• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.571-572
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• 2006

RTP (rapid thermal pressing), one of micro-pattern replication techniques like hot embossing, is focused on achieving shorter cycle time. DFSS(Design for Six Sigma) has been applied in order to enhance the completeness of the development process for RTP system. According to DIDOV roadmap, we derived design concepts and subsequently decided the main performances, design factors, and components for RTP system. In the design process of RTP system using finite element analysis, it was realized that its structural characteristics affect large area replicability. Optimizing structural design factors, based on CAE, it was checked out that its large area replicability could be improved in a virtual test. Finally, we have a plan to validate the large area replicability of the developed RTP system, by performing micro-pattern replication tests with polymeric sheets.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.3
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• pp.138-145
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• 2012

An ${\alpha}$-Ferrite (Fe) powder dispersed with 4 vol.% of $Al_2O_3$ was successfully produced by a simple miling at 210 K with a mixture of $Fe_2O_3$, Fe and Al ingredient powders, followed by 2 step high temperature consolidation: Hot Pressing (HP) at 1323 K and then Hot Isostatic Pressing at 1423 K. The microstructure of the consolidated material was characterized by standard metallographic techniques such as XRD (X-ray Diffraction), TEM and STEM-EDS. The results of STEM-EDS analysis showed that the HIPed materials comprised a mixture of pure Fe matrix with a grain size of ~20 nm and $Al_2O_3$ with a bimodal size distribution of extremely fine (~5 nm) and medium size dispersoids (~20 nm). The mechanical properties of the consolidated materials were characterized by compressive test and micro Vickers hardness test at room temperature. The results showed that the yield strength of the ODS (Oxide Dispersion Strengthened) Fe alloy are as much as $674{\pm}39$ MPa and the improvement of the yield strength is attributed to the presence of the fine $Al_2O_3$ dispersoid.

• Journal of the Korean Ceramic Society
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• v.54 no.2
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• pp.121-127
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• 2017

Gadolinium tetraboride ($GdB_4$) was synthesized by reduction of $Gd_2O_3$ using boron carbide in presence of carbon. Effect of temperature on product quality was investigated. Pure $GdB_4$ powder was obtained in vacuum at $1500^{\circ}C$. Pressureless sintering experiments revealed that sintering takes place only above $1600^{\circ}C$. A maximum density of 77.1% of the theoretical value was obtained at $1800^{\circ}C$ by pressureless sintering. Hot pressing resulted in 95.5% of theoretical density at the lower temperature of $1700^{\circ}C$ under 35 MPa pressure. Hardness and fracture toughness of dense $GdB_4$ were measured and found to be 21.4 GPa and $2.3MPa{\cdot}m^{1/2}$, respectively. After exposure to air at $900^{\circ}C$, the formation of a porous and non-protective oxide layer was observed.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.247-255
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• 2000

Silicon carbide with sialon was prepared by hot pressing and transient liquid-phase sintering, and the effects of sintering atmosphere and starting phases on their microstructural characteristics were investigated. The sintered SiC with Sialon composition(Y2O3, AlN, Si3N4) in argon atmosphere had high sintered density and large aspect ratio. But sintered specimens in nitrogen atmosphere showed low aspect ratio and small grian size, becuase of the retardation of phase transformation and grain growth. Addition of Y-Sialon powder to SiC also retarded the phase transformation to ${\alpha}$-SiC from ${\beta}$-SiC and densification. The SiC specimen prepared from the starting ${\beta}$-SiC powder with Sialon composition(Y2O3, AlN, Si3N4) showed the highest fracture toughness about 6.0 MPa$.$m1/2.

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.467-471
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• 2009

Effects of boron and carbon on the densification and thermal decomposition of an AlN-SiC-$TiB_2$ system were investigated. $SiO_2$ was mostly removed by the addition of carbon, while $Al_2O_3$ formed $Al_4O_4C$ and promoted the densification of the systems above $1850^{\circ}C$. Rather porous specimens were obtained without the additives after hot pressing at $2100^{\circ}C$, while densification was mostly completed at $2000^{\circ}C$ by using the additives. The sintering temperature decreased further to $1950^{\circ}C$ by applying spark plasma sintering. The additives promoted the shrinkage of AlN by forming a liquid phase which was originated from the carbo- and boro-thermal reduction of $Al_2O_3$ and AlN.

