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Microstructural stability of materials prepared by aditive manufacturing methods
Hyspecký, Michal ; Pantělejev, Libor (referee) ; Štěpánek, Roman (advisor)
This work deals with the microstructural thermal stability of material 2618 produced by the Selective Laser Melting metho - SLM. Microstructural stability is compared with the stability of material produced by conventional methods. Stability itself is evaluated by changes of microstructure and microhardness. The main finding is that the sample produced by SLM method reached a microhardness of 125 HV 0.3 and after sixteen hours of annealing at 200 °C a decrease of only a few units to 120 HV 0.3 was recorded. Based on the data obtained, it was concluded that the sample produced by SLM method is structurally stable, as it did not occur any significant changes in the microstructure or in the observed mechanical properties. As a result, components produced by SLM method become usable in operation in places with an elevated temperature up to 200 °C (with a given choice of criteria).
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Microstructure, it´s Stability and Fatigue Properties of Ultra-Fine Grained Copper Prepared by ECAP Method
Navrátilová, Lucie ; Konečná, Radomila (referee) ; Obrtlík, Karel (referee) ; Kunz, Ludvík (advisor)
This work deals with fatigue properties and stability of microstructure of ultrafine-grained (UFG) copper prepared by severe plastic deformation by means of equal channel angular pressing (ECAP) method. The effect of different fatigue loading regimes and thermal exposition on microstructural changes was investigated and the fatigue lifetime curves were experimentally determined. The research attention was focussed on localization of cyclic plastic deformation and fatigue crack initiation in UFG structure. Experimental results indicate that after stress-controlled fatigue loading (both symmetrical and asymmetrical) the microstructure remains ultrafine; no grain coarsening was observed. Contrary to this, strain-controlled fatigue loading results in formation of bimodal structure. Grain coarsening was observed also after thermal exposition at 250 °C for 30 minutes. Annealing at lower temperatures does not result in grain coarsening or development of bimodal structure. Fatigue loading results in development of surface relief in form of cyclic slip markings. Their density, distribution and shape differ for particular fatigue loading regimes. Differences in crack initiation mechanism in low- and high-cycle fatigue region were found. Nevertheless, the characteristic feature for all loading regimes was stability of UFG microstructure in the region of cyclic slip bands and fatigue cracks.
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Microstructural Stability of Weld Joints of Austenitic and Ferritic Steels
Šohaj, Pavel ; Stránský, Karel (referee) ; Sopoušek, Jiří (referee) ; Foret, Rudolf (advisor)
This doctoral thesis summarizes the theoretical and experimental knowledge in the field of dissimilar weld joint of progressive austenitic and ferritic creep-resistant steels. The following materials were selected for the presented study: 316Ti stabilized austenitic stainless steel, martensitic 9-12 %Cr steel P92 and ferritic ODS steel MA 956. The main attention was focused on the long-term microstructural stability during high temperature exposure of heterogeneous joints of the austenite / ferrite type. The literature analysis critically evaluates the current state of knowledge in the field of microstructural stability of advanced creep-resistant steels weld joints. The practical experimental part was carried out in two directions. On the basis of the chemical composition phase equilibrium calculations were performed for each steel using the ThermoCalc software, giving the basic concepts about the dependence of the phase composition and the chemical composition of phases on temperature. In parallel with these calculations the laboratory joints 316Ti/P92 made by resistance welding and the MA 956/316Ti electron beam weld joints were prepared, analyzed in as-weld state and further annealed at different temperature conditions. Exposed joints were subjected to microstructure and phase analysis. The stability of the weld interface was mainly observed. Attention was also focused on the agreement between the calculation and experimental data in comparison with data published in the literature. Based on the calculations, experimental results and published data the suitability of the combination of materials is discussed in the thesis and reasoning about the behavior of studied weld joints during long-term high temperature exposure was formulated. Based on the results the expected degree of microstructural stability of 316Ti/P92 joint was confirmed, while the joints MA 956/316Ti were found to be unstable.
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Microstructure stability of tungsten -ODS hetergeneous welds
Adam, Ondřej ; Sonnek, Pavel (referee) ; Jan, Vít (advisor)
The thesis is focused on microstructural stability of heterogeneous weld joint of ODS steel and tungsten. The theoretical part summarizes the basic information about the structure and properties of ODS steels and describes the methods of joining these steels with tungsten. In the experimental part, materials MA956 and WL10 were welded by using electron beam. The individual samples differ by preheating temperature or use filler material. After annealing at 800 °C/1h and 1000 °C/5h, a change of the weld metal microstructure was evaluated by using scanning electron microscope. The chemical composition was measured by energy dispersive spectroscopy. It has been found that during annealing, massive precipitation of particles occures in the whole volume of the weld metal. These particles were identified as Laves phase.
