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Wook Park - One of the best experts on this subject based on the ideXlab platform.
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Shear Stress-Triggered Deformation of Microparticles in a Tapered Microchannel
Polymers, 2020Co-Authors: Cheolheon Park, Junghyun Bae, Yeongjae Choi, Wook ParkAbstract:We demonstrate that it is possible to produce microparticles with high deformability while maintaining a high effective volume. For significant particle Deformation, a particle must have a void region. The void fraction of the particle allows its Deformation under shear stress. Owing to the importance of the void fraction in particle Deformation, we defined an effective volume index (V*) that indicates the Ratio of the particle’s total volume to the volumes of the void and material structures. We chose polyethylene glycol diacrylate (Mn ~ 700) for the fabrication of the microparticles and focused on the design of the particles rather than the intrinsic softness of the material (E). We fabricated microparticles with four distinct shapes: discotic, ring, horseshoe, and spiral, with various effective volume indexes. The microparticles were subjected to shear stress as they were pushed through a tapered microfluidic channel to measure their deformability. The Deformation Ratio R was introduced as R = 1−Wdeformed/Doriginal to compare the deformability of the microparticles. We measured the Deformation Ratio by increasing the applied pressure. The spiral-shaped microparticles showed a higher Deformation Ratio (0.901) than those of the other microparticles at the same effective volume index.
Honfei Sun - One of the best experts on this subject based on the ideXlab platform.
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Crystallographic alignment and magnetic anisotropy inducement from as-deformed disproportionated Nd(Fe,Co)B alloy with different Deformation Ratios
Journal of Alloys and Compounds, 2016Co-Authors: Liu Xiaoya, Yu Sun, Honfei SunAbstract:Abstract The process of cold Deformation and desorption-recombination vacuum annealing was proposed to produce anisotropic nanocrystalline Nd(Fe,Co)B magnet by using as-milled disproportionated nano-structured alloy powders as the precursor material. The effect of Deformation Ratio on crystal alignment and magnetic anisotropy was experimentally studied using X-ray diffraction and transmission electron microscopy, and the underlying mechanisms were clarified by referring to correlation of critical driving energy with nucleation activation energy for the reaction. Cold Deformation plays an essential role in the formation of anisotropic magnet via the induction of desired texture by vacuum annealing treatment, composed of oriented Nd2(Fe,Co)14B nano-crystals with well defined c-axis alignment, maintaining a coherency relationship with as-deformed disproportionated α-(Fe,Co) precursor described by [110]α-(Fe,Co)∥[001] Nd2(Fe,Co)14B. The formation of [00l] Nd2(Fe,Co)14B orientation stems from preferential nucleation and growth of Nd2(Fe,Co)14B crystals induced by (110) texture of α-(Fe,Co) phase during desorption-recombination process. Increasing the Deformation Ratio results in the improvement of remanence and energy product, but moderate loss in coercivity, and the former reason can be ascribed to stronger crystallographic texture along [00l] direction (c-axis alignment), while the latter is related to the absence of intergranular phase, or stray field and weaker exchange coupling caused by grain coarsening, which was further elaborated by magnetization behavior study. The optimum magnetic properties of (BH)max: 140.91 kJ/m3, Hci: 650 kA/m and Br: 0.94 T were achieved by vacuum annealing as-deformed samples with Deformation Ratio of 70% at 780 °C for 30 min, due to pronounced anisotropy and a fully recombined microstructure with uniform grains of about 45 nm in average size. The evident anisotropy and enhanced remanence of nano-grained magnet prove advantageous for the fabrication of textured nanocrystalline permanent magnet.
Fabrizio Tarterini - One of the best experts on this subject based on the ideXlab platform.
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Forging of the AA6061/23 vol.%Al2O3p composite: Effects on microstructure and tensile properties
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Lorella Ceschini, Giangiacomo Minak, Alessandro Morri, Fabrizio TarteriniAbstract:Abstract In this study, the influence of the forging process on microstructure, tensile resistance and fracture behaviour of the AA6061/Al 2 O 3 /23p composite is presented and discussed. Forging was carried out in an open die, at the temperature of 470 °C, with a Deformation Ratio of 2.5:1 then the specimens were heat treated at the T6 condition. Microstructural characterization and density measurements showed that hot forging did not induce crack of the particle on the AA6061/Al 2 O 3 /23p composite and reduced the porosity with respect to the as-cast material. Usually in literature a reduction of the degree of clustering, due to plastic Deformation, is reported. On the contrary, probably due to the low Deformation Ratio applied, no appreciable difference was observed in the degree of particles clustering, before and after forging. The concurrent effect of plastic Deformation and high temperature during forging, instead, led to a recrystallization of the aluminium alloy matrix, with a consequent grain refinement. These microstructural modifications induced an improvement in the tensile strength and an increase, from 50% at room temperature to 165% at 300 °C, of elongation at failure in the forged composite.
Marko Soderžnik - One of the best experts on this subject based on the ideXlab platform.
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Magnetic properties and microstructure evolution of hot-deformed Nd-Fe-B magnets produced by low-pressure spark-plasma sintering
Journal of Magnetism and Magnetic Materials, 2020Co-Authors: Matic Korent, Matej Komelj, Sašo Šturm, Kristina Žužek Rožman, Spomenka Kobe, Kristina Žagar Soderžnik, Marko SoderžnikAbstract:Abstract We have produced hot-deformed Nd-Fe-B magnets from commercial (MQU-F) Nd-Fe-B ribbons. The spark-plasma-sintering technique was used to deform the samples under low pressures of 40 MPa. The initial stages of the hot-Deformation process were investigated in terms of microstructures and magnetic properties. Hot-deformed magnets with different Deformation Ratios were produced and the dependence of the remanence on the Deformation Ratio was determined. In the initial stages of the hot-Deformation process, a cone-like shape of the magnet was observed for the first time. The experimental data can be qualitatively interpreted by applying the basic Stoner–Wohlfarth model.
Cheolheon Park - One of the best experts on this subject based on the ideXlab platform.
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Shear Stress-Triggered Deformation of Microparticles in a Tapered Microchannel
Polymers, 2020Co-Authors: Cheolheon Park, Junghyun Bae, Yeongjae Choi, Wook ParkAbstract:We demonstrate that it is possible to produce microparticles with high deformability while maintaining a high effective volume. For significant particle Deformation, a particle must have a void region. The void fraction of the particle allows its Deformation under shear stress. Owing to the importance of the void fraction in particle Deformation, we defined an effective volume index (V*) that indicates the Ratio of the particle’s total volume to the volumes of the void and material structures. We chose polyethylene glycol diacrylate (Mn ~ 700) for the fabrication of the microparticles and focused on the design of the particles rather than the intrinsic softness of the material (E). We fabricated microparticles with four distinct shapes: discotic, ring, horseshoe, and spiral, with various effective volume indexes. The microparticles were subjected to shear stress as they were pushed through a tapered microfluidic channel to measure their deformability. The Deformation Ratio R was introduced as R = 1−Wdeformed/Doriginal to compare the deformability of the microparticles. We measured the Deformation Ratio by increasing the applied pressure. The spiral-shaped microparticles showed a higher Deformation Ratio (0.901) than those of the other microparticles at the same effective volume index.