Tungsten Powder Research Articles

Characterization of W-Cr Metal Matrix Composite Coatings Reinforced with WC Particles Produced on Low-Carbon Steel Using Laser Processing of Precoat.

The paper presents the study results of laser processing of precoat applied on C30 steel. The precoat consisted of powder mixtures with a binder in the form of water glass. Tungsten powder, chromium, and tungsten carbide (WC) were used to produce the precoat. The laser processing was carried out using a Yb:YAG disc laser with a rated power of 1 kW. Constant producing parameters (power of laser beam, 600 W; laser beam scanning rate, 400 mm/min) were applied. Chemical composition of the precoat was a variable parameter in coating production. A mixture consisting of 50% W and 50% Cr as a metal matrix was prepared. Subsequently, WC particles in weight ratios of 25%, 50%, and 75% were added to matrix. As a result, W–Cr metal matrix composite coatings reinforced with WC particles were formed. This study focused on investigation of microstructure, microhardness, phase, and chemical composition as well as corrosion and wear resistance, of the newly formed W–Cr/WC coatings. An instrumented nanoindentation test was also used in this study. As a result of laser beam action, the newly formed coatings had an interesting microstructure and good properties which were improved in comparison to substrate material. It is anticipated that the resulting coatings, depending on the treatment parameters (e.g., W–Cr/WC powder mixture) used, can be successfully applied to metal forming or foundry tools.

Effect of titanium diboride ceramic particles on mechanical and wear behaviour of Cu-10 wt% W alloy composites processed by P/M route

Hypothesis of this research focuses on evaluating mechanical properties and thereby determine optimized conditions for lessened wear rate of powder metallurgy processed Titanium diboride (TiB2) reinforced Cu–W alloy matrix composites. Tungsten and Titanium diboride powders were mixed with copper powder to the state of homogeneity by mechanical alloying method, compacted in a computerized hydraulic press and further sintered at 900 °C for 2 h under argon environment. SEM studies revealed that TiB2 particles were disseminated evenly in Cu–W alloy. The fabricated composites were subjected to EDS and XRD studies to confirm the presence of required elements and the occurrence of oxides formed while sintering. The impact of wear test input parameters on the wear rate was identified and the optimized parameter to attain low wear rate was determined through Taguchi and ANOVA analysis by using L16 orthogonal array. The hardness, impact strength, compressive strength, and wear resistance of the composites experience considerable enhancement, with the inclusion of TiB2 particles. The optimized parameters to achieve less wear rate was arrived as A4B1C1D1 and the composite with 12 wt% TiB2 content subjected to 10 N load with 1 m/s velocity and 300 m sliding distance attained minimum wear rate.

English

In this work, a tungsten oxide nanoparticle was developed with a simple method, using tungsten powder. The orthorhombic, hexagonal and monoclinic crystalline structures obtained were characterized by X-ray diffraction, scanning electron microscopy, as well as Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The coupling of these tungsten oxide nano particles with hydrogen peroxide is carried out on methyl orange removal from wastewater. The use of Hydrated orthorhombic particles showed the highest removal rate up to 89.7% comparatively to hexagonal and monoclinic crystalline structures respectively. The reusability of these particles showed a good stability with monoclinic crystalline structure after four cycles. Key words: Dyes, Tungsten Oxide, Catalysis, H2O2.we &nbsp

LASER SURFACE ALLOYING OF 304 STAINLESS STEEL WITH TUNGSTEN POWDER

Laser surface alloying was employed to enhance the wear resistance of 304 stainless steel with pure tungsten powder. The effect of laser fluence on phase constituents, microstructure, hardness and corrosion properties was investigated. It is found that the laser fluence has a direct correlation with the phases present in the coatings. Intermetallic Fe7W6phase was found in the composite coating due to the metallurgical reaction of W with the Fe, Cr and Ni elements in the melting pool. Coatings with composite microstructure in nature were obtained resulting from the dilution of substrate and the laser-induced rapid cooling process. Intermetallic phase of Fe7W6with solid solution of Ni and Cr shows dendrite or hallo structure depending on the laser fluence. Sintering and/or consolidation of W particles is observed for samples processed with lower laser fluences. It has been found that hardness of the coatings was improved significantly compared with the 304 stainless steel substrate. Coating processed with laser fluence of [Formula: see text] J/m2shows the best corrosion resistance.

