Formation Of Tungsten Carbide Research Articles

Understanding the role of tungsten species in diamond-like carbon coatings for enhanced interaction with ionic liquids

This study investigated the impact of tungsten species in tungsten-doped diamond-like carbon (WDLC) coatings on their interactions with ionic liquids (ILs). Using analytical techniques such as in-situ neutron reflectometry, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy, we examined the adsorption mechanism of tributylmethylphosphonium dimethylphosphate on WDLC and undoped hydrogenated DLC (hDLC) coatings. These techniques provide high-resolution insights into the molecular interactions, revealing that tungsten doping enhances the formation of tungsten carbide and tungsten oxides. These species facilitate the dissociation of dimethylphosphate anions, forming a robust 0.75 nm-thick tungsten phosphate layer on the WDLC surfaces. This layer, which adheres strongly even after cleaning, underscores the role of tungsten in enhancing the effectiveness and lubrication properties of WDLC coatings with ILs.

Experimental analysis of surface integrity in electro-discharge coating process

Utilising electro-discharge machining, powdered metallurgical tool materials are applied to coat the surface pattern-wise. The tool undergoes a thorough blending process followed by hydraulic pellet press. Essential evaluations encompass the determination of material deposition rate, tool wear rate, surface roughness, microhardness, layer thickness and wear rate. Characterisations confirm the presence of tool constituents, provide insights into its constituent's composition and reveal the formation of tungsten carbides on the uppermost surface of the deposit. Significantly, a substantially higher deposition rate of 4.9 mg/min is achieved when a compact load of 10 tons and a peak current of 2.5A are applied. Notably, the top surface exhibits a microhardness of 330.5 HV, while the base material maintains a hardness level of 98.7 HV. The maximum thickness of the deposited layer reaches 293.68 μm under identical conditions. These hard materials serve to mitigate the specific wear rate effectively.

The Regularities of Titanium and Tungsten Carbide Formation from Products of Electric Explosion Destruction of Conductors

The Regularities of Titanium and Tungsten Carbide Formation from Products of Electric Explosion Destruction of Conductors

The effect of recrystallization annealing on the tungsten surface carbidization in a beam plasma discharge

<abstract> <p>Tungsten was chosen as the plasma facing material (PFM) of the ITER divertor. However, graphite and carbon-graphite materials are used as PFM in some research thermonuclear facilities, including the Kazakhstan materials science tokamak. This circumstance determines the interest in continuing the study of the formation of mixed layers under plasma irradiation. This article is devoted to the study of the effect of preliminary recrystallization annealing on the carbidization of the tungsten surface in a beam-plasma discharge (BPD), which is one of the ways to simulate the peripheral plasma of a tokamak. Experiments on preliminary isochoric and isothermal annealing of tungsten samples were carried out in the mode of direct heating of tungsten samples by an electron beam. The carbidization of tungsten samples after annealing was carried out in a methane atmosphere in the BPD at a temperature of 1000 ℃ for a duration of 3600 s. Optical microscopy (OM) and X-ray diffraction were used to analyze the structure of the tungsten surface. It has been established that differences in the structure arising during recrystallization annealing affect the transfer of carbon atoms in the near-surface area of tungsten and the formation of tungsten carbides (WC or W<sub>2</sub>C).</p> </abstract>

Tungsten doped diamond shells for record neutron yield inertial confinement fusion experiments at the National Ignition Facility

We report on fabrication and characterization of layered, tungsten doped, spherical about 2 mm diameter microcrystalline diamond ablator shells for inertial confinement fusion (ICF) experiments at the National Ignition Facility. As previously reported, diamond ICF ablator shells can be fabricated by chemical vapor deposition (CVD) on solid spherical silicon mandrels using an ellipsoidal microwave plasma reactor. In the present work, we further developed these ablator shells by embedding a W-doped diamond layer sandwiched between two undoped diamond regions. W incorporation in diamond was achieved by adding tungsten hexacarbonyl to the CH4/H2 CVD feed gas. We observe that the W doping concentration decreases with increasing deposition rate which, in turn, is controlled by adjusting the total gas pressure. Cross sectional microstructural analysis reveals sharp interfaces between doped and undoped regions of the diamond shell and uniform W distribution with concentrations up to about 0.3 at.%. At higher W concentrations (>0.3 at.%) formation of tungsten carbide precipitates is observed. Using a 3‐shock 1.6 MJ laser pulse, the targets described in this work produced the first laser driven implosion to break the 1 × 1016 neutron yield barrier, followed by experiments (described in future publications) with similar targets and slightly more laser energy producing yields as high as 4 × 1017.

