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High-entropy alloys based on refractory metals, possessing an unusual combination of physical, mechanical, tribological, electrophysical, etc. properties, can be recommended for use in various fields of industry and medicine. The aim of the work is to study the growth process of high-entropy alloys films of the Ti-Nb-Zr-Ta-Hf-Cu system in real time by X-ray phase analysis using synchrotron radiation. Experiments on the deposition of multielement metal films were carried out on the VEIPS-1 setup developed at the Institute of high current electronics Siberian branch of the Russian academy of sciences for studying the processes of the film and coating formation on a synchrotron radiation source. The process of in situ thin film structure formation with high time resolution was studied using a synchrotron radiation source – the VEPP-3 electron storage ring, the Institute of nuclear physics, Siberian branch of the Russian academy of sciences. It is shown that the deposition of Ti-Nb-Zr-Ta-Hf-Cu plasma on a HG40 substrate is accompanied by the formation of an amorphous-crystalline state represented by phases of the composition (presumably) Ti-Nb-Zr-Ta-Hf-Cu, TiZr, NbZr, and CuTiZr, formed at different stages of film deposition. The main phase is the Ti-Nb-Zr-Ta-Hf-Cu composition.

Coatings based on refractory metals and compounds have been used in various industries since the last century due to their high thermal and heat resistance, as well as their excellent mechanical and tribological properties. Advances have made it possible to apply high-tech methods for their production, which has improved their availability and expanded their range of applications. A promising area of use of coatings based on refractory systems is the anticorrosion protection of structural materials. The high wear resistance and anticorrosion ability of these materials will allow for the protection of critical units of equipment of various industries from the complex destructive effects of factors of chemical and mechanical nature. For the effective choice of coating composition, it is necessary to know the basic characteristics of refractory material layers and the method of their production. The purpose of this article is to summarize modern scientific data on methods of obtaining refractory coatings, as well as on their composition, structure, and protective properties. The information presented in this review will bridge the gap between research and industrial development and expand the niche area of utilization. [ABSTRACT FROM AUTHOR]

The present study deals with the development and characterization of Mo-35Ti-10Si and Mo-35Ti-10Si-2B (wt.%) alloy for ultra-high temperature applications beyond the temperature limit of existing super alloys. The microstructural characterization using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), electron back scattered diffraction (EBSD), x-ray diffraction (XRD) revealed that the Mo-35Ti-10Si-2B alloy was consisted of three phases, namely, (Mo, Ti)ss, (Mo, Ti)5SiB2 and (Ti, Mo)5Si3; whereas, Mo-35Ti-10Si alloy was found to be consisting of (Mo, Ti)ss, and (Mo,Ti)3Si phases. Since quantification of boron is difficult by EDS, Particle Induced Gamma-ray Emission (PIGE), a nuclear reaction analysis technique was used for chemical composition analysis of boron. The oxidation behavior of the Mo-35Ti-10Si-2B alloy in the temperature regime of 825-1250 °C was studied in detail and compared with boron-free Mo-35Ti-10Si alloy. Mo-35Ti-10Si-2B alloy exhibited superior oxidation behavior at intermediate temperatures of 825 °C, and excellent oxidation resistance at higher temperatures between 1000 and 1250 °C due to the formation of the protective borosilica and double oxide layers (TiO2 and duplex borosilica-TiO2), respectively. High-temperature oxidation mechanisms were discussed using detailed microstructural cross section analysis of the oxidized alloy samples. The micro-mechanical behavior of constitutive phases of the Mo-35Ti-10Si-2B alloy were studied by microhardness, nano-indentation and micropillar compression testing. The micropillar compression of (Mo, Ti)ss phase showed fairly ductile behavior with the evidence of activation of dislocation in the form of slip lines revealed through the post-deformation fractography. Deformation studies of (Mo, Ti)5SiB2 and (Ti, Mo)5Si3 phases were also carried out which showed large strain bursts indicating possibility of activation of dislocation activities even at room temperatures imparting low level of ductility. [ABSTRACT FROM AUTHOR]

Refractory metals have increasingly attracted the attention of researchers due to their excellent high-temperature strength, thermal conductivity, radiation resistance, and biocompatibility for applications in extreme environments such as aerospace and nuclear industries. However, beyond traditional manufacturing processes, the complex post-treatment process, high cost, and difficulty in manufacturing complex geometry components limit its further application in modern industry. Compared to conventional manufacturing processes, selective laser melting (SLM) technology, an emerging technology, can significantly simplify the production process and has the advantage of manufacturing parts with complex geometry. Therefore, there is increasing research on manufacturing refractory metals using SLM technology. This article describes the current research progress of pure refractory metals manufactured by SLM regarding the preparation process, microstructure, metallurgical defects, and mechanical properties of refractory metals (tungsten, molybdenum, niobium, tantalum, etc.). Generally speaking, there are some technical difficulties in the fabrication of refractory alloys by SLM, summarized in this paper. Finally, the article presented the prospect of developing SLM refractory metals. [ABSTRACT FROM AUTHOR]

