Tungsten Coatings Research Articles

Features of the structure of coatings of tungsten and chromium carbides during detonation-gas spraying with energy accumulation in a multichamber device

Features of the structure of coatings of tungsten and chromium carbides during detonation-gas spraying with energy accumulation in a multichamber device

Corrosion resistance of HiPIMS tungsten and tungsten-aluminium coatings in contact with liquid Sn

Pure‑tungsten and tungsten-aluminium films deposited by high power impulse magnetron sputtering (HiPIMS) on copper‑chromium‑zirconium substrates were investigated as protective coatings against liquid tin corrosion, a critical issue for nuclear fusion applications. The growth of pure‑tungsten coatings was controlled by using a negative substrate bias synchronized to the HiPIMS pulse onset, resulting in columnar films with various degree of compactness and crystallinity according to the set bias amplitude (0, 400 and 800 V). Differently, the co-sputtering of W and Al favored the formation of an amorphous layer with a compact morphology. During liquid tin corrosion experiments at 400 °C for up to 600 min, all produced coatings were not dissolved, but different protective performances were observed after localized liquid tin interaction. Pure-W coated samples suffered from tin penetration after brittle failure of the protective layer. On the contrary, under the same experimental condition, WAl coatings proved to be effective in limiting liquid tin attack.

Improved structure and enhanced properties of detonation sprayed W coating via hot isostatic pressing

Tungsten has garnered significant attention for its superior performance as a plasma-facing material in tokamak devices. However, its hardness and high ductile-to-brittle transition temperature present challenges for its application in plasma-facing components. To address these issues, this study employs the detonation spraying (DS) technique to prepare tungsten coatings on a TZM alloy substrate and further optimizes their properties through hot isostatic pressing (HIP) treatment. Advanced characterization techniques were utilized to conduct a detailed microstructural and compositional analysis of the coatings. The results indicated that the HIP treatment significantly reduced the porosity of the coatings, improving their density and overall quality. Additionally, HIP treatment led to a decrease in internal stress, a reduction in dislocations, and the grain growth within the coatings. The study also discussed how the HIP process improved the microstructure of the DS tungsten coatings through these mechanisms, thereby enhancing the coatings' thermodynamic properties. Mechanical property tests revealed that the coatings treated with HIP exhibited higher bonding strength and lower hardness, attributed to the increase in grain size and the reduction in dislocation density within the coatings. Thermal property tests demonstrated that the HIP-treated coatings possessed higher thermal diffusivity and specific heat capacity in the temperature range of 100 to 500 °C. Furthermore, the performance of the coatings under transient high heat flux conditions was significantly improved after the HIP treatment, showing better resistance to the thermal shock and cracking. These findings are of great importance for understanding the performance enhancement of DS tungsten coatings in nuclear fusion reactor applications via HIP, especially as candidate materials for the first wall of tokamak devices.

Tungstate-borate ionic liquids: structure, electrochemical behavior and electrodeposition of tungsten coatings

Tungstate-borate ionic liquids: structure, electrochemical behavior and electrodeposition of tungsten coatings

Investigation of the Processes of Retention and Release of Implanted Deuterium and Helium Ions for Tungsten and Tantalum Coatings

Investigation of the Processes of Retention and Release of Implanted Deuterium and Helium Ions for Tungsten and Tantalum Coatings

Tungsten coating technologies for agricultural machinery engine parts

The article reviews the possibilities of using tungsten for engine parts of agricultural machinery and the transition to electric motors. The use of electric motors for agricultural machinery and experience in the production of electric tractors is described. A description of the manufacturers of electric tractors and their advantages is given. The materials of motor parts are described, including the use of tungsten. CVD coatings are selected and described as a technology for electric motor applications. The technology of obtaining tungsten coatings on the electrodes of the engine of agricultural machinery by the method of obtaining CVD coatings is proposed. In this article, the CVD coating mode is selected and the properties of the obtained coating according to the selected mode are analysed. The advantages of the coating are identified and the future development of the technology is described.

Effect of electric fields on tungsten distribution in Na2WO4-WO3 molten salt.

Tungsten coatings have unique properties such as high melting points and hardness and are widely used in the nuclear fusion and aviation fields. In experiments, compared to pure Na2WO4 molten salt, electrolysis with Na2WO4-WO3 molten salt results in a lower deposition voltage. Herein, an investigation combining experimental and computational approaches was conducted, involving molecular dynamics simulations with deep learning, high-temperature in situ Raman spectroscopy and activation strain model analysis. The results indicated that the molten salt system's behaviour, influenced by migration and polarization effects, led to increased formation of Na2W2O7 in the Na2WO4-WO3 molten salt, which has a lower decomposition voltage and subsequently accelerated the cathodic deposition of tungsten. We analyzed the mechanism of the effect of the electric field on the Na2W2O7 structure based on the bond strength and electron density. This research provides crucial theoretical support for the effect of electric field on tungsten in molten salt and demonstrates the feasibility of using machine learning-based DPMD methods in simulating tungsten-containing molten salt systems.

