Han-Ki Yoon

Microstructural and mechanical characteristics of SiC/SiC composites with modified-RS process

Abstract This paper deals with the efficiency of modified-reaction sintering techniques including a impregnation pressure and a cold pressure as well as the applicability of new high performance fiber, in order to develop high performance SiC/SiC composites. SiC/BN coated Hi-Nicalon fiber, SiC coated Tyranno ZMI fiber and Tyranno SA fiber were used in this composite system. Microstructural characteristics of reaction sintered SiC/SiC composites were investigated by means of SEM, EDS and TEM. Mechanical properties and fracture mechanisms of SiC/SiC composites were also evaluated through the three-point bending test. Improved SiC/SiC composites with high density and high strength were successfully fabricated by the sequential application of low pressure impregnation and cold pressing processes. An excellent chemical stability of Tyranno SA fiber during the reaction sintering process was also revealed. Tyranno SA fiber reinforced SiC/SiC composites with no interfacial coating exhibited good flexural strength and elastic modulus, compared to those reinforced by BN/SiC coated Hi-Nicalon and SiC coated Tyranno ZMI fibers. However, this composite system needed an appropriate interfacial coating for proper CMC composite behavior.

Current R&D Activities on Korean Helium Cooled Solid Breeder Test Blanket Module

Helium Cooled Solid Breeder (HCSB) blanket is one of two blanket concepts being considered as Korean Test Blanket Module (TBM) for ITER with the aim for testing and verifying the capability of the breeding blanket concepts. R&D activities being carrying out for HCSB TBM include the development of materials, fabrication technologies, and TBM associated system design. A small sample of ferritic/martensitic (FM) steel was fabricated. It was found that the tensile strength was close to previous value. A fabrication technique of sphere pebbles of lithium titanate breeder and graphite reflector was developed. A FM/FM TIG welding was performed and the results showed that tensile strength of the welded zone was decreased about 10 %. A small punch test method of mechanical property evaluation was introduced to verify the suitability of small specimen for irradiation test by examining the relationship of the conventional uniaxial tensile test, and the tensile strengths were compared. As TBM design has complicated square channel configuration, short square channel was fabricated successfully. Finally, the components and specifications of the TBM associated systems are described in this paper.

STRENGTH CHARACTERISTICS ON RESISTANCE SPOT WELDING OF Al ALLOY SHEETS BY TAGUCHI METHOD

Optimal welding condition in resistance spot welding of 7075-T6 aluminum alloy sheets with the thickness of 0.4mm was investigated by the tensile-shear strength tests and Taguchi method in experimental design with changing various welding conditions respectively. The tensile-shear tests were carried out at cross-head speeds of 0.1mm/min in accordance with the KS B0851. Design methods were systematically performed using an L27(39) orthogonal array table. In the experimental design, three control factors of resistance spot welding conditions were electrode force, welding current and welding time. Electrode force conditions were 882N, 1323N and 1764N, and welding current were 13.5kA, 14kA and 14.5kA, and welding time were 3cycle, 4cycle and 5cycle.

Influence of the SiO and SiON buffer layer on IZO thin films deposited on PET by inclination opposite target type DC magnetron sputtering method

IZO films were deposited onto polyethylene terephthalate (PET) substrate at room temperature by the inclination opposite target type DC magnetron sputtering equipment. In this paper, SiO or SiON thin films of about 20nm thickness were introduced as buffer layers between the IZO thin films and the PET substrate. Electrical resistivity, transmittance and surface uniformity properties were investigated. It is clear that the film surface roughness of multilayer thin films was less than that of IZO monolayer thin films. The surface average roughness (Ra) of the multilayer film with 230nm IZO layer thickness was about 1.6nm, and that of IZO monolayer film was 2.4nm. All of the multilayer samples had high optical transmittance (about 90%) in the visible region. Of particular note, the transmittance of multilayer films was slightly higher than that of monolayer films when the IZO layer was thicker than 200nm. High electrical conductivity was also achieved with thick films.

