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Oxidation properties of complex concentrated alloys
Veverková, Eliška ; Minárik, Peter (advisor) ; Král, Robert (referee)
The thesis is focused on the oxidation characteristics of two complex con- centrated alloys - FeAlCrMo and FeAlCrV. Potentiodynamic polarisation tests were performed in order to characterize corrosion behavior of the alloys in two different corrosion media (aqueous solution of 3,5% NaCl and 0,5M H2SO4), in addition, high-temperature oxidation resistance was studied. All tests were perfor- med also for stainless steel used as a benchmark. An excellent corrosion resistance of both alloys was discovered, especially in the acidic solution, the studied alloys even surpassed reference stainless steel. On the contrary, poor resistance to high- temperature oxidation was observed. Particularly FeAlCrV exhibited catastrophic properties and resistance of FeAlCrMo is also inferior to stainless steel.
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Superplastic deformation of ultrafine-grained magnesium alloys containing rare earth metals and zinc
Vávra, Tomáš ; Minárik, Peter (advisor) ; Čížek, Jakub (referee)
Superplastic behavior of two ultrafine-grained (UFG) magnesium alloys was investigated in this thesis. Commercial Mg-4Y-3RE (wt.%) alloy was prepared by equal channel angular pressing (ECAP) and new experimental alloy Mg-23Zn-2Y (wt.%) was prepared by extrusion and ECAP. Eight passes of Mg-4Y-3RE through ECAP resulted in grain refinement down to ~340 nm and formation of a high volume fraction of fine secondary phase particles. UFG microstructure with an average grain size of 3.2 µm after extrusion and 1.6 µm after Ex-ECAP was achieved in Mg-23Zn-2Y alloy. The microstructure of Mg-23Zn- 2Y was observed by scanning and transmission electron microscopy. The thermal stability of both alloys was measured by microhardness tests. Superplastic behavior was investigated in the temperature range of 250-450 řC and strain rate range of 5x10-4 s-1 - 10-1 s-1 . The results revealed a high strain rate superplasticity in Mg-4Y-3RE alloy. Deformation to fracture exceeded 1000% for several deformation conditions, even at the strain rate of 10-1 s-1 . The highest elongation of 656 % in Mg-23Zn-2Y alloy was achieved in extruded state at the strain rate of 10-3 s-1 .
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Investigation of deformation mechanisms in textured magnesium alloy
Dittrich, Jan ; Minárik, Peter (advisor) ; Lukáč, Pavel (referee)
Název práce: Studium deformačních mechanism· v hořčíkové slitině s texturou Autor: Jan Dittrich Katedra: Katedra fyziky materiál· Vedoucí bakalářské práce: RNDr. Peter Minárik, PhD., Katedra fyziky materiál· Abstrakt: Předložená práce se zabývá studiem deformačních mechanism·, zá- visejících na orientaci vzork· v·či p·vodní textuře válcované hořčíkové slitiny, pomocí pokročilých in-situ i ex-situ metod. Během deformačních zkoušek, které byly prováděny v tlaku a v tahu, byla současně zaznamenávána akustická emise. Mikrostruktura deformovaných vzork· poté byla zkoumána metodami optické mi- kroskopie a difrakce zpětně odražených elektron·. V práci byla zjištěna výrazná závislost mechanických vlastností a aktivovaných deformačních mechanism· na orientaci vzork· v·či zjištěné bazální textuře válcovaného plechu hořčíkové sli- tiny AZ31. Dále byla ustanovena souvislost mezi základními parametry akus- tické emise a aktivovanými deformačními mechanismy. Rovněž byla pozorována a objasněna asymetrická odezva akustické emise při deformaci tlakem a tahem, související s rozdílným vývojem mechanického dvojčatění v pr·běhu plastické deformace. Klíčová slova: hořčíkové slitiny, deformace, dvojčatění, akustická emise, EBSD
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Effect of substantial grain refinement on microstructure and mechanical properties of precipitation hardenable magnesium alloys.
Hofman, Daniel ; Minárik, Peter (advisor) ; Janeček, Miloš (referee)
Properties of magnesium alloy WE43 and the effect of substantial grain refinement by ECAP were studied. The compressive strength test revealed a significant increase of yield strength after ECAP, resulting in yield strength of over 400 MPa after 8 ECAP passes. The material remained surprisingly ductile in both compression and tension. Thermal stability of the material was investigated via Vickers hardness test. The ultrafine-grained structure shows good thermal stability up to 300 řC, where the precipitates start to dissolve and grain size starts to increase, resulting in sharp fall of hardness. Annealing of the initial state showed best results for 210 řC where the precipitation hardening led to an increase in hardness up to ∼101 HV.
