Niobium Alloys Research Articles

Ultra-high temperature oxidation behavior of ZrB2/YSZ modified Si-Mo-W coating with a diffusion barrier on niobium alloy

To develop an ultra-high temperature resistant coating for niobium alloy, a new type of 10%ZrB2 + 5%YSZ-modified Si-Mo-18%W coating with a boride diffusion barrier was prepared by a novel three-step method. The coating with NbB2-Nb3B2 diffusion barrier can effectively protect Nb521 alloy at 1850 °C for more than 8 h, while the life of coating without diffusion barrier was only 3.5 h. The excellent performance of the coating was attributed to the present of diffusion barrier and formation of self-healing SiO2-B2O3-ZrSiO4-ZrO2 oxide scale. The diffusion barrier can effectively hinder mutual diffusion of coating and substrate, and reduce inward consumption of silicon element.

Microstructure and Oxidation Behavior of Nb-Si-Based Alloys for Ultrahigh Temperature Applications: A Comprehensive Review

Nb-Si-based superalloys are considered as the most promising high-temperature structural material to replace the Ni-based superalloys. Unfortunately, the poor oxidation resistance is still a major obstacle to the application of Nb-Si-based alloys. Alloying is a promising method to overcome this problem. In this work, the effects of Hf, Cr, Zr, B, and V on the oxidation resistance of Nb-Si-based superalloys were discussed. Furthermore, the microstructure, phase composition, and oxidation characteristics of Nb-Si series alloys were analyzed. The oxidation reaction and failure mechanism of Nb-Si-based alloys were summarized. The significance of this work is to provide some references for further research on high-temperature niobium alloys.

Impregnation of the surface of niobium alloy when grinding with corundum and silicon carbide wheels

The features of the formation of a relief after grinding a niobium alloy with abrasive tools made of corundum and silicon carbide on a ceramic bond are considered. The treated surface is studied with a scanning two-beam electron microscope. Keywords: niobium, grinding, corundum, silicon carbide, material transfer, impregnation, micro-X-ray pattern. vladim.nosenko2014@yandex.ru

Mechanical properties and microstructural characteristics of additively manufactured C103 niobium alloy

C103 is a refractory-based niobium alloy for high temperature applications in aerospace. This paper aims to evaluate the compatibility of C103 alloy as a choice of material for laser-based additive manufacturing (AM) technologies. Crack free AM specimens with relative densities of greater than 99% were successfully fabricated via laser powder bed fusion (L-PBF) method with horizontal and vertical build orientations. Static strength levels of the stress-relieved specimens exceeded that of their wrought counterparts. Higher yield and ultimate tensile strength of AM specimens were attributed to high dislocation density and the formation of dislocation cell structures, which was revealed by transmission electron microscopy. Loss of ductility in AM specimens was partially due to high density of dislocations (i.e., shorter mean free path for dislocations), while the presence of defects may also have compromised the total elongation to failure. Electron backscattered diffraction analysis revealed formation of sharp 001||BD rod texture in AM samples, which resulted in anisotropic mechanical behavior. Uniaxial tensile and compressive deformation led to the development of (001) <110> parallel to tensile direction and <111> parallel to build direction, respectively.

Electron Beam Melting of Niobium Alloys from Blended Powders.

Niobium-based tungsten alloys are desirable for high-temperature structural applications yet are restricted in practice by limited room-temperature ductility and fabricability. Powder bed fusion additive manufacturing is one technology that could be leveraged to process alloys with limited ductility, without the need for pre-alloying. A custom electron beam powder bed fusion machine was used to demonstrate the processability of blended Nb-1Zr, Nb-10W-1Zr-0.1C, and Nb-20W-1Zr-0.1C powders, with resulting solid optical densities of 99+%. Ultimately, post-processing heat treatments were required to increase tungsten diffusion in niobium, as well as to attain satisfactory mechanical properties.

