The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
Gm Gyeong Kim - One of the best experts on this subject based on the ideXlab platform.
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influence of nanofillers on the deFormation process in layered silicate polyamide 12 nanocomposites
Polymer, 2001Co-Authors: Gm Gyeong Kim, Dongho Lee, B Hoffmann, Jorg Kressler, G StoppelmannAbstract:Abstract Polymer nanocomposites based on a synthetic layered silicate and polyamide-12 (PA-12) are prepared by injection molding to study their morphology, and the influence of nanofiller particles on local deFormation processes. One of the most striking results from morphological studies by transmission electron microscopy is that although the layered silicates, locally stacked in the PA-12 matrix, are arranged on planes parallel to the injection molding direction, the fine lamellae are oriented with their planes perpendicular to the injection molding direction owing to nucleation at the interface between layered silicate and polymer matrix. The dispersion of layered silicates and the orientation of lamellae are reflected in the complexity of the deFormation mechanisms, which in turn determine the ultimate macroscopic properties. From studies of in situ deFormation under the high voltage electron microscope, it is concluded that the main deFormation mechanism is Microvoid Formation inside the stacks of layered silicates. According to the orientation of these stacks the applied energy is dissipated by splitting, opening or sliding of separate bundles in the stacks during deFormation. The nanofiller particles are load-bearing because surfaces in the Microvoids are connected and hinder further growth of the Microvoids, thus preventing catastrophic failure. As a consequence, the stiffness/strength/toughness balance has been synergistically improved. Finally, based on the present experimental results, a molecular network in polymer nanocomposites is proposed, that leads to the desired superfunctional characteristics.
Valeria Nicolosi - One of the best experts on this subject based on the ideXlab platform.
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a comprehensive analysis of extrusion behavior microstructural evolution and mechanical properties of 6063 al b4c composites produced by semisolid stir casting
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Amir Pakdel, Agnieszka Witecka, Gaulthier Rydzek, Dayangku Noorfazidah Awang Shri, Valeria NicolosiAbstract:Abstract In this study, composites of aluminum alloy 6063 reinforced with 10 wt% boron carbide microparticles were successfully fabricated by a combination of spark plasma sintering and stir casting methods, followed by hot extrusion. A systematic study on the relationship between extrusion process variables (i.e. extrusion ratio, temperature, and punch speed) and porosity, particle refinement, particle distribution and consequently tensile properties and fracture behavior of the composites was performed. Extensive electron microscopy analysis and tensile testing of the composites revealed a multifactoral interdependency of microstructural evolution and mechanical properties on the extrusion process variables. For example, while increasing the extrusion ratio at higher temperatures led to moderate particle refinement, better densification of the composites, and improvement in mechanical properties, concurrent particle fragmentation and Microvoid Formation around the particles at lower temperatures had opposing effects on the mechanical behavior. We show that the dependency of mechanical properties on all such microstructural factors makes it difficult to predict optimum extrusion conditions in aluminum matrix composites. That is, unlike the common approach, extruding the composites at higher temperatures and achieving more reduction in area may not necessarily lead to the most favorable mechanical properties.
G Stoppelmann - One of the best experts on this subject based on the ideXlab platform.
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influence of nanofillers on the deFormation process in layered silicate polyamide 12 nanocomposites
Polymer, 2001Co-Authors: Gm Gyeong Kim, Dongho Lee, B Hoffmann, Jorg Kressler, G StoppelmannAbstract:Abstract Polymer nanocomposites based on a synthetic layered silicate and polyamide-12 (PA-12) are prepared by injection molding to study their morphology, and the influence of nanofiller particles on local deFormation processes. One of the most striking results from morphological studies by transmission electron microscopy is that although the layered silicates, locally stacked in the PA-12 matrix, are arranged on planes parallel to the injection molding direction, the fine lamellae are oriented with their planes perpendicular to the injection molding direction owing to nucleation at the interface between layered silicate and polymer matrix. The dispersion of layered silicates and the orientation of lamellae are reflected in the complexity of the deFormation mechanisms, which in turn determine the ultimate macroscopic properties. From studies of in situ deFormation under the high voltage electron microscope, it is concluded that the main deFormation mechanism is Microvoid Formation inside the stacks of layered silicates. According to the orientation of these stacks the applied energy is dissipated by splitting, opening or sliding of separate bundles in the stacks during deFormation. The nanofiller particles are load-bearing because surfaces in the Microvoids are connected and hinder further growth of the Microvoids, thus preventing catastrophic failure. As a consequence, the stiffness/strength/toughness balance has been synergistically improved. Finally, based on the present experimental results, a molecular network in polymer nanocomposites is proposed, that leads to the desired superfunctional characteristics.
