Increasing Tungsten Content Research Articles

Macro-micro deformation mechanism of tantalum‑tungsten alloy flyer under explosive loading

This study investigates the macro-micro deformation mechanism of tantalum and tantalum‑tungsten alloys under extreme rate loading. Flyers with varying tungsten contents (0 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%) and different texture were subjected to explosive loading tests. Molding and penetration capabilities of the flyers were comprehensively assessed by the mild-steel witness plate, recovered penetrator and plug. Tantalum‑tungsten alloys with 10 wt% tungsten were crushed, forming discrete holes on witness plate, while those flyers with 0 wt%, 2.5 wt%, 5 wt%, and 7.5 wt% tungsten content formed complete circular perforations on the witness plate. Recovered penetrators and plugs indicated partial fracture of pure tantalum. The increased tungsten content in the alloy enhances the penetration stability and recovery integrity of the penetrator, while simultaneously reducing dynamic plastic deformation. Microstructural analysis via Electron Back Scatter Diffraction (EBSD) revealed a robust {111}//Z axial texture at impact side of the penetrator, which weakened with increasing tungsten content; While un-impacted side showed a {110}//Z axial texture. And uniform equiaxial crystalline structures outperformed long strip grain structures subjected. Therefore, the alloys' molding abilities and penetration stabilities ranked as Ta2.5 W > Ta5W > Ta&Ta7.5 W > Ta10W. These findings provide a foundation for the application of tantalum and tantalum‑tungsten alloys under explosive loading.

Tungsten and Titanium dioxide filled VMQ polymer composites-a new lead free & flexible gamma ray-shielding materials.

Flexible & lead-free gamma-ray-shielding composites were prepared using Vinyl Methyl Silicone (VMQ) matrix with Tungsten (W) and Titanium dioxide (TiO2) as fillers. The VMQ composites filled with 30Phr (parts per hundred rubber) TiO2 and 0-70Phr W were prepared by two-roll mill method. The dispersion of the filler particles in the composite matrix was analysed using Scanning Electron Microscope. Gamma ray shielding properties were studied in the energy range of 80 to 1170keV using NaI(Tl) scintillation spectrometer. The mass attenuation coefficient (μm) of the prepared composites was found to increase with increasing concentration of W. Mass attenuation coefficients of 30Phr W composites at gamma-ray energies of 356 and 1170keV were found to be 0.1444 and 0.0644cm2g-1, while those of 50Phr W composite were 0.1396 and 0.0707cm2g-1, respectively. The half value layer values of all the samples were found to decrease with increase in tungsten concentration. To appreciate the shielding ability of the prepared composites, comparison was made with the metal lead. The results show that addition of W into VMQ enhances the attenuation, whereas tensile strength and elongation at break reduces. The Shore A hardness of the W/TiO2/VMQ composites had a maximum value of 71 and the composites also prove to possess good thermal stability. Hence, the present study shows that the VMQ based W-TiO2 rubber composites serve to shield gamma radiations in medical applications and are considered as environmental friendly.

Stress evolution in sputtered vanadium-tungsten alloys

While metal alloy films are used in many applications, there remains a rather limited series of studies of their stress evolution during growth as compared to elemental films. Here, we provide measurements of the sputter deposition stress evolution of VxW1-x alloys, which is a system that forms a body centered cubic solid solution across all its compositions. By increasing either the tungsten content or the growth rate, we note an increasing trend towards a compressive stress state. Since the crystallite size is approximately the same for all alloys and growth rates, we conclude that the increasing tungsten content enhances the effect of energetic particle deposition (atomic peening) on the stress facilitating this change. The results suggest that stress can be understood in terms of the same physical processes that have been proposed previously to explain stress in elemental films. These mechanisms, described in the text include effects of non-energetic growth kinetics, microstructural evolution and energetic particle bombardment.

