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김길수(K. S. KIM),박세만(S. M. BAHK),박명균(M. K. PARK) 한국자동차공학회 1996 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1996 No.11_1
This investigation determines dynamic crack initiation roughnesses(K_id, J_id) of metallic materials such as SM20C and STD 11. Dynamic fracture toughnesses were was evaluated by conducting instrumented charpy impact tests. Specially, in this study, signals obtained from the strain gage implanted in the impact tup is transformed to Load-Time data by digital signal processings. To obtain appropriate data, the data were critically reviewed and tested against three criteria; inertia effects, limited frequency responses and energy levels. Initiation energy was determined using the method of compliance changing rate and was corrected to take into account of energy which was absorbed by inertia force.<br/>
초고속 스핀들의 내구성 향상을 위한 WC-Co 분말의 HVOF 용사 코팅
김길수(K.S. Kim),백남기(N.K. Baek),윤재홍(J.H. Yoon),조동율(T.Y. Cho),윤석조(S.J. Youn),오상균(S.K. Oh),황순영(S.Y. Hwang),천희곤(H.G. Chun) 한국표면공학회 2006 한국표면공학회지 Vol.39 No.4
High velocity oxygen fuel(HVOF) thermal spray coating of WC-Co powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and ceramics coating because of the environmental problem of the very toxic Cr6+ known as carcinogen and the brittleness of ceramics coating. WC-Co micron and nano powder were coated by HVOF thermal spraying method for the study of durability improvement of the high speed spindle. Coatings were planned by Taguchi program for the four spray parameters of spray distance, flow rates of hydrogen, oxygen and powder feed rate. Optimal coating process was obtained by the studies of coating properties such as porosity, surface roughness, micro hardness, and microstructure. WC-Co micron and nano powder were coated on the Inconel 718 substrate by the optimal coating process obtained in this study. The wear behaviors were studied by the sliding wear tester at room temperature and at an elevated temperature of 500°C for the application to high speed spindle. Sliding wear test was carried out for four most promising hard coatings of chrome coating, ceramics coatings such as Al₂O₃, Cr₂O₃ and HVOF Co-alloy T800 for the comparison of their wear behaviors. HVOF WC-Co coating was better than other coatings showing highest micro hardness of 1400 Hv and comparable friction coefficients with others. HVOF WC-Co coating is a strong candidate for the replacement of the traditional hard chrome plating for the high speed spindle.
계장화 샤피충격시험기를 이용한 재료의 동적파괴특성에 관한 연구
김길수(K. S. KIM),김기동(K. D. KIM),박세만(S. M. BAHK),박명균(M. K. PARK) 한국자동차공학회 1996 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1996 No.6_1
This investigation determines dynamic fracture characteristics of metals such as SM45C, SM20C and SS41. One of the dynamic' characteristics, dynamic fracture toughness, was evaluated by conducting instrumented charpy impact tests. Specially, in this study, signals obtained from the strain gage implanted in the impact tup is transformed to Load-Time data by digital signal processing. To obtain appropriate dynamic fracture toughness, the Load-Time data is critically reviewed and tested based on three criteria; inertia effect, limited frequency response and energy levels. This procedure ensures the reliability of the data. The data is, then, examined in view of topological aspects of fractured surfaces of the metals to reveal dynamic natures of materials failure.<br/> <br/>
자동차 피스톤용 AI-10Si 합금의 용융 산화 피막강도 측정 및 첨가원소의 영향
김기주(K.J.Kim),우정명(J.M.Woo),백영남(Y.N.Paik),김길수(K.S.Kim) 한국자동차공학회 1994 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
This study was earned out to determine the strength of oxide skins of Al-10Si alloy melts and survey the effects of adding Mg. Cu. Ni and 1Cu-0.5Mg-2Ni as the practical alloy for automobile piston. This has been observed by Rotational Die Movement equipment for the temperature range from 600℃ to over ℃ and the oxidation time range from 10min. to 60min. and strength of oxide skins of the molten alloys were much more affected by oxidation temperature than oxidation time. Mg element was also more affected than any other elements. However, the effect of adding 1Cu-0.5Mg-2Ni alloy was located in the middle of alloy which had added Mg and which had added Cu and Ni.<br/>
초초임계압 발전용 소재의 표면처리층의 고온 안정성 평가
류경환,송태권,이재현,김길수,이선호,엄기원,Ryu, K.H.,Song, T.K.,Lee, J.H.,Kim, G.S.,Lee, S.H.,Urm, K.W. 한국재료학회 2006 한국재료학회지 Vol.16 No.5
In order to improve thermal efficiency of the fossil fuel power plants, we need to develop advanced materials with superior durability in the ultra-super critical state, which requires surface modifications for superior surface properties. In this study, we coated the Incoloy 901 and 12-17Cr steels for turbine buckets and valves with nitriding, boriding, and $Cr_3C_2-NiCr$ HVOF(high velocity oxygen flow) method. Then the samples were heat treated at $650^{\circ}C$ for 100 hours in vacuum. We analyzed the evolution behaviors of nitrides such as $Fe_3N,\;Fe_4N$, and CrN and borides such as FeB and $Fe_2B$ with XRD and SEM/EDS by comparing hardnesses and compositions of the coated layers before and after the heat treatments.