Wyniki 1-3 spośród 3 dla zapytania: authorDesc:"ANDREA KOVÁČOVÁ"

Impact of strain rate on Cu mechanical properties

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Materials with ultrafine-grained (UFG) structure have been studied in the last few years because of their unique properties. The main feature of UFG metals is grain size diameter which is below as 1 μm. Considering that grain size reduces to nanometer range, the materials exhibit unique mechanical and physical properties. They have high strength and wear resistance, good ductility at room temperature and superplasticity at elevated temperature [1, 2]. At the same time they have demonstrated properties as a decrease in the elastic moduli, the decrease of the Curie temperature, enhanced diffusivity and improved magnetic properties [1, 3, 4]. The severe plastic deformation methods have been applied to UFG materials formation. The ECAP, ECAP-BP, HPT, ARB are well known technologies nowadays and have been successfully used to structure formation with grain size ~70÷500 nm [5÷7]. The unique properties of UFG metals are connected with specific microstructures features. The UFG microstructure created during SPD processes is formed by dislocations arrangement - “dislocation cell structure“ having mostly low angle boundaries [8]. Based on Valiev’s study [1], during metal processing via SPD great amount of dislocations is introduced to material resulting in high level of internal stresses and elastic distortion of crystal lattice near a boundary. Consequently, the grains boundaries are in the non-equilibrium state and deformation mechanism as grain boundary sliding and grain rotation would be enhanced. The final UFG structure contains huge amount of grain boundaries with mainly high-angle misorientations [9]. The small grain size and great density of defects (as dislocations, vacancies, triple junctions) in UFG materials cause higher strength properties achievement. At the same time, some experimental results show occurrence of superplasticity at lower temperature as well as at high strain rate in UFG metals [10, 11[...]

Mathematical simulation of deformation behaviour in Equal Channel Angular Rolling process

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During the last decade, fabrication of bulk nanostructured metals and alloys using severe plastic deformation (SPD) has been evolving as a rapidly progressing direction of modern materials science that is aimed at developing materials with new mechanical and functional properties for advanced application [1]. The principle of these developments is based on grain refinement down to the nanoscale level in bulk billets using SPD. Ultra-fine grained material produced by IPD are characterized by increased value of strength, fatigue properties and mechanical properties of superplasticity. These properties depend from nanosize grain structure, its distribution in the material, stress, texture and other structural properties. The authors [2] highlighted the important fact, that the evolution of structure during the IPD is not related to the transformation of the microstructure of UFG structure with high angled grain boundaries. After IPD using, nanosize structure polyhedral materials is achieved, by dislocations slides, or dislocations rotations inside grains and slides on grain boundaries [3, 4]. Various processes of intensive plastic deformations have been proposed for the process of drafting the UFG materials using a simple slip. The application of severe plastic deformation (SPD) to conventional polycrystalline metals provides a powerful tool for refine the grain size to the submicrometer or nanometer range [1]. Ultra-fine grained materials (UFG, grain size less than ~1 μm) with unique mechanical and physical properties can be produced by severe plastic deformation [5÷11], such as a noble technique called equal channel angular rolling (ECAR). Lee et al. [12] proposed that Φ can be adjusted from 100° to 140° for producing ultra-fine grains with high angles of mi[...]

The influence of thermomechanical processing conditions on magnetic properties of electrical steels DOI:10.15199/24.2015.8.9

  The paper deals with the influence of thermomechanical treatment on properties of non-oriented electrical steels processed at cryogenic and ambient temperature. The main objective of research was to determine the effect of annealing conditions on magnetic properties in samples processed by rolling at cryogenic temperature. From customers‘ point of view, there are high demands on the magnetic properties of products made of electrical steels, such as high magnetic induction, low coercive force and low magnetic losses. Experimental results revealed that mechanism of plastic deformation during cryogenic rolling is different than during rolling at ambient temperature. A great amount of defor- . deformation twins has been found in the sample subjected to cryogenic rolling. Moreover, the advanced magnetic properties after annealing was obtained in the cryo-rolled sample thanks to the presence of preferable texture (greater portion of a cubic component) and optimal grain size. W artykule przedstawiono analizę wpływu obróbki cieplno-plastycznej na właściwości stali elektrotechnicznych o ziarnie niezorientowanym, przetwarzanych w temperaturze kriogenicznej i pokojowej. Głównym celem badań było określenie wpływu warunków wyżarzania na właściwości magnetyczne próbek walcowanych w warunkach kriogenicznych. Wyroby ze stali elektrotechnicznych muszą charakteryzować się odpowiednimi właściwościami magnetycznymi, tzn. dużą indukcją magnetyczną, małą siłą koercji i niskimi stratami magnetycznymi. Wyniki eksperymentów wykazały, że mechanizm odkształcenia plastycznego podczas walcowania kriogenicznego jest inny niż w przypadku walcowania w temperaturze pokojowej. Ujawniono dużą ilość bliźniaków odkształcenia w próbce poddanej walcowaniu w warunkach kriogenicznych. Ponadto, po wyżarzaniu w próbce walcowanej w temperaturze kriogenicznej osiągnięto poprawę właściwości magnetycznych, dzięki obecności korzystnej tekstury (większej ilości sześciennej składowej t[...]

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