Al₂O₃/SiC 세라믹스 균열치유능력에 미치는 첨가제 양의 영향

박성원(S. W. Park),안석환(S. H. Ahn),손창석(C. S. Son),김성광(S. K. Kim),남기우(K. W. Nam) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

The four kinds of Al₂O₃ composite ceramics were prepared using a mixture of 85 wt.% Al₂O₃ (mean size 0.5 μm), 15 wt.% SiC powder with Y₂O₃ as an additive powder (0, 1, 3 and 5 wt.%). The crack-healing strengths were studied as functions of crack-healing temperature and amount of Y₂O₃. The in-situ crack-healing behavior was observed at 1,573 K for 1 h in the air. The heat treated specimen with 3 wt.% of Y₂O₃ showed better crack-healing ability than specimen with 1 or 5 wt.% of Y₂O₃. In case of specimen with 3 wt.% of Y₂O₃, the bending strength of the crack-healed specimen at 1,473 K was recovered to the bending strength of smooth specimen treated at 1573 K. The heat-resistance limit temperature of Al₂O₃ composite ceramics was 1,073 K, 1,373 K, 873 K for the specimen with 1, 3, 5 wt.% of Y₂O₃.

Y₂O₃ 첨가량에 의한 Al₂O₃ 복합재 세라믹스의 균열 치유와 고온 굽힘강도 특성

남기우(K. W. Nam),김해숙(H. S. Kim),손창석(C. S. Son),김성광(S. K. Kim),안석환(S. H. Ahn) 대한기계학회 2007 大韓機械學會論文集A Vol.31 No.11

The four kinds of Al₂O₃ composite ceramics were prepared using a mixture of 85 wt.% Al₂O₃ (mean size 0.5 ㎛), 15 wt.% SiC powder with Y₂O₃ as an additive powder (0, 1, 3 and 5 wt.%). The crack-healing strengths were studied as functions of crack-healing temperature and amount of Y₂O₃. The in-situ crack-healing behavior was observed at 1,573 K for 1 h in the air. The heat treated specimen with 3 wt.% of Y₂O₃ showed better crack-healing ability than specimen with 1 or 5 wt.% of Y₂O₃. In case of specimen with 3 wt.% of Y₂O₃, the bending strength of the crack-healed specimen at 1,473 K was recovered to the bending strength of smooth specimen treated at 1573 K. The heat-resistance limit temperature of Al₂O₃ composite ceramics was 1,073 K, 1,373 K, 873 K for the specimen with 1, 3, 5 wt.% of Y₂O₃.

〈논문〉SiO₂ 콜로이달 첨가에 의한 Si₃N₄ 복합 세라믹스의 Morphology

남기우(K. W. Nam),박승원(S. W. Park),김종순(J. S. Kim),안석환(S. H. Ahn) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Surface morphology of Si₃N₄ composite ceramics has been studied as functions of heat-treatment temperature and additive SiO₂. Additive SiO₂ colloidal and SiO₂ colloidal coating on crack could significantly increase the bending strength. Crack healing temperature decreased 300 K by additive TiO₂. Bending strength of specimen with additive SiO₂ is higher than that of non-additive SiO₂. Moreover, bending strength of specimen with SiO₂ colloidal coating is much higher that of non-coating specimen. In in-situ observation, crack-healed specimen at 1,573 K shows phenomenon like a fog on the surface. By SPM, both crack-healed specimen, non-coating and coating with SiO₂ colloidal, at 1,273 K were healed completely but both of 1,573 K exist crack. This was made by evaporation of SiO₂ at high temperature. Crack-healing materials of Si₃N₄ composite ceramics is crystallized Y₂Si₂O?, Y₂Ti₂O? and SiO₂. A large amount of Si and O, and little C were detected by EPMA. Si and a increase but C decreases according to heat treatment temperature. Specimens with additive SiO₂ were more detected Si and a than that of non-additive SiO₂. Specimen with SiO₂ colloidal coatings were much more detected O.

SiO₂ 콜로이달에 의한 Si₃N₄ 복합 세라믹스의 상온굽힘강도 및 균열치유 현상

남기우(K. W. Nam),김종순(J. S. Kim),이희방(H. B. Lee) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.7

Strength characteristics of Si3N4 composite ceramics has been studied as functions of heat-treatment temperature and additive SiO₂. SiO₂ colloidal could significantly increase the bending strength. Crack healing temperature decreased 300 K by additive TiO₂. Bending strength of specimen added SiO₂ is higher than that of non-added SiO₂. Moreover, bending strength of specimen with SiO₂ colloidal coating is much higher that of non-coated specimen. In in-situ observation, crack-healed specimen at 1,573 K shows phenomenon like a fog on the surface. By SPM, both crack-healed specimen, non-coating and coating of SiO₂ colloidal, at 1,273 K were healed completely but both of 1,573 K exist crack. This was made by evaporation of SiO₂ at high temperature. Crack-healing materials of Si₃N₄ composite ceramics is crystallized Y₂Si₂O?, Y₂Ti₂O? and SiO₂. A large amount of Si and O, and little C were detected by EPMA. Si and O increase but C decreases according to heat treatment temperature. Specimens with additive SiO₂2 were more detected Si and O than that of non-additive SiO₂. Specimen with SiO₂ colloidal coatings were much more detected O.