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Magnesium alloys designed for medical applications
Zemková, Mária ; Minárik, Peter (advisor) ; Vojtěch, Dalibor (referee)
Title: Magnesium alloys designed for medical applications Author: Mária Zemková Abstract: This Master thesis is focused on the influence of hot extrusion and equal channel angular pressing (ECAP) on the microstructure, mechanical and corrosion properties of magnesium alloys. Investigated materials include three magnesium alloys with the addition of neodymium and/or yttrium elements - N3, W3 and WN43, as a potential material for medical applications. Moreover, the influence of alloying elements in solid solution state was studied. Microstructure development was characterized by scanning electron microscopy together with transmission electron microscopy and X-ray diffraction. Mechanical properties was studied by compression deformation tests in two perpendicular directions and by microhardness tests. The linear polarization method was used to study corrosion resistance. The processing though ECAP resulted in grain refinement in all three alloys. Ultra-fine grained microstructure was achieved in W3 and WN43 alloy. The high degree of recrystallization during ECAP caused the formation of high-angle grain boundaries in all three alloys. Weak texture evolution was maintained during both processings. A different initial fraction of intermetallic phases before extrusion led to significant changes of microstructure...
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Study of deformation mechanisms in extruded magnesium alloys containing neodymium and yttrium
Hojnoš, Peter ; Minárik, Peter (advisor) ; Chmelík, František (referee)
Submitted work shows results of the investigation of ternary (WN43) and two binary magnesium alloys containing neodymium (2Nd) and yttrium (4Y) extruded at two different extrusion rates (2 and 5 mm/s). Microstructure of the investigated samples was analysed by light microscope. Additionally, texture of all samples was measured by X-ray diffraction. Mechanical properties were studied by compression deformation tests with two different deformation directions with respect to the processing direction. Acoustic emission was recorded during the deformation tests in order to correlate deformation behaviour with the micros- tructure. Analysis of the acoustic emission helps to identify deformation micro- mechanisms acting during the mechanical straining. Additionally, effect of sample size and deformation rate on the deformation mechanisms was investigated. 1
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Superplastic deformation of ultrafine-grained magnesium alloys with potential for use in medicine
Vávra, Tomáš ; Minárik, Peter (advisor) ; Málek, Přemysl (referee)
Mechanical properties of ultra-fine grain magnesium alloys AE42 and LAE442 prepared by ECAP were investigated. The study was focused on finding suitable conditions for the superplastic deformation. In the first place, the thermal stability of the microstructure was investigated. Afterwards, the strain rate sensitivity was measured in the temperature range 180-240 řC and the strain rate of =5·10-5 -2·10-3 s-1 . Conditions for tensile tests of =10-4 s-1 at 180 ř C and =10-3 s-1 at 240 řC ware selected. Finally, the microstructure change as a result of deformation was observed by AFM and EBSD. The results were discussed with mechanical tests. The best superplastic properties were observed in LAE442 alloy deformed at 180 ř C and =10-4 s-1 . Under these conditions, the achieved tensile strain was 395%.
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Effect of composition and microstructure on mechanical and corrosion properties in magnesium alloys with a potential for medical applications.
Minárik, Peter ; Král, Robert (advisor) ; Chráska, Pavel (referee) ; Landa, Michal (referee)
Title: Effect of composition and microstructure on mechanical and corrosion properties in magnesium alloys with a potential for medical applications. Author: RNDr. Peter MINÁRIK Department / Institute: Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. Dr. rer. nat. Robert Král, PhD., Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University in Prague Abstract: Doctoral thesis is focused on the effect of thermomechanical processing through ECAP on the microstructure, mechanical properties and corrosion properties. The investigation was performed on the extruded magnesium alloys AE21, AE42 and LAE442, because their potential for medical applications. Microstructure development was characterized in detail by scanning electron microscopy together with detection of back scattered electros, transmission electron microscopy and positron annihilation spectroscopy. Development of mechanical properties was investigated by tensile and compression deformation tests and microhardness measurement. Corrosion resistance was investigated by linear polarization method. Fine-grain structure with grain boundaries with high angle misorientation was achieved by the thermomechanical processing. The resulting...
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Effect of microstructure on mechanisms of plastic deformation in fine-grained magnesium alloys
Minárik, Peter
In this work were studied effects of the grain refinement on the mechanical properties and the corrosion resistance of magnesium alloys potential for medical applications - AE21 and AE42. Mechanical properties changed after ECAP pressing in consistency with literature data. Enhanced corrosion resistance in AE42 alloy was achieved by the grain refinement. Corrosion layer created on the surface was observed by light and electron microscopy. Effect of the grain size on the character of the corrosion layer was investigated. AE42 alloy is suitable for further investigation as potential biodegradable material. AE21 alloy was excluded from further investigation due to low corrosion resistance even after ECAP treatment.
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