Molten salt electrodeposition is the process of producing impressively dense deposits of refractory metals using the electrolysis of molten salts. However, predicting which electrochemical parameters and setup will best control different kinds of deposition (density, homogeneity, etc.) is an ongoing challenge, due to our limited understanding of the properties and mechanisms that drive molten salt electrodeposition. Because these advancements have been made rapidly and in different arenas, it is worth taking the time to stop and assess the progress of the field as a whole. These advancements have increasing relevance for the energy sector, the development of space materials and engineering applications. In this review, we assess four critical facets of this field: (1) how the current understanding of process variables enhances the electrodeposition of various molten salts and the quality of the resulting product; (2) how the electrochemical setup and the process parameters (e.g., cell reactions) are known to impact the electrodeposition of different metal coatings and refractory-metal coatings; (3) the benefits and drawbacks of non-aqueous molten salt electrodeposition, and (4) promising future avenues of research. The aim of this work is to enhance our understanding of the many procedures and variables that have been developed to date. The expectation is that this review will act as a stimulant, motivating scientists to delve further into the investigation of refractory-metal alloys by utilizing molten salt electrodeposition. [ABSTRACT FROM AUTHOR]

The isothermal and cyclic oxidation behavior of a multi-principal element (MPE) TiNbCr alloy at 800–1000 °C in air was studied and compared to Co-based alloy 188. The phase constitution of the MPE alloy consisted of a Nb-rich body-centered cubic (BCC) matrix and Cr-rich Laves precipitates. While isothermal tests conducted at 800 °C led to the formation of a complex mixture of Nb, Ti and Cr oxides, tests at 900 and 1000 °C resulted in the formation of an innermost Cr2O3-rich scale layer which provided improved oxidation resistance. However, for all exposure temperatures, the scaling kinetics of the alloy were linear and therefore deemed non-protective. In contrast, alloy 188 exhibited parabolic scaling kinetics and smaller mass gain per area than the MPE alloy. The similarity between isothermal and cyclic test results for the MPE alloy confirmed that the scale does not offer much protection. Additionally, for all tests, there was extensive internal oxidation and nitridation. [ABSTRACT FROM AUTHOR]

Additive friction stir deposition (AFSD) is a solid-state metal additive manufacturing technique, which utilizes frictional heating and plastic deformation to create large deposits and parts. Much like its cousin processes, friction stir welding and friction stir processing, AFSD has seen the most compatibility and use with lower-temperature metals, such as aluminum; however, there is growing interest in higher-temperature materials, such as titanium and steel alloys. In this work, we explore the deposition of an ultrahigh-temperature refractory material, specifically, a tantalum–tungsten (TaW) alloy. The solid-state nature of AFSD means refractory process temperatures are significantly lower than those for melt-based additive manufacturing techniques; however, they still pose difficult challenges, especially in regards to AFSD tooling. In this study, we perform initial deposition trials of TaW using twin-rod-style AFSD with a high-temperature tungsten–rhenium-based tool. Many challenges arise because of the high temperatures of the process and high mechanical demand on AFSD machine hardware to process the strong refractory alloy. Despite these challenges, successful deposits of the material were produced and characterized. Mechanical testing of the deposited material shows improved yield strength over that of the annealed reference material, and this strengthening is mostly attributed to the refined recrystallized microstructure typical of AFSD. These findings highlight the opportunities and challenges associated with ultrahigh-temperature AFSD, as well as provide some of the first published insights into twin-rod-style AFSD process behaviors. [ABSTRACT FROM AUTHOR]

The present study reports on additive manufacturing of a Ti-30Ta (at.%) high-temperature shape memory alloy (HT-SMA) using electron beam powder bed fusion (PBF-EB/M) technique. Detailed microstructure analysis was conducted to reveal the microstructural evolution along the entire process chain, i.e. from gas-atomised powder to post-processed material. PBF-EB/M processed structures with near full density and an isotropic, β-phase stabilised microstructure, i.e. equiaxed β-grains of around 20 µm in diameter with no preferred crystallographic orientation, are reported. As revealed by differential scanning calorimetry, post-process heat-treated Ti-Ta demonstrates a reversible martensitic phase transformation well above 100°C. Although partly unmolten Ta-particles after both gas atomisation and PBF-EB/M remain a challenge towards robust processing, PBF-EB/M appears to show significant potential for fabrication of Ti-Ta HT-SMAs, especially when functional metal parts and components with complex shapes are required, which are difficult to fabricate conventionally.

