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Research on Abnormal Solidification of Undercooled Alloy

Author: ChenHui
Tutor: XiaoJianZhong
School: Huazhong University of Science and Technology
Course: Materials Science
Keywords: high undercooling grain refinement crystal form componential asymmetry
CLC: TG111.4
Type: Master's thesis
Year: 2005
Downloads: 170
Quote: 1
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Abstract


High undercooling solidification is an extremely non-equilibrium solidification. It is realized by rapid solidification and fluxing technique. By controlling the non-equilibrium effect, we can decrease grain deflection, refine grain size. Finally we can get amorphous alloy, semiaxis alloy and nano-materials. So it has become one of the best flourishing research. In the present study, a series of abnormal crystal phenomena is investigated. Detailed work is as following: For discovering the thermodynamic reasons of Ni99.5B0.5 alloy grain refinement, we detected several models of dendrite growth, and reviewed the effects of diffusivity, temperature grads and growth velocity to interfacial form. We founded grain growth model of bamboo form and got the function of grain size and undercooling.Through non-linear imitating of undercooling and grain size, experiential formula was gotten according to the experimental results. The critical growth velocity of interface stability of Ni99.5B0.5 alloy grain was obtained using numerical calculating. Compared with grain growth velocity, we ascertained undercooling which made the interface tend to stabilization. Calculative result is consistent with experimental data and grain microstructure. Through integrating academic analysis and numerical calculating of grain size variety, the crystal form model of Ni99.5B0.5 alloy is founded. Ag-Sn（4%）、Cu90Ni10、Cu30Ni70 alloy sample were prepared using fluxing technique. Through observing microstructure of sample, we discovered componential asymmetry of rapid solidification organization. The mechanism of abnormal composition is discussed by analysis and numerical calculating.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Physics of metals > The liquid structure of the metal and solidification theory
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