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Interaction between TiAl melt and coated oxide refractories
Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The present study focuses on reactions between ceramic crucibles and molten TiAl intermetallics. Coating strategies are investigated that exhibit a potential in slowing down the decomposition of the crucible wall. Uncoated crucibles (system TiAl melt - Al2O3 crucible) and crucibles with the coat (system TiAl melt - CaO coat - Al2O3 crucible) were used in melting and casting experiments. The reference state of the coated crucible before the melting trial was also investigated. Results of the SEM, EDAX and X-ray diffraction analysis contributed to the identification of the reaction zone and its chemical composition. The melt contamination with oxide inclusions results from the erosion process in which individual components of the melt diffuse along grain boundaries of the refractory and activate chemical reactions that decompose the crucible wall. Assessment of thermodynamic parameters associated with the chemical reactions helped in identifying the nature of the erosion process.
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Stress-free and stress-assisted aging of NiTi shape memory alloys
Dlouhý, Antonín ; Bojda, Ondřej ; Fiala, J.
The present work investigates coherent Ni4Ti3 precipitates in a Ti-50,7at%Ni shape memory alloy after different thermo-mechanical treatments. The study is based on the quantitative TEM (transmission electron microscopy) image analysis using the ACC (Adaptive Contrast Control) programme. The attention is given to a number, size and volume fraction of individual crystallographic variants of the Ni4Ti3 precipitates. Preliminary results suggest that, after common heat treatments, the precipitation of Ni4Ti3 particles is inhomogeneous not only as far as the density of particles in the original B2 grains is concerned but also with respect to the distribution of the crystallographic particle variants. The possible influence of the heterogeneous Ni4Ti3 precipitation on the characteristics of the martensitic transformations B2-R-B19’ is discussed.
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Vliv tepelného namáhání na mechanické vlastnosti FeNiB amorfní slitiny
Zábranský, Karel ; Jirásková, Yvonna
An influence of thermal treatment in the temperature range of 150 - 350 °C on the structural and mechanical properties of an amorphous FeNiB alloy is investigated. The high tensile strength of 2200 MPa in the as-prepared amorphous state slightly decreases with increasing temperature of annealing up to approximately 200 °C in opposite to microhardness where an increase is observed. Above 200 °C a pronounced deterioration of both characteristics reflect the embrittlement of amorphous structure without any indications of crystallization.
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Initial stages of fatigue failure of polycrystalline materials
Man, Jiří ; Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav
Geometry of persistent slip markings (PSMs) formed during cyclic loading of polycrystalline stainless steels and superalloy was studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM-FEG). Internal dislocation structure was investigated using transmission electron microscopy (TEM). Persistent slip bands with dislocation structure corresponding to the cyclic strain localization were identified and correlated with PSMs observed on the specimen surface.
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Viscometric study of L-Lysine- and 6-aminocaproic acid-hyaluronan systems behavior within the range of low aminoacids concentrations
Šimáčková, Marcela ; Běťák, Jiří (referee) ; Chytil, Martin (advisor)
This bachelor thesis investigates the interaction between high-molecular weight hyaluronic acid (1.75 MDa HA) and amino acids, particularly lysine and 6-aminocaproic acid. The interactions should occur between the carboxyl groups of HA carrying a negative charge and a positive charge located on the nitrogen atom of the protonated amino acids. The presence of these interactions would mean the possibility of establishing bioactive compounds, e.g. drugs, on hyaluronic acid, in which it would act as a targetting carrier. The interactions were examined at low concentrations for both aminoacids, i.e. below 10 mmoldm-3, and for 6-aminocaproic acid also at high aminoacid concentrations, i.e. above 20 mmoldm-3. The presence of interaction was investigated using not only rheology, but also by measuring pH and conductivity. Based on this research, the interactions manifested in terms of a decrease in the system viscosity.
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The structural and the fundamental mechanical properties of intermatallics on the base of TiAl
Krahula, Karel ; Dlouhý, Ivo
Gamma TiAl alloys are emerging as a pervasive structural material. Remarkable progresses have been made through refining lamellar microstructure and grains, microalloying, chemistry modification, process development and/or their combination. The main thrust was to enhance resistance to creep deformation, oxidation and high cycle fatigue deformation/failure. Less or even no knowledge have been obtained in the field of the intermetalics fracture at uniaxial or bending loading, there are missing data about their behaviour at the presence of cracks and other defects. The reason is simply in the other properties that are key from application point of view. Due to their brittleness at temperature close to room temperature the investigation of the intermetalics fracture is complicated but promissible provided it bring ideas for the further development of the alloying and microstructure. The paper is focused on the first steps in this field.
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Ellipsometry of Thin Films
Novotný, Zbyněk ; Navrátil, Karel (referee) ; Nebojsa, Alois (advisor)
Diploma thesis deals with ageing process of thin films of Co and Cu on Si substrate, prepared by the IBAD method. The process of film ageing, which depends on time of exposition to the atmosphere at room conditions, was investigated with spectroscopic ellipsometry (VIS+UV) and atomic force microscopy. In case of thin Co films, approximately four days long incubation period was observed. During this time period, a change in the optical parameters of the film occurs without a measurable change of the film topography. Using non-contact atomic force microscopy, a growth of the transitional film in the island growth regime was observed. During the ageing of thin Cu films, two stages of growth of the transitional layer were observed - nucleation stage and growth stage. Both of these time periods of the transitional layer growth show direct logarithmic dependence. Using non-contact atomic force microscopy, the growth of the transitional film was observed. Using atomic force microscopy in non-contact regime, time dependent measurement was done and the process of forming of one monolayer of the transitional layer was documented. Within the diploma thesis, a series of experiments on ultra high vacuum system were performed in order to investigate phase transformation of thin Fe films (22 monolayers) on Cu(100) stabilized by CO absorption. The transformation from fcc phase to bcc phase was induced by Ar+ ion beam bombardment with the ion energy in the range (0.5-4) keV. The process of phase transformation was observed by surface magneto-optic Kerr effect, Auger electron spectroscopy and low energy electron diffraction.
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