나노인덴테이션 하에서의 알루미늄의 팝인 변형

김지수,윤존도,Kim, Jisoo,Yun, Jondo 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.4

Pop-in deformation phenomena in aluminum was studied. Whether a pop-in occurs or not depended on the surface polishing method. Pop-in did not occur in aluminum which was polished mechanically, while it occurred in aluminum which was polished electrically. When pop-in occurred, elastic deformation preceded. Pop-in mechanism based on dislocation activity was suggested. Suggested mechanism was consistent with the result of microstructure analysis by Focused Ion Beam polisher (FIB) and Transmission Electron Microscopy (TEM). 나노인덴테이션 시험시의 알루미늄의 팝인 변형에 대하여 연구하였다. 팝인 현상은 알루미늄의 표면 상태에 따라서 발생 유무가 결정되었다. 기계연마한 알루미늄에서는 팝인이 일어나지 않았고, 전해연마한 시편에서만이 팝인이 일어났다. 팝인이 일어나는 경우에는 나노인덴테이션 초기단계에서 탄성변형이 일어났으며 그 후에 갑자기 팝인 변형이 일어났으며 팝인 후에는 탄소성 변형이 일어났다. 전위 활동에 근거한 팝인 발생 메카니즘을 제시하였으며 이는 FIB와 TEM에 의한 미세구조 분석 결과와 일치하였다.

Si-N 코팅막의 기계적 물성 및 구조 분석

고철호,김봉섭,윤존도,김광호,Go, Cheolho,Kim, Bongseob,Yun, Jondo,Kim, Kwangho 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.5

Silicon nitride coating films with various ratios of nitrogen to silicon contents were prepared and characterized. The film was coated on silicon substrate by sputtering method with changing nitrogen gas flow rate in a chamber. The nitrogen to silicon ratio was found to have values in a range from 0 to 1.4. Coated film was characterized with scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, nanoindentation scanning probe microscopy, x-ray photon spectrometry, and Raman spectrometry. Silicon nitride phase in all samples showed amorphous nature regardless of N/Si ratio. When N/Si ratio was 1.25, hardness and elastic modulus of silicon nitride film showed maximum with 22 GPa and 210 GPa, respectively. Those values decreased, when N/Si ratio was higher than 1.25. Raman spectrum showed that no silicon phase exist in the film. XPS result showed that the silicon-nitrogen bond was dominant way for atomic bonding in the film. The structure and property was explained with Random Bonding Model(RBM) which was consistent with the microstructure and chemistry analysis for the coating films.

펄스지속시간에 따른 형상방전가공 특성

우정윤(Jeong Yun Woo),왕덕현(DuckHyun Wang),윤존도(JonDo Yun) 한국정밀공학회 1997 한국정밀공학회 학술발표대회 논문집 Vol.1997 No.5월

시차주사열량측정법에 의한 니켈기 초내열 합금의 열분석

윤지현,오준협,김홍규,윤존도,Yun, Jihyeon,Oh, Junhyeob,Kim, Hongkyu,Yun, Jondo 한국재료학회 2016 한국재료학회지 Vol.26 No.5

Appropriate thermo-mechanical properties of nickel-based superalloys are achieved by heat treatment, which induces precipitation and solid solution hardening; thus, information on the temperature ranges of precipitation and dissolution of the precipitates is essential for the determination of the heat treatment condition. In this study, thermal analyses of nickel-based superalloys were performed by differential scanning calorimetry method under conditions of various heating rates of 5, 10, 20, or 40K/min in a temperature range of 298~1573K. Precipitation and dissolution temperatures were determined by measuring peak temperatures, constructing trend lines, and extrapolating those lines to the zero heating rate to find the exact temperature under isothermal condition. Determined temperatures for the precipitation reactions were 813, 952, and 1062K. Determined onset, peak, and offset temperatures of the first dissolution reaction were 1302, 1388, and 1406K, respectively, and those values of the second dissolution reaction were 1405, 1414, and 1462K. Determined solvus temperature was 1462K. The study showed that it was possible to use a simple method to obtain accurate phase transition temperatures under isothermal condition.