Оценка коррозионных свойств вольфрамового покрытия контейнеров для РАО, нанесенного газофазным методом

The article summarizes the study exploring the anti-corrosion characteristics of tungsten coatings produced by chemical gas-phase deposition in a solution simulating the geochemical conditions at the Yeniseiskiy site. The study shows that a 30-micron-thick tungsten-based coating appears to be quite stable with an average corrosion rate of 1.4 microns/year. It also notes the high stability of tungsten coatings under microbial fouling conditions.

Microstructure of tungsten coatings effect on deuterium plasma-driven permeation through RAFM steel

Tungsten (W) coatings with different morphologies were deposited on CLF-1 steel by changing the sputtering time and discharge power using the magnetron sputtering method. Deuterium (D) plasma-driven permeation (PDP) experiments through W-coated CLF-1 were then carried out in the temperature range of 583–833 K. The obtained results showed that dense W coatings reduced steady-state permeation flux and prolonged the time of permeation flux reaching steady-state. Due to the existence of high-density intrinsic defects, D effective diffusivities of the coating are lower than that of bulk W. The increase of coating thickness reduced permeation flux. In addition, by changing the bias voltage and studying the influence of incident ion energy on D-PDP, it is found that the introduction of W coating affected the overall D transport by re-balancing the bulk diffusion and surface recombination processes. The thickness and microstructure of W coatings played a key role in determining the D steady-state permeation flux at varying temperatures.

Investigation on tribological behaviour of co-deposited zinc, tungsten and graphene (ZnWG) nanocomposite coatings on low-carbon steel

Investigation on tribological behaviour of co-deposited zinc, tungsten and graphene (ZnWG) nanocomposite coatings on low-carbon steel

DEPOSITION OF TEXTURED CONDENSATES OF TUNGSTEN BY HYDROGEN REDUCTION OF ITS HEXAFLUORIDE

In this work, a study of textured tungsten coatings deposited by the hydrogen reduction of tungsten hexafluoride was carried out. The formation of condensate is carried out by the natural selection of columnar grains growing perpendicular to the surface of deposition. Depending on the oversaturation of the gas phase above the growing solid one, some planes of the pyramids are subjected to a predominant growth rate, which leads to the formation of a texture. In the range of parameters studied, (100) and (111) tungsten textures are formed. The measured surface roughness is within the 5 class.

The high temperature oxidation and thermal shock behavior of a dense WSi2–TaSi2 coating on Ta substrate prepared by a novel two-step process

In order to improve the oxidation resistance of the Ta substrate, a novel two-step process including molten salt electrodeposition (Na2WO4-WO3 system) and halide activated pack cementation was adopted to prepare a WSi2–TaSi2 coating on tantalum substrate. During the electrodeposition process, dense tungsten coatings were fabricated at current densities of 30 mA/cm2, 40 mA/cm2 and 50 mA/cm2. It was observed that the grain size exhibited a log-normal distribution. When the current density was 40 mA/cm2, the grain size and flattest surface of the tungsten coating reached 9.50 ± 0.23 μm and 6.792 μm, respectively. When performing the static oxidation test, the WSi2–TaSi2 coating could effectively protect the Ta substrate oxidized at 1600 °C for 30 h. This is attributed to the presence of dense SiO2 and Ta2O5, which acted as a protective layer and suppressed the further penetration of oxygen. Furthermore, due to the matching thermal expansion coefficient between each layer and the sealing ability of semi-molten SiO2, the four-layer SiO2–W5Si3–WSi2–Ta5Si3 coating could successfully pass 721 thermal shock tests from 1600 °C to room temperature.

Improvement of the field emission lifetime of freestanding vertically aligned carbon nanotubes by coating with a metallic protective layer

In this article, we present a method to improve the field emission (FE) lifetime of freestanding vertically aligned carbon nanotubes (VACNTs) by uniformly coating the surface of VACNTs with a thin metallic layer that has low work function, high melting point and high electrical conductivity. The effects of three different metal shells on the FE performance are investigated. The FE performances of these VACNTs are evaluated by testing the turn-on electric field and long-term FE performance. The metal coatings do not have pronounced effects on turn-on electric field of VACNTs, but their FE lifetimes were improved to varying degrees. A 5 nm tungsten and gold coatings have the most significant improvement on the FE lifetime and current density stability. They have shown negligible degradation during continuous 48-h FE testing at a current density over 7 mSSA·cm −2. In addition, a 10 nm titanium, gold, and tungsten coatings also provide significant improvements in lifetime and emission current stability. Furthermore, it was observed that the metal shells are uniformly distributed on the surface of VACNTs, and they can effectively protect the VACNT from being melted by the Joule heat generated during FE. Therefore, metal-coated VACNTs have the potential to increase the lifetime of VACNT emitters during high current FE applications.