INVESTIGATION OF MAGNETIC HYSTERESIS PROPERTIES OF ISOTROPIC MAGNETICALLY HARD ALLOYS OF THE Fe-Cr-Co SYSTEM ALLOYED WITH TUNGSTEN

Hard magnetic alloys Fe-30Cr-20Co (wt.%) alloyed with tungsten in an amount of up to 3 wt.% were obtained by powder metallurgy. A study of magnetic properties showed that tungsten additions increase the values of the coercivity Hc and the maximum energy product (BH)max, but at the same time reduce the residual induction Br. This effect increases with increasing tungsten content in the material. The maximum values of Hc (55.8 kA/m) and (BH)max (17.2 kJ/m3) are observed in the alloy alloyed with 3 wt.% W. At the same time, the alloys studied in the work turned out to be sensitive to thermal conditions processing. According to X-ray phase analysis, after a full processing cycle, alloys contain a noticeable proportion of non-magnetic ɣ-phase, but the magnetic properties correspond to the level of cast analogues. During compression tests, all samples of tungsten alloyed alloys failed before reaching a deformation rate of 20%, while the unalloyed Fe-30Cr-20Co (wt.%) alloy deformed without failure under these conditions. Thus, tungsten additives reduce the ductility of the material.

Design of Ti-Mo-W Alloys and Its Correlation with Corrosion Resistance in Simulated Body Fluid (SBF)

Titanium and its based alloys are frequently selected for designing biomedical implants and it is thus necessary to study as detailed as possible their corrosion behavior in biological solutions, such as those in the human body environment. In this paper, with the use of molecular orbital calculation, we designed and developed alloys in the Ti-19Mo-xW system (x = 7, 8, 9, and 10 wt%) and investigated the influence of different contents of tungsten on the behavior of Ti-19Mo-xW alloy samples following corrosion in simulated body fluid (SBF). The values of Bo¯ (bond order) and Md¯ (the metal-orbital energy level) were calculated for each alloy and correlations were established between Bo¯ and the content of tungsten. It was found that with the increase in tungsten content, the value of Bo¯ increases. Regarding the values of the corrosion resistance in SBF that resulted from the investigated alloys, the Ti19Mo7W alloy is distinguished by the lowest value of the corrosion current density and the lowest corrosion rate.

Microstructural Evolution and Mechanical Properties of Spark Plasma Sintering of Tantalum-Tungsten Alloy

Due to the rapid sintering and densification, spark plasma sintering (SPS) technology can significantly inhibit grain coarsening, and obtain alloy with high density and uniform microstructure. Tantalum-tungsten (Ta-W) alloy had been fabricated by powder metallurgy and consolidated by SPS at temperature of 1600 °C for 5 min at the pressure of 35 MPa. Specimens of pure Ta and four tantalum-based alloys with different concentrations of tungsten ranging from 2.5 to 10 were used to investigate the behavior of developed alloys. X-ray diffraction analyses were applied for all compositions of Ta-W alloys. The morphology of fracture sections was analyzed by scanning electron microscopy (SEM). Morphologies of initial Ta and W powders, microstructures of sintering Ta-W alloy and tensile fractographs of the specimens with different components were observed. When the concentrations of tungsten were distributed with 2.5 wt%, 5 wt%, 7.5 wt% and 10 wt%, the measured densities were 16.151 g/cm3, 15.756 g/cm3, 15.711 g/cm3, 15.665 g/cm3 and 15.670 g/cm3 respectively. As the content of tungsten increased, the density of the alloy decreased and the grain was refined, meanwhile the micro-hardness of the samples increased gradually. Furthermore, the addition of tungsten could greatly enhance the strength of the alloys, but decrease the plasticity of the alloys. Ta-2.5 wt%W shows the maximum bending strength with a value of 832.29 MPa, while the percentage of transgranular fracture increased with the increase of tungsten content.

Investigations on Microstructures and Properties of (Fe, Cr, W)7C3 Carbides by First Principles and Experiments

Tungsten doping is critical for the wear resistance and application of High-Chromium Cast Iron (HCCI). A series of investigations of (Fe, Cr, W)7C3 carbides were performed by first principles calculations and experimental analysis. The calculated results showed that with the increase in tungsten content in M7C3, the equilibrium cell volumes and the density gradually increased, and the formation energy of M7C3 carbides gradually decreased. The TEM results showed that the (Fe, Cr, W)7C3 carbides were (Fe3.27Cr2.99W0.74) C3 with a hexagonal structure after adding 2.13 wt % tungsten into laser cladding coatings of High-Chromium Cast Iron with a composition of Fe-26.8 wt % Cr-3.62 wt % C. These results from calculations and in situ nanoindentation show that tungsten doping could improve the ductility and indentation modulus of (Fe, Cr)7C3 carbides, and the composition of (Fe, Cr, W)7C3 was expected to be a high hardness and softness material. The wear test results showed that the wear resistance of tungsten-bearing HCCI was better than ordinary HCCI.

