발간논문

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This article shows that the aspect of chipping damage resulting from the mechanical dicing of semiconductor silicon wafers can vary with the revolving velocity of the sawing blade. The final separation of the silicon wafers occurs along the friction-induced notch formed toward the [001]-dicing direction under the revolving velocity of the blade lower than 1000 rpm. The scope of the resulting chipping damage due to the notch effect is not meaningfull beyond from the (010)-dicing plane. On the other hands, the final separation of the silicon wafers takes place due to the cleavage fracture along {011}-crystal planes tilted by 45° from the (010)-dicing plane under the revolving velocity of the blade higher than 5000 rpm. This work makes a conclusion that the scale of chipping damage can abruptly increase with the enhanced rotation speed of the sawing blade because of the transition from the notch effect to the cleavage fracture.

keyword : semiconductor, silicon wafer, crystal structure, dicing, damage

The aim of this study was to investigate the effect of microstructures (martensite, ferrite, or mixed ferrite and martensite) on the mechanical properties. Of particular interest was the Charpy impact results for 9Cr-2W reduced-activation ferritic-martensitic (RAFM) steels. Under normalized conditions, steel with martensitic microstructure showed superior tensile strength and Charpy impact results. This may result from auto-tempering during the transformation of martensite. On the other hand, both ferrite, and ferrite mixed with martensite, showed unusually poor Charpy impact results. This is because the ferrite phases, and coarse M23C6 carbides at the ferrite-grain boundaries acted as cleavage crack propagation paths, and as preferential initiation sites for cleavage cracks, respectively. After the tempering heat treatment, although tensile strength decreased, the energy absorbed during the Charpy impact test drastically increased for martensite, and ferrite mixed with martensite. This was due to the tempered martensite. On the other hand, there were no distinctive differences in tensile and Charpy impact properties of steel with ferrite microstructure, when comparing normalized and tempered conditions.

keyword : metals, toughness, impact test, tempering, reduced activation ferritic-martensitic steel

Despite of many attractive properties, the low fracture toughness of ZrO2 limits their wide application. One of the most obvious tactics to improve the mechanical properties has been to make fabrication of a nanostructured material and composite material. Nano-powders of Cr and ZrO2 were synthesized from Cr2O3 and Zr powders using high energy ball milling. Nanocrystalline 4Cr-3ZrO2 composite was consolidated by pulsed current activated sintering method within 2 minutes from mechanically synthesized powders of ZrO2 and Cr. The relative density of the composite was 98.5%. The fracture toughness and hardness of 4Cr-3ZrO2 composite in this study are simultaneously higher than those of monolithic ZrO2.

keyword : composite, nanomaterial, synthesis, mechanical properties

This study attempted to manufacture Cu-In coating materials via the cold spray process and to investigate the effect of powder alloy composition on the microstructure and properties of the cold sprayed Cu-In based materials. Three kinds of Cu-15 at%In, Cu-20 at%In, Cu-30 at%In powders were used in this study. The results showed that the coating layers could be manufactured with Cu-15 at%In and Cu-20 at%In compositions via the cold spray process, except for Cu-30 at%In. Cold sprayed Cu-15 at%In and Cu-20 at%In coating materials possessed α-Cu, Cu4In and Cu7In3 phases. But, Cu-30 at%In powders contained only brittle Cu7In3 intermetallic phase. Post annealing heat treatments (100~500 ℃/1 hr.) were conducted on the Cu-In based coating materials to improve the densification properties. Porosity and hardness decreased as the annealing temperature increased. With the heat treatment of 500 ℃/1 hr., porosity decreased into 0.38%(Cu-15 at%In) and 0.74%(Cu-20 at%In). However, in heat treatment at temperature beyond 400 ℃, a small amount of additional In2O3 was detected. The optimal alloy composition for cold sprayed Cu-In based target material was also discussed.

keyword : alloys, powder processing, coating, microstructure, scanning electron microscopy, SEM

Effects of Li addition on the microstructure and mechanical properties of as-cast and as-extruded AZ31-xLi alloys were investigated. AZ31 alloys with different Li addition(0, 2, 5, 8 and 11 wt%) were cast under atmosphere at 720 ℃ and extruded at 200 ℃. Li addition to AZ31 resulted in the formation of AlLi and MgLi2Al intermetallic compounds and random texture. With increasing Li addition from 5 to 8 and 11 wt%, ultimate tensile strength was decreased from 264 to 232 and 193 MPa. On the other hand, the elongation was improved remarkably from 15.6% to 14.2% and 38.6% at room temperature due to the transformation from HCP to BCC crystal structure and a weaker basal texture. With increasing Li addition from 5 to 8 and 11 wt%, compression yield strength was increased from 156 to 193 and 178 MPa. MgLi2Al intermetallic compounds played a significant role for the increase of the mechanical properties.

keyword : metals, extrusion, texture, electron backscattering diffraction, EBSD, Mechanical property

