Eco-Materials Processing & Design VI

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Authors: Sang Yeup Park, Hee Gon Bang
Abstract: Alumina/Alumina: SiC laminate composites were fabricated by the pressureless sintering method. Although the laminate defect, such as channel crack, was observed under the sintering of oxidation atmosphere, laminate defects were eliminated by the sintering of non-oxidation atmospheres. Among various atmospheres, the vacuum atmosphere was effective in the elimination of laminate defects and also for homogeneous microstructure.
Authors: Wei You, Jung Hun Lee, Soo Keun Shin, Byung Hak Choe, Ung Yu Paik, Je Hyun Lee
Abstract: The embrittlement fracture mechanism caused by microstructural evolution of 17-4 PH stainless steel at long term aging was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The solution treated specimen consists largely of lath martensite with a small fraction of elongated δ-ferrite. The spherical particles existed a little in the martensite matrix, while no precipitates were present in the δ-ferrite at the solution treated specimen as non-aging. The precipitation of Fe-Cu in the δ-ferrite causes the aged hardening after long term aging accormpanied by decreases in elongation and charpy V-notch energy absorption. The increased fraction of brittle fracture on the fractured surface by impact and tensile test reveals that the embrittlement of the 17-4 PH alloys during long term aging is mainly caused by the precipitation hardening in the δ-ferrite matrix.
Authors: Kee Sung Lee, In Sub Han, Yong Hee Chung, Sang Kuk Woo, Soo Wohn Lee
Abstract: Hardness and wear resistant characteristics of reaction-bonded silicon carbides with boron carbide additions are evaluated relative to those of reaction bonded silicon carbide (RBSC). The reaction-bonded SiC-B4C composites exhibit a distinctive improvement of hardness and wear resistance, indicative of high resistance against wear environment. Removal rates for the wear tests are decisively reduced by the addition of boron carbide in the composites. Controlling the amount of carbon content in the starting composition more enhances the hardness of the reaction-bonded composites. Implications concerning the partial decomposition of B4C during reaction process are considered.
Authors: Chang Yong Lee, Won Bae Lee, Yun Mo Yeon, Seung Boo Jung
Abstract: Friction stir welding of dissimilar formed Mg alloys(AZ31/AZ91) was successfully carried out at the limited welding conditions. In a sound joint, SZ was mainly consisted of AZ31 Mg alloy which was located the retreating side. Dynamic recrystallization and grain growth occurred and β intermetallic compounds of AZ 91 Mg alloy was not observed in SZ. BM had a higher hardness than that of the weld zone. The fracture location was not weld zone but BM of the AZ91 Mg alloy in tensile test.
Authors: D.M. Lee, Cheol Ho Lim, Dong Choul Cho, Seung Y. Shin, Won Seung Cho
Abstract: N-type Bi2Te3 based thermoelectric compound was prepared by spark plasma sintering with a temperature range of 340~460°C and powder size of ~75㎛, 76~150㎛, 151~250㎛. Thermoelectric properties of the compound were measured as a function of the sintering temperature and powder size. With increasing sintering temperature, the electrical resistivity and thermal conductivity of the compound greatly changed because of the increase in relative density. The Seebeck coefficient and electrical resistivity were varied largely with increasing powder size. Therefore, the compound sintered at 460°C, with the powder of ~75㎛, showed a figure of merit of 2.44 x 10-3/K. Also, the bending strength was 75MPa.
Authors: Y. Lu, J.S. Lee, Je Hyun Lee, Dang Moon Wee, Myung Hoon Oh
Abstract: Ni3Al has been considerable research area due to its high temperature behavior increasing strength with increasing temperature. A series of directional solidification studies showed that the eutectic occurred between g’/b and the metastable eutectic of g/b forms under slightly different conditions, however, it is not well established whether the eutectic is composed of g/g‘, g’/b, or g/b . In order to understand solidification behavior of the eutectic structure, directional solidification experiments have been carried out with solidification rate near the Ni3Al composition in this study. The effects of the solidification rate and composition on formation of the equilibrium and metastable eutectics have been discussed. The (g’+g) coupled phase was also shown to form with the eutectic at the solid/liquid interface.
Authors: Bo Young Hur, Sang Hun Cho, Sang Youl Kim
Abstract: Coated sheet steels have been increasingly used in automotive industry for improving corrosion resistance. When GA outer plates processed the interfacing of the coating film and the metal matrix causes surface irregularities in the surface state of the sheet metal. Consequently, research to determine each phase composite’s friction coefficient is on-going. Investigating the effects that cause surface roughness, change and mechanical properties of outer automobile plates through temper rolling skin pass mill elongation is essential. Researching surface roughness in relation to surface friction properties requires the determination of a surface friction coefficient. This research demonstrates that there is a complex effect between the lubricant membrane and surface roughness when processing GA plates. Consequently, the strength of the lubricant membrane strongly influences the friction coefficient
Authors: Myung Ho Park, Dae Yong Shin
Abstract: Today every nation faces serious problems of energy supply. Reasonable technologies to make use of coal (including coke) can not only help the mining-related economy which is showing a downward trend but also may fit in with the governmental energy policy. In this research, we aim to supply heating systems in factories, homes, and farms with a substitute fuel by developing coke/waste tire compound fuel with high efficiency for rational use of energy and for recycling of industrial products. A coke/waste boiler was used for this experiment, and different kinds of fuel were experimented including coke, waste tire, coke/waste A and coke/waste B. Four kinds of exhaust gas were also sampled by a gas analyzer, including CO, CO2, NO and NO2 at different temperatures.
Authors: Jong Woong Kim, Sun Kyu Park, Seung Boo Jung
Abstract: Ball shear test was investigated in terms of the effects of important test parameter, i.e., shear height, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. The substrate was a common SMD type with solder bond pad openings of 460 ㎛ in diameter. It was observed that increasing the shear height, at a fixed shear speed, has the effect of decreasing the shear force. The high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces.
Authors: Dae Gon Kim, Hyung Sun Jang, Young Jig Kim, Seung Boo Jung
Abstract: In the present work, the growth kinetics of intermetallic compound layer formed in Sn-3.5Ag flip chip solder joints by solid-state isothermal aging was examined at temperatures between 80 and 150 °C for 0 to 60 days. The bumping for the flip chip devices was performed using an electroless under bump metallization. The quantitative analyses were performed on the intermetallic compound layer thickness as a function of aging time and aging temperature. The layer growth of the Ni3Sn4 intermetallic compound followed a parabolic law within a given temperature range. As a whole, because the value of the time exponent (n) is approximately equal to 0.5, the layer growth of the intermetallic compound was mainly controlled by diffusion mechanism in the temperature range studied. The apparent activation energy of the Ni3Sn4 intermetallic was 49.63 kJ/mol.

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