THE EFFECTS ON HEAT TREATMENT OF SIC COATED / GRAPHITE PLATE BY RF SPUTTERING SYSTEM

Silicon carbide film was coated by RF sputtering system onto graphite plate substrate. Surface roughness of substrate was polished by wet polishing with sand paper, number of 3000. RF power was 200 W in 0.4 Pa of argon gas. Deposition holding time was 3hours in 600 °C temperature. Specimens were heat treated by 1200, 1400 and 1500 °C for 1 hour to research the effect of heat treatment on SiC coating layer. Atomic Force Microscope (AFM) was used to characterize the surface morphology and the Sq surface roughness. AFM was used to investigate the grain size and roughness of the surface of thin coating film. X-ray diffraction (XRD) was used for detecting the coated SiC thin film by thin film mode. FE-SEM was used to characterize the microstructure of SiC coating film.

The Characteristics of Painted Coating on Aluminum Sheet by Sending Conditions

Researchers suggested painted coating characteristics of aluminum sheet by various sending condition. Painted coating is used to protect the surface of the blocks from the interior and exterior. It is also used to enhance the value of automobiles and ship materials. This process makes the materials surface for protection and elegance. Although analysis of the roughness and critical scratch load of painted coating is important, the effects of this material have not progressed much. In this study, the characteristics of painted coating in the other conditions of the polished aluminum sheet were investigated. The results of both various conditions and initial roughness values were almost similar to final values after painted coating.

Wear Characteristics of SiC by Sintered Temperature and SiO2Contents

In this study, liquid phase sintered SiC (LPS-SiC) materials were made by hot pressing method. The particle size of nano-SiC powder was 30nm. Alumina (Al2O3), yttria (Y2O3) and silica (SiO2) were used for sintering additives. To investigate effects of SiO2, ratios of SiO2 contents were changed by five kinds. Materials have been sintered for 1 hour at 1760 C, 1780 C and 1800 C under the pressure of 20MPa. The system of sintering additives which affects a property of sintering as well as the influence depending on compositions of sintering additives were investigated by measurement of density, mechanical properties such as flexural strength, vickers hardness and sliding wear resistance were investigated to make sure of the optimum condition which is about matrix of SiCf/SiC composites. The abrasion test condition apply to load of 20N at 100RPM for 20min. Sintered density, flexural strength of fabricated LPS SiC increased with increasing the sintering temperature. And in case of LPS-SiC with low SiO2, sliding wear resistance has very excellent. Monolithic SiC 1800°C sintering temperatures and 3wt% have excellent wear resistance. †책임저자, 회원, 경상대학교 기계항공공학부 E-mail : wjpark@gnu.ac.kr TEL : (055)640-3183 FAX : (055)640-3188 경상대학교 기계항공공학부, 해양산업연구소 * 회원, 경상대학교 대학원 정밀기계공학과 ** 회원, 동의대학교 기계공학과 1. 서 론 우주항공 산업 및 에너지 산업이 급속히 발전 함에 따라 세라믹스와 실리사이드 계열의 금속간 화합물을 중심으로 1000°C를 넘는 온도에서 적용 할 수 있는 고기능성 극고온 구조 재료의 개발이 활발히 진행되고 있다. 세라믹스(ceramics)는 무기 재료를 주원료로 하는 산화물(oxide), 질화물 (nitride), 탄화물(carbide) 등과 같이 금속원소와 비 금속원소들이 이온결합(ionic Bonding) 및 공유결 합(covalent bonding)을 하고 있는 화합물을 의미 한다. 금속재료, 고분자재료 등에 비하여 강도, 경도, 내식성, 내열성 및 내마모성이 매우 크며, 이러한 우수한 특성으로 인하여 공업용 내열재료 에서 관심이 점점 높아지고 있는 물질이다. 구조 용 세라믹스의 경우 기계적 특성과 열적 특성이 우수하여 각종 엔진부품, 절삭공구, 브레이크류 라이닝(linning), 메카니컬 실(mechanical seal)등과 같은 산업부품에 사용되고 있으며, 이러한 세라 믹스로서 주로 탄화규소(SiC), 질화규소(Si3N4), 알 루미나(Al2O3) 및 지르코니아(ZrO2) 등이 사용되 고 있다. 이 중 특히 탄화규소는 질화규소에 비 해 상온에서의 강도와 인성은 낮지만, 1400 C 이 상의 초고온에서도 강도와 강성이 다른 구조용 세라믹스에 비해 우수하고, 내마모성, 내산화성,

