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Microstructure and mechanical properties study of the finegrained magnesium alloys processed by severe plastic deformation
Šašek, Stanislav ; Stráská, Jitka (advisor)
Two magnesium alloys (Mg-4Y-4Gd-2Ca and Mg-2Y-2Gd-1Ca) with high ignition tem- perature were successfully processed by extrusion. Mg-2Y-2Gd-1Ca alloy was addition- ally processed by equal channel angular pressing (ECAP) to achieve ultrafine-grained microstructure. The effect of extrusion parameters on fraction of recrystallized grains, grain size, and texture was revealed by EBSD analysis. The presence of Mg2Ca, REH2 and Mg5RE secondary phases was proven by SEM and TEM. Microstructural condition including distribution and morphology of secondary phase par- ticles directly affected the mechanical properties. Yield tensile stress exceeding 200 MPa was achieved in each condition. Large non-recrystallized grains with strong {10̄10} tex- ture resulted in a significant anisotropy in mechanical properties. Processing by ECAP led to a homogeneous microstructure with a mean grain size below 1 µm. ECAP condition showed superior mechanical properties with a low anisotropy. The developed and analysed microstructural condition resulted in favourable mechanical properties. The studied alloys are therefore promising for the application in aerospace industry. 1
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Mechanical properties and microstructure of ultrafine-grained magnesium alloys containg neodymium and zinc
Šašek, Stanislav ; Stráská, Jitka (advisor) ; Krajňák, Tomáš (referee)
Two experimental magnesium alloys containing neodymium and zinc (Mg- 5Nd-1Zn and Mg-1Nd-1Zn) were processed by severe plastic deformation (SPD) method - equal channel angular pressing (ECAP). The influence of the processing on the microstructure was studied by light optical microscopy (LOM), transmis- sion electron microscopy (TEM) and also scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD). A significant grain refinement was observed after the final stage of ECAP in both alloys resulting in homogenous ultra-fine grained condition. Microstructure development had a significant influ- ence on mechanical properties which were investigated by microhardness measu- rements and compression deformation tests. Both the yield compression strength σ0,2 and the microhadness significantly increased compared to the extruded/as- cast counterparts. 1
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Biodegradable Mg-based materials for stents and bone implants
Zemková, Mária ; Král, Robert (advisor) ; Stráská, Jitka (referee)
The bachelor thesis is focused on the effect of mechanical processing rotary swaging (RS), specifically on the microstructure, mechanical properties and corrosion properties. The investigation was performed on the magnesium alloy AE42 with a different number of RS passes, which can be useful for medical applications. RS is more efficient and cheaper alternative to different material processing methods producing fine-grained struc- ture. Fine-grain structure with grain boundaries with high angle misorientation was achieved by this process. Microstructure was inhomogeneous - the grain size decreased from the surface to the center. An improvement of mechanical properties with the increase in the number of swaging steps was observed. Processing also led to a decrease in corrosion resistance in this alloy. Microstructure development was investigated by electron microscopy scanning. Development of mechanical properties was characterized by compression deformation tests and microhardness measurements. Linear pola- rization method was used for the interpretation of corrosion resistance. 1
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Microstructure and mechanical properties study of the finegrained magnesium alloys processed by severe plastic deformation
Šašek, Stanislav ; Stráská, Jitka (advisor) ; Hadzima, Branislav (referee)
Two magnesium alloys (Mg-4Y-4Gd-2Ca and Mg-2Y-2Gd-1Ca) with high ignition tem- perature were successfully processed by extrusion. Mg-2Y-2Gd-1Ca alloy was addition- ally processed by equal channel angular pressing (ECAP) to achieve ultrafine-grained microstructure. The effect of extrusion parameters on fraction of recrystallized grains, grain size, and texture was revealed by EBSD analysis. The presence of Mg2Ca, REH2 and Mg5RE secondary phases was proven by SEM and TEM. Microstructural condition including distribution and morphology of secondary phase par- ticles directly affected the mechanical properties. Yield tensile stress exceeding 200 MPa was achieved in each condition. Large non-recrystallized grains with strong {10̄10} tex- ture resulted in a significant anisotropy in mechanical properties. Processing by ECAP led to a homogeneous microstructure with a mean grain size below 1 µm. ECAP condition showed superior mechanical properties with a low anisotropy. The developed and analysed microstructural condition resulted in favourable mechanical properties. The studied alloys are therefore promising for the application in aerospace industry. 1
