|
|
The Structure and Properties of Austenitic Steel Prepared by the Cold Spray Method and Selected Laser Melting Technology
Osička, Filip ; Šmíd, Miroslav (referee) ; Hutařová, Simona (advisor)
This bachelor's thesis focuses on the comparison of two different technologies, specifically Cold Spray (CS) and Selective Laser Melting (SLM), and their effects on the properties of austenitic unstabilized stainless steel AISI 304L. The difference between these technologies is determined by the difference in their physical principles and thus their different practical applications. The theoretical part of the thesis describes in detail the principles of CS and SLM technologies applied to stainless steel. The experimental part describes the procedures for evaluating samples that were created using CS and SLM technologies, with each sample being produced under different process parameters. The analysis included not only the samples prepared by these methods but also the input material in its original state. The microstructure of the produced materials was extensively examined under a light and scanning electron microscope. Furthermore, porosity, microhardness, and flexural strength were determined. The results of the individual measurements are compared and subsequently discussed in the context of the available scientific literature.
|
|
|
Application of digital image correlation technique in studies of plastic deformation evolution in metallic materials
Pavelčík, Dalibor ; Hutařová, Simona (referee) ; Šmíd, Miroslav (advisor)
This thesis studies evolving plastic deformation of metallic materials under uniaxial tensile load. The risk of disabling or accidents due to deformation is serious because of considerable loading of engineering components during their operational period. Therefore, many non-destructive methods have been developed to investigate the material response to loading. A good example is digital image correlation (DIC), which can be used to observe plastic deformation during loading at an optional level - from examining the behavior of the entire component (light optics) to detailed observations at the submicron level (electron microscopy). Within this work, an interupted tensile test experiment of an austenitic stainless steel sample X2CrNi18-9 with simultaneous observation of the development of plastic deformation by the DIC method using a scanning electron microscope during individual test interruptions was proposed and performed. At the same time, crystallography of the deformed sample using EBSD was investigated during the deformation. The obtained crystallographic data enabled the identification of active slip systems of selected observed grains, which made it possible to obtain a comprehensive overview of the development of the localization of plastic deformation in the observed area.The obtained results showed that the distribution of plastic deformation in the structure of the studied steel is very heterogeneous, where locally it can significantly exceed the achieved macroscopic deformation of the tested sample. The proposed methodology has proven to be an effective tool for describing the relationship between microstructure and mechanical properties.
|
|
|
Optimizing the Properties of the Coatings prepared by the Cold Spray Method using Heat Treatment
Bartošík, Vojtěch ; Šmíd, Miroslav (referee) ; Hutařová, Simona (advisor)
This bachelor's thesis deals with the choice of heat treatment parameters of the metal coating of austenitic unstabilized stainless steel AISI 304L applied by the Cold spray method. With the help of suitable heat treatment, it is possible to adjust the mechanical properties, reduce the porosity and, last but not least, also remove high residual stresses in the material. The theoretical part of the work is devoted to literature research on the topic of Cold spray technology, corrosion and corrosion-resistant steels. The experimental part describes the procedures for measuring samples that have undergone heat treatment. This took place in the temperature range of 500 to 1100 °C, always with an hour's holding time at the temperature, followed by cooling in air. In addition to these samples, the material was also examined in its initial state. Porosity, microhardness and also magnetism were determined. To analyze the structure, photographs were taken on a light and electron scanning microscope. Based on the results, heat treatment with an hourly hold at 700 °C seems to be a good choice, where a significant decrease in porosity, partial recovery of the structure while maintaining high microhardness and also grain fineness was observed.
|
|
|
Fatigue-creep interaction in Ni superalloys and TiAl alloys
Šmíd, Miroslav ; Věchet, Stanislav (referee) ; Kunz, Ludvík (referee) ; Obrtlík, Karel (advisor)
The present doctoral thesis is focused on the effect of dwells on the low cycle fatigue behaviour of advanced high temperature materials. 10 minutes strain holds are introduced into the cyclic straining of cast Ni-based superalloy IN792-5A and cast intermetallic alloy TiAl-7Nb which were chosen as experimental material. Fatigue experiments were conducted in strain control mode with constant total strain amplitude and strain rate. IN792-5A was subjected to continuous cyclic loading test as well as fatigue tests either with tensile peak strain holds or compressive peak strain holds at temperature 800 °C. TiAl-7Nb was experimentally examined by continuous cyclic loading tests and also by fatigue test with tensile peak strain hold times at temperature 750 °C. Cyclic hardening/softening curves, cyclic stress-strain curves, Manson-Coffin curves and Basquin curves were obtained. Stress relaxation data were measured during hold times. Mean stress evolution was observed and documented. Microstructure of both alloys was observed in as-received state and also after cyclic loading by means of SEM and TEM. Surface relief investigation revealed cyclic plastic strain localisation as well as fatigue crack initiation sites. Fatigue crack propagation was described using fracture surface and longitudinal gauge section observations. Dislocation structures developed in the course of fatigue tests were studied and documented.
|
|
|
Determination of Shortcut Cyclic Stress-strain Curves of Superalloy Inconel 738LC at Elevated Temperatures
Šmíd, Miroslav ; Obrtlík, Karel (referee) ; Petrenec, Martin (advisor)
Multiple step tests under cyclic strain control have been performed using cylindrical specimens of cast polycrystalline Inconel 738LC superalloy at 23, 700, 500, 800 and 900 °C in laboratory atmosphere to obtain cyclic stress-strain curves. During cyclic straining of specimen were obtained cyclic hardening-softening curves. Their progress changed with temperature and strain amplitude. Evaluated cyclic stress-strain curves are shifted to lower stresses with increasing temperature. Surface relief was observed in fatigued specimens under SEM and metalography under optic microscopy. Slip markings were studied on specimen surface fatigued at 700 °C .Stress-strain response is compared and discussed in relation to the surface observations - persistent slip markings.