Study of the Silicon Carbide Wear Area after Micro-Scratching of Titanium, Zirconium, Niobium and Molybdenum at a Speed of 35 m/s

The authors conducted the study at micro-scratching of titanium, zirconium, niobium and molybdenum alloys. The content of the main element in alloys was from 99.5 to 99.7 %. Micro-cutting was carried out by specially prepared indenters with silicon carbide mono-crystals of a given shape. The state of the relief and the chemical composition of the wear area were studied using a scanning two-beam electron microscope. The micro-scratching speed was 35 m/s without cooling. The condition of the contact surfaces of silicon carbide and metals was studied at a magnification up to 100,000 times with the rotation and tilt of the microscope slide. The content of chemical elements was determined at individual spots of an object by scanning along the line and area. The authors also studied the condition of the wear area after micro-scratching of metals and after removal of metal adhesions by chemical etching. The intensity of metal transfer was determined by the average concentration of metal atoms at the wear area. The article also gives a classification of metals according to the intensity of transfer immediately after grinding and removal of metal adhesions. The influence of metal and the depth of micro-scratching on the morphology of the wear site is shown. It was found that molybdenum, having a low adhesive activity to silicon carbide, is able to penetrate microcracks and other surface defects during micro-scratching. The width of microcracks and the depth of metal penetration were determined

Prediction of Long-Term Creep Properties of Zirconium-2.5 % Niobium Alloy Using Wilshire Method

Abstract Zirconium-2.5 % niobium alloy, used as a pressure tube material in pressurized heavy water reactors, have to experience extreme stress, temperature, and radioactive conditions to serve within the designed dimensional tolerance limit. Prolonged duration under high stress and high temperature causes the creep deformation, ultimately leading to deformation beyond the permitted limit or interference with other components, or both. Hence, a priori using particular material for a specific application, mechanical testing has to be done to investigate its deformation behavior. However, creep tests of material can last from a few hours to several months or even years. The cost of testing the material can eventually impact the cost of the component. Instead of carrying out long-term creep tests, an extrapolation technique named the Wilshire method is applied to predict the creep behavior of the material under any given test conditions. This method is also capable of reconstructing the complete creep curve using the data from accelerated creep tests. Such an approach can drastically scale down the cost and time required for the long-term creep tests. In the present study, zirconium 2.5 % niobium alloy, which is used as pressure tube material in pressurized heavy water reactors, is employed as a test material for the analysis using the Wilshire method.

The Protection, Challenge, and Prospect of Anti-Oxidation Coating on the Surface of Niobium Alloy

Niobium (Nb)-based alloys have been extensively used in the aerospace field owing to their excellent high-temperature mechanical properties. However, the inferior oxidation resistance severely limits the application of Nb-based alloys in a high-temperature, oxygen-enriched environment. Related scholars have extensively studied the oxidation protection of niobium alloy and pointed out that surface coating technology is ideal for solving this problem. Based on the different preparation methods of Nb-based alloys’ surface coatings, this article summarizes the relevant research of domestic and foreign scholars in the past 30 years, including the slurry sintering method (SS), suspension plasma spraying method (SPS), and halide activated pack cementation method (HAPC), etc. The growth mechanism and micromorphology of the coatings access by different preparation methods are evaluated. In addition, the advantages and disadvantages of various coating oxidation characteristics and coating preparation approaches are summarized. Finally, the coating’s oxidation behavior and failure mechanism are summarized and analyzed, aiming to provide valuable research references in related fields.

Size effects on microstructure and mechanical properties of additively manufactured copper–chromium–niobium alloy