Abstract Our research focuses on enhancing the broadband absorption capability of organic solar cells (OSCs) by integrating plasmonic nanostructures made of Titanium nitride (TiN). Traditional OSCs face limitations in absorption efficiency due to their thickness, but incorporating plasmonic nanostructures can extend the path length of light within the active material, thereby improving optical efficiency. In our study, we explore the use of refractory plasmonics, a novel type of nanostructure, with TiN as an example of a refractory metal. TiN offers high-quality localized surface plasmon resonance in the visible spectrum and is cost-effective, readily available, and compatible with CMOS technology. We conducted detailed numerical simulations to optimize the design of nanostructured OSCs, considering various shapes and sizes of nanoparticles within the active layer (PM6Y6). Our investigation focused on different TiN plasmonic nanostructures such as nanospheres, nanocubes, and nanocylinders, analyzing their absorption spectra in a polymer environment. We assessed the impact of their incorporation on the absorbed power and short-circuit current (Jsc) of the organic solar cell.

This work focuses on the parameter development and microstructural characterization of Nb-based alloy C103 for thin wall structures produced via laser powder – directed energy deposition (LP – DED). Laser power and scanning speeds were varied as part of a design of experiments to identify adequate print parameters. Combinations were evaluated for relative density, porosity, and geometrical accuracy. A combination of a laser power of 1420 W and scanning speed of 14 mm/s resulted in a relative density >99%, exhibited a consistent weld bead profile and was used for further microstructural evaluation. A mix of optical and scanning electron microscopy (SEM) revealed small, slightly elongated grains along the edges and large epitaxial grains in the central region along the Build – Transverse view. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis revealed Hf rich columnar cells in the center that transition into an evenly spaced cellular structure towards the edges of the built sample. Electron backscatter diffraction (EBSD) scans show a sharp [001] texture when looking at the cross section of the sample along the build direction. The Build – Scan view revealed a zig – zag pattern that follows the back – and – forth deposition strategy that was used. Finally, microhardness measurements were taken in the as – built (AB) and stress relieved (SR) conditions to baseline preliminary mechanical properties. The AB condition exhibited a large amount of scatter in the data and averages up to 11% larger than the SR condition. The reduction in scatter upon applying the SR cycle are indicative of a large concertation of dislocations present in the AB condition.

This study focuses on synthesizing and characterizing mechanically alloyed refractory high entropy alloys (RHEA) containing TiMoNb, Cr, W, and Cr + W. Analytical techniques including XRD, SEM, EDX, DTA, and TGA were employed to explore the influence of Cr and W on the alloys' structure, morphology, and thermal stability towards oxidation. XRD analysis confirmed the formation of a single-phase bcc solid solution in TiMoNbCr, TiMoNbW, and TiMoNbCrW alloys. Crystallite size decreased as milling progressed, yielding average sizes of approximately 7.2 nm, 7.4 nm, and 9.7 nm, with lattice strains of 1.143%, 1.148%, and 1.15%, respectively. Both experimental and calculated values of lattice parameters converged to around 3.1685 ± 0.002 and 3.1791 ± 0.010 Å for all three alloys. The synergy of Cr and W in TiMoNb was observed for the first time, impacting dislocation density, hardness, and oxidation stability. TiMoNbCrW exhibited reduced dislocation density and the highest hardness (502 HV). TGA indicated enhanced oxidation resistance up to 400 °C for TiMoNbCrW compared to the most vulnerable TiMoNbCr alloy. [ABSTRACT FROM AUTHOR]

