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Phase transformation in magnesium MgZnAl-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor)
In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.
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Microstructure and mechanical properties of ultra-fine grained titanium alloys
Václavová, Kristína ; Stráský, Josef (advisor)
Title: Microstructure and mechanical properties of ultra-fine grained titanium alloys Author: Bc. Kristína Václavová Department / Institute: Department of Physics of Materials Supervisor of the master thesis: PhDr. RNDr. Josef Stráský, Ph.D. Abstract: Metastable β-Ti alloys Ti-15Mo and Ti-6.8Mo-4.5Fe-1.5Al (TIMETAL LCB) were subjected to severe plastic deformation by high pressure torsion. Microhardness of Ti-15Mo and TIMETAL LCB alloys increases with increasing inserted deformation, i.e. with increasing number of HPT rotations and also with increasing distance from the centre of the sample. The highest microhardness after HPT exceeds significantly the microhardness of two-phase α + β heat-treated material. Increasingly deformed microstructure was also demonstrated by scanning electron microscopy and by electron back-scattered diffraction (EBSD). Significant twinning was observed in both studied alloys. Mechanism of multiple twinning contributes notably to the fragmentation of grains and thus to the refinement of the microstructure. Defect structure in Ti-15Mo alloy was studied by positron annihilation spectroscopy. It was proved that dislocations are the only detectable defects in the material by positron annihilation spectroscopy and that dislocation density increases with the number of HPT revolution and...
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Microstructural evolution of equal-channel angular pressed IF steel
Krajňák, Tomáš
Equal channel angular pressing (ECAP) belongs to advanced technologies for improving mechanical properties of materials. In the present work the influence of number of pressing by route BC on grain size, density and type of dislocation, evolution of microstructure and mechanical properties of IF steel has been investigated by means of optical microscopy, electron back-scattering diffraction (EBSD), diffraction profile analysis, microhardness testing and tensile deformations. It has been found, that the grain size decreasing with increasing number of passes. Simultaneously, the microhardness, density of dislocation and maximum true strength has been increased. The evolution of microstructure with increasing pressing number, particularly the forming of high-angle boundaries has been also examined.
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Effect of molybdenum content on phase transformations in binary Ti-Mo alloys
Valešová, Veronika ; Stráský, Josef (advisor) ; Janeček, Miloš (referee)
Title: Effect of molybdenum content on phase transformations in binary Ti-Mo alloys Author: Veronika Valešová Department: Department of Physics of Materials Supervisor: PhDr. RNDr. Josef Stráský, Ph.D., Department of Physics of Mate- rials Abstract: β titanium alloys are highly appreciated group of structural materials. They provide an extraordinary combination of strength, toughness and fatigue resistance. These alloys are used predominantly in aerospace sector, chemical industry and medical engineering. We have studied three binary titanium alloys: Ti-12Mo, Ti-15Mo and Ti-18Mo (wt %). Apart from low temperature hexagonal close packed α phase and high temperature base centered cubic β phase, a metastable ω phase can be also found in this type of alloys. The ω phase is created in a diffusionless process by shifting the planes in the β phase and affects both mechanical properties and the α phase precipitation. We have examined the phase transformations occurring in the studied alloys using both in-situ and ex-situ methods. Resistometry, dilatometry and differential scanning calorimetry were used as the indirect in-situ methods. For the ex-situ methods, scanning electron microscopy and microhardness measurement were used. Complex characterization of β metastable titanium alloys showed the formation of the...
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Influence of surfactants in electroless nickel bath on properties of Ni-P coatings on AZ91 magnesium alloy
Buday, Patrik ; Wasserbauer, Jaromír (referee) ; Buchtík, Martin (advisor)
This bachelor thesis deals with the effect of surfactants on mechanical properties and structure of Ni-P coatings on AZ91 magnesium alloy. The theoretical part of the thesis includes summary of basic knowledge about magnesium alloys, surfactants and electroless deposition of Ni-P coatings, including a detailed description of Ni-P reduction on substrate. The theoretical part is concluded by current research in the field of Ni-P coatings. In the experimental part, morphology of Ni-P coatings was observed by electron microscopy (SEM). Using a light microscope (LM), the effect of surfactants on the deposition rate was observed. By means of energy dispersion analysis, the average phosphorus content of Ni-P coatings was determined. The hardness as a mechanical property of these coatings was determined using a micro hardener.
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Multi-element Systems of Biomaterials Based on Magnesium and Zinc
Hasoňová, Michaela ; Nový, František (referee) ; Vojtěch, Dalibor (referee) ; Doležal, Pavel (advisor)
Dissertation thesis deals with basic research in the field of materials from pure Zn powders and Mg, Zn, and Ca binary mixtures prepared by powder metallurgy. General powder metallurgy principles and methods, a brief description of Mg, Zn, and Ca structure and properties, and the latest research in the field of bulk materials preparation from these elements via powder metallurgy are summarized in the theoretical part of the thesis. The experimental part focuses on the preparation of materials from finer and coarser Zn powder particles by hot pressing at 300 and 400 °C using the pressure of 100, 200, 300, 400, and 500 MPa. Binary mixtures based on Mg with the addition of Zn or Ca were prepared by hot pressing in the solid-state (300 °C) and hot pressing in the semi-solid state (400 °C, 450 °C in the case of Mg-Ca system) using the pressure of 500 MPa. Binary mixtures based on Zn with the addition of Mg or Ca were prepared by hot pressing in the semi-solid state (400 °C) using the pressure of 500 MPa. The prepared materials were evaluated in terms of microstructure, elemental and phase composition, microhardness, flexural strength, and fractography. The results showed that in the case of processed from pure Zn powders, a better combination of the flexural strength and displacement was achieved in the case of the finer Zn powder, namely in the material prepared at a temperature of 400 °C and a pressure of 500 MPa. In the case of mixtures, the best connection between the powder particles was achieved in the case of a material based on finer Zn powder with 0.5 wt.% of Mg, which had a significant effect on the achieved values of flexural strength and displacement. The amount of minor powder in the mixture had a significant effect on the prepared material structure and phase composition, while the processing conditions influenced the reached strength characteristics and fracture mechanism.