Microstructure, mechanical and tribological properties of cold sprayed Cu[sbnd]W coatings

This paper presents the results of the investigation of the microstructure and properties of copper‑tungsten coatings with different compositions on aluminum alloy substrates. Coatings were obtained by cold spray method using powder mixtures as feedstock. The effect of the powder mixture composition on the deposition efficiency and the tungsten content in the coating have been studied. X-ray diffraction analysis was used to investigate the phase composition and to reveal the peculiarities of changes in the crystalline structure of copper and tungsten particles after cold spraying in relation to the coating composition. Using the method of instrumental indentation on cross-sections of the coatings mechanical properties were measured. It was shown that increasing of tungsten content in the coatings contributes to increasing the microhardness and Young's modulus of the coatings. The mapping images showed that all coatings were characterized by non-uniformity of mechanical properties over the cross-section. The bonding strength of coatings significantly increases with increasing tungsten content in the feedstock. CuW coatings are characterized by lower specific wear rate values and higher coefficients of friction under dry sliding wear conditions in a ball-on-flat mode compared to pure copper coating.

Selective surface modification of SS304 using hybrid powder-mixed EDC process

ABSTRACT The present study acclaims the influence of hybrid powders (MoS2 +W) mixed dielectric fluid on the surface properties of SS304 by the electro-discharge coating (or EDC) process. Hard, wear-resistant, and lubricating surfaces are produced using different blending ratios of the powders infused in the dielectric liquid. The combined effect of both powders on the substrate’s surface properties is studied. The process performance is evaluated in terms of wear analysis, surface roughness, coefficient of friction, micro-hardness, and compositional study at different peak current and duty factors. The experimental results show an aggregate increment of micro-hardness from 119.3% to 255.2% compared to substrate. The average surface roughness increases (2.69–4.32 μm) with an increase in tungsten content (from 5% to 50%) in the dielectric and decreases with MoS2 content. The wear test results reveal a substantial decrease in coefficient of friction (COF = 0.104) with maximum concentration of MoS2 and 0.274 for maximum tungsten.

Simulation study of the influence on the tungsten concentration due to the cross-field transport in the scrape-off layer

It is critical to keep a low level of tungsten impurity concentration in the core plasma of the fusion reactor. Using the OEDGE code, the influence on the tungsten concentration due to the cross-field transport in the scrape-off layer is studied. Based on the design parameters of the China Fusion Engineering Test Reactor, the background plasma with the peak target electron temperature of 15 eV is generated using the onion-skin model. The neon impurity with the assumed concentration of 0.2% inside the separatrix is included for estimating the tungsten sputtering source. In a series of simulations of tungsten transport, the diffusion coefficient D ⊥ is varied from 0.1 to 10 m2 s−1, and the hypothetical inward pinch velocity V IMP is in the range of 0–5 m s−1. The tungsten concentration inside the separatrix increases with decreasing diffusion coefficient and exceeds 10−5 for the diffusion coefficient lower than about 0.2 m2 s−1. When the hypothetical inward pinch is included, the tungsten concentration increases. The relation between the relative increase in tungsten concentration and V IMP/D ⊥ is fitted.

Characteristics of microwave melting H13 steel powder with different tungsten contents

Different amounts of tungsten powder (0.07%, 0.4%, 0.6%, 0.8% and 1% on a mass basis) were added to H13 mold steel and the mixtures were microwave sintered. X-ray fluorescence spectroscopy showed tungsten contents of 0.039%, 0.358%, 0.526%, 0.742% and 0.976%, respectively. Under each tungsten load, the standard value of tungsten was lower than expected. The samples showed different degrees of ablation, which was related to the hollow material. Laser-induced spectral analysis showed that the surface composition of the sample was uniform. Furthermore, by using a metallographic microscope, the grain size of the samples was shown to decrease with the increase of tungsten content, which had the effect of refining the grain. A 300-g sample was sintered for 10 min in a microwave at 1300 °C, and the Vickers hardness values of the samples were W1: 565.2; W2: 570.6; W3: 572.8; W4: 584.8; W5: 593.2.

