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1

The Internal Friction of Single Crystals, Bicrystals and Polycrystals of Pure Magnesium

Jiang W. B., Kong Q. P., Magalas L. B., Fang Q. F.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 1

371--375

EN

The internal friction of magnesium single crystals, bicrystals and polycrystals has been studied between room temperature and 450°C. There is no internal friction peak in the single crystals, but a prominent relaxation peak appears at around 160°C in polycrystals. The activation energy of the peak is 1.0 eV, which is consistent with the grain boundary self-diffusion energy of Mg. Therefore, the peak in polycrystals can be attributed to grain boundary relaxation. For the three studied bicrystals, the grain boundary peak temperatures and activation energies are higher than that of polycrystals, while the peak heights are much lower. The difference between the internal friction peaks in bicrystals and polycrystals is possibly caused by the difference in the concentrations of segregated impurities in grain boundaries.

PL

Badania tarcia wewnętrznego w monokryształach, bikryształach i polikryształach magnezu przeprowadzono w zakresie temperatur między temperaturą pokojową a 450°C. W monokryształach magnezu nie występuje pik tarcia wewnętrznego, ale wyraźny pik relaksacyjny pojawia się przy około 160°C w polikryształach. Energia aktywacji piku wynosi 1,0 eV, co jest zgodne z energią autodyfuzji Mg przez granice ziaren. Z tego względu pik tarcia wewnętrznego występujący w polikryształach można przypisać relaksacji granic ziaren. W przypadku trzech badanych bikryształów temperatury pików pochodzących od granic ziaren i ich energie aktywacji są wyższe niż w przypadku polikryształów, ale wysokości tych pików są znacznie niższe. Różnica między pikami tarcia wewnętrznego w bikryształach i polikryształach jest prawdopodobnie spowodowana przez różnicę stężeń zanieczyszczeń segregujących na granicach ziaren.

2

Development of numerical tools for the multiscale modelling of recrystallization in metals, based on a digital material framework

Bernacki M., Chastel Y., Digonnet H., Resk H., Coupez T., Logé R.

Computer Methods in Materials Science

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2007

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Vol. 7, No. 1

142-149

EN

This work is currently under development within the framework of an American-European project (Digimat Project) whose principal purpose is to model recrystallization in metals using a multiscale approach. The modelling effort is centered around a digital material framework. This framework is based on a digital representation of the material structure, where data coming from different scales can be stored or probed. The digital representation can be converted into finite element meshes, which are then used to model plastic deformation and subsequent recrystallization. The local behaviour of individual microstructure components is computed through models operating at different scales. In particular, grain constitutive models are derived from crystal plasticity concepts, with appropriate hardening/recovery laws which are linked to lower scale approaches at the dislocation level. Grain boundary motion is similarly described by connecting the continuum mechanical and thermal fields to simulations at the atomistic/dislocations levels. A detailed confrontation of the multiscale approach with experiment will be done at the ESRF synchrotron facility in Grenoble (France). In this paper, the needed development of numerical tools is presented together with the first finite element simulations. The development of the DIGIMAT software, dedicated to the concept of digital material, is first detailed. The construction of the virtual material consists in building a multi-level Voronoi tesselation. A polycrystalline microstructure made of grains and sub-grains can be obtained in a random or deterministic way. The software is at a stage of its development where it is possible to cut the microstructure along given planes, to approximate the grain shapes by a set of fitting ellipsoids, to roughly optimize the digital microstructure, and to generate a coarse mesh of the microstructure at each level of the microstructure (level 1 = external shape, level 2 =grains, level 3 = sub-grains). A second part of the work concerns the first finite elements simulations of a uniaxial compression test under large strain. The initial mesh is fine and anisotropic, taking into account the presence of interfaces between grains and sub-grains. A level-set approach is used to follow the grain boundaries during the deformation. In fact, with this method, the interface is modelled by the zero level-set of a time dependant level-set function which moves according to the mesh velocity field. The most complex test case carried out to date is a multi-domains Stokes problem, deforming at 85\% a cubic Volume Element made of 250 grains. Boundary conditions use a constant velocity in the compression direction, and free motion in the plane perpendicular to that direction. The constitutive law is a viscoplastic power law with a rate sensitivity of 0.2, and a variable hardness from one grain to another. The constitutive law will soon be replaced by a crystallographic formulation. Automatic isotropic and anisotropic remeshing, and parallel computation were successfully implemented, both features being crucial with respect to the Digimat project objectives (large strain to induce recrystallization, and large number of elements for a good representation of the microstructure). Finally, the bases of our first recrystallization simulations will be explained, including the description of nucleation and grain growth.

