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Plasma spraying from liquids: plasma liquid interaction and coating build up
Tesař, Tomáš ; Mušálek, Radek ; Medřický, Jan ; Lukáč, František
Plasma spraying from liquid feedstocks is a rapidly developing field of thermal spraying since the coatings prepared from liquids exhibit some unique features, such as high hardness, thermal shock resistance or low thermal and electric conductivity. The key factor influencing the final coating character and properties is the input material which may be in the form of a suspension or a solution. Parameters of the selected suspension (solids concentration, viscosity, surface tension, chemical composition, etc.) or solution (concentration, etc.) determine its interaction with the plasma jet which strongly influences the coating buildup. This proceeding introduces the problematics of the interaction between the liquid feedstock material with the plasma jet and presents the way of evaluation of the coating buildup.
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First experiments with suspension sprayed coatings of Al2O3 using hybrid plasma torch
Tesař, Tomáš ; Mušálek, Radek ; Medřický, Jan ; Kotlan, Jiří ; Pala, Zdeněk
Hybrid water stabilized plasmatron WSP-H represents an interesting alternative to common torches for thermal spraying, because it provides a unique combination of plasma velocity and enthalpy available for material processing. In this paper, influence of deposition parameters on coating characteristics was studied. Nanometric Al2O3 powder dispersed in ethanol was used as a model material. The coating was examined by scanning electron microscopy and X-ray diffraction and the results showed clear dependence of microstructure and phase composition on spraying distance and feed rate of the suspension. Results are promising for further optimization of the deposition process.
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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
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Chemical aspects of antiballistic cermets preparation
Brožek, Vlastimil ; Kubatík, Tomáš František ; Chráska, Tomáš ; Mušálek, Radek ; Janata, Marek ; Mastný, L.
The paper aims to demonstrate the possibilities of metal-ceramic material deposition on different types of metal or ceramic substrates using plasma deposition. A number of self-supporting components and the preparation of metal-braced composites are described and the results of plasma depositions of two particular extremely hard ceramic materials, boride and nitride of titanium are presented. The plasma deposition of these material is performed in technological conditions which prevent undesirable high-temperature oxidation. The paper describes deposition conditions that may lead to materials suited to create anti-ballistic protection and complicated shapes or improve parameters of surface layers of present anti-ballistic ceramics.
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Properties of Novel Hybrid Water-Gas DC Arc Plasma Torch
Chráska, Tomáš ; Hrabovský, Milan ; Glanc, Aleš ; Mušálek, Radek ; Medřický, Jan
A new type of plasma torch with combined stabilization of electric arc by water vortex and gas flow is presented. This hybrid water/gas stabilization offers the possibility of adjusting plasma jet parameters within a wide range from high-enthalpy low-density plasmas typical for liquid stabilized torches to lower enthalpy higher density plasmas generated in gas stabilized torches. Moreover, gas flow in the cathode part protects a cathode tip and thus a consumable graphite cathode used in water-only stabilized plasma torches could be replaced by a fixed tungsten cathode. Examples of hybrid WSP torch utilization for high temperature application are given.
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Special methods for observation of failure of plasma-processed materials
Mušálek, Radek
This paper presents examples of several methods, which may be used for failure study of materials prepared by plasma processing - plasma spraying or plasma sintering. Microstructure of these materials significantly differs from that of bulk construction materials which limits use of conventional methods. Typically, because not enough volume of material in one piece is available for testing. Aim of this paper is to ilustrate benefits of using combined study of materials changes during loading and their macroscopic properties
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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
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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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Thermal spraying of suspensions and solutions
Mušálek, Radek
Recently beginning to be selected for some applications of thermal spraying interesting administration of nanometric or micrometric powders in suspension, or preparation of particles from a solution directly over zinc deposition. This paper provides basic information about this new route of administration and its benefits for technical practice.
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Tungsten coatings and free standing parts
Brožek, Vlastimil ; Ctibor, Pavel ; Matějíček, Jiří ; Mušálek, Radek ; Weiss, Z.
Tungsten powders, 20 – 100 µm in size, were melted in the jet of thermal plasma generated by a water-stabilized spray system WSP®. The molten tungsten was deposited on steel and graphite or boron nitride substrates, whereas the spray-ability itself was tested as well as cohesion with other substrates. One of the goals of this experimentation was to gain skills for covering variously shaped walls of nuclear fusion devices (Tokamaks). Also spraying of free-standing tungsten bodies was realized, by means of substrates easily machainable-out after deposition, as graphite and BN. Other option consists of covering a tungsten mesh or plates armored with tungsten wires. Protection of tungsten against oxidation in the plasma jet was a problem to be solved – the best results were gained with shroud gas, Ar with 7% hydrogen, and simultaneous placement of the substrates into graphite cells. The whole spray process was maintained to avoid temperatures over 700°C at which the oxidation is
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