Wyniki wyszukiwania - Biblioteka Nauki

1

Eutectic Structures Competition in the Stripes Strengthening the (Zn) – Single Crystal

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Wołczyński W. , Kjelstrup S. , Bedeaux D. , Szajnar J. , Billia B.

Archives of Foundry Engineering

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2014

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tom Vol. 14, iss. 4

95--102

EN

Some eutectic stripes have been generated in a hexagonal (Zn) - single crystal. The stripes are situated periodically with the constant inter stripes spacing. The eutectic structure in the stripes consists of strengthening inter-metallic compound, Zn16Ti, and (Zn) – solid solution. The rod-like irregular eutectic structure (with branches) appears at low growth rates. The regular lamellar eutectic structure is observed at middle growth rates. The regular rod-like eutectic structure exists exclusively in the stripes at some elevated growth rates. A new thermodynamic criterion is recommended. It suggests that this eutectic regular structure is the winner in a morphological competition for which the minimum entropy production is lower. A competition between the regular rod-like and the regular lamellar eutectic growth is described by means of the proposed criterion. The formation of branches within irregular eutectic structure is referred to the state of marginal stability. A continuous transitions from the marginal stability to the stationary state are confirmed by the continuous transformations of the irregular eutectic structure into the regular one.

2

Wpływ warunków krystalizacji na powstawanie defektów w kryształach czteroboranu litu

100%

Kisielewski J. , Świrkowicz M. , Gałązka Z. , Szyrski W.

Materiały Elektroniczne

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1998

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tom T. 26, nr 2

55-62

PL

Zbadano wpływ warunków krystalizacji na zdefektowanie kryształów czteroboranu litu. Prze-prowadzono badania optyczne uzyskanych monokryształów oraz oszacowano w nich naprężenia. Ustalono wymagania, które muszą być spełnione, aby monokrysztaty odpowiada ty jakością materiałowi podłożowemu dla akustycznych fal powierzchniowych.

EN

Thermal system with 70 mm diameter platinum crucible was constructed and the optimal growth condictions for LBO were found. Lithium tetraborate single crystals obtained earliery were used as a charge material. Core-free single crystals also free of other macroscopic defects were obtained in case of diameter not higher than 20 mm. Optical measurements were undertaken and also trains were estimated.

3

Wzrost i właściwości scyntylacyjne monokryształów LuAlO3

100%

Gałązka Z. , Wojtowicz A. , Szyrski W. , Łukasiewcz T. , Drozdowski W. , Szupryczyński P. , Wiśniewski D.

Materiały Elektroniczne

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2002

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tom T. 30, nr 1-2

20-28

PL

Opracowano nową technikę wzrostu kryształów LuAP metodą Czochralskiego, która umożliwia uzyskanie struktury perowskitu bez jakiejkolwiek domieszki szkodliwej dla scyntylacji fazy granatu. Zmierzone właściwości scyntylacyjne potwierdzają wysoką jakość optyczną uzyskanych krystałów, krótki czas zaniku impulsu scyntylacyjnego, oraz możliwość znacznego zwiększenia wydajności scyntylacji w porównaniu do opublikowanych wartości [2-6].

EN

New techniqe of growth of LuAP crystals by the Czochralski method has been worked out. The technique enable one to obtain perovskite structure without any garnet phase which is harmful for scintillating process. Measured scintillation properties confirm high optical quality of the obtained crystals, short decay constant of scintillating pulse, and possibility of large increase of light yield in comparison to published values [2-6].

4

The development of lec technology for GaAs single crystal growth from laboratory scale to mass production

100%

Jurisch M. , Eichler S.

Materiały Elektroniczne

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2003

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tom T. 31, nr 1-2

7-17

EN

Mass production of SI GaAs single crystals based on an advanced LEC growth process has been established during the last decade of the last century. Two key issues had to be solved : Scaling up of the growth equipment and carbon control. The progress in modelling of thermal heat transfer (radiation, conduction and turbulent convection) due to high computer power and advanced codes has made it possible to optizme the equipment and the processes in rather short time and at lower costs.