Microstructure and mechanical properties of matrix alloy (Ni-Fe-Co-W) derived from tungsten heavy alloys

Abstract Present work attempts a correlation between microstructure and mechanical properties of five matrix alloys processed with tungsten content varying from 30 to 50% wt. % and Ni, Fe, Co in the ratio 2:2:1. All the alloys were sintered at 1320 °C for 2 h in hydrogen atmosphere and furnace cooled. The microstructure of the alloy comprised fcc (γ) phase along with tungsten particles. The volume fraction of tungsten increased with increasing tungsten content. Strength ranging from 500 to 600 MPa and ductility from 18 to 20% were obtained in as sintered condition. Forging resulted in increase in strength (1000–1200 MPa) with concomitant loss in ductility (3%). No significant enhancement in tensile properties was observed with heat treatment following forging. Both transgranular and ductile fracture features were observed in the failed tensile specimens. The loss in ductility following swaging/heat treatment was primarily attributed to the presence of increased W particles.

Tensile properties of tungsten/glass composites at elevated temperatures

The quasi-static tensile behavior of tungsten/glass composites containing 40–50 vol% tungsten at elevated temperatures in the range of 550–750 °C was investigated. Results show that the composites present absolute brittleness at temperatures up to 650 °C while exhibit brittle-to-ductile transition in the temperature range of 650–700 °C and super-plasticity at 750 °C due to the decreasing viscosity of glass matrix. The strength of the composites declines with the increase of tungsten content at temperatures lower than 650 °C and increases with increasing the volume fraction of tungsten at 750 °C. In the temperatures between 650 and 700 °C, 55BH/45W exhibits the highest strength while 60BH/40W presents the lowest one. The elongations of the composites reduce with increasing tungsten content at 750 °C because of the amount of W/W and W/G interfaces increasing. In addition, the effects of temperature and tungsten content on the deformation and fracture mechanism of the composite were analyzed.

Effect of tungsten doping on laser ablation and graphitization of diamond-like nanocomposite films

Laser surface microstructuring of diamond-like nanocomposite (DLN) films is a promising technique to improve their properties. For industrial applications, UV excimer or IR lasers with high pulse repetition rate are commonly used. In this paper, we investigate the influence of metal (tungsten) doping of DLN film on the ablation and graphitization behavior of the films using KrF laser (λ = 248 nm, τ = 20 ns) and Yb:Yag laser (λ = 1030 nm, τ = 8 ps). The response is found to be sensitive to the laser wavelength and pulse duration. For UV ns-pulses, the ablation threshold is insensitive to W-doping, showing only a slight increase for the highest tungsten concentration of 27 at.%, while the ablation rate decreases. Conversely, an increase of tungsten content in the case of the irradiation by IR ps-pulses induces a drop in the ablation threshold and an increase in the ablation rate. The structural modification of the films is analyzed by Raman spectroscopy, which also allows us to estimate the thickness of a residual graphitized layer on the surface after laser irradiation. It is found that laser-induced graphitization is stronger for doped DLN films after multipulse irradiation.

Electrical Conductivity of Tungsten-Containing Ammonia Solutions and Calculation of Its Activation Energy

Abstract—The activation energy of the electrical conductivity of ammonium hydroxide–tungstate ion solutions is determined in the NH4OH concentration ranges 0.01–6 and 0.01–0.2 mol/L (based on the metal). For all solutions, the activation energy decreases substantially with increasing temperature and decreases insignificantly with increasing tungsten content in a solution at a constant ammonium hydroxide concentration. An increase in the NH4OH concentration at a constant tungsten content in a solution is found to cause an increase in the activation energy. All calculated activation energies suggest that the charge transfer in the system under study is determined by diffusional restraints.

