Search Results (103)

Rebar is a critical material in concrete constructions like high-rise buildings and seismic-resistant structures. To enhance its properties, microalloying with nitrogen is employed, but traditional methods using micro alloy additives such as vanadium (FeV), niobium (FeNb), titanium (FeTi), and vanadium nitride (VN) face issues of high costs, reduced purity, and difficulty in controlling molten steel composition. This article presents a novel approach of injecting top-blown O₂–N₂ mixed gas to increase nitrogen content efficiently. Experiments simulated HRB400 steel samples, varying N₂ ratios (10%, 20%, 30%, 40%), temperatures (1500 °C, 1550 °C, 1600 °C), and blowing times (1, 2, 3 min). Results show that optimized parameters enable nitrogen content adjustment from 50 to 104 ppm, with nitrogen utilization improved to 5.4%. This method utilizes inexpensive N₂ gas, reduces impurities, and provides precise control, offering a cost-effective and sustainable solution for high-performance steel production by replacing costly alloys and meeting nitrogen requirements. Full article

The continuous casting of Ti-Nb microalloyed steel was simulated with high temperature confocal laser scanning microscopy (HTCLSM). Evolution of the sample surface morphology was observed in-situ, during cooling conditions chosen to represent different locations in a cast slab. Calculations with a thermodynamics model of carbonitride precipitate formation agreed with the transmission electron microscopy (TEM) analysis that fine reliefs observed on the sample surface were actually caused by interior precipitation of (Ti,Nb)(C,N). Precipitation and the resulting reliefs changed with location beneath the slab surface, simulated casting speed, and steel composition. With the same casting speed and steel composition, reliefs in the simulated slab surface sample appeared earlier and were larger than in the slab center. With increased casting speed, reliefs were observed later and decreased in size. With increased titanium or niobium content, reliefs appeared earlier and increased in number. TEM measurement showed that the precipitate diameters were mainly smaller than 4 nm, with a few between 4 and 8 nm. The property of surface reliefs observed via HTCLSM correlated qualitatively with the number and size of internal precipitates measured with TEM, showing this to be an effective tool for indirectly characterizing nanoscale secondary phase precipitation inside the sample. Full article

Lead ferrite (Pb₂Fe₂O₅) is a promising multiferroic material that exhibits both ferroelectric and magnetic properties at room temperature. This study investigates how substituting niobium and adjusting the synthesis temperature affect the structural, morphological, and ferroelectric properties of lead ferrite thin films deposited via reactive magnetron sputtering. Niobium-substituted PFO films (Pb₂Fe_2(1−x)Nb_2xO₅), where x corresponds to Nb₂O₅ contents of 3 wt.%, 5 wt.% and 10 wt.%, were prepared for this study, and denoted as PFONb3, PFONb5 and PFONb10, respectively. X-ray diffraction analysis confirmed the formation of Nb-substituted PFO phases, while polarization–electric field measurements demonstrated an increase in remnant polarization (P_r), with higher Nb content reaching a maximum P_r of 65 µC/cm² at 10 wt.% Nb and a substrate temperature of 500 °C. Scanning electron microscopy and energy-dispersive spectroscopy revealed a uniform distribution of elements and a well-defined surface structure. These results highlight the need to fine tune synthesis parameters, such as temperature and substitution concentrations, to achieve optimal ferroelectric characteristics. Full article

This study develops a comprehensive artificial neural network (ANN) model for predicting the mechanical properties of carbon–manganese cast steel, specifically, the yield strength (YS), tensile strength (TS), elongation (El), and reduction of area (RA), based on the chemical composition (16 alloying elements) and heat treatment parameters. The neural network model, employing a 20-44-44-4 architecture and trained on 400 samples from an industrial dataset of 500 samples, achieved 90% of test predictions within a 5% deviation from actual values, with mean prediction errors of 3.45% for YS and 4.9% for %EL. A user-friendly graphical interface was developed to make these predictive capabilities accessible, without requiring programming expertise. Sensitivity analyses revealed that increasing the copper content from 0.05% to 0.2% enhanced the yield strength from 320 to 360 MPa while reducing the ductility, whereas niobium functioned as an effective grain refiner, improving both the strength and ductility. The combined effects of carbon and manganese demonstrated complex synergistic behavior, with the yield strength varying between 280 and 460 MPa and the tensile strength ranging from 460 to 740 MPa across the composition space. Optimal strength–ductility balance was achieved at moderate compositions of 1.0–1.2 wt% Mn and 0.20–0.24 wt% C. The model provides an efficient alternative to costly experimental trials for optimizing C-Mn steels, with prediction errors consistently below 6% compared with 8–20% for traditional empirical methods. This approach establishes quantitative guidelines for designing complex multi-element alloys with targeted mechanical properties, representing a significant advancement in computational material engineering for industrial applications. Full article