5

Microstructure Evolution and Texture Development in a Cu-8.5%AT. AL Material Subjected to Hydrostatic Extrusion

100%

Jakubowska D. , Zdunek J. , Kulczyk M. , Mizera J. , Kurzydłowski K. J.

Archives of Metallurgy and Materials

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2016

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tom Vol. 61, iss. 2B

933--936

EN

The aim of the present paper was to investigate microstructure and texture evolution of two single crystals and polycrystal of Cu-8.5%at.Al material. All of mentioned samples were deformed by HE to achieve true strain ε = 1.17. For microstructure analyzes observations by transmission electron microscope (STEM) were done. Crystalline size for samples after SPD were determine using XRD method. The global texture measurements were done using Bruker D8 Discover diffractometer equipped in Cr radiation. Microstructure investigations revealed nanocrystalline structure in single crystals with initial orientations <110> and <100> and polycrystalline Cu-8.5%at.Al material after SPD. The global texture measurements have shown the stability of initial orientation of <100> Cu-8.5%at.Al single crystal after HE, whereas the same SPD process strongly brakes up the orientation <110> Cu-8.5%at. Al single crystal.

6

Thermodynamical theory of inelastic single crystals

100%

Perzyna P.

Engineering Transactions

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2002

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tom Vol.50, iss.3

107-164

EN

The paper aims at the development of the thermodynamic theory of elasto-viscoplasticity of single crystals which takes account of the evolution of the dislocation substructure. The next objective is the application of the theory developed for the investigation of the adiabatic shear-band formation in single crystals under dynamic loading processes. The description of the kinematics of finite elasto-viscoplastic deformations of single crystal is based on notions of the Riemannian space of manifolds and the tangent space. A multiplicative decomposition of the deformation gradient is adopted and the Lie derivative is used to define all objective rates for the introduced vectors and tensors. A general constitutive model is developed within the thermodynamic framework of the rate-type covariance constitutive structure with finite set of the internal state variables, and takes account of the effects as follows: (i) thermomechanical coupling; (ii) influence of covariance terms, lattice deformations and rotations and plastic spin; (iii) evolution of the dislocation substructure; (iv) deviation from the Schmid rule of a critical resolved shear stress for slip; (v) rate sensitivity (viscosity). A notion of covariance is understood in the sense of invariance under arbitrary spatial diffeomorphisms. The developed thermoviscoplasticity theory of single crystals is based on the axioms as follows: (i) existence of the free energy function; (ii) invariance with respect to any diffeomorphism (any superposed motion); (iii) assumption of the entropy production inequality; (iv) assumption of the evolution equations for the internal state variables in the particular rate-dependent form. To describe the evolution of the dislocation substructure, a finite set of the internal state variables is interpreted as follows: the density of mobile dislocations, the density of obstacle dislocations and the concentration of the point defects. Physical foundations and experimental motivations are given. Two fundamental constitutive equations of the rate-type for the Kirchhoff stress tensor and temperature are formulated. To show that the thermodynamic theory of viscoplasticity of single crystals takes account of all the mentioned effects, an analysis of the thermomechanical couplings and internal dissipation is presented. Particular attention is focused on synergetic effects, generated by cooperative phenomena of thermomechanical couplings and the influence of the evolution of the dislocation substructure. The initial boundary value problem (the evolution problem) for rate-dependent elasto-plastic single crystal has been proved to be well posed. Criteria for adiabatic shear-band localization of plastic deformation are obtained by assuming that some eigenvalue of the instantaneous adiabatic acoustic tensor for rate-independent response is equal to zero. The formation of the adiabatic shear-band is investigated. It has been found that the synergetic effects generated by cooperative phenomena of thermomechanical couplings and the influence of the evolution of the dislocation substructure play a fundamental role in the inception of localization. The results obtained are compared with available experimental observations.

