발간논문

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The tensile response of Lean Duplex 329LA stainless steel was investigated over various strain rates. It was observed that the mechanical response, including in particular the total elongation of the tested alloy, was strongly affected by the strain rate. As the strain rate decreased from 10-1 s-1 to 10-4 s-1, the elongation increased. As the strain rate increased, the deformation mode in an austenite phase was dominated by dislocation glide, resulting in deterioration of the elongation. The substructure of the ferritic phase showed a dislocation cell structure, independent of the applied strain rate. The optimum mechanical properties of lean duplex stainless steel thus can be obtained by controlling the deformation mode in the austenitic phase.

keyword : stainless steel, stress-strain, phase transformation, deformation, metals, mechanical properties, electron backscattering diffraction, EBSD

A DLC coating was deposited onto diamond micro-blades with Cu/Sn bond metal doped with WS2 and MoS2 as a solid lubricant to enhance the cutting efficiency. In comparison with blades without the DLC coating, the blades with the DLC coating showed a decreased specific wear rate in a ball-on-disc wear test and less momentary energy consumption in a dicing test. This is ascribed to reduction of the lateral friction coefficient with the work piece. A qualitative analysis of the reduction of momentary energy consumption was carried out to evaluate the effect of DLC coating on dicing performance. Chipping sizes of the diced workpiece surfaces were reduced by the DLC coating, which is beneficial for accurate machining.

keyword : DLC coating, dicing efficiency, diamond micro-blades, friction coefficient, momentary energy consumption

In this study, the microstructural evolution and various characteristics of Al-20~45wt%Zn alloys were investigated. In terms of microstructure, as the amount of Zn addition to the alloys increased, the α-phase size decreased and the α+η non-equilibrium solidification phase fraction increased. Also, increasing Zn content improved the wear resistance of the alloys, but reduced the damping capacity and toughness of the alloys. Their physical properties of the Al-Zn alloy with high Zn content, specifically the wear resistance and toughness, were superior to those of commercial ALDC12 alloys for die-casting. Based on these results, we considered the possibility of application of the developed Al-Zn alloy as a structural material.

keyword : alloys, casting, mechanical properties, hardness test, impact test

Leaching of rare earth metals (REEs) from the polymetallic manganese nodule was carried out using HCl solution. The leaching behavior of all REEs except Ce was very similar. The leaching efficiency of Ce was lower than that of other REEs due to poor solubility. Concentration of HCl was identified as a critical factor that enhanced the dissolution of REEs, and REEs were completely leached at 4.0 N HCl. The dissolutions of REEs and iron with different HCl concentrations indicated that half of the REEs are likely to exist in iron oxide phase with the remainder occurring in a different phase. Effective leaching, about 40.0 %, of total REEs was observed at a HCl concentration of 0.5 N, a time of 1 h and a temperature of 30 ℃ with low dissolution of other base metals.

keyword : manganese nodule, metals, recycling, recovery

Influences of surface oxygen plasma treatment on the work function of ITO thin films were studied. As a result of plasma etching, the roughness of the film was reduced with increasing plasma treatment time. The REELS measurement with primary electron energy of 300eV revealed that the band gap of the extreme surface of the thin film was increased by 1.03eV. At 1700eV, however, the band gap of the film remained unchanged. The UPS results indicated that the work function increased by 0.82eV and from the XPS spectra the valence band maximum was measured to be 5.32eV after the plasma treatment. The change in the work function of the extreme surface of the film was attributed to an increase in the amount of oxygen after the plasma treatment, which did not affect the electrical conductivity or the value of the band gap. XPS was used to examine whether the oxygen plasma treatment caused any change in the composition ratio of the ITO thin film. The spectra showed that almost all of the peaks for the carbon compounds of C-H-O were eliminated after the plasma treatment. In addition, In-O bonds and O=O bonds were increased as a result of abundant oxygen in the surface of the film. Our results demonstrated that the electronic, optical, and structural properties of plasma-treated ITO thin films in an oxygen environment were greatly improved.

keyword : surface modification, indium tin oxide, ITO, reflected electron energy loss spectroscopy, REELS, wltra violet photoelectron spectro scopy, UPS, x-ray photoelectron spectroscopy, XPS