Research on the effect of liquid-liquid doping processes on the doped powders and microstructures of W–ZrO2(Y) alloys

In previous researches, there are few studies on the mechanisms involved in liquid-liquid doping techniques for preparing oxide particle doped tungsten powders. In this research, based on different polytungstate species, three liquid–liquid doping techniques for synthesizing different doped precursor powders were proposed and compared. The extremely homogeneous hexagonal (NH4)0.33WO3·H2O microspheres and flaky (NH4)6H2W12O40·5H2O were synthesized. The synthesis mechanisms of precursors, the doping processes and reaction mechanisms for preparing yttrium-stabilised ZrO2 in ternary liquid phase system were discussed. The doped powder prepared through azeotropic distillation method exhibits higher quality due to the highly dispersed ZrO2(Y) phase uniformly distributed in flaky precursor, and the corresponding alloy possesses more excellent microstructure and mechanical properties. The proposed azeotropic distillation method offers a general pathway and is readily adapted to large-scale industrial production of high-quality oxide particle doped W powders.

Synthesis of Visible-Light Active Monoclinic WO<sub>3</sub> by Thermal Oxidation of Tungsten Powder for Photoreduction of Cr(VI)

In this paper, visible-light-active monoclinic WO3 powders were synthesized by thermal oxidation of W powders at 200 – 1000 °C in air atmosphere. Morphology and crystal structure of annealed W powders were characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), respectively. Based on SEM and XRD results, a spherical orthorhombic-W3O8 obtained at 200 °C was transformed into a dendritic monoclinic WO2 + tetragonal WO3 + monoclinic WO3 structures at 400 °C accompanied by a color transition from grey into green. At 600 °C, yellow monoclinic WO3 + monoclinic WO2.96 powder was produced that ascribed to oxygen vacancies. Photocatalytic activity of annealed W powders demonstrated 70.7% Cr (VI) removal after 150 min on sample annealed at 1000 °C. This ascribed to high photoactivity of monoclinic WO3. Nevertheless, the dendritic monoclinic WO2 + tetragonal WO3 + monoclinic WO3 obtained at 400 °C exhibited the lowest Cr (VI) photoreduction i.e. 45.2% implies less photoactive monoclinic WO2 and sluggish electron transport at oxide-oxide interfaces.

Effect of Phosphorus Impurities in Precursors on Characteristics of Magnesiothermic Tungsten Powders

We have studied tungsten powders prepared by reducing the MgWO4 and Ca3WO6 tungstates containing 0.05–1.5 wt % phosphorus at temperatures from 700 to 800°C. The reduction of MgWO4 containing less than 0.3 wt % phosphorus was accompanied by separation of reaction products. Most of the magnesium oxide formed was located beyond the reaction zone. The tungsten powders prepared by reducing MgWO4 consisted of α-W. The powders prepared by reducing Ca3WO6 at a temperature below 740°C consisted of a mixture of the α- and β-phases. Raising the percentage of phosphorus in the starting tungstate led to an increase in the percentage of the β-phase. The highest β-W content of the powder was 60 wt %.

Strength enhancement of nanocrystalline tungsten under high pressure

Three tungsten powder samples—one coarse grained (c-W; grain size: 1 µm–3 µm) and two nanocrystalline (n-W; average grain sizes: 10 nm and 50 nm)—are investigated under nonhydrostatic compression in a diamond anvil cell in separate experiments, and their in situ X-ray diffraction patterns are recorded. The maximum microscopic deviatoric stress in each tungsten sample, a measure of the yield strength, is determined by analyzing the diffraction line width. Over the entire pressure range, the strength of tungsten increases noticeably as the grain size is decreased from 1 µm–3 µm to 10 nm. The results show that the yield strength of tungsten with an average crystal size of 10 nm is around 3.5 times that of the sample with a grain size of 1 µm–3 µm.

The effect of particle size on the densification kinetics of tungsten powder during spark plasma sintering

The influence of particle size on the densification kinetics of tungsten powder during spark plasma sintering was investigated. The densification rate of tungsten powder in the intermediate sintering stage decrease with increasing particle size, resulting in a delay in the sintering stages of coarse powder. The isothermal densification kinetic behaviors of tungsten powder show that the densification of tungsten powder can be divided into two kinetic stages: a low-stress exponent segment (n = 1.5) and a high-stress exponent segment (n = 3 or 4). With increasing of particle size, n increases from 3 to 4, and the activation energy decreases from 304 to 254 kJ/mol for the high-stress exponent segment. This is because the densification mechanism has a tendency to change from diffusion creep to dislocation creep or dislocation glide as the particle size increases. The evolution of the activation energy exactly matches the transformation of the deformation mechanism, indicating that the densification activation energy does not reflect a barrier to densification, but rather a barrier to deformation with different deformation mechanisms.