7

Growth and EPR properties of KSm(WO4)2 and KEr(WO4)2 single crystals

100%

Leniec G. , Skibiński T. , Kaczmarek S. , Iwanowski P. , Berkowski M.

Open Physics

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2012

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tom 10

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nr 2

500-505

EN

Growth conditions and electron paramagnetic resonance investigations of two well oriented KSm(WO4)2 and KEr(WO4)2 single crystals have been presented and discussed. Hyperfine structure of Sm3+ ion was detected and analyzed for angular and temperature dependences. EPR spectra of KEr(WO4)2 and its angular dependence showed the presence of 5 magnetically nonequivalent Er centers in the crystal. A change in the type of magnetic interactions was analyzed using mixed (Gaussian and Lorentzian) fits of the EPR spectra.

8

EPR and optical properties of KYb(WO4)2 and KTb0.2Yb0.8(WO4)2 single crystals

100%

Kaczmarek S. , Macalik L. , Fuks H. , Leniec G. , Skibiński T. , Hanuza J.

Open Physics

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2012

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tom 10

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nr 2

492-499

EN

Well oriented KYb(WO4)2 and KTb0.2Yb0.8(WO4)2 single crystals have been investigated for their magnetic and optical properties using the Raman and EPR techniques. The registered EPR signal is dominated by three lines ascribed to ytterbium ions: one main and two satellites. Tb ions, although non-paramagnetic, distinctly modify magnetic properties of the KYb(WO4)2 single crystal. Basic parameters of the spin Hamiltonian, including Zeeman and hyperfine terms (g and A matrices) as well the spatial orientation between principal and crystallographic axes systems were determined for both crystals.

9

Temperature dependence of Bi4Ge3O12 photoluminescence spectra

100%

Kaczmarek S. M. , Tsuboi T. , Nakai Y. , Berkowski M. , Huang W. , Kowalski Z.

Materials Science Poland

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2014

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tom Vol. 32, No. 1

7--11

EN

Bi4Ge3O12 single crystals were obtained using Czochralski growth method. Photoluminescence spectra were analyzed versus temperature from 12 to 295 K. Besides the previously observed emission bands at 610 and 820 nm, the new emission band at 475 nm was found by a careful temperature dependence measurement in the present study. The influence of basic and defect structure on the shape and position of the spectra versus temperature was discussed.

10

Czochralski-Based Growth and Characteristics of Selected Novel Single Crystals for Optical Applications

100%

Shimamura K. , Víllora E. G.

Zeszyty Historyczne Politechniki Warszawskiej

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2014

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tom z. 16

113--121

EN

In the Year of Professor Jan Czochralski, we with pleasure review the representative recent works of our group, Optical Single Crystals Group, NIMS, Japan. Our group has been working on the development of novel single crystals for optical applications based on the Czochralski technique. Here, 4 kinds of topics are reviewed. 1st one is ferroelectric fluoride BaMgF4 single crystals for UV nonlinear optical applications including quasi-phase matching device fabrications. 2nd one is transparent conductive β-Ga2O3 single crystals as semiconductor, which has large band-gap, 4.8 eV, for LED applications. 3rd one is F-doped core-free Y3Al5O12 single crystals as a potential new lens material for UV/VUV wavelength region. Last one is superior magneto-optical {Tb3}[Sc2-xLux](Al3)O12 single crystals for near infrared to visible region, and CeF3/PrF3 single crystals for UV region.

11

A single crystal EPR study of {CuCl(C6H9N3O3)2xH2O}2Cl2

100%

Wojakowska H. , Januszczyk M. , Pietrzak J.

Bulletin of the Polish Academy of Sciences. Chemistry

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2000

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tom Vol. 48, No. 2

117-123

EN

Single crystal of the [CuCl(C6H9N3O3)2 o H2O}2C12 was studied by EPR in 9.4 GHz at room temperature. The components of the g tensor were found to be gc* = 2.241, 0j = 2.094 and ga = 2.062. Since the local symmetry at the cupric ion site is no lower than rhombic, the EPR results were interpreted in terms of the theory for axial symmetry (4 + 1). A consistent explanation of the EPR and optical data is discussed. A comparison of experimental and theoretical resonance line widths suggests that the magnetic system is zero dimensional and the dominant superexchange interaction involves next-nearest neighbour Cu(II) ions.

