발간논문

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Samples with compositions of 80 wt% Mg-14 wt% Ni-6 wt% Fe2O3 (named Mg-Ni-Fe2O3), and 78 wt% Mg-14 wt% Ni-6 wt% Fe2O3-2 wt% CNT (named Mg-Ni-Fe2O3-CNT ) were prepared by reactive mechanical grinding. Hydriding and dehydriding properties and effects of CNT addition on the hydriding and dehydriding rates of Mg-Ni-Fe2O3 were then investigated. Activation of the Mg-14Ni-6Fe2O3 sample was completed after three hydriding (under 12 bar H2)-dehydriding (under 1.0 bar H2) cycles at 573 K. The addition of CNT to the Mg-14Ni-6Fe2O3 sample made the activation process unnecessary, with a small decrease in the hydrogen-storage capacity.

keyword : hydrogen absorbing materials, mechanical alloying/milling, microstructure, X-ray diffraction, CNT addition

The microstructure of Cu-24 wt.%Ag filamentary nanocomposite fabricated by a thermo-mechanical process has been investigated by transmission electron microscopy (TEM) observations. This study is focused on the stability of Ag filaments formed by cold drawing; the effects of thermal treatment on the precipitation behavior and distribution of Ag-rich precipitates were also investigated. The Ag filaments elongated along the <111> orientation were observed in Cu-rich α phase of the as-drawn specimen and the copper matrix and the silver filament have a cube on cube orientation relationship. Annealing at temperatures lower than 200℃ for the as-drawn specimen caused insignificant change of the fibrous morphology but squiggly interfaces or local breaking of the elongated Ag filaments were easily observed with annealing at 300℃. When samples were annealed at 400℃, discontinuous precipitation was observed in supersaturated Cu solid solution. Ag precipitates with a thickness of 7-20 nm were observed along the <112> direction and the orientation relationship between the copper matrix and the Ag precipitates maintained the same orientation relationship in the as-drawn specimen. The interface between the copper matrix and the Ag precipitates is parallel to {111} and micro-twins were observed in the Ag precipitates.

keyword : Cu-Ag nanocomposite, nanostructured materials, deformation, precipitation, transmission electron microscopy (TEM)

The formation of TiC and Al2O3 particles based on the self-combustion reaction of the Al-TiO2-CCuO system in an Al alloy melt was investigated. With an adequate amount of CuO in the system, a spontaneous reaction occurred within the Al alloy melt at 850℃ and thereafter was self-maintained, producing an Al matrix composite reinforced with thermodynamically stable TiC and Al2O3 particles. TiC and Al2O3 particles contributed to a considerable increase in the strength and stiffness, demonstrating the feasibility of this method as a practical application for structural parts.

keyword : metal matrix composite, self-combustion reaction, in-situ reaction synthesis