In-situ synthesis of WC and WC-17Co powder under hydrogen atmosphere by solid carbothermic reduction method

WC ceramic is considered one of the advanced engineering ceramics due to its favorable properties. The weakness of this ceramic is, however, its brittleness, which can be tackled by composite making and addition of compounds such as Co to the structure of WC. In this research, WC and WC-17Co powders were synthesized by the in-situ carbothermic reduction from active carbon raw materials including WO3 and Co3O4. The main goal of this research was to determine the appropriate amount of carbon in the composition of raw materials. For this purpose, the raw materials were mixed in different ratios of excess carbon as the primary variable. All the samples were heat treated with a heating rate of 10°C.min−1 to a temperature of 1200°C for 3 h in a hydrogen atmosphere. Thermodynamic studies showed that cobalt and tungsten were regenerated from Co3O4, and WO3 at the temperature of 250°C and 700°C, respectively; by raising the temperature to about 1200°C, the formation of tungsten carbide was complete. According to the results, a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) and X-ray diffraction pattern (XRD) were obtained. The main reason for the lack of carbon in the total production of the WC phase was the reaction of carbon with hydrogen in the furnace atmosphere at temperatures less than 500°C, which could be solved by adding further carbon to the raw materials. The combinations (118.37gr WO3-147.06gr C) and (56.95gr C-23.15gr Co3O4-98.25gr WO3) created the best conditions for the production of WC and WC-17Co powders. The results of microstructural studies also showed that the size of grains in the WC-17Co composite powder was larger (less than 200 μm) than that in the WC ceramic powder (less than 20 μm). This was related to the presence of Co3O4 in the raw materials and cobalt in the WC-17Co cermet powder.

Microstructure, Adhesion, and Properties of Multilayer Structure WC/W/MCrAlY Coating on γ‐TiAl Alloy Prepared by Plasma Surface Metallizing Technique and Microwave Plasma Chemical Vapor Deposition

The WC coatings with a multilayer structure are synthesized on a γ‐TiAl alloy by the combined treatments of plasma surface metallizing technique and microwave plasma chemical vapor deposition. The morphology, microstructure, and phases of the coatings are examined by a white light profilometer, scanning electron microscope, and X‐ray diffraction analysis techniques. The formation of tungsten carbide coating leads to high hardness and good wear resistance. Because of a W transition layer and MCrAlY bonding layer, the good adhesion is achieved between coatings and substrate. This result provides a new approach for designing refractory metals and/or their carbide coatings on metals/alloys substrates, for example, WC and/or W coating on TiAl alloy and titanium alloys.

Investigation of long term stability of W/B4C multilayer structures

The long term stability of as-deposited, annealed, and synchrotron radiation exposed W/B4C multilayer structures was investigated. The multilayer structures were studied using hard X-ray reflectivity, grazing incidence X-ray diffraction (GIXRD), extended X-ray absorption fine structure (EXAFS), and atomic force microscopy (AFM). The structural degradation in annealed and synchrotron radiation exposed samples occurs at faster rate as compared to untreated samples. The structural degradation rate clearly depends on the thickness of B4C layer in multilayer structures. GIXRD measurements confirm the formation of tungsten carbide and boride phases. From EXAFS measurements at the W L3-edge, we find that the increase in the diffusion of oxygen is responsible for the observed structural degradation at faster rate in annealed samples consisting of thinner B4C layer. AFM images reveal that the surface modifications occur at slower rate in untreated samples as compared to annealed samples. Moreover, B4C proves to be an efficient cap layer to protect the as-deposited and annealed multilayer structures from oxidation.

