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Influence of minor solutes on thermal properties of MgYNd-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor) ; Kekule, Tomáš (referee)
The development of magnesium alloys has the growing trend and leads mainly to the transport industry and modern medicine. The use of the alloying elements, especially rare- earth elements, is a way to improve the material utility. In the present work, there was studied thermal evolution of the phase transformations in the MgYNd alloys containing additional elements by differential scanning calorimetry. The thermal responses at different heating rates were observed and the activation energies of the processes were calculated. On the basis of confrontation with literature the precipitation and dissolution of stable, metastable phases were assigned to the observed processes. The thermal response corresponding to the precipitation of the stable β phase was observed in all materials. The activation energies of the stable β phase precipitation are practically identical for all materials investigated.
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Studium fázových transformací ve slitinách Ti
Zháňal, Pavel ; Harcuba, Petr (advisor) ; Vlach, Martin (referee)
In this work phase transformations in metastable β Ti-15Mo alloy were studied using electrical resistivity measurements. The alloy was subjected to a solution treatment at a temperature higher than β- transus and quenched in water. In this condition, the microstructure of Ti-15Mo alloy consists of a metastable β - matrix and ω-phase particles. During in-situ electrical resistivity measurement in a specially designed furnace, significant temperature points which indicate phase transformations in the material were detected. The dependence of electrical resistivity on the temperature changes during heating between increasing and decreasing according to the ongoing phase transformation. The changes were observed at temperatures 225, 356 and 560 řC. A further study of these phase transformations using electrical resistivity measurements was performed on various heat treated specimens. In order to control the microstructure evolution in the material, scanning and transmission electron microscopy was used. Mechanical properties were studied using Vickers microhardness testing. The obtained results serve to identify the type and sequence of phase transformations which take place in the Ti-15Mo alloy. Powered by TCPDF (www.tcpdf.org)
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Phase transformations in Mg-Gd alloys
Stíbal, Adam ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
ývoj hořčíkový h slitin má ekonomi koEekologi ké opodst-tněníF yužití tě hto slitin je n- vzestupné tenden i - z-s-huje zejmén- do tr-nsportního pr·mysluD -le svoje upl-tnění n- hází i v medi íněF tedn- z metod zlepšení vl-stností hořčíku je legování jinými prvkyF vláš¡' do rý h výsledk· dos-huje legování prvky vzá ný h zeminF "ento typ slitinD kde legují ím prvkem je g-doliniumD jsou studovány v předklád-né prá i ve tře h tl-kově litý h slitiná h do kon entr- e IS hmF7F ředmětem prá e ylo studium fázový h tr-nsforE m- í při žíhání m-teriálu pomo í metody diferenční skenov- í k-lorimetrie při neizotermi kém žíháníF fyly pozorovány tři pro íh-jí í pro esy - spočteny jeE ji h -ktiv-ční energieF "ěmto pro es·m ylo n- zákl-dě srovnání s liter-turou přiř-zeno kl-strování -tom· qd - pre ipit- e met-st- ilní h fází β - β F I
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Study of twinning anisotropy of AZ31 magnesium alloy
Zdražilová, Zuzana ; Mathis, Kristián (advisor) ; Vlach, Martin (referee)
In the present work the deformation behaviour of magnesium-based alloy AZ31 which was produced by horizontal continual casting is investigated. Samples with two different orientations are deformed in tension and compression at strain rate of 10-3 s-1 in temperature range of 20 řC to 300 řC. Simultaneously, the acoustic emission is recorded and studied with focused on mechanical twinning. The mechanisms of plastic deformation of material and anisotropy between tension and compression are discussed. Dependence of deformation behaviour on temperature is analyzed. The microstructure of original and deformed material is also studied by means of optical microscopy.
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Positron annihilation study of precipitation effects in Mg-Tb alloy
Hruška, Petr ; Čížek, Jakub (advisor) ; Vlach, Martin (referee)
Magnesium alloys are currently widely used in industry as a modern material. Magnesium based alloys with rare earth elements shows very promising mechanical properties. In the present work the precipitation effects and the deve- lopment of microstructure of the Mg13Tb alloy (containing 13 wt.% of terbium) during isochronal annealing were studied by positron annihilation spectroscopy, microhardness measurement and differential scanning calorimetry. According to the results the creation of the precipitates β′′ , β′ and β in the studied alloy was observed and activation energies of these precipitates were determined by the Kissinger method. By microhardness measurement the natural ageing at room temperature of the Mg13Tb alloy was observed and described. 1
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Effect of production method on properties of light structural alloys
Hylský, Josef ; Stulíková, Ivana (advisor) ; Vlach, Martin (referee)
A difference in phase transformations in the Mg-Y-Nd-Sc-Mn alloy prepared by two different methods - squeeze casting and powder metallurgy - was studied by relative resistivity changes and hardness measurements. The measurements took place at 77K and at room temperature in the isochronal annealing procedure of 30 řC / 30 min in temperature range of 90 řC - 510 řC. Results achieved in the squeeze cast alloy are in agreement with results of parallel research of microstructure, which proved the existence of thin hexagonal plates up to 390 řC, which are parallel to matrix basal planes. Prismatic plates of the stable phase Mg5(NdxY1-x) developed during annealing melt into solid solution above 390 řC, while particles of the Mn2Sc phase pass even annealing at 510 řC and only coarsen. Previous heating at high temperatures, when solid solution is enriched by Y and Nd atoms, stress precipitation processes, which correspond to precipitation sequence of the Mg-Y-Nd system with two metastable phases and one Mg5(NdxY1-x) equilibrium phase. Only indistinctive resistivity and hardness changes caused by dissolution of thin basal hexagonal plates and by a development of temperature stable Mn2Sc particles are observed during annealing up to 420 řC of the material prepared by powder metallurgy. A dissolution of the equilibrium...
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The impact of noise and light pollution on voice activity of Blackbird (Turdus merula)
Vlach, Martin ; Zasadil, Petr (advisor) ; Musilová, Zuzana (referee)
Abstract
Cities represent a new environment where organisms are exposed to different environmental conditions than the original natural habitats. This is essentially a noise and light pollution. The growing number of studies show that these factors can have a significant impact on voice activity of birds.Light pollution may alter the timing of vocalization.Urban noise can overlay the acoustic signals of birds, change the melody, volume, and the timing of singing. The main objective of this thesis was to investigate the influence of noise and light pollution to voice activity Blackbird (Turdus merula). In 2015 it was recorded vocalizations to 4 types of sites: a) on the site only with noise pollution (unlit busy road), b) on the site only with light pollution (Parks), c) on location with noise and light pollution (busy roads in cities), d) on the site without the noise and light pollution (forests). Recording was done with the help of voice recorders from early March until the end of May when the weather was good (no strong winds and storms) every week to thoroughly map the seasonal voice activity of the birds. Quiet location and localities with noise pollution have been in the woods near the town of Beroun near the D5 highway. Locations with light and noisy pollution is found in Hradec Kralove and Prague. In each locality they were searched individuals Blackbird and placed recorder into their territory. The recordings were taken 180 minutes before sunset, throughout the night and morning was the end of the recording 180 minutes after sunrise. The results showed the influence of the sites primarily on the morning vocalization when in the localities affected by light and noise vocalized significantly earlier than the quiet and noisy areas. In the evening times was vocalization without significant differences. The greatest intensity of vocalizations Blackbird was light-noisy areas, opposite to others. The evening was the greatest intensity of the sound recorded in quiet locations. Finally, the night vocalization has been demonstrated only in localities light-noisy.
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