12

Magnetic properties of Dy5Pd2 single crystal

100%

Klimczak M. , Talik E. , Kusz J. , Hofmeister W. , Winiarski A. , Troć R.

Materials Science Poland

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2007

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tom Vol. 25, No. 2

263--267

EN

Thermal variation of the lattice parameters, magnetic susceptibility and magnetization of a Dy5Pd2 single crystal has been measured. The single crystal obtained by the Czochralski method crystallized in the cubic Dy5Pd2 type structure. The compound exhibits two characteristic temperatures. The former equals about 40 K, and the latter about 20 K, being connected with the complex ordering of the rare earth sublattice and the reorientation process of the magnetic moments, respectively.

13

Synthesis, Characterization and Thermal Decomposition of a New Energetic Salt of 1H,1′H-5,5′-Bistetrazole-1,1′-diol

100%

Xiao L. , Jin B. , Shang Y. , Liu Q. , Guo Z. , Peng R.

Central European Journal of Energetic Materials

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2018

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tom Vol. 15, no. 3

405--419

EN

1,1-Dimethylbiguanidium 1H,1′H-5,5′-bistetrazole-1,1′-diolate (MGBTO), a novel nitrogen-rich energetic salt, was synthesized by cation exchange. Its structure was characterized by elemental analysis, FTIR, NMR, DTA and TG-DTG. Single crystal X-ray diffraction analysis revealed that MGBTO was crystallized in the monoclinic space group C2/c. Thermal analysis demonstrated that its thermal stability extended up to 531.1 K. The nonisothermal kinetic and apparent thermodynamic parameters of the exothermic decomposition of MGBTO were determined by the Kissinger and Ozawa methods. Its detonation velocity and detonation pressure were calculated on the basis of the Kamlet-Jacobs equation and were 6342 m·s–1 and 15.78 GPa, respectively. The impact and friction sensitivities of MGBTO were quantified using standard BAM (10 kg drop hammer) procedures. The results revealed that the salt has good mechanical sensitivity (FS > 120 N, IS > 40 J), thus indicating its potential applications as an energetic material.

14

Czochralski growth of SrLaAlO4 and SrLaGaO 4 single crystals and its implications for the crystal morphology

100%

Pajaczkowska A. , Gloubokov A. , Klos A. , Woensdregt C. F.

Zeszyty Historyczne Politechniki Warszawskiej

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2014

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tom z. 16

85--89

EN

Single crystals of SrLaAlO4 (SLA) and SrLaGaO4 (SLG) have been grown from nonstoichiometric melts by the Czochralski method making use of different seed orientations, [100] (SLA, SLG), [110] (SLA) and [001] (SLG). The anisotropic properties of the crystal structure are reflected in the growth morphology of the crystals. In the case of (SLA) {101} facets appear at the crystal/melt interface and in that of [100] SLG {101} and {103} facets occur, while for [001] SLG {001} and {103} facets are present. SLA crystals are very similar to the theoretical growth forms computed according to the Hartman-Perdok theory for models with an effective charge on oxygen, qO −2|e|. However the habit of SLG crystals corresponds better to the theoretical growth forms based on an effective charge qO = −1.5|e| due to the presence of oxygen vacancies.

15

Growth, optical and EPR properties of Li1.72Na0.28Ge4O9 single crystals pure and slightly doped with Cr

88%

Jasik A. , Berkowski M. , Kaczmarek S. , Suchocki A. , Kaminska A. , Leniec G. , Nowakowski P. , Domukhovski V.

