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17-4PH 스테인레스강의 기계적 , 화학적 성질에 미치는 회수재의 사용과 조성변화의 영향
이선호,강춘식,이경환,김도경 ( Seon Ho Lee,Choon Sik Kang,Kyong Hwan Lee,Do Kyong Kim ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.2
N/A Mechanical and chemical properties of the 17-4PH have been investigated after recycled melting. As the result, it has been ascertained that the change of Ni, Cu, Nb, C amount affects the mechanical and chemical properties. It is important to minimize contamination of impurities and to control the amount of Ni, Cu, Nb, C.
세라믹 주형법에 의하여 주조된 SM50C 강의 탈탄과 그 방지에 관한 연구
이선호,이경환,강춘식 ( Seon Ho Lee,Kyong Hwan Lee,Choon Sik Kang ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.4
N/A Decarburization phenomena of SM50C steel casted in ceramic mold was investigated. As result, decarburized depth increased by increased by increasing the volume-to-surface area ratio and mold temperature. And the relations between them is y(㎝)=(1.96×10^(-5)T+0.0135)×M-1.05×10^(-5)T+9.73×10^(-3). When mold is controlled by Ar ags, reducing atmosphere, decarburized depth is decreased. In case of adding graphite powder in the mold, decarburization is decreased more. Specially, when graphite powder is added on the mold materials and the wax is layed on the mold, decarburization is almost prevented.
플라즈마 용사한 NiCrAlY/NiCrAlY+8wt%Y2O3-ZrO2/8wt%Y2O3-ZrO2 3층 단열코팅층의 특성에 관한 연구
이선호,강춘식,유재성 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.6
Thermal barrier coatings(TBCs) fabricated by plasma spray process is generally used for gas turbine and diesel engine to improve their efficiency and service life. In this study, intermediate mixed layer between bond and ceramic layer was sprayed to improve thermal shock lifetime through increase of adhesion strength. On spraying the mixed Layer, each melted droplet of bond and ceramic powder was not mixing. Thus, interface shape between bond and ceramic Layer showed the complicated morphology. The adhesion strength and the thermal shock lifetime were improved by maximum 1.2 and 1.5 times. respectively. It was judged that improvement of thermal shock lifetime was due to increase of adhesion strength and tensile residual stress. From the stress analysis of thermal shock procedure. it was proved that enlargement of fractured region was occurred because horizontal crack in the vicinity of interface propagated in the direction of surface.
플라즈마 용사한 NiCrAlY/8wt% Y2O3-ZrO2 2층 단열코팅층의 레이저 표면개질에 관한 연구
김종영,이선호,강춘식,유재성 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.12
NiCrAlY/8wt%Y₂O₃-ZrO₂, two layer TBC was fabricated by plasma spray method and its surface modification was performed by CO₂ laser and then the change of characteristics and failure mechanism during thermal shock test were investigated. The more specific energy of laser beam, the more crack width and thickness of melted layer originated by laser treatment. In the same specific energy, they decreased by reducing laser power. After laser treatment, residual stress was altered tensile stress, adhesion strength reduced due to the horizontal crack at the bottom of interface between melted and unmelted layer, surface corrosion of ceramic layer was suppressed due to densification and the life cycle by thermal shock test were increased. The failure procedure during the thermal shock test was as follows; buckling occurred first, then spalling followed after a few cycles and fracture region was expanded. The failure resulted from buckling is believed to occur because of compressive stress developed by cooling. It is thought that thermal shock lifetime after laser treatment is improved owing to the stress relaxation caused by vertical crack to surface and residual tensile stress.
MCrAlY/ZrO2-8wt%Y2O3 단열코팅의 열피로 파괴거동 및 레이저 처리의 효과
김종영,이선호,강춘식,진만복 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.5
Isothermal and thermal fatigue tests were carried out for plasma sprayed and laser treated MCrAly/ZrO₂ 8wt%Y₂O₃ thermal barrier coatings(TBCs) to discuss the failure mechanism and the effects of laser-treatment. Phase transformation of the ceramic coating was not occurred during testing. In thermal fatigue test, at the temperature range of 1100℃∼RT, specimens were investigated prior to and after failure. Cracks initiated, grew and combined by stresses due to thermal expansion mismatch and oxidation of the bond coating near the bond/ceramic coating interface. So, failure of the TBC without laser-treatment occurred suddenly. In case of laser-treated TBCs, vertical cracks arisen from laser-treatment and cracks which initiated and grew near the interface-combined. But failure of the laser-treated TBC occurred gradually. Thermal fatigue Iife of the laser-treated TBC was increased 1.7 times than the TBC without laser-treatment.