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Additive manufacturing of tungsten (W) is challenging due to its high melting point, high thermal conductivity, oxidation tendency, and brittleness from grain boundary (GB) oxides. In this study, the processing of W through laser powder bed fusion is investigated. Parts are fabricated under argon (Ar) and nitrogen (N2) atmospheres using the same processing parameters. The part produced in Ar has cracks with oxide precipitates decorating the fractured GBs. On the other hand, crack‐free W samples are produced under N2 atmosphere without any additional process modification. In both cases, the oxygen (O) content in the LPBF samples is similar to the starting powder. Interestingly, the analysis of the samples fabricated in nitrogen suggests that nitrogen is retained beyond the equilibrium solid solubility limit, while high‐resolution electron micrographs of fractured surfaces reveal reduced levels of oxides at GBs. Increased hardness for samples processed under N2 atmosphere is observed. Density Functional Theory (DFT) calculations performed to study the influence of interstitial nitrogen on oxygen diffusion in W indicated a hindrance to O diffusion from the presence of dissolved N. [ABSTRACT FROM AUTHOR]

Rhenium is utilized as an additive to improve the high-temperature strength and stability of materials, such as nickel-based superalloys, which are employed in jet engine turbine blades, alloys for ultrahigh-temperature thermocouples, and platinum catalysts, which are used in oil refining. Currently, around 80% of rhenium demand is for superalloy production, and this demand has been increasing with the increase in demand for aircrafts. The abundance of rhenium in the earth's crust is only 1 ppb (10−9), which is less than those of platinum and gold. Owing to the rare and unevenly distributed nature of rhenium, there is the risk of supply disruption and rapid increases in its price. In this article, the recent situation of rhenium and its compounds are reviewed, especially with respect to their demand, distribution characteristics, smelting, and recycling. Some of the technologies recently developed for smelting and recycling rhenium are also introduced. [ABSTRACT FROM AUTHOR]

The basic principle of electron beam melting (EBM) technology is the additive generation of structures by the selective melting of metal powder layer by layer with an electron beam under vacuum conditions. The cooling rate of the EBM process can be reduced drastically by increasing the temperature of the powder bed to avoid the formation of solidification cracks by brittle materials such as tungsten (W). This refractory metal is a promising candidate as plasma facing material for future fusion reactors. The selection of tungsten is owing to its physical properties such as the melting point of 3420 °C, the high strength and high thermal conductivity, the low thermal expansion and low erosion rate. Disadvantages are the low ductility, and fracture toughness at room temperature. Furthermore, the manufacturing by mechanical machining, such as milling and turning, is extremely cost and time consuming. An interesting alternative process route to conventional manufacturing technologies is EBM. It allows the near-net shape fabrication of prototype structures with geometrical freedom and has proven its capability for mass production by the manufacturing of hip prostheses made of titanium.This manuscript describes the fabrication of tungsten parts via electron beam melting, with application to the manufacturing of divertor armour. The investigation comprises the microstructure examination, crystallographic texture, as well as mechanical characterization via tensile and Charpy impact testing. This is followed by the presentation of process routes to fabricate mock-ups with different designs and copper cooling structures.Furthermore, the different mock-ups were exposed to high heat flux (HHF) applying transient thermal loads to assess thermal shock and thermal fatigue performance of EBM tungsten.Post mortem analyses were performed quantifying the occurring damage with respect to reference tungsten grades by microscopical means.The achieved results demonstrate the high potential to process tungsten via electron beam melting.

A tungsten carbide (WC) ceramic coating is fabricated by a new method of Fe-coating-mediated carburization, in which the tungsten substrate is carburized using a pre-electroplated Fe coating. In this carburization process, the electroplated Fe coating is transformed into a carbon steel coating, and a significant number of interstitial carbon atoms in the carbon steel coating diffuse into the tungsten substrate, forming a WC ceramic coating on it. The so-formed WC ceramic coating is nonporous, uniform in thickness, and has a microstructure with grain size gradient. The thickness of the electroplating Fe coating had no effect on the microstructure and growth rate of WC coating when the thickness of the electroplating iron coating was in the range of 5–20 μm. The hardness of the coating reached 2800 HV0.05, and the adhesion strength between the substrate and coating was greater than 100 N. Compared with conventional solid carburization, Fe-coating-mediated carburization can generate nonporous ceramic coatings over wider ranges of temperature and carbon potential at a higher growth rate. Accordingly, the microstructure and properties of the coating could be optimized further.

