발간논문

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Nanotubular structure formation on the Ti-6Al-4V and Ti-Ta alloy surfaces by electrochemical methods has been studied using the anodizing method. A nanotube layer was formed on Ti alloys in 1.0 M H3PO4 electrolyte with small additions of F- ions. The nanotube nucleation and growth of the α-phase and β-phase appeared differently, and showed different morphology for Cp-Ti, Ti-6Al-4V and Ti-Ta alloys. In the α-phase of Cp-Ti and martensite α′, and in the α″ and β-phase of the Ti-Ta alloy, the nanotube showed a clearly highly ordered TiO2 layer. In the case of the Ti-Ta alloy, the pore size of the nanotube was smaller than that of the Cp-Ti due to the β-stabilizing Ta element. In the case of the Ti-6Al-4V alloy, the α-phase showed a stable porous structure; the β-phase was dissolved entirely. The nanotube with two-size scale and high order showed itself on Ti-Ta alloys with increasing Ta content.

keyword : Nanotubular structure, Ti-Ta alloy, β-stabilizing element, anodizing

By measuring the absorbed hydrogen quantity as a function of the number of cycles, the cycling properties of the Mg-15 wt%Ni-5 wt%Fe2O3 alloy were investigated. The absorbed hydrogen quantity decreased as the number of cycles increased. The Ha value varied almost linearly with the number of cycles. The maintainability of absorbed hydrogen quantity at n=100 was 89.0% for the hydriding reaction time of 10 min. After the 150th hydriding-dehydriding cycle, Mg, Mg2Ni, Mg(OH)2, MgO, and Fe were observed. The phases were analyzed by Rietveld analysis from the XRD patterns of the Mg-15 wt%Ni-5 wt%Fe2O3 alloy after 150 hydriding-dehydriding cycles. The crystallite size and strain of Mg were then estimated with the Williamson-Hall technique.

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

The main purpose of this study was to evaluate the endurance against Al alloy melts and wear resistance of an in-situ synthesized titanium matrix composite (TMC) sleeve for aluminum alloy die-casting. The conventional die-casting shot sleeve material was STD61 tool steel. TMCs have great thermal stability, wear and oxidation resistance. The in-situ reaction between Ti and B4C leads to two kinds of thermodynamically stable reinforcements, such as TiBw and TiCp. To evaluate the feasibility of the application to a TMCs diecasting shot sleeve, the interfacial reaction behavior was examined between Al alloys melts with TMCs and STD61 tool steel. The pin-on-disk type dry sliding wear test was also investigated for TMCs and STD61 tool steel.

keyword : composites, self-propagating synthesis, wear, scanning electron microscopy

Hydrogen was generated by the reaction of metal hydride with water. The variation of hydrogen generation with the kind of powders (milled MgH2, and MgH2 milled with various contents of MgO, MgCl2 or Ni+Nb2O5) was investigated. MgH2 powder with a hydrogen content of 6.05 wt% from Aldrich Company was used. Hydrogen is generated by the reaction of Mg as well as MgH2 with water, resulting in the formation of byproduct Mg(OH)2. For about 5 min of reaction time, milled 95%MgH2+5%MgO has the highest hydrogen generation rate among milled MgH2+x%MgO (x=0, 5, 10, 15 and 20) samples. Milled 90%MgH2+10%MgCl2 has the highest hydrogen generation rate among all the samples.

keyword : hydrogen absorbing materials, mechanical allaying/milling, X-ray diffraction, surface properties, hydrogen generation