Wyniki wyszukiwania - Biblioteka Nauki

1

Structure and properties of dispersion hardened submicron grained copper

100%

Stobrawa J. P. , Rdzawski Z. M. , Głuchowski W.

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2007

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tom Vol. 20, nr 1-2

195-198

EN

Purpose: The objective of the work was to investigate changes in structure and properties of Cu-WC microcomposites which take place in the process of controlled hot deformation of materials of nanometric initial structure. Design/methodology/approach: Tests were made with the Cu-WC micro-composites containing up to 2% of a hardening phase. These were obtained by powder metallurgy techniques and further hot deformation. The mechanical properties and microstructure (by the optical, scanning and transmission electron microscopy) were examined. Findings: Analysis of the initial nanocrystalline structure of these materials was made, and its evolution during hot deformation process was investigated with an account of the changes in the mechanical and electrical properties. Research limitations/implications: The powder metallurgy techniques make it possible to obtain copper-based bulk materials. Globular structure and high porosity of this materials result in their limited mechanical properties. This is the reason why additional operations, should be applied. The investigations have revealed that controlled hot deformation, within the temperature range of 500-550 degrees centigrade, gives possiblity for obtaining submicron grain size and more advantageous mechanical properties of Cu-WC microcomposites. Practical implications: A growing trend to use new copper-based functional materials is observed recently world-wide. Within this group of materials particular attention is drawn to dispersion hardened microcomposites with nanometric or submicron grain size of a copper matrix, which exhibit higher mechanical properties. Originality/value: The paper shows instability of nanostructure of Cu-WC microcomposites in the processes of hot deformation. A controlled process, which can lead to destruction of globular structure, significant improvement of density and obtaining of submikron size, gives possibility for significant improvements in functional properties of the materials.

2

Microstructure and properties of nanocrystalline copper - yttria microcomposites

100%

Stobrawa J. P. , Rdzawski Z. M. , Głuchowski W. J.

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2007

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tom Vol. 24, nr 2

83-86

EN

Purpose: The objective of the work was to investigate changes in structure and properties of Cu-yttria microcomposites which take place in the process of controlled sintering and deformation of materials of nanometric initial structure. Design/methodology/approach: Tests were made with the Cu-yttria micro-composites containing up to 3 % of a hardening phase. These were obtained by powder metallurgy techniques and further deformation. The mechanical properties and microstructure (by the optical, scanning and transmission electron microscopy) were examined. Findings: Analysis of the initial nanocrystalline structure of these materials was made, and its evolution during deformation process was investigated with an account of the changes in the mechanical and electrical properties. Research limitations/implications: The powder metallurgy techniques make it possible to obtain copper-based bulk materials. Globular structure, high porosity and low sintering temperature of this materials result in their limited mechanical properties. Practical implications: A growing trend to use new copper-based functional materials is observed recently world-wide. Within this group of materials particular attention is drawn to dispersion hardened microcomposites with nanometric or submicron grain size of a copper matrix, which exhibit higher mechanical properties. Originality/value: A controlled process of milling compacting, sintering and cold deformation, allow to obtain nanocrystalline copper based materials with improved functional properties.

3

Interaction of point defects in piezoelectric materials - numerical simulation in the context of electric fatigue

84%

Goy O. , Mueller R. , Gross D.

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2006

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tom Vol. 44 nr 4

819-836

EN

The paper is concerned with the problem of electric fatigue in functional materials such as piezoelectric sensors and actuators. The fatigue degrades electromechanical properties with an increasing number of working cycles during which ionic and electronic charge carriers interact with each other within the bulk and on the interfaces of a material. This, in turn, influences local electric and mechanical fields coupled via the piezoelectric effect. It is assumed in the paper that the electric charges (vacancies) can be modelled as point defects, which tend to agglomerate and finally form clusters, especially in the vicinity of electrodes. As a result, the piled up defects affect the distribution of polarisation. To solve the problem quan\-ti\-tatively, the analysed system is discretised with a grid of square cells and then transformed by FFT. Several numerical examples are formulated. Migration of a single defect, attraction of two and clustering of more point defects are thoroughly discussed and illustrated in the paper.

PL

Praca dotyczy zagadnienia zmęczenia elektrycznego materiałów funkcjonalnych, takich jak piezoelektryki używane do wyrobu czujników i elementów wykonawczych. Zmęczenie elektryczne powoduje degradację właściwości elektromechanicznych z rosnącą liczbą przebytych cykli roboczych, w czasie których jonowe ładunki elektryczne lub elektrony oddziaływują ze sobą wewnątrz i na skraju danego materiału. To z kolei wpływa na lokalne pola elektryczne i mechaniczne sprzężone ze sobą efektem piezoelektrycznym. Założono w pracy, że ładunki elektryczne (dziury) będą zamodelowane defektami punktowymi, które mają skłonność do gromadzenia się i tworzenia skupisk, zwłaszcza w pobliżu elektrod. W rezultacie, nagromadzone defekty zmieniają rozkład polaryzacji układu. Do ilościowego rozwiązania zagadnienia zastosowano dyskretyzację badanego układusiecią kwadratowych komórek i następnie przeprowadzono szybką transformatę Fouriera. Obliczenia wykonano na kilku przykładach. Szczegółowo przedyskutowano problem migracji pojedynczego oraz wzajemnego przyciągania dwóch defektów, by wreszcie zilustrować proces tworzenia skupisk przez całe gromady defektów punktowych.

4

Stability of properties in silver - lanthanum alloy

84%

Głuchowski W. J. , Rdzawski Z. M.