Alloy 625 is a widely utilized nickel-based superalloy known for its excellent mechanical strength and corrosion resistance in aggressive environments. However, its high niobium (Nb) content can lead to the formation of detrimental phases, such as Laves and MC carbides, during welding processes, compromising the mechanical integrity and long-term performance of the weld overlay. This review systematically examines recent research findings on the implications of reducing Nb content in Alloy 625 weld overlays, particularly with respect to microstructure evolution, mechanical behavior, and corrosion performance. Key advancements, including the understanding of segregation behavior, solidification paths, and secondary phase formation, are presented based on recent studies. This paper aims to provide a discussion on the trade-offs and future directions for optimizing Alloy 625 weld overlay claddings through Nb content modification. Full article

This work evaluates the effectiveness of in situ and ex situ passivation methods for mitigating the pyrophoricity of uranium–6 wt.% niobium spherical powders produced via the hydride–dehydride process coupled with plasma spheroidization. Oxide layer thickness was characterized using STEM/EDX, and pyrophoricity was assessed by a UN-recommended test method, which involves directly dropping the powders in the air. In situ passivation, performed by introducing flowing oxygen during spheroidization, produced oxide layers ranging from tens to hundreds of nanometers but resulted in inconsistent pyrophoricity mitigation at lower oxygen flow rates. Ex situ passivation, achieved by slow oxygen exposure over several months, formed uniform oxide layers of approximately 20 nm and consistently mitigated pyrophoricity. Despite requiring higher bulk oxygen content, in situ passivation enables faster processing and control of oxygen, while ex situ passivation achieves superior oxide uniformity with lower oxygen incorporation. These findings highlight the trade-offs between passivation methods and provide a foundation for improving the safety and scalability of reactive metal powder production. Full article

Critical-size bone defects do not heal spontaneously and require external support, making bone regeneration a central challenge in tissue engineering. Polymeric/ceramic composite scaffolds offer a promising approach to mimic the structural and biological properties of bone. In this study, we aimed to evaluate the effect of different doping oxides in bioactive glass (BG) on the performance of polycaprolactone (PCL)-based composite scaffolds for bone tissue engineering applications. Composite scaffolds were fabricated using solvent casting, hot pressing, and salt-leaching techniques, combining PCL with 25 wt% of BG or doped BG containing 4 mol% of tantalum, zinc, magnesium, or niobium oxides, and 1 mol% of copper oxide. The scaffolds were characterized in terms of morphology, mechanical properties, and in vitro biological performance. All scaffolds exhibited a highly porous, interconnected structure. Mechanical compression tests indicated that elastic modulus increased with ceramic content, while doping had no measurable effect. Cytotoxicity assays confirmed biocompatibility across all scaffolds. Among the tested materials, the Zn-doped BG/PCL scaffold uniquely supported cell adhesion and proliferation and significantly enhanced alkaline phosphatase (ALP) activity—an early marker of osteogenic differentiation—alongside the Nb-doped scaffold. These results highlight the Zn-doped BG/PCL composite as a promising candidate for bone regeneration applications. Full article

To explore the impact of niobium (Nb) addition on the austenitization behavior of Fe-Mn-Al-C lightweight steels, the effects were examined through Thermo-Calc thermodynamic simulations, optical microscopy, transmission electron microscopy (TEM), and the development of austenite grain growth models. Three distinct Fe-Mn-Al-C steel compositions, each containing different Nb contents (0.38%, and 0.56%), were subjected to various austenitization temperatures and aging conditions, and a kinetic model for austenite grain growth was established. The results demonstrate that for heating temperatures below 950 °C, the austenite grain growth rate of the steels was similar. However, at temperatures above 950 °C, the grain growth rate of the steel without Nb (Steel No. 1) increased significantly compared to the niobium-containing alloys. Austenite grain size increased with higher heating temperatures. At constant heating temperatures, longer holding times resulted in larger grain sizes, though the rate of grain size growth diminished over time. Based on the experimental data and the kinetic theory of austenite grain growth, a grain growth model of No. 2 Steel (which contained 0.38% Nb) was established. The predicted grain size values derived from this model closely matched the experimental measurements, indicating a strong correlation and providing valuable insights for future studies. Full article