The paper presents the results of creating protective coatings on niobium and tantalum samples. These coated samples are tested for heat resistance in air in the temperature range of 1700–1900°C. The coating is formed by the method of activated vacuum diffusion saturation at temperatures of 1150–1310°C. When forming a part of the protective coatings, a layer of slurry is applied to the surface of the samples, followed by chemical and thermal treatment in a vacuum in the presence of NaCl vapours. A thermodynamic analysis of possible chemical reactions taking place in the process of formation of protective coatings is carried out. The developed heat-resistant coatings provide protection of niobium samples from air oxidation at a temperature of 1700°C from 8 to 13.5 hours. Heat-resistant coatings created on samples with Nb and Ta protect them from exposure to an oxidizing environment from 3 to 6.3 hours at a temperature of 1800°C and for 0.5 hours at a temperature of 1900°C. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of refractory metal on the high temperature properties of phenolic resin matrix composites, modified quartz fiber reinforced ceramizable composites were prepared by a molding process with a refractory component, tungsten, as the functional component and boron carbide as the ceramic forming agent. The effects of the tungsten and the boron carbide on the heat resistance of the composite were investigated. The results showed that the introduced refractory metal tungsten and the boron carbide can react to form tungsten borides and tungsten carbides at high temperature, and form a ceramic layer on the surface of the composite, which can fill the defects caused by pyrolysis of matrix and improve the high temperature performance of the composite. When the content of boron carbide was 10 wt% and the content of tungsten powder was 30 wt%, the flexural strength of the composite before and after heat treatment at 1200 °C were increased by 54.6% and 30.2% respectively compared with that without filler. [ABSTRACT FROM AUTHOR]

Due to their excellent high-temperature strength, good processing plasticity and corrosion resistance, refractory metals and their alloys are extensively utilized in the aviation, aerospace and nuclear industries, serving as important high-temperature structural materials. However, their susceptibility to oxidation often causes serious oxidation before reaching service temperatures, leading to rapid failure. High performance high-temperature protective coatings are essential for maintaining the performance of these refractory alloy materials at present. However, the actual service conditions of high-temperature protective coatings on surfaces of refractory metals and their alloy are very harsh, often accompanied by strong thermal shock, which is an important reason for coating failure. Therefore, a high-temperature protective coating on refractory metals must have excellent constant temperature oxidation resistance and good thermal shock resistance. In this paper, the thermal shock failure mechanism of high-temperature protective coatings on the surfaces of refractory metals was reviewed, and the key parameters affecting the coatings’ thermal shock resistance were discussed. The research status of the thermal shock resistance of three main coating systems, including silicides, metals and composite coatings on the surface of refractory metals, was expounded. Additionally, the modification methods and their improvement effects, such as optimizing the coating structure, adding ceramic particles and designing composite coatings to improve the thermal shock resistance of coatings, were reviewed. Finally, the future development direction of high-temperature protective coatings for refractory metals was prospected from three aspects: reducing the mismatch of thermal expansion coefficient between the coating and the substrate, improving the interface bonding performance between the substrate and coating and designing composite gradient coatings.

The development of Refractory High Entropy Alloys (RHEAs) for Additive Manufacturing has been advancing rapidly in recent years, buoyed by the triumph of RHEAs generated using traditional techniques in various applications. RHEAs, a recent category of materials possessing extraordinary high-temperature attributes, have only lately emerged. However, owing to their intricate microstructure, the production of RHEAs employing conventional methods such as casting and forging poses a challenge. On the other hand, Additive Manufacturing (AM) has exhibited significant potential for creating RHEAs due to its ability to generate intricate microstructures and complex geometries with minimal material wastage. The fundamentals of AM and RHEAs are introduced at the outset, in conjunction with the unique attributes of 3D-printed RHEA products, such as their enhanced strength and unique microstructure. The techniques for producing RHEA powders, including atomization and mechanical alloying, as well as the characteristics of the powder, are then elucidated. In this review article, we will provide a comprehensive overview of RHEAs produced using Additive Manufacturing (AM). We will examine the most innovative AM methods presently available for producing RHEAs, their microstructure, attributes, and potential applications.

Refractory metals and their carbides possess extraordinary properties when subjected to high temperatures and extreme environments. Consequently, they can act as key material systems for advancing many sectors, including space, energy and defence. However, it has been difficult to process these materials using the conventional routes of manufacturing. Additive manufacturing (AM) has shown a lot of potential to overcome the challenges and develop new material systems with tailored properties. This review provides a fundamental understanding of the challenges in the processing of refractory metals and their carbides, including microcracking, formation of brittle oxide phases and high ductile to brittle transition temperature (DBTT). We also highlight some of the novel approaches that have been taken to improve the processability of these challenging material systems using AM. These include in-situ reactive printing, ultrasonic vibration, laser beam shaping, multi-laser deposition and substrate pre-heating with a focus on microstructural changes to improve the properties of printed parts. [ABSTRACT FROM AUTHOR]

