National Repository of Grey Literature 11 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
Tungsten-steel and tungsten-chromium composites prepared by RF plasma spraying
Matějíček, Jiří ; Klečka, Jakub ; Čížek, Jan ; Veverka, Jakub ; Vilémová, Monika ; Chráska, Tomáš ; Ganesh, V.
For future fusion reactors, materials able to withstand harsh environments are needed. In particular, this concerns the plasma-facing components which are foreseen to consist of tungsten based plasma-facing armor and structural and cooling part made of steel. Currently, joining of these materials presents a significant challenge. The stress concentration at their interface, which arises due to thermal exposure and the difference in thermal and mechanical properties, can be reduced by composite/graded interlayers. Plasma spraying is among the prospective technologies for their preparation. In this work, tungsten-steel and tungsten-chromium composites were prepared by radio-frequency inductively coupled plasma (RF-ICP) spraying. Initial optimization of the spraying process for pure materials as well as their mixtures was carried out. Basic characterization of the layers for their structure, porosity and composition is presented.
On tungsten spraying using inductively coupled plasma system - First results
Klečka, Jakub ; Mušálek, Radek ; Vilémová, Monika ; Lukáč, František
Thanks to its unique properties such as high melting point and density, tungsten and tungsten-based alloys are commonly used in a wide range of applications. Among others, these materials are promising candidates for the plasma facing components in the future fusion reactors. One of considered ways of production of these parts is plasma spraying. There are however several limitations for conventional gas stabilized torches, mainly in plasma enthalpy (i.e. the ability to efficiently melt tungsten particles in considerable feed rates) and susceptibility of tungsten to oxidation (which complicates spraying in oxidizing open-air atmosphere). The radio frequency inductively coupled plasma torch (RF-ICP) is a unique system which can potentially overcome both these problems and can be used for efficient tungsten spraying. The tungsten powder, which can be finer than the one used for the conventional systems, is fed axially into the hot plasma core, both factors lead to a more efficient melting of the particles. The deposition is performed in a chamber with controlled atmosphere of inert gas or decreased pressure, the oxidation is therefore suppressed. In this first study carried out with the newly commissioned RF-ICP system TekSpray 15 (Tekna), samples of tungsten coatings on graphite substrates were prepared. The X-ray diffraction and SEM images of the free surfaces and cross-sections were obtained, documenting high purity of the deposits and appropriate flattening of the splats leading to a dense coating microstructure. The effect of substrate preheating on the microstructure, porosity and hardness was also studied.
PHASE STABILITY IN MILLED Y2O3 AND W-Y2O3.
Illková, Ksenia ; Vilémová, Monika ; Lukáč, František
Properties of milling-induced high-pressure B phase in Y2O3 and W-Y2O3 powders were studied by differential thermal analysis and X-Ray diffraction. It was found that phase stability strongly depends on the heating rate and holding time.
ADHESION OF BIOCOMPATIBLE TiNb COATING
Kolegar, T. ; Matoušek, M. ; Vilémová, Monika ; Starý, V.
Preparation of a coating with a high quality requires good adhesion of the film to the substrate. The paper deals with the adhesion of biocompatible TiNb coating with different base materials. Several materials such as titanium CP grade 2, titanium alloys Ti6Al4V and stainless steel AISI 316L were measured. Testing samples were made in the shape of small discs. Those samples were coated with a TiNb layer by using the PVD method (magnetron sputtering). Onto the measured layer of TiNb an assistant cylinder was stuck using a high strength epoxy adhesive E1100S. The sample with the assistant cylinder was fixed into a special fixture and the whole assembly underwent pull-off testing for adhesion. The main result of this experiment was determining the strength needed to peel the layer and morphology and size of the breakaway. As a result, we will be able to determine the best base material and conditions where the coating will be remain intact with the base material.
Black Chromia Coatings on Metal Tubes for the Solar Collectors
Brožek, V. ; Mastný, L. ; Novák, M. ; Vilémová, Monika ; Kubatík, Tomáš František
This paper describes the results of the first phase of the study preparation, structure and properties of coatings modification of black chromium oxide on copper, aluminium, iron and zirconium tubes for solar collectors. The coatings are prepared by plasma spraying of liquid chromate method which is known as liquid precursor plasma spraying. Coatings have the function of an energy trap for thermal radiation wavelengths of 1 μm – 3 μm i.e. in the IR region. At the same time, the coating increases the corrosion resistance of metal substrates. The nanometric structure and thickness of the coating depend of the feeding distance and the concentration of chromate precursors. For the deposition of nanometric splats of melt chromiumIII oxide, a new type of feeder that injects precursors into the water stabilized thermal plasma produced by the WSP® generator has been\ndeveloped.\n
Black Chromia Plating for the Solar Radiation Absorbers
Brožek, Vlastimil ; Březina, Václav ; Brom, Petr ; Kubatík, Tomáš František ; Vilémová, Monika ; Mastný, L. ; Novák, M.
