Papers by Keyword: Nanocrystalline Material

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Authors: Harald Rösner, Gerhard Wilde
Abstract: In this study we show that in-situ tensile tests performed in a transmission electron microscope (TEM) in combination with high-resolution TEM are feasible, and, that this method is appropriate to elucidate the deformation processes in nanocrystalline materials directly. First results on nanocrystalline Pd produced by repeated cold-rolling with intermediate folding of metal sheets are presented revealing that the material ruptured during the in-situ tensile tests along grain boundaries. Deformation twinning was observed in grains next to the crack indicating that the deformation processes must have originated from the grain boundaries.
Authors: Xiao Ming Fu, Zhao Wen Liu, Liang Yi Zhou, Chen Chen Xie
Abstract: β-Ni(OH)2 flower-like spheres and nanoflakes were synthesized with strong ammonia water as precipitator and nickel nitrate as nickel source by the hydrothermal method. The phase structure and morphologies were analyzed using XRD and SEM. The results showed that under the same conditions of the pH value and the reaction time, the low temperature was propitious to synthesize β-Ni(OH)2 flower-like spheres. High temperature was in favor of the synthesis of β-Ni(OH)2 nanoflakes. Namely, β-Ni(OH)2 flower-like spheres were obtained at 180 °C for 48.0 h with pH=9.0. β-Ni(OH)2 nanoflakes were prepared at 240 °C for 48.0 h with pH=9.0. The formation mechanism was explored through observing influence of the conditions of the hydrothermal method on the morphologies of the samples.
Authors: Jiao Xia Lan, Yong Zhong Wu, You Shi Hong
Abstract: Molecular dynamics simulations have show that nanocrystalline (NC) materials can be treated as composite materials consisting of two phases of grain and grain boundary. In this paper, the incremental stress-strain relation is derived based on deformation mechanism of NC materials and internal variable theory from micromechanics point of view. The developed model is exemplified by the pure copper subjected to uniaxial tension. Implicated iteration algorithm is then employed to obtain the stress-strain relation. Moreover, the effects of grain shape and statistical distribution of grain sizes are also discussed, and predicted results are compared with experimental values to verify the model.
Authors: Yan Wu, B.Y. Zong, M.T. Wang
Abstract: Abnormal grain growth was simulated by phase field model in order to find ways of producing scattered a few enormous grains in a nano-structural single phase AZ31 alloy to improve its ductility. It is shown that the abnormal grain growth is controlled by the three keys factors of interface energy, strain restored energy and interface mobility. Therefore, the microstructure with scattered a few enormous grains in the nano-structural matrix can be achieved after an annealing treatment if there is a small group of specially orientated nano-size grains in the original nao-structure with local low grain boundary energy or local high strain energy or local high interface mobility. The morphology of abnormal grains is also examined as function of annealing time to optimize the microstructure.
Authors: W.P. Tong, L.M. Wang, G.J. Ma, N.R. Tao, Liang Zuo
Abstract: A nanostructured surface layer on a pure iron sample was prepared by surface mechanical attrition treatment (SMAT). The thermal stability of SMAT sample was investigated at different temperatures with or without a high magnetic field (H =12T). It was found that a high magnetically annealing enhanced grain growth at the early stage of annealing, and produced a uniform nanocrystalline grain structure. After homogeneous grains developed, further grain growth became restrained.
Authors: Juan Bartolomé, F. Luis, L.M. García, F. Bartolomé, F. Petroff, C. Deranlot, F. Wilhelm, A. Rogalev, P. Bencok, N.B. Brookes
Abstract: The effect of capping with Cu, Au and Pt of an array of Co nanoparticles is revised. The magnetic surface anisotropy KS was found to be the dominant contribution to the effective anisotropy Keff of the particles. Recent X-ray Magnetic Circular Dichroism (XMCD) measurements show that there is hybridization between the 3d Co electrons and the d and 4p electrons of the capping metal. By comparison to the mechanisms which give rise to the surface anisotropy in thin films, it is argued that this hybridization governs the modification of KS, and hence, of Keff.
Authors: José Trinidad Elizalde Galindo, Reiko Sato Turtelli, Roland Grössinger, José Andrés Matutes-Aquino
Abstract: Nanocrystalline YCo5 powders with high coercivity were prepared by mechanical milling and subsequent heat treatment at 820 °C for different annealing times, ta = 2.5, 3.0, 3.5 and 4.5 min, obtaining average crystallite sizes of  17, 19, 32 and 39 nm., respectively. The coercivity values were determined from the hysteresis loops measured at maxima fields of Hm = 5 and 20 T. The highest coercivity was obtained for the sample exhibiting  19 nm, where at room temperature and Hm = 5 T, the coercivity value is of 9.0 kOe. At 77 K and Hm = 5 T, the coercivity increase to 11.8 kOe and for Hm = 20 T, a higher value such as 13.1 kOe was found. The Ms/Mr ratio is enhanced to 0.62 indicating the occurrence of exchange interaction among nanocrystalline magnets.
Authors: Li Jun Wang, Jie Qiong Li, Hong Jing Wang
Abstract: Application of nanocrystalline magnetic materials in electromechanical devices is increasingly being adopted, helping to solve energy-saving problems and global warming. Compared with conventional silicon steel materials, nanocrystalline materials show faster flux reversal, lower magnetic loss and more versatile property modification, which result in the successful application in modern electronic devices. Nanocrystalline magnetic materials will be increasingly popularized and used in power electronics, telecommunication equipment and electronic article surveillance systems due to the demands for smaller and efficient devices in the future.
Authors: P. Butvin, B. Butvinová, J. Novák, Gabriel Vlasák, P. Duhaj
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