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Physical properties of ultrafine-grained polycrystals of magnesium based alloys
Vrátná, Jitka ; Janeček, Miloš (advisor) ; Kužel, Radomír (referee)
The objective of the thesis is the study of microstructure evolution, mechanical properties, defect structure and corrosion resistance of ultra-ne grained magnesium alloy AZ31 prepared by a combined two-step process: the extrusion and the equal-channel angular pressing (ECAP). The microstructure development was studied using light and transmission electron microscopy and electron backscatter diffraction (EBSD). Mechanical properties were studied by microhardness measurement and tensile tests and the defect structure by positron annihilation spectroscopy (PAS). The results of tensile tests indicates that the characteristic stress 0.2 increases slightly with increasing number of ECAP passes only to the second pass and then decreases signicantly with additional ECAP straining. This behaviour is in accordance with the results of PAS. EBSD measurements show that the microstructure of extruded and ECAPed material has a bimodal distribution of grain sizes. The bimodal distribution becomes homogeneous with increasing number of ECAP passes and no remaining large grains are observed after 8 passes. The average grain size in the specimen after 8 passes is in the submicrometer range and the fraction of high-angle grain boundary (HAGB) is approximately 80%. The extruded specimens after 8 ECAP passes show the best...
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Study of mechanical properties and microstructure development of fine-grained Cu and Cu alloy polycrystals
Srba, Ondřej ; Janeček, Miloš (advisor)
The objective of the thesis is the study of mechanical properties, microstructure development and corrosion resistance of technical purity copper and Cu-0.18 wt.% Zr polycrystals prepared by ECAP. The tensile tests showed that the characteristic stresses 0,2 and max increase with increasing strain imposed by ECAP. The improvement of mechanical properties is compensated by the drop of ductility in the deformed state. The microstructure after 8 passes of ECAP is almost homogeneous consisting of equiaxed grains of the average size of 200 nm. The severe plastic deformation resulted in the grain size reduction of the factor of 1000. The specimen after 8 passes contains almost 50% of high angle grain boundaries. From the thermodynamic viewpoint the deformation did not change significantly the corrosion properties. However, the corrosion in the deformed material is slower and much more homogeneous.
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The hip fracture register, optimalization of hip hemiarthroplasty position
Skála - Rosenbaum, Jiří ; Bartoníček, Jan (advisor) ; Chomiak, Jiří (referee) ; Janeček, Miloš (referee)
The study examines the monocentric epidemiological data of patients with hip fractures from 1997-2007. Adult patients treated for hip fracture between the years 1997-2007 were included in the study. Retrospective statistical assessment of continually gathered data focused on epidemiology and demographics. The second part of the study was concerned on risk factors on protrusion of hemiarthroplasty into the acetabulum. The goal was to specify exact indication, proper operative technique and selection of the implant. The study involved 3 683 patients (2 678 women, 1 005 men). Patients older than 70 years accounted for 82 % of all cases. There was an increase in the number of hip fractures resulting in a significant increase in pertrochanteric fractures (AO-31A1+2) (p<0.001). The ratio of trochanteric to neck hip fractures increased from 0.99 to 1.53. Continual monitoring of patients with hip fracture offers data which allows comparisons between regions and countries. The importace of a continual increase in the number of hip fractures has its importance in macroeconomical planning in traumatology. Hemiarthroplasty was conversed to total hip arthroplasty in 12 patients in our department. The indication, time period to conversion and hemiarthroplasty position were retrospectively assessed. The direction of...
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Study of mechanical properties and microstructure development of fine-grained Cu and Cu alloy polycrystals
Srba, Ondřej ; Janeček, Miloš (advisor) ; Hadzima, Branislav (referee)
The objective of the thesis is the study of mechanical properties, microstructure development and corrosion resistance of technical purity copper and Cu-0.18 wt.% Zr polycrystals prepared by ECAP. The tensile tests showed that the characteristic stresses 0,2 and max increase with increasing strain imposed by ECAP. The improvement of mechanical properties is compensated by the drop of ductility in the deformed state. The microstructure after 8 passes of ECAP is almost homogeneous consisting of equiaxed grains of the average size of 200 nm. The severe plastic deformation resulted in the grain size reduction of the factor of 1000. The specimen after 8 passes contains almost 50% of high angle grain boundaries. From the thermodynamic viewpoint the deformation did not change significantly the corrosion properties. However, the corrosion in the deformed material is slower and much more homogeneous.
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