This study quantifies size effects on microstructure and mechanical properties of Laser Powder Bed Fusion (L-PBF) Copper–Chromium–Niobium Alloys, specifically GRCop-42 (Copper-4at% Chromium-2at% Niobium Alloy). Thin-wall structures made of copper-based alloys are desirable for applications requiring a combination of high thermal conductivity and strength. Additive manufacturing offers the ability to produce copper alloy thin-wall structures without the need for complex tooling. However, consideration must be given to the effect of wall thickness on solidification rate and process as it can affect material and part characteristics including the microstructure, porosity, and surface roughness. This investigation aims to determine which of these characteristics are most influenced by variations in wall thickness and how they affect the mechanical properties. Additionally, we investigate how these characteristics and their influence on mechanical properties are changed by heat treatment. The results show that surface roughness, grain size, and texture do not appear to be greatly influenced by the build thickness, while porosity appeared to be highly dependent on thickness. By increasing wall thickness from 0.7 mm to 2.0 mm, porosity decreases by 74.7% in the as-built condition and 99.7% in the hot isostatic press (HIP) condition. The variability in porosity has a notable effect on the mechanical properties of the thin-wall structures: yield strength and ultimate tensile strength decrease by more than 20% for both as-built and HIP samples as thickness decreases from 2.0 mm to 0.7 mm. This decrease in strength appears to be attributable to the increased porosity in thin-wall samples, as scanning electron microscopy (SEM) images show crack networks linking internal voids along the fracture surface.

Selective laser melting additive manufacturing of tungsten with niobium alloying: Microstructure and suppression mechanism of microcracks

Microcrack suppression is a challenging issue in additive manufacturing of tungsten heavy alloys (WHAs) due to the high melting point and brittleness of tungsten (W). In this study, W-5Nb samples with a high density and few defects were successfully manufactured by introducing niobium (Nb) using selective laser melting (SLM) technique, and the influence of process parameters on the density and microstructure of W-5Nb was investigated. The effect of Nb addition on the mechanism of the microcrack formation was mainly analyzed. The results revealed that the densification first increased and then decreased with the increase of energy density (E). When E was 397 J/mm3, samples with the relative density of 98% and W-Nb solid solution phase were obtained, and the microcracks were basically suppressed. The distribution segregation extent and density of nanopores formed by WxOy gasification were reduced, which was beneficial for improvement of grain bonding strength. Solid solution strengthening occurred in W with Nb alloying and also contributed to improvement of grain bonding strength. The percentage of the large-angle grain boundaries (>15°) was reduced by 67% (12.9% for E = 397 J/mm3 and 39.6% for E = 556 J/mm3) due to uniform grain deformation with grain bonding strength being enhanced.

Evolution of Texture and Deformation Mechanisms During Repeated Deformation and Heat Treating Cycles of U-6Nb

The evolution of the crystallographic texture and lattice strain of uranium 6-weight percent niobium alloy samples are tracked during multiple deformation and heat treating cycles in an effort to understand and control the mechanical properties of the material following thermo-mechanical processing. The heavily twinned microstructure and low-symmetry crystal structure of U-6Nb result in multiple sequential active deformation mechanisms associated with distinctive deformation textures in strain ranges from 0-0.15 true strain. It is found that heating into the high-temperature γ-phase erases much of the texture formed during deformation at room temperature in the α′′-phase and resets the active deformation mechanisms. Through a small number of deformation/heat treat cycles to moderate strains, i.e., ~ 0.13 per cycle, the flow strength of the material is recovered to its original value. However, on the fourth such cycle, a reduction of strength is observed and the sample failed.

Precipitation behavior in a Nb-5W-2Mo-1Zr niobium alloy fabricated by electron beam selective melting

Refractory niobium-based alloy Nb521 (Nb-5 W-2Mo-1Zr) was fabricated by electron beam selective melting (EBSM). The microstructure feature of as-built Nb521 alloy was systematically studied in combination with the unsteady thermal cycling inherent in the EBSM process. The content of precipitates gradually increased from the top region to the bottom region for EBSM-built Nb521 samples. Dot-like or rod-like precipitates with different morphologies were distributed inside grains or along grain boundaries in the as-built sample, whereas needle-like precipitates with a large aspect ratio existed in Nb521 alloy ingot. All precipitates in the EBSM-built Nb521 sample mainly contain (Nb, Zr)C and Nb2C. With prolonging the thermal balance holding time, the elongated precipitates were partially broken, and became fine and uniform. It is expected that the results obtained in this study can lay a solid theoretical and technological basis for the fabrication of refractory Nb-based alloy by the EBSM process.