PL

Praca jest realizowana w ramach Amerykańsko-Europeskiego projektu (Digimat Project). W artykule opisano rozwój numerycznych narzędzi przeznaczonych do cyfrowej reprezentacji struktur metalicznych oraz do generowania powiązanych siatek anizotropowych dla modelowania metodą elementów skończonych dużych odkształceń polikrystalicznych mikrostruktur. Metoda ustalonych poziomów stosowana do opisu mikrostruktury stanowi wspólną bazę dla wszystkich analizowanych rozwiązań.

3

The Voigt bound of the stress potential of isotropic viscoplastic FCC polycrystals

Bohlke T.

Archives of Mechanics

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2004

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Vol. 56, nr 6

425-445

EN

The Voigt bound of the stress potential of face-centered cubic (fcc) polycrystals without texture is numerically determined for all types of strain rate states. The numerical findings reveal the dependence of the stress potential on both the second and the third principal invariant of the strain rate deviator. The dependence on the determinant vanishes only for a linear viscoplastic behavior. Due to the dependence of the stress potential on the third principal invariant, the determinant, the viscoplastic flow is generally nonproportional to the stress deviator. A simple analytical expression is found, which reproduces the numerical findings over the full range of strain rate sensitivities.

4

The influence of nitrogen on the deposition and structure of polycrystalline diamond films

Benzhour K., Patyk J.

Karbo

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2001

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Nr 11

378-381

EN

The structural investigations results have been presented of thin diamond films settled by hot filament method from the mixture of hydrogen, propane-butane and nitrogen. During investigations temperature of substrate was changed in the range from 570 to 800°. The analysis of surface morphology of the obtained thin diamond films with the use if scanning microscopy proved they possess polycrystalline structure with dominating grain size going from (111) to (100) together with increase of additive content (nitrogen). The quality of these films was investigated with the use of Raman spectroscopy.

PL

Przedstawiono wyniki badań strukturalnych cienkich warstw diamentowych osadzanych metodą gorącego włókna z mieszaniny wodoru, pro-panu-butanu i azotu. W czasie badań zmieniano temperaturę podłoża w zakresie od 570 do 800°C. Analiza morfologii powierzchni otrzymanych cienkich warstw diamentowych za pomocą mikroskopii skaningowej dowiodła, że posiadają one strukturę polikrystaliczną o dominującym przekroju ziaren przechodzącym od (111) do (100) w miarę wzrostu zawartości domieszki (azotu). Jakość tych warstw została przebadana przy wykorzystaniu spektroskopii Ramana.

5

XRF analysis of powder microsamples of multielement mono- and polycrystals. Determination of Cr, Mn, Ni, Cu, Zn, Ga, As, Se, Sb, Yb

Jurczyk J., Sitko R., Zawisza B.

Chemia Analityczna

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2000

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Vol. 45, No. 3

415-428

EN

A quick method has been worked out for preparation of powder samples in the sub-microanalytical area for XRF analysis. Investigations were carried out using as an example three- and four-component mono- and polycrystals: CuZnCrSe, ZnGaCrSe, CuNiCrSe, ZnNiCrSe, YbZnSb, YbMnAs, ZnMnAs. The concentrations of elements being determined were in the range: Cu 12-40%, Zn 2.7-28%, Cr 0.8-24%, Se 53-67%, Ni 0.5-13%, Yb 24-49%, Mn 23-37%, As 28-43%, Sb -48%, Ga -0.4%. Powdered and weighed material (0.5 mg) is transferred onto the substrate (a Millipore filter) and a few drops of carbon tetrachloride are dropped. After drying a sample with uniformly distrib-uted material is formed. Then acetone is dropped and after drying at room temperature a Millipore filter forms a smooth thin film with "embedded" grains of the analyzed material. Minimization of matrix effects due to application of thin layer method allows to prepare calibration curves common for various materials. The obtained limits of detection for 0.5 mg samples are, in ug: Cr - 0.34, Mn - 0.22, Ni - 0.20, Cu - 0.29, Zn - 0.32, Ga -0.27, As - 0.37, Se - 0.40, Sb - 1.82, Yb - 1.27.