Refractory metals offer exceptional benefits for high temperature electronics including high‐temperature resistance, corrosion resistance and excellent mechanical strength, while their high melting temperature and poor processibility poses challenges to manufacturing. Here this work reports a direct ink writing and tar‐mediated laser sintering (DIW‐TMLS) technique to fabricate three‐dimensional (3D) refractory metal devices for high temperature applications. Metallic inks with high viscosity and enhanced light absorbance are designed by utilizing coal tar as binder. The printed patterns are sintered into oxidation‐free porous metallic structures using a low‐power (<10 W) laser in ambient environment, and 3D freestanding architectures can be rapidly fabricated by one step. Several applications are presented, including a fractal pattern‐based strain gauge, an electrically small antenna (ESA) patterned on a hemisphere, and a wireless temperature sensor that can work up to 350 °C and withstand burning flames. The DIW‐TMLS technique paves a viable route for rapid patterning of various metal materials with wide applicability, high flexibility, and 3D conformability, expanding the possibilities of harsh environment sensors. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) are among the promising candidates for the design of structural materials in advanced nuclear energy systems. The effects of Cr, V, Ta, and Ti elements and ball milling on the microstructural evolution and mechanical properties of model RHEAs were investigated. The results show that W-rich BCC1 and Ta-rich BCC2 solid solution phases were generated after a long milling duration. After high-temperature sintering, the (Cr, Ta)-rich phase associated with the Laves phase was observed in the Cr-containing model RHEAs. In addition, a high level of Ti, Ta, and V contents promoted the in situ formation of oxide particles in the alloys. Complex TiTa2O7 and Ta2VO6 oxide phases were identified by TEM, which suggests a solid-state reaction of Ti-O, Ta-O, and V-O subjected to high-energy ball milling. The oxide particles are uniformly dispersed in the BCC matrix, which can result in dispersion strengthening and the enhancement of mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract Refractory metals offer exceptional benefits for high temperature electronics including high‐temperature resistance, corrosion resistance and excellent mechanical strength, while their high melting temperature and poor processibility poses challenges to manufacturing. Here this work reports a direct ink writing and tar‐mediated laser sintering (DIW‐TMLS) technique to fabricate three‐dimensional (3D) refractory metal devices for high temperature applications. Metallic inks with high viscosity and enhanced light absorbance are designed by utilizing coal tar as binder. The printed patterns are sintered into oxidation‐free porous metallic structures using a low‐power (

Exploding Wire Pulsed Plasma System (EWPPS) used in oil recovery operations has been construct and developed with an initial energy release of 1.5 kJ in a fusion laboratory. Recently, the final experiments have been carried out on the purpose device operating in microsecond time scale in air and fluid medium successfully. In this setup, a single wire feeder is used for tests. Also, to study and develop the shock waves caused by wire explosions in the industry, the diagnostic tools of voltage probe, current coil, pressure probe and photodiode have been used. Choosing the optimal material of wire is one of the basic factors in creating a suitable shock wave. In addition, the impact of wire inductance on discharge current, voltage, pressure and shock wave strength has been investigated by applying two sets of wires, refractory (Cu, Cu-Ni, and Steel) and non-refractory (W, W-Al, Mo). The results show that the strongest shock wave is produced while the transition from warm wire to dense plasma happens. The soft X-ray intensity of both wire series has been measured using a photodiode BPX-65 (<10 keV). The comparison shows higher X-ray intensity for non-refractory wires than that for refractory wires. In good agreement, the maximum value of the shock wave was 8.7 and 6.6 MPa for non-refractory metals with high inductance and refractory metals with low inductance, respectively. • Design of a novel 1.5 kJ Exploding Wire Pulsed Plasma System (EWPPS). • Successful implementation and testing of EWPPS. • Successful experiments in air and fluid medium under μs time scale. • Optimization of the EWPPS efficiency using the inductance of the circuit. • Utilizing of the photodiode BPX-65 to reveal the soft X-ray intensity of wire. [ABSTRACT FROM AUTHOR]

Pure molybdenum (Mo) additively manufactured via laser powder bed fusion is challenging due to its high laser reflectivity and sensitivity to cracking. To achieve crack-free pure Mo alloy and enhance production efficiency, this study employs a high-power (350 W) printing process with a layer thickness of 30 μm, resulting in the successful fabrication of pure Mo with a relative density of 99.2%. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) revealed that the pure Mo specimens prepared by LPBF process exhibited different preferential grain orientations and lattice distortions in various building directions, with higher texture strength on the XOZ plane and greater lattice distortion on the XOY plane. The hardness of the pure Mo specimens reached 208 HV, with uniaxial compressive strength and elongation at 535 MPa and 20.9%, respectively, surpassing existing literature values by 37.2% and 8.0%. Furthermore, the dry friction behavior and mechanism of LPBF-manufactured pure molybdenum were investigated for the first time and compared to traditional powder metallurgy. Consequently, this research offers valuable insights for manufacturing crack-free LPBF pure molybdenum components with 30 μm layer thickness, boasting superior mechanical and wear resistance. • Pure Mo was successfully fabricated with a relative density of 99.2% and no cracks using a high-power LPBF printing process. • Compressive performance and wear resistance of LPBF pure Mo were studied for the first time. • The coefficient of friction for LPBF pure Mo is lower compared to PM pure Mo. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) are among the promising candidates for the design of structural materials in advanced nuclear energy systems. The effects of Cr, V, Ta, and Ti elements and ball milling on the microstructural evolution and mechanical properties of model RHEAs were investigated. The results show that W-rich BCC1 and Ta-rich BCC2 solid solution phases were generated after a long milling duration. After high-temperature sintering, the (Cr, Ta)-rich phase associated with the Laves phase was observed in the Cr-containing model RHEAs. In addition, a high level of Ti, Ta, and V contents promoted the in situ formation of oxide particles in the alloys. Complex TiTa2O7 and Ta2VO6 oxide phases were identified by TEM, which suggests a solid-state reaction of Ti-O, Ta-O, and V-O subjected to high-energy ball milling. The oxide particles are uniformly dispersed in the BCC matrix, which can result in dispersion strengthening and the enhancement of mechanical properties.

