the alloy has α + α″ phases. Regarding the lattice parameters, adding niobium to the alloys increased the lattice parameter of the β phase. Concerning the β phase micro-strain and average crystal size, the heat treatments increased the average size and micro-strain due to the crystallization of the crystals. β-Ti alloys in the solubilized heat treatment condition, followed by rapid cooling, showed better mechanical biocompatibility results due to the low elastic modulus, highlighting the metastable β Ti-25Ta-10Zr-15Nb alloy, which showed a low elastic modulus of 50 GPa. • Zr act as a β-stabilizing element when combined with Nb addition to Ti-25Ta alloys; • Young modulus decreases in metastable β-Ti alloy (Ti-25Ta-10Zr-15Nb) • High addition of Nb and Zr formed stable β-Ti alloys with high Young modulus values; • The Ti-25Ta-10Zr-15Nb alloy has Young modulus value of 50 GPa. [ABSTRACT FROM AUTHOR]

Intermetallic γ (TiAl)-based alloys find their application as high-temperature materials for aero engine and automotive components. Microstructure optimization and microalloying play key roles in optimizing these alloys. Several pioneering experimental works showed improved mechanical properties of γ (TiAl)-based alloys containing Niobium (Nb). Despite Nb being a key alloying element, its contribution remains debated, if not least understood, due to the TiAl microstructure's complexity with hierarchical interfaces. This work examines the effects of Nb on the high-temperature deformation behavior of TiAl alloys using atomistic simulations. These revealed that Nb alloying retarded the stress-induced phase transformation of γ → α 2 , favoring a refined microstructure with the dislocation sources from microstructure boundaries and interfaces at high temperature and improving thus the ductility. Our microstructure-informed atomistic models reveal a comprehensive picture of the underlying nanomechanical events. • In-depth study of Nb contributions with varying chemical and microstructure environments in TiAl alloys at atomic resolution. • Nb proximity to microstructure boundaries plays an important role besides the ratios of twin- and phase boundaries. • A novel insight on Nb delaying the γ to α 2 phase transformation to improve ductility at the cost of the strength. [ABSTRACT FROM AUTHOR]

This study aims at checking the suitability of Nb-1% Zr-0.1% C alloy as coolant channel for carrying molten lead-bismuth eutectic (LBE). Molten LBE is used to carry heat from the reactors to heat exchangers in the compact high temperature reactors. Corrosion properties of the base metal (BM), heat-affected zone (HAZ) and fusion zone (FZ) of the weld of niobium alloy were compared at the temperature of 1050 °C in LBE solution in open-air condition. The presence of lead and bismuth at grain-boundary and triple junctions of the grain boundaries is evitable in both the BM and FZ, and the material loss can be attributed to oxidation corrosion. Nb 2 O 5 and NbO 2 being brittle and permeable oxides of niobium did not inherit the characteristics of hindering further oxidation-corrosion at elevated temperature. The corrosion rates of FZ, HAZ and BM were observed to be equal to 24.16 mm/year, 20.83 mm/y and 27.80 mm/y, respectively, and this difference occurred mainly due to the formation of nitrides of zirconium (ZrN) and carbides of zirconium (ZrC) and niobium (NbC). ZrO 2 could be confirmed by the micro-hardness profile, which appeared to be flat throughout the FZ and BM. The formation of these carbide and nitride phases was confirmed through XPS and XRD analyses. The differences of surface roughness values expressed in root mean square (Sq.) values, determined before and after the corrosion, were found to be equal to 0.267 and 0.230 for the base metal and weld zone, respectively. It signifies that FZ was more corrosion-resistant than BM. It is not recommended to use this alloy in open-air condition for the coolant channels, due to the high corrosion rate in the BM, FZ and HAZ, which leads to material loss beyond the acceptable limit. [Display omitted] • Deals with Laser welding of Nb-Zr-C Alloy. • Studies corrosion analysis of Nb-Zr-C Alloy in lead-bismuth eutectic solution. • Deals with oxidation corrosion of Nb-Zr-C Alloy. • Does not recommended the use of Nb-Zr-C Alloy in open atmosphere. [ABSTRACT FROM AUTHOR]

