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Tungsten-Steel Composites and FGMs Produced by Hot Pressing
Matějíček, Jiří ; Boldyryeva, Hanna ; Brožek, Vlastimil ; Čižmárová, E. ; Pala, Zdeněk
Tungsten-steel composites and FGMs are being developed for potential application in plasma facing components of fusion devices. In this study, uniform composites and graded layers produced from tungsten and steel powders by hot pressing were investigated. Formation of dense composites with uniform distribution and good bonding of the phases was observed. A thin layer of intermetallic phase Fe7W6 formed at the interfaces. Thermal and mechanical properties of the composites in the as-produced and annealed state were characterized.
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Tungsten cermets with zirconium and hafnium carbides
Brožek, Vlastimil ; Ctibor, Pavel ; Matušek, M. ; Sedláček, J.
Cermets with tungsten matrix and functional components of ZrC and HfC with absolutely highest meeting points are materials with good properties at high temperature exposure. Tungsten based cermets with 10, 20 and 30 % of the functional component were prepared by two different procedures and their properties were compared. The first series of the samples was manufactured by powder metallurgy. A homogenized and preformed mixture of powders was sintered at 2000°C and pressure 6 GPa by hot-pressing technique in the apparatus of BELT-type. The second series was prepared by plasma spraying with water-stabilized plasma WSP® by two different procedures. In the first case the powders of W and ZrC (or W and HfC) were injected into the plasma jet by two separate feeders. The feeding distance 25 to 75 mm was affected by different kinetic parameters, different size distribution and density. The second case represents deposition of pre-spheroidized powder mixtures prepared by spray drying
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Optimalizace vnášení prášku při plazmovém stříkání wolframu a mědi
Matějíček, Jiří ; Mušálek, Radek
Coatings of tungsten, copper and their composites can be used in various thermal management applications. For plasma spraying, injection of the feedstock powder is critical to achieve proper melting in the plasma jet and to produce coatings of desired properties. In this study, powder injection parameters were optimized while varying the injection location and carrier gas flow. Behavior of the particles in the plasma jet was observed using in-flight particle diagnostics; deposition efficiency as well as several coating properties were measured. Based on the results, the optimal injection conditions were selected, and composites and graded layers produced.
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Vliv podávání prášku na mechanické vlastnosti plazmových nástřiků mědi a wolframu
Mušálek, Radek ; Matějíček, Jiří
Nuclear fusion is considered to be a promising energy source for the future. One of the biggest problems which has to be solved is the development of inner wall material of the fusion reactor. For the inner parts which will be exposed to high levels of heat and particle flux, a combination of tungsten layer on copper parts was proposed. Tungsten is refractory material resistant to high heat and particle flux, while copper can efficiently remove heat due to its high thermal conductivity. But high stress concentration on the materials interface can occur due to the thermal expansion coefficient (CTE) mismatch of both materials when exposed to high temperatures. Therefore plasma spraying is promising technology for this application. One of the critical plasma spraying parameters is the carrier gas flow which has to be optimized to ensure proper particle trajectory along the centerline of the plasma flame. Obtained results are currently being used for the development of FGM coatings.
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Krystalinita a slinovatelnost wolframu
Brožek, Vlastimil ; Maixner, J. ; Domlátil, J. ; Janča, J. ; Eliáš, M.
Sintering activity of tungsten powders of various origin was tested by modified technique according Agte. The size of crystallites calculated according to Scherrer formula corresponds with density values detected by Mercury porosimetry. Tungsten poder obtained by reduction of tungstates in hydrogen plasma can be recovered to 93 % of theoretical density at the temperature 1350°C. Next increase of the density needs simultaneous application of high pressure. By the BELT technique 95 % density was reached, by plasma spheroidization up to 98 %.
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Cermety z karbidu hafnia
Brožek, Vlastimil ; Ctibor, Pavel ; Dong-Ik, Ch. ; Eun-Pyo, K.
Cermets of the HfC in W matrix were prepared firstly by hot pressing at the temperature 2000°C and pressure 5.5 GPa and secondly by plasma spraying using water stabilized plasma gun WSP. Microhardness, elastic modulus and thermal expansion coefficients were measured for 10 % HfC and compared with pure tungsten.
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Tungsten filters
Brožek, Vlastimil ; Matějíček, Jiří ; Neufuss, Karel
Spheroidized tungsten powder was sintered by HIP and BELT methods at 1750°-1950°C. Sintering temperature and sintering pressure, which controls the pore distribution in final products, was optimized by increased hardness of tungsten particles through the formation of unreacted WC ore W2C core. Porosity and permeability of tungsten filters, which application is foreseen in high temperature filtration of metals and melts inorganic substances were measured.
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Plasma spray deposition of tungsten matrix cermets
Brožek, Vlastimil ; Matějíček, Jiří ; Neufuss, Karel
This article describes experimental results of plasma spray deposition of tungsten carbide molten by a water stabilized plasma in a WSP® generator. During the deposition on ceramic or metallic substrates, chemical changes take place: decrease of bonded carbon content and formation of metallic tungsten. In the deposit, tungsten forms a matrix that fixates the unreacted monocarbide WC from the starting powder and hemicarbide W2C formed by the thermal decomposition. the ration of these carbides and the tungsten matrix can be controlled by a complex array of spraying parameters. These parameters, such as starting powder size, injection velocity, feeding distance, spraying distance and cooling mode, are confronted with the final product properties – structure, composition and mechanical properties (hardness and Young’s modulus). The materials presented here reached Young’s moduli between 135 and 250 MPa and microhardness of the matrix around 9.23 GPa.
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Plasma deposition of tungsten coatings
Brožek, Vlastimil ; Matějíček, Jiří ; Neufuss, Karel
Tungsten coatings on steel or ceramic substrates were prepared by water stabilized plasma generator WSP®. It operates on the Gerdien arc principle and produces plasma reaching temperatures up to 28000 K and velocities several Mach at the nozzle exit. Tungsten particles are melted and accelerated to velocities 30-70 m/s in the turbulent plasma that transports them to the substrate, where the particles rapidly solidify, forming characteristic splats and porous coatings. Protection of the molten 20-63 μm tungsten particles against oxidation by argon and acetylene shrouding was found to be inadequate. Therefore, a new method was tested, using hydrogen as a carrier gas in a special, house-built powder feeder. Another modification of the spraying process consisted of admixture of stoichiometric amount of tungsten monocarbide. During melting, it decomposes to W2C and carbon, which oxidizes and forms a protective cloud of carbon monoxide around the particles.
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