Polymerization and Transformation of Tungsten(VI) Species in Acidic Aqueous Solution by Electrospray Ionization Time-of-Flight Mass Spectrometry

Deep understanding of the polymerization and transformation of tungstate species in aqueous solution is of great significance for hydrometallurgical and chemical separation processes, such as solvent extraction, membrane separation and crystallization. In order to study the polymerization and transformation of tungstate species, the semi-quantitative characterization method of electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) was developed. In this paper, the tungsten speciation in simulative leaching solution was investigated in detail between pH 2.5 and 7 under various conditions (e.g. acid species, initial concentration, pH), and the results indicated that HCl was more conducive than HNO3 for the polymerization of tungsten at the same pH, and HAc accelerated the polymerization of tungsten species, especially in acid solution at lower pH; the morphological changes of each tungsten species tended to be consistent with the increase of tungsten concentration; pH strongly influenced the distribution of tungsten species. Then, the polymerization and transformation laws of tungstate species are summarized. W1 (monomers) are dominant species in weak acid and neutral solution, and aggregate into oligomeric species (e.g. W2, W4, W6). Transformations also exist among W2, W4 and W6. The polymerization process from W4 and W6 species to higher poly-tungstate (W10–12) was observed with the consumption of H+. This work aims to understand the polymerization and transformation of tungsten speciation using ESI-TOF-MS, which should provide useful information for the understanding and optimizing of industrial production and environmental processes, building a bridge between micro tungsten speciation and macro industrial applications.

Mechanical properties of several newly produced RAFM steels with Tungsten content in the range of 2 wt%

Abstract The contribution of ENEA together with Rina-CSM to the Eurofusion programme “WPMAT-Advanced Seels” deals with the development of innovative RAFM steels able to withstand the critical temperatures typical of the different operational environments foreseen for the blanket of the first DEMO reactor. The optimization of the chemical composition and the Thermo Mechanical Treatment for these materials should be done according to the blanket operating temperatures that are related to two possible working conditions: the WCLL-BB (Water Cooled Lead Lithium Breeding Blanket) or the H(D)CLL-BB (Helium (Dual) Cooled Lead Lithium Breeding Blanket). On the one hand the “water-cooling” option implies a minimum irradiation temperature for the blanket material in the range of 280–350 °C. On the other hand, the “helium-cooled” and the “dual-coolant” solutions imply an operating temperature for the blanket material in the range of 650 °C. Therefore in the first case the target is the improvement of the toughness of the martensitic alloys; whilst concerning the second scenario the target is the development of more creep resistant martensitic steels, suitable to tolerate such a high operating temperature. In both the cases the Tungsten content plays a key role, both in terms of solid solution hardening and influence on the DBTT. Two alloys aimed at fulfilling the specifications for the two DEMO operating conditions, both with increased Tungsten content respect to Eurofer, have been produced and characterized. The mechanical properties of these two alloys are hereby reported and discussed.

COMPOSITION AND SURFACE MORPHOLOGY OF COMPOSITE ELECTROLYTIC COATINGS CO-W-ZRO2

possibility of electrosynthesis and control of the composition and surface morphology of the composite electrolytic coatings of cobalt with refractory metals by varying the pulse current density has been proved. Composites deposited on copper substrate from biligand citrate-pyrophosphate electrolytes at 4 A/dm2 are distinguished by a developed surface and a more uniform distribution of components on the surface, increased tungsten content, almost 5 times higher than coatings deposited at 10 A/dm2, and a half reduction in oxygen percentage (up to 5.5%). This is explained by the inhibition of the hydrogen gas evolution reaction and the participation of hydrogen ad-atoms in the chemical reduction of intermediate tungsten oxides to metal when polarization is interrupted. Coatings obtained using pulsed current can be considered as composites of the composition Co-W-ZrO2, in which the oxide phase is formed directly in the electrode process as an intermediate for the incomplete reduction of tungstates. The topography of the films is characterized by the presence of grains of elliptical and spherical shape with crystallite sizes of 80 – 180 nm. On the main surface there are protrusions (large grains) with a diameter of 1 – 3 microns. The fractal dimension of the surface is 2.77, which indicates the 3D crystal growth mechanism during coating formation. According to the surface roughness parameters Ra and Rq, coatings belong to the 9th roughness class. By phase composition, composites are predominantly amorphous materials, which include nanocrystalline cobalt and intermetallic compounds Co3W and Zr3Co. Due to the quantitative and phase composition, surface morphology and fractality, the microhardness and corrosion resistance of Co-W-ZrO2 systems deposited at a current density of 4 А/dm2 are 20% higher than the coatings obtained at 10 A/dm2, and 3 times higher than the corresponding characteristics of the substrate.