Optimizing the design of low-tungsten-content alloys represents an effective approach to address the insufficient strength and toughness of conventional tungsten alloys. This study focuses on the design and fabrication of low-tungsten-content alloys, specifically investigating the effects of Nb addition on the low-temperature sintering microstructure and mechanical properties of 50W–Ni–Fe alloy. The results demonstrate that Nb significantly lowers the liquid phase formation temperature, shifting the densification mechanism from solid phase sintering to liquid phase sintering. Nb primarily dissolves in the γ-(Ni,Fe) matrix phase and forms nanoscale γ″-Ni₃Nb precipitates. These γ″-Ni₃Nb precipitates maintain coherent interfaces with the γ-(Ni,Fe) matrix phase, exhibiting excellent interfacial bonding, which markedly enhances the hardness and modulus of the matrix phase. Through the strengthening effects of solid solution strengthening and precipitation strengthening, the tensile strength of the alloy increases to 1259 MPa while maintaining a total elongation of 23.1%. The fracture mode of the 50W-Ni-Fe-Nb alloy transitions to a mixed mechanism involving cleavage fracture of W and ductile rupture of the matrix phase. Full article

The research and related tests aimed to investigate the effect of different heat inputs on the microstructure and properties of the joint when using laser-backing welding for X80 steel, with the purpose of guiding a reasonable adjustment of heat inputs to obtain a sound and high-quality joint, and ultimately laying the foundation for the engineering application of laser-backing welding. The fiber-laser-backing welding is performed on a 22 mm thick X80 steel, before which a groove is prepared and assembled; joints were obtained under different heat inputs (162, 180, 210, 270 J/mm) with orthogonal combinations of laser power and welding speed. The microstructure and properties of the joints were characterized by using an optical microscope, scanning electron microscope, and microhardness tester. According to this investigation, the morphology of the joint is directly affected by the heat input, and insufficient heat input (<180 J/mm) will lead to an unacceptable weld profile. The width of the weld and heat-affected zone gets bigger as the heat input increases. The hardness nephograms of the joints under different heat inputs show that the weld has the highest hardness, followed by the coarse-grain heat-affected zone and the fine-grain heat-affected zone, sequentially. The less heat input, the lower the joint hardness; when the heat input increases to 270 J/mm, the coarse-grain zone near the fusion line shows obvious hardening. In addition, heat input also affects the impact toughness of the weld. The grain size of X80 steel with a lower content of niobium easily becomes coarse under excessive heat input (270 J/mm), resulting in the degradation of the grain-boundary slip ability; hence, the impact toughness of the joint deteriorates. The optimal heat input of 210 J/mm was identified, achieving a grain size of nearly 14 µm and providing a balanced combination of lower strength and higher impact toughness. Full article

This work presents an integrated directed energy deposition (DED) approach utilizing a multi-powder feeder with real-time continuously variable composition functionality, a multi-powder mixer and a multi-powder nozzle to fabricate Ti-Ni-Nb gradient alloys with controlled compositional variations. The high-throughput methodology enables rapid alloy design and optimization by allowing precise manipulation of chemical composition and phase structures within a single deposited track. The EDS analysis confirms a gradual increase in titanium content, a nearly constant nickel content and a decrease in niobium along the scanning path, aligning with the expected powder-feeding trends. X-ray diffraction (XRD) analysis further reveals a phase transition from niobium-rich intermetallic compounds (NbNi₄, Nb₈Ni) at the beginning of the deposition to titanium-rich phases (Ti, Ti₂Ni) at the end, demonstrating the ability to tailor phase distributions through real-time composition control. This high-throughput methodology enables rapid alloy design and optimization by integrating theoretical predictions with experimental phase screening. This study establishes a novel framework for the rapid discovery and optimization of functionally graded materials, paving the way for advanced applications in aerospace, biomedical implants and high-performance structural components. Full article