Исследование тонкой структуры образцов из ниобиевого сплава 5 ВМЦ после внутреннего азотирования

The paper considers the possibility of studying the fine structure of samples made of niobium alloy 5 VMC (grade 5B2MC-2), which underwent internal nitriding by X-ray diffraction analysis.The calculation of the dislocation density, which represents one of the parameters of the fine structure using various techniques, is shown. Its influence on the possible modes of internal nitriding is considered.

Plasma Electrolyte Polishing of Titanium and Niobium Alloys in Low Concentrated Salt Solution Based Electrolyte

Today, world enterprises specializing in the production of titanium and niobium alloy products and having modern high-tech equipment are still forced to use outdated, costly and environmentally unsafe methods of polishing and surface cleaning, based on electrochemical treatment in toxic solutions. The complex geometric shape of the processed products does not allow the use of mechanical polishing methods, due to high labor costs and low efficiency. These materials are difficult to process, and the processes of their polishing require the use of toxic electrolytes. An alternative to existing methods of electrochemical polishing is plasma electrolyte polishing in aqueous solutions of salts with a concentration of up to 5%. We have developed fundamentally new modes of plasma electrolyte polishing of products from titanium and niobium alloys using simple electrolytes based on an aqueous solution of fluoride salt, the use of which can significantly increase the surface quality class. The advantage of the plasma electrolyte polishing over classical electrochemical polishing is its safety due to the use of an electrolyte based on an aqueous solution of salt. The paper presents the results of an investigation of the characteristics and morphology of the surface after processing using the developed method. Modes that provide the maximum change in roughness with minimal metal removal were obtained.

Dynamic Recrystallization Mechanisms of Nickel Niobium Alloys during Hot Working

This present work examines the influence of niobium in solid solution on the microstructural evolution of pure nickel at various deformation conditions. On this purpose, high-purity nickel and six model nickel-niobium alloys (Ni–0.01, 0.1, 1, 2, 5 and 10 wt. % Nb) were subjected to hot torsion test to large strains within the temperature range from 800 to 1000 °C at strain rates of 0.03, 0.1 and 0.3 s–1. Microstructural analyses were carried out using both optical and scanning electron microscopy-based electron back-scattered diffraction technique. The overall results showed the key role played by the Nb amount when coupled with various DRX mechanisms involved, i.e. DDRX, CDRX, and GDRX with respect to the prescribed deformation conditions, in reducing grain size and retarding DRX kinetics from which the microstructures of the examined materials such as Ni 2 and 10 wt. % Nb were seen evolving in different ways. In all these deformed materials, a transition from discontinuous dynamic recrystallization to continuous dynamic recrystallization was observed at low temperature and high strain rate whereas only discontinuous dynamic recrystallization occurred at high temperature.

Molecular dynamics study of special quasirandom structure of Zr-Nb alloys

Irradiation damage to zirconium alloys (e.g., zirconium niobium (Zr-Nb) alloy) is the key to the design of fission-reactor structural materials and fuel rod cladding materials. Atomic scale computational simulations such as molecular dynamics and first principles are often needed to understand the physical mechanism of irradiation damage. For the simulation of randomly substitutional solid solution, it is necessary to construct large-sized supercells that can reflect the random distribution characteristics of alloy elements. However, it is not suitable to use large-size supercells (such as ≥ 200 atoms) for first principle calculation, due to the large computational cost. Special quasirandom supercells (SQS) are usually used for first principles calculation. The SQS can partly reflect the random distribution characteristics of alloy elements, but it only corresponds to one configuration for specific components, hence whether this model can reflect the statistical average of multiple local configurations in a real randomly substitutional solid solution is still an open question, and needs further studying and verifying. Molecular dynamics (MD) simulation can be carried out on the randomly substitutional solid solution with a larger scale based on random substitution (RSS) method, these supercells include more local configurations. Therefore, the MD studies of Zr-Nb alloy are carried out for the RSS and SQS-extended supercells. The critical size of RSS supercell which can truly reflect the statistical properties of solid solution alloy is determined. Then the lattice constant, formation energy and energy-volume relationship of SQS-extended supercell of Zr-Nb alloy and a series of RSS supercells are calculated and compared. The results show that the lattice constants, the formation energy and energy volume curves of the solid solution obtained by SQS supercell simulation are close to a series of corresponding statistical values of the physical properties of RSS supercells, so the SQS supercells can be used to study the random substitution of solid solution alloys.

