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Structural and Mechanical Characteristics of Nickel-Alloyed Ductile Cast Iron
Tesařová, Hana ; Kohout, Jan (referee) ; Kruml, Tomáš (referee) ; Konečná,, Radka (referee) ; Pacal, Bohumil (advisor)
The aim of this dissertation work is the evaluation of the influence of nickel alloying on the structure and mechanical properties, both monotonic and dynamic, of nodular cast iron with ferritic and bainitic matrix. Two chock melts with 0.5 and 2.7 % Ni were used to study the nickel influence. The quantitative evaluation of structure of these melts using image analysis was done and basic tensile mechanical properties were determined. Subsequently, the time optimization of two-stage ferritic annealing and isothermal austempered heat treatment at 375 °C was performed with the aim to obtain optimal ferritic and bainitic structures with best static and dynamic mechanical properties. After ferritic annealing the nickel alloying contributes to substitution hardening of ferritic matrix which positively affects its strength and other mechanical properties. The higher nickel content in the bainitic structure causes the shift of phase transformation times to longer times which results in restricted production of small carbides and in bigger volume of retained austenite. These features were confirmed by observation in transmission electron microscope. Precise tensile and low cycle fatigue tests at temperatures 23 and – 45 °C were performed on the optimized structures of both nodular cast irons. As a result of the notch effect of graphite nodules, microplastic deformation of both nodular cast irons was observed at stresses which were lower than the yield stress. The Hollomon's equation very well describes the individual parts of tensile curves for both nodular cast irons including their mutual comparison. From the low cycle fatigue tests, the cyclic hardening/softening curves, the evolution of elastic modulus and hysteresis loop shape parameters, cyclic stress-strain curves and fatigue life curves were obtained for both temperatures and materials. Moreover, the decrease of retained austenite volume was measured by neutron diffraction and the evolution of surface relief was characterized during cyclic straining for both austempered nodular cast irons at both temperatures. On the basis of these results both cyclic plasticity and fatigue degradation mechanisms in relation to the cyclic strain localization were described for both nodular cast irons.
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Study of deformation processes of perspective magnesium-based composites
Farkas, Gergely ; Mathis, Kristián (advisor) ; Száraz, Zoltán (referee)
The goal of the present work is investigation of deformation mechanisms in magnesium-based metal matrix composites and examination of the influence of morphology of strengthening phase on the mechanical properties. The microstructure of the specimen was studied by means of light optical and electron microscopy (SEM). Compression tests in the temperature range of 20řC-300řC were preformed. Acoustic emission measurements were performed during compression test at room temperature, whose help us elucidate the ongoing micromechanisms during the straining. Furthermore residual stress in the magnesium matrix at different strain levels was measured by neutron diffraction.
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Investigation of basic deformation mechanisms of magnesium alloys by means of advanced in-situ methods and theoretical modeling
Čapek, Jan ; Mathis, Kristián (advisor) ; Landa, Michal (referee) ; Šiška, Filip (referee)
The work is focused on developing testing methods for investigating of the deformation mechanisms of magnesium alloys. The work involves the measurement of in-situ acoustic emission and neutron diffraction and comparison to the theoretical models. Mg + 1wt.% Zr alloy was selected for investigation of the compression - tension asymmetry. Advanced analysis of acoustic emission and neutron diffraction data revealed activation of different slip systems during deformation. Moreover, the different evolution of twinning was explained. The same methods were used to investigate the aluminum influence on deformation mechanisms. The hardening of basal slip and twinning and increasing importance of prismatic slip was observed.
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Magnetic properties of R2TIn8 and related tetragonal compounds
Čermák, Petr ; Javorský, Pavel (advisor) ; Isnard, Olivier (referee) ; Honda, Fuminori (referee)
Title: Magnetic properties of R2TIn8 and related tetragonal compounds Author: Petr Čermák Department / Institute: Department of Condensed Matter Physics Supervisor of the doctoral thesis: doc. Mgr. Pavel Javorský, Dr., Department of Condensed Matter Physics Abstract: Intermetallic compounds R2TIn8 (R = rare earth, T = transition metal), commonly called "218" because of stoichiometry, are structurally related to a class of well- known Ce-based heavy-fermions like CeCoIn5 or CeRhIn5. They are located between fully 3D cubic compound (e.g. CeIn3) and quasi-2D "115" superconductors, which makes them ideal candidates to study structural dimensionality effects on various properties. Recent developments in this field showed that it is possible to grow compounds with T = Pd or Pt with "218" stoichiometry. Therefore further study of "218" compounds is desired since much less is known about them compared to "115" compounds. We have focused mainly on the determination of magnetic structures and crystal field effects along the series of Rh based "218" compounds for various rare-earth elements. The single crystals of compounds with R = Nd, Tb, Dy, Ho, Er, Tm, La, Lu, Y were successfully grown. Results of bulk measurements (specific heat, susceptibility) together with magnetic structures determined from several neutron...
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Study of deformation processes in hexagonal materials
Čapek, Jan ; Mathis, Kristián (advisor) ; Karlík, Miroslav (referee)
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation.
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Study of deformation processes of perspective magnesium-based composites
Farkas, Gergely
The goal of the present work is investigation of deformation mechanisms in magnesium-based metal matrix composites and examination of the influence of morphology of strengthening phase on the mechanical properties. The microstructure of the specimen was studied by means of light optical and electron microscopy (SEM). Compression tests in the temperature range of 20řC-300řC were preformed. Acoustic emission measurements were performed during compression test at room temperature, whose help us elucidate the ongoing micromechanisms during the straining. Furthermore residual stress in the magnesium matrix at different strain levels was measured by neutron diffraction. Powered by TCPDF (www.tcpdf.org)
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Study of deformation processes in hexagonal materials
Čapek, Jan
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation. Powered by TCPDF (www.tcpdf.org)
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