Abstract A study into the effects of irradiation temperature on the damage structures that form during proton-irradiation has been carried out on two commercial Zr alloys in order to develop a more mechanistic understanding of the effect of niobium on dislocation loop evolution. The two Zr alloys (Zircaloy-2 and Low-Sn ZIRLO™) were proton irradiated to a damage level of ∼2 dpa at 280 °C, 350 °C and 450 °C. Detailed dislocation analysis was carried out using on-axis bright-field scanning transmission electron microscopy combined with spectral imaging and synchrotron x-ray line profile analysis. The analysis revealed a significant difference in the effect of irradiation temperature on loop size between the two alloys. In the case of the Nb-free Zr-alloy (Zircaloy-2), an increase in irradiation temperature results in a marked increase in a-loop diameter, by a factor of ∼7.5 from 280 to 450 °C, and a stark decrease in the dislocation line density. In contrast, the Nb-containing Zr-alloy (Low-Sn ZIRLO™) showed very little variation of loop size and line density over the same radiation temperature range. The STEM-based spectral imaging revealed irradiation-induced nano-clustering found throughout the matrix in Low-Sn ZIRLO™, which is not present in the case of Zircaloy-2. Therefore, it is proposed that Nb plays a crucial role in the evolution of dislocation loops in Zr through the formation of irradiation precipitation throughout the matrix. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Laser welding was performed on a U6wt%Nb uranium alloy using a 400 W solid state laser with welding speeds from 20 to 2500 mm/s. This speed range spanned melt pool sizes from traditional welding to surface modification and additive manufacturing. With increasing scan speed, the ratio of weld length relative to depth and width increased, with melt pool lengths being more than 5x greater than the width and 10x greater than the depth at the highest speeds. Keyhole mode welds were shown to occur at low speeds, while conduction mode welds occurred at 700 mm/s or higher as the weld depth dropped off more rapidly than width at higher speeds. Microstructures that form at the boundary between the fusion zone and base metal were observed to have a nonconventional appearance consisting of interpenetrating dark and light contrast phases before cells or dendrites appear. Dendrites with secondary arms form from this boundary in keyhole welds and refine to no visible secondary arms near the weld center. Primary and secondary dendrite arms, where present, were shown to refine in size inversely with cooling rate raised to the 0.465 and 0.375 powers respectively. Dendrites were largely absent from the conduction mode welds at higher speeds, and were replaced by a banded microstructure that appears to form by an oscillatory solidification front mechanism. Graphical abstract A solid-state fiber laser was used to make welds on an as-cast U6Nb alloy with a fixed laser power of 400 W and travel speeds from 20 to 2500 mm/s. Microstructure refinement of approximately 10x was shown to occur as the scan speed increased from 20 mm/s to 2500 mm/s, and the corresponding calculated cooling rate, ε, increased from 7.1 × 103 K/s to 2.4 × 106 K/s. Primary and secondary dendrite arm spacing and solidification band spacing measurements in cast U 6Nb plotted on log-log coordinates versus: a) laser scan speed, and b) calculated cooling rate in the center of the six welds that were numerically modeled. Best fit parameters to the cooling rate data are indicated. Image 1 [ABSTRACT FROM AUTHOR]

Abstract The strong and ductile single-phase body-centered-cubic (BCC) HfNbTaTiZr refractory high-entropy alloy (RHEA) is a potential structural material for high-temperature applications. However, the BCC phase stability in the intermediate temperature range (500–900 °C) needs to be better understood to make this alloy applicable to industry. In the present work, the phase decomposition of the HfNbTaTiZr RHEA is examined at different temperatures (500–1000 °C). Additionally, the formation of BCC Ta-Nb-rich and hexagonal-close-packed (HCP) Hf-Zr-rich precipitates are studied as a function of annealing time at 700 °C using a combination of atom probe tomography, transmission electron microscopy, and X-ray diffraction. We found that these BCC and HCP precipitates have preferred orientations with the BCC matrix. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Orientation relationships of (1 1 1) NbN //(1 1 2) NbCrN and 0 1 1 ¯ NbN / / 1 1 ¯ 0 NbCrN have been observed. • NbN provides nucleation site and niobium for the formation of secondary NbCrN. • Secondary NbCrN tends to consume NbN by nucleation and growth mechanism. Abstract Precipitation behavior of Z-phase (NbCrN) is investigated in 25Cr-20Ni-Nb-N austenitic stainless steel during long-term aging. The early precipitation of secondary NbN appears when the steel is aged for 100 h, and the secondary NbCrN precipitates adhere to the pre-existing NbN particles during the subsequent aging. A semi-coherent relation between (1 1 1) NbN and (1 1 2) NbCrN is identified, which provides favorable sites for the nucleation of secondary NbCrN on secondary NbN. Subsequently, secondary NbN will dissolve to supply niobium and nitrogen for the growth of secondary NbCrN. [ABSTRACT FROM AUTHOR]

