The quasicrystals are characterized by unusual rotational symmetries that are not observed in the crystalline materials, which is the cause of their interesting material properties. Because of that a particular attention was paid to quasicrystalline structures in the literature research. The research also contains a description of electron beam technology, spark plasma sintering method and introduction to the problematics of wear. As the default materials for the experimental part were selected Titanium Grade 2 powder and Cristome A5 powder which was partially composed of quasicrystalline phase. The first series of samples was sintered only from powder Cristome A5. The second series was sintered from the mixture of 80 % Titanium Grade 2 powder and 20 % Cristome A5 powder. For the compaction of samples spark plasma sintering technology was selected. Samples were then systematically modified by electron beam and subjected to pin on disc tests. Samples modified at 750 °C had the best wear resistance. Samples modified at 1150 °C contained increased amount of quasicrystalline phase.

Název práce: Studium defekt· v kvazikrystalech Autor: Marián Vlček Katedra: Katedra fyziky nízkých teplot Vedoucí disertační práce: doc. Mgr. Jakub ížek, Ph.D., Katedra fyziky nízkých teplot Abstrakt: V predloženej práci boli pomocou spektroskopie doby života poz- itrónov a koincidenčnej spektroskopie Dopplerovského rozšírenia anihilačného píku študované zliatiny WE43 s prídavkom zinku a ternárne zliatiny Mg-Zn-Y. V týchto zliatinách bola nedávno zistená prítomnos' ikosahedrálnej fázy Mg3Zn6Y1 s kvázikryštalickou štruktúrou, čo pritiahlo pozornos' výskumníkov. Spektroskopia doby života pozitrónov preukázala prítomnos' unikátnych vakanciám podobných defektov na rozhraní ikosahedrálnej fázy a horčíkovej matrice, ktoré sú charakter- istické pre horčíkové zliatiny obsahujúce ikosahedrálnu fázu. Tepelné spracovanie skúmaných zliatin vedie k významným zmenám morfológie hraničných fáz. Ke¤že vakanciám podobné defekty spojené s ikosahedrálnou fázou sa vyskytujú na jej rozhraní s horčíkovou matricou, zmeny v morfológii ikosahedrálnej fázy vedú k výrazným zmenám koncentrácie týchto defektov. "alej boli skúmané vzorky pripravené uhlovým pretláčaním kanálom rovnakého prierezu. Typy defektov prítomné v týchto zliatinách a ich teplotná stabilita bola určená pomocou spektroskopie doby života pozitrónov a merania tvrdosti...

The aim of this diploma thesis is to investigate microstructure and thermal stability of ultra fine grained magnesium alloys. The thesis first summarises methods using plastic deformation in order to achieve ultra fine grained structure that are used to process metals. Then experimental methods employed in the experimental part including microhardness testing, scanning electron microscopy and positron annihilation spectroscopy are described. Brief summary of previous research on MgZnY alloys strengthened by quasicrystalline phases and Mg22Gd alloys is given. Finally, results of experimental investigation of MgZnY alloys with various Zn/Y ratios and Mg22Gd alloy are discussed. These results suggest that presence of phases in MgZnY alloys depend on Zn/Y ratio, hardness of these alloys depends on Zn content and that rapid cooling of MgZnY alloys annealed at 500 řC lead to significant increase in volume fraction of quasicrystalline icosahedral phase. In the second section of the experimental part thermal behaviour of Mg22Gd alloy is investigated. Furthermore, formation of GdH2 particles in Mg22Gd is examined and attributed to reaction of hydrogen decomposed from water vapour with gadolinium in areas rich in gadolinium. Finally, significant hardening of Mg22Gd alloy processed by high pressure torsion has been...