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A typical brightener-propargyl alcohol-was added to enhance the cutting performance during Ni-diamond composite electrodeposition. Electrochemical analysis was performed and mechanical properties such as hardness and wear resistance were examined. In addition, the surface morphology of composite coating layers was observed using an optical microscope, and using image analysis software, the dispersivity of the diamond particles was analyzed to calculate the number of single diamond particles. A galvanostatic test was employed to identify the electrodeposition mechanism as a function of the concentration of propargyl alcohol. When 0.1 mg/ℓ of propargyl alcohol was added, the dispersivity and adhesion performances of the Ni-diamond coating layer were optimized for cutting tools. (Received September 22, 2015)

keyword : composites, deposition, wear, image analysis, diamond

In the present work, the effect of Ca additions on microstructure and corrosion characteristics of high pressure die-cast Mg-4Al-2Sn alloy has been investigated. Mg-4Al-2Sn-xCa (x= 0, 0.3 and 0.7wt.%) alloy was prepared by using a high pressure die-casting method. Results indicated that the microstructure of Mg-4Al-2Sn alloy consisted of α-Mg, Mg17Al12 and Mg2Sn phase. With increase of Ca additions, CaMgSn phase was newly formed and grain size was sharply decreased. From the test results, the corrosion resistance of die-cast Mg-4Al-2Sn alloy was significantly improved by Ca addition. It is considered that stabilization of Mg(OH)2 layer and refinements of microstructure with increase of Ca additions. (Received October 14, 2015)

keyword : metals, casting, corrosion, scanning electron microscopy, SEM

The influence of the size distribution and particle interaction on packing behaviors is investigated for water/gas-atomized STS 316L powders with polydisperse and bimodal size distributions. In most cases, the experimentally estimated packing fraction matched well with the results predicted by the Desmond model, which implies that the packing fraction increases with the polydispersity and skewness. When the powder size decreases below ~10 μm, however, the calculation starts to positively deviate from the experimental data, presumably because particle interaction plays a significant role in the powder packing behavior. The Desmond model is modified to consider the effects of particle interaction as well as of size distribution on the packing behavior, and the modified model shows better accordance with the experimental data, particularly for fine powders, than does the original Desmond model. †(Received August 25, 2015)

keyword : metals, powder processing, microstructure, scanning electron microscopy, SEM, packing fraction

The effects of Al and Sm additions on microstructure and mechanical properties of as-cast and as-extruded Mg-8Li alloys were investigated. The microstructure of as-cast Mg-8Li alloy consists of α-Mg and β-Li phases. On the other hand, the addition of Sm led to significant grain refinement of Mg alloys due to the formation of Mg41Sm5 particles. Sm addition to Mg-Al resulted in the formation of the MgLi2Al, AlLi, and Al2Sm intermetallic compounds. The microstructure and precipitates of Al and Sm addition alloys were refined and elongated in the extrusion direction because of severe deformation during extrusion. The maximum values of the yield strength and ultimate tensile strength were 195.9MPa and 221.4MPa at Mg-8Li-5Al-2Sm alloy content. MgLi2Al, AlLi, and Al2Sm intermetallic compounds played significant roles in the increase of the mechanical properties. (Received June 29, 2015)

keyword : alloys, casting, extrusion, mechanical properties, scanning electron microscopy, SEM

Hot deformation behavior of Ti-4Al-4Fe-0.25Si alloy with martensite microstructure was investigated by compression tests at temperatures of 1023 - 1173 K (α+β phase region) and strain rates of 10-3 - 1 s-1. By analyzing the deformation behavior, plastic deformation instability parameters including strain rate sensitivity, deformation temperature sensitivity, efficiency of power dissipation, and Ziegler’s instability were evaluated as a function of deformation temperature and strain rate, and they were further examined by drawing deformation processing maps. The microstructure evolution was also studied to determine the deformation conditions under which equiaxed α phase was formed in the microstructure without remnants or kinked α phase platelets and shear bands, these last two of which cause severe cracks during post-forming process. Based on the combined results of the processing maps and the microstructure analysis, the optimum α+β forging conditions for Ti-4Al-4Fe-0.25Si alloy were determined. (Received January 20, 2016)

keyword : metals, thermomechanical processing, microstructure, compression test, processing map

