Papers by Keyword: Coarsening

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Authors: Hamed Ravash, Eckard Specht, Jef Vleugels, Nele Moelans
Abstract: Liquid phase sintering (LPS) is widely used as a materials processing technique for hightemperature applications. In LPS, particle-particle contact size and distribution, 3-D coordination number, connectivity, and contiguity are important microstructure parameters which, to a large extent, determine the mechanical properties of the sintered materials. These features all depend on the grain size, solid volume fraction and dihedral angle during sintering. The dihedral angle is an important parameter in LPS. It is the angle formed between the 2 solid-liquid interfaces at the intersection of a grain boundary with the liquid. A higher solid volume fraction, on the other hand, favors a larger 3-D coordination number, connectivity, and contiguity. In practice, studying the correlation between these parameters and direct measurement of them is not a trivial task. Among them, 3-D measurement of dihedral angle is believed to be the most challenging one. In the current study, phase-field modeling is employed to simulate LPS in two phase systems (solid and liquid). Simulations are performed for the different ratios of grain boundary to solid-liquid energies and the different solid volume fractions. To create initial structures with high solid volume fraction, an advanced particle packing algorithm is employed. An extended sparse bounding-box algorithm is used to speed-up the computations and makes it computationally efficient for 3-D simulations. Contiguity, connectivity, and three dimensional coordination number were measured in the self similar regime. The results were compared with empirical rules and experimental data and are used to estimate the mean 3-D dihedral angle.
Authors: Andrey V. Sarikov, A.I. Klimovskaya, O. Oberemok, O. Lytvyn, O. Stadnik
Abstract: Formation of the patterns of catalytically active metal containing droplets on substrates is an important process for the growing Si wire-like crystals because it predetermines the main crystal parameters. Understanding physical mechanisms of droplet evolution during thermal treatments and derivation of associated parameters are the clue to the controlled formation of droplet ensembles and thus to the predicted growing Si wire-like crystals. In this work, the kinetics of the evolution of droplet ensembles on the surface of substrate as a result of coalescence and atom evaporation is studied theoretically. Obtained theoretical results are compared to the experimental data on the evolution of the ensembles of Au/Si droplets on Si substrate formed by rapid thermal anneals of thin gold film in the temperature range from 900 to 1050°C. The activation energy of droplet diffusion on the surface of substrates is estimated.
Authors: H. Meidani, S. Hossein Nedjad, Mahmoud Nili-Ahmadabadi
Abstract: A new process for fabrication of semisolid billets is introduced, which involves equal channel angular pressing and isothermal heating in the semisolid state. The process leads to a relatively fine globular microstructure. The microstructure evolution during isothermal treatment is studied and it is shown that dendrites breaking up has happened during equal channel angular pressing in semisolid state. The microstructural evolution during isothermal heating and the mechanism for the formation of the globular structure is tried to be understood and also modeled.
Authors: Ming Yang, Xin Ma, Ming Yu Li
Abstract: The coarsening behavior of Cu6Sn5 grains formed at the Sn37Pb/Polycrystalline Cu interface is investigated in terms of their orientation evolution during solid-state aging. The results show that the coarsening behavior of the interfacial Cu6Sn5 grains during solid-state aging are quite different from that during liquid-state soldering. The occurrence of the coarsening in the solid-sate reaction is caused by the different surface energies between two adjacent grains. In addition, the texture morphologies of the interfacial grains affect their coarsening rates. In particular, the interfacial Cu6Sn5 grains formed at 200 oC exhibit a texture with the [0001] direction normal to the interface after 16 days of aging at 150 oC, and the formation of this texture accelerates the coarsening process of the interfacial Cu6Sn5 grains.
Authors: Harshad K.D.H. Bhadeshia
Authors: D. Hamana, Zakaria Boumerzoug
Authors: Ivan Popov, P. Prudnikov
Abstract: In the past few years, systems with slow dynamics have attracted considerable interest. Coarsening effects are exhibited in a wide range of systems. Non-equilibrium critical behavior of 2D XY-model demonstrates slow dynamics in a wide temperature range. The coarsening in pure and diluted 2D XY-model are investigated for various defects concentration. The period of logarithmic grows of cluster size was found.
Authors: C.H. Chiang, Chi Y.A. Tsao
Abstract: The coarsening behavior of spray-formed A-35wt%Si and A-45wt%Si alloys in the semisolid state were studied. The coarsening kinetic and Si size distributions after coarsening at various temperatures and times in the semi-solid state were investigated. The coarsening exponents, n, the rate constants, K, in the LSW theory, and the modified rate constants were determined from previous works. The coarsening activation energies of the two spray-formed alloys were calculated from the slopes of ln(KT) vs. 1/T plots. The Si size distribution functions after holding at various temperatures and times in the semisolid state were determined for the two spray-formed alloys. The effects of the stokes-motion in addition to pure diffusion mechanism on the variations of coarsened Si size distribution were also investigated.
Authors: Felipe Hernandez-Santiago, Victor M. Lopez-Hirata, Maribel L. Saucedo-Muñoz
Abstract: A study of the coarsening process of the decomposed phases was carried out in the Cu-34wt.%Ni-4wt.%Cr and Cu-45wt.%Ni-10wt.%Cr alloys using transmission electron microscopy. As aging progressed, the morphology of the coherent decomposed Ni-rich phase changed from cuboids to platelets aligned in the <100> Cu-rich matrix directions. Prolonged aging caused the loss of coherency between the decomposed phases and the morphology of the Ni-rich phase changed to ellipsoidal. The variation of mean radius of the coherent decomposed phases with aging time followed the modified LSW theory for thermally activated growth in ternary alloy systems. The coarsening rate was faster in the symmetrical Cu-45wt.%Ni-10wt.%Cr alloy due to its higher volume fraction of precipitates. The activation energy for thermally activated growth was determined to be about 182 and 102 kJ mol-1 in the Cu-34wt.%Ni-4wt.%Cr and Cu-45wt.%Ni-10wt.%Cr alloys, respectively. The size distributions of precipitates in the Cu-Ni-Cr alloys were broader and more symmetric than that predicted by the modified LSW theory for ternary alloys.
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