|
|
|
Optimizing the Properties of the Coatings prepared by the Cold Spray Method using Heat Treatment
Bartošík, Vojtěch ; Šmíd, Miroslav (referee) ; Hutařová, Simona (advisor)
This bachelor's thesis deals with the choice of heat treatment parameters of the metal coating of austenitic unstabilized stainless steel AISI 304L applied by the Cold spray method. With the help of suitable heat treatment, it is possible to adjust the mechanical properties, reduce the porosity and, last but not least, also remove high residual stresses in the material. The theoretical part of the work is devoted to literature research on the topic of Cold spray technology, corrosion and corrosion-resistant steels. The experimental part describes the procedures for measuring samples that have undergone heat treatment. This took place in the temperature range of 500 to 1100 °C, always with an hour's holding time at the temperature, followed by cooling in air. In addition to these samples, the material was also examined in its initial state. Porosity, microhardness and also magnetism were determined. To analyze the structure, photographs were taken on a light and electron scanning microscope. Based on the results, heat treatment with an hourly hold at 700 °C seems to be a good choice, where a significant decrease in porosity, partial recovery of the structure while maintaining high microhardness and also grain fineness was observed.
|
|
|
Interaction of Creep and High Cycle Fatigue of IN 713LC Superalloy
Horník, V. ; Šmíd, Miroslav ; Hutař, Pavel ; Kunz, Ludvík ; Hrbáček, K.
The study deals with the interaction of creep and high cycle fatigue of cast polycrystalline nickel-based superalloy IN 713LC at high temperatures. Previous works indicated that creep lifetime of superalloy structures was un-affected or even slightly increased in the cases with superimposed vibrations. The reason for this behaviour was not well described up to now. Therefore, set of fatigue tests was conducted at high mean stresses level to observe this phenomenon. The mean stress was kept constant while the stress amplitudes were selected in order to measure wide range of conditions from pure creep to pure fatigue. Fractographic analysis by scanning electron microscopy (SEM) was done with the aim to identify governing damage mechanisms for particular test conditions as a preliminary evaluation of conducted tests.
|
|
|
Fatigue-creep interaction in Ni superalloys and TiAl alloys
Šmíd, Miroslav ; Věchet, Stanislav (referee) ; Kunz, Ludvík (referee) ; Obrtlík, Karel (advisor)
The present doctoral thesis is focused on the effect of dwells on the low cycle fatigue behaviour of advanced high temperature materials. 10 minutes strain holds are introduced into the cyclic straining of cast Ni-based superalloy IN792-5A and cast intermetallic alloy TiAl-7Nb which were chosen as experimental material. Fatigue experiments were conducted in strain control mode with constant total strain amplitude and strain rate. IN792-5A was subjected to continuous cyclic loading test as well as fatigue tests either with tensile peak strain holds or compressive peak strain holds at temperature 800 °C. TiAl-7Nb was experimentally examined by continuous cyclic loading tests and also by fatigue test with tensile peak strain hold times at temperature 750 °C. Cyclic hardening/softening curves, cyclic stress-strain curves, Manson-Coffin curves and Basquin curves were obtained. Stress relaxation data were measured during hold times. Mean stress evolution was observed and documented. Microstructure of both alloys was observed in as-received state and also after cyclic loading by means of SEM and TEM. Surface relief investigation revealed cyclic plastic strain localisation as well as fatigue crack initiation sites. Fatigue crack propagation was described using fracture surface and longitudinal gauge section observations. Dislocation structures developed in the course of fatigue tests were studied and documented.
|
|
|
Determination of Shortcut Cyclic Stress-strain Curves of Superalloy Inconel 738LC at Elevated Temperatures
Šmíd, Miroslav ; Obrtlík, Karel (referee) ; Petrenec, Martin (advisor)
Multiple step tests under cyclic strain control have been performed using cylindrical specimens of cast polycrystalline Inconel 738LC superalloy at 23, 700, 500, 800 and 900 °C in laboratory atmosphere to obtain cyclic stress-strain curves. During cyclic straining of specimen were obtained cyclic hardening-softening curves. Their progress changed with temperature and strain amplitude. Evaluated cyclic stress-strain curves are shifted to lower stresses with increasing temperature. Surface relief was observed in fatigued specimens under SEM and metalography under optic microscopy. Slip markings were studied on specimen surface fatigued at 700 °C .Stress-strain response is compared and discussed in relation to the surface observations - persistent slip markings.
|
|
|
Fatigue life and fracture of cast gamma TiAl intermetallic alloy at room and elevated temperatures
Petrenec, Martin ; Šmíd, Miroslav ; Polák, Jaroslav
The low-cycle fatigue properties, surface relief and fracture surfaces of cast TiAl alloys with 2 at.% Nb having nearly lamellar microstructure were studied at room temperature and at 750 degrees C. Cyclic stress-strain curves (CSSC) and fatigue life curves were obtained at both temperatures. The surface relief and the fracture surfaces of fractured specimens were observed using scanning electron microscopy. At room temperature, significant cyclic hardening is observed whereas at 750 degrees C cyclic response was stable. Parameters of the CSSC, the Manson-Coffin law and the Basquin law were determined. Persistent slip markings formed along interlamellar interfaces were predominant locations for fatigue cracks at both temperatures. The cracks initiated at surface or in sub-surface region led to the formation of smooth flat areas on the fracture surface corresponding to the persistent slip bands.
|
guest ::
RSS feed.