This paper is a study of the microstructure and other selected properties of solid-state, high-speed, rotary friction-welded tungsten and mild steel (S355) joints. Due to the high affinity of tungsten for oxygen, the welding process was carried out in a chamber with an argon protective atmosphere. Joints of suitable quality were obtained without any macroscopic defects and discontinuities. Scanning electron microscopy (SEM) was used to investigate the phase transformations taking place during the friction welding process. Chemical compositions in the interfaces of the welded joints were determined by using energy dispersive spectroscopy (EDS). The microstructure of friction welds consisted of a few zones, fine equiaxed grains (formed due to dynamic recrystallization) and ultrafine grains in the region on the steel side. A plastic deformation in the direction of the flash was visible mainly on the steel side. EDS-SEM scan line analyses across the interface did not confirm the diffusion of tungsten to iron. The nature of the friction welding dissimilar joint is non-equilibrium based on deep plastic deformation without visible diffusive processes in the interface zone. The absence of intermetallic phases was found in the weld interface during SEM observations. Mechanical properties of the friction-welded joint were defined using the Vickers hardness test and the instrumented indentation test (IIT). The results are presented in the form of a distribution in the longitudinal plane of the welded joint. The fracture during strength tests occurred mainly through the cleavage planes at the interface of the tungsten grain close to the friction surface. [ABSTRACT FROM AUTHOR]

The objective of this research was to demonstrate that the damage tolerance of Si3N4 could be significantly improved by forming laminate composites with refractory metals, providing materials that undergo graceful failure, rather than the fast-fracture mechanism exhibited by monolithic Si3N4. A damage tolerant Si3N4 could be used as a ring material in an all-ceramic bearing, decreasing the chance for catastrophic failure if the ring is stressed in tension during operation. The technical approach formed a laminate composite material using alternating Si3N4-metallic layers, with both outer layers being Si3N4 to take advantage of its greater wear resistance, chemical stability, and thermal stability. The metallic layers are designed to arrest any cracks in the outer layers, thus producing a toughened Si3N4 and avoiding the catastrophic failure behavior exhibited by monolithic ceramics. The laminate composites were fabricated using a combination of tape-casting Si3N4 and metals from slurries, as well as metal foils, followed by hot pressing at 1500°C. The metallic materials employed were chromium, titanium, and tantalum. Analysis confirmed that the interfaces were well formed, and the laminates with chromium and titanium formed intermetallic compounds more readily than the composites with tantalum. The Si3N4-Ta laminates demonstrated crack deflection and bridging behavior during failure and flexural strength of 800–900 MPa. The hardness and elastic modulus of Si3N4-Ta laminates measured by nanoindentation were similar to those reported in literature. The hardness across the interface of the Si3N4-Ta composite varied according to the composition of the interface, which displayed a profile indicative of a diffusion bond. [ABSTRACT FROM AUTHOR]

Polymeric precursors with refractory metal in the main chain while still possess meltable/soluble characteristics are highly desired for ultra-high temperature ceramics (UHTCs). Herein, we proposed a stepwise synthesis of polyzirconosilane (PZCS) with Zr-C-Si-N polymeric chain. The reaction mechanism was discussed based on the frontier molecular orbital theory and atom transfer radical polymerization, which was initiated and propagated by a low oxidation state active specie of Cp 2 Zr(II). The PZCS precursor has excellent soluble and meltable properties with a softening point of 80.8 ~ 89.2 oC, which could be spun into green fibers by melt spinning technique. The ceramization process of PZCS was studied, and the resulted SiZrNC multinary ceramics were composed of ZrC/SiC nanocrystals embedded by graphitized carbon phase. The excellent mouldable properties, oxygen-free compositions and high Zr content of PZCS make it an ideal precursor for the preparation of UHTCs matrixes and fibers. • In this work, the conclusions and innovations are as follows: • A novel polymeric precursor with Zr-C-Si-N main chain structure was synthesized through a two-step method using Cp 2 ZrCl 2 , Mg, and [ClCH 2 Si(CH 3) 2 ] 2 NH as raw materials. The low oxidation state active specie of Cp 2 Zr(Ⅱ) with two semi-filled outer orbits was obtained by the reaction of Cp 2 ZrCl 2 with Mg, which played an important role in the reaction. • The synthesized PZCS precursor exhibited excellent soluble and meltable properties with a softening point of 80.8 ~ 89.2 oC, which could be spun into green fibers by melt spinning. In addition, the green fibers can well preserve the organic structure and morphology when placed in air for a few hours. • The pyrolysis of PZCS precursor was studied in detail, and its ceramic yield was 50.82 wt%. Thermal treatment of the prepared single-source precursor resulted in SiZrNC composites with ZrC/SiC nanocrystals dispersed in graphitized carbon matrix. [ABSTRACT FROM AUTHOR]