Formation of tungsten carbide by focused ion beam process: A route to high magnetic field resilient patterned superconducting nanostructures

A scale for magnetic field resilience of a superconductor is set by the paramagnetic limit. Comparing the condensation energy of the Bardeen–Cooper–Schrieffer (BCS) singlet ground state with the paramagnetically polarized state suggests that for an applied field μ0H>1.8 Tc (in SI), singlet pairing is not energetically favorable. Materials exceeding or approaching this limit are interesting from fundamental and technological perspectives. This may be a potential indicator of triplet superconductivity, Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) pairing, and other mechanisms involving topological aspects of surface states and may also allow Cooper pair injection at high magnetic fields. We have analyzed the microscopic composition of such a material arising from an unexpected source. A microjet of an organo-metallic gas, W[(CO)6], can be decomposed by a gallium ion-beam, leaving behind a track of complex residue of gallium, tungsten, and carbon with remarkable superconducting properties, like an upper critical field, Hc2>10 T, above its paramagnetic limit. We carried out atomic probe tomography to establish the formation of nano-crystalline tungsten carbide (WC) in the tracks and the absence of free tungsten. Supporting calculations show that for Ga distributed on the surface of WC, its s,p-orbitals enhance the density of states near the Fermi energy. The observed variation of Hc2(T) does not show features typical of enhancement of critical field due to granularity. Our observations may be significant in the context of some recent theoretical calculation of the band structure of WC and experimental observation of superconductivity in a WC-metal interface.

Study of the temperature dependence of a carbidized layer formation on the tungsten surface under plasma irradiation

The paper considers a method of tungsten surface carbidization using a beam-plasma discharge (BPD), which was implemented in a plasma-beam installation (PBI). The advantage of this method is to create conditions for chemical reactions and physical processes as close as possible to those possible in thermonuclear installations. The BPD makes it possible to generate plasma using different working gases. Methane was used as a plasma-forming gas. The working gas pressure in a chamber was (1,3–1,4)·10–1 Pa. The temperature dependence of the carbidized layer formation on the tungsten surface under plasma irradiation was determined in the temperature range of 700 °C–1700 °C. The formation of tungsten carbides in surface layers was confirmed by SEM and x-ray diffraction analysis. It was found that interaction between tungsten and methane in a wide temperature range can proceed with simultaneous or sequential formation of the carbide phases W2C and WC.

Investigation of micro-hardness of H11 die steel using composite material electrodes in EDM

Electrical Discharge Machining (EDM), a non-traditional material removal process has been well recognized for itsability for precision machining of electrically conducting hard materials. Repetitive heating and cooling of the workpiecesurface during the machining make the surface hard. During this process, the transfer of material into workpiece surface dueto diffusion of material from the tool electrodes results in the desire surface modifications. This paper investigates the effectof electric discharge machining on H11 die-steel materials with composite material electrodes fabricated by stir casting aswell as powder metallurgy process. Copper (85% by weight) has been used as matrix material with tungsten and carbonnanotubes (10%-5% by weight). The performance of fabricated composite electrodes has also been compared withconventional copper electrode. Microhardness achieved has been found to be best when H11 die-steel surface ismachined with composite electrodes fabricated by powder metallurgy process. Also, the microhardness has been enhancedby 19.57% with optimal input parameters. Results show that optimum microhardness has been observed at high peak currentvalue when surface is machined with copper conventional electrode while pulse on time has been found to the majorcontributor when surface is machined by composite material electrode. XRD analysis indicates the formation of tungsten-carbide, iron-carbide, chromium- nickel and copper on the machined surface of the workpiece

Preparation of tungsten-based thin films using a F-free W precursor and tert-butyl hydrazine via 2- and 3-step atomic layer deposition process