Abstract Nb 3 Al superconductors with high superconducting performance are of interest as potential materials for using in high magnetic fields. The phase formation mechanism plays a vital role in preparing high quality Nb 3 Al superconductor, especially with better superconducting transition temperature (T c). In this work, the phase evolution of Nb Al system during mechanical alloying and subsequent sintering process was studied, and the corresponding kinetics mechanism of Nb 3 Al phase formation was investigated in detail. It was found that the Nb 3 Al phase can be formed through two different routes: one is reaction between Nb 2 Al and Nb, the other is transformation from Nb Al supersaturated solid solution (Nb(Al) ss) directly. Mechanical alloying promotes the transformation of Nb Al pre-alloyed powders from local Nb Al amorphous to Nb(Al) ss , controlling the different formation routes of Nb 3 Al phase. According to the kinetics calculation of the Nb 3 Al phase formation during sintering process, the values of activation energy (E) for the reaction between Nb 2 Al and Nb forming Nb 3 Al is higher than that for the transformation from Nb(Al) ss to Nb 3 Al in the initial stage, but decreases sharply with the reaction going on. Moreover, Nb 3 Al bulk synthesized via reaction between Nb 2 Al and Nb obtained a higher value of T c (about 15.8 K) compared with the Nb 3 Al bulk synthesized via Nb(Al) ss. The results in our work suggest that the phase formation mechanism of Nb 3 Al during mechanical alloying and subsequent sintering process actually influence their final superconductivity performance and can give an effective guide for optimizing the technique of preparing Nb 3 Al superconductors. Graphical abstract Image 1 Highlights • Two formation routes of Nb 3 Al phase are found during mechanical alloying and subsequent sintering. • The formation of Nb 3 Al phase is dominated by interface reaction and random nucleation. • Nb 3 Al bulk synthesized via reaction between Nb 2 Al and Nb obtained a higher value of T c. [ABSTRACT FROM AUTHOR]

Abstract A pre-deformation process was employed for a TiAl alloy via high-temperature torsion, in which the stability of the constituent phases was tailored, resulting in enhanced hardening capability and ductility via a gradient microstructure. A sample with a pre-torsion of 360° exhibited a yield strength of 475 MPa and an ultimate tensile strength of 592 MPa, with a tensile ductility of 47% at 850 °C. The tensile properties were significantly enhanced compared with the as-forged sample, which exhibited values of 395 MPa, 494 MPa, and 4.6%, respectively. The physical mechanisms for the significant enhancement of the mechanical property of the TiAl alloys were studied in-depth via of transmission electron microscopy, electron-backscattered diffraction, and high-energy X-ray diffraction techniques. The high strength is mainly attributed to the twin structure formed during torsion, while high fracture elongation correlates to the recrystallization of the γ phase at twin-twin sections and the load partitioning regulated by a hierarchical microstructure. When the tensile micro-strains along the loading direction and transverse direction in the γ phase of the pre-deformed TiAl alloy, a higher mechanical performance was obtained. Moreover, the fracture mode of the pre-torsional tensile sample is a combination of pores and cleavage facets which resulted from the microstructure after torsion. The gradient twin structure approach in this study provides a strategy for developing TiAl alloys with exceptionally high-temperature tensile property, and the results of the micromechanical behavior-microstructure-property relationship may improve the understanding of the plastic deformation of TiAl alloys. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Under neutron irradiation, radiation enhanced beta-Nb nano-precipitates develop within the α-grains of the Zr-Nb alloys. This radiation enhanced precipitation is of great interest since it may have some influence on the post-irradiation mechanical behavior of the material. In this paper the shape, the orientation relationship and the interface structure of such nano-particles are studied by means of both conventional and high-resolution transmission electron microscopy. The radiation damage was annealed out, thanks to a prior heat treatment and a creep test, in order to easily observe the beta-Nb nano-particles. The nano-particles exhibit a needle-like shape with a short thickness along the c-direction of 1.5 nm on average, a length and a width respectively of 6 nm and 3 nm, on average, in the basal plane. Using high-resolution TEM, a near Pitsch-Schrader orientation relationship is identified for a nano-particle. The interface atomic structure at various locations around the nano-particle has been accurately determined and an atomic model of the interface structure has been proposed. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract The compositional window leading to the crystallization of primary α-Nb phase and the eutectic (α-Nb + TiCo) phase in Nb-Ti-Co alloys is of high technical relevance due to its favourable properties with respect to hydrogen permeation. To this end, a new compositional window for hydrogen-permeable Nb-Ti-Co alloys is discussed and established for the first time in this study. It is found that improving the hydrogen permeability and increasing the durability are in contradiction with each other, and are closely related to the alloy composition. Optimization of the design of these alloys is therefore a compromise between above-mentioned two parameters. As-cast Nb 45 Ti 25 Co 30 shows a good balance between permeability and durability. Secondly, Nb-Ti-Co amorphous (a -) membranes have been successfully prepared by the melt-spinning technique. The importance of the annealing condition in determining crystallization behaviour, hydrogen permeability and durability is brought out. Subsequent annealing decreases the hydrogen permeation flux of the a - membrane, but significantly increases its thermal stability and durability, compared with its amorphous state, which is attributed to the microstructural change from amorphous to a duplex structure. Typically, a - Nb 30 Ti 35 Co 35 membrane after annealing at 1000 °C for 12 h shows a high hydrogen permeation flux of 15.55 cc H 2 cm−2 min−1 and excellent durability of ~ 112 h at 400 °C. Thirdly, the permeability of crystallized (c -) Nb 30 Ti 35 Co 35 membrane obtained by annealing at 1000 °C for 12 h towards hydrogen was tested and evaluated under the mixed atmosphere of H 2 /CO or H 2 /CO 2. This membrane possesses a relative stable H 2 flux and good durability without corrosion/chemical reaction-induced failure. The present work demonstrates that Nb-Ti-Co amorphous alloys followed by proper annealing are an attractive candidate material for hydrogen separation membrane. Highlights • A new compositional window for hydrogen permeable Nb-Ti-Co alloys is established. • Permeability/durability can be optimized by adjusting the alloy composition. • Nb 30 Ti 35 Co 35 amorphous membranes were successfully fabricated. • A H 2 flux of ~ 15.55 cc H 2 cm−2 min−1 is derived for the c - Nb 30 Ti 35 Co 35. • The c - Nb 30 Ti 35 Co 35 exhibits robust H 2 flux for gas mixture. [ABSTRACT FROM AUTHOR]