The effect of surface morphology of Co-W-ZrO2 electrolytic composite coatings on the functional properties of alloys

The possibility of electrosynthesis and control of the composition and surface morphology of the composite electrolytic coatings (CEC) of cobalt with refractory metals by varying the pulse current density has been proved. Composites deposited on copper substrate from biligand citrate-pyrophosphate electrolytes at 4 A/dm2 are distinguished by a developed surface and a more uniform distribution of components on the surface, increased tungsten content, almost 5 times higher than coatings deposited at 10 A/dm2, and a half reduction in oxygen percentage (up to 5.5%). This is explained by the inhibition of the hydrogen gas evolution reaction and the participation of hydrogen ad-atoms in the chemical reduction of intermediate tungsten oxides to metal when polarization is interrupted. Coatings obtained using pulsed current can be considered as composites of the composition Co-W-ZrO2, in which the oxide phase is formed directly in the electrode process as an intermediate for the incomplete reduction of tungstates. The topography of the films is characterized by the presence of grains of elliptical and spherical shape with crystallite sizes of 80 – 180 nm. On the main surface there are protrusions (large grains) with a diameter of 1–3 microns. The fractal dimension of the surface is 2.77, which indicates the 3D crystal growth mechanism during coating formation. According to the surface roughness parameters Ra and Rq, coatings belong to the 9th roughness class. Due to the quantitative composition, surface morphology and fractality, the microhardness and corrosion resistance of Co-W-ZrO2 systems deposited at a current density of 4 А/dm2 are 20% higher than the coatings obtained at 10 A/dm2, and 3 times higher than the corresponding characteristics of the substrate. It was shown the catalytic activity of tungsten containing CEC in ethanol oxidizing reaction and corrosion resistance in media of different acidity.

Nanostructured gradient material based on Cu—Cr—W pseudo alloy prepared by high energy ball milling and spark plasma sintering

This study was conducted to obtain nanostructured mechanically activated composite particles from immiscible metals Cu, Cr and 5÷70 wt.% W, nanostructured bulk materials based on them and Cu / Cu—Cr—W nanostructured gradient material with different tungsten content by combined short-term (up to 150 min) high-energy ball milling (HEBM) and spark plasma sintering (SPS). Cu— Cr—W mechanically activated composites were obtained by HEBM of Cu + Cr + (5÷70 wt.%)W powder mixtures in the Activator-2S ball planetary mill at the rotating speed of 1388 rpm for the grinding chamber and 694 rpm for the planetary disk in an argon atmosphere for 150 min. Cu—Cr—W mechanically activated composite particles were consolidated by SPS in the temperature range of 800— 1000 °C at a pressure of 50 MPa for 10 min. The nanostructured gradient sintered material based on Cu—Cr—W pseudo alloys was pressed layer by layer in the following sequence (from pure copper to pseudo alloy with increasing tungsten content): Cu / Cu—Cr—5%W / Cu—Cr—15%W / Cu—Cr—70%W and sintered at 800 °C for 10 min. The crystal structure, microstructure, and properties of Cu— Cr—W mechanically activated composites and consolidated materials based on them were studied depending on production conditions. It was shown that the nanostructure formed in mechanically activated composites at the short-term HEBM stage (up to 150 min) was preserved for all Cu—Cr—W (5÷70 wt.% W) compounds after SPS. Based on SEM and EDX, refractory particles of W (d ~ 20÷100 nm) and Cr ( d ~ 20÷50 nm) were uniformly distributed in the material volume (in the copper matrix). The hardness of Cu—Cr—W (15 wt.% W) bulk samples obtained from nanostructured powder mixtures (after 150 min HEBM) by SPS at 800 °C was approximately 6 times higher than the hardness of samples sintered from the mixture of starting components (without HEBM). For the Cu—Cr—70%W nanostructured compound ( t sps = 1000 ° С ) the hardness value was ~3 times higher than that for microcrystalline analogues. The highest re­lative density of 0.91 was achieved for Cu—Cr—15%W and Cu—Cr—70%W samples. Electrical resistivity for nanostructured Cu—Cr—W composites were 2 times higher than for microcrystalline samples. Apparently, this is due to an increase in grain boundaries and various defects accumulated in the material at the HEBM stage. The obtained results show that combined short-term HEBM and subsequent SPS is a promising way to produce nanocrystalline Cu—Cr—W composites and gradient materials based on them.