Open Physics

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2012

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tom 10

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nr 2

506-513

EN

Single crystals of lithium-sodium-tetragermanate, a member of the solid solution series Li2−xNaxGe4O9 with x=0.28, pure and slightly doped with Cr3+ ions (0.03 mol.% and 0.1 mol.%), were grown in ambient atmosphere by the Czochralski technique from stoichiometric melt. The crystals with dimensions up to 20 mm in diameter and 50 mm in length were obtained. The crystal structure has been determined by means of X-ray diffraction. Phase analysis and structural refinement of the Li1.72Na0.28Ge4O9 crystals were performed by X-ray powder diffraction using Ni-filtered Cu Kα radiation with a Siemens D5000 diffractometer. The absorption, excitation and photoluminescence spectra of the crystals were measured in the UV-VIS and IR range at low temperatures. EPR investigations were performed using a conventional X-band Bruker ELEXSYS E 500 CW-spectrometer operating at 9.5 GHz with 100 kHz magnetic field modulation. Temperature and angular dependences of the EPR spectra of the crystal samples were recorded in the 3–300 K temperature range.

16

Synthesis and spectroscopic properties of LiIn(WO4)2 nanopowders and single crystals doped with chromium(III) ions

88%

Skibiński T. , Fuks H. , Kaczmarek S. , Bodziony T. , Hermanowicz K. , Maczka M. , Ptak M. , Hanuza J.

Open Physics

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2013

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tom 11

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nr 11

1559-1566

EN

LiIn(WO4)2 single crystals and nanopowders doped with chromium(III) ions were synthesized and investigated, including their EPR spectra and magnetic properties. The EPR spectra have shown low and high field lines attributed to isolated chromium ions with an electron spin S=3/2 and complex chromium centers with higher spin value, respectively. Magnetic susceptibility measurements revealed an almost linear dependence on the magnetic field. The electron resonance and magnetic properties have been related to the structural and spectroscopic data of the studied material.

17

Otrzymywanie i badanie własności optycznych i laserowych monokryształów YAG domieszkowanych Er 3+ i Yb3+

88%

Mierczyk Z. , Kopczyński K. , Gietka A. , Frukacz Z. , Łukasiewcz T. , Kisielewski J.

Materiały Elektroniczne

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1999

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tom T. 27, nr 1-4

13-23

PL

W pracy przedstawiono wyniki badań warunków wzrostu oraz własności optycznych i spektroskopowych kryształów granatu itrowo-aluminiowego domieszkowalnego jonami Er3+ i Yb3+ potencjalnego ośrodka aktywnego laseró bezpiecznych dla oka. Monokryształy YAG:Er3+, Yb3+ otrzymywane były Metodą Czochralskiego. Badanie jakości optycznej otrzymanych kryształów przeprowadzono metodą elastoskopowa i interferometryczną. Wyznaczono widma absorpcji w zakresie spektralnym od 190 do 5000 nm. Badano również widma luminescencji wzbudzonej promieniowaniem emitowanym przez diodę laserową 970nm oraz wyznaczono czasy życia jonów Er3+ na górnym poziomie laserowym.

EN

Erbium and ytterbium doped YAG single crystals were obtained by the Czochralski method. Fundamental conditions of growth of the obtained crystals and the results of optical homogenity measurements are presented. Absorption spectra of Er3+ and Yb3+ doped YAG crystals were measured in a spectral range of 190-5000 nm at room temperature. Excitation and luminescence spectra were also recorded at room temperature with a JOBIN-YVON spectrofluorometer using a diode laser 970 nm as an excitation source. Measurements of lifetime of ER3+ ions in the upper laser level of the samples were made by a direct method with pulse excitation.

18

Electron spin resonance of FeVO4

88%

Bojanowski B. , Kaczmarek S. M.

Materials Science Poland

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2014

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tom Vol. 32, No. 2

188--192

EN

We report on electron spin resonance (ESR) investigations of a FeVO4 single crystal. Temperature and angular dependences of ESR resonance positions were measured and calculated in temperature range of 35 – 100 K. The spectra show rich angular dependences of the linewidth, the shape and the resonance field. They consist of a single broad line with asymmetric distortion. Due to the low symmetry of the crystal lattice this distortion can be explained by taking into account the influence of non diagonal dynamic susceptibility.