The effect of transition-metal seeding powder on deposition and growth of diamond synthesized by hot filament chemical vapor deposition processes on cemented carbide substrates and its characterization

Hot Filament Chemical Vapor Deposition is a well-established method to synthesize diamond thin films on a non-diamond substrate. Here, we have deposited microcrystalline diamond on tungsten carbide cutting tool insert by using conventional Hot Filament Chemical Vapor Deposition technique. The substrates were ultrasonically seeded with Carbon, Diamond, Iridium, Molybdenum, Palladium, Platinum, Tantalum, Tungsten and Chromium natural powders and thereafter were deposited with the same deposition parameters to observe the effects of different seeding powders on the diamond coating. The coated tools were characterized by X-ray Diffraction and the quality of diamond crystals was assessed by using micro Raman spectroscopy. The surface morphology was studied by utilizing Scanning Electron Microscope. The discrete spherical diamond crystals were formed with carbon powder seeding while very dense along with uniform coatings were deposited on the diamond powder seeded substrate. Larger diamond crystals with good density were observed on the palladium seeded substrate. The micro Raman spectroscopy showed mixed results of sp3 and sp2 bonding. But the palladium seeding showed clear sp3 bonding due to the formation of crystals with bigger size. The Vickers microhardness value for the substrate with diamond seeding was found to be much higher than other coated tools.

The influence of morphology and composition of metal–carbide coatings deposited on the diamond surface on the properties of copper–diamond composites

In this work, tungsten- and molybdenum-containing coatings on diamond were obtained by rotary chemical vapor deposition (RCVD) or by treating the diamond microcrystals in a hot press (HP)/spark plasma sintering (SPS) facility. In the HP facility, heating was realized by external heating elements; no electric current was passing through or induced in the die. In RCVD, tungsten carbonyl W(CO)6 was used as a precursor. In the case of HP and SPS, powders of tungsten, molybdenum and tungsten trioxide WO3 were used as sources of the metal. It was found that the morphology and phase composition of the coatings depend on the deposition conditions and the metal source. HP and SPS were further used for fabricating bulk copper–50 vol% diamond composites. The thermal conductivity of the copper–diamond composites decreased as the holding time during their consolidation by HP or SPS increased owing to delamination of the WC coating from the diamond surface. A Mo-containing coating deposited by the SPS treatment allowed obtaining a copper–diamond composite with a thermal conductivity of 420 W m−1 K−1.

Investigating the effects of copper cadmium electrode on Inconel 718 during EDM drilling

One of the effective unconventional machining processes used in industries is Electrical Discharge Drilling. High quality material removal, good surface finish, high tolerance but with minimal tool wear are the key features expected in a drilling operation. These can be accomplished by adding of powder particles with dielectric fluid by proportionately varying process parameters. This project focus on the Tool Wear Rate (TWR) of Tungsten Powder Mixed for Electrical Discharge Drilling (W-PMEDD) of Inconel 718 superalloy using single channel hollow Copper Cadmium as electrode. Response Surface Methodology (RSM) is used as an experimental analysis tool in order to compare the input variable such as peak current (Ip), pulse on time (Ton), pulse off time (Toff). ANOVA table was used to determine the capability of varying parameter in the drilling operation and finally came to a conclusion that Ip, Ton and, Toff is the most significant parameters.

Vacuumless synthesis of tungsten carbide in a self-shielding atmospheric plasma of DC arc discharge

The goal of this paper is to simplify and reduce the cost of manufacturing tungsten carbide. The work presents the results of experimental studies that prove the possibility of synthesizing fine and ultrafine crystalline phases of tungsten carbide in the DC arc discharge plasma ignited in open air by a developed vacuumless technique. The synthesis is implemented in the process of arc discharge burning between the graphite rod (anode) placed inside the cavity of the graphite cathode in the presence of graphite and tungsten powders used as initial precursors. The cathode cavity (reaction zone) is shielded from oxygen by a stream of carbon monoxide and carbon dioxide gases, which are generated during the arc discharge burning in an open air. After studying the influence of main process parameters (parameters of the discharge circuit and graphite electrode's dimensions) and optimizing the system, the authors obtained tungsten carbide phases without impurities of oxide phases. This allows simplifying significantly the technology of tungsten carbides synthesis by excluding the stage of vacuum creation.

