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Properties and Rapid Consolidation of Nanostructured NiTi by Pulsed Current Activated Sintering
Wonbaek Kim,Na-Ri Kim,Sung-Wook Cho,박제신,손인진,고인용 대한금속·재료학회 2011 METALS AND MATERIALS International Vol.17 No.2
Highly dense nanostructured TiNi with a relative density of up to 99 % was obtained within two minutes by pulsed current activated sintering under a pressure of 80 MPa. The advantage of this process is that it allows very quick densification to near theoretical density and prohibits grain growth in nano-structured materials. The microstructural and mechanical properties of the dense TiNi produced by PCAS were investigated.
Synthesis of TiN Nanoparticles by Explosion of Ti Wire in Nitrogen Gas
Kim, Wonbaek,Park, Je-shin,Suh, Chang-yul,Cho, Sung-wook,Lee, Sujeong,Shon, In-Jin The Japan Institute of Metals 2009 MATERIALS TRANSACTIONS Vol.50 No.12
<P>Nano-sized Titanium nitride powders were synthesized by electrical explosion of Ti wire under nitrogen atmosphere ranging from 0.2 to 1.5 atm. Electron microscopy and X-ray diffraction studies revealed that the reaction products are cube-shaped single phase TiN nanoparticles. The lattice parameter of TiN nanoparticles increased with nitrogen pressure in the chamber. The nitrogen content of nanoparticles was estimated from their lattice parameter being comparable to the stoichiometric composition of TiN. Small amount of TiN<SUB>0.3</SUB> phase was formed when nitrogen pressure in the chamber was low.</P>
Electrical Wire Explosion of Cr-Coated Ti Wire in N<sub>2</sub> Gas
Kim, Wonbaek,Lee, Sujeong,Suh, Chang-yul,Cho, Sung-wook,Ryu, Taegong,Park, Je-shin,Shon, In-Jin The Japan Institute of Metals 2010 MATERIALS TRANSACTIONS Vol.51 No.11
<P>Cr-coated Ti wire was electrically exploded in N<SUB>2</SUB> gas. The diameter of Ti wire was 0.289 mm and the thickness of Cr coating was 0.033 mm, which corresponds to the average composition of about 25 at% Cr. X-ray diffraction and FE-TEM study revealed that the explosion products consisted of cube-shaped TiN, sphere-shaped Cr<SUB>2</SUB>N, and clusters of extremely fine particles. The average particle size of TiN and Cr<SUB>2</SUB>N was about 35 and 38 nanometers, respectively. The size of the fine particles was small as a few nanometers and clustered heavily. Therefore, it was not possible to examine individually. The particles contained about 28 at% Cr. In some part of the high resolution TEM image, cubic structure could be recognized. The lattice parameter of the particles calculated assuming cubic structure was smaller than TiN and larger than CrN. As a result, it was concluded that the fine particles are (Ti,Cr)N.</P>
Ti-Cr Nanoparticles Prepared by Electrical Wire Explosion
Kim, Wonbaek,Park, Je-shin,Suh, Chang-yul,Cho, Sung-wook,Lee, Sujeong The Japan Institute of Metals 2009 MATERIALS TRANSACTIONS Vol.50 No.9
<P>We previously proposed a new method to synthesize nano-sized powders of various alloys and intermetallic compounds. The method consisted of electrical wire explosion of electrodeposted metal wires. In this study, the method was applied for Ti-Cr alloy. The overall composition of the Cr-coated Ti wire was about Ti-25 at% Cr. The explosion products consisted of equilibrium phases of α-Ti and TiCr<SUB>2</SUB> phases along with meta-stable Ti-rich β phase. The composition of β phase estimated from its lattice parameter was Ti-13 at% Cr. The β phase decomposed completely to α-Ti and TiCr<SUB>2</SUB> phases during isothermal aging at 600°C for one day.</P>
박제신,Wonbaek Kim,Changyoul Suh,Sangbae Kim 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.2
Amorphous Zn65Ni35 alloy, the composition of which lies between β1-NiZn and γ-NiZn phases, was pre-pared by mechanical alloying for 200 hours. The alloy was heat treated at various temperatures and leached in NaOH solution in an effort to enhance the catalytic properties for hydrogen production from methanol. X-ray diffraction study revealed that the amorphous phase crystallized during the heat treat-ment to the equilibrium β1-NiZn and γ-NiZn phases. It was found that Zn65Ni35 alloy leached after heat treatment at 928 K showed the highest catalytic activity for steam reforming of methanol. It is believed that the enhanced catalytic activity of the Zn65Ni35 alloy heat treated at 928 K is due to the dispersed Ni particles on β1-ZnNi matrix which was formed during leaching of the γ-Zn21Ni5 phase.
Microstructure of Ti-Cr Nanoparticles Prepared by Electrical Wire Explosion
Lee, Sujeong,Kim, Wonbaek,Park, Je-shin,Suh, Chang-yul,Cho, Sung-wook The Japan Institute of Metals 2011 Materials transactions Vol.52 No.2
<P>The reaction products of electrical wire explosion with 25 at% Cr-coated Ti wire were identified as β-TiCr<SUB>2</SUB>, α-Ti, β(Ti,Cr) and α-TiCr<SUB>2</SUB> based on the selected area electron diffraction patterns. There was a bimodal size distribution where Ti-Cr particles were 40–50 nm in size, and fine particles less than 10 nm were determined to be pure Ti or Cr. The Ti-Cr nanoparticles are not only a mixture of Ti-Cr phases but they are also heterogeneous themselves at a single particle level, due to the non-equilibrium effects of the EWE process. The very rapid collision and subsequent coalescence of Ti and Cr atom clusters are believed to have contributed to the formation of chemically segregated particles.</P>