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Chemical-heat treatment of steels
Rozum, Jakub ; Pokorný, Zdeněk (referee) ; Sedlák, Josef (advisor)
This thesis deals with study of surface layers of low-carbon steels formed by chemical-heat treatment. The first three chapters consist of theoretical part of the thesis, there are explained basic physical principles of these technologies and described individual types, the third chapter deals with the application of chemical-heat treated low-carbon steels in mechanical engineering. The experimental part of thesis deals with analysis of surface layers of two low-carbon steels formed using plasma nitrocarburizing and gas nitrocarburizing. The properties of these layers are evaluated based on the results of mechanical tests (hardness tests) and observation of microstructure. The thesis is completed by discussion, where the achieved results are evaluated.
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Complete characterization and comparison of lacquer / Ni-P / AZ91 and lacquer / AZ91 systems
Šomanová, Pavlína ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis was to compare the influence of Ni-P coating and varnish on the corrosion properties and chemical – physical properties (adhesion) of the magnesium alloy AZ91. The theoretical part contains the information about the alloy AZ91 itself and its microstructure, following by discussion about Ni-P coating, its properties, the process of the electroless deposition and composition it the nickel bath. Next chapter focuses on information about varnishes, its function and the process of its application on the surface of the substrate. Theoretical part closes with the summary of current research in the field of Ni-P coatings applied on magnesium alloys. The experimental part focuses on analysis of the microstructure of AZ91 alloy. The microstructure of the Ni-P coating and of the system Mg alloy/Ni-P coating/varnish was 4 examined by scanning electron microscope (SEM) and inverted microscope. During the next phase was thickness and hardness measured and composition measured by EDS analysis. The factor of the heat treatment of the samples and its impact on the final microstructure, hardness and corrosion resistance was taken in account. Finally, several samples were modified with the layer of the varnish and its thickness and the influence on the corrosion resistance ware measured. Samples were tested with electromechanical impedance spectroscopy (EIS), the corossion resistance were tested by neutral salt spray (NSS) and adhesive test was performed. The results showed, that Ni-P coating and the layer of varnish had positive impact on the corrosion resistance and the hardness of AZ91. The corrosion resistance of the samples modified with heat treatment was much lower, because of the contracting, which causes creation of the cracks. Also, the layer of varnish had positive effect on anticorrosion properties of tested AZ91 alloy.
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CMT advanced application in industrial practice
Šoulák, Petr ; Sigmund, Marian (referee) ; Kubíček, Jaroslav (advisor)
In presented diploma thesis is studied problematics of welding of high strength steels. This work also describes arc welding in protective atmosphere CMT Advanced. In experimental part of this work is CMT Advanced method compared with conventional arc welding in protective atmosphere in shortcut mode used for welding of Hardox 450 and Weldox 700 E. Comparing of mechanical properties of weld material are realized via transverse tensile testing and measuring of microhardness. Macrostructure and microstructure of weld was evaluated too. In the last part of this thesis is a brief economical assessment of both studied methods.
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Structure and mechanical properties of magnesium materials processed by HPT
Poloprudský, Jakub ; Němec, Karel (referee) ; Doležal, Pavel (advisor)
This thesis is focused on processing of pure magnesium by high pressure torsion method (HPT). This process belongs to the group of intensive plastic deformation methods (SPD). SPD methods are in the centre of scientific interest for several decades. Theoretical part of this thesis puts an effort to summarize basic knowledge and principles of SPD methods with extra focus on method HPT. As theoretical part continues magnesium as technical material is presented. Influence of SPD on use and properties of pure magnesium is then presented. This trend is further developed in effort to describe the effect of individual HPT process variables on the properties of pure magnesium and its alloys. Focus of practical part of this thesis is in influence of number of revolutions. Samples were processed at 1/8, 1/4, 1/2, 1, 4 and 8 turns at room temperature. Speed of process was 1rpm and applied pressure was 6 GPa. The structure of commercially pure magnesium prepared by casting and moulding were observed with focus on differences caused by input material. The structure was observed by both light microscopy and back scattered electron diffraction (EBSD), focusing on structure development, grain size and grain orientation. Compared to other works on similar topic, the emphasis here is on observing the microhardness on the vertical edge of the sample. The hardness shows a steep increase right after 1/8 of a turn. With increasing number of turns gradual homogenization of microhardness is presented accompanied by slight decrease in microhardness. No trend in microhardness relative to the distance from anvil has occurred. Structure observed with EBSD shows a bimodal character with larger grains oriented in the same direction. The three-point bending test didn’t end up as expected, and the approach to evaluation of magnesium-based HPT needs to be re-evaluated for future work. A three-point bending test was designed for the initial assessment of the basic mechanical properties of the material.
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