Gue-Serb Cho

Effect of V addition on microstructure and mechanical property in the Nb–Si alloy system

Abstract Microstructure and mechanical property of vanadium-added two-phase alloys consisting of α-Nb 5 Si 3 phase and Nb solid solution (Nb ss ) were investigated in terms of a variation of chemical composition and compression test at room temperature and at 1773 K. The equilibrium phase field of α-Nb 5 Si 3 and Nb ss in the Nb–Si–V ternary alloy system was examined at 1773 K using scanning electron microscopy equipped with wavelength dispersive X-ray spectroscopy and X-ray diffraction. The α-Nb 5 Si 3 phase formed in the Nb–Si–V system was extended along the Nb 5 Si 3 –V 5 Si 3 pseudo-binary line without a solubility range of Si at 1773 K, while vanadium is soluble continuously along the Nb–V phase boundary with Si solubility of about 0.7 at%. It is observed that volume fraction ratio of the present alloy is predominantly dependent on Si content but exhibited no dependence on vanadium content. With increasing vanadium content, primary α-Nb 5 Si 3 and Nb ss phases became finer through the whole composition studied. The 0.2% offset yield strength at room temperature increased with increasing volume fraction of α-Nb 5 Si 3 phase and with increasing vanadium content in Nb ss . In contrast, the 0.2% offset yield strength at 1773 K decreased with increasing vanadium content in Nb ss . Details will be discussed in correlation with microstructure, phase relation and mechanical property.

Combination of reinforcing powders and matrix alloys for fabrication of aluminum matrix composites by plasma synthesis method

Several kinds of powders and aluminum alloys are adopted to study the feasibility of the fabrication of aluminum matrix composites through plasma synthesis. Some powders do not incorporate into the molten aluminum due to reflection on the melt surface and dissolution in the plasma arc. On the contrary, iron powders are well incorporated into the molten aluminum. The iron powders incorporated into the molten aluminum make angular Al13Fe4 intermetallic compounds in the matrix. In addition, some portion of iron powders dissolve into the matrix and change the microstructures of the matrix alloys. The effects of dissolved Fe on the microstructures and mechanical properties of the composites are examined.

Characteristic variation of spark plasma-sintered Ta compacts

In the present study, we applied the SPS process to obtain a tantalum (Ta) compact for a sputtering target. Sintered Ta compacts were characterized with respect to microstructure, relative density, Vickers hardness and phase composition of the inside and the surface. By radio frequency (RF) thermal plasma treatment, a spherical ultra-fine Ta powder was obtained; however, the oxygen content increased due to severe passivation during powder handling. Higher sintering temperature and the RF plasma treatment increased the densification of the sintered compact and also the Vickers hardness. From XRD analysis, only Ta was identified in the cross section of compacts, and TaC formed by the reaction between Ta and the graphite mould was found in the surface of the compacts. The evacuation of the chamber and the reduction by the graphite mould promote the purification of the compact.

Effects of cementation factors on the Cu nanoparticle deposit of Cu-multi-wall carbon nanotubes composites.

Copper (Cu) coated carbon nanotubes (CNTs) were prepared and investigated by chemical reduction or cementation method. The morphology changes of Cu nanoparticles deposited onto the multiwall carbon nanotubes with metallic zinc (Zn) as a reducing agent have been examined at different cementation factors. The precipitated Cu nanoparticles from the copper ion in the reaction solution were deposited onto and entangled with the CNT substrates. CNTs used were multi-wall carbon nanotubes with average diameter of 10-20 nm and length of 10-50 μm. As-prepared CNTs products were purified by nitric acid solution, and then the CNTs were washed several times with distilled water, and dried in vacuum. The pre-treated CNTs were suspended in solvent. Then, the copper salt was dissolved in the suspension containing the CNTs. The deposited morphology and distribution of copper particles on the CNTs substrate were investigated by changing the solute, solvent and reducing agent. The Cu/CNTs agglomerates were obtained in the presence of copper chloride and copper sulphate salts, and water and ethanol were used as the solvents. And the raw CNTs were pretreated with glacial acetic acid for increasing the coverage rate of copper particles over the CNTs surface at different acid concentrations. The Cu deposited CNTs were characterized in respect of morphology and distribution of CNTs and Cu particles with field emission scanning electron microscopy (FESEM). The copper crystals were identified by X-ray diffraction patterns.