This article reports the preparation of tungsten metal (W) and other tungsten-based thin films using a F-free W metalorganic precursor tris(3-hexyne) mono-carbonyl tungsten [W(EtCCEt)3(CO)] (Et = C2H5), THMCT], tert-butyl hydrazine (TBH), and H2 plasma via 2- and 3-step atomic layer deposition (ALD) process. Density functional theory (DFT) calculations were performed to simulate the possible mechanisms of W4(EtCCEt)4(CO)4, as the model of chemisorbed THMCT on the growing surface, with TBH. The experimental findings agree well with the DFT results that the thermal ALD of THMCT and TBH could not deposit the pure W metal films. Instead, THMCT and TBH led to form an amorphous, tungsten oxycarbide, WOxCy (with a minor nitrogen content and a negligible amount of W metal phase), resulting in a very high resistivity of ∼80,000 μΩ-cm (at 300 °C). Nevertheless, the typical characteristics of ALD, such as the self-limiting growth, and a linear dependency of the film thickness with cycle variation, were obtained with a growth-per-cycle (GPC) of ∼0.4 Å. Post-annealing of the films in the H2 atmosphere resulted in a slight increase in the metallic phase formation with a significant drop in resistivity to ∼3500 μΩ-cm. However, the annealing also facilitated the formation of the tungsten oxide phase owing to the oxygen incorporated in the as-deposited films. Introducing an additional H2 plasma pulse step at the end of each ALD cycle (3-step ALD process) significantly altered the film composition and helped reduce the as-deposited film's resistivity drastically to ∼650 μΩ-cm. Also, the process results in the formation of tungsten carbide (WCx) as the predominant phase. Finally, the additional high-temperature-post-annealing of these 3-step ALD grown films resulted in extremely low resistivity of ∼200 μΩ-cm owing to the formation of body-centered-cubic (BCC) α-W. Thus, the envisaged path in this study to achieve W thin films also provides rooms to grow oxide or carbide dominant phase of W as studied in detail with the help of X-ray photoelectron spectroscopy

Influence of temperature on tungsten carbide formation in a beam plasma discharge

This paper presents a method of tungsten surface carbidization using a plasma-beam setup to assess the effect of temperature on the formation of tungsten carbides. Methane was used as a plasma-forming gas. The working gas pressure in the chamber was (1.3–1.4)10−1 Pa. Experiments on the formation of carbides were carried out at different temperatures (700-1000°C). It was recorded that at a temperature of 700°C, crystallization centers of a carbon film appear on the sample surface. With an increase in the irradiation temperature to 800°C and 900°C, the surface of the samples is covered with a continuous carbon film. As a result of the experimental work carried out, it was found that the formation of tungsten semicarbide occurs at 900°C. A further increase in temperature leads to the formation of tungsten monocarbide.

Improvement of thermal conductivity by adding tungsten and/or copper wire in F82H

ABSTRACT The F82H, which is one of reduced activation ferritic/martensitic steels, is a strong candidate structure material for fusion reactor because of its satisfactory mechanical property and high swelling resistance in the operating temperature range. One disadvantage of F82H would be its low thermal conductivity as a structural material for divertor. In this study, we have fabricated several F82H-based composite materials by the spark plasma sintering to improve its thermal conductivity by adding tungsten and/or copper wires. F82H-20 vol.% W and F82H-10 vol.% W-10 vol.% Cu composites included reaction layers at the interface between tungsten wire and F82H matrix, resulting in the decrease in ductility and tensile strength because of the formation of tungsten carbide. On the other hand, F82H-20 vol.% Cu composite, sintered for 120 min at 1000°C, included no reaction layers and showed the highest thermal conductivity with a high relative density. Furthermore, it showed a great tensile property, which is comparable to that of the original F82H.