PL

Opracowano szybką metodę przygotowywania próbek proszkowych w obszarze sub-mikroanalitycznym do analizy XRF. Badania prowadzono na przykładzie trój- i cztero-składnikowych mono- i polikryształów: CuZnCrSe, ZnGaCrSe, CuNiCrSe, ZnNiCrSe, YbZnSb, YbMnAs, ZnMnAs. Oznaczane pierwiastki występowały w zakresie stężeń: Cu 12-40%, Zn 2.7-28%, Cr 0.8-24%, Se 53-67%, Ni 0.5-13%, Yb 24-49%, Mn 23-37%, As 28-43%, Sb -48%, Ga -0.4%. Rozdrobniony i odważony materiał (0.5 mg) przenosi się na podłoże (sączek Millipore) i nakrapla kilka kropel tetrachlorku węgla. Po wyschnięciu z utworzonej zawiesiny tworzy się próbka z równomiernie rozprowadzonym materiałem. Następnie nakrapla się aceton, po wysuszeniu w temperaturze pokojowej sączek Millipore tworzy cienki, gładki film z „wtopionymi" ziarnami analizowanego materiału. Minimalizacja efektów matrycy dzięki zastosowaniu techniki cienkiej warstwy pozwoliła na sporządzenie wykresów kalibracyjnych wspólnych dla różnych materiałów. Uzyskane granice wykrywalności dla próbek o masie 0.5 mg wynoszą w mg: Cr-0.34, Mn-0.22, Ni-0.20, Cu-0.29, Zn-0.32, Ga - 0.27, As - 0.37, Se - 0.40, Sb - l .82, Yb - l .27.

6

A new approach to the analysis of polycrystal plasticity

Peng X., Fan J.

Archives of Mechanics

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2000

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Vol. 52, nr 1

103-125

EN

When a polycrystal is subjected to inelastic deformation, there inevitably exist residual microstress fields in a polycrystalline material due to its nonhomogeneous morphology. The energy stored in these microstress fields may partly be released and influence the material behavior during subsequent inelastic deformation. Correspondingly, a simple mechanical model is introduced to formulate the constitutive equation for a slip system and the hardening law for single crystal. The corresponding approach for the analysis of polycrystalline materials is obtained based on KBW's self-consistent theory. The proposed approach employs no yield criterion and the corresponding numerical analysis is greatly simplified because it involves no additional process for determination of the activation of slip systems and slip direction. A mixed averaging approach is used in polycrystalline plasticity analysis. The response of 316 stainless steel subjected to typical biaxial nonproportional plastic strain cycling is described and the validity of the proposed approach is demonstrated by the satisfactory agreement between the calculated result and experimental observation.

7

Thin sample in the XRF analysis. A new method of preparing microsamples of mono- and polycrystals and of silicate rocks

Jurczyk J., Sitko R., Buhl F., Jendrzejewska I.

Chemia Analityczna

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1999

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Vol. 44, No. 2

167-186

EN

The authors have described a new method ofpreparation ofthin samples, which consists in digesting of the material studied directly on the substrate. Investigations were carried out in the sub- and microanalytical area with mono- and polycrystals of spinel structure (samples' mass from D. I to 1.2 mg), and in the semimicroanalytical area with silicate rocks (samples' mass from 5 to 5D mg). Relative thicknesses of samples as well as errors resulting from the lack of linear relationship between concentration and intensity of radiation have been determined using simple mathematical methods. A simplified method of performing the calibration has been applied by using one standard of diversified masses In the case of submicroanalysis of mono- and polycrystals, a possibility of neglecting the interelement influences allowed for using a linear regres-sion in the calibration. In the semimicroanalytical area (rock analysis), the appropriate mathematical models have been used to improve the results

PL

Autorzy opisali nowy sposób przygotowania cienkich próbek polegający na roztwarza-niu badanego materiału bezpośrednio na podłożu. Badania przeprowadzono w obszarze sub- i mikroanalitycznym na przykładzie mono- i polikryształów o budowie spineli (odważki od D. I do 1.2mg) oraz w obszarze semimikroanalitycznym na przykładzie skał krzemianowych (odważki od 5 do 5Dmg). Stosując proste metody matematyczne wY-znaczono względne grubości próbek oraz blędy wynikające z braku liniowej zależności pomiędzy koncentt.acją a intensywnością promieniowania. Zastosowano uproszczony sposób wykonania kalibracji z wykorzystaniem jednego wzorca o zróżnicowanych masach. W przypadku submikroanalizy mono- i polik1-yształów możliwość zaniedbania wpływów międzypierwiastkowych pozwolił a na wykorzystanie regresji liniowej do kalibracji. W obszarze semimikroanalitycznym (analiza skał) do poprawy wyników wykorzystano odpowiednie modele matematyczne-