• Journal of the Korean Society for Heat Treatment
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• v.31 no.3
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• pp.135-142
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• 2018

In this study, we have fabricated n-type $Bi_2Te_{2.85}Se_{0.15}$ compounds by different processing routes such as crushing, milling and mixing respectively. Subsequently, the obtained powders were consolidated by spark plasma sintering (SPS). The phase crystallinity of bulk samples were identified using X-ray diffraction technique. Powder morphology and fracture surface of bulk samples were observed using the scanning electron microscopy (SEM). The Seebeck coefficient and electrical conductivity values were significantly increased for the milling sample than crushing and mixing samples. As a result, the maximum power factor was obtained $2.4mW/mK^2$, which is thrice than that of crushing process. The maximum figure of merit (ZT) of 0.77 was achieved at 400 K for the milling sample. Furthermore, relatively high hardness and density values were noticed for the different processed samples.

• Resources Recycling
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• v.31 no.1
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• pp.21-28
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• 2022

The smelting reduction of spent lithium-ion batteries results in metallic alloys of cobalt, nickel, and copper. To develop a process to separate the metallic alloys, leaching of the metallic mixtures of these three metals with H₂SO₄ solution containing 3% H₂O₂ dissolved all the cobalt and nickel, together with 9.6% of the copper. Cyanex 301 selectively extracted Cu(II) from the leaching solution, and copper ions were completely stripped with 30% aqua regia. Selective extraction of Co(II) from a Cu(II)-free raffinate was possible using the ionic liquid ALi-SCN. Three-stage cross-current stripping of the loaded ALi-SCN by a 15% NH₃ solution resulted in the complete stripping of Co(II). A process was proposed to separate the three metal ions from the sulfuric acid leaching solutions of metallic mixtures by employing solvent extraction.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.64-70
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• 2012

Samples of pure Mg, 76.5 wt%Mg-23.5 wt%Ni, and 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ were prepared by reactive mechanical grinding and their hydriding and dehydriding properties were then investigated. The reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation and to shorten diffusion distances of hydrogen atoms. After hydriding-dehydriding cycling, the 76.5 wt%Mg-23.5 wt%Ni and 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ samples contained $Mg_2Ni$ phase. In addition to the effects of the creation of defects and the decrease in particle size, the addition of Ni increases the hydriding and dehydriding rates by the formation of $Mg_2Ni$. Expansion and contraction of the hydride-forming materials (Mg and $Mg_2Ni$) with the hydriding and dehydriding reactions are also considered to increase the hydriding and dehydriding rates of the mixture by forming defects and cracks leading to the fragmentation of particles. The reactive mechanical grinding of Mg-Ni alloy with $Fe_2O_3$ is considered to decrease the particle size.

• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1056-1063
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• 2010

We present a new joining method for Pd-Cu membrane foils used as permeation tubes to collect $CO_2$. Since foils have poor mechanical strength, joining should be done at low temperatures to reduce residual stresses and without joining pressure. This contradicts the well known conditions for good contact between base materials that determines joint qualities. We selected Sn-Ag-Cu alloys that are highly reactive with Pd and Cu as a filler metal. As the filler melts at joining temperatures as low as $220{\sim}280^{\circ}C$, Pd and Cu are dissolved into the melt and react with the filler elements, which raises the melting temperature of the filler based on eutectic structures among the elements. Then, isothermal solidification progresses for the rest of the joining time. Intermetallic compounds (IMC) in the joints, one of the main factors for brittle joints, are inevitably formed. However, by optimizing both joining time and temperature, we balanced the wettability with IMC. Sealing test results confirmed that the joints are mechanically reliable during operation.

• Korean Journal of Metals and Materials
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• v.48 no.4
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• pp.297-304
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• 2010

The microstructure and hardness of $CO_2$ laser welds were investigated in the Ti-stabilized ferritic stainless steel 409L. The observed specimen was welded in a fully penetrated condition in which the power was 5 kW and the welding speed 5 m/min. The grain structure near the bond line of the laser welds was produced by epitaxial growth. The grain size was the largest in the fusion zone, and HAZ showed nearly the same grain size as that of the base metal. The HAZ microstructure consisted of subgrains and precipitates that were less than 100 nm in size and that were located along the subgrain boundaries. On the other hand, the hardness was the highest in the fusion zone due to the large amount of small precipitates present. These were composed of TiN, Ti(C,N) and $TiO_2$+Ti(C,N). The hardness decreased continuously from the fusion zone of the base metal. The HAZ hardness was slightly greater than that of the base metal due to the existence of subgrains and precipitates in the subgrain boundary.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.05a
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• pp.1-1
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• 2000

