Papers by Keyword: Nucleation

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Authors: Shan Dai, Jin Gang Qi, Zuo Fu Zhao, Jian Zhong Wang
Abstract: In the unmodified and EP-modified melt of Q235 steel, the solidification behavior including the nucleation and growth of crystals has been observed in situ by use of a confocal scanning laser microscope combined with an infrared image furnace, and meanwhile, described the characteristic of phase transformation. The result shows that the every stage of phase transformation is advanced; the phase transformation time is shortened, and temperature is reduced during heating proceeds. On the other hand, it can be observed that the nucleation density of solid phase increases and has an even distribution among the liquid phase.
Authors: Olivier Kim-Hak, Maher Soueidan, Gabriel Ferro, Olivier Dezellus, Ariadne Andreadou, Davy Carole, Efstathios K. Polychroniadis, Jean Claude Viala
Abstract: Twin-free 3C-SiC layers were recently obtained by Vapour-Liquid-Solid mechanism on a a-SiC(0001) substrate using Si-Ge melt. The formation of cubic layers is rather unexpected since growth from the melt is known to promote lateral growth and should thus give homoepitaxial layers. The study of the early stage of such growth, after a simple contact between the melt and the substrate (without adding propane), reveals the precipitation of 3C-SiC elongated islands upon the substrate surface. The chemical interactions inside the Ge-Si-C ternary phase diagram suggest an initial dissolution of the SiC seed in contact with a Ge-rich melt (below 1200°C). When the Si content of the melt subsequently increases upon heating, the dissolved carbon atoms precipitate on the seed surface under the form of 3C-SiC islands. When propane is added, these islands enlarge and coalesce to form a complete 3C layer.
Authors: A.S. Shirinyan, Yu. S. Bilogorodskyy
Abstract: The process of phase formation at the initial stage of the reaction diffusion and growth of a new phase particles - at the atomic level by applying the Monte-Carlo simulation of the crystalline nanoalloy is presented. The influence of initial composition on the kinetics of phase separation in a binary alloy with the fcc crystal lattice has been analyzed in detail. The dependences of various parameters of tire process - the average size of new-phase particles, volume of new-phase clusters, size distribution function, dispersion and supersaturation - on time have been calculated. The obtained results demonstrate the opportunity of a three-stage separation process at low initial supersaturation values and a two-stage separation at large initial supersaturation values.
Authors: I.V. Sobchenko, Andriy Gusak, K.N. Tu
Authors: Zsuzsanna Sükösd, Kristofer Hannesson, Gui Lin Wu, Dorte Juul Jensen
Abstract: The distribution of nucleation sites in 90% cold rolled aluminium (AA1050) annealed for 1h at 280°C has been determined by serial sectioning the sample and characterizing each section using the electron back scattering pattern (EBSP) method in the SEM. In total 1844 nuclei are identified. It was found that the nuclei are not randomly distributed but clustered preferentially along TD-RD planes in the sample. The results are presented and implications of clustered nucleation on recrystallization kinetics are discussed.
Authors: Matthew R. Barnett, Aiden G. Beer
Abstract: An analytical approximation for the steady state dynamic recrystallized grain size is combined with a simple nucleation criterion to assess the propensity for dynamic recrystallization. In line with observation, the criterion predicts dynamic recrystallization in 99.9995% pure Al but not in material 99.5% pure. It also agrees with the observation that zone refined ferrite can display dynamic recrystallization at high temperatures and low strain rates but not at lower hot working temperatures. The criterion is applied here to common wrought magnesium alloys to argue that conventional dynamic recrystallization is expected under "normal" hot working conditions.
Authors: Ji Yong Yao, D.A. Graham, Malcolm J. Couper
Authors: Shao Bo Zheng, Cun Bo Yang, Dan Zhao, Hui Gai Li
Abstract: A computational model which is based on the classical homogenous nucleation theory was developed to analyse the alumina inclusion-nucleation process in molten steel in this paper. The idea, 'pseudomolecules', proposed by Lifeng Zhang[1,2], was cited as the basic unit of the physical process of nucleation. However, the nucleation stage was evolved to be controlled by the diffusion of pseudomolecules groups than single pseudomolecule, which is much closer to the actual situation. The differential equations of different pseudomolecules size distribution were given and calculated by computer programs using Runge-Kutta method. Some key parameters, such as supersaturation, nucleation rate, and inclusion population were calculated and compared with some others' conclusion.
Authors: Glenn E. Beltz, Margherita Chang, Anna Machová
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