This study systematically investigates the correlation between the concentration of niobium oxide (Nb₂O₅) in carbon nanofibers (CNFs) and the microstructural characteristics and electrochemical performance of the composites. Through rational optimization of Nb₂O₅-to-CNFs mass ratios, we demonstrate that 50% Nb₂O₅ CNFs composite achieves an optimal balance between enhanced rate capability and structural stability. The composites transition from brittle to flexible with increasing Nb₂O₅ content, achieving unprecedented bending durability at 50% loading. This mechanical–electrochemical synergy positions Nb₂O₅ CNFs as viable candidates for flexible energy storage devices. Comprehensive characterization reveals that appropriate Nb₂O₅ incorporation significantly improves specific capacity (181 mA h g⁻¹ at 0.1 A g⁻¹) and rate performance compared to pristine CNFs. However, excessive Nb₂O₅ doping (>50%) induces detrimental hydrolysis reactions during synthesis, compromising both material processability and electrochemical reversibility. This work contributes to the development of flexible self-supporting frameworks that are superior to hard carbon for constructing high-performance flexible sodium-ion batteries. Full article

This study focuses on the effects of vanadium and niobium microalloying elements on the mechanical properties and high-temperature oxidation behavior of austenitic stainless steels. Vanadium–niobium elements were confirmed to play an effective role in fine-grain strengthening at room temperature, achieving a tensile strength and yield strength of approximately 768.8 MPa and 464.6 MPa, respectively, with the additions of 0.32 wt% V and 0.21 wt% Nb. During the high-temperature oxidation process, the weight gain and cracking of the oxide layer increased with increasing niobium–vanadium content. The loose structure and delamination of the oxide layer during the oxidation process were caused by the enhanced internal stress of the oxide layer and the molten state of V₂O₅ at 850 °C. Full article

Phosphate invert glasses (PIGs) have been attracting attention as materials for bone repair. PIGs have a high flexibility in chemical composition because they are composed of orthophosphate and pyrophosphate and can easily incorporate various ions in their glass networks. In our previous work, incorporation of niobium (Nb) into melt-quench-derived PIGs was effective in terms of controlling their ion release, and Nb ions promoted the activity of osteoblast-like cells. In the present work, a liquid-phase method was used for synthesizing Nb-containing PIGs, as this method allows us to prepare a glass precursor solution at room temperature, which can be attributed to improved glass-shape design. Nb-containing PIGs were successfully prepared, and their ion release behavior was controlled by changing the Nb content in the PIGs. The functions of Nb varied according to its content. For example, in the case of PIGs containing a larger amount of Nb, Nb acted as both the network modifier and former while also inducing the formation of chain-like structures. These glasses possessed a gradual ion release in a tris-HCl buffer solution. Cotton-wool-like structured scaffolds were fabricated using the synthesized Nb-containing glass using a wet-spinning method. Because the scaffolds possess excellent flexibility and controllable ion release, they are good candidates for new biomaterials. Full article

The additive manufacturing technique performed via laser powder bed fusion has matured as a technology for manufacturing cemented carbide parts. The parts are built by additive consolidation of thin layers of a WC and Co mixture using a laser, depending on the power and scanning speed, making it possible to create small, complex parts with different geometries. NbC-based cermets, as the main phase, can replace WC-based cemented carbides for some applications. Issues related to the high costs and dependence on imports have made WC and Co powders emerge as critical raw materials. Furthermore, avoiding manufacturing workers’ health problems and occupational diseases is a positive advantage of replacing WC with NbC and alternative binder phases. This work used WC and NbC as the main carbides and three binders: 100% Ni, 100% Co, and 50Ni/50Co wt.%. For the flowability and spreadability of the powders of WC- and NbC-based alloy mixtures in the powder bed with high cohesiveness, it was necessary to build a vibrating container with a pneumatic turbine ranging from 460 to 520 Hz. Concurrently, compaction was promoted by a compacting system. The thin deposition layers of the mixtures were applied uniformly and were well distributed in the powder bed to minimize the defects and cracks during the direct sintering of the samples. The parameters of the L-PBF process varied, with laser scanning speeds from 25 to 125 mm.s^─1 and laser power from 50 to 125 W. Microstructural aspects and the properties obtained are presented and discussed, seeking to establish the relationships between the L-PBF process variables and compare them with the liquid phase sintering technique. Full article