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Joining alumina ceramics by thin metallic layers
Poloprudský, Jakub ; Krajňáková, Petra (referee) ; Jan, Vít (advisor)
This bachelor thesis is about the problematics of structural bonds between ceramics and metals with special focus on brazed bonds. First theoretical part describes thoroughly the majority of currently used methods for ceramics joining. Special attention is given to the explanation of phenomenon of bad wettability of ceramics by molten metals and how to solve it. In practical part the work focuses on an analysis of representatives of active and non-active brazing alloys with some added elements. For analysis of microstructures it was necessary to master the basics of preparation of ceramic-metal composite specimens. Important part of the practical section of the work is dedicated to an effort of making a test with comparable results that could be used for ceramic-metal brazed composites evaluation.
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Structure and mechanical properties of magnesium materials processed by HPT
Poloprudský, Jakub ; Němec, Karel (referee) ; Doležal, Pavel (advisor)
This thesis is focused on processing of pure magnesium by high pressure torsion method (HPT). This process belongs to the group of intensive plastic deformation methods (SPD). SPD methods are in the centre of scientific interest for several decades. Theoretical part of this thesis puts an effort to summarize basic knowledge and principles of SPD methods with extra focus on method HPT. As theoretical part continues magnesium as technical material is presented. Influence of SPD on use and properties of pure magnesium is then presented. This trend is further developed in effort to describe the effect of individual HPT process variables on the properties of pure magnesium and its alloys. Focus of practical part of this thesis is in influence of number of revolutions. Samples were processed at 1/8, 1/4, 1/2, 1, 4 and 8 turns at room temperature. Speed of process was 1rpm and applied pressure was 6 GPa. The structure of commercially pure magnesium prepared by casting and moulding were observed with focus on differences caused by input material. The structure was observed by both light microscopy and back scattered electron diffraction (EBSD), focusing on structure development, grain size and grain orientation. Compared to other works on similar topic, the emphasis here is on observing the microhardness on the vertical edge of the sample. The hardness shows a steep increase right after 1/8 of a turn. With increasing number of turns gradual homogenization of microhardness is presented accompanied by slight decrease in microhardness. No trend in microhardness relative to the distance from anvil has occurred. Structure observed with EBSD shows a bimodal character with larger grains oriented in the same direction. The three-point bending test didn’t end up as expected, and the approach to evaluation of magnesium-based HPT needs to be re-evaluated for future work. A three-point bending test was designed for the initial assessment of the basic mechanical properties of the material.
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INFLUENCE OF THE DEPOSITION PARAMETERS ON MICROSTRUCTURE AND PROPERTIES OF HVOF SPRAYED WC-CRC-NI COATING
Vražina, Tomáš ; Šulák, Ivo ; Poloprudský, Jakub ; Zábranský, K. ; Gejdoš, P. ; Hadraba, Hynek ; Čelko, L.
This paper investigates the influence of thermal spray parameters of the high-velocity oxygen fuel (HVOF) process on the properties of cermet coatings prepared from commercially available Amperit 551 WC-CrC-Ni powder. Three different processing parameters were applied to optimize the production process with the aim to achieve preeminent mechanical properties and fully dense material without microstructural defects. The deposition was carried out by a GLC5 gun. The velocity and temperature of powder particles in the spray stream were monitored by Accuraspray Tecnar diagnostic tool. The quality of deposited coatings was analyzed by means of light microscopy, scanning electron microscopy, and X-ray diffraction. The chemical composition of the used powder and sprayed WC-CrC-Ni coating was determined by energy dispersive spectroscopy. It was found that the spray parameters have a negligible effect on the resulting microstructure and phase composition of the coating. However, the porosity and surface roughness were significantly affected by the variation in process parameters. To assess the basic mechanical properties of HVOF sprayed coating instrumented Vickers hardness measurements were utilized. The coating hardness reached mean values over 1400 HV 0.1 and the indentation modulus varied from 152-279 GPa.
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Structure and mechanical properties of magnesium materials processed by HPT
Poloprudský, Jakub ; Němec, Karel (referee) ; Doležal, Pavel (advisor)
This thesis is focused on processing of pure magnesium by high pressure torsion method (HPT). This process belongs to the group of intensive plastic deformation methods (SPD). SPD methods are in the centre of scientific interest for several decades. Theoretical part of this thesis puts an effort to summarize basic knowledge and principles of SPD methods with extra focus on method HPT. As theoretical part continues magnesium as technical material is presented. Influence of SPD on use and properties of pure magnesium is then presented. This trend is further developed in effort to describe the effect of individual HPT process variables on the properties of pure magnesium and its alloys. Focus of practical part of this thesis is in influence of number of revolutions. Samples were processed at 1/8, 1/4, 1/2, 1, 4 and 8 turns at room temperature. Speed of process was 1rpm and applied pressure was 6 GPa. The structure of commercially pure magnesium prepared by casting and moulding were observed with focus on differences caused by input material. The structure was observed by both light microscopy and back scattered electron diffraction (EBSD), focusing on structure development, grain size and grain orientation. Compared to other works on similar topic, the emphasis here is on observing the microhardness on the vertical edge of the sample. The hardness shows a steep increase right after 1/8 of a turn. With increasing number of turns gradual homogenization of microhardness is presented accompanied by slight decrease in microhardness. No trend in microhardness relative to the distance from anvil has occurred. Structure observed with EBSD shows a bimodal character with larger grains oriented in the same direction. The three-point bending test didn’t end up as expected, and the approach to evaluation of magnesium-based HPT needs to be re-evaluated for future work. A three-point bending test was designed for the initial assessment of the basic mechanical properties of the material.
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Joining alumina ceramics by thin metallic layers
Poloprudský, Jakub ; Krajňáková, Petra (referee) ; Jan, Vít (advisor)
This bachelor thesis is about the problematics of structural bonds between ceramics and metals with special focus on brazed bonds. First theoretical part describes thoroughly the majority of currently used methods for ceramics joining. Special attention is given to the explanation of phenomenon of bad wettability of ceramics by molten metals and how to solve it. In practical part the work focuses on an analysis of representatives of active and non-active brazing alloys with some added elements. For analysis of microstructures it was necessary to master the basics of preparation of ceramic-metal composite specimens. Important part of the practical section of the work is dedicated to an effort of making a test with comparable results that could be used for ceramic-metal brazed composites evaluation.
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