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Twinning Evolution as a Function of Loading Direction in Magnesium

100%
Čapek J., Stráská J., Clausen B., Máthis K.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
762-764
EN
The twinning activity in random textured cast magnesium during monotonic, room temperature tension and compression tests was monitored by neutron diffraction. Decrease of integrated intensity which characterizes the twinned volume fraction of selected reflections was compared to its Schmid factor. The comparison shows that twinned fraction correlates with the maximum value of the Schmid factor with high precision during tensile test and with the average value of the Schmid factor during compression test.
2
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Properties of Biodegradable Alloys Usable for Medical Purposes

100%
Kubásek J., Vojtěch D., Čapek J.
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EN
Magnesium alloys are promising materials for production of biodegradable implants that may be used for fixation of fractured bones. Magnesium itself is an essential element that plays important roles in many biological processes. However, some common alloying elements of magnesium alloys such as aluminium or copper may cause health problems to the organism. A major problem is the high corrosion rate of magnesium and its alloys in physiological environment that contains chloride anions. Currently, the research focuses on alloys doped by rare-earth elements and zinc. All these elements affect corrosion resistance and mechanical properties of magnesium alloys. This work was dealing with the study of Mg-Gd binary alloy and Mg-Gd-Y, Mg-Gd-Zn ternary alloys that were prepared from pure metals by melting in induction furnace. Various alloy compositions were tested. Corrosion behaviours in 9 M NaCl saline environments (exposure tests, potentiodynamic measurements) were studied on alloys in the cast state. Good corrosion resistance and uniform corrosion were observed in the case of binary Mg-Gd alloy. The influence of the addition of Y or Zn to the Mg-Gd system is discussed.
3
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Analysis of Structure Transformations in Rail Surface Induced by Plastic Deformation via Barkhausen Noise Emission

88%
Neslušan M., Zgútová K., Kolařík K., Šramek J., Čapek J.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1099-1101
EN
This paper reports about magnetic Barkhausen noise emission of the rail surface exposed to long time cyclic plastic deformation. Severe plastic deformation of the rail surface induces remarkable structure transformations and alterations of stress state which contribute to valuable decrease of the Barkhausen noise emission compared to untouched surface of the rail. The paper analyses correlation between the Barkhausen noise signals (as well as extracted Barkhausen noise envelopes) and surface state (expressed in terms of micrographs, microhardness readings and residual stresses). This study would contribute to a possible concept for preventing unexpected rails deformation (or cracking) due to their thermal dilatation via the Barkhausen noise technique.
4
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Neutron Diffraction Studies of a Fully Asymmetric Diffraction Geometry of a Bent Perfect Crystal with the Output Beam Compression

88%
Mikula P., Vrána M., Šaroun J., Em V., Čapek J.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
1114-1117
EN
In this paper studies of neutron diffraction properties of the double crystal (+n,-m) setting of a bent perfect crystal Si(311) in the fully asymmetric diffraction geometry with the output beam compression and the bent perfect crystal Si(220) in a symmetric diffraction geometry, are presented. The properties of the (+n,-m) setting were studied for different curvatures of the individual crystal slabs. It has been found that after a beam condensation this fully asymmetric diffraction geometry can provide a monochromatic beam of a small width and of a practical use.
5
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Effect of Loading Mode on the Evolution of the Dislocation Structure in Magnesium

76%
Máthis K., Gubicza J., Csiszár G., Čapek J., Clausen B., Šíma V., Lukáš P.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
700-703
EN
The evolution of the dislocation structure in randomly textured cast magnesium as a function of loading mode is studied using whole neutron diffraction pattern line profile analysis and elasto-plastic self-consistent modeling. Both the experimental results and the theoretical data indicate the onset of basal slip at low stresses and the key role of prismatic slip in the macroscopic yield. Dependence of the second-order pyramidal slip on the loading mode is revealed.
6
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Alpha Variant Selection Determined from Grain Misorientations in Ti-6Al-7Nb Alloy with a Duplex Microstructure

76%
Harcuba P., Václavová K., Čapek J., Stráský J., Janeček M., Janovská M.
Acta Physica Polonica A
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2015
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vol. 128
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issue 4
570-573
EN
Titanium occurs in two structures; a high temperature body-centered cubic structure which is known as β phase and an ambient temperature α phase which has the hexagonal closed-packed structure. In the present study a biomedical Ti-6Al-7Nb alloy was investigated. The so-called duplex structure consisting of α lamellae and equiaxed primary α-grains was prepared by a thermal treatment. The α lamellae are created during cooling from a β-field according to the Burgers relation. This relation allows the formation of the α lamellae with different crystallographic orientations - so-called variants. The preferential misorientation between α lamellae was studied by a detailed electron backscattered diffraction analysis. The misorientation of grains in the duplex structure was modelled by a sum of random Mackenzie distribution and Gaussian peaks related to the preferred misorientations according to the Burgers relation. The preferred misorientations based on the Burgers relationship were identified in the biomedical Ti-6Al-7Nb alloy with duplex structure. It is confirmed that the variant selection of α lamellae is not random.
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