니켈기 초내열합금 분말의 고용화 열처리 후 냉각속도에 따른 크리프특성 분석

전찬,이영선,배병범,김홍규,홍성석,김동훈,윤존도,윤은유,Jun, Chan,Lee, Youngseon,Bae, Byeong Beom,Kim, Hong-Kyu,Hong, Seong Suk,Kim, Donghoon,Yun, Jondo,Yoon, Eun Yoo 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.3

In this study, solid solution heat treatment of consolidated nickel-based superalloy powders is carried out by hot isotactic pressing. The effects of the cooling rate of salt quenching, and air cooling on the microstructures and the mechanical properties of the specimens are analyzed. The specimen that is air cooled shows the formation of serrated grain boundaries due to their obstruction by the carbide particles. Moreover, the specimen that is salt quenched shows higher strength than the one that is air cooled due to the presence of fine and close-packed tertiary gamma prime phase. The tensile elongation at high temperatures improves due to the presence of grain boundary serrations in the specimen that is air cooled. On the contrary, the specimen that is salt quenched and consists of unserrated grain boundaries shows better creep properties than the air cooled specimen with the serrated grain boundaries, due to the negative creep phenomenon.

Characterization of Cold Metal Transfer Welding Coated Steel

송현수(Hyun Soo Song),최보성(Bo Sung Choi),윤존도(Jondo Yun),박승태(Seung Tae Park) Korean Society for Precision Engineering 2015 한국정밀공학회지 Vol.32 No.10

자전연소합성법으로 제조한 여러 가지 탄화물의 모폴로지 및 그 형성 메카니즘

윤존도,방환철 경남대학교 신소재연구소 1998 論文集 Vol.10 No.-

자전연소합성법(SHS)을 이용하여 탄소섬유와 지르코늄, 니오븀 및 몰리브데늄 원료분말로부터 섬유상 탄화물의 합성을 시도하였다. 합성된 탄화물의 미세구조관찰 결과 ZrC와 NbC는 속이 빈 섬유상이 Mo2C는 응융물층이 형성되었음을 알수 있었다. 자전연소 합성법으로 합성된 SiC, B4C, WC, ZrC, NbC 및 Mo2C 탄화물의 모폴로지 분석을 통하여, 탄화물의 형상을 크게 섬유상 과 비섬유상의 2가지로 분류하였다. 탄화물의 형상은 원료성분의 융점, 확산속도, 탄화물의 융점 및 단열온도와 관계가 있었으며, 각 섬유상 탄화물에 대한 형성 메카니즘을 제시하였다. Fabrication of fibrous carbides was attempted by self-propagating high temperature synthesis using carbon fibers and elementary powders(Zr. Nb. Mo). It was found that ZrC and NbC had fiber forms but Mo₂C did not. Synthesized carbides(SiC. B₄C. WC. ZrC. NbC. Mo₂C) were found to have two types of morphologies : ① fibrous shape(SiC. ZrC. NbC. B₄C). and ② non-fibrous shapet(WC. Mo₂C). It was suggested that shape of synthesized carbides were determined by the difference in the diffusion rates between metals and carbon in carbides, and existence of liquid phase during the reaction.