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Pure molybdenum produced by additive laser powder bed fusion (LPBF) processes has a coarse, epitaxially-grown columnar grain structure with cracks located at high-angle grain boundaries, which are embrittled through oxygen segregation. The tensile strength of these pure molybdenum specimens is only 50 MPa, or 11% of the strength of powder metallurgically sintered, deformed, and recrystallized molybdenum. Alloying molybdenum with carbon can reduce cracks, increase density to 99.5%, and thus increase tensile strength to 650 MPa. The addition of carbon prevents embrittled grain boundaries and high residual porosity by outgassing oxygen, trapping any residual oxygen in the oxygen-soluble Mo2C carbide, and increasing the grain boundary surface on which the oxygen is distributed. In this study, we investigated the grain size, tensile strength, and hardness of five different molybdenum-carbon alloys produced via LPBF at constant process parameters. Our alloys ranged from pure molybdenum to 2.2 wt% carbon, which corresponds to a near-eutectic composition. In the absence of extrinsic nucleant particles in the melt, the relationship between grain size and solute concentration—and thus the growth restriction factor—follows an inverse exponential Arrhenius-type equation. We attributed grain refinement at higher carbon contents to increasing thermal and constitutional supercooling. The supercooling allows grains to nucleate and grow on the underlying solidified layer, where the fastest growth direction 〈100〉 is better aligned to the thermal gradient than that of the epitaxially growing grains.

A multi-component diffusion couple of diamond/Mo/FeCoCrNi HEA composite structure was designed and fabricated, and the refractory metal Mo was introduced to construct a diffusion barrier between diamond and HEA. The interfacial diffusion and microstructural evolution of the diffusion couple were studied. The results indicated that, after diffusion, the Diamond/HEA composite structure formed equiaxed Cr-rich σ phase and polycrystal graphite at interface. In contrast, the Diamond/Mo/HEA composite structure formed Mo-rich μ phase at the interface. The graphitization in Diamond/Mo/HEA was significantly reduced compared to the Diamond/HEA composite structure. Due to the low solubility of Fe, Co and Ni in μ phase, and the low interdifussion coefficient of Co, Ni in Mo, the Mo layer was manifested as an effective diffusion barrier against the diffusion of HEA into the diamond. Moreover, the metallurgical bonding with high interfacial bonding strength was formed at the interface of the composite structures due to the semi-coherent interface and incoherent interface in Diamond/HEA and Diamond/Mo/HEA, respectively.

Spin‐orbit torque (SOT)‐based magnetization switching is a promising candidate for the innovation and developments of spintronic devices. However, the necessity of an in‐plane magnetic field to induce deterministic switching is an obstacle to feasibility in practical applications. Here, it is shown that the field‐free current‐induced magnetization switching in a perpendicular magnetized Pt1−xMox/Co/Ru heterostructure with x = 0, 0.04, 0.07, 0.12, and 0.17. Applying an in‐plane charge current through the Pt1−xMox layer, the device can achieve a high‐efficiency field‐free current‐induced magnetization switching with competing spin currents generated from a single Pt1−xMox alloy layer due to opposite spin Hall angles (θSHA) of Pt and Mo atoms and locally induced electric field. Remarkably, the large θSHA of about 0.35 is achieved in the optimal composition of Pt0.88Mo0.12 alloy, which is much higher than that of the pure Pt structure. The results pave the way to resolve the future problems of scalability and thermal stability for SOT‐driven magnetic tunnelling junctions. [ABSTRACT FROM AUTHOR]