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2007

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tom Vol. 24, nr 2

103-106

EN

Purpose: The objective of the work was to investigate changes in structure and properties of Ag+(0,5%wt)La alloy and its difference to the comparative Ag+(7,5%wt)Cu and pure Ag materials. Design/methodology/approach: Tests were made with samples obtained by melting and casting in inductive furnace. Further plastic deformation was provided by KOBO(R) extrusion and drawing. The mechanical properties (at room temperature, elevated temperature and after annealing) and microstructure (by the optical, scanning and transmission electron microscopy) were examined. Findings: Analysis of the initial microstructure of these materials was made, and its evolution during deformation process was investigated with respect to the changes in the mechanical and electrical properties. Research limitations/implications: Significant changes in microstructure after extrusion were observed. Alloy with addition of lanthanum had an excellent electrical conductivity close to the conductivity of pure silver. Mechanical properties examination after annealing gave grounds to conclude that also this alloy had increased properties stability at elevated temperature. Practical implications: Alloy with addition of lanthanum after further investigations could be considered as a material for producing electric or electronic parts which are designed to work in environment of elevated temperature or with a risk of temperature changes. Originality/value: The paper shows properties stability in new designed silver alloy with addition of lanthanum. Wire made of this material could be easy produced with examined methods, without any annealing process. Having stable properties and excellent electrical conductivity this alloy could be considered as a material for producing advanced electrical or electronic equipment.

5

Thermal stability of properties in silver - rare earth metals alloys

84%

Głuchowski W. , Rdzawski Z. M.

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2008

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tom Vol. 28, nr 2

143-150

EN

Purpose: The objective of this work was to investigate the changes taking place in the structure and properties of Ag-La (0.5%) and Ag-mishmetal (1 and 4%) alloys caused by severe plastic deformation compared to the Ag+(7.5 wt %)Cu alloy and pure Ag materials. Design/methodology/approach: Tests were made with the samples obtained casting and further plastic working included KOBO® extrusion process and drawing. Wires were annealed in temperature range 50-500° C. The mechanical properties (at room temperature, elevated temperature and after annealing) and microstructure were examined (by the optical, scanning and transmission electron microscopy with EDS and electron diffraction analysis). Findings: Structure of the extruded material was fine and homogenous. The alloys with an addition of lanthanum or mishmetal had high electrical conductivity, which was decreasing with an increase in the content of alloy additives. Fine coherent precipitates were found on the preferred planes in the silver matrix. Practical implications: The alloy with an addition of La or mishmetal could be considered, after further investigations, as a material suitable for use in the production of electrical or electronic components operating at elevated temperatures or exposed to temperature changes. Originality/value: This work has demonstrated that the properties of newly designed silver alloys with an addition of La or mishmetal exhibit temperature stability. It can be concluded from this study that an addition of rare earth metals to silver gives three main benefits: deoxidation during melting in an open furnace, very fine structure and precipitation hardening. The dispersion hardening with coarse particles (size about several žm) is very small. The wire made from this material could be easily produced by the developed processing methods, without the need to use annealing operations.

6

Silver-mishmetal alloy for application at elevated temperature

84%

Głuchowski W. , Rdzawski Z.

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2008

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tom Vol. 26, nr 2

123-126

EN

Purpose: The aim of this work was to investigate the changes taking place in the structure and properties of silver-mishmetal alloys caused by severe plastic deformation compared to the Ag+(7.5 wt %)Cu alloy and pure Ag materials. Design/methodology/approach: Tests were made with samples obtained by melting and casting in an induction furnace. Further plastic working included KOBO® extrusion process and drawing. The mechanical properties (at a room temperature, elevated temperature and after annealing) and microstructure were examined (by the optical, scanning and transmission electron microscopy). Findings: Structure of the extruded material was fine and homogenous. The alloys with an addition of mishmetal had high electrical conductivity, which was decreasing with an increase in the content of alloy additives. Examination of the mechanical properties has shown that these alloys exhibited (after annealing) an increased stability of properties at elevated temperatures. Practical implications: The alloy with an addition of mishmetal could be considered, after further investigations, as a material suitable for use in the production of electrical or electronic parts operating at elevated temperature or exposed to temperature changes. Originality/value: This work demonstrated that properties of the newly designed silver alloys with an addition of mishmetal exhibit temperature stability. The wire made from this material could be easily produced by the developed processing methods, without the need to use annealing operations. Due to the stable properties and excellent electrical conductivity, this alloy is suitable for use in the production of an advanced electrical or electronic equipment.

7

Methods of preparing polymeric gradient composites

67%

Stabik J. , Dybowska A.

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2007

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tom Vol. 25, nr 1

67-70

EN

Purpose: The goal of this work is to introduce basic methods of preparing polymeric gradient materials, which allow to join two different components to ensure the required properties and structure of the functionally gradient materials. Design/methodology/approach: In this paper few of methods of preparing functionally gradient polymeric materials are briefly described which were successful employed in many investigations performed during last few years. Findings: It was noticed that the knowledge about polymeric gradient materials is still developing what can allow to manufacture new products characterized by unique properties. Research limitations/implications: Most of methods presented in this paper are also used for conventional products, the difference between conventional products and products with gradient are quantity of components, shape and size of reinforcements, and properties of ready materials. Practical implications: Presented methods can be applied in preparing FGMs for future research programmes and also in industrial processes. Originality/value: Techniques are presented that can be useful in future scientific work concerning functionally gradient materials containing polymer materials.