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Mechanical properties and microstructure of ultrafine-grained magnesium alloys containg neodymium and zinc
Šašek, Stanislav ; Stráská, Jitka (advisor) ; Krajňák, Tomáš (referee)
Two experimental magnesium alloys containing neodymium and zinc (Mg- 5Nd-1Zn and Mg-1Nd-1Zn) were processed by severe plastic deformation (SPD) method - equal channel angular pressing (ECAP). The influence of the processing on the microstructure was studied by light optical microscopy (LOM), transmis- sion electron microscopy (TEM) and also scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD). A significant grain refinement was observed after the final stage of ECAP in both alloys resulting in homogenous ultra-fine grained condition. Microstructure development had a significant influ- ence on mechanical properties which were investigated by microhardness measu- rements and compression deformation tests. Both the yield compression strength σ0,2 and the microhadness significantly increased compared to the extruded/as- cast counterparts. 1
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Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques
Stráská, Jitka ; Janeček, Miloš (advisor) ; Dlouhý, Antonín (referee) ; Kalvoda, Ladislav (referee)
Title: Physical properties of ultrafine-grained magnesium based alloys prepared by various severe plastic deformation techniques Author: Jitka Stráská Department / Institute: Department of Physics of Materials Supervisor of the doctoral thesis: Doc. RNDr. Miloš Janeček, CSc. Abstract: The objective of the doctoral thesis is the complex investigation of ultrafine-grained magnesium alloy AZ31 prepared by two different severe plastic deformation techniques, in particular the hot extrusion followed by equal-channel angular pressing (EX-ECAP) and high pressure torsion (HPT). These severe plastic deformation methods, and as well as many others, are described in detail in the introductory theoretical section. Experimental results are summarized in the following experimental part of the thesis. Mechanical properties, lattice defect structure and especially microstructure were investigated using various experimental techniques. Thermal stability of ultrafine-grained microstructure of AZ31 after EX-ECAP was investigated and the activation energies for grain growth in different temperature ranges were calculated using kinetic equation for grain growth and Arrhenius equation. Results from the dislocation density measurements proved temperature ranges of the recovery and the following grain growth. Results from the...
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Mechanical properties of ultrafine-grained magnesium alloys
Nováková, Helena ; Stráská, Jitka (advisor) ; Král, Robert (referee)
This work is focused on the mechanical properties of ultrafine-grained magnesium alloy AZ31 prepared by EX-ECAP method. The main goal of the bachelor thesis is to find external conditions of superplastic deformation: deformation temperature (measured in the range 150 řC - 350 řC) and strain rate (measured in the range 10-5 s-1 - 10-2 s-1 ). Properties related to the mechanisms of superplasticity (strain rate sensitivity parameter, maximum stress and maximum elongation) were evaluated. Deformation mechanisms were furthermore observed using atomic force microscopy.
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Biodegradable Mg-based materials for stents and bone implants
Zemková, Mária ; Král, Robert (advisor) ; Stráská, Jitka (referee)
The bachelor thesis is focused on the effect of mechanical processing rotary swaging (RS), specifically on the microstructure, mechanical properties and corrosion properties. The investigation was performed on the magnesium alloy AE42 with a different number of RS passes, which can be useful for medical applications. RS is more efficient and cheaper alternative to different material processing methods producing fine-grained struc- ture. Fine-grain structure with grain boundaries with high angle misorientation was achieved by this process. Microstructure was inhomogeneous - the grain size decreased from the surface to the center. An improvement of mechanical properties with the increase in the number of swaging steps was observed. Processing also led to a decrease in corrosion resistance in this alloy. Microstructure development was investigated by electron microscopy scanning. Development of mechanical properties was characterized by compression deformation tests and microhardness measurements. Linear pola- rization method was used for the interpretation of corrosion resistance. 1
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