Pt and Pt alloys are used as a structural material for the fabrication of glass because it has a high strength and good volatilization properties at high temperature. Especially Pt-Au alloys, which increase a contact angle between glass and the Pt alloy, have been received a lot of attention, however, there have not been many studies related with the volatilization properties at high temperatures. In this study, volatilization properties of Pt-4%Au-0.3%ZrO2 were conducted at elevated temperature. The volatilization properties of Pt-4%Au-0.3%ZrO2 were compared with those of Pt and Pt-0.3%ZrO2. The results showed that the volatilization rate of Pt-4%Au-0.3%ZrO2 was the fastest. It was confirmed that Au was dominantly volatilized because the vapor pressure of Au was higher than Pt oxide at over 1473 K. Also, the concentration gradient of Au between surface and inside of Pt-4%Au-0.3%ZrO2 specimens was generated owing to high vapor pressure of Au at over 1473 K. At this time, Au atoms in the inside of the specimen diffuse to the surface of the specimen, and Pt atoms diffuse opposite way. However, the diffusion rate of Au atoms is higher than that of Pt atoms. Therefore, micro-pores are generated in the inside of the specimen because Pt atoms cannot fill the site where Au atoms occupy until it diffuses to the surface of the specimen.

keyword : Platinum, Pt-Au, Volatilization, Vapor pressure, High temperature

Thermodynamic study on CaO-SiO2-Al2O3 slag system was carried out to understand the refining ability of Ca and Al in ferrosilicon. The effect of slag composition and oxygen partial pressure on refining ability of slag was also thermodynamically evaluated. Experimental results indicated that equilibrium concentrations of Ca and Al are both decreased with increasing SiO2 activity of slag and oxygen partial pressure. Also, the effect of activity coefficients of Ca and Al in molten alloy was not significant, while activities of each component in slag were important determining factors. Refining ability of Ca and Al of CaO-SiO2-Al2O3 slag from ferrosilicon is possibly increased by controlling interfacial oxygen partial pressure and activities of components of slags.

keyword : ferrosilicon, metals, purification, thermodynamics properties

Various 0.45 cm2 dye-sensitized solar cell (DSSC) devices of glass/FTO/blocking layer/TiO2/dye/electrolyte/nano-thick Pt/glass structure were prepared by varying the Pt layer thickness from 10 to 100 nm. The phase and roughness of Pt layers were examined using XRD and AFM measurements. The catalytic activity of Pt was checked by cyclic voltammetry. The sheet resistance and interface resistance of Pt were examined using four point probe and impedance measurements. The reflectance of Pt was measured by uv-vis-nir spectroscopy. The photovoltaic energy conversion efficiency (ECE) was checked using a solar simulator and potentiostat. The XRD and AFM showed that crystalline Pt layers were formed with even surface roughness in nano thicknesses. The catalytic activity and conductivity of Pt increased with increasing thickness. The UV-Vis-NIR result revealed that the average reflectance decreased drastically as Pt layer thickness decreased less than 30 nm. The ECEs of DSSCs showed as 4.11% and 6.57% with thicknesses of 10 nm and 100 nm. The ECEs of DSSCs showed the same above 30 nm. Our results implied that a Pt thickness of larger than 30 nm might offer appropriate ECE.

keyword : solar cells, sputtering, optical properties, solar simulator, nano thickness

We investigated the photoelectrochemical (PEC) properties of CdS/CIGS thin films as the hydrogengenerating photo-electrode in Na2SO4 electrolyte. The onset potential of CIGS of thin film by itself which is a point of beginning redox reaction for hydrogen generation was .0.6 V under illumination of 200 mW. However, with the deposition of CdS layer on CIGS film, CdS/CIGS structures produced three times enhanced photocurrents at .0.1 V vs compared with only CIGS thin film. CdS layer has ideal band-gap energy and position for redox reaction under visible light irradiation. Also, CdS layer could make P-N junction with CIGS film and form stepwise band-gap structure, which help electrons and holes transfer more easily. From these results, CdS/CIGS thin films could be regarded as a promising photo-electrode cell structure for hydrogen generation.

keyword : photoelectrochemisty, PEC, photoelectrode, hydrogen generation, CdS, CIGS

Blast furnace is generally known for iron mass production vessel with a long campaign life. However during the blast furnace operation, erosion of inner wall by the burden descent is unavoidable and it becomes the most important factor for determining the campaign life of the blast furnace. Lining of the furnace is composed of refractory and cooling Cu stave. Due to the erosion of the refractory brick, the Cu stave built in the refractory brick is exposed after several years use of the furnace. Wear of stave surface is then accelerated by the burden descent rapidly especially at high temperature and high pressure condition. Therefore, wear characteristics of Cu stave are needed to be predicted. Wear of Cu samples is tested at high temperature friction conditions using a ring-on-disc type on custom-built equipment. The wear conditions by burden descent could be changed by the operating temperature and pressure of furnace, coke particle size, hardness of Cu in high temperature, and the cooling temperature, etc. The experimental results are used to predict the life of blast furnace through the measurement of Cu wear loss.

keyword : metals, hot working, wear, Cu stave, blast furnace