• 한국분말재료학회지
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• 제16권2호
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• pp.98-103
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• 2009

The ultrafine titanium carbonitride particles ($TiC_{0.7}N_{0.3}$) below 100nm in mean size were successfully synthesized by Mg-thermal reduction process. The nanostructured sub-stoichiometric titanium carbide ($TiC_{0.7}$) particles were produced by the magnesium reduction at 1123K of gaseous $TiC_{l4}+xC_2Cl_4$ and the heat treatments in vacuum were performed for five hours to remove residual magnesium and magnesium chloride mixed with $TiC_{0.7}$. And final $TiC_{0.7}N_{0.3}$ phase was obtained by nitrification under normal $N_2$ gas at 1373K for 2 hrs. The purity of produced $TiC_{0.7}N_{0.3}$ particles was above 99.3% and the oxygen contents below 0.2 wt%. We investigated in particular the effects of the temperatures in vacuum treatment on the particle refinement of final product.

• 한국주조공학회지
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• 제34권1호
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• pp.1-5
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• 2014

The austempering transformation behavior in Fe-0.7wt.%C-2.3wt.%Si-0.3wt.%Mn steel is investigated. Each specimen was austenitized for 60 min at $900^{\circ}C$, and austempered at $380^{\circ}C$ for different time periods varying from 2 min to 256 min. After the austempering heat treatment, the Stage I and II evolutions are performed using optical metallography, X-ray diffraction and image analyses. Variations in the X-ray diffraction patterns and lattice parameters of the ferrite and austenite demonstrate that the residual austenite decomposes into ferrite and carbide during the Stage II evolution; moreover the amount of ferrite increases during the Stage I evolution. While the amount of austenite increases during Stage I, it dicreases during Stage II. Overall, the variations in the volume fractions of the microstructure and carbide formation in stages I and II meet high temperature austempering reaction of the ausferrite microstructure.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.221-229
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• 2004

In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as $0^{circ},\;30^{circ},\;45^{circ},\;60^{circ}\;and\;90^{circ}$. The plastic zone expands more at the upper side of the composite beam than at the lower side for $30^{circ},\;45^{circ}\;and\;60^{circ}$ orientation angles. Residual stress components of ${\sigma}_{x}\;and \;{\tau}_{xy}$ are also found in the section of the composite beam.

• Bulletin of the Korean Chemical Society
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• 제28권4호
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• pp.533-537
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• 2007

This paper describes the heteroepitaxial growth of single-crystalline 3C-SiC (cubic silicon carbide) thin films on Si (100) wafers by atmospheric pressure chemical vapor deposition (APCVD) at 1350 oC for micro/nanoelectromechanical system (M/NEMS) applications, in which hexamethyldisilane (HMDS, Si2(CH3)6) was used as a safe organosilane single-source precursor. The HMDS flow rate was 0.5 sccm and the H2 carrier gas flow rate was 2.5 slm. The HMDS flow rate was important in obtaing a mirror-like crystalline surface. The growth rate of the 3C-SiC film in this work was 4.3 μm/h. A 3C-SiC epitaxial film grown on the Si (100) substrate was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Raman scattering, respectively. These results show that the main chemical components of the grown film were single-crystalline 3C-SiC layers. The 3C-SiC film had a very good crystal quality without twins, defects or dislocations, and a very low residual stress.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.337-341
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• 2004

Engineering ceramics have superior heat resistance, corrosion resistance, and wear resistance. Consequently, these art significant candidates for hot-section structural components of heat engine and the inner containment of nuclear fusion reactor. Besides, some of them have the ability to heal cracks and great benefit can be anticipated with great benefit the structural engineering field. Especially, law fracture toughness of ceramics supplement with self-healing ability. In the present study, we have been noticed some practically important points for the healing behavior of silicon nitride, alumina, mullite with SiC particle and whisker. The presence of silicon carbide (SiC) in ceramic compound is very important for crack-healing behavior. However, self-healing of SiC has not been investigated well in detail yet. In this study, commercial SiC was selected as sample, which can be anticipated in the excellent crack healing ability. The specimens were produced three-point bending specimen with a critical semi-circular crack of which size that is about $50-700{\mu}m$. Three-point bending test and static fatigue test were performed cracked and healed SiC specimens. A monotonic bending load was applied to cracked specimens by three-point loading at different temperature. The purpose of this paper is to report Strength Properties and Elastic Waves Characteristics of Silicon Carbide with Crack Healing Ability.

• 한국기계가공학회지
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• 제1권1호
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• pp.55-62
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• 2002

This investigation reports the grinding characteristics of titanium alloy(Ti-6AI-4V). Grinding experiments were performed at various grinding conditions. The grinding forces were measured to investigate the grindability of titanium alloy with the five different wheels including Green carbide, Alumina, Resin Diamond, Resin CBN and Vitrified CBN. To investigate the grinding characteristics of titanium alloy grinding force, force ratio, specific grinding energy and grinding-ratio were measured. Surface roughness was also measured with tracer and the ground surfaces were observed with SEM Residual stress measurement was conducted on the X-Ray Diffractometer. Force ratio of grinding of titanium alloy was very lower than that of grinding of SKD-11 Surface roughness with Resin Diamond wheel was a little larger and rougher surface than that with other wheels Grinding ratio of titanium alloy was a little lower than that of other materials. Grinding ratio of titanium alloy with Diamond wheel was almost six times larger than that With CBN wheel. As a result of five different wheels, the most excellent wheel in grinding of Titanium alloy was Resin Diamond wheel.

