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Quality evaluation of unprocessed steels for corrosion
Holubářová, Michaela ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
This bachelor thesis is based on quality evaluation of unprocessed steels for corrosion. Visual control of the steel quality by a microscope is not sufficient, as this method of resistance assessment lacks quantified values. Current instruments are already able to provide specific corrosion values and therefore the SmartCET has been used to electrochemically characterize the supplied steel materials. The theoretical part includes general description and basic division of steel and corrosion. It also contains a summary of thermodynamic and kinetic corrosion aspects and methods of metal resistance evaluation. The experimental part deals with the measurements and evaluation of electrochemical characteristics (general corrosion rate, pitting factor and B value) over time compared to visual control.
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Preparation and Characterization of Advanced Thermally-sprayed Coatings on Magnesium Alloys
Buchtík, Martin ; Hadzima, Branislav (referee) ; Fintová, Stanislava (referee) ; Ptáček, Petr (advisor)
The proposed dissertation thesis deals with the characterization of HVOF and APS-thermally sprayed coatings prepared on the AZ31 and AZ91 magnesium substrates. The theoretical part of the thesis describes in-detail Mg substrates used in the experimental part of the thesis. There are also characterized materials and coatings based on NiCrAlY and FeCrNiMoSiC metals, WC-CoCr cermets, and YSZ ceramic materials. At the end of the theoretical part, the literary research summarizing the characterization and analysis performed on thermally sprayed coatings on Mg alloys. Based on the theoretical knowledge, the characterization of Mg substrates and deposited coatings was performed in terms of the surface morphology, microstructure, and the chemical composition using the light microscopy (LM) and scanning electron microscopy with energy-dispersive spectroscopy (SEM+EDS). The phase composition of the coatings was analyzed using the X-ray diffraction (XRD). The diffractions corresponding to the sprayed coatings were compared with the feedstock powders, i.e. materials used for the spraying of the coatings. The characterization of the prepared coatings in terms of the mechanical and tribological properties was performed. The hardness and microhardness of the coatings as well as the coefficient of friction, and the wear rate were measured. The last chapter of the experimental part deals with the evaluation of the electrochemical corrosion properties by the potentiodynamic measurements in a 3.5% NaCl solution. In the case of exposed samples, the evaluation of the surface and coating/substrate interface was performed using LM and SEM with EDS. The mechanism of the corrosion attack and degradation was determined from the acquired knowledge and base on the results of the short-term measurements. Based on the measured results, it can be stated that the deposited coatings were successfully applied on the surface of both Mg alloys. All the coatings increase the surface hardness of the Mg alloys and significantly improve their tribological properties. However, except for FeCrNiMoSiC coatings, the corrosion properties of Mg alloys deteriorate due to the fact that the corrosion environment can pass through the coating to the less noble Mg substrate and the corrosion microcells are created.
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Effect of hyaluronic acid on the corrosion of AZ31 magnesium alloy
Holubářová, Michaela ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
Magnesium and its alloys are interesting materials due to their many physical properties. They have considerable potential, especially in medical applications, where they can serve as a material for the production of orthopedic and cardiovascular implants. The disadvantage of these materials is their sensitivity to corrosion. As a result, it is necessary to know the corrosive properties of magnesium and its alloys in contact with substances that occur in the human body. Hyaluronan is a polysaccharide that is naturally present in the human body and can interact with implants. This master's thesis deals with the influence of low molecular weight (80–130 kDa) and high molecular weight (1 500–1 750 kDa) hyaluronan on the corrosion properties of magnesium alloy AZ31 in the environment of two simulated physiological solutions (0,9 % NaCl and synovial fluid). Potentiodynamic polarization (PD) and electrical impedance spectroscopy (EIS) were used for electrochemical tests. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to reveal the chemical composition of the corrosion products and the surface morphology after corrosion.
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Study of phytic acid-based organic conversion coatings on magnesium alloys
Zbíral, Roman ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
This thesis deals with organic conversion coatings based on phytic acid, on the magnesium alloys. In theoretical part it deals with corrosion properties of magnesium and magnesium alloys, usage of magnesium alloys for biomedicine applications. There are also summarized information’s about usage of phytic acid, it’s reactions with magnesium and magnesium alloys. At the end of theoretical part is search about phytic acid conversion coatings deposited on magnesium alloys. There are studied optimal conditions for application of phytic acid coatings such as pH, concentration, time of deposition, etc. Based on the knowledge from the theoretical part, a layer based on phytic acid was deposited on the surface of Mg alloy AZ31. The coating was evaluated in the experimental part in terms of its morphology and structure, chemical and corrosion behaviour. Scanning electron microscope (SEM) images showed the presence of microcracks in the dried coating. The chemical nature of the phytic acid-based conversion coating was investigated by energy dispersive spectroscopy (EDS) techniques in combination with Fourier transform infrared spectroscopy (FTIR). The electrochemical corrosion behaviour of Mg alloy AZ31 and coated Mg alloy was investigated by potentiodynamic polarization in Hank's solutions. Based on the obtained values of the corrosion potential and the corrosion current density, it can be stated that the applied layer of the conversion coating leads to an improvement of the corrosion properties. From the results of SEM analysis of samples after exposure in a corrosive environment, it was found that during potentiodynamic measurements no significant manifestation of corrosion attack was observed in coated samples, as was the case with Mg alloy AZ31.