The results of the modification of metal materials treated by high temperature pulst:d plasma fluxes (HTlPPF) with a specific power of incident flux changing in the $(3...100)10^5{]\;}W/cm^2$ range and a pulse duration lying from 15 to $50{\;}\mu\textrm{s}$ have been presented. The results of HTPPF action were studied on the stainless steels of 18Cr-l0Ni, 16Cr- 15Ni, 13Cr-2Mo types; on the structural carbon steels of (13...35)Cr, St. 3, St. 20, St. 45 types; on the tool steels of U8, 65G, ShHI5 types, and others; on nickel and high nickel alloy of 20Cr-45Ni type; on zirconium- and vanadium-base alloys and other materials. The microstructure and properties (mechanical, tribological, erosion, and other properties) of modified materials and surface alloying of metals exposed to HTPPF action have been investigated. It was found that the modification of materials by HTPPF resulted in a simultaneous increase of several properties of the treated articles: microhardness of the surface and layers of 40...60 $\mu\textrm{m}$ in depth, tribological characteristics (friction coefficient, wear resistance), mechanical properties ({\sigma_y}, {\;}{\sigma_{0.2}}.{\;}{\sigma_r}) on retention of the initial plasticity ($\delta$), corrosion resistance, radistanation erosion under ion irradiation, and others. The determining factor of the changes observed is the structural-phase modification of the near-surface layers, in particular, the formation of the fine cellular structure in the near-surface layers at a depth of $20{\;}{\mu\textrm{m}}$ with dimension of cells changing in the range from 0.1 to $1., 5{\;}\mu\textrm{m}$, depending on the kind of material, its preliminary treatment, and the parameters of plasma fluxes. The remits obtained have shown the possibility of purposeful surface alloying of metals exposed to HTPPF action over a depth up to 20...45 $\mu\textrm{m}$ and the concentration of alloying element (Ni, Cr, V) up to 20 wt.%. Possible industrial brunches for using the treatment have been also considered, as well as some results on modifying the serial industrial articles by HTPPF.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.2
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• pp.121-129
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• 1996

The solubility of Ti in Al matrix was determined by X-ray diffraction method on two different mechanical alloying systems, i.e Al+$Al_3Ti$ and Al+Ti alloys. Starting powder compositions of two systems were chosen for final volume fraction of $Al_3Ti$ phase being 25%. The solubility of Ti in ${\alpha}$-Al was estimated by the lattice parameter measurement of Al. For Al+$Al_3Ti$ mixture, it appeared that some of $Al_3Ti$ particles decomposed during milling and maximum solubility of Ti in Al was about 0.99%. The majority of $Al_3Ti$ particles were dispersed uniformly in Al matrix, having approximate size of 100~200 nm. On the other hand, higher Ti solubility of 1.24 wt.% was found in Al+Ti system, with starting composition of Al+10 wt.%Ti. After 15 hours of milling, Ti phase was identified as 20 nm sized particles embedded in Al matrix. The annealing of mechanically alloyed powders from Al+$Al_3Ti$ and Al+10 wt.%Ti systems was followed in the temperature range of 200 to $600^{\circ}C$ to study thermal stability of supersaturated solution of Al(Ti). After annealing, the lattice parameter of Al reverted back to that of pure Al, and the peak intensity ratio of $Al_3Ti$/Al was increased more than the original value before annealing. These results suggest that Ti dissolve into alpha-Al solutions during milling, and by annealing, $Do_{22}-Al_3Ti$ phase forms from Al(Ti) solution.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.589-597
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• 2010

In the present study, the effect of variation in alloying elements on the carbide formation behavior during casting and homogenization treatment of M2 high speed steels was investigated. M2 high speed steels of various compositions were produced by vacuum induction melting. Contents of C, Cr, W, Mo, and V were varied from the basic composition of 0.8C, 0.3Si, 0.2Mn, 4.0Cr, 6.0W, 5.0Mo, and 2.0V in weight percent. Homogenization treatment at $1150^{\circ}C$ for 1.5 hr followed by furnace cooling was performed on the ingots. Area fraction and chemical compositions of eutectic carbide in as-cast and homogenized ingots were analyzed. Area fraction of eutectic carbide appeared to be higher in the ingots with higher contents of alloying elements the area fraction of eutectic carbide also appeared to be higher on the surface regions than in the center regions of ingots. As a result of the homogenization treatment, $M_2C$ carbide, which was the primary eutectic carbide in the as-cast ingots, decomposed into thermodynamically stable carbides, MC and $M_6C$. The latter carbide was found to be the main one after homogenization. Fine carbides uniformly distributed in the matrix was found to be MC type carbide and coarsened by homogenization.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.263-268
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• 1999

In this study, a new concept of aluminum-matrix composites and the possibility of in-situ processing are suggested, and preliminary results on AI- Ti system are presented. Fine powders of AI-lO% Ti were prepared by the gas atomization so that fine $Al_3Ti$ formed into flake shape. A 25v/o $Al_3Ti/Al$ composite sample was made by the pow­d er metallurgy process involving hot extrusion. Microstructure and mechanical behavior both at room temperature and high temperatures were analysed by OM, SEM, TEM and tension test. Microstructural characteristics and mechanical properties of the composites exhibited similar behavior to those of $SiC_w/2124$ composites. Merits and drawbacks of the $Al_3Ti/Al$ composites are discussed together with a possibility of further improvement.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.49-56
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• 2010

This study investigated how the surface of Al-12wt.%Si alloy modified by the plasma electrolytic oxidation process (PEO). The PEO process was performed in an electrolyte with sodium hexametaphsphate as a conducting salt, and the effect of ammonium metavanadate on variations in the morphology of electrochemically generated oxide layers on the alloy surface was investigated. It is difficult to form a uniform passive oxide layer on Al alloys with a high Si content due to the differences in the oxidation behavior of the silicon-rich phase and the aluminum-rich phase. The oxide layer covered the entire surface of the Al-12WT.%Si alloy uniformly when ammonium metavanadate was added to the electrolyte. The oxide layer was confirmed as a mixture of $V_2O_3$ and $V_2O_5$ by XPS analysis. In addition, the oxide layer obtained by the PEO process with ammonium metavanadate exhibited a black color. Application of this surface modification method is expected to solve the problem of the lack of uniformity in the coloring of oxide layeres caused by different oxidation behaviors during a surface treatment.