In the present study, we fabricated tungsten carbide (WC) coatings on tungsten using a recently proposed two-step interstitial carburization method and systematically investigated their mechanical behavior, including their responses to indentation, scratch, and wear. The coatings comprised WC and a very small amount of W 2 C dispersed at the coating–substrate interface. The volume fraction of the carbide phases nearly reached 100 %, and the grain size of WC increased with increasing distance from the surface, thus exhibiting a distinct gradient microstructure with columnar WC grains. Indentation experiments on the coating surface showed that the coating attained a hardness of 25 GPa and cracks were generated when the indentation load exceeded 5 N. The fracture toughness of the coating was estimated to be 2.5 MPa m1/2. The response of the coating to scratching was not sensitive to the scratching speed, and an increase in the scratching speed did not alter the geometry of the grooves, but it resulted in an earlier occurrence and a higher density of cracks; further, it leads to increased acoustic emission. Delamination of the coating did not occur when the normal load was in the range of 0–100 N, indicating that the adhesion strength of the coating was greater than 100 N. We studied the wear behavior using a ball-on-disc tribometer and found that the WC coatings exhibited extraordinarily high wear resistance, and both abrasive wear and adhesive wear mechanisms acted concurrently during wear. Therefore, we verified that the WC coatings prepared by interstitial carburization have a high hardness and excellent scratch and wear resistance. [ABSTRACT FROM AUTHOR]

This paper is a study of the microstructure and other selected properties of solid-state, high-speed, rotary friction-welded tungsten and mild steel (S355) joints. Due to the high affinity of tungsten for oxygen, the welding process was carried out in a chamber with an argon protective atmosphere. Joints of suitable quality were obtained without any macroscopic defects and discontinuities. Scanning electron microscopy (SEM) was used to investigate the phase transformations taking place during the friction welding process. Chemical compositions in the interfaces of the welded joints were determined by using energy dispersive spectroscopy (EDS). The microstructure of friction welds consisted of a few zones, fine equiaxed grains (formed due to dynamic recrystallization) and ultrafine grains in the region on the steel side. A plastic deformation in the direction of the flash was visible mainly on the steel side. EDS-SEM scan line analyses across the interface did not confirm the diffusion of tungsten to iron. The nature of the friction welding dissimilar joint is non-equilibrium based on deep plastic deformation without visible diffusive processes in the interface zone. The absence of intermetallic phases was found in the weld interface during SEM observations. Mechanical properties of the friction-welded joint were defined using the Vickers hardness test and the instrumented indentation test (IIT). The results are presented in the form of a distribution in the longitudinal plane of the welded joint. The fracture during strength tests occurred mainly through the cleavage planes at the interface of the tungsten grain close to the friction surface.

In this study, Ta powder was produced from Ta scarp via chemical processes using Mg and Ca powders. Initially, tantalum scraps were converted to tantalum oxide (Ta2O5) at 1100 °C in an oxygen atmosphere. Tantalum oxide was then reduced to Tantalum powder with Mg in a vacuum environment at 950 to 1200 °C for 3 hours. The obtained Ta powders further were reacted with Ca at 950 °C for 5 hours in a vacuum atmosphere. The powders were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as conducting oxygen content measurement. The results showed that the average particle size of the produced Ta powders was around 58 nm with oxygen contents of 250 ppm. [ABSTRACT FROM AUTHOR]

A new strategy for preparing TaC coatings on easily oxidized tantalum by non-vacuum carburizing is proposed, which is called Fe-coating-mediated carburization. Fe-coating-mediated carburization is the carburization of Ta substrate with a pre-electroplated Fe coating. During carburization, the electroplated Fe coating was transformed into a carbon steel coating, while a high concentration of interstitial carbon atoms in the carbon steel coating diffused into tantalum, forming a TaC coating. The Fe coating isolated the tantalum from oxygen and changed the state of active carbon atoms in contact with the tantalum surface. The TaC coatings are nonporous, have fine grains with grain size gradients, and combine high hardness (32 GPa) and excellent coating-substrate adhesion strength (>100 N). The Fe-coating-mediated carburization realizes the carburization of oxidizable carbide-forming metals under non-vacuum conditions, providing a new strategy to prepare protective coatings with both high hardness and high coating-substrate adhesion for carbide-forming metals. • A surface hardening method called Fe-coating-mediated carburization is proposed. • Non-vacuum carburization of easily oxidized tantalum is realized. • The coating is nonporous and has a gradient microstructure with fine TaC grains. • The hardness reaches 32 GPa and the adhesion strength exceeds 100 N. • The function of the Fe coating and the advantages of this method are elucidated. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) additive manufacturing of pure tungsten encounters nearly all intractable difficulties of SLM metals fields due to its intrinsic properties. The key factors, including powder characteristics, layer thickness, and laser parameters of SLM high density tungsten are elucidated and discussed in detail. The main parameters were designed from theoretical calculations prior to the SLM process and experimentally optimized. Pure tungsten products with a density of 19.01 g/cm3 (98.50% theoretical density) were produced using SLM with the optimized processing parameters. A high density microstructure is formed without significant balling or macrocracks. The formation mechanisms for pores and the densification behaviors are systematically elucidated. Electron backscattered diffraction analysis confirms that the columnar grains stretch across several layers and parallel to the maximum temperature gradient, which can ensure good bonding between the layers. The mechanical properties of the SLM-produced tungsten are comparable to that produced by the conventional fabrication methods, with hardness values exceeding 460 HV0.05 and an ultimate compressive strength of about 1 GPa. This finding offers new potential applications of refractory metals in additive manufacturing.