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Microstructural stability of materials prepared by aditive manufacturing methods
Hyspecký, Michal ; Pantělejev, Libor (referee) ; Štěpánek, Roman (advisor)
This work deals with the microstructural thermal stability of material 2618 produced by the Selective Laser Melting metho - SLM. Microstructural stability is compared with the stability of material produced by conventional methods. Stability itself is evaluated by changes of microstructure and microhardness. The main finding is that the sample produced by SLM method reached a microhardness of 125 HV 0.3 and after sixteen hours of annealing at 200 °C a decrease of only a few units to 120 HV 0.3 was recorded. Based on the data obtained, it was concluded that the sample produced by SLM method is structurally stable, as it did not occur any significant changes in the microstructure or in the observed mechanical properties. As a result, components produced by SLM method become usable in operation in places with an elevated temperature up to 200 °C (with a given choice of criteria).
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Microstructure stability of tungsten -ODS hetergeneous welds
Adam, Ondřej ; Sonnek, Pavel (referee) ; Jan, Vít (advisor)
The thesis is focused on microstructural stability of heterogeneous weld joint of ODS steel and tungsten. The theoretical part summarizes the basic information about the structure and properties of ODS steels and describes the methods of joining these steels with tungsten. In the experimental part, materials MA956 and WL10 were welded by using electron beam. The individual samples differ by preheating temperature or use filler material. After annealing at 800 °C/1h and 1000 °C/5h, a change of the weld metal microstructure was evaluated by using scanning electron microscope. The chemical composition was measured by energy dispersive spectroscopy. It has been found that during annealing, massive precipitation of particles occures in the whole volume of the weld metal. These particles were identified as Laves phase.
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Microstructural Stability of Weld Joints of Austenitic and Ferritic Steels
Šohaj, Pavel ; Stránský, Karel (referee) ; Sopoušek, Jiří (referee) ; Foret, Rudolf (advisor)
This doctoral thesis summarizes the theoretical and experimental knowledge in the field of dissimilar weld joint of progressive austenitic and ferritic creep-resistant steels. The following materials were selected for the presented study: 316Ti stabilized austenitic stainless steel, martensitic 9-12 %Cr steel P92 and ferritic ODS steel MA 956. The main attention was focused on the long-term microstructural stability during high temperature exposure of heterogeneous joints of the austenite / ferrite type. The literature analysis critically evaluates the current state of knowledge in the field of microstructural stability of advanced creep-resistant steels weld joints. The practical experimental part was carried out in two directions. On the basis of the chemical composition phase equilibrium calculations were performed for each steel using the ThermoCalc software, giving the basic concepts about the dependence of the phase composition and the chemical composition of phases on temperature. In parallel with these calculations the laboratory joints 316Ti/P92 made by resistance welding and the MA 956/316Ti electron beam weld joints were prepared, analyzed in as-weld state and further annealed at different temperature conditions. Exposed joints were subjected to microstructure and phase analysis. The stability of the weld interface was mainly observed. Attention was also focused on the agreement between the calculation and experimental data in comparison with data published in the literature. Based on the calculations, experimental results and published data the suitability of the combination of materials is discussed in the thesis and reasoning about the behavior of studied weld joints during long-term high temperature exposure was formulated. Based on the results the expected degree of microstructural stability of 316Ti/P92 joint was confirmed, while the joints MA 956/316Ti were found to be unstable.
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Microstructure, it´s Stability and Fatigue Properties of Ultra-Fine Grained Copper Prepared by ECAP Method
Navrátilová, Lucie ; Konečná, Radomila (referee) ; Obrtlík, Karel (referee) ; Kunz, Ludvík (advisor)
This work deals with fatigue properties and stability of microstructure of ultrafine-grained (UFG) copper prepared by severe plastic deformation by means of equal channel angular pressing (ECAP) method. The effect of different fatigue loading regimes and thermal exposition on microstructural changes was investigated and the fatigue lifetime curves were experimentally determined. The research attention was focussed on localization of cyclic plastic deformation and fatigue crack initiation in UFG structure. Experimental results indicate that after stress-controlled fatigue loading (both symmetrical and asymmetrical) the microstructure remains ultrafine; no grain coarsening was observed. Contrary to this, strain-controlled fatigue loading results in formation of bimodal structure. Grain coarsening was observed also after thermal exposition at 250 °C for 30 minutes. Annealing at lower temperatures does not result in grain coarsening or development of bimodal structure. Fatigue loading results in development of surface relief in form of cyclic slip markings. Their density, distribution and shape differ for particular fatigue loading regimes. Differences in crack initiation mechanism in low- and high-cycle fatigue region were found. Nevertheless, the characteristic feature for all loading regimes was stability of UFG microstructure in the region of cyclic slip bands and fatigue cracks.
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