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Preparation and Characterization of Porous Magnesium Based Materials
Březina, Matěj ; Pacal, Bohumil (referee) ; Vojtěch, Dalibor (referee) ; Ptáček, Petr (advisor)
Bulk magnesium materials produced nowadays via powder metallurgy are based on a vastly extensive technological spectrum, which makes it possible to create a wide range of materials. This work focuses on the preparation of bulk materials from magnesium powder by cold pressing and hot pressing, sintering and field assisted sintering. The bulk materials were prepared in a series of compacting pressures from 100 MPa to 500 MPa and the sintering temperatures were selected in the range of 300 ° C to 600 ° C in order to characterize the influence of the manufacturing conditions and technology on the final properties of bulk materials. Prepared materials were evaluated in terms of microstructure, hardness, microhardness, three-point bend test, and fractography. From the hot pressed materials, the samples prepared at 400 and 500 MPa and 400 °C had the highest strength and hardness. The classic sintering of magnesium in the furnace with argon atmosphere proved to be ineffective due to the oxide layer on the surface and the presence of oxygen in technical argon. The SPS sintering (Spark Plasma Sintering) was the more effective with the lower applying pressure used to make the preforms and with the higher applied pressure during the SPS process itself. Highest strength and hardness were achieved in this case of materials sintered at 600 ° C prepared from free powder and the most porous preform (100 MPa). The bulk materials were prepared using all methods used, but the properties of these materials varied considerably depending on the technology used.
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Preparation and characterization of Ni-P coating on AZ91 cast magnesium alloy
Brescher, Roman ; Buchtík, Martin (referee) ; Wasserbauer, Jaromír (advisor)
This bachelor thesis deals with electroless deposition of nickel-phosphoric (Ni-P) coating on AZ91 magnesium alloy. At the beginning of the theoretical part, there is a summary of basic knowledge about magnesium alloys with focus on AZ91 alloy and the influence of alloying elements and impurities and its microstructure. The theoretical part continues with the discussion of the Ni-P coating, focusing on the composition of the bath, the influence and the effect of its individual components. Next, there is a comparison with galvanic nickeling. At the end of the theoretical part, the current research of the use of electroless deposition of Ni-P layer on AZ91 magnesium alloy is summarized. In the practical part, there is the preparation of the Ni-P coating on the AZ91 magnesium alloy, the observation the microstructure of the magnesium alloy and the Ni-P layer, and rate of deposition, the thickness, the microhardness and the composition of the coating was measured. The effect of its heat treatment was also observed. It has been found that it is possible to produce a high-quality Ni-P coating on an AZ91 magnesium alloy which has no visible defects or obvious undesirable interlayers, however the heat treatment of the coating causes its cracking. To determine the corrosion resistance, a potentiodynamic measurement was performed, resulting in the finding that the Ni-P coating without heat treatment was a suitable corrosion protection. However, after heat treatment, the corrosion resistance due to cracking of the surface deteriorated to a level of bare AZ91 alloy.
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Study of the microstructure of deposited Ni-P coatings with different phosphorus contents
Najser, Tomáš ; Kosár, Petr (referee) ; Wasserbauer, Jaromír (advisor)
The aim of this bachelor thesis was the preparation and characterization of Ni-P coatings with different phosphorus contents on the substrate of AZ91 magnesium alloy. The theoretical part deals with magnesium alloys and specifies the utilized substrate AZ91. It also focuses on Ni-P coatings, their microstructure and their properties. However, there are also described factors affecting the rate of deposition and the resulting behavior of these coatings. Last but not least, the theoretical part summarizes the basic principles of laboratory methods used in the experimental part for observation and characterization of samples. Conclusion of the theoretical part consists of several background researches where the authors deal with similar problems and factors influencing the resulting behavior of Ni-P coatings. The experimental part is focused on the deposition of each Ni-P coatings on the AZ91 alloy and their characterization. The study of deposited Ni-P layers was focused on the determination of their microstructural texture by XRD method, mechanical properties and elemental composition depending on phosphorus content.
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Advanced Magnesium Alloys Surface Modification by Ni-P Based Coatings
Kosár, Petr ; Pacal, Bohumil (referee) ; Nový,, František (referee) ; Havlica, Jaromír (advisor)
The dissertation thesis deals with the modification of the surface of advanced magnesium alloys with Ni-P based coatings. At the beginning of the theoretical part, the structures of the used magnesium alloys and the influence of individual alloying elements on their properties are characterized. In the following part of the thesis the current knowledge in the field of electroless deposition on metal substrates is summarized. The theoretical part of the thesis is closed with contemporary research study in the field of clarification and determination of possible mechanism of electroless deposition. For the subsequent investigation of the mechanism of electroless deposition on magnesium alloys, it was necessary to characterize the microstructure and composition of individual magnesium alloys in the first phase of the experimental part. The exact composition of elements was determined using glow discharge optical emission spectroscopy and scanning electron microscopy with EDS was used for composition of phases of magnesium alloys. Using scanning electron microscopy and detailed elemental analysis of the coated magnesium substrate, it was found that for optimal Ni-P coating deposition on magnesium alloys, acid pickling prior coating is required in a mixture of acetic acid and sodium nitrate. Using the XPS method, it was found that the phosphorus atom in the sodium dihydride-diphosphate reducing agent has a + V charge. 4 At the end of the experimental part scanning electron microscopy and detailed elemental analyses were used for monitoring of the Ni-P particles nucleation and growth in the first 120 seconds of the coating process.
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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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Phase transformation in magnesium MgZnAl-based alloys
Kodetová, Veronika ; Vlach, Martin (advisor) ; Mathis, Kristián (referee)
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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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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Study of properties of Titanium prepared by SPD methods
Zháňal, Pavel ; Harcuba, Petr (advisor) ; Král, Robert (referee)
In present work the properties of comercially pure titanium fouth grade processed by equal channel angular pressing (ECAP) were studied. Experimental techniques such as Vickers microhardness, measurement of electrical resistivity, light and electron microscopy were used in this research. The dependence of the degree of the strain imposed by ECAP on microhardness of the material was measured. Microhardness measurement was used to indirectly investigate thermal stability of the prepared material, which is essential for ultra fine grained (UFG) materials. That was also the reason for establishing dependence of the electrical resistivity on the temperature. This method allows to detect changes in the material microstructure. Using scanning electron microscopy (SEM) the results obtained by previous methods were confirmed. It was found that the UFG titanium processed by ECAP is thermally stable aproximatelly up to 450řC. At this temperature begins recovery of the material which results in a decrease of the microhardness values and electrical resitivity. For the temperatures higher than 520řC material recrystalization begins.
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Heat treatement of gear steels
Šnevajs, Matěj ; Řehořek, Lukáš (referee) ; Jan, Vít (advisor)
This bachelor thesis deals with suitable types of heat and heat-chemical treating of case hardening steel for production of gear wheels. The experimental part focuses on examination of two specific gear wheels made of 14 224 and ZF1A steel, which were donated by the company TATRA TRUCKS a.s. This bachelor thesis presents results of their hardenability, microstructure, hardness and microhardness of the case hardening layer.
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High temperature corosion of SiMo type ductile iron
Viskupič, Adam ; Kaňa, Václav (referee) ; Roučka, Jaromír (advisor)
While using iron castings behind temperature of 500 C namely at cyclic heat straining degradation of structure and breaching iron castings. For this purpose introduce cast iron with content of Si and Mo. Focusing on improvement of SiMo51 for increased high-temmperature corrosion-and fatigue life in exhaust-gas temperatures up to 800 C. Thesis set up chemical microheterogeneity, properties, high temperature corosion and microhardness
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