|
|
Evaluation of corrosion properties of biodegradable ZE41 magnesium alloy in simulated body fluid
Handlíř, Tadeáš ; Minda, Jozef (referee) ; Tkacz, Jakub (advisor)
The bachelor thesis is focused on the evaluation of the effect of processing of biodegradable magnesium alloy ZE41 on its corrosion properties. The corrosion properties of ZE41 wrought magnesium alloy specimens with polished and ground surface were evaluated based on the results of the electrochemical characteristics that took place in the simulated body fluid. Short-term tests were performed using linear polarization method, by which the corrosion potential, corrosion current density and corrosion rate was determined. Long-term evolution of corrosion behavior in terms of polarization resistance was studied by electrochemical impedance spectroscopy (EIS) during 168 hours. Also, the corrosion products were studied by scanning electron microscope (SEM). Based on the results, the influence of surface treatment and phase composition on corrosion characteristics was evaluated.
|
|
|
FATIGUE CHARACTERISTICS OF MODIFIED MAGNESIUM ALLOYS AFTER CORROSION DEGRADATION
Němcová, Aneta ; Očenášek, Vladivoj (referee) ; Hadzima, Branislav (referee) ; Pacal, Bohumil (advisor)
This doctoral thesis deals with the determination of the influence of plasma electrolytic oxidation (PEO) on fatigue behaviour of extruded AZ61 magnesium alloy in air and in the 3.5% NaCl solution. The coatings were formed in the silicate-phosphate electrolyte under pulsed current conditions at a frequency of 50 Hz. The influence of current density on coating formation was examined under current densities of 70, 130 and 200 mA cm-2 for different durations up to a maximum of 1800 s. 8 g dm-3 of KF were added to the electrolyte to study the influence of fluoride ions in plasma electrolytic oxidation. It is shown that fluoride ions inhibit localised oxidation in the initial stage of the process, associated with the secondary particles based on Al–Mn. The presence of fluoride also modified the sparking characteristics, decreased the rate of coating growth and changed the morphologies of the coatings. The influence of fluoride on the coating hardness, and the corrosion resistance of the alloy during exposure to salt spray, was negligible. Based on previous optimised PEO conditions, coatings formed under a current density of 130 mA cm-2 for 300 s in the electrolyte containing KF were chosen for fatigue testing. The high-cycle fatigue tests were carried out on cylindrical samples under a force controlled sinusoidal tension-tension cycle with asymmetry parameter R=0. The experimental data were fitted with Kohout & Věchet function. The fatigue limit of uncoated alloy in air for 107 cycles was determined at 145.4 MPa and the combination of PEO coating with chloride ions caused a reduction of ~55 %. Attention was paid to the fatigue crack initiation in different conditions of cyclic loading. The fracture surfaces underwent detailed fractography analysis including secondary crack observation on the gauge length. The contribution of Al–Mn particles were confirmed on the uncoated alloy in air and the presence of chloride ions were observed as another influential contributor to local corrosion attack. The cyclic loading caused spalling of the outer layer, and the multiple initiation was observed on PEO coated alloy, caused by cracks in the coating and stress transferring to the alloy.
|
|
|
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.
|
|
|
Characterization of the thermally-sprayed metal-ceramic WC-CoCr coating on the AZ91 magnesium alloy
Knoflíčková, Lenka ; Wasserbauer, Jaromír (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis is to evaluate metal-ceramic coating WC-CoCr on magnesium alloy AZ91 to terms of microstructure, chemical and phase structure and mechanical properties. Deposition was made by HVOF (High Velocity Oxy-Fuel). The theoretical part is devoted to magnesium alloys focusing on alloy AZ91. Further there is said about methods of heat spraying. Where this part is focused on metal-ceramic WC-CoCr coatings made by HVOF method. The theoretical part is ended by current research, that is focused on characterization of WC-CoCr on magnesium alloys. Experimental part is about characterization of microstructure of alloy AZ91, WC-CoCr powder and WC-CoCr coating on magnesium alloy AZ91 with optical, SEM and XRD analysis. With heat spraying was observed that phase W2C was made by decay of phase WC in coating which leaded to dissolve of WC in matrix. For measuring of mechanical properties was used measurement by Vickers (hardness test). As result of WC-CoCr coating on surface of magnesium alloy AZ91 was increase of average hardness from 71 ± 5 HV0,3 to 1116 ± 109 HV0,3.
|
|
|
Development of WAAM process parameters for thin-walled components made of magnesium alloy AZ61
Šváb, Čeněk ; Němeček, Stanislav (referee) ; Slavíček, Jakub (advisor)
The thesis deals with the development of WAAM (Wire Arc Additive Manufacturing) process parameters for thin-walled parts made of magnesium alloy AZ61. The aim of the thesis is to find suitable process parameters and describe their influences on the welding process. To achieve this goal, these parameters were experimentally tested. It was found that the parameter of boost phase current and the duration of its application have the highest influence on the weld geometry. The stability of the welding process was then influenced by the electrode feed rate during the boost and burn phases. Based on these results, a final set of parameters was created, which successfully welded a thin-walled part composed of 50 layers and reaching a height of 130 mm.