Laser-Induced Tar-Mediated Sintering of Metals and Refractory Carbides in Air.

Refractory metals and their carbides possess extraordinary chemical and temperature resilience and exceptional mechanical strength. Yet, they are notoriously difficult to employ in additive manufacturing, due to the high temperatures needed for processing. State of the art approaches to manufacture these materials generally require either a high-energy laser or electron beam as well as ventilation to protect the metal powder from combustion. Here, we present a versatile manufacturing process that utilizes tar as both a light absorber and antioxidant binder to sinter thin films of aluminum, copper, nickel, molybdenum, and tungsten powder using a low power (<2W) CO2 laser in air. Films of sintered Al/Cu/Ni metals have sheet resistances of ∼10-1 ohm/sq, while laser-sintered Mo/W-tar thin films form carbide phases. Several devices are demonstrated, including laser-sintered porous copper with a stable response to large strain (3.0) after 150 cycles, and a laserprocessed Mo/MoC(1-x) filament that reaches T ∼1000 °C in open air at 12 V. These results show that tar-mediated laser sintering represents a possible low energy, cost-effective route for engineering refractory materials and one that can easily be extended to additive manufacturing processes.

Metal-Polymer Composite as an Acoustic Attenuating Material for Ultrasonic Transducers

This work reports the acoustic evaluation of a tungsten-epoxy composite which is functioned as a backing material of an ultrasonic transducer. The composite is prepared by mixing tungsten powder in epoxy at a weight ratio of 4:1 using a shaker milling and curing the mixture under a vacuum condition. The sound velocity and acoustic attenuation in the prepared composite is measured by propagating a 200-kHz ultrasonic wave with a through transmission mode. The prepared composite is subsequently assembled with a 1-MHz piezoelectric disk (PZT-8) and an epoxy layer as the active element and the matching layer, respectively, into a fabricated ultrasonic transducer. A square-wave burst pulse is used as an excitation signal for the evaluation of the fabricated transducer. The generated ultrasonic wave shows a higher damping in the presence the backing layer. In addition, the measured sound velocity and acoustic attenuation of prepared composite showed that the ratio of 4:1 is sufficient composition in order to apply as a backing material. In conclusion, control the transducer characteristics is determined by the acoustic properties of tungsten-epoxy composite.

Dust sampling in WEST and tritium retention in tokamak-relevant tungsten particles

Abstract The paper presents complementary approaches based on experimental and numerical works to address the behavior of tokamak-relevant tungsten particles loaded with tritium. Sampling of particles inside the WEST tokamak have been realized thanks to an in situ particle collection system called Duster Box. This method allowed to identify various types of tungsten particles among them spherical shaped micro-particles between 5 µm and 30 µm in diameter. Based on these results a surrogate tungsten powder has been provided by means of spheroidization process and sieving method. Moreover, the powder tritium retention capacity was measured and specific activities of 90 MBq.g−1 and 280 MBq.g−1 were obtained for particles with 17 µm and 11.5 µm median diameters, respectively. Considering such tritium activities trapped in the particles, Monte-Carlo simulation were performed to estimate the electrostatic self-charging rates and the corresponding electrical charge carried by the radioactive tungsten dust. The results of these experiments provide robust data for the assessment of the dispersion of toxic/radioactive material in the environment that could follow a loss of containment.

Effects of processing parameters on phase, morphology, mechanical and corrosion properties of W–Cu nanocomposite powder prepared by electroless copper plating

Because of excellent physical properties and wide range of applications in electrodes, electrical connections, microelectronic packaging, and heating mineral, Tungsten–copper (W–Cu) composite powders have been significantly remarkable. The substantial differences in the density and lack of fusion of copper and tungsten in both solid and liquid phases, led to occur some problems in W–Cu composite powders. Among the various methods of preparing tungsten–copper composites, the electroless plating process is one of the conventional methods as it is easy to use, efficient, and inexpensive. In this paper, the copper electrolyte solution containing copper sulfate as the main salt, formaldehyde as the reducing agent, sodium ethylene diamine tetra-acetate as the sophisticated agent, has been employed in the electroless copper plating process of tungsten powder. The effects of main parameters of electroless copper plating including NaOH concentration, time and operating temperature, and pre-activation of tungsten powder on the amount of deposited copper layer were investigated. Then, the phase behavior, morphology, mechanical, and corrosion behavior were evaluated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy(EDS), Vickers hardness tester, and electrochemical impedance spectroscopy (EIS), respectively. Results demonstrated an improvement in the morphology and amount of the copper, which was deposited on the surface of the activated tungsten powder. Indeed, the defects formed on the surface of the tungsten powder increased the sites for nucleation and growth of copper particles. In agreement with the Fick's 2nd law, the maximum deposition rate of 7.9 vol% was obtained at 14 g/l NaOH, 100 °C and processing time of 90 min, with a (111) orientation on the activated tungsten powder surface. The higher capacitance and the charge transfer resistance along with the highest ndl at the 14 g/l NaOH concentration demonstrated the homogeneity and integrity of W–Cu composite, the lowest hardness of 149.0 ± 2.8 Hv and a compressive strength of 187 ± 11 MPa.