The Erosion of selected tungsten coatings by ion beam and plasma sources compared to calculated predictions

Tungsten is proposed as a tokamak divertor armour due to its good erosion resistance. Combining tungsten coatings with copper as a base material can overcome problems with machinability, lower the weight and reduce the component cost. The erosion rate must be known to estimate the lifetime of plasma facing components.This work aims to compare selected tungsten coatings to check if the erosion rate remains as good. It also compares the experimental data to a developed code based on previous work that aims to be quick and simple while giving reasonable results.In this study a set of erosion experiments were undertaken to measure the sputter yield in different conditions at partner organisations; Helium ion beam erosion at Huddersfield University, Helium plasma erosion at the University of Liverpool, Argon plasma erosion at Plasma Quest Ltd and Xenon Focussed Ion Beam (FIB) erosion at University of SurreyThis work compares sputter yields different tungsten samples: sheet material, Chemical Vapour Deposition tungsten coating, Additive Manufacture deposited tungsten and tungsten coatings laid down by Thermal Plasma Spray. These coatings are available commercially so are ready to deploy today.The experimental sputter yields were compared to theoretical predictions, based on previously published work. While the experimental results agreed well with the models in trend and angular dependence the quantitative agreement was only well predicted to within a factor of four.It was found that the coatings have similar, and sometimes slightly lower sputter yields, and therefore, on occasion, slightly better erosion performance than the stock tungsten sheet samples.

Study of process parameters and characteristics properties of W coatings deposited by rf plasma sputtering

Tungsten coatings were deposited on silicon substrates by radio frequency (rf) magnetron sputtering from a metallic target in Ar atmosphere. The process parameters during the sputtering process were evaluated by a Langmuir probe, particularly, the electron density and electron temperature were measured by changing the rf power and gas pressure. The morphological and structural properties of the coatings were studied as a function of the pressure. Significant correlations were found between process parameters and characteristics properties of W coatings. The influence of deposition parameters on electrical properties was investigated. The electrical resistivity of the coatings was increased from 1.3 × 10−6 to 3 × 10−5 Ω m as the pressure increased as well.

Atmospheric plasma sprayed W coating/Detonation sprayed W-steel composite coating/steel substrate-based coating system for the tokamak first wall

To study the manufacturing method of the tungsten armored first wall of tokamak devices, the W-316 L steel (W-SS) composite coatings were fabricated on 316 L steel substrates by detonation spraying (DS) as the interlayer of pure tungsten coatings manufactured by atmospheric plasma spraying (APS). The main characteristics and performance under transient heat shocks of the APS W/DS W-SS /substrate-based three-layer coating system were studied and compared with the APS W/substrate-based coating system. The results showed the porosity of the DS W-SS was about 1.9% with most of the pores smaller than 70 nm. In contrast, the porosity of the APS W reached about 8.6% and most of the pores were up to hundreds of nanometers. The bonding strength tests proved that both the adhesions of APS W to DS W-SS and DS W-SS to the substrate were much higher (almost 1.5 times) than the adhesion of APS W to the substrates. The three-layer specimens performed much better than the APS W/substrate specimens during the transient heat shock tests as expected. Besides, a special microstructure variation occurred on the three-layer specimens before its damage under the tests which was considered helpful to prolong its life-span under high heat flux. In a conclusion, the DS W-SS interlayer improved the service performance of the APS W/substrate-based coating significantly and demonstrates its potential for application in current tokamak experimental devices.

The effect of MOx (M = Zr, Ce, La, Y) additives on the electrochemical preparation of tungsten in eutectic Na2WO4–WO3 melt

In order to prepare dense and smooth tungsten coatings, a class of additives MOx (M = Zr, Ce, La, Y) were mixed into Na2WO4–WO3 molten salt. Composition and microstructure of tungsten coatings were characterized by X–ray diffraction (XRD), and scanning electron microscopy (SEM). Different MOx additives produce significant differences in the phase, micromorphology and performance of the coatings. The coatings electrodeposited in Na2WO4–WO3–CeO2 molten salt have the finest grains, resulting in the microhardness of coating surface reaches the maximum value of 643.5 HV. The thermal shock resistance in air atmosphere is related to the phase and grains size of the coatings. The electrodeposition mechanism was explored by cyclic voltammetry (CV), linear scan voltammetry (LSV), square wave voltammetry (SWV), chronoamperometry (CA) and open circuit chronopotentiometry (OCP). The results indicated that the electrodeposition of tungsten ions is W(VI) → W(IV) → W, and Zr4+ and Ce4+ ions are electroreduced in two steps, while La3+ and Y3+ are electroreduced in one step. The differences between cathodic electroreduction potential and overpotential induced by different additives were probed. What’s more, the relationship between micromorphology and performance of coatings is discussed.