Sintering of tungsten nominally requires several hours at ultrahigh temperatures. We show this refractory metal can be sintered quickly by direct injection of current into dog bone shaped specimens. The current rate was varied from 10 A s−1 (fast) to 0.1 A s−1 (slow), leading to sintering in 2–200 s, respectively. Sintering occurred at the same current density, regardless of the current rate. In all instances, the samples sintered when they reached 1000°C. The phenomenological behavior of flash sintering of metals is described by three stages: an incubation time followed by electroluminescence, and finally by abrupt sintering to full density. It is conjectured that rapid sintering is instigated by the formation of Frenkel pairs (vacancies and interstitials), as well as electrons and holes. The point defects accelerate mass transport, whereas electrons and holes recombine to form photons. Calorimetric measurements show an endothermic reaction attributed to the creation of defects. Estimates suggest an unusually large concentration of Frenkel pairs. PS: Flash sintering is different than electro‐discharge‐sintering where a capacitor is discharged in a few milliseconds to sinter a metal. Here, instead of dumping large amount of energy at once, a power supply is programed to control the rate of current injection. [ABSTRACT FROM AUTHOR]

Outstanding inherent environmental resistance is a precondition for the use of superalloys in high-temperature applications. Besides high Al and Cr levels, also refractory metal concentrations (W and Ta) are reported to affect protective scale formation, as these elements are expected to affect the chemical activity and also the transport of protective scale formers within the alloy. In this study, we elucidate the high-temperature oxidation behavior of 3 Co-based (Co/Ni ratio: 1.4) and 3 Ni-based (Co/Ni ratio: 0.7) superalloys differing in W and Ta levels. Time-resolved thermogravimetric analysis (TGA) in synthetic air at 1050 °C and 1150 °C for 100 h, scanning electron microscopy analysis (SEM), thermodynamic calculations using the CALPHAD software Thermo-Calc, and diffusion couple experiments were conducted to assess the impact of the Co/Ni ratio and the refractory metal content on the oxidation performance. The results indicate that a low W content (3 vs. 5 at.%) and a high Ta content (2.1 vs. 1.5 at.%) beneficially affect the oxidation resistance, as alumina scale formation is facilitated. [ABSTRACT FROM AUTHOR]

The present study reports on additive manufacturing of a Ti-30Ta (at.%) high-temperature shape memory alloy (HT-SMA) using electron beam powder bed fusion (PBF-EB/M) technique. Detailed microstructure analysis was conducted to reveal the microstructural evolution along the entire process chain, i.e. from gas-atomised powder to post-processed material. PBF-EB/M processed structures with near full density and an isotropic, β-phase stabilised microstructure, i.e. equiaxed β-grains of around 20 µm in diameter with no preferred crystallographic orientation, are reported. As revealed by differential scanning calorimetry, post-process heat-treated Ti-Ta demonstrates a reversible martensitic phase transformation well above 100°C. Although partly unmolten Ta-particles after both gas atomisation and PBF-EB/M remain a challenge towards robust processing, PBF-EB/M appears to show significant potential for fabrication of Ti-Ta HT-SMAs, especially when functional metal parts and components with complex shapes are required, which are difficult to fabricate conventionally. [ABSTRACT FROM AUTHOR]

Abstract—The possibility of deposition of an Al–Zr–V–Nb coating in the form of a powder with a fraction of 0.063 mm and a humidity of 0.33%, which are measured using an AND MX-50 device, on a substrate made of 08Kh18N10 steel is considered. The deposition was carried out using a laser installation consisting of an LS-5 laser radiation source and a KUKA KR-60 ha robot in a protective argon atmosphere. Gas blowing was carried out 0.3 s before deposition and 1 s after it. For reliable bonding of the coating powder (Al–Zr–V–Nb) with the surface of the base material (08Kh18N10 steel), a mixture of powder with polyvinyl alcohol is applied onto the steel before melting. According to the data obtained on a Carl Zeiss EVO 40 scanning electron microscope, the optimum conditions of Al–Zr–V–Nb powder deposition on the base material corresponds to a power of 250 W, a processing speed of 0.5 m/s, and a coating thickness of 0.6 mm. At a lower power of 230 W, the coating cannot melt qualitatively; as a result, insufficient melting of the base metal by the coating metal (adhesion) occurs and partial separation takes place. If the power is increased to 270 W, the base and coating materials interact with each other well and create a high-strength coating monolayer, just as that under the optimum conditions. However, cracking occurs and microcracks appear during cooling because of a significant difference in the cooling rates (08Kh18N10 steel plate does not have time to cool at the rate of the coating material). Thus, there is a need to further increase the number of passes or to perform additional melting to create a reliable coating with no discontinuities and islands. Vickers microhardness (HV) measurements during the deposition of an Al–Zr–V–Nb coating demonstrate an increase in HV by more than two times compared to the base material, which is a sufficient reason for using an Al–Zr–V–Nb powder as a strengthening coating for 08Kh18N10 steel. [ABSTRACT FROM AUTHOR]

