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1

Microstructural characterization and mechanical properties of Mg-xSn-Al-Zn alloys

Kim B., Jeon J., Park K., Park B., Park Y., Park I.

Archives of Materials Science and Engineering

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2008

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Vol. 30, nr 2

93-96

EN

Purpose: In this study, the microstructure and mechanical properties of as-cast Mg-xSn-Al-Zn alloys were investigated. Design/methodology/approach: Ingot was fabricated by a squeeze cast. The alloys were induction melted at 750stopniC in a mild steel crucible under CO2+2%SF6 mixed gas atmosphere and cast into a permanent mould coated with boron nitride spray held at approximately 350 stopniC . Tensile tests were carried out at room temperature in a screw-driven tensile testing machine and crosshead speed was 0.2 mm/min. Microstructural observation was carried out using a optical microscope (OM) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDS). Findings: It is found that the tensile strength and elongation decreased at room temperature increased with Sn concentration. As a consequence, 5wt% Sn addition was the one exhibiting the best tensile properties at room temperature. The micro-hardness of the alloy continuously increased with increasing the Sn concentration. Practical implications: The investigations of microstructure of commercially magnesium alloys are important for achieving desired mechanical behaviour of the material. Originality/value: The fracture behaviors of magnesium alloys are investigated.

2

Chemical and low-expansion treatments for purifying natural graphite powder

Kim J., Kim B.

Physicochemical Problems of Mineral Processing

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2007

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Vol. 41

37-49

EN

Fine natural graphite powder shows good properties in heat resistance, heat expansion and electric conductivity, and has been used as the materials for high-efficient secondary batteries, lubrication, etc. Graphite powder, as a high-tech material, is made through purifying and surface control processes. Developed countries produce high functional graphite powders by additional intercalation processes and sub-micronizing. This study is conducted to utilize low grade natural graphite powders as nanomaterial resources. Prior to production of the ultrafine graphite powder, studies on its pretreatments were performed. Typical acid/alkali treatments with expansion process were conducted. Expanding temperature for gasification process is set low compared to those of the traditional processes. This will make possible to give appropriate expansion ratio for effective chemical treatments and grinding processes. Expansion ratios were controlled as 20 ∼ 30% of the original volume at 200 ∼ 250 st.C, since excessive expansion of graphite powder by traditional approach at high temperature leads to a low grinding efficiency.

PL

Naturalny rozdrobniony grafit wykazuje dobrą odporność na ogrzewanie, niską rozszerzalność oraz małe przewodnictwo i jest używany do jako materiał wysoko wydajnych baterii, do smarowania, itd. Proszek grafitowy, aby mógł być zastosowany jako materiał zaawansowanych technologii, jest oczyszczany i modyfikowany powierzchniowo. Kraje rozwinięte produkują wysokiej jakości proszek grafitowy metodą interkalacji i sub-mikronowego rozdrabniania. Obecnie badania zostały przeprowadzone dla wykorzystania niskiej jakości naturalnego grafitu jako źródło nano-materiału. Dla produkcji ultradrobnego proszku grafitowego przeprowadzono badania dotyczące wstępnej modyfikacji stosując typowy proces ekspansji i modyfikacji „kwas/zasad”. Zastosowano niską temperaturę gazyfikacji w porównaniu do tradycyjnego procesu, co pozwala uzyskać odpowiedni stopień ekspansji w celu efektywnej obróbki chemicznej i rozdrabniania. Proces ekspansji prowadzono w temperaturze 200 ∼ 250 ° dla uzyskania 20 ∼ 30% wzrostu objętości ponieważ ekspansja proszku grafitowego, stosując tradycyjne podejście, tj. wysokie temperatury, prowadzi do słabej efektywności rozdrabniania.

3

Microstructure and orientation of alpha + beta CuZnSi brasses for superplastic deformation

Dutkiewicz J., Szpunar J., Kim B., Nciri R., Malczewski P., Kuśnierz J.

Inżynieria Materiałowa

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2004

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R. XXV, nr 3

347-350

EN

Two brasses containing up to 60.8% Cu, 39.3% Zn, 0.3% Si and 0.2% Ti (in wt%) with almost equal amount of alpha and beta phases were investigated. The thermomechanical treatment consisted of hot roIling, quenching from the beta range, cold rolling and annealing at 773K what resulted in grain refinement down to 1.5 - 3 žm. The tensile tests were conducted at various rates and temperature range 623-823K in order to determine the strain rate sensitivity coefficient m. It was done using step strain rate change. The m attained highest value of about 0.65 for temperature 773K allowing total elongation close to 500% at the deformation rate of 4 ź 10^-3 s^-1. Orientation imaging microscopy (OIM) was performed on specimens tensile deformed 0 and 500%. It allowed to establish grain size and misorientation changes. The grain size of the alpha phase increased from the initial 1.6 žm to 2.7 žm for the sample deformed 500% and that of the beta phase from 1.8 žm to 2.3 žm. The evolution of the alpha boundaries misorientation during superplastic deformation reveals that there is an increase of low angle boundaries (below 10 degrees) and decrease of that of a high angle. The analysis of the Coincidence Site Lattice or CSL boundaries reveals that they increase within beta phase and decrease within alpha phase. It means that the beta phase deforms more by slip as the soft phase in the alpha/beta brass. TEM studies of samples deformed superplastically at 773K up to 100% of elongation, confirmed presence of deformation twins of sigma 3 within beta phase and indicated higher average dislocation density within beta phase than that of the alpha phase. Frequent subgrain boundaries within alpha and beta grains confirmed the results of OIM studies.

