|
|
Mechanical properties of magnesium alloy AZ91E prepared by ECAP method
Darida, Jiří ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
This thesis deals with mechanical and fatigue properties of magnesium alloy AZ91 processed by EX-ECAP method. This method involves the application of extrusion followed by equal-channel angular pressing. To obtain basic mechanical characteristics, the tensile test were carried out at room and elevated temperatures. Further the fatigue tests were performed and obtained data were used to compile S-N curve. The work also includes metallographics analysis of microstructure and fractographic analysis of fracture surfaces of tensile and fatigue test specimens.
|
|
|
Structure and properties of magnesium alloys Mg-Ca-Zn
Hlavnička, Jiří ; Pacal, Bohumil (referee) ; Doležal, Pavel (advisor)
This master’s thesis deals with design and preparation of a new biodegradable magnesium alloy based on Mg-Ca-Zn. Based on information from literature, the Mg-3Zn-2Ca alloy was designed. The base material was produced by gravity casting and the evaluation in the as-cast and heat treated state was performed. For preparation of the experimental material, following methods were designed: squeeze casting, hot rolling and the ECAP. During preparation by hot rolling, no optimal conditions were found and significant cracks occurred in both as-cast and heat treated material. In the case of experimental material, prepared by the ECAP method with back-pressure, better combination of stress-strain properties was observed. Also the squeeze casting method showed improvement; especially the amount of casting defects was eliminated. The evaluation of microstructure and mechanical properties was performed by the light and scanning electron microscopy, RTG phase analysis and the tensile and compression tests.
|
|
|
Fatigue Properties of Ultra-fine Grain Copper Produced by ECAP Method
Navrátilová, Lucie ; Němec, Karel (referee) ; Pantělejev, Libor (advisor)
This diploma thesis describes properties of ultra-fine grain Cu prepared via ECAP procedure. The influence of fatigue loading with positive mean stress on S-N curve (i.e. fatigue life), cyclic plastic behaviour and grain size was investigated. It was found that tensile mean stress leads to shorter lifetime in comparison with fatigue loading with zero mean stress. During main part of the lifetime, significant hardening of UFG Cu was observed. There is no distinct effect on microstructural orientation and stability.
|
|
| |
|
|
Screw press 50t
Švábenský, Pavel ; Pavlík, Jan (referee) ; Omes, Jiří (advisor)
Diploma thesis is focused on desing of the screw press, which is used for laboratory testing of materials by ECAP. Thesis included design of individual scructural groups and their destcription, including the creating of 3D model.
|
|
|
Structure and mechanical properties biodegradable Mg-3Zn-2Ca alloy processed by ECAP
Havlíček, Štěpán-Adam ; Podrábský, Tomáš (referee) ; Doležal, Pavel (advisor)
Zaměření této bakalářské práce je na mechanické vlastnosti a mikrostrukturu biodegradabilní hořčíkové slitiny Mg-3Zn-2Ca zpracované pomocí uhlového protlačování skrze shodné kanály (ECAP). Každý vzorek se liší počtem protlaku ve směru Bc. Zpracovaná hořčíková slitina ukazuje zlepšení napěťových a deformačních charakteristik, avšak s rostoucím počtem protlaků začínají klesat deformační charakteristiky. Aplikace ECAP metody způsobila v mikrostruktuře zjemnění zrn a ve směru protlačování prodloužení zrn. Ke studiu mikrostruktury bylo využito světelné mikroskopie a studium tahových vlastností bylo provedeno tahovými zkouškami.
|
|
|
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.
|
|
| |
|
|
Application of Electron Backscatter Diffraction in Materials Engineering
Man, Ondřej ; Vodárek, Vlastimil (referee) ; Svoboda, Milan (referee) ; Švejcar, Jiří (advisor)
The thesis deals with principles and common applications of the electron backscatter diffraction (EBSD) method. Some practical experience in application of the method to a study of highly deformed structure of copper and its thermal stability is described on one hand, and, on the other hand, to a study of phase composition of TRIP steel on various levels of imposed strain. The limitations of EBSD method are discussed along with its resolution in comparison with other complimentary techniques.
|
|
|
Complex investigation of fine-grained polycrystals of Cu and CuZr alloy processed by equal channel angular pressing a high pressure torsion
Srba, Ondřej ; Janeček, Miloš (advisor) ; Hadzima, Branislav (referee) ; Karlík, Miroslav (referee)
Title: Complex investigation of fine-grained polycrystals of Cu and CuZr alloy processed by equal channel angular pressing and high pressure torsion Author: RNDr.Ondřej Srba Department: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University Prague Supervisor: Doc. RNDr. Miloš Janeček, CSc. Abstract: In the thesis the microstructure development, mechanical, elastic and corrosion properties of deformed specimens of pure Cu and binary alloy CuZr processed by equal channel angular pressing (ECAP) are investigated. Several properties of pure Cu processed by ECAP are compared with properties of the same material processed by high pressure torsion (HPT). The microstructure development is characterized in detail by several experimental techniques (light and electron microscopy, electron back scatter diffraction, positron annihilation spectroscopy, etc.). The microstructure development in specimens processed by ECAP is characterized by the continuous fragmentation of the initial coarse grain structure and the formation of new grains having the sizes in the submicrocrystalline range (of 460 nm and 260 nm in Cu and CuZr alloy, respectively). During the deformation by ECAP the fraction of high-angle grain boundaries, the dislocation density and the concentration of vacancies are...
|
guest ::