• 한국전기전자재료학회논문지
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• 제23권2호
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• pp.98-102
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• 2010

This paper describes that single crystalline 3C-SiC (cubic silicon carbide) thin films have been deposited on carbonized Si(100) substrates using hexamethyldisilane (HMDS, $Si_2(CH_3){_6}$) as a safe organosilane single precursor and a nonflammable mixture of Ar and $H_2$ gas as the carrier gas by APCVD at $1280^{\circ}C$. The deposition was performed under various conditions to determine the optimized growth condition. The crystallinity of the 3C-SiC thin film was analyzed by XRD (X-ray diffraction). The surface morphology was also observed by AFM (atomic force microscopy) and voids between SiC and Si interfaces were measured by SEM (scanning electron microscopy). Finally, residual strain and hall mobility was investigated by surface profiler and hall measurement, respectively. From these results, the single crystalline 3C-SiC film had a good crystal quality without defects due to viods, a low residual stress, a very low roughness.

• 한국광학회지
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• 제27권3호
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• pp.106-113
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• 2016

본 논문에서는 37채널을 갖는 적응광학계용 SiC(Silicon Carbide) 변형거울의 파면 보상 성능 검증에 관한 내용을 다룬다. 컴퓨터 시뮬레이션을 통해 SiC 변형거울의 파면 보상 성능을 예측하였고, 실제 closed-loop 적응광학계를 구성하여 파면 보상 성능을 확인 하였다. Closed-loop 적응광학계는 광원, 위상판, SiC 변형거울, 고속 샥-하트만 센서 그리고 제어용 컴퓨터로 구성되어있다. 회전하는 위상판에 의해 왜곡된 파면을 샥-하트만 센서로 측정하고, SiC 변형거울을 이용하여 왜곡된 파면을 보상해주는 시스템이다. 결과적으로 closed-loop 적응광학계에서 500 Hz의 속도로 PV(Peak-to-Valley) $0.3{\mu}m{\sim}0.9{\mu}m$, RMS(Root-Mean-Square) $0.06{\mu}m{\sim}0.25{\mu}m$의 왜곡된 파면을 PV $0.1{\mu}m$, RMS $0.03{\mu}m$이하로 보상시킬 수 있었다.

• Nuclear Engineering and Technology
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• 제45권4호
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• pp.513-522
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• 2013

The ODSCC detected in the TSP position of Ulchin 3&4 SGs are typical ODSCC of Alloy 600MA tubes. The causative chemical environment is formed by concentration of impurities inside the occluded region formed by the tube surface, egg crate strips, and sludge deposit there. Most cracks are detected at or near the line contacts between the tube surface and the egg crate strips. The region of dense crack population, as defined as between $4^{th}$ and $9^{th}$ TSPs, and near the center of hot leg hemisphere plane, coincided well with the region of preferential sludge deposition as defined by thermal hydraulics calculation using SGAP computer code. The cracks developed homogeneously in a wide range of SGs, so that the number of cracks detected each outage increased very rapidly since the first detection in the $8^{th}$ refueling outage. The root cause assessment focused on investigation of the difference in microstructure and manufacturing residual stress in order to reveal the cause of different susceptibilities to ODSCC among identical six units. The manufacturing residual stress as measured by XRD on OD surface and by split tube method indicated that the high residual stress of Alloy 600MA tube played a critical role in developing ODSCC. The level of residual stress showed substantial variations among the six units depending on details of straightening and OD grinding processes. Youngwang 3&4 tubes are less susceptible to ODSCC than U3 and U4 tubes because semi-continuous coarse chromium carbides are formed along the grain boundary of Y3&4 tubes, while there are finer less continuous chromium carbides in U3 and U4. The different carbide morphology is caused by the difference in cooling rate after mill anneal. There is a possibility that high chromium content in the Y3&4 tubes, still within the allowable range of Alloy 600, has made some contribution to the improved resistance to ODSCC. It is anticipated that ODSCC in Y5&6 SGs will be retarded more considerably than U3 SGs since the manufacturing residual stress in Y5&6 tubes is substantially lower than in U3 tubes, while the microstructure is similar with each other.

• 센서학회지
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• 제22권3호
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• pp.175-180
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• 2013

This paper describes the characteristics of cubic silicon carbide (3C-SiC) films grown on a carbonized Si(100) substrate, using hexamethyldisilane (HMDS, $Si_2(CH_3)_6$) as a safe organosilane single precursor in a nonflammable $H_2$/Ar ($H_2$ in Ar) mixture carrier gas by atmospheric pressure chemical vapor deposition (APCVD) at $1280^{\circ}C$. The growth process was performed under various conditions to determine the optimized growth and carbonization condition. Under the optimized condition, grown film has a single crystalline 3C-SiC with well crystallinity, small voids, low residual stress, low carrier concentration, and low RMS. Therefore, the 3C-SiC film on the carbonized Si (100) substrate is suitable to power device and MEMS fields.