Youngho Kim - One of the best experts on this subject based on the ideXlab platform.
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effect of cu electroplating parameters on Microvoid Formation and high speed shear strength in sn 3 0ag 0 5cu cu joints
Journal of Alloys and Compounds, 2017Co-Authors: Jaeyong Park, Wonil Seo, Sehoon Yoo, Youngho KimAbstract:Abstract The effect of Cu electroplating parameters, i.e., the bath composition and current density, on the impact strength of Sn-3.0Ag-0.5Cu (SAC)/Cu joints was investigated using a high-speed ball shear test. An SAC solder ball was attached to an electroplated Cu layer by a reflow at a peak temperature of 260 °C. Thermal aging at 180 °C formed a Cu 3 Sn intermetallic compound (IMC) between the Cu 6 Sn 5 IMC and the electroplated Cu, and Microvoids were formed within the Cu 3 Sn IMC layer. The total Microvoid area increased with increased Cu electroplating current density. When Cl − ions alone were added to the electroplating bath, the total Microvoid area decreased with thermal aging. In contrast, when both polyethylene glycol (PEG) and Cl − ions were added to the bath, the total Microvoid area increased. However, the overall IMC thickness was similar for all samples, irrespective of the electroplating parameters. The shear strength of the SAC solder joint reflowed on the electroplated Cu decreased with increased aging time. For the same aging time, the shear strength decreased with increased current density. In addition, the shear strength decreased when the electroplating bath contained both PEG and Cl − ions. As the aging time increased, the fracture site shifted from the solder/Cu 6 Sn 5 interface to the Cu 3 Sn/Cu interface. An increase in the total Microvoid area in the Cu 3 Sn IMC as well as an increase in the IMC thickness decreased the shear strength of the SAC solder on the electroplated Cu.
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mechanism of the delayed growth of intermetallic compound at the interface between sn 4 0ag 0 5cu and cu zn substrate
Electronic Materials Letters, 2010Co-Authors: Youngmin Kim, Kyoung Moo Harr, Youngho KimAbstract:A Cu-Zn wetting layer was very effective to depress the excessive growth of intermetallic compound (IMC). The effect of Zn addition to the Cu layer on the IMC growth and Microvoid Formation in the solder interface was similar to the effect of Zn addition into the Sn-Ag-Cu (SAC) solders. In this study, the mechanism of slow IMC growth at the SAC/Cu-Zn interfaces was investigated. As the aging time increased, Zn atoms accumulated at the Cu6Sn5/Cu interface and formed a Zn-rich layer. By adding Zn into the Cu wetting layer, the IMC growth was delayed due to the retardation of the Formation of the Cu3Sn layer. Since the low driving force for the Formation of Cu3Sn became smaller by adding Zn, the diffusion of Cu in Cu-Zn into SAC solder was delayed. Also, the CuZn phase formed at the Cu6Sn5/Cu-Zn interface plays a role as a diffusion barrier of interdiffusion of Cu and Sn.
Ilyas Uygu - One of the best experts on this subject based on the ideXlab platform.
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effects of deep cryogenic treatment on the wear resistance and mechanical properties of aisi h13 hot work tool steel
Journal of Materials Engineering and Performance, 2015Co-Authors: Adem Cicek, Fua Kara, Turgay Kivak, Ergu Ekici, Ilyas UyguAbstract:In this study, a number of wear and tensile tests were performed to elucidate the effects of deep cryogenic treatment on the wear behavior and mechanical properties (hardness and tensile strength) of AISI H13 tool steel. In accordance with this purpose, three different heat treatments (conventional heat treatment (CHT), deep cryogenic treatment (DCT), and deep cryogenic treatment and tempering (DCTT)) were applied to tool steel samples. DCT and DCTT samples were held in nitrogen gas at −145 °C for 24 h. Wear tests were conducted on a dry pin-on-disk device using two loads of 60 and 80 N, two sliding velocities of 0.8 and 1 m/s, and a wear distance of 1000 m. All test results showed that DCT improved the adhesive wear resistance and mechanical properties of AISI H13 steel. The Formation of small-sized and uniformly distributed carbide particles and the transFormation of retained austenite to martensite played an important role in the improvements in the wear resistance and mechanical properties. After cleavage fracture, the surfaces of all samples were characterized by the cracking of primary carbides, while the DCT and DCTT samples displayed Microvoid Formation by decohesion of the fine carbides precipitated during the cryo-tempering process.