Abstract A NbSi 2 /SiO 2 -Nb 2 O 5 multilayer coating, consisting of a NbSi 2 inner layer and a SiO 2 -Nb 2 O 5 outer layer, was prepared on Nb alloy through halide activated pack cementation (HAPC) and microarc oxidation (MAO). The hot corrosion behaviors of the single NbSi 2 coated and the NbSi 2 /SiO 2 -Nb 2 O 5 coated Nb alloys were comparatively investigated with a mixture of Na 2 SO 4 /NaCl (3:1 wt.%) salt at 900 °C. The growth kinetics of the corroded scales follow the parabolic laws, and the parabolic rate constants of the NbSi 2 coated and the NbSi 2 /SiO 2 -Nb 2 O 5 coated specimens were 2.16 × 10−3 mm s−2 and 1.04 × 10−3 mm s−2, respectively. During the corroding process, the SiO 2 -Nb 2 O 5 outer layer that serves as a barrier promotes the formation of continuous SiO 2 scale, and isolates the NbSi 2 layer from the corrosion salt. The lower corrosion rate of the NbSi 2 /SiO 2 -Nb 2 O 5 coated specimens is attributed to the formation of the protective SiO 2 corroded scale. Graphical abstract Image 1 Highlights • A multilayer coating was formed on Nb alloy by HAPC combined with MAO. • The coating consists of a SiO 2 -Nb 2 O 5 ceramic outer layer and a NbSi 2 inner layer. • The coated Nb alloys shows superior hot corrosion resistance due to SiO 2 -Nb 2 O 5 layer. • The superior hot corrosion resistance is due to formation of glassy corroded scale. [ABSTRACT FROM AUTHOR]

A Ni-doped Al 2 O 3 coating was prepared on Ti-45Al-8.5 Nb alloys by the cathodic plasma electrolysis (CPE) process in a 1.2 mol/L Al(NO 3 ) 3 ethanol solution containing different concentrations of Ni(NO 3 ) 2 . The coatings deposited in these solutions mainly consisted of γ-Al 2 O 3 , NiAl 2 O 4 and some metallic Ni. The Ni-doped Al 2 O 3 coating exhibited increased oxidation resistance and adhesion compared with that of a pure Al 2 O 3 coating. The mass gain of the Ti-45Al-8.5 Nb alloys after oxidation was significantly reduced if Ni was added to the coating. A large number of craters on the coating surface were filled with NiAl 2 O 4 and metallic Ni that inhibited the oxide from contacting the substrate through the craters and pores. The metallic Ni and Al 2 O 3 were also transformed to NiAl 2 O 4 during oxidation at 900 °C. The structure of the coating was also stabilized by the formation of NiAl 2 O 4 . Therefore, the addition of Ni can be used as a sealing technology for ceramic coatings prepared by the CPE process. [ABSTRACT FROM AUTHOR]