SiC/SiC 복합재료 기지재의 균열 폭에 따른 균열치유 특성

서임술(I. S. Seo),안우상(W. S. Ahn),남기우(K. W. Nam) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

SiC/SiC composites are among the most promising structural materials for fusion because of their potential application for high performance reactors and superior safety characteristics compared to metallic materials. And a recently developed SiC fiber, Tyranno-SA, was also used as the reinforcement in several SiC/SiC composites. In this study, we examined the relationship between various crack size and bending strength in order to analyze the mechanical properties under the room temperature. The mechanical properties and fracture behaviors were investigated using three-point bending test. we observed an aspect of crack-healing regarding both SiC/SiC composite ceramics and SiC monolithic ceramics as the matrix using a scanning electron microscope. And it was showed that crack healing effect by SiO₂ nano colloidal coating on SiC/SiC composite ceramics was not confirmed clearly. Therefore, we examined the crack-healing effect depending on the size of surface crack on SiC matrix, focusing on the strength recovery of the SiC ceramis as the matrix of SiC/SiC composite ceramics. As the result, It was found that the crack-healing behavior occurred effectively within a width of 1.4 ㎛, regardless of the crack length. And we improved the crack-healing effect, appling to the Hydrostatic Pressure Infiltration in SiO₂ nano colloidal coating method, repeatedly.

배관 감육부의 소성 붕괴 강도

안석환(S. H. Ahn),이수식(S. S. Lee),남기우(K. W. Nam) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-

In pipes used at energy plants, those had exposed to various degradations such as fatigue, creep and corrosion etc. in-service periods. Of them, sometimes, the local wall thinning may result from severe erosion-corrosion damage. Therefore, fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, studies on the effects of local wall thinning on strength and fracture behaviors of piping system are rarely. In this paper, so, the monotonic bending test was performed of full-scale carbon steel pipes with local wall thinning. A monotonic bending load was applied to wall thinned straight pipe specimens by four-point loading at ambient temperature without internal pressure. From the tests, fracture behaviors and plastic collapse strength of locally thinned pipes were manifested systematically. The observed failure modes were divided into four types; ovalization, crack initiation after ovalization, local buckling and crack initiation after local buckling. Also, the strength and the allowable limit of piping system with local wall thinning were evaluated.

SACM645소재 윤활상태에서의 마모특성에 관한 연구

김현수 (H. S. Kim ),김남석 (N. S. Kim ),성기용 (K. Y. Seong ),안석환 (S. H. AHN ),남기우 (K. W. Nam ) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.6

Oil hydraulic piston pumps are being extensively used in the world, because of simple design, light weight and effective cost etc. An oil hydraulic pump is likely to have serious problems of high leakage, friction and low energy efficiency according to large time use. In the oil hydraulic piston pumps the clearance between the valve block and piston plays an important role for volumetric and overall efficiency. In this paper, the wear property of the SACM645 material used the hydraulic piston pump has been work out by experimentation with variable heat treatment. To investigate the effect according to the piston surface condition, seven different types specimen were prepared.

내압을 받는 외부 국부 감육 T 배관의 파손거동

남기우(K. W. Nam),이장원(J. W. Lee),김수영(S. Y. Kim) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11

The pipelines are apt to erosion/corrosion because of the high-speed flow of water and steam with high temperatures/high pressures. This study was carried out to provide an experimental analysis on the fracture behavior of T pipes with local wall thinning under internal pressure. Local wall thinning was machined on the pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area included an eroded ratio of d/t=0.80∼0.963 and an eroded length of l=25 ㎜, 50 ㎜ and 102 ㎜. Three-dimensional elastic-plastic analyses were also carried out using the finite element method, which is able to accurately simulate failure behaviors. In regards to the relation ship between pressure and eroded ratio, the criterion that can be used safely under operating pressure and design pressure were obtained from this calculation. The results of this calculation were in relatively good agreement with that of the experiment.

감육배관의 파괴양식에 따른 AE 특성

김진환(J.H. Kim),안석환(S.H. Ahn),김현수(H.S. Kim),남기우(K.W. Nam),김선진(S.J. Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. However, effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. Acoustic emission(AE) has been widely used in various fields, because of its extreme sensitivity, dynamic detection ability and location of growing defects. In this study, we investigated failure modes of local wall thinning pipes and AE signals by bending test. As results of test, we could divide four types of failure modes of ovalization, ovalization+cracking, local buckling and buckling+cracking. And fracture behaviors of Elastic range, yield range, plastic range and cracking progress could be evaluated in bending test by AE counts, accumulation counts and time frequency analysis. It is expected to be basic data that can protect a risk according to local wall thinning of pipes, as a real time test of AE.

소결보조재 Al₂O₃ 및 Y₂O₃ 첨가에 따른 Sialon 특성

남기우(K. W. Nam),문석재(S. J. Moon),박승원(S. W. Park),안석환(S.H. Ahn),김종순(J. S. Kim) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Various Sialon ceramics were fabricated by hot-pressing mixtures of Si₃N₄, Y₂O₃ and Al₂O₃ powder. The polished specimen of SiAION Ⅰ~Ⅲ showed increased strength by heat treatment, heat treated non-polished specimen were similar or up in strength to polished specimen. The polished specimen of SiAIONN Ⅳ and Ⅴ showed a very high strength, but couldn't obtain increased strength by heat treatment, all specimens were fractured surfaces and inner flaws. Surfaces fractures were initiated from polished surface flaw and comer flaw. inner fractures were initiated from an internal defect.