We demonstrate that the atomic size mismatch, δ, can be used to predict the boundary between amorphous and crystalline phase formation ranges in ZrNbCrMo thin films. The concentrations of all alloying elements are varied systematically, which induces a change in δ. The formation of an amorphous phase is observed by x-ray diffraction for δ ≥ 6.9%, whereas crystallization is detected for δ ≤ 6.9%. The crystallization temperature increases from 575 to 625 ∘C by increasing Nb + Mo content from 10 to 34 at.%, and decreases to 475 ∘C upon further additions of Nb + Mo. Calphad calculated liquidus temperatures, Tl, increases monotonously and δ decreases monotonously with Nb and Mo additions. Consequently, δ and Tl do not serve as predictors for thermal stability of ZrNbCrMo thin films.

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nb (niobium) and Nb-based alloys are promising refractory materials for use at high temperatures. However, due to the weak resistance to high temperature oxidation, a dramatic modification in oxidation resistance is required to use Nb-based refractory materials. Alloying Nb with other elements improves its mechanical properties and oxidation resistance to some extent. An improvement in oxidation resistance by forming Al (aluminum) based coating with dense Al2O3 by utilizing different methods seems a prospective way for developing Nb-based refractory materials. In the current study, halide activated pack cementation (HAPC) and subsequent plasma electrolytic oxidation (PEO) were combined to form an oxidation-resistant coating on niobium base metal. Prospective Al2O3 phases in amorphous or various kind of crystalline forms at the top were formed by anodic oxidation of cementation layer and modified to oxidation resistant -Al2O3 by subsequent annealing at 1000oC for 2 hours in argon gas. Comparing weight changes after oxidation tests shows that formed protective oxide film has a noticeable positive effect on the protection of Nb metal at high temperatures.

Electromagnetic wave absorbers with very long absorption spectra have become an important target for optoelectronic materials and technology. In this paper, we propose a titan-based resonator to achieve near-perfect wide spectrum absorption of solar radiation. In the whole spectrum of the study, the average absorption of the absorber is up to 93.17%. Using surface plasmon resonance, up to 1759 nm in the range of absorption over 90% in the absorption spectrum studied (166.8–1926.6 nm). Furthermore, the absorption spectrum of the absorber is not sensitive to polarization. Since the material constituting the absorber is a mainly refractory metal, it can work under a complex electromagnetic environment (solar radiation) and high-temperature conditions. Later, the influence of various parameters on the absorption spectrum and the mechanism of forming broadband absorption was explored. It is also found that other refractory metals similar to titanium have a good effect on the absorber with this structure. We report a numerical study of an ideal solar broadband absorber based on refractory titanium. By optimizing the design, the average solar absorption efficiency of the absorber in the studied wavelength range (100–2000 nm) is as high as 93.17%. Image 1 • The absorber is capable of obtaining ultra-wide spectrum absorption of solar energy. • The absorbency of the absorber can be adjusted by optimizing the structural parameters. • The absorber is insensitive to changes in the angle of incidence and polarization. • The absorber has certain versatility to other refractory materials. [ABSTRACT FROM AUTHOR]

To clarify the inherent differences between solid and interstitial carburization in the fabrication of carbide coating on tungsten, tungsten was carburized using these two carburization methods at a unified temperature (1100 °C) and carbon potential, and the coating microstructure, formation mechanism, hardness and scratch resistance were compared. The coating prepared by solid carburization was composed of fine equiaxed WC grains, while the coating prepared by interstitial carburization consisted of larger columnar WC grains and a small quantity of W 2 C dispersedly distributed at the interface of the coating and the substrate. Compared to solid carburization, the growth rate and nanohardness of the coatings prepared by interstitial carburization were significantly higher. The main reason for the differences in microstructure and growth rate of the coating is the influence of Fe element, which is inevitably present in the coatings fabricated by interstitial carburization. The other reason is that interstitial carburization is more efficient in the process of introducing carbon atoms into tungsten, because interstitial carbon atoms can enter tungsten without surface absorption. The research deepens the understanding of the inherent characteristics of the two carburizing methods. • The inherent differences of solid and interstitial carburization are clarified. • The coatings are different in microstructure, growth rate and mechanical performance. • The differences in microstructure and growth rate stem from the influence of Fe. • Interstitial carburization is more efficient than solid carburization. [ABSTRACT FROM AUTHOR]

This study synthesized refractory metal-oxide-doped titanate nanotubes (TNTs) using a hydrothermal process and investigated their photocatalytic activity under ultraviolet and visible light irradiation. Refractory metal doping ions such as Mo6+ and W6+ can be supplied from molybdenum oxide and tungsten oxide sources. The refractory metal-doped TNT may act as an electron trap or enhance the adsorption capacity, which increases the number of active sites and promotes separation efficiency.