산화알루미늄-탄화티타늄 세라믹복합체의 물성과 방전가공성에 미치는 탄화티타늄함유량의 영향

윤존도,고철호 경남대학교 신소재연구소 1997 論文集 Vol.9 No.-

도전성 이차상인 TiC를 10-52무게%까지 함유하는 Al₂O₃-TiC 세라믹복합체를 핫프레스로 제조하여 TiC함유량에 따른 기계적 물성과 전기전도도 및 방전가공성을 조사하였다. TiC함유량이 10무게%에서 52무게%로 증가함에 따라 비커스 경도는 1700Hv에서 2200Hv로 증가였고, 4점 꺾임강도도 380MPa에서 670MPa로 증가하였다. TiC함유량이 33무게%이상일 때 방전가공속도가 급격히 증가하는 것으로 나타났는데, 이는 이 조성에서 전기전도도가 급격히 증가하기 때문인 것으로 분석되었다. Mechanical properties, electrical conductivity and electrical discharge machinability were examined on the A1₂O₃-TiC ceramic composite with varing amount of conductive TiC content. With increasing TiC content from 10wt% to 52wt%. Vickers hardness increased from 1700Hv to 2200Hv. and four-point bending strength increased from 380MPa to 670MPa. At about 33wt% or higher TiC content, electrical conductivity abruptly increased from the value less than 5×10_{-5}(Ωcm)_{-1} to the value higher than 2×l0²(Ωcm)^{-1}. and materials removal rate(MRR) abruptly increased, too.

자전연소 합성에 의한 섬유상 탄화물의 제조

윤존도,방환철 경남대학교 신소재연구소 1997 論文集 Vol.9 No.-

자전연소합성(SHS) 화학로법을 이용하여 탄소섬유와 규소, 붕소 및 중석 원료분말로부터 섬유상 탄화물의 합성을 시도하였다. 반응실험 결과, 세가지 경우 모두 SiC, B₄C, 또는 WC가 양호하게 합성된 것으로 나타났다. 합성된 시편의 미세구조관찰결과, SiC와 B₄C는 섬유상을 하고 있으나, WC는 섬유상을 하고 있지는 않았다. 합성된 SiCtjadb는 표면이 판상입자와 휘스커로 둘러싸여 있었고, 섬유상 B₄C는 섬유내부가 균일하게 형성되어 있지 않은 것으로 관찰되었다. WC섬유가 형성되지 않은 원인으로는 WC내에서의 W와 C의 확산 속도차이 때문인 것으로 분석되었다. Fabrication of fibrous carbides was attempted by self-propagating high temperature synthesis using chemical furnace. X-ray diffractometer analysis showed that SiC. B₄C, or WC were synthesized by the reaction when the samples were packed in the enough amount of chemical fuel powders. It was found that SiC and B₄C had fibrous forms but WC did not. Microstructural analyses by SEM showed that fibrous SiC was surrounded by whiskers and platelets, and unreacted C remained inside fibrous B₄C. The difference in the diffusion rates of W and C in WC was suggested to be the main reason why fibrous WC was not formed.

자전연소 합성에 의한 섬유상 TiC의 형성 메카니즘

윤존도,방환철 慶南大學校 附設 工業技術硏究所 1998 硏究論文集 Vol.15 No.3

자전연소 합성법(SHS)을 이용하여 섬유상 TiC를 합성할 때 섬유형성 기구를 분석하였다. TiC-C공정온도인 2776℃를 임계로하여 공정온도 이상에서는 액상이 안정하여 탄소섬유가 녹고 TiC 섬유가 형성되지 않으나, 공정온도 이하에서는 고상 C와 TiC가 안정하여 TiC 섬유가 잘 형성되는 것으로 분석되었으며 이는 실험결과를 잘 설명하고 있다. 희석제로 TiC를 30무게% 첨가하였을 때 섬유상 TiC가 잘 형성되었다. 합성된 TiC 섬유는 내부에 속이 비어 있었는데 이는 TiC 내에서는 C와 Ti의 확산속도 차이와 C가 TiC로 변화할 때의 몰부피로 설명되었다. Forming mechanism of fibrous TiC during self-propagating high temperature synthetic reaction was analyzed and suggested. It was revealed that critical temperature for the stable fiber formation was not the melting point of TiC, but the eutectic reaction temperature of TiC and C. The explanation was consistent with the experimental results. Optimum amount of diluent addition was determined to be 30%. Synthesized fibers were found hollow tube-like. The morphology was explained by the diffusion rates of C and Ti in TiC, and by the molar volume change of C during the reaction.