Physical and chemical behaviour of tungsten oxide in the presence of nickel additive under hydrogen and carbon monoxide atmospheres

The physical and chemical behaviour of bulk tungsten oxide (WO3) and Ni doped tungsten oxide (15% Ni/WO3) were examined by performing a temperature-programmed reduction (TPR) technique. The chemical composition, morphology, and surface composition of both samples before and after reduced were analysed by X-ray diffraction (XRD), scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) analysis. The XRD pattern of calcined Ni doped tungsten oxide powder comprised of WO3 and nickel tungstate (NiWO4) phases. The reduction behaviour was investigated by a non-isothermal reduction up to 900 °C achieved under (10 and 20% v/v) hydrogen in nitrogen (H2 in N2) and (20 and 40% v/v) carbon monoxide in nitrogen (CO in N2) atmospheres. The H2-TPR were indicated the reduction of bulk WO3 and 15% NiWO3 proceed in three steps (WO3 → WO2 → WO2 + W) and (WO3 → WO2 → W + Ni4W) respectively under 20% H2. Whereas, the reduction of 15% WO3 under 40% CO involves of two following stages: (i) low temperature (<800 °C) transformation of WO3 → WO2.72 → WO2 and, (ii) high temperature (>800 °C) transformation of WO2 → W → WC. Furthermore, NiWO4 alloy phase was transformed according to the sequence NiWO4 → Ni + WO2.72 → Ni + WO2 → Ni + W → Ni4W + W at temperature >700 °C and >800 °C in H2 and CO atmospheres, respectively. It can be concluded that the reduction behaviour of WO3 is matched with the thermodynamic data. In addition, the reduction under H2 is more favourable and have better reducibility compared to the CO gas. It is due to the small molecule size and molecule mass of H2 that encourages the diffusion of H2 molecule into the internal surface of the catalyst compared to CO. Moreover, Ni additive had improved the WO3 reducibility and enhancing the CO adsorption and promotes the formation of tungsten carbide (WC) by carburisation reaction. Besides, the formation of Ni during the reduction of 15% Ni/WO3 under CO reductant catalysed the Boudouard reaction to occur, which disproportionated the carbon monoxide to carbon dioxide and carbon (CO → CO2 + C).

Carbon clustering and effect on hydrogen trapping in tungsten: A first-principles study

The clustering of carbon (C) in tungsten (W) with and without vacancies and the effects of C content at a vacancy on the hydrogen (H) trapping have been investigated by first-principles computer simulations using density functional theory. The calculations were performed in 128-atom or 432-atom supercells. The results indicate that the nascent formation of tungsten carbide is based on a pair of C atoms located at two neighbor octahedral interstitial sites along the 〈111〉 direction with a distance of 0.284 nm. Small interstitial C atoms prefer to form a zigzag chain on a {110} plane, and the C binding energy increases with increasing number of C until four C atoms and then remains constant at 0.7 eV for larger C clusters. The presence of vacancies enhances the interactions between C and its first nearest neighbor (1NN) W atoms because of strong hybridization between the C-p state and the d state of its 1NN W, strengthening the C trapping at vacancies. Meanwhile, the presence of C increases the stability of the di-vacancy in W. The H binding energies to carbon-vacancy-hydrogen (CmVHx−1) complexes decrease with increasing C contents. For a given C content, the H binding energies to CmVHx−1 complexes basically decrease with increasing number of H. The ultimate H contents that can be trapped by CmV complexes essentially decreases monotonically with increasing C content, and the C effect on H trapping is dependent on temperature.

Formation of tungsten carbide nanoparticles by wire explosion process

AbstractTungsten carbide nanoparticles (NPs) were synthesized by wire explosion process (WEP) in gas ambient as carbon source. Formation of tungsten carbide (WC1−X) in a single step by WEP using methane and argon‐acetylene mixture as carburizing medium, is detailed. X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to observe the phase and morphology of the produced NPs. In WEP, morphology and phase of NPs are controlled using different levels of energy ratio, K (ratio of energy supplied to wire and sublimation energy of wire), type and pressure, P of ambience. High purity WC1−X NPs was synthesized in methane ambience with a high K (=19) and a high P (270 kPa). A thorough study has been made to understand the impact of type of carburizing medium. Methane‐acetylene mixture gave two phases of carbides. Argon‐acetylene ambience provided complete carburization in specific cases. In general, the formed NPs are spherical in shape. Formation mechanism of tungsten carbide NPs is detailed in the work.