Hydrogen has been receiving great attention as an energy carrier for potential green energy applications. Hydrogen storage is one of the most crucial factors controlling the hydrogen economy and its future applications. Amongst the several options of hydrogen storage, light metal hydrides, particularly nanocrystalline magnesium hydride (MgH2), possess attractive properties, making them desired hydrogen storage materials. The present study aimed to improve the hydrogen storage properties of MgH2 upon doping with different concentrations of zirconium carbide (ZrC) nanopowders. Both MgH2 and ZrC were prepared using reactive ball milling and high-energy ball milling techniques, respectively. The as-prepared MgH2 powder was doped with ZrC (2, 5, and 7 wt%) and then high-energy-ball-milled for 25 h. During the ball milling process, ZrC powders acted as micro-milling media to reduce the MgH2 particle size to a minimal value that could not be obtained without ZrC. The as-milled nanocomposite MgH2/ZrC powders consisted of fine particles (~0.25 μm) with a nanosized grain structure of less than 7 nm. Besides, the ZrC agent led to the lowering of the decomposition temperature of MgH2 to 287 °C and the reduction in its apparent activation energy of desorption to 69 kJ/mol. Moreover, the hydrogenation/dehydrogenation kinetics of the nanocomposite MgH2/ZrC system revealed a significant improvement, as indicated by the low temperature and short time required to achieve successful uptake and release processes. This system possessed a high capability to tackle a long continuous cycle lifetime (1400 h) at low temperatures (225 °C) without showing serious degradation in its storage capacity.

In this paper, we designed an ultra-wideband solar energy absorber and approved it numerically by the finite-difference time-domain simulation. The designed solar energy absorber can achieve a high absorption of more than 90% of light in a continuous 3.506 μm (0.596 μm–4.102 μm) wavelength range. The basic structure of the absorber is based on silicon dioxide colloidal crystal and Ti. Since the materials have a high melting point, the designed solar energy absorber can work normally under high temperature, and the structure of this solar energy absorber is simpler than most solar energy absorbers fabricated with traditional metal. In the entire wavelength band researched, the average absorption of the colloidal crystal-based solar energy absorber is as high as 94.3%, demonstrating an excellent performance under the incidence light of AM 1.5 solar spectrum. In the meantime, the absorption spectrum of the solar energy absorber is insensitive to the polarization of light. In comparison to other similar structures, our designed solar energy absorber has various advantages, such as its high absorption in a wide spectrum range and that it is low cost and easy to make.

In this study, Ta powder was produced from Ta scarp via chemical processes using Mg and Ca powders. At first, Tantalum scraps were converted to Tantalum oxide (Ta2O5) at 1100˚C in an oxygen atmosphere. Tantalum oxide was reduced to Tantalum powder with Mg in a vacuum environment at 950 to 1200˚C for 3 hours. The obtained Ta powders further were reacted with Ca at 950˚C for 5 hours in a vacuum atmosphere. The powders were analyzed through X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), as well as oxygen measurement. The results show that the average particles size of the produced Ta powders is about 58 nm with oxygen contents of 250 ppm.

Addition of Al can decrease density and improve oxidation resistance of refractory high entropy alloys (RHEAs), but may cause complicated precipitation and further affect mechanical properties. The present work studied the microstructural evolution of Al-contained RHEAs at elevated temperatures. The effects of Al on precipitation behavior were discussed. Results show that, TiNbTa0.5ZrAlx alloys (x ≤ 0.5) have single BCC (Body Centered Cubic) structure, but the primary BCC phase is supersaturated. Precipitation of BCC2(Nb,Ta)-rich solid solution phase, HCP(Zr,Al)-rich intermetallic phase, and ordered B2 phase can occur during heat treatment at 600~1200 °C. The precipitation of BCC2 phase mainly exists in RHEAs with low content of Al, while HCP (Hexagonal Close Packed) precipitates prefer to form in RHEAs with high content of Al. Interestingly, ordered B2 precipitates with fine and basket-weave structure can form in TiNbTa0.5ZrAl0.5 alloy after annealing at 800 °C, producing significant precipitation hardening effect.

