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Young's Modulus on the Interface of Elastic and Elastic-Plastic Material
Kocmanová, Lenka ; Haušild, P. ; Materna, A. ; Matějíček, Jiří
The paper is aimed at determining the Young's modulus at the sharp interface between two materials, where one material is elastic and the other elastic-plastic. To determine the Young's modulus was used 3D numerical model of nanoindentation with conical indenter. The interface between the materials with the normal plane perpendicular to the direction of penetration. The goal is to simulate the combination of metal and ceramic materials.\n Young modulus according to the standardized distance from the interface are approximated inverse beta distribution and is determined by the relation between parameters inverse beta distribution of the size of the area affected by the second phase
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Structural and Mechanical Characterization of Spark Plasma Sintered Tungsten
Čech, J. ; Haušild, P. ; Kocmanová, Lenka ; Matějíček, Jiří
The main objective of this paper is to describe the microstructure and mechanical properties of spark plasma sintered tungsten. The indentation tests, which are very advantageous because of their semi-nondestructive character and low requirements on the volume of investigated material, were carried out using Berkovich and spherical indenters. Indentation techniques with spherical indenters are less frequently used than those with sharp indenters but they offer variation of strain with the indentation depth and, therefore, they could be used for determination of stress-strain curves. Local stress-strain behavior obtained by this method showed good correspondence with the results of compression tests. Observation of the microstructure and the fracture surfaces helped to explain some phenomena which occurred during the mechanical testing
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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
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FITTING OF ELASTIC MODULUS ON THE INTERFACE BETWEEN TWO MATERIALS
Kocmanová, Lenka ; Materna, A. ; Haušild, P. ; Matějíček, Jiří
The paper is aimed to determinate of Young modulus near a sharp interface. The 3D elastic numeric model was used for prediction of the Young modulus. The simulated specimen was composed of tungsten and steel. The interface was plane which a normal vector was perpendicular to the indentation force. The indenter geometry for which numerical solutions were accomplished was a rounded cone indenter. An indentation depth is studied as function of a distance indenter-interface. The distance was normalized by depth of indentation. All values of Young modulus lay on one curve after distance normalization due to elasticity. The curve was fitted by inverse beta function. The curve determine the size of area of one material influenced by a second material.
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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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Preparation of multiphase materials with spark plasma sintering
Mušálek, Radek ; Dlabáček, Zdeněk ; Vilémová, Monika ; Pala, Zdeněk ; Matějíček, Jiří ; Chráska, Tomáš
Spark plasma sintering (SPS), also called Field Assisted Sintering Technique (FAST), represents a novel method of preparation of sintered materials from powders. The main advantage of the SPS method is a high achievable heat rate (>200 °C/min) and high sintering temperatures (up to 2200 °C in our laboratory). Combination of high heating rate, rather high pressures (up to 80 MPa) and electric field fluctuations leads to an effective sintering and significant reduction of sintering time for both coarse-grained and nanocrystalline powders. Composite materials may be easily obtained by mixing or layering of different powders. The paper will introduce several examples of multiphase materials sintered by SPS at our institute and the establishment of procedures for routine testing of sub-sized specimens.
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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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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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Použití metody konečných prvků pro předpověď mechanických vlastností žárově nanášených vrstev
Mušálek, R. ; Kovářík, O. ; Matějíček, Jiří
Feasibility of finite elemenent method (FEM) for prediction of mechanical properties of thermally sprayed coatings was studied. First, finite element models of microstructures with idealized pores were designed. The influence of pores presence on mechanical response of the structure was evaluated. Secondly, mathematical model based on real tungsten coating microstructure was created using OOF2 software and submitted for further FEM analysis using ABAQUS CAE. Values of Young’s moduli in in-plane and out-of plane directions were estimated. The predictions are compared to the experimental data.
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