Intensification of the process of metallizing tungsten­containing ore raw materials by the powder metallurgy method

X-ray diffraction phase analysis of samples performed on a DRON-6 diffractometer has shown that the processes of CaWO 4 transition to WC and W 2 C had the highest probability in the temperature range of 1,173–1,473 K. The end-product CaWO 4 , thermally treated with carbon, was represented by carbon in oxycarbide and carbide phases. The processes of tungsten reduction from its oxides through the phases of formation of tungsten carbide and oxygen compounds (higher and lower) and finally tungsten metal were shown. Basic chemical and phase transformations occurred within the temperature range of 300–1,800 K. This opens the prospect of producing tungsten as an alloying material without formation of liquid phases in a heterogeneous system and enables production of tungsten based alloying material at relatively low temperatures which significantly reduces power consumption. Qualitative and quantitative composition of charge materials for laboratory studies and industrial tests in a form of briquettes for metallization of tungsten-containing compounds in a furnace with induction heating was presented. The mechanism of phase and structural transformations occurring in reduction of tungsten from scheelite concentrates in the temperature range of 1,273–1,473 K and microanalysis of samples of chemical transformations were studied. A furnace unit with induction heating in which industrial tests were performed in stages was schematically shown. The tests have shown that a 1.3 times sample weight reduction and a 23 % specific density reduction occurred in the process of heat treatment of the samples based on scheelite concentrate. Several batches of spongy tungsten instead of standard ferrotungsten were produced and tested in smelting high speed steels. Advantages of the new technology of tungsten metallization from a scheelite concentrate and positive efficiency of using the new material in special metallurgy were shown.

Observable Two-Step Nucleation Mechanism in Solid-State Formation of Tungsten Carbide.

The nucleation of crystals from ubiquitous solid-state reactions impacts a wide range of natural and synthetic processes and is fundamental to physical and chemical synthesis. However, the microscopic organization mechanism of amorphous precursors to nanoscale clusters of ordered atoms (nucleus) in an all-solid environment is inaccessible by common experimental probes. Here, by using in situ transmission electron microscopy in combination with theoretical simulations, we show in the reactive formation of a metal carbide that nucleation actually occurs via a two-step mechanism, in which a spinodal-structured amorphous intermediate reorganizes from an amorphous precursor and precedes the emergence of a crystalline nucleus, rather than direct one-step nucleation from classical consideration. We further isolated a series of sophisticated dynamics during formation and development of the nucleus in real-space and interpreted them by thermodynamic favorability. We anticipate that such an indirect organization mechanism which contains a metastable intermedium among the free energy gap between precursors and nanocrystals has its chance in underlying most solid-state crystallizations, whereas the as-established experimental method represents a step forward in exploring fundamentals in chemical reaction, material engineering, etc.

Microstructural and compositional effects of transition metal carbide additions on dispersion-strengthened tungsten fabricated via spark plasma sintering

Tungsten is the plasma-facing material of choice for the divertor region in ITER as it has favorable properties under ion irradiation. However, tungsten is a very brittle material whose fabrication is complicated by its high melting point and low recrystallization temperature. Spark plasma sintering is a powder consolidation technique that can rapidly compact tungsten powder to high relative densities while preserving fine grain sizes. Dispersing fine transition metal carbide particles within the tungsten matrix has been proposed to enhance the ductility of tungsten by re-arranging the impurity distribution. Tungsten samples consolidated with 0.5–10 wt% zirconium carbide, titanium carbide, or tantalum carbide have been fabricated via spark plasma sintering to >90% relative density. Consolidated samples have transition metal-rich dispersoids uniformly distributed at grain boundaries and within the micron-sized tungsten grains. The presence of the dispersed second phase particles successfully refined the final grain size, as the average grain size decreased from 11 μm for the pure W samples to ~1 μm for the samples with 10 wt% second phase. Correspondingly, the hardness as measured via Vickers hardness rises as the grain size decreases and volume fraction of the second phase increases. XRD and XPS analyses show that formation of tungsten carbide and transition metal oxide complexes alter the impurity distribution and material performance.