Papers by Author: Yi Hyun Park

Abstract: Nano infiltration transient eutectic ceramic (NITE-SiC) was fabricated by hot pressing method using Al2O3 and Y2O3 as sintering additives. The ratio of the Al2O3/Y2O3 additives was changed between 6:4 and 4:6. The densification and mechanical properties were investigated for the sintered temperature. The starting powder was high purity β -SiC nano-powder with an average particle size of 30nm. The bending strength characterization and densification of NITE-SiC was investigated by the FE-SEM and three point bending test.

Abstract: SiC has been extensively studied for high temperature components in advanced energy system and gas turbine because of its excellent high temperature mechanical properties and good thermal-chemical stability etc. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, SiCf/SiC composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of SiCf/SiC composites by hot pressing method. In the present work, monolithic Liquid Phase Sintered SiC (LPS-SiC) was fabricated by hot pressing method in Ar atmosphere at 1800oC under 20MPa using Al2O3, Y2O3 and SiO2 as sintering additives. The starting powder was high purity β-SiC nano-powder with an average particle size of 30nm. The characterization of LPS-SiC was investigated by means of SEM and three point bending test. Base on the composition of sintering additives-, microstructure- and mechanical property correlation, the compositions of sintering additives are discussed.

Abstract: SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. SiCf/SiC composites are promising for various structural materials. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of the process temperature and pressure is key requirements for the fabrication of SiCf/SiC composites by hot pressing method. In the present work, monolithic LPS-SiC was fabricated by hot pressing method at various temperatures. The starting powder was high purity β-SiC nano-powder with an average particle size of 30nm. Compositions of sintering additives were Al2O3 / Y2O3 = 0.7 and 1.5 (wt.%). Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the process temperature. Particularly, relative density of LPS-SiC fabricated at 1820oC with additive composition of Al2O3/Y2O3=1.5(wt.%) was 95%. Also, flexural strength and elastic modulus were 900MPa and 220GPa, respectively. In the fracture surface of this specimen, the size and shape of SiC grains grew up and changed. Also, tortuous crack paths and occurrence of interfacial debonding were observed.

Abstract: The high temperature creep behaviors of heat machine systems such as aircraft engines, boilers and turbines in power plants and nuclear reactor components have been considered as an important and needful fact. There are considerable research results available for the design of high temperature tube materials in power plants, based on uni-axial tension creep tests. However, few studies on the Initial Strain Method (ISM) capable of securing repair, maintenance, cost loss and life loss have been made. In this method, a long time prediction of high temperature creep characteristics can be dramatically reduced through a short time experiment. The purpose of present study is to investigate the high temperature creep life of 1Cr-0.5Mo steel using the Initial Strain Method. The creep test was performed at 500°C, 550°C and 600°C under a pure loading. In the prediction of creep life for 1Cr-0.5Mo steel, the equation of ISM was superior to those of LMP. Especially, the long time prediction of creep life was identified to improve the reliability.

Abstract: Carbon fiber reinforced aluminum layer laminate (CARALL), which were consisted of various numbers of CFRP prepregs, adhesive films and aluminum sheets, were fabricated by an autoclave. Impact damage behaviors of carbon fiber reinforced plastic (CFRP) and CARALL were investigated. The impact damage resistance of CARALL was significantly higher than that of CFRP. Compression after impact (CAI) tests was conducted to investigate the effect of impact damage on the compression strength of CARALL and CFRP specimens. The CAI strength of CFRP and CARALL decreased with increase of impact energy. However, CAI strength of CARALL is higher than that of CFRP, which can be attributed to the excellent impact damage absorbability of aluminum sheet in CARALL.

Abstract: Reduced activation ferritic (JLF-1) steel is one of the leading candidates for blanket/first-wall structures in D-T fusion reactors. In fusion applications, structural materials will suffer the effects of repeated temperature changes. Therefore, a database of tensile strength and fracture toughness are very important as the temperature is 400 ° C and it's TIG welded joint. In this paper, fracture toughness J_IC and KIC) and tensile tests were carried out at room temperature (RT) and at elevated temperature (400 ° C). The tensile properties of the TIG welding joint of JLF-1 steel was also investigated. It was shown that the tensile strength and fracture toughness values of the JLF-1 steel are slightly decreased with as increase in temperature. The fracture toughness values of JLF-1 steel at room temperature and at 400°C show excellent JIC values of about 530 kJ/m2 and 340 kJ/m2, respectively.