Tungsten heavy alloys are two-phase metal matrix composites that include W–Ni–Fe and W–Ni–Cu. The significant feature of these alloys is their ability to acquire both strength and ductility. In order to improve the mechanical properties of the basic alloy and to limit or avoid the need for post-processing techniques, other elements are doped with the alloy and performance studies are carried out. This work focuses on the developments through the years in improving the performance of the classical tungsten heavy alloy of W–Ni–Fe through doping of other elements. The influence of the percentage addition of rare earth elements of yttrium, lanthanum, and their oxides and refractory metals such as rhenium, tantalum, and molybdenum on the mechanical properties of the heavy alloy is critically analyzed. Based on the microstructural and property evaluation, the effects of adding the elements at various proportions are discussed. The addition of molybdenum and rhenium to the heavy alloy gives good strength and ductility. The oxides of yttrium, when added in a small quantity, help to reduce the tungsten’s grain size and obtain good tensile and compressive strengths at high temperatures.

Abstract The design of sub-wavelength structure with full-spectrum near-unity solar absorption is a long-sought-after goal of crucial importance for optoelectronic materials and technology. To date, numerous attempts to tackle this problem consisted either of using stronger absorption-but narrowband or the broader spectrum-but moderate light trapping mechanisms. Herein, a novel strategy that achieves perfect absorption for solar energy in the full-spectrum range of the sun's radiance is presented by the thin-film refractory metal resonators. This impressive absorption mainly stems from the cooperative effect of strong plasmonic resonances and the intrinsic broadband spectral responses by the refractory metals, such as Ti, V, W, etc. The full-spectrum weighted solar absorption efficiency is exceeding 98%, showing a near-unity light trapping for the sun's radiation. Moreover, excellent thermal emitting with the spectral averaged efficiency ~ 91% is achieved in the wavelength range (280–4000 nm) by the W-based absorber, suggesting a platform for near-perfect blackbody emitting source. More importantly, the investigations on achieving full-spectrum solar absorbers and thermal emitters provide new insight on the mechanism and philosophy for the design. Just like the proverb, in order to catch bandits, the first thing is to catch the ringleader. As for the purpose of achieving full-spectrum near-unity absorbers or radiators, the key point is to perfectly trap or excite the solar/thermal power in the main distribution ranges for the sunlight or the blackbody radiation. Accordingly, these attractive properties and findings suggest that the investigation and the related full-spectrum solar absorbers and blackbody radiator might have promising applications in the fields related to energy harvesting and conversion. Graphical abstract fx1 Highlights • A feasible way is demonstrated for achieving full-spectrum thin-film solar absorbers. • The averaged solar absorption efficiency η A is > 98% for the sunlight (280–4000 nm). • Near-perfect thermal emitter with similar properties to the ideal blackbody radiator is demonstrated. • The key important factor for designing near-unity full-spectrum absorber/ emitter is obtained. [ABSTRACT FROM AUTHOR]

Highlights • Large area graphene is grown by chemical vapor deposition on Ta and Re catalysts at temperatures much higher than 1000 °C. • The growth parameters and material characterizations are given in detail. Graphene with reasonable quality has been achieved. • Negative effects of using refractory metals in the graphene CVD are summarized. Abstract Large area graphene is usually grown by chemical vapor deposition on Cu or Ni catalysts at ∼1000 °C. For most materials, high temperature leads to high quality. However, graphene growth at even higher temperatures is rarely reported. Therefore, here we systematically investigate the graphene deposition on refractory metals i.e. metals with extremely high melting points. The growth parameters and material characterizations are given in detail. On Ta which readily forms carbides during the carbon deposition, the growth mode is monolayer due to the chemical absorption of excess carbon in the bulk metal. On Re, there is no carbide formed (except in extreme conditions), which greatly simplifies the scenario. Because of the relatively high carbon solubility in Re, the growth temperature has to be limited in order not to drift into the dominantly multilayer graphene regime caused by the carbon segregation. Graphene with reasonable quality has been achieved, although not as good as expected. For example, on Ta, the residual bonds between the graphene and substrate deteriorate the graphene crystalline quality. Despite the difficulties in refractory metal etching, the transfer technique of the graphene is also explored. This research contributes to the fundamental understanding of the graphene growth theory and technology on refractory metals. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) additive manufacturing of pure tungsten encounters nearly all intractable difficulties of SLM metals fields due to its intrinsic properties. The key factors, including powder characteristics, layer thickness, and laser parameters of SLM high density tungsten are elucidated and discussed in detail. The main parameters were designed from theoretical calculations prior to the SLM process and experimentally optimized. Pure tungsten products with a density of 19.01 g/cm3 (98.50% theoretical density) were produced using SLM with the optimized processing parameters. A high density microstructure is formed without significant balling or macrocracks. The formation mechanisms for pores and the densification behaviors are systematically elucidated. Electron backscattered diffraction analysis confirms that the columnar grains stretch across several layers and parallel to the maximum temperature gradient, which can ensure good bonding between the layers. The mechanical properties of the SLM-produced tungsten are comparable to that produced by the conventional fabrication methods, with hardness values exceeding 460 HV0.05 and an ultimate compressive strength of about 1 GPa. This finding offers new potential applications of refractory metals in additive manufacturing. [ABSTRACT FROM AUTHOR]