Fabrication of ultrafine-grain and great-performance W–Ni–Fe alloy with medium W content

The tungsten alloy with medium W content (wt.%) is a combination of high strength and high toughness, which has wide potential applications in related fields. In order to fabricate high-performance W–Ni–Fe alloy with medium W content, ultrafine tungsten powder obtained by sol-spray drying-hydrogen reduction method was employed as raw material. The medium W content W–Ni–Fe alloys with different compositions were systematically studied for the first time, i.e., 50W–25Ni–25Fe, 50W–35Ni–15Fe, 70W–15Ni–15Fe and 70W–21Ni–9Fe. The results show that the mechanical properties of medium W content W–Ni–Fe alloys prepared by this method are excellent, the highest tensile strength is 945 MPa, the highest elongation is 31.7%. The tensile strength, density and elongation of tungsten alloy with Ni/Fe ratio of 7:3 are better than those of tungsten alloy with Ni/Fe ratio of 1:1 when W content is fixed. With the same Ni/Fe ratio, the density of tungsten alloy with 50W series is higher than that of tungsten alloy with 70W series, but the tensile strength is lower. The microstructure of tungsten alloys with four components are uniform and fine, the grain size of tungsten is just 3–5 μm. The two main fracture modes of samples are the cleavage fracture of tungsten grains and the dimple fracture between tungsten grains and γ phase.

The Mechanical Properties of the Novel Nanocrystalline Refractory Tantalum Alloys

The nanocrystalline tantalum alloys were investigated in terms of mechanical properties. The materials were obtained by powder metallurgy techniques—mechanical alloying (MA) and hot pressing (pulse plasma sintering mode). Pure powders of niobium, molybdenum, and tungsten were used for tantalum as an additive element in the concentration of 5, 10, 20, and 40 wt %. The analysis of XRD (Williamson–Hall equation) and TEM confirmed a significant reduction of the grain size (5.3–25.7 nm) for pure powders and (12.5–171.5 nm) for bulk hot-pressed elements. The nanoindentation test was used to study the mechanical properties. The load-displacement curves show high uniformity of the mechanical properties. The nanocrystalline alloys show very high hardness and stiffness. The highest value of hardness reached 1481 HV for Ta–10Mo composition. Significantly higher values of hardness compared to pure Ta-nano were measured for Ta–W system. The Young’s modulus increased twice up to 343 GPa for Ta–20Mo in comparison to the unalloyed nanocrystalline Ta (163 GPa). In the novel nanocrystalline tantalum alloys, both solid solution and grain boundary strengthening affected on high mechanical properties.

텅스텐 제조를 위한 소결공정의 영향과 기계적 특성 평가

The monolithic tungsten materials were fabricated by a hot pressed sintering process using a chromium powder as an additive material in this study. Especially, mechanical properties of tungsten materials including the flexural strength and hardness were evaluated due to the sintering temperature and the effect of additive amount. SEM was also used to analyze the microstructural characteristics of the sintered tungsten material. It was found that both sintered density and flexural strength of tungsten materials increased with the increase in sintered temperature and additive Cr amount, accompanying to the grain growth in the microstructure. The relationship between microstructure and mechanical properties of flexural strength is discussed for producing the optimal fabricating condition of tungsten materials. The bending strength and Vickers hardness of tungsten sintered material increased with increasing sintering temperature. The bending strength of the tungsten sintered material was about 580 MPa and the Vickers hardness was about 470 Hʋ when 7 wt% of chromium powder was added at sintering temperature of 1,600℃. At the sintering temperature of 1,600℃, the sintering density of tungsten sintered material increased with promotion of microstructure densification as the content of chromium added to tungsten powder increased. In particular, it showed excellent sintered density of about 17.04 g/㎤ at a chromium content of 7 wt%.