|
|
|
Evaluation of the effect of chelating agents on the properties of phosphate coatings on AZ31 magnesium alloy prepared by hydrothermal method
Molva, Vojtěch ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis was to evaluate the influence of chelating agents on the properties of CaP coatings deposited on the AZ31 magnesium alloy by hydrothermal method. The theoretical part deals with magnesium and its alloys useful not only in biomedicine. Subsequently, the possibilities of surface treatments in the field of biomedical applications are described, with a focus on calcium phosphate (CaP) coatings. The theoretical part further discusses these coatings and the influence of selected chelating agents on the formation of CaP coatings. The theoretical part is concluded with a review of the experiments already carried out for the preparation of CaP coatings on Mg alloys. The experimental part includes the preparation and analysis of the protective Mg(OH)2 layer necessary for the deposition of CaP coatings. Within the experimental part, the influence of chelating agents (Chelaton III, citric acid, magnesium gluconate hydrate) at concentrations of 5, 50, and 500 mM at different pH of the reaction mixture on the structure, morphology, composition, and quality of the prepared CaP coatings was studied. The morphology, structure, and composition of the deposited coatings were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Based on these analyses, an assessment of the quality of the coatings was performed. In terms of coating quality, the coating prepared with the addition of 50 mM of Chelaton III at pH 7 and with the addition of 5 mM of magnesium gluconate hydrate at pH 5 appeared to be the best. The corrosion resistance was investigated by potentiodynamic tests in 0.15M NaCl, always with the sample from each batch that showed the best quality. The corrosion potential (Ecorr) and current corrosion density (icorr) values were determined from the polarization curves using the Tafel extrapolation method. Based on the measurements made, the most corrosion-resistant coated sample was the one with the addition of 5 mM magnesium gluconate hydrate at pH 5.
|
|
|
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.
|
|
|
Study of mechanical and thermal properties of nanoparticle-reinforced composites
Németh, Gergely ; Mathis, Kristián (advisor) ; Lukáč, Pavel (referee)
Title: Study of mechanical and thermal properties of composites reinforced by nanoparticles Author: Gergely Németh Department: Department of Physics of Materials Supervisor: RNDr. Kristián Máthis, Ph.D. Abstract: In the present work the deformation behavior of magnesium-based alloy AZ31 reinforced by SiC nanoparticles which was produced by horizontal continual casting is studied. Tension tests in the room temperature, compression tests in the temperature range of 20řC-300řC have been preformed. Samples was with two different orientation. Deformation strain rate was 10-3 s-1 . Simultaneously, the acoustic emission is recorded and studied. The mechanisms of plastic deformation of material are discussed mainly in term of mechanical twinning. Dependence of deformation behavior in compression on temperature is analyzed. The microstructure of original and deformed material is also studied. Keywords: magnesium alloys, composit material, mechanical twinning, metals with hexagonal structures.
|
|
|
Investigation of deformation mechanisms in Mg-Gd alloys
Szabóová, Andrea ; Mathis, Kristián (advisor) ; Drozdenko, Daria (referee)
Title: Investigation of deformation mechanisms in Mg-Gd alloys Author: Andrea Szabóová Department: Department of Physics of Materials Supervisor: doc. RNDr. Kristián Mathis, DrSc. Abstract: In the present work, the deformation behavior of magnesium-gadolinium binary alloys was investigated. Dependence on the concentration of Gd and deformation temperatures was studied. Extruded samples had relatively strong initial texture. Compression tests were done at room temperature and 200řC. Simultaneously with deformation acoustic emission was recorded. Data from acoustic emission was analyzed with advanced statistical methods. Results of the combination of these two experimental methods indicated that at the beginning of the deformation twinning is the dominant mechanism. In the following stage of plastic deformation non-basal slip systems became the governing deformation mechanism. With higher content of Gd the size of twins decreases as a result of the decreased mobility of twin boundaries caused by solute atoms. At higher temperatures twinning activity was increasing. In addition, results were confirmed by optical light and scanning electron microscopy. Keywords: magnesium alloy, deformation tests, acoustic emission, microscopy
|
|
|
Effect of alloying elements and texture on plastic deformation of extruded magnesium alloys
Horváth, Klaudia ; Dobroň, Patrik (advisor)
This work is focused on the study of the relationship between microstructure, texture and deformation mechanisms in aluminum-free magnesium (Mg) alloys. Extruded alloys containing zirconium, zinc, manganese and neodymium (ZK10, MN11, ZN11) in a form of rectangular profiles were deformed at room temperature. Uniaxial tensile and compression tests were performed in the extrusion (ED), transversal (TD) and normal direction (ND). The concurrent acoustic emission (AE) measurement was used in order to study the collective dislocation dynamic and the nucleation of twins. The deformation texture was studied by X-ray diffraction on samples deformed in compression up to different stress levels.
|
guest ::
