Papers by Keyword: High Undercooling

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Authors: Hui Xie, Gen Cang Yang, Lei Jia, Zhen Lin Lu
Abstract: The kinetic process of liquid-liquid phase separation in the undercooled Ni-20at%Pb hypermonotectic alloy melts was analyzed theoretically. The results showed that liquid-liquid separation could not be inhibited due to smaller nucleation barrier and bigger nucleation rate of Pb-rich droplets. In the course of liquid-liquid phase separation, the volume fraction of Pb-rich droplets was thought as a function of time or temperature. At a certain cooling rate, the volume fraction was mainly controlled by the undercooling of Ni-Pb hypermonotectic melts. Based on the above results, a homogeneous solidification criterion for the undercooled Ni-20at%Pb hypermonotectic alloy melts was developed. Such a criterion predicted that the homogeneous microstructure could be obtained at the undercooling 263K, and the experimental results accorded with the predicting ones on the whole.
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Authors: Hui Xie, G. H. Bai, Lei Jia, Zhen Lin Lu, Sheng Zhong Kou
Abstract: Bulk Fe-50at%Ni alloy melts were undercooled using cyclic superheating and glass slag purification. As a result, a maximum undercooling up to 217 K could be achieved. As-solidified microstructures were observed by means of optical microscope. Phase identification of Fe-50at%Ni alloys was performed using the Shimadzu X-ray diffractometer (XRD) system. The chemical constitution revealed using a JEOL Model JSM-6700F scanning electron microscope equipped with energy dispersive X-ray spectroscopy (EDX). The magnetic properties of the alloys were measured by vibrating sample magnetometer (VSM) with a DC M-H analyzer. The results indicated that there were twice grain refinements occurred within an undercooling range of 55-217K, where the first could be ascribed to dendrite-remelting, and the second to recrystallization. The phase composition of undercooled Fe-50at%Ni alloys comprised two phases, i.e., solid solution phases with bcc and fcc structure. At various undercoolings, the saturation magnetization Ms and Hc related closely to the measured grain size D, and they were in proportion to D-1 by the regression analysis.
357
Authors: Hui Xie, G.H. Bai, L. Jia, E.K. Liu, Zhen Lin Lu
Abstract: Bulk Fe-80at%Ni melts were undercooled by using cyclic superheating and glass slag purification technique, and the maximum undercooling 340 K could be achieved. The microstructures of Fe-80at%Ni alloys were observed by means of optical microscope (OM). The phase composition was identified by X-ray diffraction (XRD) analysis. The magnetic properties of Fe-80at%Ni alloys were measured by vibrating sample magnetometer (VSM) with a DC M-H analyzer. The results showed that there was only single γ-(Fe, Ni) phase existing in undercooled Fe-80at%Ni alloys. Two grain refinements and one grain coarsening were observed in the undercooling range from 28 K to 340 K. The first grain refinement could be ascribed to dendrite-remelting, and the second to recrystallization induced by the stress originating from rapid solidification. The grain coarsening could be considered as a result of solid-state grain coalescence. The measurement of soft magnetic properties showed that the grain size D decreases with an increase of undercooling, the maximum Ms is 109.98emu/g, corresponding to minimum grain size 42.9μm or undercooling 210 K, and the coercive force Hc is in proportion to the reciprocal of grain size D-1.
327
Authors: Dan Li, K. Eckler, Dieter M. Herlach
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