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Deformation of tool steels after quenching in vacuum furnaces
Abu Khait, Yosef ; Němec, Karel (referee) ; Pacal, Bohumil (advisor)
In this thesis, the deformation stages, which take place in tool steels after quenching in vacuum furnaces, were studied. This study was focused on the heating and cooling conditions during this type of quenching. In the experimental part, the deformation changes in particular samples made of tool steel after vacuum quenching were analyzed. Minor changes in the volume of samples at higher quenching temperatures compared to lower temperatures were observed.
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Stainless steel for steam sterilizer components
Hradil, David ; Němec, Karel (referee) ; Pacal, Bohumil (advisor)
The thesis titled "Stainless steel for steam sterilizer components" is focused on the selection of the optimum stainless steel for the device, in our case, pure steam generator. In this thesis are introduced the main mechanisms and types of corrosion. There are divided and characterized by various types of stainless steels. The choice of material is carried out with regard to the working environment and the technological possibilities of the individual types of stainless steels.
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Structure and properties of magnesium alloys Mg-Ca-Zn
Hlavnička, Jiří ; Pacal, Bohumil (referee) ; Doležal, Pavel (advisor)
This master’s thesis deals with design and preparation of a new biodegradable magnesium alloy based on Mg-Ca-Zn. Based on information from literature, the Mg-3Zn-2Ca alloy was designed. The base material was produced by gravity casting and the evaluation in the as-cast and heat treated state was performed. For preparation of the experimental material, following methods were designed: squeeze casting, hot rolling and the ECAP. During preparation by hot rolling, no optimal conditions were found and significant cracks occurred in both as-cast and heat treated material. In the case of experimental material, prepared by the ECAP method with back-pressure, better combination of stress-strain properties was observed. Also the squeeze casting method showed improvement; especially the amount of casting defects was eliminated. The evaluation of microstructure and mechanical properties was performed by the light and scanning electron microscopy, RTG phase analysis and the tensile and compression tests.
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The effect of plastic strain of the reinforcement of aircraft panel made from aluminium alloy on the corrosion process
Valoušek, Tomáš ; Tulka, Jaromír (referee) ; Pacal, Bohumil (advisor)
This bachelor thesis is focused on study of corrosion of reinforcement panel of aircraft in environment of salt fog. The reinforcement material is aluminum alloy AlZnMgCu1,5 after solution annealing, release stress relieving and artificial aging, can be slighly deformed to compliance limit deviation. Material is not provided with any coating. The aim was to find out what is the effect of plastic deformation on the corrosion behavior of this alloy. In the experimental part of this thesis were studied the size and type of corrosion attack of samples with different plastic deformation. These values were furhter processed, evaluated and were drawn from them conclusions.
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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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Al-alloy die-castings-trends in industrial
Rýdel, David ; Pacal, Bohumil (referee) ; Čech, Jaroslav (advisor)
The objective of this diploma thesis is to state the influence of porosity, DAS and shape factor on mechanical characteristics for the cast transmission cover made in Kovolit Modrice a.s.Which was molten from AlSi9Cu3. It was used an imaging software (Olympus Five) for classification of metallographical structures.
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Corrosion of Nonferrous Metal Materials
Ševčíková, Barbora ; Nový,, František (referee) ; Pacal, Bohumil (referee) ; Havlica, Jaromír (advisor)
In the presented dissertation thesis, I closely focused on corrosion resistance of non-ferrous metals. For full understanding of the possibilities for increasing corrosion resistance, it was vital to initially recognize the influences to the corrosion system of the samples and their surrounding environment. For this purpose, I focused on heat treatment, corrosion, and protective coatings, in the theoretical part of the thesis. For the subsequent research, it was necessary to define several constant variables, first. For this purpose, I have chosen a group of magnesium alloys, namely AZ91 Alloy and 3.5 % NaCl Electrolyte. AZ91 Alloy is of heterogenous structure formed by a solid solution of aluminum in magnesium, intermetallic phase in Mg17Al12, and their eutectic. Local microcells tend to occur in these heterogenities, which leads to faster corrosion. In order to increase corrosion resistance of the alloy, I used a combination of heat treatment and protective phosphate coating. For creating of the desired structure, which further affects compact coating formation, I selected a process involving solution heating with precipitation hardening T6. Secondary goals of the thesis involved optimization of standard technical procedures for the sake of increasing efficiency. With regard to this goal, I introduced optimized heat treatment T6 using accelerated cooling of a sample in water and liquid nitrogen. A modification besides the standard phosphating procedure was carried out with no activation step. For evaluation of corrosion resistance of the samples, I conducted water immersion tests using electrochemical methods; such as potenciodynamic curves combined with electrochemical impedance spectroscopy. In order to streamline the evaluation of the corrosion surface in technical practice, I used automatic detection. Substantial improvement of corrosion resistance of the above mentioned system, compared to heat-untreated samples, was proven through electrochemical methods. Due to accelerated cooling, a more homogeneous structure was achieved, which could be further utilized to create more uniform protective coating. For some phosphate coating, specifically manganese phosphate coating, I identified certain modifications that were in line with the set goals; i.e. skipping the activation phase, and using automatic detection for evaluation of uniform corrosion on the samples.
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Phase Transformations during Heat Treatment of Fe - C Materials
Škvarka, Jakub ; Pacal, Bohumil (referee) ; Molliková, Eva (advisor)
The goal of this thesis is a study of heat treatment of iron-carbon alloys from a physical angle. Characteristics of main components from this system and their modifications are described there. There is also described what is going on during heat treatment especially from an angle of thermodynamics and kinetics, thanks to available information from literature. The knowledge is applied on specific types of heat treatment of material and processes which can follow it.
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