PL

Do badań wybrano dwa mosiądze zawierające 60.8% Cu, 39.3% Zn, 0.3%Si i 0.05 lub 0.2% Ti (w % wag.) o zbliżonej zawartości faz alfa i beta. Zastosowana obróbka termomechaniczna polegała na walcowaniu na gorąco, hartowaniu z zakresu fazy beta, i walcowaniu na zimno oraz wyżarzaniu w 773K, co doprowadziło do rozdrobnienia ziarna do 1.5-3 žm. Próby rozciągania prowadzone przy temperaturach 623-823K i skokowo zmienianych szybkościach pozwoliły na określenie współczynnika m czułości na szybkość rozciągania. Osiągnął on najwyższe wartości 0.65 dla 773K co pozwoliło na osiągnięcie 500% deformacji. Zastosowanie techniki OIM (Orienation Imaging Microscopy) pozwoliło na określenie zmian orientacji ziaren alfa i beta. Metoda ta pozwoliła na precyzyjne określenie zmiany wielkości ziaren fazy alfa z 1.6 do 2.7 žm i fazy beta z 1.8 do 2.3 žm po deformacji do 500%. Pomiary dezorientacji ziaren fazy alfa pozwoliły na stwierdzenie wzrostu ilości granic nisko-kątowych (poniżej 10°) i spadek ilości wysokokątowych. Analiza zmiany liczby koincydencji granic ziaren pozwoliła na stwierdzenie jej wzrostu w ziarnach fazy beta i spadku w ziarnach fazy alfa. Świadczy to o większym udziale deformacji przez poślizg w ziarnach fazy beta jako fazy o mniejszej twardości. Badania TEM po deformacji superplastycznej 100% w 773K potwierdziły obecność granic bliźniaczych o sigma = 3 w fazie beta i potwierdziły wyższą gęstość dyslokacji w tej fazie. Częste występowanie podziarn w fazach alfa i beta potwierdziły wyniki OIM.

4

Electrical properties of conductive polymers: pet - nanocomposites’ fibres

Kim B., Koncar V., Devaux E.

Autex Research Journal

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2004

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Vol. 4, no. 1

9--13

EN

Researches in the field of conductive polym ers have attracted considerable attention for more then 20 years. Among the conductive polymers, polyaniline and polypyrrole have drawn considerable interest because of their economical importance, good environmental stability and satisfactory electrical conductivity when doped. On the other hand, electrically conductive materials such as aluminium powder, graphite and carbon nanotubes have very interesting conductive properties and are promising in the synthesis of new composite conductive materials. In almost all studies, conducting polymer films are developed and then electrical and mechanical properties are tested. In our paper, the conducting polymer fibres have been obtained by melt mixing and chemical coating on the fibres. Different conductive materials have been used in order to obtain conductive polypropylene-based fibres with specific electrical and mechanical properties. The electric conductivity and morphol ogical characteristics of these fibres have been investigated and the results are discussed. The originality of our approach lies in our having created conductive fibres based on conductive polymers. These fibres are intended for use in creating conductive yarns and realising connections in smart clothing, or producing conductive fabrics which can be used as electromagnetic shields. These developments have been carried out in order to create new multifunctional textile structures for different applications in the field of intelligent and communication apparel or other similar branches.

5

Load balancing algorithm for parallel vision system using cots pcs and networks

Kim Y., Kim B.

Image Processing & Communications

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2002

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Vol. 8, no 2

43-56

EN

We developed a real-time parallel vision system (PAVIS) along with suitable parallel vision algorithms. PAVIS is designed for cost-effectiveness and flexibility, which is composed of several isotypic commercially off-the-shelf (COTS) PCs with an Ethernet switch that constitute a logically fully connected parallel system. Image partitioning method using the equal area criterion has been used for load distribution in parallel vision processing. Since the load is not the pixels but the feature points for high-level vision operations, we propose an image partitioning method named perpendicular image partitioning (PIP), which partitions image data not by the area of image but by the number of features. PIP functions as an efficient load distribution method, since image partitioning and load balancing are simultaneously performed. Real-time vision algorithm for corner detection and feature matching are also devised. Since the objects on the temporally successive sequence of image have motion continuity, we can speedup vision operations by reducing search area for corners or matching pairs along the motion trajectories found from the prey ions image frames. PAVIS is applied to the real-time depth determination problem for mobile robot navigation. The experimental results confirm the validity of proposed algorithms, and its real-time performance within the frame rate.

6

Design and implementation of infrared readout circuit using a new input circuit of current mirroring direct injection (CMDI)

Yoon N., Kim B., Lee H., Kim C.

Opto-Electronics Review

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1999

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Vol. 7, No. 4

321-326

EN

A new readout structure for infrared (IR) focal plane arrays (FPA) is presented in this paper. By applying a new input circuit of current mirroring direct injection (CMDI), we realised a high-performance readout circuit for IRFPA. It was found from the SPICE simulation that the CMDI inherently makes the detector bias stable as well as has almost 100% injection efficiency to the readout circuit from the detector even for low RDA values because it has almost zero input impedance. Compared with previous other input circuits, it has also many advantages such as small area and low power consumption. A readout chip including the CMDI inputt circuit has been designed and fabricated for MWIR 1x128 staggered linear HgCdTe infrared detector arrays using 1.2 um single-poly-double-metal N-well CMOS technology. From the measurement results of the fabricated chip, the readout function was successfully verified at 77 K with 5 V supply voltage.