Black chromia layers were produced on copper, zirconium and aluminium substrates. These layers are aimed to serve as solar collectors. Efficiency of the layers during UV-VIS, UV radiation and WSP® plasma torch radiation is described. The chromia layers were prepared by a new procedure, i.e. deposition of ammonium dichromate solution using plasma torch or so called Liquid Precursor Plasma Spraying (LPPS). Solution of ammonium dichromate is fed into plasma stream, where dissociation takes place under temperatures of 4000 K – 25000 K. Up to nanometric oxide particles can be produced; the resulting size is dependent on solution concentration and feeding nozzle diameter. The particles impact on substrate and form coating. Using 2 wt.% to 5 wt.% solution of ammonium dichromate and feeding nozzle of 0.2 mm in diameter is the size of produced chromia particles about 6 µm which results in formation of 2 µm to 3 µm thick coating, i.e. according to the theory an optimal thickness 2.5 um for absorption layers, necessary condition for formation energy traps for IR radiation emitters up to 100°C. Moreover, black chromia coating is a suitable corrosion barrier of metallic substrates. \n\n
Mechanical and chemical properties of plasma sprayed bronze CuAl10 coating on magnesium and magnesium alloy AZ91
Kubatík, Tomáš František ; Vilémová, Monika ; Mušálek, Radek ; Janata, Marek
The most common magnesium alloy AZ91 is widely used as a structural material, but its use is limited at higher temperatures and high humidity. Plasma spraying is a technology that allows to prepare protective metallic and nonmetallic coatings on a wide variety of substrates including magnesium and its alloys. In this study, CuAl10 was plasma sprayed on magnesium and magnesium alloy AZ91 with the aim to study corrosion resistance of the magnesium substrates. The work focuses on optimization of the plasma spraying process, on chemical composition of the coatings, on interface between the coating and substrate, as well as on adhesive strength of the coatings. The coating were deposited after two passes of the spraying torch resulting in thickness of 150 micro m on magnesium substrate and 110 micro m on AZ91 substrate. Chemical microanalysis showed that deposition of CuAl10 alloy on magnesium results in formation of an intermetallic layer at the interface. The layer provides a
THERMAL AND MECHANICAL PROPERTIES OF TUNGSTEN COMPACTS PREPARED BY SPS
Nevrlá, Barbara ; Vilémová, Monika ; Matějíček, Jiří
Tungsten is a promising candidate material for use in the tokamak device aimed at future production of nuclear fusion power. Here, tungsten is intended for the application in the part called first wall,with the function of a heat-resistant plasma facing armor.In the present work,two fractions of tungsten powder (2 and 4 μm) were used to prepare two consolidated samples by spark plasma sintering (SPS),using a combination of pressure,temperature and electric power.This sintering technique produces samples of near theoretical density which is positive for the application.Tungsten compacts were then studied to determine some basic thermal and mechanical properties, namely thermal conductivity using the laser-flash method and hardness by Vickers test.The measurements were focused on thermal conductivity of the compacts because high thermal conductivity is crucial for the material of tokamak first wall,loaded by high heat flux from the plasma.High hardness is desirable for good resistance
Silicon carbide for chemical application prepared by SPS method
Brožek, Vlastimil ; Kubatík, Tomáš František ; Vilémová, Monika ; Mušálek, Radek ; Mastný, L.
Silicon carbide discovered more than 121 years ago has a wide usage in the mechanical engineering industry as well as in electrical engineering.It is an excellent abrasive medium as well as a construction material with high resistance to mechanical and chemical deterioration.Under standard condition, silicon carbide has no melting point (decomposes at 2700 °C – principle used for industrial production of silicon),thus the bulk form must be prepared in a composite form with a metallic, ceramic or polymer binder. This method is suitable for tailoring of mechanical properties; nevertheless,it does not produce SiC form applicable for laboratory purposes.Binder-free sintering of SiC is practically impossible, despite decreased chemical resistivity of the produced material. Pure SiC is insoluble in all acids except hydrofluoric acid.Reaction of SiC with HF is enabled only due to residual SiO2 created during the industrial production.However, SiO2 located between the planes of growth of SiC
Composites of titanium carbide with scandium matrix
Brožek, Vlastimil ; Pala, Zdeněk ; Vilémová, Monika ; Kubatík, Tomáš František ; Mušálek, Radek ; Nevrlá, Barbara ; Mastný, L.
First reference about existence of ultrahard composite in the TiC-ScCx system was made by G.V. Samsonov in the year 1962. Further research performed on ICT Prague and University of Vienna proved a discrepancy in the structure and stoichiometry of scandium carbide. Analogously to cubic carbides and nitrides of 3rd period metals, Scandium was also expected to have extreme hardness, high chemical stability and to enable solid solution formation (Vegard rule) with controlled regulation of physical parameters. Higher hardness of the cubic carbides is related to the decrease of lattice parameter, thus is was expected that smaller atomic radius of Sc in TixSc1-xC solid solution will lead to increase in hardness. However it was discovered that scandium carbide differs chemically as well as structurally, e.g. Sc15C19 is hydrolyzed and the product of the reaction is hydrogen, allylen and other hydrocarbons. Due to high price of Sc compounds, CVD and PVD layers of TiAlN or TiScAlN on sintered

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