Influence of titanium and chrome on the structure and heat resistance of layered composites from a multicomponent Nb-alloy and intermetallic compounds of aluminium

Investigations of the structure and measurements of the strength characteristics of layered composites of niobium alloys prepared by diffusion welding under pressure have been carried out. It was found that titanium has a strong effect on the formation of microstructure and strength of composites. Higher values of short-term strength and fracture toughness are demonstrated by layered composites with a lower titanium content.

ИНТЕРМЕТАЛЛИДНОЕ СОЕДИНЕНИЕ AlхTi – ПЕРСПЕКТИВНЫЙ МАТЕРИАЛ ДЛЯ ПОВЫШЕННЫХ ТЕМПЕРАТУР (обзор) Часть 2. Механические свойства интерметаллида Al2Ti и влияние легирования

Intermetallide alloys based on the Al2Ti compound are the most promising heat-resistant materials for future energy plants.The review examines the mechanical properties of the Al2Ti Intermetalide, two-phase alloys based on it and the doped niobium alloy. For use at temperatures of up to 950 °С, alloys with phase composition r-Al2Ti + γ-TiAl and platemicrostructure with additional doping of refractory elements are of interest.

Heat protective coatings on niobium alloys

The article shows that during plasma-diffusion deposition, a multilayer coating was formed on the surface of the niobium alloy. A highly porous plasma-sprayed layer of molybdenum silicide has a significant spread in thickness (h=100...350 μm, Hμ20=6880 MPa). When studying the microstructure of samples with a plasma-diffusion coating after testing, it was found that cracks in the coating originate in the process of creep, mostly at the interface between the plasma and diffusion layers of the coating. The source of their origin is individual discontinuities in the diffusion layer as delivered. Crack propagation occurs both into the plasma and diffusion layers of the coating. Crack growth in the plasma layer is inhibited due to the rounded nature of the pores and the increased plasticity of this layer. The growth of cracks deep into the sample is, as a rule, inhibited by a boride sublayer. The advantage of plasma-diffusion technology provided an increased plasticity of the coating, the presence of thin barrier sublayers, a discontinuous coating structure, the presence of low-melting compounds that contribute to the healing of defects in the coating, an increase in its corrosion resistance and resistance to thermal fatigue destruction. The combination of these properties made it possible to provide an increase in durability compared to silicide and borosilicide coatings under conditions of isothermal creep in air (1400°C, 50 MPa) 1.9...3.7 times and under conditions of thermal cyclic creep (1400-250°C, 50 MPa) in 6.8...8.5 times. It has been determined that the use of a discrete structure will increase the thickness of the coating layer and ensure an increase in their working properties.

Вплив Al, Cr, Mo, Zr, Si і C на температурні інтервали зміцнення багатокомпонентних сплавів на основі ніобію

The effect of alloying and the strain rate on the occurrence and features of the manifestation of temperature ranges in which the strengthening of niobium alloys doped with Ti, Al, Cr, Mo, Zr, Si, C occurs was studied. It was found that in multicomponent solid solutions based on niobium up to sufficiently high temperatures more efficient hardening is provided than in precipitation hardened carbide alloys. It is shown that in multicomponent niobium alloys, which are a solid solution, the selection of alloying can be used to control the manifestation of a high-temperature hardening peak in a wide range. It is possible to change the temperature range of the peak manifestation, its height, sensitivity to the strain rate. The appearance of a high-temperature hardening peak is explained by the loss of stability of the multicomponent solid solution upon deformation in the dislocation field, which leads to the precipitation of dispersed particles of the second phase that pin the dislocations. Keywords: multicomponent niobium alloys, structure, temperature dependence of strength.