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Computer modeling of high-entropy alloys
Papež, Pavel ; Jan, Vít (referee) ; Zelený, Martin (advisor)
This Master’s thesis is focused on theoretical study of the high entropy alloy CoCrNi using ab initio calculations. The focus was on the effect of short range order on the relative stability of FCC and HCP structures and the value of stacking fault energy.The results show increase of stability in both types of structures wtih decreasing number of Cr-Cr nearest neighbours. The effect of the number of Cr-Cr nearest neighbours on the stacking fault energy previously shown in literature was not observed. However the strong dependency was found on the change of short range order caused by the shift of (1 1 1) planes after the transformation from the FCC to HCP structure. The effect of interstitial atoms C a N was also studied. Both these interstitials stabilise FCC structure and thus cause the increase of stacking fault energy. Both interstitials prefer octahedral positions with higher amount of Cr in their nearest neighbour shell.
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Strucure and mechnical properties of cold sprayed Ti-6Al-4V layer
Sabela, Jakub ; Zelený, Martin (referee) ; Řehořek, Lukáš (advisor)
Diploma thesis deals in the first part with recent knowledge of cold spray, its mechanism and parameters of deposition, advanced coatings made by cold spray and their applications, knowledge of Ti-6Al-4V coatings and their heat treatment. Deposit of Ti- 6Al-4V powder was made by cold spray process. In experimental part, microstructure and mechanical properties of supplied and its heat treated material were observed and examined. Mechanical properties and microstructure remained unchanged by annealing at 600 °C as in the case of supplied material. Recrystallization occured in microstructure of and phases by annealing at 800 °C. Grains were emerged in microstructure and mechanical properties were decreased. Mechanical properties were improved by annealing at 900 °C due to quenching. Microstructure consists of and ’ phases. Mechanical properties were the worst for annealed material at 1000 °C because of coarsed grains. Material which was annealed at 800 °C, quenched and precipitation hardened had the best microstructure and mechanical properties.
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Study of inter-atomic interactions in advanced materials with help of ab initio calculations
Janovec, Jozef ; Šob, Mojmír (referee) ; Zelený, Martin (advisor)
Pomocou COHP analýzy sme študovali chemickú väzbu v diboridoch prechodných kovov ako aj v zliatine Ni2MnGa. Elektrónová štruktúra študovaných materiálov bola vypočítaná použitím výpočtov z prvých princípov pomocou metódy PAW. V prípade diboridov tranzitných kovov z výsledkov vyplýva, že sila väzby bór-bór je silne závislá od transferu elektrónov na atómy bóru. Zvyšujúci sa počet valenčných elektrónov v kove spôsobuje destabilizáciu alfa štruktúry kvôli vzájomnej interakcii elektrónov prislúchajúcich jednému atómu (on-site interakcie) v blízkosti Fermiho hladiny. Pre zliatinu s tvarovou pamäťou Ni2MnGa bola použitá metóda DFT+ U upravujúca popis lokalizácie elektrónov. V prípade použitia parametra U na Ni dochádza k destabilizácii kubického austenitu a k stabilizácii tetragonálneho nemodulovaného martenzitu. Naopak, zvýšenie lokalizácie elektrónov mangánu martenzit destabilizuje. Analýza väzieb ukázala, že najsilnejšou väzbou je Ni-Ga s kovalentným charakterom. Zvýšená lokalizácia valenčných elektrónov Mn zvyšuje podiel kovalentnosti Mn-Ni väzby a kovový charakter Ni-Ni väzby. Vplyvom zvýšenej lokalizácie Ni elektrónov sa Mn-Ni väzba stáva viac kovovou.
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WiFi and BT monitoring tool
Zelený, Miroslav ; Zamazal, Michal (referee) ; Valach, Soběslav (advisor)
This bachelor thesis deals with possibilities and ways of detection of devices using Bluetooth or Wi-Fi technology, with the possibility of future use for monitoring of human movement. Detection is only in the 2.4 GHz band. It introduces Wi-Fi and Bluetooth technology and their detection. Device detection was performed using Kismet software and Raspberry Pi platform.
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Operation of a distribution system with resistance welders
Zelený, Miroslav ; Šlezingr, Jan (referee) ; Drápela, Jiří (advisor)
This Diploma thesis deals with assessment of the influence of two fundamental types of resistance welders operation on chosen power quality parameters at the point of common coupling (PCC) of the power network. The assessed parameters of power quality are the total harmonic distortion of the supply voltage, asymmetry of the supply voltage and the level of short term flicker at the point of common coupling. The assessment is based on the comparison of the results of computer simulations done in PSCad 4.2.0 with the requirements of technical standards. The outcome of this thesis is the determination of allowable limits for physical and operation parameters for the general arrangement of a power distribution network and a resistance welder that should guarantee the power quality compliance.
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Observation of twin boundaries in Ni-Mn-Ga alloys
Čech, Jan ; Jan, Vít (referee) ; Zelený, Martin (advisor)
This bachelor’s thesis is focused on observation of twin boundaries in a magnetic shape memory alloy based on Ni2MnGa with 10M martensitic structure. Theoretical part of the thesis describes materials with shape memory effect, their response on mechanical or magnetic loading, phenomenon of twinning, which is closely connected to the shape memory effect, and various levels of twinning. Experimental part studies different types of twin boundaries in monocrystal of alloy Ni49.2Mn30.4Ga20.4 using optical and electron microscopy. The thesis also deals with detection of structural orientations in different twin variants. A holder of samples was designed and constructed for real time observation of twin-boundary movement by optical microscopy. Deformation by pressure shows, that stress necessary for movement of Type II twin boundaries is ~0.2 MPa, whereas it is ~0.6 MPa for movement of Type I.
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