The appropriate hetero interfacial structure between metal and ceramics is a challenging topic in materials science. In this paper, a sandwich hybrid cladding structure made of SiCf/SiC composite and refractory metal niobium (Nb) is designed for application in a lead-cooled fast reactor. A diffusion reactive interfacial layer composed of β-SiC | NbC | Nb5Si4C | α-Nb5Si3 | β-Nb2C | Nb between SiCf/SiC composite and Nb is experimentally validated after heat treatment in a simulating reactor environment. Moreover, Kirkendall voids are found at the interface between Nb5Si4C and Nb5Si3 sublayers when the annealing temperature is higher than 1500 °C. Lastly, the formation mechanisms of interfacial structures are revealed based on thermodynamics and kinetics, meanwhile the diffusion coefficients k at 1500 °C and activation energy are calculated to be 2.81 × 10−14 m2/s and 270 kJ/mol, respectively. This work provides a practical strategy for developing hybrid composites of metal/ceramic matrix composites.

Additive friction stir deposition (AFSD) is a solid-state metal additive manufacturing technique, which utilizes frictional heating and plastic deformation to create large deposits and parts. Much like its cousin processes, friction stir welding and friction stir processing, AFSD has seen the most compatibility and use with lower-temperature metals, such as aluminum; however, there is growing interest in higher-temperature materials, such as titanium and steel alloys. In this work, we explore the deposition of an ultrahigh-temperature refractory material, specifically, a tantalum–tungsten (TaW) alloy. The solid-state nature of AFSD means refractory process temperatures are significantly lower than those for melt-based additive manufacturing techniques; however, they still pose difficult challenges, especially in regards to AFSD tooling. In this study, we perform initial deposition trials of TaW using twin-rod-style AFSD with a high-temperature tungsten–rhenium-based tool. Many challenges arise because of the high temperatures of the process and high mechanical demand on AFSD machine hardware to process the strong refractory alloy. Despite these challenges, successful deposits of the material were produced and characterized. Mechanical testing of the deposited material shows improved yield strength over that of the annealed reference material, and this strengthening is mostly attributed to the refined recrystallized microstructure typical of AFSD. These findings highlight the opportunities and challenges associated with ultrahigh-temperature AFSD, as well as provide some of the first published insights into twin-rod-style AFSD process behaviors.

An impact mill has been developed to produce powders from shavings of refractory metals using the impact grinding method for reuse in electrometallurgy in devices with screw feed, for example, in 3D printers. The proposed device provides high uniformity of grinding with a minimum content of dust fraction and impurity content at low technical and economic costs. The result is achieved using a Laval nozzle, which operates in the supersonic jet formation mode. In the area of the first Mach disk, there are rod fenders arranged in a cascade, and the impact plate is located in the turbulence zone and is equipped with winglets with holes for separating crushed metal. [ABSTRACT FROM AUTHOR]

The characteristics of spherical powders of (Mo,Nb) and (Nb,Mo) alloys prepared by the spark erosion technique are described. Two modes (U = 24 V, I = 10 A and U = 24 V, I = 20 A in distilled water) were chosen for powder preparation. The pyrolysis of the dielectric liquid during spark erosion leads to the formation of stable oxides NbO and NbO2 as thin crusts and spherical inclusions from 10 nm to 10 μm in powder particles. The largest deviations from electrode compositions (from 3 to 7 wt % Nb) are inherent to Mo alloys with 9 and 10 wt % of Nb. The number of NbO and, to a lesser extent, NbO2 inclusions in spherical powder increases with increasing Nb content in the alloy, but only in the series of (Mo,Nb) samples. Such regularity is not observed for (Nb,Mo) series. A decrease in current value results in a change in the granulometric compositions of spherical powders. The main fraction of powders at I = 20 A is 40–80 μm and I = 10 A is 20–50 μm. [ABSTRACT FROM AUTHOR]

Refractory metals such as molybdenum, tantalum, tungsten, niobium and their alloys have the characteristics of high melting point and good high temperature performance, which play a major role in the field of protection. However, due to their high cost, high melting point, low thermal conductivity and high brittleness, their processing is relatively difficult. By using specific processes to prepare refractory metal coatings on the substrate surface to achieve excellent mechanical properties and high-temperature performance of refractory metals without changing the substrate properties, and effectively reduce manufacturing costs, which has significant research value for equipment surface protection. Because the refractory metal coatings play an increasingly important role in the manufacturing industry, the plasma spraying, explosive spraying, laser cladding and cold spraying preparation technology of molybdenum, tantalum, tungsten, niobium and other refractory metal coatings were introduced firstly, and the characteristics of each process were summarized. On this basis, the microstructure and properties of refractory metal coatings prepared by different processes were analyzed and compared, and the improvement progress was summarized from three aspects of coating material composition and structure, process parameters and post-treatment. Finally, the existing problems and development directions of the refractory metal coating preparation technology were prospected.