We suggest a new OLED encapsulation method involving an LMPA-epoxy double line structure using joule heating. First, an underlayer that consists of a heating layer, an insulating layer, and a sacrificial layer was manufactured in the form of a line with 0.5 mm width and thousands of Å thickness. A mixture of Sn-58Bi and UV curing epoxy was then printed over the underlayer pattern. Applying 5.8 W of electrical power on the heating layer for 60 seconds, Sn-58Bi was separated from the epoxy. The LMPA-epoxy double line structure was stabilized and sufficient adhesion strength between the two substrates was secured by UV curing. The thickness of the Cu sacrificial layer and the content of the epoxy in the mixture were optimized through experiments. (Received August 11, 2014)

keyword : alloys, annealing, melting, scanning electron microscopy (SEM), organic light emitting diode, OLED

The resistive switching properties driven by low voltage in a nano-scale resistiverandom- access-memory device composed of Al(top)/TiO2-X/TiO2/Al(bottom) were investigated in this paper. TiO2-X and TiO2 layers were deposited by the atomic layer deposition method and a TiO2-X layer was added during the process of rapid-thermal-annealing at 600 °C to induce oxygen vacancies. Structural analyses by using X-ray diffraction suggested that the TiO2-X film annealed at this temperature changes from an amorphous to a rutile phase. The oxygen vacancies of the TiO2-X region acted as traps for electrons and led to memory behavior. The device exhibited resistive-random-access-memory behavior consistent with resistive switching properties such as a high current on/off ratio greater than 1000:1, low-voltage driving less of han 0.5 V, and nonvolatility for over 1.0 × 105s.

keyword : amorphous materials, annealing, electrical properties, electrical, rutile TiO2-X/TiO2 layer

Glass/FTO/compact TiO2/mesoporous TiO2/perovskite layer dispersed MgO nanopowder structured samples were prepared from a mixture of CH3NH3PbI3 (methylammonium lead iodide, MAPbI3) and MgO with a sol-gel process involving PbI2+MgO and CH3NH3I (methylammonium iodide, MAI). The phase and color change of MAPbI3 with MgO was examined by XRD and micro-Raman analyses, and by using a uv-vis-nir-colorimeter. Optical microscopy and field emission scanning electron microscopy (FE-SEM) were employed to evaluate the evolution of the microstructure. The XRD analysis confirmed that MAPbI3 with MgO added degrades more slowly compared to MAPbI3 alone due to Mg(OH)2 formation. Micro-Raman analysis results showed only the existence of MAPbI3. Optical microscopy and FE-SEM revealed degradation in color and microstructural change in all samples as time passed. However, the degradation was confirmed to occur more slowly for the MAPbI3 with added MgO. A lab color analysis with uv-vis-nir also supported the results of the color changes by degradation. These results indicate that the degradation of MAPbI3 may be dramatically delayed by the addition of nano MgO powders. (Received November 03, 2014)

keyword : MgO, CH3NH3PbI3, degradation, perovskite solar cells

The present study develops a two-dimensional numerical code that can predict the performance of a thermoelectric generator module including a p-leg/n-leg pair and top and bottom electrodes. The present code can simulate the detailed thermoelectric phenomena including the heat flow, electric current, Joule heating, Peltier heating, and Thomson heating, together with the efficiency of the modules whose properties depend on the temperature. The present numerical code can be used for the design optimization of a thermoelectric power generator. (Received December 03, 2014)

keyword : numerical modeling, efficiency, thermoelectricity, Seebeck effect, Peltier effect, Joule heating, Thomson heating

Optimum heat treatment conditions to improve the hardness and corrosion resistance of ternary Mg-Ca-Zn alloys have been studied, based on the theoretical models and DSC (Differential scanning calorimetry) experimental data. Two-step heating process at 420 ℃ and 480 ℃ has been applied and we have found that the low melting point phase, Ca2Mg6Zn3 can effectively be dissolved into α-Mg matrix without premature melting. Due to preceding treatment at lower temperature followed by the second stage solid solution heat treatment at 480 ℃, Mg-1.4 wt%Ca-xwt%Zn alloys (x=0, 1.5 and 4.0) exhibit improved corrosion resistance than that from the single step solid solution treated alloy at 480 ℃. However, aging treatment of the alloy at 200 ℃ has led to the homogeneous precipitation of Ca2Mg6Zn3 and Mg2Ca phases in the matrix as well as at the grain boundary. This microstructural change results in the deterioration of corrosion resistance mainly originated from galvanic corrosion between the matrix and the precipitates. The hardness of Mg-1.4%Cax% Zn alloy, on the other hand, significantly increases with Zn addition by applying two-step solid solution and aging heat treatment.

keyword : alloys, casting, mechanical property, solid solution hardening, corrosion resistance