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Effect of humic acid on the corrosion of carbon steel
Horák, Tomáš ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
Bachelor thesis deals with influence of humic acids on corrosion of ČSN 12020 steel. For this purpose, potentiodynamic tests and electrochemical impedance spectroscopy (EIS) in leaches of humic acids, isolated from South Moravian lignite were executed. Results suggest that corrosion is initially promoted by humic acids, but after a longer time (about 98 hours) an inhibitory effect is exerted due to the adsorption of humic acids on the corrosion products. Adsorption efficiency of humic acids on surface of corrosion products was about 30 %. Results also suggest that the presence of humic acids may influence the composition of corrosion products of the steel.
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Fluoride conversion coatings on composite Mg/MgO materials
Peroutka, Jakub ; Buchtík, Martin (referee) ; Hasoňová, Michaela (advisor)
Bachelor thesis deals with preparation of composite materials based on Mg/MgO and their subsequent coating with fluoride conversion coating. Materials based on Mg/MgO were prepared by powder metallurgy. The theoretical part contains of basic magnesium information, advantages and disadvantages of Mg and brief Mg preparation. In the next part there are summarized basic principles, advantages and disadvantages in powder metallurgy. The second theoretical part deals with basic properties of MgO, literary research which deals with description of MgO on chemical structure of different varieties of Mg alloys or composition materials based on Mg/MgO. The last part of theoretical part describes conversion coatings, brief description of chemical reaction kinetics and diffusion of fluoride conversion coating. The experimental part deals with preparation of composite materials based on Mg/MgO by powder metallurgy. The main goal of experimental part was description of possible effect of MgO content on the formation of fluoride conversion coating.
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Structural analysis of Fe48Cr28Ni16Mo4,5Si1,5C1,75 thermally-sprayed coatings on AZ91 magnesium alloy
Kobzinková, Eliška ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The bachelor thesis deals with the analysis of thermally sprayed Fe48Cr28Ni16Mo4,5Si1,5C1,75 coatings on AZ91 magnesium alloy and evaluation of their structural and mechanical properties. The theoretical part deals with magnesium alloys, focusing on AZ91 alloy, thermal spray methods, specifically the High Velocity Oxygen Fuel method of depositing (HVOF), and Fe and Fe-Cr-Ni based materials. The theoretical part concludes with a review of current research in the field of Fe-based coatings deposited by the HVOF method. The experimental part is devoted to the structural analysis of AZ91 magnesium alloy and the Fe-based thermally sprayed coating deposited on this alloy. The microstructure was analyzed by light microscopy (LM) and scanning electron microscopy (SEM). Elemental and phase analysis was performed using energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The hardness of the coating and alloy was measured by the Vickers method. The application of thermally sprayed coating increased the surface hardness from 87 ± 10 HV0.3 (AZ91) to 536 ± 94 HV0.3.
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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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Hydrothermal synthesis and characterization of calcium phosphate-based coatings on AZ31 magnesium alloy
Knoflíčková, Lenka ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this diploma thesis was to summarize all necessary knowledge needed for preparation of a quality CaP coating on AZ31 wrought magnesium alloys, and to implement its optimization for use in simulated body fluids. The theoretical part discusses biomaterials and their classification. Subsequently, the potential of magnesium alloys, their corrosion, and the possibility of surface treatment for in vivo applications are described in detail. The theoretical part concludes with the mechanism of deposition of CaP coatings on magnesium alloys and methods to evaluate their corrosion resistance. The experimental part includes the process of optimization of Mg alloy pretreatment and optimization of CaP coatings preparation, where the quality evaluation criteria were the appearance of the coating and its electrochemical and corrosion properties. These were evaluated by potentiodynamic tests. The microstructure and the chemical composition of deposited coating were observed and measured by optical and scanning electron microscopy. Long-term corrosion tests using electrochemical impedance spectroscopy (EIS) were performed on the optimized CaP coatings and these results were then compared with the corrosion properties of the uncoated AZ31 alloy.
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