19

Wzrost i obróbka monokryształów szafiru o średnicach 1'' i 2''

75%

Hofman W. , Kisielewski J.

Materiały Elektroniczne

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2003

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tom T. 31, nr 3-4

5-38

PL

W pracy omówiono warunki krystalizacji oraz cykl operacji obr6bczych prowadzących do przetworzenia 1" i 2" krysztat6w szafiru as grown orientacji (0001) na jednostronnie polerowane płytki podłożowe przygotowane do osadzania warstw epitaksjalnych. Z uwagi na wysoką temperaturę topnienia (~2054°C) i dużą twardość (2200 kG/mm2) szafiru należało rozwiązać szereg trudnych zagadnień technicznych, wymagających nowatorskiego podejścia. W zakresie wzrostu kryształu kluczowym problemem okazało się opracowanie odpowiedniego układu termoizolacyjnego generującego niskogradientowe pole temperatur nad cieczą.. Zastosowanie relatywnie dużego, czynnego dogrzewacza irydowego okazało się wysoce efektywne w tym względzie. Natomiast w zakresie obrobki najtrudniejszą operacji okazało się ciecie kryształu na płytki. Problem ten rozwiązano minimalizując odcinek bieżącego kontaktu krawędzi tnącej z kryształem (< 1 mm) oraz maksymalizując kąt natarcia krawędzi na wałek szafirowy. Zaproponowany sposób zawęził grubości ciętych płytek do zakresu 0.6 -r 0.7 mm poprawiając tym samym wydajność całego cyklu. Najbardziej czasochłonnym zabiegiem było pocieniająco - wyrównujące szlifowanie po-wierzchni płytek przed polerowaniem. Uzyskane podłoża spełniały wymagania w zakresie parametrów kształtu oraz jakości powierzchni przeznaczonej do epitaksji.

EN

This paper describes the crystallization conditions and the cycle of machining operation that lead to processing of as grown (0001) sapphire crystals into 1" and 2" epiready substrate wafers. On account of high melting temperature (~2054°C) and high hardness (2200 kG/mm2) of sapphire material, several difficult technical problems had to be solved by applying an innovative approach. All work connected with crystal growth was aimed at reduction of temperature gradients above melt what could be achieved by using relative large active afterheater coupled with Ir crucible. On the other hand, slicing of crystal into thin wafers appeared to be the most difficult opera tion among all connected with machining. This difficulty was overcome by applying an original cutting technique that was based on minimization of current contact length between cutting edge and crystal and maximization of tool rake on sapphire cylinder. Above technique permits to reduce wafer thickness to 0.6 - 0.7 mm and allow to rice a yield of cycle considerably. The coarse and fine lapping operations of wafer faces were the most time consumming. All fabricated substrates showed proper shape and good quality of polishing surfaces.

20

A minimal gradient-enhancement of the classical continuum theory of crystal plasticity. Part I: The hardening law

75%

Petryk H. , Stupkiewicz S.

Archives of Mechanics

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2016

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tom Vol. 68, nr 6

459--485

EN

A simple gradient-enhancement of the classical continuum theory of plasticity of single crystals deformed by multislip is proposed for incorporating size effects in a manner consistent with phenomenological laws established in materials science. Despite considerable efforts in developing gradient theories, there is no consensus regarding the minimal set of physically based assumptions needed to capture the slip-gradient effects in metal single crystals and to provide a benchmark for more refined approaches. In order to make a step towards such a reference model, the concept of the tensorial density of geometrically necessary dislocations generated by slip-rate gradients is combined with a generalized form of the classical Taylor formula for the flow stress. In the governing equations in the rate form, the derived internal length scale is expressed through the current flow stress and standard parameters so that no further assumption is needed to define a characteristic length. It is shown that this internal length scale is directly related to the mean free path of dislocations and possesses physical interpretation which is frequently missing in other gradient-plasticity models.