The most promising directions of the development of heat-resistant alloys (HRAs) based on refractory metals are analyzed. The microstructures characteristic of HRAs, which it is advisable to form in promising alloys, are considered. The stability factors of the microstructure with respect to the diffusion coarsening of the hardening phases are discussed. Two groups of alloys are considered as the most promising HRAs based on refractory metals. First, the principles for design of HRAs based on (Pt, Ir)-Sc with heterophase γ-γ’ microstructure, where γ-matrix is a (Pt, Ir) solid solution with a FCC lattice, and γ’ is a strengthening phase with the structure L12 by analogy with Ni-base superalloys, are developed. The resistance of γ-γ’ microstructure in Ni, Pt and Ir alloys against the process of diffusion-limited coarsening is analyzed. It is shown that the diffusion permeability of Pt is several times less than that of Ni, so one should expect that Pt-based HRAs will not be inferior to Ni-based HRAs in terms of structural stability. The second group includes HRAs based on many not noble refractory metals. It is shown that solid solutions of the system (Ti, Zr, Hf, Ta, Nb) with a BCC lattice can be considered as a matrix of advanced refractory HRAs. The results of experimental studies of alloys based on (Ti, Zr, Hf, Ta, Nb) additionally alloyed with elements contributing to the formation of strengthening intermetallic and silicide phases are discussed. The issues of segregation of alloying elements at the grain boundaries of refractory alloys and the effect of segregation on the cohesive strength of the boundaries are considered.

Binary Ti-Ta and ternary Ti-Ta-Al alloys attracted considerable attention as new potential biomaterials and/or high-temperature shape memory alloys. However, conventional forming and manufacturing technologies of refractory based titanium alloys are difficult and cost-intensive, especially when complex shapes are required. Recently, additive manufacturing (AM) emerged as a suitable alternative and several studies exploited elemental powder mixing approaches to obtain a desired alloy and subsequently use it for complex shape manufacture. However, this approach has one major limitation associated with material inhomogeneities after fabrication. In present work, novel pre-alloyed powder material of a Ti-Ta-Al alloy was additively manufactured. Hereto, electron beam powder bed fusion (PBF-EB/M) technique was used for the first time to process such Ti-Ta based alloy system. Detailed microstructural analysis revealed that additively manufactured structures had a near full density and high chemical homogeneity. Thus, AM of pre-alloyed feedstock material offers great potential to overcome major roadblocks, even when significant differences in the melting points and densities of the constituents are present as proven in the present case study. The homogeneous microstructure allows to apply short-term thermal post treatments. The highly efficient process chain detailed will open up novel application fields for Ti-Ta based alloys.

A series of electric explosions were carried out on single and twisted conductors of various diameters made of titanium (Ti) and tungsten (W) in propane-butane. Analysis of the electro-physical characteristics of the explosion showed that the process of resistive heating of the conductors is characterized by two monotonically increasing sections on the voltage and current curves, separated by a flat segment (plateau), which corresponds to a relatively stable specific electrical resistance of refractory metals in a liquid state. The energy introduced into the conductor during the resistive heating stage, which can be higher or lower than the energy of sublimation of the conductor and can be regulated by changing the external parameters of the discharge circuit, is a key indicator that determines the structural-phase state of the destruction products and the chemical interaction of the conductor. Conditions were realized under which micro- and nanosized powder products of the electric explosion do not contain residual metals and consist entirely of carbide phases (TiC with an average microhardness of 29 580 MPa in the explosion of titanium conductors, and a mixture of W2C + WC1 – x dominated by stabilized high-temperature nonstoichiometric cubic carbide WC1 – x with an average microhardness of 16 770 MPa in the explosion of tungsten conductors). [ABSTRACT FROM AUTHOR]

