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Comparison of different approaches in ab initio modeling of mechanical and magnetic properties of materials
Čavojec, Martin ; Řehák, Petr (referee) ; Zelený, Martin (advisor)
Tato diplomová práce se zabývá zkoumáním vlivu kvantově-mechanického popisu mezi-atomárních interakcí na výsledky ab initio výpočtů magnetických a mechanických vlastností Fe, -TiAl a Ni2MnGa. Zkoumány byly dvě metody pro popis interakcí, jmenovitě metoda projektovaných přidružených vln a metoda lineární kombinace atomových orbitalů, které jsou implementovány v ab initio softwarech VASP a SIESTA. Hodnoty magnetických momentů v závislosti na objemových a tetragonálních deformačních drahách poukazují na relativní srovnatelnost napříč těmito metodami. Avšak výsledky elastických konstant poukazují na nevhodnost ab initio softwaru SIESTA pro výpočet elastických konstant metodou napětí-deformace (stress-strain metoda). Součástí praktické části této diplomové práce je vytvoření skriptu pro výpočet elastických konstant v programovacím jazyku Python.
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Magnetic shape memory alloys - ab initio approach
Heczko, Martin ; Šesták, Petr (referee) ; Zelený, Martin (advisor)
This Bachelor’s thesis is focused on theoretical study of magnetic shape memory alloys based on Ni2MnGa using ab initio calculations of electronic structure within the projector augmented wave method. In particular, the effect of increasing concertation of manganese instead of gallium was studied on total-energy and magnetic moment profiles along the tetragonal deformation path between austenite phase with cubic L21 structure and phase of nonmodulated martensite. Further, the effect of manganese atoms distribution within the gallium sublattice was studied as well as changes of this distribution under applied tetragonal deformation. At last but not at least, the elastic constants for austenitic and martensitic structures of studied alloys were calculated. The results show that the non-modulated martensite stabilized with increasing concentration of manganese, because its total energy decreased. The energetic barrier between austenitic and martensitic structures also decreased, which means the metastable austenite will change to unstable.
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Visual Editor of Drum Rhythms
Zelený, Martin ; Beran, Vítězslav (referee) ; Herout, Adam (advisor)
This bachelor's thesis is about visual editor of drum rhythms. The editor can make special type of music notation. This notation is used for recording percussion drum rhythms. The editor needs to be user-friendly and effective to use. Recorded notation can be printed directly.
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Ab initio calculations of the phase stability in Ni-Mn-Ga alloys
Pongrácz, Jakub ; Šesták, Petr (referee) ; Zelený, Martin (advisor)
This thesis deals with theoretical study of magnetic shape memory alloy based on Ni2MnGa with help of ab initio calculations of electronic structure within the projector augmented wave method. In particular the effect of Co- and Cu-doping is studied on total-energy profile along the tetragonal deformation path between austenite phase with cubic L21 structure and phase of nonmodulated martensite. Obtained results are used for estimation of doping influence on martensitic transformation temperature. Transformation temperature increases in the alloy doped by 3.125 at. % of copper instead of gallium whereas transformation temperature decreases in the alloy doped by 3.125 at. % of cobalt instead of nickel. If both type of doping are used the transformation temperature increases slightly because the effect of copper is stronger. Comparison of results from this work with available results obtained with help of the coherent potential approximation shows that a local lattice distortion around doping atom has negligible effect on studied properties.
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Computer modeling of twin-boundaries in shape memory alloys
Heczko, Martin ; Pokluda, Jaroslav (referee) ; Zelený, Martin (advisor)
This Master‘s thesis is focused on theoretical study of twinning in magnetic shape memory alloys based on Ni2MnGa using ab initio calculations of electronic structure within the projector augmented wave method. In particular, the effect of increasing concentration of manganese at the expense of gallium was studied on total energy and stress profiles along different deformation paths in the (10-1)[101] shear system of non-modulated martensite. Further, this work deals with the effect of the concentration of manganese on the energy of planar fault caused by presence of partial dislocation due to motion of twin boundary. The results show that the shear modulus in studied shear system increases with the increasing concentration of manganese as well as energy barrier and deformation characteristics along shear deformation paths increases, which makes the shear more difficult in Mn-rich alloys. Increasing concentration of manganese also leads to rising the planar fault energy. All these effects can be responsible for lower mobility of twin boundaries in alloys with higher concentration of manganese.
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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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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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