EFFECT OF WEIGHT LOSS AND MICROSTRUCTURE BY HEAT TREATMENT AND FABRICATION OF LPS-SIC CERAMICS

In the present work, monolithic LPS-SiC was fabricated by hot press method with the addition of Al2O3, Y2O3 and SiO2 and annealed at different temperatures to observe microstructure evolution. Process temperature was varied from 1760°C to 1800°C. Process pressure and maturing time are 20MPa and 1h respectively. Hot pressed samples were cut into rectangular bars. Three-point flexural strength was measured at room temperature in air with a cross-head speed of 0.1 mm/min and a lower span of 18 mm. Flexural strength and elastic modulus measurement was performed using a universal test machine (INSTRON 5581, USA). The apparent density of the sintered body was measured by the Archimedes method. The specimen dimension of the heat treatments is 4W×25L×1.5T mm. The specimens used for weight-loss measurement were set into an open carbon crucible to avoid nonuniform temperature distribution within the furnace. Post-fabrication heat treatment was performed in vacuum atmosphere (PO2 ≈ 0.01 Pa). The temperature was increased at a rate of 20 K/min to the heat-treatment temperature and maintained for 10 hours, after which the specimens were furnace cooled. After heat-treatment, weight of heat-treated specimens was carefully measured by an electronic balance. In order to reveal the microstructural change in heat-treated specimen, X-ray diffractometry and microstructure observation were performed and compared with those of the as-fabricated one.

Mechanical properties of ITO/PET thin film deposited by DC MG method

The ITO film was deposited onto the PET substrate at room temperature by the inclination opposite target type DC magnetron sputtering equipment. An indium tin alloy (In/sub 2/O/sub 3/ (90 wt%) + SnO/sub 2/ (10 wt%)) target was used. The total sputtering pressure was varied from 2.6/spl times/10/sup -1/ to 8.3/spl times/10/sup -1/ Pa. The experimental result showed that the ITO film produced at room temperature had microstructure in which an X-ray diffraction peak is not clear, regardless of the total sputtering pressure. All the film showed a high optical transmittance. The ITO films prepared at low pressure gave low electrical resistivity. The elastic modulus and hardness of ITO films on various total sputtering pressures was increased with decreasing the total sputtering pressure and this tendency was similar to the change in electrical resistivity with decreasing the total sputtering pressure.

Thermal and Structural Analyses of Semi-metallic Gasket Joined with Graphite Seal for Ship Engine Piping Flange

We performed thermal and structural analyses to evaluate the structural integrity of a semi-metal gasket for a flange with increases in the internal fluid temperature and pressure using a commercial FEA program. As a thermal analysis result, the temperature distribution of the gasket body increased with an increase in the internal fluid temperature until the maximum fluid temperature of 600 °C. In addition, the structural analysis showed that contact pressures of more than 35 MPa occurred uniformly in the graphite seal regions. It was found that no fluid leakage occurred under the load conditions for the structural analysis because the contact pressure in the graphite seal region was greater than the maximum internal fluid pressure of 35 MPa. Therefore, we demonstrated the structural integrity of the semi-metal gasket by performing the thermal and structure analyses under the maximum fluid temperature of 600 °C and the internal fluid pressure of 35 MPa. Received 28 March 2017, revised 18 September 2017, accepted 19 October 2017 Corresponding author In-Sup Lee: +82-51-890-2287, islee@deu.ac.kr It is noted that this paper is revised edition based on proceedings of KIM 2016 Gyeongju. c 2017, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.