• Corrosion Science and Technology
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• v.6 no.1
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• pp.24-28
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• 2007

Alumina coated SiC whiskers were prepared by homogeneous precipitation of aluminum sulfate. The Si3N4 composites reinforced with coated SiC whiskers were fabricated by hot-pressing at $1800^{\circ}C$ for 2 h under an $N_{2}$ atmosphere of 0.1 MPa to examine the effects of coated whiskers on the mechanical properties of SiC whisker reinforced $Si_{3}N_{4}$ composite. By the addition of alumina coated SiC whiskers instead of as received ones, the fracture toughness of composite was about 6.7 $MPam^{1/2}$ which was slightly lower than as received SiC whisker reinforced composite. This result seems to be caused by the fact that the crack deflection and whisker pull-out were decreased. Thus, alumina coated SiC whiskers were considered to form relatively strong interface bond with $Si_{3}N_{4}$ matrix.

• Korean Journal of Materials Research
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• v.16 no.6
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• pp.341-345
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• 2006

[ $Ni_2Si$ ] mixed powders were mechanically alloyed by a ball mill and then processed by hot isostatic pressing (HIP) and spark plasma sintering (SPS). In the powder that was mechanically alloyed for 15minutes(MA 15 min), only Ni and Si were observed but in the powder that was mechanically alloyed for 30minutes(MA 30 min), $Ni_2Si$, Ni and Si were mixed together. Some of the MA 15 min powder and MA 30 min powder were processed by HIP under pressure of 150MPa at the temperature of $1000^{\circ}C$ for two hours and some of them were processed by SPS under pressure of 60 MPa at the temperature of $1000^{\circ}C$ for 60 seconds. Both methods completely compounded the powders to $Ni_2Si$. The maximum density of sintered lumps by HIP method was 99.5% and the maximum density of the sintered lump by SPS method was 99.3%. with the hardness of HRc 66 with the hardness of HRc 63. Therefore, the SPS method that can sinter in short time at low cost is considered to be more economical that the HIP method that requires complicated sintering conditions and high cost and the sintering can produce target materials in desired sizes and shapes to be used for thin film.

• Tribology and Lubricants
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• v.24 no.5
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• pp.269-274
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• 2008

Carbon nanotube composite is considered to be a good candidate material for composite material because of its excellent mechanical property and low density under high temperature as well as good wear and frictional properties. In this study, tribological characteristics of carbon nanotube aluminum composite were evaluated using pin-on-disk wear tester. Spark Plasma Sintering method is more effective than Hot Pressing method in terms of wear and friction. The composite with 1% CNT has the lowest friction and wear characteristic.

• Korean Journal of Metals and Materials
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• v.46 no.6
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• pp.390-401
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• 2008

The objective of this study is to evaluate various machining characteristics of AlN-hBN machinable ceramics in micro end-milling process for its further application. First, AlN based machinable ceramics with hBN contents in the range of 10 to 20vol% were prepared by hot-pressing. Material properties of the composites, such as relative density, Vickers hardness, flexural strength, Young's modulus and fracture toughness were measured and compared. Then, micro end-milling experiments were performed to fabricate micro channels using prepared system. During the process, cutting forces, vibrations and AE signals were measured and analyzed using applied sensor system. Machined micro channel shapes and surface roughness were measured using 3D non-contact type surface profiler. From the experimental results, it can be observed that the cutting forces, vibrations and AE signal amplitudes decreased with increasing hBN contents. Also, measured surface roughness and profiles were improved with increasing hBN contents. As a result of this study, optimum machining conditions can be determined to fabricate desired products with AlN-hBN machinable ceramics based on the experimental results of this research.

• Electronic Materials Letters
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• v.14 no.6
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• pp.725-732
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• 2018

The thermoelectric and transport properties of Ti-doped FeVSb half-Heusler alloys were studied in this study. $FeV_{1-x}Ti_xSb$ (0.1 < x < 0.5) half-Heusler alloys were synthesized by mechanical alloying process and subsequent vacuum hot pressing. After vacuum hot pressing, a near singe phase with a small fraction of second phase was obtained in this experiment. Investigation of microstructure revealed that both grain and particle sizes were decreased on doping which would influence on thermal conductivity. No foreign elements pick up from the vial was seen during milling process. Thermoelectric properties were investigated as a function of temperature and doping level. The absolute value of Seebeck coefficient showed transition from negative to positive with increasing doping concentrations ($x{\geq}0.3$). Electrical conductivity, Seebeck coefficient and power factor increased with the increasing amount of Ti contents. The lattice thermal conductivity decreased considerably, possibly due to the mass disorder and grain boundary scattering. All of these turned out to increase in power factor significantly. As a result, the thermoelectric figure of merit increased comprehensively with Ti doping for this experiment, resulting in maximum thermoelectric figure of merit for $FeV_{0.7}Ti_{0.3}Sb$ at 658 K.