Innovative Tungsten Coatings for an Application in Modern and Future Fusion Devices

Tungsten is foreseen presently as the plasma-facing material for divertors in fusion power plants. In order to achieve durable operation of divertors of current fusion reactors, an efficient way of maintaining the divertor functionality is needed. A system capable of in situ tungsten coating of the divertor via low-pressure plasma spraying was proposed to maintain the divertor integrity. In this work, tungsten was deposited on NB31 carbon fibre composite substrates using the low-pressure plasma spraying technology to evaluate the feasibility of this technique. The thickness, porosity, composition, adhesion, and microstructure of the coatings were investigated by scanning electron microscopy image analysis and energy dispersive spectroscopy. Based on the initial results, the spray parameters were iteratively improved in a campaign-based study. The coatings exhibited improving properties through an adjusting of the carrier gas flow, the scanning speed, and the spray distance. By lowering the carrier gas flow, the porosity of the coatings was reduced, resulting in coatings of 98% bulk density. Adjusting the carrier gas flow reduced the amount of semi-molten particles in the coatings significantly. A decrease in both scanning speed and spray distance increased the substrate’s temperature, which led to better adhesion and porosity.

Towards a Large-Scale “Green Energy”: Multifunctional Protective Coatings for Nuclear Engineering Structural Materials

The main task of the research is to analyze the possibility of using tungsten protective coatings in fast nuclear power reactors cooled by a lead. The author uses computational and optimization research methods. A comprehensive analysis of the properties of tungsten, including the properties of thin tungsten coatings, has been carried out. The results obtained make it possible to consider tungsten coatings of structural materials as multifunctional protective coatings. They perform the functions of protecting against corrosion and erosion of structural materials in liquid lead. They increase the thermal conductivity of fuel claddings and contribute to a decrease in the maximum fuel temperature in the nominal and emergency operating modes of the reactor. The only disadvantage of tungsten when used in nuclear technology is associated with a high neutron absorption cross section. This disadvantage can be an advantage in minimizing the void reactivity effect. The necessary neutron balance is ensured by using a coolant based on lead thorium ores and innovative ceramic fuel with the addition of uranium metal nanopowder. The significance of research is determined by the possibility of the transition of nuclear energy to the status of “green” environmentally acceptable and safe energy in the near future.

Cold plasma studies on the influence of surface microstructured thickness in the secondary electron emission from tungsten coatings

The Secondary Electron Emission (SEE) from the Plasma Facing Components, (PFCs) affects the plasma sheath and edge structure of magnetically confined toroidal plasmas with effects on the Scrappe Off Layer (SOL), heat transport and incident plasma heat flux to the divertor targets. It is also behind the performance degradation in aerospace devices as Hall thrusters. In future reactor prototypes using tungsten (W) components, much more demanding and longer term conditions for the exposed PFCs are expected. These scenarios will exacerbate the material degradation of the exposed surfaces that will change its morphology, thus modifying its plasma material interaction behavior. In such scenario, specific studies on the influence of the microstructure in the tungsten SEE yields become necessary. In these laboratory experiments, the SEE emission of different microstructured tungsten coatings exposed to helium Glow Discharge (GD) plasmas has been analyzed by using a previously developed laboratory technique. It enables the characterization of the I-V characteristics of the biased sample and, at the same time, the acquisition of the electron incident flux by using a gridded probe adjacent to the exposed sample. Different microstructured W coated samples differing in coating thickness (2500 nm and 500 nm) and primal substrate surface finishing (translated in final differences within the W coating topologies) were analyzed, also including cold rolled tungsten and original stainless steel (SS) substrate (material in which the microstructured tungsten film was deposited) as benchmarks for comparison. The overall results have shown that the presence of a 2500 nm thick microstructured W coating decreases the SEE yield of tungsten (cold rolled) up to a factor 40% at electron mean energies of 100-175 eV. Conversely, 500 nm coatings did not reduce the SEE yield even showing an increase at 25-100 eV. The final increase/decrease in the obtained SEE yields seems to be more influenced by the microstructured coating thickness (where the role of intrinsic differences in oxygen content of the surfaces is discussed) rather than other questions possibly derived by the differences in surface topology (ordering, directionality and/or roughness of the microstructure features).