The purpose of this research is to report on the fabrication and characterizations of Pd/ZnO nanorod-based Schottky diodes for optoelectronic applications. ZnO nanorods (NRs) were grown on silicon (Si) substrates by a two step hydrothermal method. In the first step, a seed layer of pure ZnO was deposited from a solution of zinc acetate and ethyl alcohol, and then in the second step, the main growth of the ZnO NRs was done over the seed layer. The structural morphology and optical properties of the ZnO NR films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-vis spectroscopy. The electrical characterization of the Pd/ZnO NR contacts was studied using a current-voltage (I-V) tool. The ZnO NR films exhibited a wurtzite ZnO structure,and the average length of the ZnO NRs were in the range of 750 nm to 800 nm. The values of ideality factor, turn-on voltage and reverse saturation current were calculated from the I-V characteristics of Pd/ZnO NR-based Schottky diodes. The study demonstrates that Pd/ZnO NR Schottky contacts fabricated by a simple and inexpensive method can be used as a substitute for conventional Schottky diodes for optoelectronic applications. (Received November 5, 2015)

keyword : zinc oxide, hydrothermal, nanorods, schottky contact, ideality factor

Sn-doped indium oxide (ITO) films and ITO/ZnO bi-layered films were prepared on polycarbonate substrates by RF magnetron sputtering without intentional substrate heating. In order to consider the influence of the ZnO thickness on the structural, optical, and electrical properties of ITO/ZnO films, the thickness of the ZnO buffer layer was varied from 5 to 20 nm. As-deposited ITO films show an average optical transmittance of 79.2% in the visible range and an electrical resistivity of 3.0×10-4 Ωcm, while films with a 5-nm thick ZnO buffer layer film show an electrical resistivity of 2.6×10-4 Ωcm and films with a 20-nm thick ZnO buffer layer show an optical transmittance of 82.0%. Based on the figure of merit, it is concluded that the ZnO buffer layer enhances the optical and electrical performance of ITO films used as transparent conducting oxides in flexible display applications. (Received October 13, 2015)

keyword : optoelectronic materials, optical properties, x-ray diffraction, sputtering, AFM

Much research has been performed on the synthesis of magnesium hydride with added catalysts, leading to the preparation of magnesium hydride with additives. High pressure, high temperature, and long periods are required to prepare a sample with an MgH2 phase without additives. In order to synthesize an additive(s)-free sample with a single MgH2 phase, 90 wt% Mg+10 wt% MgH2 (named 90Mg+10MgH2) was milled in a hydrogen atmosphere of 15 bar for 10 h. Hydrogen absorption and release properties of the prepared samples were investigated, and compared with those of a purchased MgH2. A sample whose large fraction is the MgH2 phase was prepared. Particles of 90Mg+10MgH2 after hydriding-dehydriding cycling have a form of agglomerates consisting of fine particles and have more defects than are present in MgH2 after hydriding-dehydriding cycling. 90Mg+10MgH2 released 0.06 wt% H for 8 min, 0.40 wt% H for 10 min, 4.66 wt% H for 20 min, 5.54 wt% H for 25 min, 5.62 wt% H for 30 min, 5.64 wt% H for 50 min, and 5.65 wt% H for 60 min at 648 K in the first cycle. (Received September 2, 2015)

keyword : hydrogen absorbing materials, mechanical alloying/milling, hydrogen, X-ray diffraction, an additive(s)-free MgH2 sample

A reaction-bonded SiC-Ti3SiC2 ceramic composite was produced for use in a ceramic-metal composite cladding tube. The diffusion reaction between TiC and Si was investigated with respect to process pressure. The mole-fraction of TiC and Si was controlled to be 3:2 to obtain a Ti3SiC2 phase in the ceramic composite. Sintering was conducted at 1450℃ where TiC particles could react with melted Si. SiC ceramic composites consisting of Ti3SiC2 and TiSi2 matrix phases were obtained. The formation of the constituent phases was strongly related to the processing pressure. The number of second phases in the SiC-Ti3SiC2 composite was controlled by adjusting the processing pressure. When the powder compacts were not pressurized, no Ti3SiC2 phase was formed. However, the Ti3SiC2 phase was formed under pressurizing during compaction and/or sintering. The higher the pressure the higher the purity of SiC-Ti3SiC2. The dual-phased SiC-Ti3SiC2 composite, however, revealed the decreased resistance to high-temperature oxidation. It is suggested that the incorporation of TiSi2 in the composite increases the oxidation resistance as well as mechanical property. (Received September 24, 2015)

keyword : ceramics, sintering, microstructure, X-ray diffraction, oxidation resistance

This study presents the development of a heat transfer model for the continuous heat treatment of thin metal wires. The cross-section of the wires was regarded as a lumped capacitance system. The final heat transfer equation had the form of a one-dimensional problem. The model included Joule heating of the conducting wire as well as cooling by convection and radiation heat transfers. The model employed temperature-dependent thermophysical properties and yielded results different from the solution with constant properties. Movement of the wire skewed the temperature profile in the moving direction in the heating region. The profiles of electrical resistivity and electrical potential gradient were not uniform in the heating region, resulting in non-uniform heat generation. Also, we tried to estimate the convection heat transfer coefficient, which is not fixed for a material, by comparing the numerical results to the experimental ones. (Received July 28, 2015)

keyword : wire, rolling, annealing, joule heating, heat transfer