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Study of deformation processes in hexagonal materials
Čapek, Jan ; Mathis, Kristián (advisor) ; Karlík, Miroslav (referee)
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation.
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Mechanical properties of pre-compressed Mg-Zn-Ca alloy
Hegedüs, Marius ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
In wrought Mg alloys, their hexagonal closed packed structure together with a pronounced basal texture lead to anisotropy of mechanical properties. This bachelor thesis is focused on understanding the influence of previous deformation with further relaxation and/or additional heat treatment on deformation behaviour of the extruded Mg-Zn-Ca alloy. The significant influence of twins formed after pre-compression on mechanical properties was investigated. Evolution of microstructure, especially a formation of twins, is observed by light and scanning electron microscopy. The acoustic emission technique is used to determine active deformation mechanisms: dislocation slip and twinning. The results can be used for developing Mg alloys with enhanced properties.
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Study of deformation processes in hexagonal materials
Čapek, Jan
The deformation mechanisms of commercially pure magnesium using advanced in-situ methods were investigated in the present work. Compression and tensile test were done at room temperature. Simultaneously, the neutron diffraction was measured and the acoustic emission was recorded. The microstructure of the deformed material was also studied by means of optical microscopy and electron back-scattered diffraction. These measurements provided information about twin nucleation and growth, microstructure changes and the influence of the orientation of grains on the number of twins and their shape. The values obtained were compared to the Elasto-Plastic Self-Consistent model, which provides information about the activity of deformation mechanisms. We focused on clarifying the influence of twinning activity on asymmetry between tensile and compression deformation. Powered by TCPDF (www.tcpdf.org)
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Investigation of deformation mechanisms in textured magnesium alloy
Dittrich, J. ; Čapek, J. ; Knapek, Michal ; Minárik, P.
Advanced in-situ and ex-situ methods were used to reveal active deformation mechanisms during deformation of magnesium alloy with a strong texture. Three sets of samples were prepared from the rolled sheet of commercial AZ31 alloy with respect to its strong basal texture - normal direction (ND), rolling direction (RD) and 45 degrees between RD and ND, and were deformed in both compression and tension. The signal of acoustic emission (AE) was measured concurrently during the deformation. Electron backscattered diffraction (EBSD) was used to study the microstructure after the selected stages of the deformation. It is shown that the extension twinning played an important role during the plastic deformation in the samples having favorably oriented basal texture component, whereas in the unfavorably oriented samples, the role of twinning was marginal. Pronounced activation of twinning only in some samples caused a considerable variation in the deformation behavior and AE response. A consistent link between the energy and amplitudes of the AE signal and the microstructure changes investigated by EBSD was established.
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Mechanical properties of WN43 magnesium alloy prepared by spark plasma sintering
Knapek, Michal ; Minárik, P. ; Greš, A. ; Zemková, M. ; Cinert, Jakub ; Král, R.
The spark plasma sintering (SPS) method was used to prepare bulk materials form WN43 magnesium alloy atomized powder. Compression tests were carried out in order to investigate the effect of different sintering regimes (10 min at 400, 450, or 500 degrees C) on the mechanical properties of the material. Furthermore, complementary in-situ acoustic emission (AE) recording was employed to reveal the dynamics of deformation processes during compression. It was shown that by increasing the sintering temperature, the ultimate compressive strength and ductility were significantly improved. The AE data and microstructure observations suggest that pronounced twin nucleation takes place around the yield point whereas twin growth and dislocation activity are the dominant deformation mechanisms in the later stages of deformation.
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Computer modeling of twin-boundaries in shape memory alloys
Heczko, Martin ; Pokluda, Jaroslav (referee) ; Zelený, Martin (advisor)
This Master‘s thesis is focused on theoretical study of twinning in magnetic shape memory alloys based on Ni2MnGa using ab initio calculations of electronic structure within the projector augmented wave method. In particular, the effect of increasing concentration of manganese at the expense of gallium was studied on total energy and stress profiles along different deformation paths in the (10-1)[101] shear system of non-modulated martensite. Further, this work deals with the effect of the concentration of manganese on the energy of planar fault caused by presence of partial dislocation due to motion of twin boundary. The results show that the shear modulus in studied shear system increases with the increasing concentration of manganese as well as energy barrier and deformation characteristics along shear deformation paths increases, which makes the shear more difficult in Mn-rich alloys. Increasing concentration of manganese also leads to rising the planar fault energy. All these effects can be responsible for lower mobility of twin boundaries in alloys with higher concentration of manganese.
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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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Mechanical properties of pre-compressed Mg-Zn-Ca alloy
Hegedüs, Marius ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
In wrought Mg alloys, their hexagonal closed packed structure together with a pronounced basal texture lead to anisotropy of mechanical properties. This bachelor thesis is focused on understanding the influence of previous deformation with further relaxation and/or additional heat treatment on deformation behaviour of the extruded Mg-Zn-Ca alloy. The significant influence of twins formed after pre-compression on mechanical properties was investigated. Evolution of microstructure, especially a formation of twins, is observed by light and scanning electron microscopy. The acoustic emission technique is used to determine active deformation mechanisms: dislocation slip and twinning. The results can be used for developing Mg alloys with enhanced properties.
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Investigation of basic deformation mechanisms of magnesium alloys by means of advanced in-situ methods and theoretical modeling
Čapek, Jan ; Mathis, Kristián (advisor) ; Landa, Michal (referee) ; Šiška, Filip (referee)
The work is focused on developing testing methods for investigating of the deformation mechanisms of magnesium alloys. The work involves the measurement of in-situ acoustic emission and neutron diffraction and comparison to the theoretical models. Mg + 1wt.% Zr alloy was selected for investigation of the compression - tension asymmetry. Advanced analysis of acoustic emission and neutron diffraction data revealed activation of different slip systems during deformation. Moreover, the different evolution of twinning was explained. The same methods were used to investigate the aluminum influence on deformation mechanisms. The hardening of basal slip and twinning and increasing importance of prismatic slip was observed.
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