The photovoltaic cells have undergone a series of metamorphosis since the perovskite materials are being used as light absorber in it. Owing to its superior light absorbing ability, perovskite materials have offered a bit of hope for future photovoltaic application. However, the stability and toxicity of perovskite-based solar cells have always remained a major concern. In this context, electronic characteristics pertaining to compounds of refractory metals, i.e., molybdenum and tungsten; and non-toxic properties of tin halide-based perovskite material may be considered to vanquish the issues related to durability and toxicity. This paper comprehends SCAPS 1D simulation and study of tin-based perovskite solar cell structures consisting of oxides and dichalcogenides of refractory metals viz oxides of molybdenum (Mo O x) , tungsten di-selenide (WS e 2) , molybdenum di-telluride (MoT e 2) and molybdenum di-sulfide (Mo S 2) as hole transport materials (HTMs). Post simulation, the optimized efficiencies were observed to be 31.95%, 30.89%, 31.92% and 31.86% for Mo O x , WS e 2 , MoT e 2 and Mo S 2 , respectively. Among these, perovskite solar cell consisting Mo O x as hole transport layer (HTL) displayed conspicuous result exhibiting open circuit voltage ( V oc ) of 1.1093 V, short circuit current density ( J sc ) of 33.88 mA/ cm 2 , fill factor (FF) of 85.01% and power conversion efficiency (PCE) of 31.95%. These parameters indicate that oxides and dichalcogenides of refractory metals viz oxides of molybdenum (Mo O x) , tungsten di-selenide (WS e 2) and molybdenum di-telluride (MoT e 2) can be optimistic materials for future generation solar cells. A comparative analysis of the proposed perovskite solar cells is carried out using oxides and dichalcogenides of refractory metals as HTLs, i.e., MoOx, WSe2, MoTe2 and MoS2 using SCAPS 1D simulator. Power conversion efficiency, fill factor, short circuit current density and open circuit voltage of the proposed device are characterized by thickness, doping concentrations, defect density and temperature. The proposed solar cells with MoOx, MoTe2 and MoS2 as HTLs, yielded high performance as compared to existing one. [ABSTRACT FROM AUTHOR]

General information about the method of electrospark plasma sintering (ESPS) of powder materials is presented, and its advantages and disadvantages are given. A review of results and achievements of domestic and foreign researchers in the field of refractory metal ESPS and their compounds is provided. The ESPS method is especially effective in consolidating powders of materials with a high melting point that are difficult to deform. During electrospark plasma sintering special attention should be paid to raw powder quality and cleaning processes for interparticle surfaces in order to obtain optimum finished product properties. Methods of comparative temperature measurement should be used to obtain more reliable data for ESPS, for example, according to input power. [ABSTRACT FROM AUTHOR]

Diboride‐based ultra‐high temperature ceramics (UHTCs) are a special class of ceramics with excellent comprehensive properties, which have extensive potential applications in extreme environments. However, their practical applications are limited, mainly due to the poor fracture toughness and thermal shock resistance. Refractory metals have high melting points, good ductility, and high toughness, which have huge potential to improve the properties of diboride‐based ceramics. As a special class of additives, they have been adopted to promote densification, improve microstructure, and properties. However, diboride‐based ceramics containing refractory metals have not received adequate attention due to relatively weak practical effects on property improvement. The present review highlights the progress and existing problems of transition metal diborides with refractory metal additives, including W, Ta, Mo, Nb, Hf, V, Cr, and Zr, focusing mainly on the microstructure change and property improvements, followed by challenges and possible future development strategies. [ABSTRACT FROM AUTHOR]

Electrodeposition of composite coatings based on cobalt, including refractory metals, allows obtaining coatings with a unique combination of physicochemical properties that cannot be achieved with other coating methods. The application of high-quality electrochemical composite coatings is only possible by establishing the characteristics of the electrolyte and electrolysis parameters. The characteristics of the scattering ability and specific electrical conductivity of Co-MoOx-WOx, Co-WOx-ZrO2, and Co-MoOx-ZrO2 electrolytes for depositing cobalt-based composite coatings have been established. The electrical conductivity values of the electrolytes for depositing cobalt-based composite coatings linearly increase with the temperature of the electrolyte, but their values at 25-30°C are sufficient for the deposition of high-quality coatings. It has been determined that within the current density range of 0.5--3.0 A/dm2 for Co-MoOx-WOx and up to 4.0 A/dm2 for Co-MoOx-ZrO2 and Co-WOx-ZrO2, the scattering ability remains above 85 %. The calculated activation energy of the electrical conductivity of complex electrolytes ranges from 22 to 29 kJ/mol, indicating the occurrence of mass transfer processes in the diffusion regime. Using insoluble inert stainless steel anodes in the technological process is justified. [ABSTRACT FROM AUTHOR]